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Isothiazolone derivatives selectively inhibit telomerase from human and rat cancer cells in vitro.
Hayakawa N; Nozawa K; Ogawa A; Kato N; Yoshida K; Akamatsu Ki; Tsuchiya
December 30, 1999
Biochemistry. 1999 Aug 31;38(35):11501-7. Unique Identifier : AIDSLINE

The telomere hypothesis postulates stabilization of telomere length and telomerase activation as key events in cellular immortalization and carcinogeneses. Accordingly, telomerase has been suggested as a novel and highly selective target for design of antitumor drugs. Screening of a chemical library including 16 000 synthetic compounds yielded six that strongly inhibited telomerase activity in extracts of cultured human cells, including four isothiazolone derivatives and two unrelated compounds. The most potent inhibitor was 2-[3-(trifluoromethyl)phenyl]isothiazolin-3-one (TMPI), a concentration of 1.0 microM inhibited telomerase activity by 50% according to a telomere repeat amplification protocol (TRAP) assay. Analysis using partially purified telomerase from AH7974 rat hepatoma cells demonstrated noncompetitive inhibition with the telomere-repeat primer and mixed inhibition with the dNTPs; the inhibition constant was 2.5 microM. TMPI did not inhibit eukaryotic DNA polymerase alpha, beta, or human immunodeficiency virus reverse transcriptase (HIV RT). Thus, inhibition by TMPI was highly selective for telomerase. Inhibition by TMPI was quenched by 1 mM of dithiothreitol or glutathione, suggesting that TMPI inhibits telomerase by acting at a cysteine residue. TMPI inhibition of this enzyme may find application as an antineoplastic agent.

JOURNAL ARTICLE Animal Antineoplastic Agents/ANTAGONISTS & INHIB/CHEMISTRY/*PHARMACOLOGY Dithiothreitol/PHARMACOLOGY DNA Polymerase beta/METABOLISM DNA Polymerase I/METABOLISM Enzyme Inhibitors/CHEMISTRY/*PHARMACOLOGY Glutathione/PHARMACOLOGY Human HIV-1 Reverse Transcriptase/METABOLISM HL-60 Cells Male Rats Rats, Inbred Strains Sulfhydryl Reagents/PHARMACOLOGY Telomerase/*ANTAGONISTS & INHIB/METABOLISM Thiazoles/ANTAGONISTS & INHIB/CHEMISTRY/*PHARMACOLOGY Tumor Cells, Cultured