WR-2721 protects against the hematologic toxicity of cyclophosphamide: a controlled phase II trial.

WR-2721 S-2-(3-aminopropylamino) ethyl phosphorothioic acid, is an organic thiophosphate compound that in the animal model selectively protects against the hematologic toxicity of cyclophosphamide by factors of 1.5 to 2.0. Preliminary data from our controlled phase I trial of WR-2721 and cyclophosphamide suggested that WR-2721 protected against cyclophosphamide-induced granulocytopenia. Since variable drug doses and infusion rates were used in these early studies, we initiated a controlled phase II trial using constant drug doses to establish more precisely WR-2721's level of protection. Initially, 21 patients received 1,500 mg/m2 of cyclophosphamide alone and were retreated 4 weeks later after hematologic recovery was complete with 740 mg/m2 of WR-2721 before the same dose of cyclophosphamide. With WR-2721 pretreatment, 19 of 21 (90%) patients had improved WBC and granulocyte counts. The mean WBC increased from 1,760/mL with cyclophosphamide alone to 2,500/mL with WR-2721 pretreatment (P less than .0005)...