Mélanie Donnette

Mourad Hamimed

Joseph Ciccolini
email: joseph.ciccolini@univ-amu.fr

Yael Berda-Haddad

Elise Kaspi

Geoffroy Venton

Bruno Lacarelle

Regis Costello

Regis Costello F , L'

Houcine Ouafik

Laure Farnault

Raphaelle Fanciullino

Joseph Pr

Ciccolini

Pharmacokinetics and pharmacogenetics of liposomal cytarabine in AML patients treated with CPX-351

Keywords: liposomal cytarabine, cytidine deaminase, pharmacokinetics, drug release, modelling

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Cytarabine and daunorubicin are the mainstay for treating Acute Myeloid Leukemia (AML). Those drugs are given following the canonical "7+3" regimen. To improve efficacy of this combination and reduce its side-effects, CPX-351 (Vyxeos®), a liposomal nanoparticle co-encapsulating both drugs in a 5:1 molar ratio, has been developed and recently approved for treating AML patients. This newly formulated combination is expected to enhance pharmacokinetics (PK) parameters and better target bone marrow.

The high affinity of liposomal sphingolipids for proliferative myeloblasts should increase the antiproliferative efficacy of the encapsulated drugs, while sparing healthy cells, thus reducing systemic toxicity [START_REF] Mayer | CPX-351: a nanoscale liposomal co-formulation of daunorubicin and cytarabine with unique biodistribution and tumor cell uptake properties[END_REF]. Registration studies with CPX-351 showed that plasma elimination half-life of cytarabine is prolonged as compared with standard drug, suggesting a reduced clearance [START_REF] Mayer | CPX-351: a nanoscale liposomal co-formulation of daunorubicin and cytarabine with unique biodistribution and tumor cell uptake properties[END_REF]. We have previously demonstrated that CDA deficiency, a condition leading to impaired ability to detoxify nucleoside analogs in the liver, was associated with marked changes in the PK of standard cytarabine, with subsequent increased risk for severe/lethal toxicities but a trend as well towards prolonged survival [START_REF] Fanciullino | CDA as a predictive marker for life-threatening toxicities in patients with AML treated with cytarabine[END_REF].

Of note, in a previous study we observed that incidence of CDA deficiency was markedly higher in patients with blood disorders (i.e., 48%) than in patients with solid tumors (13.9%) or patients with no cancers (6.6%) [3].This higher incidence of CDA deficiency in patients with leukemia calls for further investigating to what extent differences in CDA activity could have an influence in leukemia patients treated with nucleoside analogs.

Liposomal drugs are expected to skip at least partly liver metabolism [START_REF] Rodallec | Seek and destroy: improving PK/PD profiles of anticancer agents with nanoparticles[END_REF], but to what extent differences in CDA status should thus have a limited impact on the PK of liposomal cytarabine in CPX-351 patients remains to be demonstrated. In this proof-of-concept study, we have performed full PK monitoring of cytarabine in adult AML patients treated with the CPX-351 nanoparticles, to evaluate whether CDA has an influence on liposomal cytarabine clearance and subsequent exposure levels among individuals.

Material & Methods

Patients

This was an ancillary study to the clinical trial registered as EUDRACT #2017-A00070-53 on cytarabine pharmacogenetics and pharmacokinetics in adult patients with AML. The study was performed at La Conception University Hospital of Marseille, France, in accordance with the Declaration of Helsinki and the principles of Good Clinical Practices.

Ethical Committee approval (Comité de Protection des Personnes -Sud Méditerranée, application file registered as 17.005), ANSM French health authority, and signed informed consents were obtained prior starting this study. Eligibility criteria was only to be ≥18 years old and be scheduled for liposomal CPX-351 for a newly diagnosed AML with myelodysplasia-related changes (AML-MRC) or therapy-related AML (AML-t). There were no exclusion criteria.

Treatment

Liposomal CPX-351 was administered according to drug label recommendations. For first induction cycles of treatment, equivalent of daunorubicin 44 mg/m 2 and cytarabine 100 mg/m 2 were administered via intravenous infusion over 90 minutes on day 1, 3 and 5.

Endpoints

The primary objective of this ancillary study was to estimate individual PK parameters and derive cytarabine systemic exposure parameters (i.e., Cmax, Ctrough, and AUC0-inf) of patients treated with CPX-351 during the induction phase, with respect to CDA status. The secondary objectives were to estimate the accumulation of liposomal cytarabine in bone marrow and to tentatively associate PK parameters of liposomal cytarabine with clinical outcome.

Clinical outcome

Response was evaluated primarily by bone marrow examination. Complete remission (CR) was defined as bone marrow blasts <5%; absence of circulating blasts and blasts with Auer rods; absence of extramedullary disease; absolute neutrophil count >1.0 x 10 9 /L; platelet count >100 x 10 9 /L. Complete remission with incomplete hematologic recovery (CRi) was defined as all CR criteria except for residual neutropenia [<1.0 x 10 9 /L] or thrombocytopenia [<100 x 10 9 /L]. Treatment-related toxicities were monitored and graded using standard CTCAE-4 guidelines [START_REF]Common Terminology Criteria for Adverse Events[END_REF].

CDA status determination

CDA activity was measured from serum using an ex-vivo enzymatic test based upon spectrophotometric method [START_REF] Ciccolini | Cytidine deaminase residual activity in serum is a predictive marker of early severe toxicities in adults after gemcitabine-based chemotherapies[END_REF]. Results were expressed as U/mg of serum proteins.

Patients were subsequently categorized as Poor Metabolizer (PM, i.e., CDA < 2 U/mg), Extensive Metabolizer (EM, i.e., CDA ≥ 2 U/mg) or Ultra-Rapid Metabolizer (UM, i.e., CDA> 6U/mg) [START_REF] Fanciullino | CDA as a predictive marker for life-threatening toxicities in patients with AML treated with cytarabine[END_REF]. When informed consent for germinal genomic analysis was obtained, CDA gene was sequenced. Genomic DNA was isolated using blood sample collected in EDTA-tubes before administration of CPX-351, using QIAsymphony SP/AS (Qiagen France). Resulting DNA was quantitated, and purity checked using the NanoDrop TM 1000 spectrophotometer (Thermo Fisher Scientific, France). DNA samples were stored at -20°C in Tris-EDTA buffer until sequencing. Primers were designed for four exons of the CDA gene (data not shown) used for the PCR amplification. The human genome GRCh37/hg19 was used as a reference sequence. Sequencing was performed by SANGER method using the 3500 Dx Genetic Analyzer (Thermo Fisher Scientific, France).

All sequences were next analyzed using the Variant Reporter Software 2.0.

PK blood sampling and bioanalysis

Blood for cytarabine assay was collected during the first induction phase on Day-5 90 minutes before the 3d administration, then 4, 6, 8, 24, 48, 72, 96 and 168 hours after administrating CPX-351. To separate released and encapsulated cytarabine, plasma was filtered on Vivaspin® filters (Sartorius France), using an ultracentrifuge (Beckman Coulter France). Both free and encapsulated cytarabine plasma levels were next measured separately using a validated high-performance liquid chromatography with tandem mass spectrometry detection method (LC-MS/MS) [START_REF] Donnette | Simultaneous determination of cytosine arabinoside and its metabolite uracil arabinoside in human plasma by LC-MS/MS: Application to pharmacokinetics-pharmacogenetics pilot study in AML patients[END_REF]. Limit of Quantification was 1 ng/mL, and both precision and accuracy were below 15%. For assaying encapsulated cytarabine, liposomes were first destroyed by vortexing in methanol. Resulting solution was next 1/100 diluted in MilliQ water, and 100µl were further proceeded prior to LC-MS/MS analysis as previously described. Total cytarabine for each time-point was calculated as the sum between free and encapsulated cytarabine. Plasma concentrations were expressed as ng/mL. When myelogram was available on D15 or D30 for blast count, concentration of total cytarabine in the bone marrow was measured as well using the same LC-MS/MS technique.

