A first-in-human phase I study of CZ48, a lactone ring protected oral camptothecin, in patients with advanced solid tumors.

Abstract

2578 Background: CZ48, the 20-O-propionate ester of camptothecin (CPT), is a prodrug of CPT first described by Cao et al. in 1998. The side-chain is enzymatically cleaved in tissues. This gives rise to CPT, a potent inhibitor of topoisomerase I. Methods: An open-label, single-arm, dose-escalation Phase I study was performed to determine the maximum tolerated dose (MTD) of CZ48 in patients with advanced solid tumors. Initial dosing started qd po 80mg/m2, advancing to 2560mg/m2 for 21 consecutive days, followed by 7 days rest. Dosing was restarted in cohorts of 3 patients tid po at 18mg/m2 and escalated to 1g/m2on a 5 days on, 2 days off schedule for 28 days. Patients were prescreened by measuring CPT levels in plasma following a single pilot dose of CZ48. Dose was doubled until occurrence of at least Grade 2 adverse event, at which time 3+3 patient cohorts with a dose escalation of 33%-100% were implemented. DLT in 2/6 patients defined the MTD as the preceding DLT dose. PK parameters were measured prior to dosing, days 1-5, and day 28 of Cycle 1. Results: Poor absorption led to initial qd dosing reaching 2560mg/m2 with no signs of DLT. Subsequent tid dosing showed improved plasma levels and arrival at DLT. 34 patients were treated across 8 dose levels from 18 to 1000 mg/m2. The most frequent study-related adverse effects were cystitis, vomiting, diarrhea and fatigue. Grade IV toxicities observed were febrile neutropenia, anemia, and thrombocytopenia. Preliminary PK data in the qd dosing showed poor correlation between dose and Cmax or AUC, while PK in tid patients showed slightly improved correlation between dose and both CZ48 AUC (Pearson's correlation coefficient ϱ=0.476, p<0.01) and CZ48 Cmax(ϱ =0.51, p<0.01). Evidence of clinical activity with stable disease ≥ 6 months was observed in 2 heavily pre-treated colon and one breast cancer patient. Conclusions: The MTD of tid po CZ48 administered 5 days on, 2 days off of 28-day cycle is between 750 mg/m2 and 576 mg/m2. Overall toxicity is relatively mild, with DLT being cystitis and myelosuppression. Even with tid dosing, PK values correlate poorly to dose. A new formulation with 3-5 fold higher preclinical absorption values is being considered for introduction into the trial. Clinical trial information: NCT00947739.