Novel Population Pharmacokinetic Modeling of Arabinosyl Cytosine Triphosphate: Insights On Potential Preferential Formation of Ara-CTP Directly From Elacytarabine As Well As From Ara-C

Abstract 3547 Objectives: Elacytarabine (CP-4055) is an elaidic acid ester of arabinosyl cytosine (Ara-C), administered as a liposomal formulation, that is being developed to treat hematologic malignancies. CP-4055 is metabolized to Ara-C, which is transformed intracellularly to active arabinosyl cytosine triphosphate (Ara-CTP) and inactive deaminated metabolite arabinosyl uracil (Ara-U). The present analysis aimed to elucidate the pharmacokinetics (PK) of Ara-CTP and identify its relationship with CP-4055, Ara-C, Ara-U and various blood parameters measured in the target patient population. Methods: Patients suffering from hematologic malignancies, including refractory/relapsing acute myeloid leukemia (AML), who participated in Phase I or II CP-4055 trials, were included in this analysis. CP-4055 monotherapy was given as an intravenous infusion over 2 h/day for 5 days, 4 h/day for 5 days or continuously over 120 hours at doses ranging from 200 to 2500 mg/m2/day. Blood samples were collected at various time-points (until 168 hours post-dose) and plasma was assayed for CP-4055, Ara-C, and Ara-U using a validated LC-MS/MS method. Ara-CTP was measured by HPLC in isolated leukemic blast cells from AML patients. Cholesterol levels were also measured. Population PK analyses were conducted using the iterative two-stage method in ADAPT 5®. First, a model was determined for cholesterol, which was incorporated into a PK model for CP-4055, Ara-C and Ara-U. Individual PK parameters from this model were fixed and then used for the analysis of Ara-CTP. For Ara-CTP modeling, 1-compartment (cpt) models were tested with various routes of formation. For all models, model discrimination was performed using standard criteria (residual variability, quality of fit graphs, Akaike information criterion test). Results: In the cholesterol analysis, 13 patients (57 concentrations) were included while 43 patients (around 27 concentrations per patient) were included in the modeling of CP-4055, Ara-C and Ara-U. A subset of 17 patients (46 concentrations) was part of the Ara-CTP analysis. Cholesterol was described by an indirect model with a rate of elimination and a rate of formation that was increased by phospholipids infused along with CP-4055. CP-4055 PK was best described by a 2-cpt model, where the central cpt was partitioned into 2 sub-cpts. The first sub-cpt represented a lipid depot cpt where liposomal-bound CP-4055 was infused, and which transferred CP-4055 into the other sub-cpt, which represented CP-4055 released from liposomes. The transfer of CP-4055 from the liposomes was unidirectional and saturable, and cholesterol level influenced the size of the second sub-cpt. Ara-CTP appeared to be formed from unbound CP-4055, presumably within cancer cells, and was also formed as expected from Ara-C which was best described by a 2-cpt model, while Ara-U followed a 1-cpt model with an elimination that was dependent upon creatinine clearance. The proposed model is depicted below. Based on the model, terminal elimination half-life values for CP-4055, Ara-C, Ara-U and Ara-CTP were around 9, 68, 5 and 3 hours, respectively, and were independent of dose and infusion time. Residual variabilities for cholesterol, CP-4055, Ara-C, Ara-U and Ara-CTP were 21.0%, 34.0%, 39.4%, 12.5% and 29.2%, respectively. Conclusions: For the first time, a population PK approach was used to describe the PK of a triphosphate metabolite in relation to a parent drug as well as other metabolites. Indeed, the novel multi-cpt model developed herein simultaneously described and explained the PK of cholesterol, elacytarabine, Ara-C, Ara-U and Ara-CTP. The inclusion of cholesterol levels in the model improved the overall quality of fit, especially for administered liposomal-elacytarabine. The proposed PK model describing Ara-CTP disposition suggests that Ara-CTP is formed not only from Ara-C but also from elacytarabine, presumably within cancer cells, although the exact mechanism is unknown. Disclosures: Seng Yue: Learn and Confirm: Employment; Clavis Pharma: Consultancy. Gandhi:Clavis Pharma: Research Funding. O'Brien:Clavis Pharma: Research Funding. Ravandi:Clavis Pharma: Research Funding. Jacobsen:Clavis Pharma: Employment, Equity Ownership. Dirven:Clavis Pharma: Employment. Hagen:Clavis Pharma: Employment, Equity Ownership. Hals:Clavis Pharma: Employment. Ducharme:Learn and Confirm: Employment, Equity Ownership; Clavis Pharma: Consultancy.

A Case of Acute Lymphoblastic Leukemia with Eosinophilia.

