Background: Raltitrexed is a novel thymidylate synthase inhibitor with single agent activity in colorectal, nonsmall cell lung, and breast carcinomas. The recommended Phase II dose of raltitrexed administered as a single agent is 3 mg/m2 every 3 weeks. Paclitaxel also has a broad spectrum of activity. A Phase I study of both agents in combination therapy was conducted.
Methods: Eligible patients had refractory solid tumors and a Cancer and Leukemia Group B performance status of 0 to 2. Cohorts of patients were treated with escalating doses of raltitrexed as a 15-minute intravenous infusion immediately followed by 175 mg/m2 of paclitaxel administered over 3 hours. Dose-limiting toxicity was defined as World Health Organization Grade 4 neutropenia with fever, Grade 4 thrombocytopenia requiring platelet transfusion, a nonhematologic toxicity of Grade 3 or higher (excluding nausea, emesis, and alopecia), or failure of toxicities to recover to Grade 1 or lower within 21 days after causing a dose delay.
Results: A total of 33 patients enrolled in the study. Raltitrexed was escalated in increments of 0.5 mg/m2, from 0.5 mg/m2 to the recommended Phase II dose of 3 mg/m2. Dose-limiting toxicity first was observed at a raltitrexed dose of 2 mg/m2. At a dose of 3 mg/m2, dose-limiting neutropenia was observed in 2 of 12 patients. Diarrhea was the other dose-limiting toxicity. Two patients achieved a partial response (one patient with carcinoma of the head and neck and another with gallbladder carcinoma).
Conclusions: The authors conclude that raltitrexed and paclitaxel may be administered in combination at their respective single agent Phase II doses. Phase II testing of this combination is indicated.