A phase I–II study of N-(phosphonacetyl)-l-aspartic acid (PALA) added to 5-fluorouracil and folinic acid in advanced colorectal cancer

N-(phosphonacetyl)-l-aspartic acid (PALA) inhibits the enzyme l-aspartic acid transcarbamoylase (ATCase) which is important in de novo pyrimidine synthesis. Low dosages of PALA modulate the in vitro activity of 5-fluorouracil (5-FU) and PALA (250 mg/m2) inhibits pyrimidine synthesis in patients. PALA (250 mg/m2 day 1) was combined with an established 5-FU/folinic acid (FA) regimen [FA (200 mg/m2 over 2 h days 2+3) and bolus and 22 h infusional 5-FU (300–500 mg/m2 days 2+3)] without the need for dose reduction of 5-FU or FA. 35 patients were entered. Treatment was well tolerated; 427 patients experienced ≥ ECOG grade 3 toxicity at full 5-FU dosage (500 mg/m2 bolus/infusion). However, the response rate in 33 evaluable patients was only 6.1% [95% confidence intervals (C.I.) 0.2–21.8%]. Median response duration was short (4 months, 95% C.I. 3–6 months) and overall median survival was 10 months (95% C.I. 7–16 months). Although PALA (250 mg/m2) can be combined with full dosage 5-FUFA, the combination has poor activity in colorectal cancer.