Comparative cytotoxicity of folate-based inhibitors of thymidylate synthase and 5-fluorouracil +/- leucovorin in MGH-U1 cells.
Thymidylate synthase (TS) is a critical enzyme in the synthesis of DNA and an important target for cancer chemotherapy. 5-Fluorouracil (5FU) combined with leucovorin (LV) has been used to inhibit TS, and inhibition is dependent on the formation of a ternary complex between a folate cofactor, TS, and 5-fluorodeoxyuridine monophosphate (FdUMP), a metabolite of FU. The folate-based TS inhibitors CB3717, its analogs, and BW1843U89 have been synthesized as specific inhibitors of TS that do not require activation or the presence of a cofactor. We have compared the cytotoxicity of 5FU +/- LV with that of these folate-based TS inhibitors in human bladder cancer MGH-U1 cells using a colony-forming assay. After a 6-h exposure, FU+LV, CB3717, dCB3717, or C2 methyl dideazafolate analogs demonstrated similar cytotoxic potency that was 0.96 to 2.9 times that of 5FU alone. A 24-h exposure did not increase the potency of 5FU+LV relative to 5FU alone, but there was a marked increase in the cytotoxicity of the dideazafolates as compared with 5FU+LV. Similarly, BW1843U89 was more cytotoxic than 5FU/LV. This was reflected in a 3.2- to 1333-fold decrease in the 50% inhibitory concentration (IC50). Simultaneous exposure to LV and thymidine (TdR) protected MGH-U1 cells from the cytotoxicity of CB3717, its analogs, and BW1843U89. We conclude that (a) the folate-based TS inhibitors are more potent than 5FU+LV after a 24-h exposure, (b) protection by LV and TdR indicates that TS inhibition is the primary site of action, and (c) BW1843U89 is more potent than D1694 in MGH-U1 cells.
Erlichman
C
C
Division of Experimental Therapeutics, Ontario Cancer Institute, Toronto, Canada.
Mitrovski
B
B
D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D005472:Fluorouracil / Q000008:administration & dosage / Q000494:pharmacology*; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology*; D005971:Glutamates / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007211:Indoles / Q000737:chemistry / Q000494:pharmacology*; D054833:Isoindoles; D002955:Leucovorin / Q000008:administration & dosage / Q000494:pharmacology*; D011799:Quinazolines / Q000737:chemistry / Q000494:pharmacology*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy*
D000970:Antineoplastic Agents; D005971:Glutamates; D007211:Indoles; D054833:Isoindoles; D011799:Quinazolines; C079601:1843U89; C031662:CB 3717; D005492:Folic Acid; D013940:Thymidylate Synthase; D002955:Leucovorin; D005472:Fluorouracil