Inactivation of the ketoreductase gilU gene of the gilvocarcin biosynthetic gene cluster yields new analogues with partly improved biological activity

Four new analogues of the gilvocarcin-type aryl-C-glycoside antitumor compounds, namely 4′-hydroxy gilvocarcin V (4′-OH-GV), 4′-hydroxy gilvocarcin M, 4′-hydroxy gilvocarcin E and 12-demethyl-defucogilvocarcin V, were produced through inactivation of the gilU gene. The 4′-OH-analogues showed improved activity against lung cancer cell lines as compared to their parent compounds without 4′-OH group (gilvocarcins V and E). The structures of the sugar-containing new mutant products indicate that the enzyme GilU acts as an unusual ketoreductase involved in the biosynthesis of the C-glycosidically linked deoxysugar moiety of the gilvocarcins. The structures of the new gilvocarcins indicate substrate flexibility of the post-polyketide synthase modifying enzymes, particularly the C-glycosyltransferase and the enzyme responsible for the sugar ring contraction. The results also shed light into biosynthetic sequence of events in the late steps of biosynthetic pathway of gilvocarcin V.