Bm. Oconnor et al., BIOLOGICAL-ACTIVITY OF A NOVEL RATIONALLY DESIGNED LIPOPHILIC THYMIDYLATE SYNTHASE INHIBITOR, Cancer chemotherapy and pharmacology, 34(3), 1994, pp. 225-229
AG-331 fonyl)benzyl]N-6-methyl-2,6-diamino-benz[cd]indole glucuronate}
is a novel lipophilic thymidylate synthase (TS) inhibitor. The proper
ties of this compound were investigated in H35 rat hepatoma cells and
in three variant cell lines resistant to antifolates by differing mech
anisms. There was no evidence for any intracellular effect of AG-331 o
n dihydrofolate reductase (DHFR); however, the low degree of cross-res
istance found for the H35FF line, which has elevated TS levels, sugges
ted that TS may not be the sole locus of action of AG-331 in hepatoma
cells. TS-directed effects of AG-331 were suggested by the pattern of
its inhibition of deoxyuridine incorporation into DNA and the lesser e
ffects on purine incorporation. In addition, H35 cells treated with 10
mu M AG-331 were shown to accumulate in the S phase of the cell cycle
, and this effect could be reversed by coadministration of thymidine.
However, when treatments were conducted at a 5-fold higher concentrati
on of AG-331, no S-phase block was apparent, suggesting the loss of a
TS-directed effect at high inhibitor concentrations. Thymidine and fol
inic acid also failed to protect cells against AG-331 cytotoxicity, su
ggesting an alternate mode of action. Similar results were also obtain
ed in protection experiments with a human hepatoma cell line, HEPG2, a
lthough previous results obtained in colon- and breast-cancer cell lin
es have suggested TS specific effects for AG-331. The possibility that
biotransformation of AG-331 to other toxic species may occur in liver
-derived cell lines has yet to be investigated.