STUDIES ON THE ANTITUMOR EFFECTS OF ANALOGS OF 5,8-DIDEAZAISOFOLIC ACID AND 5,8-DIDEAZAISOAMINOPTERIN

Six new analogues of 5,8-dideazaisofolic acid and 5,8-dideazaisoaminop terin were synthesized in an effort to obtain enhanced antitumor activ ity. The modifications included the replacement of the 2-amino group b y hydrogen or methyl as well as the inclusion of a methyl substituent at position 9. Based upon activity against L1210 leukemia cells in cul ture, three of the new analogues together with one compound described previously were evaluated for cytotoxicity in vitro using three human tumor cell lines (Cole 320 DM, Hep G2 and HL-60). The most effective c ompound was 2-desamino-N-9-methyl-5,8-dideazaisoaminopterin (2c) with the HL-60 cells being the most sensitive to its cytotoxic effects. The se analogues were evaluated in vitro as inhibitors of dihydrofolate re ductase (DHFR) and thymidylate synthase (TS) from human as well as bac terial (Lactobacillus casei) sources. All four of the 4-amino analogue s were most effective toward L. casei DHFR compared with human DHFR, w ith 2-desamino-2-methyl-5,8-dideazaisoaminopterin (2d) and its 9-methy l derivative (2e) having 818- and 430-fold greater selectivity (L. cas eilhuman). Most of the compounds studied were found to be only modest inhibitors of human TS (I-50 values = 1.5 to 20 mu M) and were therefo re at least 40-fold less inhibitory than 10-propargyl-5,8-dideazafolic acid. Nevertheless, reversal of cytotoxicity studies with thymidine, hypoxanthine and folinic acid using the HL-60 cell line suggested that TS is the primary target for these analogues.