Mechanism-based model characterizing bidirectional interaction between PEGylated liposomal CKD-602 (S-CKD602) and monocytes in cancer patients.

S-CKD602 is a PEGylated liposomal formulation of CKD-602, a potent topoisomerase I inhibitor. The objective of this study was to characterize the bidirectional pharmacokinetic-pharmacodynamic (PK-PD) interaction between S-CKD602 and monocytes. Plasma concentrations of encapsulated CKD-602 and monocytes counts from 45 patients with solid tumors were collected following intravenous administration of S-CKD602 in the phase I study. The PK-PD models were developed and fit simultaneously to the PK-PD data, using NONMEM(®). The monocytopenia after administration of S-CKD602 was described by direct toxicity to monocytes in a mechanism-based model, and by direct toxicity to progenitor cells in bone marrow in a myelosuppression-based model. The nonlinear PK disposition of S-CKD602 was described by linear degradation and irreversible binding to monocytes in the mechanism-based model, and Michaelis-Menten kinetics in the myelosuppression-based model. The mechanism-based PK-PD model characterized the nonlinear PK disposition, and the bidirectional PK-PD interaction between S-CKD602 and monocytes.

Population pharmacokinetics of pegylated liposomal CKD-602 (S-CKD602) in patients with advanced malignancies.

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.

Bidirectional pharmacodynamic interaction between pegylated liposomal CKD-602 (S-CKD602) and monocytes in patients with refractory solid tumors.

BACKGROUND: STEALTH(®) liposomal CKD-602 (S-CKD602), a camptothecin analog, is eliminated by the reticuloendothelial system (RES), which consists of cells, including monocytes. We evaluated the relationship between monocyte and absolute neutrophil counts (ANCs) in the blood and pharmacokinetic disposition of S-CKD602 and nonliposomal CKD-602 (NL-CKD602) in patients. METHODS: As part of a phase I study of S-CKD602 and phase I and II studies of NL-CKD602, the percent decreases in ANC and monocytes at their nadir were calculated. After S-CKD602, the amount of CKD-602 recovered in urine was measured. RESULTS: For S-CKD602 in patients <60 years, the percent decrease in ANC and monocytes were 43 ± 31 and 58 ± 26%, respectively (P = 0.001). For S-CKD602 in patients ≥60, the percent decrease in ANC and monocytes were 41 ± 31 and 45 ± 36%, respectively (P = 0.50). For NL-CKD602 (n = 42), the percent decrease in ANC and monocytes were similar (P > 0.05). For S-CKD602, the relationship between the percent decrease in monocytes and CKD-602 recovered in urine was stronger in patients <60 (R(2) = 0.82), compared with patients ≥60 (R(2) = 0.30). CONCLUSIONS: 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.

Phase I and pharmacokinetic study of pegylated liposomal CKD-602 in patients with advanced malignancies.

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 0.1 to 2.5 mg/m2. 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 (21 males) 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/m2, grade 3 and 4 bone marrow suppression in two of three patients at 2.5 mg/m2, and grade 3 febrile neutropenia and anemia in one of six patients at 2.1 mg/m2. The maximum tolerated dose was 2.1 mg/m2. Partial responses occurred in two patients with refractory ovarian cancer (1.7 and 2.1 mg/m2). High interpatient 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 2.1 mg/m2 i.v. once every 3 weeks are planned. Prolonged plasma exposure over 1 to 2 weeks is consistent with STEALTH liposomes and provides extended exposure compared with single doses of nonliposomal camptothecins.

Disposition of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite in relation to ABC transporter genotypes.

PURPOSE: The source of the pharmacokinetic variability of 9-nitrocamptothecin (9NC) and its 9-aminocamptothecin (9AC) metabolite is unknown. ATP-binding cassette (ABC) transporters have been reported to modulate camptothecin analogues, are associated with camptothecin resistance, and might also affect 9NC and 9AC pharmacokinetics. The aim of this study was to evaluate the functional consequence of known single nucleotide polymorphisms in the transporter genes ABCB1, ABCC2, and ABCG2 on the pharmacokinetic disposition of 9NC and 9AC. EXPERIMENTAL DESIGN: Pharmacokinetic and genotyping studies were performed in 55 patients as part of two phase I studies of 9NC in patients with refractory solid tumors, a phase II study of 9NC in patients with advanced colon cancer, and a study evaluating the disposition of 9NC after administration of a single dose under fasting conditions. DNA was isolated from plasma and analyzed for variants in ABCB1, ABCC2, and ABCG2 genes. The ABCB1 1236C>T (n = 43), ABCB1 2677G>T/A (n = 43), ABCB1 3435C>T (n = 43), ABCC2 3972C>T (n = 39), and ABCG2 421C>A (n = 42) variants were analyzed using Pyrosequencing. RESULTS: The ABCG2 421C>A genotype significantly affected the pharmacokinetics of 9AC. The mean 9AC lactone AUC/dose for wild-type (n = 25) and heterozygous (n = 2) patients were 14.3 ng/mL x h and 51.1 ng/mL x h, respectively (P = 0.032). The mean +/- SD 9AC total AUC/dose for wild-type (n = 39) and heterozygous (n = 3) patients were 91.9 +/- 78.3 ng/mL x h and 129.0 +/- 90.5 ng/mL x h, respectively (P = 0.40). 9NC and 9AC disposition were not significantly influenced by variants in ABCB1, ABCC2, and ABCG2, and ABCB1 and ABCC2, respectively (P > 0.05). CONCLUSION: 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.