Bone Marrow search for liposomes

Optical microscopy-analysis was performed on available bone marrow collected on D15 or D30 to search for liposomal nanoparticles. May-Grünwald Giemsa (MGG) staining was performed according to the manufacturer's instructions (Merck, France) and lipid staining was performed using Oil Red O kit (Biognost, Belgium) according to the manufacturer's instructions. Briefly, slides were fixed in 4% Formaldehyde and, after washing, slides were stained in Oil Red reagent working solution for 10 minutes. Nuclei were counterstained in Hematoxylin. Bone marrow previously collected from leukemia patients who were not treated with CPX-351 were used as negative control.

Evaluation of the predictive performance of cytarabine PopPK models

Model-based identification of PK parameters was performed on total cytarabine only since no population parameters were made available in the literature for free cytarabine released from liposomes or for liposomal cytarabine only. With respect to the small number of blood samples made available, compartmental analysis for those two forms was not possible.

Only two published popPK models were available for total cytarabine: the Nikanjam model, a one-compartment model fitted on PK data from a phase I study [START_REF] Nikanjam | Persistent cytarabine and daunorubicin exposure after administration of novel liposomal formulation CPX-351: population pharmacokinetic assessment[END_REF], and the Wang model, a two-compartments model built from pooled data from 3 clinical studies [START_REF] Wang | Population Pharmacokinetics and Exposure-Response Analyses for CPX-351 in Patients With Hematologic Malignancies[END_REF]. Modelbased predictions of concentration were performed on Monolix® 2019R2 software (Lixoft, France) [START_REF]Monolix 2018R1 User guide[END_REF], taking into account patient demographics, biology data and PK observations, using a Bayesian data assimilation approach. Post-processing of Monolix® output was performed using R Statistical software (R Project, Austria) [START_REF]The R Project for Statistical Computing[END_REF]. Selecting the best model included prediction-and simulation-based diagnostics through both numerical metrics and graphical methods as proposed by Sheiner and Beal [START_REF] Sheiner | Some suggestions for measuring predictive performance[END_REF]. The best model was further evaluated by Simulation-based diagnostics, which consisted in a normalized prediction distribution errors (NPDEs) analysis. The internal dataset was simulated 500 times with the inclusion of the inter-individual and residual unexplained variabilities. Diagnostic graphs and statistic tests were performed to examine whether the NPDE data followed a standard normal distribution.

Individual parameters estimation

Bayesian PK parameters estimates for each patient were calculated and used to derive individual concentration-time profiles for total cytarabine. Non-compartmental analysis was performed using PKanalix software (version 2019R2, Lixoft SAS, Antony, France) [START_REF]PKanalix documentation -application for the NCA and CA analysis[END_REF].

Maximum observed plasma concentration (i.e., Cmax) and residual plasma levels on day 5 (i.e., Ctrough) were determined directly from the individual data. Cumulative area under the plasma concentration-time curve from time zero to infinity (i.e., AUC0-inf) was derived from the clearance and the dose. Regarding free cytarabine (i.e., released from the liposomes) and liposomal cytarabine, AUC was evaluated using trapezoidal rule, because no PK model for released cytarabine or encapsulated cytarabine was made available to estimate individual parameters. The resulting AUC (AUCtau) was truncated (i.e., from 96 to 144h) following recommendations from Wang et al. [START_REF] Wang | Population Pharmacokinetics and Exposure-Response Analyses for CPX-351 in Patients With Hematologic Malignancies[END_REF].

Statistical Considerations

With respect to the small sample size (9 patients), all statistical analysis were performed using Wilcoxon Exact test non-parametric testing on R Statistical software (R Project, Austria) [START_REF]The R Project for Statistical Computing[END_REF].

Results

Patients' characteristics and CDA status

Nine adult patients hospitalized in La Conception University Hospital of Marseille, France, between January 2019 and January 2020, and treated with CPX-351 were recruited. This subset of patients (6F/3M) was 66 ±13 years old (range: 37-76). Patients' characteristics are summarized in Table 1. Mean CDA value was 1.5 ±1.7 U/mg. Seven patients were subsequently categorized as CDA deficient or poor-metabolizer (PM, mean CDA = 0.92 ±0.51 U/mg) whereas two patients were considered as extensive-metabolizer (EM, mean CDA = 4.43 ±2,0 U/mg). No ultra-rapid metabolizer (UM) patient was found. patients are provided in Table 2. A total of 9 exonic and intronic SNPs were observed (i.e.,

Cytarabine Plasma concentrations.

Plasma concentrations of total cytarabine, liposomal cytarabine and released cytarabine are displayed in Figure 1. The Tmax of released cytarabine was delayed as compared with liposomal drug (Cmax observed at 110h, i.e., 14h after the 3 d administration). Interpatient variability ranged from 47 to 75% for released cytarabine concentrations, from 14

to 90% for liposomal cytarabine concentrations and from 31 to 74% for total cytarabine concentrations, depending on the sampling time (i.e., from -90 min to 168 h after the 3 d injection).

Determination of plasma exposure to free cytarabine and liposomal cytarabine

Because no popPK parameters were made available, it was not possible to identify the PK parameters of released cytarabine and liposomal cytarabine. Exposure levels were therefore estimated using graphical tools such as the trapezoidal rule.

Mean AUC (±SD) for free cytarabine was 682 ± 403 h.mg/L and mean AUC for liposomal cytarabine was 942 ± 305 h.mg/L.

Cytarabine bone marrow concentrations

Myelogram on D15 was available only for a single patient, all other patients being sampled on D30. Total cytarabine concentration measured in the bone marrow of this patient was 31 697 ng/mL. Plasma concentration for the same patient sampled at the same time was 13 876 ng/mL, i.e., a 2.3-times difference. Myelograms collected on D30 had all cytarabine levels below the limit of quantitation, including for the patient who had cytarabine in his bone marrow on Day-15 (data not shown).

Bone Marrow search for liposomal nanoparticles

Bone marrow smears revealed aplastic bone marrow with macrophages and plasma cells on Day 15. A small contingent of macrophages with empty cytoplasmic round vacuoles with heterogenous size were observed, and subsequent Oil Red O staining revealed lipidic nanoparticles in these macrophages, as well as many extracellular lipids. Bone marrow smears collected on Day 30 from the same patient presented no such lipidic inclusions anymore. Samples collected from patients who were not treated with CPX-351 and used as negative control showed no such lipidic inclusions (Figure 2). a Except for patient 4 (who received the dose on days 1 and 3 only), all patients received their doses on days 1, 3 and 5 of the treatment cycles.

b Observed and estimated Ctrough are defined by concentration of cytarabine measured 4 hours at maximum before the 3rd administration (from 92 to 96 hours after the initiation of treatment)

PK Parameter

Value, Mean (CV%, n) Median (min -max)

16

The estimated means for CL and Vc were 0.164 L/h and 5.39 L, respectively. Mean AUC0inf was 4465 h.mg/L. Inter-individual variability (IIV) expressed as CV% ranged between 20 and 61%, depending on the parameters. Comparison of median observed Ctrough (19.1 mg/L) and predicted Ctrough (17.9 mg/L) showed close values, thus confirming the good performance of the Bayesian predictor. Figure 3 displays the fit between simulated concentrations and measured concentrations of total cytarabine.

Influence of CDA status on the PK of cytarabine after CPX-351 administration

Although only two patients were categorized as EM on the CDA status, marked differences were observed between those patients and the rest of the subset when considering cytarabine PK parameters and exposure levels. As compared with PM patients, total cytarabine clearance was 142% higher in the EM patient (0.29 ±0.12 vs. 0.

Exposure-effect relationships

Individual clinical outcome, both in terms of response and occurrence of toxicities, are summarized in Table 4. One patient (#7) was lost to follow-up and could not be evaluated. In the remaining subset, ORR (i.e., CR + CRi) was 75% (i.e., 6 out of 8 assessable patients). Two patients showing progressive disease (PD) after induction phase failed also to respond next the consolidation cure and died due to complication of the disease. There was no significant difference between responders and non-responders with respect to total cytarabine AUC0inf, (3855 ±2418 vs. 4739 ±1010 h.mg/L, Wilcoxon-test: p=0.64).

