A phase I study of selective cyclin dependent kinase inhibitor P1446A-05 administered on an intermittent schedule in patients with advanced refractory tumors.

Abstract

3011 Background: Cyclin-dependent kinases (Cdks) have emerged as important targets in anticancer drug development. P1446A-05 is a potent and specific inhibitor of Cdk4-D1 (IC50-0.09µM), Cdk1-B (IC50-0.025µM), and Cdk9-T (IC50-0.022µM). This study was designed to determine the maximum tolerated dose (MTD), dose limiting toxicity (DLT), safety profile, pharmacokinetics, and antitumor activity of orally administered P1446A-05 in patients with advanced refractory tumors. Methods: This study was conducted at 5 centers in India. P1446A-05 was administered in escalating doses across 5 cohorts of eligible pts starting with a dose of 75 mg once a day (OD) for 14 days in a 21 day cycle utilizing a modified Fibonacci scheme for dose escalation. 10 pts positive for cyclin D1 expression in the tumor were enrolled at MTD. Treatment was continued until unacceptable toxicity or disease progression. For pharmacokinetic analysis, blood samples were collected on days 1 and 13/14 of cycle 1 at multiple time points. In consenting pts, skin and tumor tissue biopsies were collected on days 1 (pre-dose), 8 and 15 of cycle 1. Results: A total of 29 patients were dosed. Two DLTs (abdominal pain and acute renal failure) were reported at 850 mg/d. The MTD was 600 mg/d and diarrhea was reported as 1 DLT at this dose level. Six SAEs including one death related to study drug were reported. Pharmacokinetic analysis demonstrated a median half-life of 16 to 26 h and linear increase in exposure at steady state across tested doses. Plasma concentration at 300 mg/d dose level crossed efficacy exposure of 100mg/kg of five day dosing in SCID mice. The recommended phase II dose is 600 mg OD on this schedule. Stable disease for 4 to 6 cycles was reported in 5 pts. Of them, one patient each with breast cancer, spindle cell sarcoma in neck, and nasopharyngeal carcinoma had cyclin D1 over expression. No objective responses were observed in this group of heavily pretreated patients. Conclusions: The safety profile of P1446A-05 is considered acceptable. On this dosing schedule, the MTD is determined as 600 mg/day. Further testing of P1446A-05 in phase II studies is planned.