Pyrazine diazohydroxide (NSC-361456) - Phase I clinical and pharmacokinetic studies

Pyrazine diazohydroxide (NSC-361456) was identified as an active congener of pyridine 2-diazohydroxide with enhanced stability under physiologic conditions. In this phase I study, 35 patients with advanced cancer received 62 courses of PZDH administered intravenously every 3 weeks at doses ranging from 15-608 mg/m². The dose-limiting toxicity was myelosuppression and the maximal tolerated dose was 487 mg/m². Hematologie toxicity was delayed and prolonged with median time to recovery about 5 weeks. Mild gastrointestinal toxicity in the form of nausea and vomiting was fairly common. Ondansetron was effective in reducing nausea and vomiting at higher dose levels. Other less common reactions included stomatitis, diarrhea, fatigue, alopecia, and mild abnormalities of renal function and hepatic enzymes. PZDH pharmacokinetics were characterized in 16 patients who received doses of 100-608 mg/m². Plasma elimination was fit to one (12/16) or two (4/16) compartment model with a mean k₁₀ half-life of 11.5 min. Clearance was dose dependent. Hematologic toxicity was related to PZDH dose, AUC and peak plasma concentration. The sigmoidal relationships between hematologic toxicity and AUC or peak plasma concentration were well described by the Hill equation. There were no objective responses observed in this study. Based on this study, the recommended dose for phase II evaluation of PZDH using this schedule is 390 mg/m².