Acute lymphoblastic leukemia with eosinophilia (ALL/E0) is a rare clinical entity. Since Spitzer and Garson’s first description, only less than 100 cases have been reported. Here we report a 48-year-old man who was diagnosed with ALL/E0 in our hospital. The patient presented with pitting edema at both his ankles on March 10, 2005. His complete blood cell counts at out patient clinic showed a WBC count of 39800/mm3 with 68% eosinophils. He was admitted. Abdominal examination showed an enlarged liver of 3cm and spleen of 4cm size, but no lymphadenopathy. No rash or purpuric patche was found. Total leucocyte count after admission was 411000/mm3 with 42% eosinophils. Platelet count was 80000/mm3, and hemoglobin was 115g/l. Bone marrow examination showed 70% blasts and 3% eosinophils, and was diagnosed as acute lymphoblastic leukemia of L3 type. Flow cytometric immunophenotyping of these blasts showed expression of CD10 (86.87%), CD22 (96.68%), CD79a (86.82%), and HLA-DR (92.59%). Cytogenetic analysis of the bone marrow showed a karyotype of 46, XY, del (1)(p32. There was no evidence of parasitic, viral or bacterial infection, drug reaction, allergic/immunologic disorder and other neoplastic disease. A diagnosis of ALL-E0 was made and the patient was start on induction chemotherapy with vincristine (4 mg, d 1,8), daunomycin (70 mg, d 1~3), cyclophosphamide (1.0 g d1, 0.6 g d8) and prednisone (60 mg, d1~14) on March 22. The eosinophils in the blood disappeared the same day after chemotherapy and the bone marrow examination on July 5 showed remission and the percentage of eosinophils was normal. Two more causes of VDCP and two additional courses of high dose arabinosyl cytosine were given, and he remains hematological remission. Eosinophilia can present before, concurrent with, or following the diagnosis of ALL. Several hypotheses seek to explain the hypereosinophilia in ALL. Il-3 plays an important role in the differentiation of the progenitor cells differentiating into mature eosinophils. In the specific cytogenetic abnormality t (5; 14)(q31; q32) and t (5; 9)(q31; p24), immunoglobulin heavy gene enhancer region joins to the promoter region of the IL-3 and JAK2 (9p24) gene, respectively, which causes high levels of IL-3 by leukaemic cells. In addition, when the purine and pyrimidine nucleotide content of the eosinophils in ALL-E0 patients was compared with that of eosinophils from healthy donors and from patients with eosinophilia not associated with leukemia, the ratios of purine: pyrimidine and of uracil:cytosine nucleotides were decreased, while the total nucleotide concentration was increased, especially the concentration of UDP-sugars and pyrimidine nucleotides. Similar changes were also detected in leukemic cells of patients with ALL compared to normal lymphocytes. Thus, it has been suggested that the eosinophils in the patients with ALL-E0 has a malignant character, and it might be an intrinsic part of the lymphoproliferative disorder and not a reaction to leukemic process. Patients with these this syndrome characteristically have cytogenetic abnormalities involving t(5;14), whereas our patient was found to have 46, XY, del(1)(p32). The prognosis of ALL- E0 seems to be determined by the effect of the chemotherapy on ALL, complications of chemotherapy and hypereosinophilia. After having been diagnosed, our patient accepted three course of VDCP (vincristine, daunomycin, Cyclophosphamide and prednisone), two courses of high dose arabinosyl cytosine. He is still in hematological remission and is preparing for allogenetic hemopoietic stem cell transplantation.

A randomized study of interferon-α versus interferon-α and low-dose arabinosyl cytosine in chronic myeloid leukemia

Interferon-α (IFN-α) has significantly prolonged survival in chronic myeloid leukemia (CML), but some patients do not respond and many responses are not durable. To improve the results, IFN-α has been combined with other treatments, but so far only the association with low-dose arabinosyl cytosine (LDAC) has been shown to increase the response rate and to prolong survival. Here are reported the results of a study of 538 Philadelphia chromosome–positive CML patients who were assigned at random to treatment with IFN-α2a alone or in combination with LDAC. The scheduled dose of IFN-α2a was 56IU/m2/d. The scheduled dose of AC was 40 mg/d for the first 10 days of each month of treatment. The efficacy endpoints were a complete hematologic response rate at 6 months (62% in the IFN-α–plus–LDAC arm versus 55% in the IFN-α arm; P = .11), major cytogenetic response (MCgR) rate at 24 months (28% versus 18%; P = .003), and overall survival (5-year survival, 68% versus 65%; P = .77). Treatment did not affect overall survival within different prognostic risk groups: low, intermediate, or high. Also the duration of MCgR was identical. The results of this study confirm the results of a similar French study only for the response rate, not for survival, suggesting that the relationship between cytogenetic response and survival may be extremely variable and that a meta-analysis of these and other studies of IFN-α versus IFN-α plus LDAC is required to settle the issue of the role of LDAC in the treatment of CML.

Modulation of human deoxycytidine kinase activity as a response to cellular stress induced by NaF.

Deoxycytidine kinase (dCK) is one of the key enzymes of deoxynucleoside salvage supplying resting lymphocytes with DNA precursors for synthesis and repair. The level of dCK activity is especially important in chemotherapy with the use of deoxynucleoside analogues like arabinosyl cytosine (Citarabid, ara-C), or 2-chloro-deoxyadenosine (Cladribine, CdA). Previous results showed that Cladribine treatment of human lymphocytes increased several fold the activity of dCK without increasing the amount of dCK protein itself (Sasvári-Székely, et al., 1998, Biochem. Pharmacol. 56, 1175), and a possible post-translational modification was suggested. This theory was further investigated using NaF as an inhibitor of protein phosphatases. It was shown that NaF treatment of cells elevated dCK activity while inhibiting DNA synthesis. The possible mechanism of dCK activation/inactivation induced by exposure of cell cultures to different agents is discussed.