Objectives: CI-994 (N-acetyl dinaline, PD 123654) is a novel oral agent active in a broad variety of murine and human tumor xenografts. While cytotoxic in the Brown Norway (BN) rat leukemia model, growth inhibition in other murine and human tumor xenografts is predominantly cytostatic. Its specific mechanism of action remains unknown. Following CI-994 administration, inhibition of both histone deacetylation and cellular proliferation at the G1 to S transition phase of the cell cycle are observed. This Phase 1 study in patients with solid tumors was carried out to determine a maximum tolerated daily oral dose (MTD) for CI-994 administered on a chronic basis.
Methods: Fifty-three patients received CI-994 daily for treatment durations ranging from 2 to 10 weeks. Dosage escalation proceeded in 2 phases; an Acute Dosing Phase (n = 11) to define the MTD for CI-994 administered over 2 weeks and a Chronic Dosing Phase (n = 29) to define the MTD for daily administration for 8 weeks. Upon completion of the Chronic Dosing Phase, a third cohort of patients (n = 13) received CI-994 at the recommended Phase 2 dose and schedule with 2 additional single doses of drug administered separated by a 1-week washout to assess the effect of food on CI-994 pharmacokinetics.
Results: Thrombocytopenia was dose limiting at the MTD of 8 mg/m2/day for 8 weeks. Other toxicities included fatigue and gastrointestinal effects such as nausea, vomiting, diarrhea, constipation and mucositis. Pharmacokinetic studies revealed that peak plasma levels and AUC's generally increased with dose and that food intake did not affect the rate or extent of drug absorption. One patient with heavily pre-treated adenocarcinoma of the lung achieved a Partial Response (PR) lasting over 2 years and 3 additional patients achieved Stable Disease (SD), 1 each with non-small cell lung, colorectal, and renal cancer.
Conclusions: The recommended Phase 2 starting dose is 8 mg/m2/day for 8 weeks repeated after a 2-week drug-free interval.