Regarding haematological toxicities, all patients had febrile neutropenia. A trend was observed between higher exposure levels to total cytarabine and non-hematological severe toxicities (Ctrough 23.2 vs. 18.8 mg/L, AUC0-inf 4638 ±2070 vs. 4167 ±2757 h.mg/L) (Figure 5). One toxic-death was observed (11%) due to colonic obstruction 40 days after initiating CPX-351. This patient was a 55-years old female with no comorbidities with PM phenotype (CDA = 0.64 U/mg, i.e., lower than the mean CDA value of 0.92 U/mg recorded in PM patients). Consequently, total cytarabine clearance was 0.083 L/h with an estimated half-life of 43.9 days, i.e., the longest elimination half-life of all patients. Model-based estimation of AUC of total cytarabine was 2237 h.mg/L whereas exposures to released cytarabine and liposomal cytarabine estimated by trapezoidal rule were 1027 and 1091 h.mg/L, respectively, in this patient. However, with respect to the small sample size and the high inter-patient variability, this difference was not statistically significant (Wilcoxon test for both metrics: p>0.05).

Similarly, exposure-response analysis on released and encapsulated cytarabine exposure levels demonstrated that none of those were predictive of efficacy or severe toxicities (Figure 6). Still for released cytarabine, as for total cytarabine, a trend was observed between exposure and severe toxicities (AUCtau = 581 ± 310 h.mg/L for patients without severe toxicities vs. 759 ± 492 h.mg/L for patients with severe toxicities). However with respect to the small sample size, this difference was not significant.

DISCUSSION

Nanoparticles represent an appealing strategy to improve the efficacy/toxicity balance in oncology. However, only few entities have made their way from prototyping steps and experimental proof-of-concepts to clinical development, and even fewer of them have been finally approved for clinical use in patients with cancer. In this study, we present modelderived PK parameters of liposomal cytarabine in AML patients treated with liposomal CPX-351. Estimates of PK parameters on total cytarabine are consistent with those previously published with this nanoparticle during registration trials [START_REF] Nikanjam | Persistent cytarabine and daunorubicin exposure after administration of novel liposomal formulation CPX-351: population pharmacokinetic assessment[END_REF] . Here we observed a large inter-patient variability in PK parameters (i.e., up to 63% on clearance values) and exposure levels (i.e., >40% for AUC). This variability is much larger than the 30% variability previously reported with standard cytarabine [START_REF] Solans | Population Pharmacokinetics of Volasertib Administered in Patients with Acute Myeloid Leukaemia as a Single Agent or in Combination with Cytarabine[END_REF]. This difference is consistent with the fact that liposomal drugs frequently show a higher PK variability than standard drugs, much probably due to differences in patients immunity [START_REF] Schell | Meta-analysis of inter-patient pharmacokinetic variability of liposomal and non-liposomal anticancer agents[END_REF][START_REF] Rodallec | Pharmacokinetics variability: Why nanoparticles are not just magic-bullets in oncology[END_REF]. Our results confirmed the sustained plasma exposure in cytarabine achieved in patients treated with liposomal CPX-351. Indeed, here mean cytarabine clearance was 99.9% lower when administered as liposomes as compared with standard cytarabine (i.e., 0.16 vs. 272 L/h) [START_REF] Nikanjam | Persistent cytarabine and daunorubicin exposure after administration of novel liposomal formulation CPX-351: population pharmacokinetic assessment[END_REF][START_REF] Krogh-Madsen | Simultaneous determination of cytosine arabinoside, daunorubicin and etoposide in human plasma[END_REF]. Similarly, mean plasma half-life of liposomal cytarabine was 28 h, i.e., 9 up to 28times longer than the half-life of standard cytarabine reported elsewhere [18]. Although limited to a single patient, we have for the first time demonstrated that liposomal nanoparticles could be observed transiently in bone marrow two weeks after treatment by liposomal CPX-351. Quite remarkably, we found that cytarabine concentration in bone marrow on D15 was by far greater than plasma levels (i.e., 2.3-times higher). However, no more liposomes could be observed later (i.e., on D30) and cytarabine was not detectable anymore in bone marrow. Importantly, we found that the mean ratio between released cytarabine and total cytarabine was 47% in our patients, a figure markedly higher than the claims by the manufacturer with CPX-351 (i.e., 20%) [19]. Of note, here no clear PK/PD relationships could be demonstrated because efficacy was not associated with any of the metrics we collected regarding total cytarabine, released cytarabine or encapsulated cytarabine levels. Non-hematological toxicities only showed a trend towards being more frequent in patients with higher exposures to total cytarabine. Similarly, a relationship was observed between severe toxicities and exposure to released cytarabine, although not statistically significant because of the small sample size.

Although this small number of patients in our study prompt us to be cautious, some new observations are to be highlighted. First, differences in CDA status could strongly influence the fate of liposomal CPX-351 in the body and participate to the large inter-patient variability we observed. CDA is the liver enzyme responsible for the detoxification of several nucleoside analogs widely used to treat a variety of cancers [START_REF] Ciccolini | Pharmacokinetics and pharmacogenetics of Gemcitabine as a mainstay in adult and pediatric oncology: an EORTC-PAMM perspective[END_REF]. This enzyme is coded by a gene which is highly polymorphic with resulting impaired activity, possibly worsening clinical outcome with standard cytarabine and 5-azacytidine in leukemia patients [START_REF] Fanciullino | Lethal toxicity after administration of azacytidine: implication of the cytidine deaminase-deficiency syndrome[END_REF][START_REF] Fanciullino | Yin and yang of cytidine deaminase roles in clinical response to azacitidine in the elderly: a pharmacogenetics tale[END_REF]. Importantly, CDA PM status is a rare syndrome in patients with solid tumors but seems to be much more frequent in patients with hematological disorders [3].

In the present study, 7 out of 9 patients (i.e., 77%) were categorized as PM individuals, a remarkably high incidence probably due to chance since our previous studies showed that PM patients were rather around 50% in leukemia patients [3]. Here no clear genotype-tophenotype relationships was found with CDA, an observation consistent with previous reports [START_REF] Ciccolini | Cytidine deaminase residual activity in serum is a predictive marker of early severe toxicities in adults after gemcitabine-based chemotherapies[END_REF]. Still, CDA functional status could play a major role in the PK variability we report here. Indeed, the EM patients had 142% higher Cl values and 66% lower AUC0-inf , with 60% shorter half-life than PM patients. Similarly, higher exposure to released cytarabine and liposomal cytarabine were observed in PM patients as compared with EM patients. Surprisingly, the difference in PK profiles between EM and PM patients was similar to that we observed previously with standard cytarabine [START_REF] Donnette | Simultaneous determination of cytosine arabinoside and its metabolite uracil arabinoside in human plasma by LC-MS/MS: Application to pharmacokinetics-pharmacogenetics pilot study in AML patients[END_REF], thus suggesting that encapsulation into liposomes does not allow CPX-351 to totally skip liver metabolism.

Inter-individual variability on clearance was 33% in PM and 39% in EM patients, i.e., lower than the 63% measured in unsorted PM+EM patients. This suggests that differences in CDA status explain a major part of the high variability we observed with CPX-351. Finally, CDA status also has an influence on the ratio: released/total cytarabine. This ratio was 47% in PM patients but only 19% in EM patients, much probably because the released cytarabine is catabolized much more quickly in EM individuals, making the free form decreasing as soon as it leaks from the nanoparticles. Overall, the high incidence of PM patients associated with higher and sustained plasma exposure plus bone marrow infiltration by lipidic nanoparticles could partly explain why ORR was 75% in our patients, a figure markedly higher than the 47.7% or CR + CRi reported in registration trials [START_REF] Lancet | CPX-351 (cytarabine and daunorubicin) Liposome for Injection Versus Conventional Cytarabine Plus Daunorubicin in Older Patients With Newly Diagnosed Secondary Acute Myeloid Leukemia[END_REF].

