Mechanisms of action of FdUMP[10]: metabolite activation and thymidylate synthase inhibition.
FdUMP[10] is a multimer of FdUMP, a suicide inhibitor of thymidylate synthase (TS), and was designed to bypass resistance to 5-fluorouracil (5FU). The aim of the study was to compare the effect of FdUMP[10] with 5FU and 5-fluoro-2-deoxyuridine (FUdR) in their efficacy to inhibit their target TS in resistant cells. Therefore cell lines FM3A/0, FM3A/TK- (deficient in thymidine kinase) and FM3A/TS- (deficient in thymidylate synthase) were used to determine TK dependency and specificity for TS inhibition. FdUMP[10] inhibited cell growth with greater potency than 5FU and FdUMP. Direct folate-based inhibitors Raltitrexed, GW1843U89 and Pemetrexed were also evaluated using these cell lines. In TK-deficient cells these folate-based inhibitors had greater potency than the fluoropyrimidines (FPs). Surprisingly, Pemetrexed even inhibited cell growth in TS-deficient cells. Incubation with nucleotidase and phosphatase inhibitors resulted in a reduction of cytotoxicity of FdUMP[10], indicating that the drug can be degraded outside the cells. In the TS in situ inhibition assay (TSIA) 24 h exposure of FM3A cells to 0.5 microM FdUMP and 0.05 microM FdUMP[10] decreased TSIA to 7 and 1% of control. Inhibition of nucleotidase and phosphatase activities reduced the effect of FdUMP[10], while the inhibitory effect was lower in cells lacking TK. FdUMP[10] can enter the cells intact, but also to some extent after dephosphorylation. In conclusion, FdUMP[10] can bypass resistance to FUdR by direct inhibition of TS.
Bijnsdorp
I V
IV
Department of Medical Oncology, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
Comijn
E M
EM
Padron
J M
JM
Gmeiner
W H
WH
Peters
G J
GJ
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005468:Fluorodeoxyuridylate / Q000494:pharmacology*; D005472:Fluorouracil / Q000494:pharmacology*; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D005971:Glutamates / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D051379:Mice; D015394:Molecular Structure; D000068437:Pemetrexed; D011799:Quinazolines / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D005493:Folic Acid Antagonists; D005971:Glutamates; D011799:Quinazolines; D013876:Thiophenes; D000068437:Pemetrexed; D005468:Fluorodeoxyuridylate; D006147:Guanine; D013940:Thymidylate Synthase; C068874:raltitrexed; D005472:Fluorouracil