Mechanism of action of 2-crotonyloxymethyl-4,5,6-trihydroxycyclohex-2-enone, a sh inhibitory antitumor antibiotic, and its effect on drug-resistant neoplastic cells

An inhibitor of alkaline phosphodiesterase was isolated from a soil Streptomyces. The agent was identified with 2-crotonyloxymethy1-4 (COTC) by UV, IR, NMR and ¹⁸C NMR spectrometry. The mechanism of tumor-inhibitory action of COTC was studied with murine lymphoblastoma L5178Y cells. COTC blocked alkaline phosphodiesterase; IC₅₀ was 60 µg/ml by the method employed. The growth of L5178Y cells was inhibited by COTC; IC₅₀ was 4.4 DNA biosynthesis was preferentially prevented by COTC over RNA and protein syntheses; of DNA synthesis was 7~25 µg/ml COTC significantly inhibited DNA polymerase a even in the presence of dithiothreitol. The mitosis was markedly blocked by COTC; complete inhibition was observed at a drug concentration of 20 µg/ml Adriamycin-, aclarubicin- and bleomycin-resistant cell sublines showed collateral sensitivity to COTC. COTC and aclarubicin exhibited synergistic activity on aclarubicin-resistant cells, but not on the parental cells. COTC increased uptake of [³H]adriamycin or blocked the drug efflux in the resistant cells, but not in the parental cells. The effects of COTC on macromolecular syntheses, mitosis and membrane functions may be attributed to the interaction with the sulfhydryl group of various enzymes. Although COTC is a multifunctional drug, the inhibition of DNA polymerase a and a certain mitotic process seems to be related to the lethal action.