Similarly, this could explain why 100% of our patients had febrile neutropenia, an incidence much higher than the 60% reported with CPX-35 1 in registration trials [START_REF] Krauss | FDA Approval Summary: (Daunorubicin and Cytarabine) Liposome for Injection for the Treatment of Adults with High-Risk Acute Myeloid Leukemia[END_REF][START_REF]Anonymous, Vyxeos liposomal (previously known as Vyxeos)[END_REF].

Of note, the patient who experienced lethal toxicities was profoundly deficient in CDA with a markedly prolonged half-life of total cytarabine. In addition, in this patient exposure to released cytarabine was slightly higher than liposomal cytarabine (1091 h.mg/L vs. 1027 h.mg.L), thus suggesting that overexposure to the free, active drug, could explain the toxic death. There is a continuous effort today to develop precision medicine in oncology, i.e., by developing personalized dosing or scheduling with anticancer agents, provided that appropriate decision making tools are made available [START_REF] Ferrer | Towards Rational Cancer Therapeutics: Optimizing Dosing, Delivery, Scheduling, and Combinations[END_REF]. Despite its limitations due to the small sample size, the present study suggests that CDA phenotype could be used as a baseline biomarker to forecast the clearance of cytarabine in patients treated with CPX-351. Because severe non-hematological toxicities could be associated with PM status, CDA could thus be used to customize dosing a priori in frail patients such as elderly patients or patients presenting with several comorbidities, especially when profound deficiency in CDA is detected. Should exposure-response relationships be confirmed in further, larger studies, this could pave the way for CDA-based adaptive dosing strategies in the future. In addition to a priori tailoring of CPX-351 dosing, it is possible as well to identify individual PK parameters for total cytarabine using Bayesian estimate, based upon a couple of blood samples. This could be used to further predict plasma exposure over the repetitive administrations of CPX-351.

CONCLUSION

Our study suggests that CDA status could be a major cause for the variability observed in patients treated with liposomal CPX-351, with possible impact on safety. A trend between exposure and severe toxicities, including lethal toxicities, was observed. Further investigations on a larger cohort of patients should help understanding exposure-response relationships with CPX-351.

  c.-92A>G (rs602950), c.-31delC (rs3215400) and c.79A>C (rs2072671) in the first exon, c.435C>T (rs1048977) in the fourth exon, and c.267-77T>A (rs488991), c.324+71T>C (rs3738130), c.325-56G>A, (rs77158575), c.325-36G>A, (rs61781969) and c.325-23C>T (rs61781970) in intron). No difference in CDA genotypes was observed between EM and PM patients.

Figure 1 .

 1 Figure 1. Mean concentration-time profiles of total, liposomal and released cytarabine

Figure 2 .

 2 Figure 2. Optical microscopic-analysis (x100) performed after MGG (Figure 2A and 2B)

Figure 3 .

 3 Figure 3. EBE-derived individual concentration-time profiles of total cytarabine. Red

Figure 4 .

 4 Figure 4. Exposure (AUC, trough levels) and PK parameters (Cl, Half-Life) of total cytarabine depending on CDA phenotype in patients.

Figure 5 .

 5 Figure 5. Exposure (AUC, trough levels on Days-5) in total cytarabine in patients with and

Figure 6 .

 6 Figure 6. Relationships between exposure to released and liposomal cytarabine and clinical endpoints. Abbreviations: Progressive Disease (PD) and Complete Response/ Partial Response (CR/PR).

Table 1 .

 1 Baseline patients' characteristics

			CDA status²
	Characteristic	Overall, N = 9 1			p-value 3
			EM, n = 2 1	PM, n = 7 1
	Age (years)	64 ± 12 (38, 77) 73 ± 4 (70, 76)	61 ± 12 (38, 77)	0.30
	Body Weight (kg)	66 ± 9 (55, 79)	66 ± 15 (55, 76)	66 ± 8 (58, 79)	0.89
	Body surface area (m²)	1.74 ± 0.11 (1.59, 1.95)	1.73 ± 0.19 (1.59, 1.86)	1.75 ± 0.11 (1.65, 1.95)	0.89
	Total bilirubin (µmol/L)	10.0 ± 7.1 (5.0, 28.0)	5.5 ± 0.7 (5.0, 6.0)	11.3 ± 7.7 (6.0, 28.0)	0.076
	Aspartate amino transferase (IU/L)	26 ± 23 (10, 81) 46 ± 50 (10, 81)	20 ± 12 (11, 40)	>0.99
	Alanine amino transferase (IU/L)	30 ± 29 (6, 75)	34 ± 33 (11, 57)	29 ± 30 (6, 75)	0.88
	Gamma-glutamyl transferase (IU/L)	84 ± 118 (12, 385)	34 ± 26 (16, 53)	98 ± 133 (12, 385)	0.66
	Alkaline Phosphatase (IU/L)	77 ± 32 (39, 148)	80 ± 1 (79, 80)	77 ± 37 (39, 148) 0.89

Only 7 out of 9 patients provided specific informed consent for germinal genotyping and had subsequently their CDA gene sequenced. Results of CDA gene sequencing in those 7

Table 2 .

 2 Results from CDA sequencing

	ID	CD	rs6029	rs32154	rs20726	rs4889	rs37381	rs77158	rs61781	rs61781	rs10489
		A	50	00	71	91	30	575	969	970	77
		stat
		us
	1	PM	AA	C-	AA	AA	TC	GA	GA	CT	CT
	2	PM	AG	C-	AC	AA	TT	GG	GG	CC	CC
	4	EM	AG	--	AC	AA	TT	GA	GA	CT	CT
	5	EM	AG	--	CC	AA	TT	GG	GG	CC	CC
	7	PM	AG	C-	AC	AA	TT	GG	GG	CC	CC
	8	PM	AA	CC	AA	AA	TT	GG	GG	CC	CC
	9	PM	AA	C-	AA	AA	TC	GA	GA	CT	CT

Abbreviation: ID, identifier; CDA, Cytidine Deaminase.

Table 3 .

 3 Individual Bayesian estimates and summary statistics of total cytarabine pharmacokinetic parameters and estimated exposures during induction cycle 1, following the FDA-approved dosing regimen a .

	Individual Parameters

  ±6.9 h p= 0.055 Wilcoxon Exact test), and exposure was consequently markedly reduced with 77% lower trough level (4.7 vs. 20.4 ±6 L/h, p= 0.071 Wilcoxon Exact test), 66% lower AUC0-inf (1784 ±895 vs. 5536 ±1784 h.ng/mL p=0.055 Wilcoxon Exact test), respectively.Figure4shows PK parameters and exposure levels depending on CDA status (i.e., PM vs.

	EM) for total cytarabine. The ratio: released/total cytarabine in plasma based upon
	respective their AUC's was 47% in PM patients and 18 % in EM patients. Of note, whereas
	inter-individual variability on clearance was 63% for the whole patients, this variability was
	reduced to 33 and 39% when considering PM and EM subsets, respectively.

12 ±0.04 L/h, p= 0.055 Wilcoxon Exact test), plasma half-life was 60% shorter (13.7 ±2.7 vs. 33.9

Regarding free and liposomal cytarabine, plasma exposure (AUC and Cmax) could not be determined for patient 4 and 9 due to missing samples. Free cytarabine AUC and Cmax were 772 ± 356 h.ng/mL and 18.1 ± 8.6 mg/L, respectively, among PM patients. In EM patient, free cytarabine AUC and Cmax were 144 h.ng/mL and 4.87 mg/L. Similarly, CDA PM patients showed higher exposure levels for the encapsulated form as compared with EM patients (988 ± 307 h.ng/mL vs. 668 h.ng/mL).

Table 4 .

 4 Clinical outcome: response and severe toxicities

	ID	Efficacy	Grade 3 to 5 AEs (CTCAE 4.0)
			Number of AEs, n	Non hematological AEs	Hematological AEs
	1	CR	1	-	Febrile Neutropenia
	2	PD	2	Hemorrhoid	Febrile Neutropenia
	3	CR	3	Constipation, Toxic	Febrile

Abbreviations: OR, Overall response; CR, Complete Response; PR, Partial Response; PD, Progressive Disease a Lost to follow-up patients.

