Biochemical modulation of bolus fluorouracil by PALA in patients with advanced colorectal cancer.

Abstract

PURPOSE N-(phosphonacetyl)-L-aspartic acid (PALA) is a pyrimidine synthesis inhibitor that modulates fluorouracil (FU) cytotoxicity. Two previous studies of patients with colorectal carcinoma documented complete response (CR) and partial response (PR) rates of 40% and 43% using weekly low-dose PALA followed by a 24-hour FU infusion. We investigated whether comparable results could be obtained with biochemical modulation by low-dose PALA using bolus instead of infusional FU. PATIENTS AND METHODS Forty-five patients without prior chemotherapy who had advanced colorectal carcinoma were treated with PALA 250 mg/m2 followed 24 hours later by bolus FU at three dose levels, 600, 700, 800 mg/m2, repeated weekly for 6 weeks followed by a 2-week break. RESULTS The CR and PR rate was 15 of 43 patients or 35% (95% confidence interval [CI], 21% to 49%), with an overall median survival of 18 months. Grade 3 or 4 diarrhea was the major toxicity observed in 24% of patients receiving FU at 700 mg/m2 and in 43% of patients receiving 800 mg/m2. Hematologic toxicity was observed only with an FU dose of 800 mg/m2, and 29% (four of 14) of patients developed grade 4 leukopenia. We also noted the development of ascites in six patients, mild hyperbilirubinemia in 16 patients, and a decreased albumin level in 22 patients; these abnormalities occurred more frequently in responding patients. CONCLUSIONS The observed response rate, median survival, and toxicity in this study are similar to those obtained with PALA plus infusional FU and with other methods of FU modulation. Larger phase III studies are needed to compare bolus FU/PALA regimens with other PALA and non-PALA-containing combinations. Our future focus will be attenuate this regimen's toxicity while maintaining or improving its response rates and survival.