A phase I clinical trial of novobiocin, a modulator of alkylating agent cytotoxicity.

Antineoplastic drug resistance is a major obstacle to improved treatment of most adult cancers in humans. Novobiocin, an antibacterial agent which inhibits the eukaryotic topoisomerase II enzyme, increases the cytotoxicity of several alkylating agents in vitro by the formation of lethal DNA-DNA interstrand cross-links, perhaps by decreasing the repair of drug monoadducts. In murine tumors treated in vivo novobiocin markedly potentiates alkylating agent cytotoxicity without concomitant increases in host toxicity. With this background, a Phase I trial of novobiocin and cyclophosphamide was performed in refractory cancer patients. Novobiocin was given p.o. for 96 h; 750 mg/m2 of i.v. cyclophosphamide was administered at 48 h. Thirty-four patients received 65 courses. The dose-limiting toxicity of novobiocin in this trial was vomiting. The maximum tolerated dose was 6 g/day. Six of 34 patients had Grade III or IV mylosuppression but no dose escalation effect was noted. Three patients developed allergic reactions which resolved completely. No other significant toxicity occurred. While no dose-dependent effect on serum novobiocin levels occurred, 18 of 19 patients treated at greater than or equal to 4 g daily had serum levels greater than or equal to 100 micrograms/ml at steady state, a level which corresponds to levels used in vitro and seen in vivo where the murine novobiocin half-life of 82 min is far less than that seen in humans (6.0 h). Two of 30 evaluable patients had partial responses. Four other patients had stable disease. Four of six had prior disease progression on cyclophosphamide combination therapy. Novobiocin is well tolerated in patients receiving cyclophosphamide and blood levels are in the drug-potentiating range. Phase II trials in cyclophosphamide refractory patients are anticipated.