This study was partly supported by the AORC-Junior-2017 grant from the APHM, Marseille France This study was partly presented by Melanie Donnette during the PAMM-EORTC 2021 Spring Meeting Young Investigators session

Comparative testing of the Nikanjam [START_REF] Nikanjam | Persistent cytarabine and daunorubicin exposure after administration of novel liposomal formulation CPX-351: population pharmacokinetic assessment[END_REF] and the Wang [START_REF] Wang | Population Pharmacokinetics and Exposure-Response Analyses for CPX-351 in Patients With Hematologic Malignancies[END_REF] models was done and showed that the Nikanjam's model had superior predictive performances. For instance, Bayesian predictions showed a small bias (mean prediction error of 5%) and the percentage of predicted values within ±15% interval of the observed concentrations (F15) was 60.3% for Nikanjam's model. Moreover, frequency histogram and Q-Q plot of NPDEs confirmed a normal distribution around each individual observation within the predictions of the model with a p-value, for Shapiro-Wilk normality test, higher than the predefined significance level (> 0.05). Individual PK parameters for total cytarabine plus mean parameters were therefore identified using the Nikanjam model [START_REF] Nikanjam | Persistent cytarabine and daunorubicin exposure after administration of novel liposomal formulation CPX-351: population pharmacokinetic assessment[END_REF] and are presented in Table 3. Manuscript approval: all authors.


Hind Lamkaouane

Hajar Ftouhi

Mimoun Zazoui

Mohammed Addou

Linda Cattin

Jean-Christian Bernède

Guy Louarn

Yamina Mir

Lamkaouane

Jean Christian Bernède

Improvement of inverted planar heterojunction solar cells efficiency by using KI/Alq3 hybrid exciton blocking layer

Keywords: Inverted organic solar cell, planar heterojunction, hybrid thin film, exciton blocking layer, KI thin layer, vacuum thermal deposition

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Organic photovoltaic cells (OPVs) are among the most studied and interesting technology in the photovoltaic field due to their many advantages such as low cost, lightweight, large area, and flexibility [START_REF] Lin | Small molecule semiconductors for high-efficiency organic photovoltaics[END_REF] [START_REF] Zhang | Organic Semiconductors for Vacuum-Deposited Planar Heterojunction Solar Cells[END_REF]. Recently, wide attention has been paid to bulk heterojunction solar cells (BHJs) for increasing their efficiency [START_REF] Su | Development of Block Copolymers with Poly(3-hexylthiophene) Segments as Compatibilizers in Non-Fullerene Organic Solar Cells[END_REF] [START_REF] Lin | 17.1% Efficient Single-Junction Organic Solar Cells Enabled by n-Type Doping of the Bulk-Heterojunction[END_REF]. BHJs are considered as one of the effective cells owing to development of new organic materials replacing the fullerene derivative [START_REF] Cnops | 8.4% efficient fullerene-free organic solar cells exploiting long-range exciton energy transfer[END_REF] [START_REF] Yin | Recent progress of all-polymer solar cells -From chemical structure and device physics to photovoltaic performance[END_REF]. As a matter of fact, it is known that "champion OPVs" are issued from the family of the BHJ-OPVs due to the larger area of the interface between the electron donor and the electron acceptor [START_REF] Nakano | Organic Planar Heterojunctions: From Models for Interfaces in Bulk Heterojunctions to High-Performance Solar Cells[END_REF]. In recent times, dramatic advances of the performances of OPVs have been achieved using new promising molecules and polymers, mainly non fullerene acceptors (NFA) [START_REF] Gao | A New Acceptor for Highly Efficient Organic Solar Cells[END_REF][9] [START_REF] Liu | 18% Efficiency organic solar cells[END_REF].

Nevertheless, it is difficult to obtain reproducible results with BHJs because it is complicated to control the morphology of the blend, while, with time, there is progressive phase separation and performance degradation [START_REF] Schaffer | A Direct Evidence of Morphological Degradation on a Nanometer Scale in Polymer Solar Cells[END_REF]. Moreover, the synthesis of the new materials such as NFAs is not trivial. Thus, in the near future, it would be difficult to transfer the lab-scale device fabrication to that of the industry. It is therefore interesting to study the performances of cells using small molecules, although less efficient, but easier to obtain with perfectly controlled synthesis and reproducible properties [START_REF] Wang | Efficient as-cast thick film small-molecule organic solar cell with less fluorination on the donor[END_REF][13] [START_REF] Zhang | Small-molecule solar cells with efficiency oover 9%[END_REF] [START_REF] Po | Beyond efficiency: Scalability of molecular donor materials for organic photovoltaics[END_REF].So, the spirit of our study is to seek to understand how OPVs work so as to propose new possibilities for improving their performance in the future. Planar heterojunctions are well suited for investigating new materials, as materials can be characterized independently before device fabrication and many parameters, such as light absorption and film morphology, can be determined experimentally.

In the present work, in a first time we used a very classical well known and cheap dye, CuPc, even if its limits are known, to test the validity, or not, of our new hybrid exciton blocking layer (EBL). Then, it will be possible to use some more performing molecule, where upon some more sophisticated process, such as co-evaporation to form BHJ in order to try improving the efficiency of the structures. For instance, the results obtained by "Heliatek" prove that significant improvement can be obtained through use of "pin" structures deposited under vacuum [16].

PHJ-OPVs contain two organic semiconductors, an electron donor (ED) and an electron acceptor (EA). Both stacked layers are inserted between two electrodes, the cathode top electrode is characterized by low work function and high reflectivity as Aluminum (Al), the second is the bottom anode electrode with high work function and high transparency as indium thin oxide (ITO). One of the important factors to achieve a high efficiency is a good band matching between the organic semiconductors and electrodes, which implies that the energy offset should be minimized between the donor's HOMO, the acceptor's LUMO and the work function of anode and the cathode respectively [START_REF] Martinez | Influence of the presence of Ca in the cathode buffer layer on the performance and stability of organic photovoltaic cells using a branched sexithienylenevinylene oligomer as electron donor[END_REF]. On the other hand, classical PHJ-OPVs lifetime is affected mainly by environmental conditions.

Actually, the moisture and oxygen could diffuse through the cathode and cause irreversible electronic structure modifications of the acceptor underlayer. Fullerene (C60) is the most used as acceptor material and it is highly sensitive to ambient atmosphere leading to quite fast OPV degradation [START_REF] Hao | Novel cathode buffer layer of Ag-doped bathocuproine for small molecule organic solar cell with inverted structure[END_REF][19] [START_REF] Werner | Reaction of molecular oxygen with C 60 : spectroscopic studies[END_REF]. Encapsulation and introduction of interfacial layer between the low work function metal and the photoactive layer are possible ways to protect the fullerene (C60) [START_REF] Lare | Influence of the exciton blocking layer on the stability of layered organic solar cells[END_REF] [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF]. Another approach to improve the OPVs lifetime and stability is to use an inverted configuration, where the acceptor material is deposited under the donor material preventing its oxidation and therefore the cells degradation [START_REF] Hao | Novel cathode buffer layer of Ag-doped bathocuproine for small molecule organic solar cell with inverted structure[END_REF]. Moreover, the insertion of thin buffer layer is not only beneficial in terms of power conversion efficiency enhancement but also in terms of device stability [START_REF] Lare | Influence of the exciton blocking layer on the stability of layered organic solar cells[END_REF] [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF].

In this study, we focused on the enhancement of the interfacial layer between the organic acceptor layer and the cathode using cathode buffer layer named exciton blocking layer (EBL). This thin layer has the ability to block the excitons, preventing any exciton quenching by the cathode [START_REF] Lee | Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics[END_REF].

Bathocuproine (BCP) and Tris-(8-hydroxyquinoline) (Alq3) have already been used as efficient EBLs [START_REF] Lee | Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics[END_REF][24] [START_REF] Na-Na | Photocurrent analysis of organic photovoltaic cells based on CuPc/C 60 with Alq 3 as a buffer layer[END_REF][26] [START_REF] Oida | Cathode Work Function Dependence of Electron Transport Efficiency through Buffer Layer in Organic Solar Cells[END_REF]. However, the BCP is not stable as much as Alq3 towards the moist environment.

