Lithocholic acid (LCA), one of the major components in secondary bile acids, promotes carcinogenesis in rat colon epithelial cells induced by N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG), which methylates DNA. Base‐excision repair of DNA lesions caused by the DNA methylating agents requires DNA polymerase β (pol β). In the present study, we examined 17 kinds of bile acids with respect to inhibition of mammalian DNA polymerases in vitro. Among them, only LCA and its derivatives inhibited DNA polymerases, while other bile acids were not inhibitory. Among eukaryotic DNA polymerases α, β, δ, η, and γ, pol β was the most sensitive to inhibition by LCA. The inhibition mode of pol β was non‐competitive with respect to the DNA template‐primer and was competitive with the substrate, dTTP, with the Ki value of 10 μM. Chemical structures at the C‐7 and C‐12 positions in the sterol skeleton are important for the inhibitory activity of LCA. This inhibition could contribute to the tumor‐promoting activity of LCA.

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.

Taurospongin A (1), a novel acetylene-containing natural product consisting of a taurine and two fatty acid residues, has been isolated from the Okinawan marine sponge Hippospongia sp. and its structure elucidated by spectral data and chemical means. Taurospongin A (1) exhibited potent inhibitory activity against DNA polymerase β and HIV reverse transcriptase. The absolute configurations of taurospongin A (1) were established to be 3R, 7S, and 9R by synthesis of the MTPA ester of a degradation product of 1.

Measurement of LV volumes and EF by 3DE is clinically feasible and has the potential to significantly alter clinical decision-making.