Phase I trial of combretastatin a-4 phosphate with carboplatin

Preclinical evidence of synergy led to a phase I trial employing combretastatin A-4 phosphate (CA4P), a novel tubulin-binding antivascular drug, in combination with carboplatin.

Based on preclinical scheduling studies, patients were treated on day 1 of a 21-day cycle. Carboplatin was given as a 30-minute i.v. infusion and CA4P was given 60 minutes later as a 10-minute infusion.

Sixteen patients with solid tumors received 40 cycles of therapy at CA4P doses of 27 and 36 mg/m(2) together with carboplatin at area under the concentration-time curve (AUC) values of 4 and 5 mg min/mL. The dose-limiting toxicity of thrombocytopenia halted the dose escalation phase of the study. Four patients were treated at an amended dose level of CA4P of 36 mg/m(2) and carboplatin AUC of 4 mg min/mL although grade 3 neutropenia and thrombocytopenia were still observed. Three lines of evidence are adduced to suggest that a pharmacokinetic interaction between the drugs results in greater thrombocytopenia than anticipated: the carboplatin exposure (as AUC) was greater than predicted; the platelet nadirs were lower than predicted; and the deviation of the carboplatin exposure from predicted was proportional to the AUC of CA4, the active metabolite of CA4P. Patient benefit included six patients with stable disease lasting at least four cycles.

This study of CA4P and carboplatin given in combination showed dose-limiting thrombocytopenia. Pharmacokinetic/pharmacodynamic modeling permitted the inference that altered carboplatin pharmacokinetics caused the increment in platelet toxicity.