S-CKD602 is a pegylated liposomal formulation of CKD-602. This study is the first to evaluate the factors affecting the high interpatient variability in the pharmacokinetic disposition of S-CKD602. S-CKD602 was administered intravenously (i.v.) every 3 weeks as part of a phase I study. Pharmacokinetics studies of the liposomal encapsulated and released CKD-602 in plasma were performed. The pharmacokinetic variability of S-CKD602 is associated with both linear and nonlinear clearances. Patients > or =60 years of age have a 2.7-fold higher exposure of S-CKD602 as compared with patients <60 years of age (P = 0.02). Patients with a lean body composition have a higher plasma exposure of S-CKD602 (P = 0.02). Patients who have received prior therapy with pegylated liposomal doxorubicin (PLD) have a 2.2-fold higher exposure of S-CKD602 as compared with patients who have not received PLD (P = 0.045). Prolonged exposure of the encapsulated drug in plasma over 1-2 weeks provides significant pharmacologic advantages. The high interpatient variability in the pharmacokinetic disposition of S-CKD602 was associated with age, body composition, saturable clearance, and prior PLD therapy.

Monocytes are more sensitive to S-CKD602, compared with neutrophils, and the increased sensitivity is related to the liposomal formulation, not CKD-602. These results suggest that monocytes engulf S-CKD602, which causes the release of CKD-602 from the liposome and toxicity to the monocytes, and that the effects are more prominent in patients <60.

Purpose: S-CKD602 is a pegylated liposomal formulation of CKD602, a semisynthetic camptothecin analogue. Pegylated (STEALTH) liposomes can achieve extended drug exposure in plasma and tumor. Based on promising preclinical data, the first phase I study of S-CKD602 was done in patients with refractory solid tumors. Experimental Design: S-CKD602 was administered i.v. every 3 weeks. Modified Fibonacci escalation was used (three to six patients/cohort), and dose levels ranged from 0.1to 2.5 mg/m 2 . Serial plasma samples were obtained over 2 weeks and total (lactone + hydroxyl acid) concentrations of encapsulated, released, and sum total (encapsulated + released) CKD602 measured by liquid chromatography-tandem mass spectrometry. Results: Forty-five patients (21males) were treated. Median age, 62 years (range, 33-79 years) and Eastern Cooperative Oncology Group status, 0 to 1 (43 patients) and 2 (2 patients). Dose-limiting toxicities of grade 3 mucositis occurred in one of six patients at 0.3 mg/m 2 , grade 3 and 4 bone marrow suppression in two of three patients at 2.5 mg/m 2 , and grade 3 febrile neutropenia and anemia in one of six patients at 2.1 mg/m 2 . The maximum tolerated dose was 2.1 mg/m 2 . Partial responses occurredin two patients with refractory ovarian cancer (1.7 and 2.1mg/m 2 ). Highinterpatient variability occurred in the pharmacokinetic disposition of encapsulated and released CKD602. Conclusions: S-CKD602 represents a promising new liposomal camptothecin analogue with manageable toxicity and promising antitumor activity. Phase II studies of S-CKD602 at 2.1mg/m 2 i.v. once every 3 weeks are planned. Prolonged plasma exposure over 1to 2 weeks is consistent with STEALTH liposomes and provides extended exposure compared with single doses of nonliposomal camptothecins.

S-CKD602 is a pegylated long-circulating liposomal formulation of CKD-602, a potent topoisomerase I inhibitor. A population pharmacokinetic (PK) model for encapsulated and released CKD-602 following administration of S-CKD602 was developed to assess factors that may influence S-CKD602 PK. Plasma samples from 45 patients with solid tumors were collected in a phase 1 study. S-CKD602 was administered as a 1-hour intravenous infusion with doses ranging from 0.1 to 2.5 mg/m(2) . Plasma concentrations of encapsulated and released CKD-602 were used to develop a population PK model using NONMEM. PK of encapsulated CKD-602 was described by a 1-compartment model with nonlinear clearance, and PK of released CKD-602 was described by a 2-compartment model with linear clearance for all patients. Covariate analysis revealed that tumor in the liver was a significant covariate for clearance of encapsulated CKD-602 and that age significantly influenced the release rate of CKD-602 from S-CKD602. Maximum elimination rate in patients with liver tumor is 1.5-fold higher compared with patients without liver tumor. Release rate of CKD-602 from S-CKD602 in patients less than 60 years old was 2.7-fold higher compared with patients 60 years old or older. These observations have potential implications in the optimal dosing of liposomal agents.

These findings suggest that inter-individual variability in 9AC disposition, but not 9NC, may be influenced, in part, by ABCG2 genotype. In contrast, there was no evidence for a relationship between ABCG2 and the disposition of 9NC, or for relationships between ABCB1 and ABCC2 genotypes and the disposition of 9NC or 9AC.