Thus, the Alq3 is beneficial for efficiency improvement and lifetime [START_REF] Lare | Influence of the exciton blocking layer on the stability of layered organic solar cells[END_REF][28] [START_REF] Vivo | Influence of Alq3/Au cathode on stability and efficiency of a layered organic solar cell in air[END_REF].

In the present work, inverted PHJ-OPVs based on fullerene and copper phthalocyanine (C60/CuPc) as photoactive layers were investigated. MoO3 thin layer is well known as an anode buffer layer. So it has been selected as an interfacial layer to improve the hole extraction at the anode/ electron donor interface [START_REF] Jouad | Improved electron collection in fullerene via caesium iodide or carbonate by means of annealing in inverted organic solar cells[END_REF][31] [START_REF] Hao | Novel cathode buffer layer of Ag-doped bathocuproine for small molecule organic solar cell with inverted structure[END_REF].ITO/EBL/C60/CuPc/MoO3/Al is the structure of the inverted PHJ-OPV studied here (Fig. 1). In classical configuration, the EBL is chosen to block the excitons at the cathode/ electron acceptor interface. Moreover, it prevents metal diffusion into the electron acceptor layer during cathode deposition. Also, it allows better extraction of electrons from the acceptor material towards the cathode [START_REF] Lee | Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics[END_REF]. Alq3 with a wide band gap (3 eV) is considered as a good EBL with an optimal thickness of 9 nm. Such thickness is too high to permit the passage of the electrons by tunnel effect [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF]. Instead of the tunnel effect mechanism, the electron transport mechanism in classical configuration is explained by another physical process, where the electrons transport takes place by means of channels induced by metal-diffusion during the cathode deposition [START_REF] Lee | Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics[END_REF] [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF]. At this point, the electron transport mechanism remains the challenge in inverted-PHJ, where no metal diffusion occurs in the EBL. To surpass this difficulty, some studies have been done to enhance the cathode/ acceptor interface using an ITO modified by mean of EBL such as ZnO and TiOx, which are often produced by wet chemical synthesis, the thins layers obtained could be an efficient EBL. However, these techniques have downsides as the difficulties in the thickness control and require additional temperature treatment to remove organic impurities [START_REF] Kuwabara | Mechanistic Insights into UV-Induced Electron Transfer from PCBM to Titanium Oxide in Inverted-Type Organic Thin Film Solar Cells Using AC Impedance Spectroscopy[END_REF] [START_REF] Lare | Effect of a zinc oxide, at the cathode interface, on the efficiency of inverted organic photovoltaic cells based on the CuPc/C60 couple[END_REF][34] [START_REF] Schmidt | Transient characteristics of inverted polymer solar cells using titaniumoxide interlayers[END_REF]. Likewise, we can find EBLs produced by vacuum techniques such as ZnO: Al which showed good results compared with thin films produced by processed solution [START_REF] Lare | Effect of a zinc oxide, at the cathode interface, on the efficiency of inverted organic photovoltaic cells based on the CuPc/C60 couple[END_REF]. Ag:BCP thin layer deposited by co-evaporation was also reported as an efficient EBL where the electron transport is ensured by a gap state generated by the interaction between the Ag, BCP, and C60 [START_REF] Hao | Novel cathode buffer layer of Ag-doped bathocuproine for small molecule organic solar cell with inverted structure[END_REF]. We have already shown that calcium is efficient with Alq3 as double EBL [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF]. CsI as cathode buffer layer contributes to a good ohmic contact at the cathode/C60 interface which permits to increase Voc [START_REF] Jouad | Improved electron collection in fullerene via caesium iodide or carbonate by means of annealing in inverted organic solar cells[END_REF].The good results obtained by our team on the use of potassium layer introduced in the EBL of the IOPV based on SubPc [START_REF] Cattin | Power Conversion Efficiency Improvement of Planar Organic Photovoltaic Cells Using an Original Hybrid Electron-Transporting Layer[END_REF], motivated us to choose the potassium halide salts especially potassium iodide as the second layer with Alq3 as EBL to achieve an efficient device with low cost. Moreover, KI is easier to manage than pure K, which has a higher sensitivity to oxidation. Potassium iodide is mostly used as an additive in perovskite solar cells, where the use of a small quantity could improve the perovskite crystallinity, reduce density in trap states and therefore enhance the device performance's [START_REF] Wu | Improving Two-Step Prepared CH3NH3PbI3 Perovskite Solar Cells by Co-Doping Potassium Halide and Water in PbI2 Layer[END_REF].

Here in, a hybrid EBL based on KI and Alq3 is proposed. This combination is supposed to improve the cell performance by enhancing the electron extraction from the C60 leading to the energy level alignments between the cathode work function and the LUMO of the acceptor thin layer by using potassium iodide (KI), while Alq3 keeps the properties as a good exciton blocking layer. In this study, KI was incorporated at both interfaces ITO/Alq3 and Alq3/C60 with various thicknesses. We found that the OPVs performances were well enhanced when 1nm of KI thin layer was inserted in ITO/Alq3 interface. The power conversion efficiency was improved by 36% and the open-circuit voltage by 25% in comparison with inverted PHJ-OPV without the inclusion of KI thin layer.

Experimental process

Organic photovoltaic cells deposition process

Inverted organic solar cells with the following structures ITO/EBL/C60/CuPc/MoO3/Al (Fig. 1) were elaborated successfully by evaporation/sublimation under vacuum with a pressure of 10 - 6 mbar (all chemical products were supplied by CODEX). Before loading the substrates into the vacuum chamber, the 2/3 parts of the ITO coated glass substrate with a dimension of 25 mm x 25 mm and sheet resistance of 30 Ω were masked by using an adhesive tip. Then, the third part was chemically etched with Zn powder and hydrochloric acid (HCL) to obtain the under electrode. This step was followed by a cleaning with a dilute detergent solution and distilled water respectively. Then the ITO coated substrate was heated in an oven for 10 min after drying with a stream of air to clear out any trace of water. All layers were deposited successively without the need of breaking the vacuum. The thickness and the deposition rate of each layer were measured by a quartz monitor. First, the EBL was the double layer KI/Alq3, Alq3/KI, or then Alq3 alone. The thickness of the KI thin layer was taken as parameter while the thickness of Alq3 thin films was fixed at 9 nm. 0.01nm/s and 0.02 nm/s were the growth rate of the KI thin layer and Alq3, respectively. 0.04 nm/s and 0.09 nm/s were the growth rate, 30 nm and 40 nm were the thicknesses of CuPc and C60, respectively. Then the MoO3 thin layer was deposited with fixed thickness of 6 nm. At the last, Aluminum anode (Al) also was deposited in situ through shadow masks forming the cell active area which equals in our study 0.16 mm 2 .

The inverted OPVs with the following structures were investigated, the device with Alq3 alone as EBL was used here as reference cell.

The energy level diagram for the device with Alq3 thin layer alone, and with the hybrid KI/Alq3 as EBL are shown in Fig. 2.

. Characterization techniques

The current density vs voltage (J-V) characteristics were measured at room temperature using J-V tester. The measurements were carried out with solar simulator (oriel 300 W) in the dark and under simulated AM 1.5 solar illumination. The external quantum efficiency measurements were carried out by an apparatus build up in our laboratory and the measurement of the incident photocurrent conversion efficiency were done with monochromatic continuous light without modulation. The surface morphology of the different films was visualized using a scanning electron microscope (SEM) JEOL 7600F with operating voltage 5kV, (Centre de microcaractéristion, Institut des Matériaux Jean Rouxel, Université de Nantes). The surface morphology of the thin films was measured by using atomic force microscopy (AFM) in tapping mode at room temperature, the instrument used for this study is dimension edge-barker, the cantilever has the following characteristics: Force constant of 10 to 130 N/m, Resonance frequency 204-497 KHz with a resistivity of 0.01-0.02 Ωcm. XPS measurements were taken by An Axis instrument from Kartos analytical spectrophotometer with Al Kα line (1486,6 eV) as excitation source has been used , the core level spectra were recorded with an energy step of 1eV, the C1s at binding energy 284.6 eV was considered as a reference.

