Background: 3-Aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) is a novel small-molecule ribonucleotide reductase inhibitor. This study was designed to estimate the maximum tolerated dose (MTD) and oral bioavailability of 3-AP in patients with advanced-stage solid tumors. Methods: Twenty patients received one dose of intravenous and subsequent cycles of oral 3-AP following a 3 + 3 patient dose escalation. Intravenous 3-AP was administered to every patient at a fixed dose of 100 mg over a 2-h infusion 1 week prior to the first oral cycle. Oral 3-AP was administered every 12 h for 5 consecutive doses on days 1-3, days 8-10, and days 15-17 of every 28-day cycle. 3-AP was started at 50 mg with a planned dose escalation to 100, 150, and 200 mg. Dose-limiting toxicities (DLT) and bioavailability were evaluated. Results: Twenty patients were enrolled. For dose level 1 (50 mg), the second of three treated patients had a DLT of grade 3 hypertension. In the dose level 1 expansion cohort, three patients had no DLTs. No further DLTs were encountered during escalation until the 200-mg dose was reached. At the 200 mg 3-AP dose level, two treated patients had DLTs of grade 3 hypoxia. One additional DLT of grade 4 febrile neutropenia was subsequently observed at the de-escalated 150 mg dose. One DLT in 6 evaluable patients established the MTD as 150 mg per dose on this dosing schedule. Responses in the form of stable disease occurred in 5 (25%) of 20 patients. The oral bioavailability of 3-AP was 67 ± 29% and was consistent with the finding that the MTD by the oral route was 33% higher than by the intravenous route. Conclusions: Oral 3-AP is well tolerated and has an MTD similar to its intravenous form after accounting for the oral bioavailability. Oral 3-AP is associated with a modest clinical benefit rate of 25% in our treated patient population with advanced solid tumors.
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