Phase I and pharmacodynamic study of Triapine, a novel ribonucleotide reductase inhibitor, in patients with advanced leukemia.

In a phase I study, 24 patients with refractory leukemia received Triapine, a novel ribonucleotide reductase (RR) inhibitor, as a continuous intravenous infusion over 96 h beginning on days 1 and 15 or days 1 and 8. On the days 1 and 15 regimen, the starting dose was 120 mg m(2) per day, and the maximum tolerated dose (MTD) was 160 mg m(2) per day. Three of eight patients receiving 160 mg m(2) per day in the first course, and one patient escalated to this dose in a second course, developed hepatic dose-limiting toxicity (DLT). For the days 1 and 8 regimen, the first 96 h infusion was administered at a fixed dose of 140 mg m(2) per day. The dose of the second infusion beginning on day 8 was escalated from 120 to 160 mg m(2) per day without observing DLT. No objective responses occurred. Over 70% of patients had a 50% reduction in white blood cell counts. The steady-state levels of Triapine were between 0.6 and 1 microM. As expected from the in vitro studies, at these plasma concentrations there was a decline in dATP and dGTP pools and a decrease in DNA synthetic capacity of the circulating leukemia cells. Based on these clinical, pharmacokinetic, and pharmacodynamic data, Triapine warrants further study in patients with hematologic malignancies.