Other techniques were used to characterize the thin films with and without KI thin layer, the structure was characterized by X-ray diffraction Siemens D8 diffractometer using CuKα radiation (Lambda Kα=0.15) and the UV-visible absorption spectra of the thins film were measured at normal incidence in the spectral range 300nm -800nm at room temperature using Perkin Elmer 3D WB Det.Module.

Results and discussion

The structures of PHJ devices are shown in Fig. 1. After optimization of the reference OPV using Alq3 alone, several cells were carried out to investigate the effect of potassium iodide thin layer on the cell performances as a function of its thickness in both ITO/Alq3 and Alq3/C60 interfaces. Fig. 3 displays the current-voltage (J-V) curves of the elaborated cells with and without potassium iodide. The photovoltaic parameters, the power conversion efficiency (ɳ), open-circuit voltage (Voc), current density (Jsc), series resistance (Rs), and shunt resistance (Rsh) are summarized in Table .1.

According to the results presented in Fig. 3 andTable.1, it was found that the OPVs performances were improved significantly when a thin layer of KI is introduced at the ITO/Alq3 interface. The best PCE of 2,2% was achieved by using KI/Alq3 as EBL where the thickness of KI is only 1 nm. The Voc = 0,54 V and Jsc = 8,03 mA/cm 2 , are significantly improved compared to the reference cell which has a Voc = 0,40 V, Jsc = 6,73 mA/cm 2 . The efficiency of the reference OPV being 1,40%, and the efficiency of the OPV with KI/Alq3 EBL, 2.2%, is improved by 36%.

When the thickness of the KI thin layer is 1.4 nm, good results were obtained. We can clearly observe a large increase in the fill factor to 58% due to the decrease of series resistance (2,2Ω), which is inversely proportional to the J(V) slope at the Voc point. The decrease of the series resistance can be assigned to lacks the traps in the electrodes/organic materials interfaces. However, the Voc is reduced, which induces a decrease in efficiency from 2.2 % to 1.97%.

In another hand, when the KI is inserted between the Alq3 and the active layer, the results obtained by the two different cells using 1,6 nm or 0,2 nm have an efficiency of 1,41% and 1,48% respectively, which are quite homogenous compared with reference cell. It indicates that KI inserted between Alq3/C60 interface does not significantly affect the power conversion efficiency. The device using the hybrid KI/Alq3 as EBL shows a higher short circuit current density value in comparison to the device without KI thin layer. To understand the origin of this improvement of the Jsc, we have measured the external quantum efficiency (EQE) for both cells. The EQE is extremely important for the device evaluation, which is complementary to the power conversion efficiency. It is defined as the ratio of the number of electrons collected by the photovoltaic cells to the number of incidents photons [START_REF] Li | Organic thin-film solar cells: Devices and materials[END_REF]. According to EQE spectra presented in Fig. 4(a), both cells exhibit two photo-responses domains in the visible region: a photo-response located between 500nm and 800nm, and another one is located below 500 nm.

As it is known, the EQE spectrum largely depends on the absorption of the photoactive layer.

So, by comparison to the absorption spectra displayed in Fig. 4(b), we can attribute the first photo-response to the contribution of CuPc, while the second corresponds to the contribution of CuPc and C60, showing that both layers contribute to the photocurrent generation.

Moreover, the EQE signal of the inverted OPV with the hybrid EBL KI(1nm)/Alq3 is increased on the whole wavelengths in the visible region by comparison with the OPV without KI thin layer. One can see that the total absorption of the active layer is slightly enhanced in the wavelength region from 550nm to 850nm when the KI thin layer was introduced (Fig. 9(b)), which is in accordance with EQE enhancement. It can be concluded that the increase of the EQE justifies the Jsc improvement of the OPV with KI/Alq3 as EBL. To understand the improvement observed in the case of the cell using KI (1nm)/Alq3 as EBL, we performed morphological characterization by scanning electron microscopy and atomic force microscopy, as well as chemical surface analysis by XPS which are important to rely between the optoelectronic properties and the photovoltaic performances [START_REF] Hao | Novel cathode buffer layer of Ag-doped bathocuproine for small molecule organic solar cell with inverted structure[END_REF]. The EBLs morphologies were investigated using AFM measurements. .2.

The surface smoothness can be considered as a good factor to minimize the interfacial charges recombination in the ITO/C60 interface [START_REF] Wang | Efficient as-cast thick film small-molecule organic solar cell with less fluorination on the donor[END_REF]. The XPS analysis was carried out to investigate the effect of KI on the Alq3 thin layer. Fig. 6 shows the survey spectrum of the KI (1nm)/Alq3 (9nm) sample, from this spectrum we found that no signal can be attributed to iodine (inset of Fig. 6) which shows that there is decomposition of KI during the deposition process. that is generated by the K-doped atoms such that the angle changes of C=N-C bond [START_REF] Lee | Bond cutting in K-doped tris(8-hydroxyquinoline) aluminium[END_REF].

From this investigation, we can confirm that K diffuses in the Alq3, which creates a chemical interaction between K and Alq3 molecules. In the case of the sequence Alq3/KI, as shown by Fig. 8 (c), there is no low binding energy contribution, which explains that there is no improvement of the OPV performance. It was already shown that the Alq3 isomerization does not change and retains the same orientation upon the K doping. However, there is a modification of electron distribution [START_REF] Sakurai | Study of the interaction of tris-(8-hydroxyquinoline) aluminum (Alq3) with potassium using vibrational spectroscopy: Examination of the possible isomerization upon K-doping[END_REF]. As reported in Ref 30, using K/Alq3 as cathode buffer layer, the diffusion of K in Alq3 shifts the valance band of Alq3 from 1.82 eV to 2.70

eV below the Fermi level. Thus that reduces the electronic injection barrier and consequently improves the Voc value [START_REF] Cattin | Power Conversion Efficiency Improvement of Planar Organic Photovoltaic Cells Using an Original Hybrid Electron-Transporting Layer[END_REF]. A similar effect has been shown using Alq3:K2CO3 and Alq3:Li2CO3 as cathode buffer layer in light-emitting diode [40][42]. It was found that the injection barrier was reduced, due to the Alq3 Fermi level shifts toward the lowest unoccupied molecular orbital (LUMO). This shift results from the increase of anions concentration generated by the chemical reaction between K2CO3 and Alq3 [START_REF] Kao | Role of K 2 CO 3 as an n-type dopant in enhancing the electron injection and transport of organic light-emitting devices[END_REF]. In our case, the KI is decomposed during sublimation, and only K interacts with Alq3 molecules. Note that the work function of K is equal to 2.5 eV that is lower than the Alq3 [START_REF] Jouad | Improved electron collection in fullerene via caesium iodide or carbonate by means of annealing in inverted organic solar cells[END_REF], so we can conclude that this interaction between K and Alq3 as above mentioned may be responsible for the decreasing of the injection barrier between the cathode (ITO) Fermi level and LUMO of the acceptor material (C60) due to decrease in the ITO work function [40][36]. Moreover, when the thickness of KI is increased to 1.4 nm, the Voc is decreased which induces a reduction of the efficiency to 1.97%, but even so, the fill factor is significantly enhanced compared with device using KI (1nm)/Alq3 as EBL which indicates that the interfacial recombination's is reduced [START_REF] Jouad | Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction[END_REF]. For this purpose, we have verified the interfacial properties of C60/CuPc, the structure, and the optical density of the active layers to know the effect of hybrid EBL on the whole device. Fig. 9 represents the top-view of SEM images of both samples ITO/EBL/C60/CuPc where EBL is the KI (1nm)/Alq3 or Alq3 alone. Without KI thin layer CuPc surface shows a continuous and regular morphology consisted of elongated grains or rods formed on the film surface [43][44]. A transition in the grain's morphology was observed when the KI thin layer is introduced at ITO/Alq3 interfaces. The grains turn from rod-like CuPc to spherical grains on the film surface. These spherical grains have a diameter of about 200 nm. The growth of these random grains increases the grain boundaries, which induces defect in the film surface. Thus, they tend to increase the leakage current justifying the slight decrease of the fill factor from 52.5% to 51% for the device without and in the presence of KI, respectively. Additionally, we have verified the structure of both samples using X-Ray diffraction (Fig. 9 (a)). XRD patterns exhibit peaks attributed to ITO thin film. There is no peak diffraction attributed to C60 which has an amorphous phase [START_REF] Rusu | Organic donor, acceptor and buffer layers of small molecules prepared by OVPD technique for photovoltaics[END_REF] The changes in the structural and optical properties of CuPc thin film with the presence of KI thin layer mainly depend on the under-layer and its microstructure properties. We have checked the C60 surface morphology with and without KI thin layer. From the top view of SEM images of C60 thin film deposited on ITO/Alq3 and ITO/KI/Alq3(Fig. 11), we can observe that the whole film surface without KI thin layer is covered with spherical grains, and when KI is introduced, the grains become less dense on the film surface (Fig. 11 (b)). For more details about the C60 surface morphology, the samples were examined using AFM.

