A phase I study of the novel ribonucleotide reductase inhibitor 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, Triapine) in combination with the nucleoside analog fludarabine for patients with refractory acute leukemias and aggressive myeloproliferative disorders.

Triapine is a potent ribonucleotide reductase (RR) inhibitor that depletes intracellular deoxyribonculeotide pools, especially dATP. We designed a Phase I trial of Triapine followed by the adenosine analog fludarabine in adults with refractory acute leukemias and aggressive myeloproliferative disorders (MPD). Two schedules were examined: (A) Triapine 105 mg/m(2)/day over 4 h followed by fludarabine daily x 5 (24 patients, fludarabine 15-30 mg/m(2)/dose); (B) Triapine 200 mg/m(2) over 24h followed by 5 days of fludarabine 30 mg/m(2)/day (9 patients). Complete and partial responses (CR, PR) occurred in Schedule A (5/24, 21%), with CR occurring at the 2 highest fludarabine doses (2/12, 17%). In contrast, no CR or PR occurred in Schedule B. Four of the 5 responses occurred in patients with underlying MPD (4/14, 29%). Drug-related toxicities included fever and metabolic acidosis. Triapine 105 mg/m(2) followed by fludarabine 30 mg/m2 daily x 5 is active in refractory myeloid malignancies and warrants continuing study for patients with aggressive MPD.