A NEW ANALOG OF 10-DEAZAAMINOPTERIN WITH MARKEDLY ENHANCED CURATIVE EFFECTS AGAINST HUMAN TUMOR XENOGRAFTS IN MICE

Purpose: These studies sought to evaluate the biochemical and cellular pharmacokinetic properties, cytotoxicity and antitumor efficacy of a new analogue of 10-deaza-aminopterin (PDX) against human tumors. Metho ds: Studies were conducted with a group of human tumor cell lines in c ulture examining PDX and other folate analogues as permeants for media ted membrane transport, as inhibitors of dihdrofolate reductase and as substrates for folylpolyglutamate synthetase. These same analogues we re examined for their cytotoxicity following a 3-h pulse exposure, in experiments providing a value for IC50. Other studies with these analo gues were conducted in nude mice bearing subcutaneously implanted huma n tumors. Treatment of the mice was initiated 4 days after implantatio n of the tumor using a schedule of administration of one dose per day for 5 days. The tumors were measured 6 days after cessation of therapy and compared to controls for assessment of response. Results: In the CCRF-CEM cell system, PDX was 2- to 3-fold less effective as an inhibi tor of dihydrofolate reductase than aminopterin (AMT), methotrexate (M TX) or edatrexate (EDX) but much more effective as a permeant for one- carbon, reduced folate transport inward (PDX > AMT similar or equal to EDX > MTX) and substrate for folylpolyglutamate synthetase (PDX > AMT > EDX >MTX). As predicted by these results, PDX was 15- to 40-fold mo re cytotoxic than MTX and 3- to 4-fold more cytotoxic than the highly potent EDX following a 3-h pulse exposure in culture of CCRF-CEM cells and cells from a panel of three human breast and two human nonsmall-c ell (NSC) lung cancers. The same relative differences were shown for t he therapeutic efficacy of these three analogues at equitoxic doses in studies with the human MX-1 and LX-1 tumors and the human A549 NSC lu ng tumor xenografted in nude mice. On a schedule of qd x 5 given 3-4 d ays posttransplant, MTX was minimally active (modest tumor growth dela y) against all three tumors. EDX was highly active (25-35% complete re gressions and 5-10% cures) against the MX-1 and LX-1 tumors but very m odestly active (no regressions) against the A549 tumor. In contrast, P DX was even more active (75-85% complete regressions and 25-30% cures) than EDX against the MX-1 and LX-1 tumors and highly active (30% comp lete regressions and 20% cures) against the A549 tumor. Conclusions: T hese studies showed significantly enhanced antitumor properties of PDX compared with MTX and EDX. Based upon these results, clinical trials of PDX in patients with metastatic breast and NSC lung cancer appear t o be warranted.