A PHASE I II STUDY OF CONTINUOUS-INFUSION SURAMIN IN PATIENTS WITH HORMONE-REFRACTORY PROSTATE-CANCER - TOXICITY AND RESPONSE/

Introduction: Suramin is a synthetic polysulfonated naphthylurea which has been used for the treatment of African trypanosomiasis and onchoc erciasis, but since the mid-1980s has received attention as a possible antiretroviral and antineoplastic agent. Objective: This clinical tri al of suramin was undertaken as a phase I/II study in patients with ho rmone-refractory prostate cancer,with the hypothesis that the intensit y of therapy with suramin could be increased significantly if measures were undertaken to maintain the plasma concentrations of the drug und er 300 mu g/ml. Methods: We report the clinical results of this trial, wherein patients were treated at three different targeted plasma sura min concentrations (275, 215 and 175 mu g/ml) for varying periods of t ime (2, 4 or 8 weeks), with delivery of the drug by continuous intrave nous infusion. Results: The major toxicity observed in this trial was neurologic, consisting of a motor and sensory peripheral neuropathy th at resulted in both paresis and paralysis of the limbs. Nearly all of this severe (CTEP grade III, IV) neurologic toxicity was observed in t he patients treated at a plasma suramin concentration of 275 mu g/ml f or 4 or more weeks. A single patient treated at 215 mu g/ml for 8 week s developed moderate (CTEP grade III) proximal lower extremity weaknes s, and no patient treated at 175 mu g/ml developed this toxicity. The second most common toxicity observed was infection of the central veno us catheter. The overall response rate for all of the evaluable patien ts was 17% (13 of 75 patients). In addition, prostate-specific antigen (PSA)-defined responses were observed in six patients receiving thera py at 175 mu g/ml, but these responses were confounded by cessation of therapy with flutamide during suramin treatment. Conclusions: In summ ary, although plasma suramin concentrations were maintained below 300 mu g/ml, neurologic toxicity nonetheless occurred with high frequency in patients treated at 275 mu g/ml for 4 or more weeks. Therapy at 215 and 175 mu g/ml was in general well tolerated, but central Venous cat heter-related infection, as well as the inconvenience and expense of c ontinuous infusional therapy, make this method of drug delivery imprac tical. Only moderate antitumor activity was observed during this trial , but it is possible that both continuation of flutamide and flutamide withdrawal during suramin therapy confounded the assessment of surami n's activity in hormone-refractory prostate cancer.