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Biochemical effects of folate-based inhibitors of thymidylate synthase in MGH-U1 cells

  • Original Article
  • Thymidylate Synthase, Inhibitors, Antifolate
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Abstract

The TS-inhibitory effects induced by a 24-h exposure to the folate-based TS inhibitors CB3717, C2-desamino analogs of CB3717 including D1694, and BW1843U89 were quantitated using the MGH-U1 human bladder carcinoma. The effects of D1694 on the time course of TS inhibition and on intracellular deoxyuridine monophosphate (dUMP) accumulation and deoxyuridine (dUrd) production were evaluated. D1694 and BW1843U89 were the most active TS inhibitors with IC50 values of 2.4 and 0.5 nM, respectively. The C2-desamino C2-methyl dideazafolates were 27–292 times more potent than the parent CB3717 as TS inhibitors. A methyl group at the C2 position of CB3717 had the most dramatic effect, whereas a thiazole substitution for a benzyl added a small benefit and N10 substitution had a limited impact on TS-inhibitory potency and clonogenic survival. There was a significant correlation between the IC50 values for TS inhibition and those for cytotoxic potency obtained for these drugs. LV and thymidine protected cells from these folate-based TS inhibitors. Intracellular dUMP levels following 24 h D1694 (IC50) exposure increased 7-fold. Levels of dUrd effluxing into the media increased up to 4.5 μM following a 24-h exposure to D1694 (IC90). We conclude that (a) C2-desamino C2-methyl dideazafolates are potent TS inhibitors, (b) TS inhibition requires prolonged exposure with these folate TS inhibitors, (c) survival is correlated with inhibition of TS for the folate-based TS inhibitors and (d) the biochemical consequences of TS inhibition include increased dUMP and dUrd levels.

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Abbreviations

TS:

thymidylate synthase

D1694 :

N-{5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino]-2-thenoyl}-L-glutamic acid

BW1843U89 :

(S)-2-(5-[{1,2-dihydro-3-methyl-1-oxo-benzo(F)quinazolin-9-yl]-methyl}amino]1-oxo-2-isoindolinyl) glutamic acid

CB3717 :

N 10-propargyl-5,8-dideazafolic acid

dCB3717 :

2-desamino-N 10-propargyl-5,8-dideazafolic acid

LV :

leucovorin

FPGS :

folylpolyglutamate synthetase

IC 50 :

IC 90 concentrations necessary to inhibit function by 50% and 90%, respectively

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Authors and Affiliations

  1. Division of Experimental Therapeutics, The Ontario Cancer Institute, 500 Sherbourne Street, M4X 1K9, Toronto, Ontario, Canada

    Biserka Mitrovski, Josie Pressacco, Saul Mandelbaum & Charles Erlichman

  2. Department of Medicine, Pharmacology and Medical Biophysics, University of Toronto, M5S 1A8, Toronto, Ontario, Canada

    Josie Pressacco & Charles Erlichman

Authors
  1. Biserka Mitrovski
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  2. Josie Pressacco
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  3. Saul Mandelbaum
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  4. Charles Erlichman
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This study was supported by a grant from the National Cancer Institute of Canada

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Mitrovski, B., Pressacco, J., Mandelbaum, S. et al. Biochemical effects of folate-based inhibitors of thymidylate synthase in MGH-U1 cells. Cancer Chemother. Pharmacol. 35, 109–114 (1994). https://doi.org/10.1007/BF00686631

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  • DOI: https://doi.org/10.1007/BF00686631

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