Conclusion

In this study, a hybrid exciton blocking layer or cathode buffer layer and its effect on inverted PHJ-OPVs performances was investigated. This hybrid EBL is composed of potassium iodide (KI) and the well-known Alq3 thin film. Using XPS analysis, we found that the KI is decomposed during the deposition process and only potassium (K) diffuses in the Alq3 thin film. The potassium introduced between the ITO and Alq3 thin film tends to enhance the device efficiency. This reflects that the hybrid EBL KI/Alq3 can effectively reduce the electron barrier collection at the organic active layer (C60) and the cathode (ITO) interface.

We found that the introduction of K enhances the Alq3 surface smoothness, which has an advantageous effect on the photoactive layer morphology. As shown, upon the insertion of the hybrid EBL, the CuPc crystallinity and its optical properties are enhanced. The effect of KI/Alq3 on the whole device mostly depends on the thickness of KI inserted. The best performances were obtained by inclusion of 1nm KI thin layer vacuum deposited on the ITO/Alq3 giving the highest OPV efficiency of 2.2% which is 36% higher than the device with only Alq3 as EBL. The present works shows that KI/Alq3 is a very efficient EBL in

Fig. 1 .

 1 Fig.1.Schematic structure of inverted PHJ-OPV

Fig. 3 .

 3 Fig.3. J-V characteristic of inverted PHJ with (a) KI/Alq3and (b) Alq3/KI as cathodes buffers layers.

Fig. 4 .

 4 Fig.4. (a) EQE spectra of inverted PHJ-OPVs using KI/Alq3 as EBL and the another using Alq3 alone and (b) absorption spectra of CuPc and C60 thin films.

Fig. 5 (

 5 a) and Fig. 5(b) represent the 2-dimensional AFM topographic images. From the 2D images, the Alq3 surface deposited on ITO/KI is smooth and homogeneous as compared with the surface of Alq3 deposited on bare ITO. The root mean square (rms) of the Alq3 surface slightly decreased from 1.44 nm to 0.757 nm when 1 nm of KI is introduced, the rms and mean roughness are shown in Table

Fig. 5 .

 5 Fig.5. 2D AFM images(5µm x 5µm) of (a) ITO/Alq3 and (b) ITO/KI/Alq3.

Fig. 6 .

 6 Fig. 6. Survey spectrum of ITO/KI/Alq3.

Fig. 7

 7 Fig.7displays the carbon core level spectrum where the K2p doublet signal appeared at binding energies 295.4 eV and 292.6eV. Even more interesting, the N1s signal located at a binding energy of 399.3 eV as can be seen in Fig.8. In the presence of K, this signal shifts for higher binding energy by 0.3 eV[START_REF] Lee | Bond cutting in K-doped tris(8-hydroxyquinoline) aluminium[END_REF][START_REF] Kao | Role of K 2 CO 3 as an n-type dopant in enhancing the electron injection and transport of organic light-emitting devices[END_REF]. After Gaussian-Lorentzian fitting an appearance of another peak (A) is observed at low binding energy (397.9 eV) (Fig.8 (b)), this peak is generated when K is introduced. As already reported by Lee et al, the N1s peak is assigned to N atom in C=N-C bond in pyridyl ring and the peak detected at low binding energy as named here peak (A) is attributed to the strained environment near N atoms in pyridyl ring in Alq3

Fig. 7 .Fig. 8 .

 78 Fig.7.C 1s core level spectrum of (a) Alq3 deposited on bare ITO and (b) Alq3 deposited on ITO/KI.

Fig. 9 .

 9 Fig.9. SEM images of (a) ITO/Alq3/C60/CuPc sample (b) and ITO/KI/Alq3/C60/CuPc, the inset figures are the magnified images of the same surface film.

  , indicating that the C60 structure does not change upon the use of KI thin layer. The peak located at 2θ=6.85° is attributed to the crystalline phase α-CuPc corresponding to the diffraction from the (2 0 0) lattice plane indicating that the CuPc molecules stand perpendicular to the substrate[START_REF] Sullivan | Structural templating as a route to improved photovoltaic performance in copper phthalocyanine/fullerene (C60) heterojunctions[END_REF][44][47][START_REF] Kinoshita | Control of open-circuit voltage in organic photovoltaic cells by inserting an ultrathin metal-phthalocyanine layer[END_REF]. The peak intensity of α-CuPc was significantly increased in the presence of KI thin layer which means that the CuPc crystallinity increases. The UV-visible spectra shown in Fig.9(b) exhibit two absorption peaks at 623 nm and 695 nm in the visible region. They correspond to the Q band (π-π* transition) absorption of CuPc thin film[START_REF] Barkat | Efficient hole-transporting layer MoO 3 :CuI deposited by co-evaporation in organic photovoltaic cells[END_REF]. The absorption of CuPc thin film is slightly increased in the visible region when the KI thin layer is introduced, which is an advantage for increasing the free carrier formation.

Fig. 10 .

 10 Fig.10. ( a) X-ray diffraction and (b) optical absorbance of ITO/ETLs/C60/CuPc where ETL is Alq3 and KI/Alq3.

Fig. 11 .

 11 Fig.11. SEM images of (a) ITO/Alq3/C60 and (b) ITO/KI/Alq3/C60

Fig. 12 .

 12 Fig. 12. AFM 3D image (a) ITO/Alq3/C60 (b) ITO/KI/Alq3/C60 .

Table 1 . Photovoltaic parameters obtained from the J-V characteristic of the inverted PHJ- OPVs with different extracting buffer layers.

 1

	EBL	Thickness	Voc(V)	Jsc(mA/cm 2 ) FF (%) ɳ (%)	Rs(Ω)	Rsh(Ω)
		of KI (nm)
	Alq3	0	0.40	6.73	52.5	1.40	3	350
	KI/Alq3 1.4	0.45	7.58	58	1.97	2.2	520
		1	0.54	8.03	51	2.2	14	380
	Alq3/KI 1.6	0.419	6.13	50	1.41	4.5	340
		0.2	0.401	6.7	55	1.48	3.70	1000

Table 2 . Rms and Ra of ITO/ETLs and ITO/ETLs/C60 where ETLs= Alq3 or KI/Alq3.

 2

	EBLs	Area (5µmx5µm)	Area (10µmx 10µm)
		RMS (nm)	Ra (nm)	RMS (nm)	Ra (nm)
	Alq3	1.694	1.379	1.44	1.144
	KI/Alq3	0.764	0.556	0.757	0.562
	Alq3/C60	1.835	1.341	2.944	1.749
	KI/Alq3/C60	1.77	1.285	2.149	1.404

Acknowledgements:

We gratefully acknowledge le Partenariat Hubert Curien (PHC) francomarocain TOUBKAL project, under contract No. 41406ZC for supporting this work.