- Micah D Shepherd: Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 789 South Limestone Street, Lexington, KY 40536-0596, USA.
A combinatorial biosynthetic approach was used to interrogate the donor substrate flexibility of GilGT, the glycosyltransferase involved in C-glycosylation during gilvocarcin biosynthesis. Complementation of gilvocarcin mutant Streptomyces lividans TK24 (cosG9B3-U(-)), in which the biosynthesis of the natural sugar donor substrate was compromised, with various deoxysugar plasmids led to the generation of six gilvocarcin analogues with altered saccharide moieties. Characterization of the isolated gilvocarcin derivatives revealed five new compounds, including 4-β-C-D-olivosyl-gilvocarcin V (D-olivosyl GV), 4-β-C-D-olivosyl-gilvocarcin M (D-olivosyl GM), 4-β-C-D-olivosyl-gilvocarcin E (D-olivosyl GE), 4-α-C-L-rhamnosyl-gilvocarcin M (polycarcin M), 4-α-C-L-rhamnosyl-gilvocarcin E (polycarcin E), and the recently characterized 4-α-C-L-rhamnosyl-gilvocarcin V (polycarcin V). Preliminary anticancer assays showed that D-olivosyl-gilvocarcin and polycarcin V exhibit antitumor activities comparable to that of their parent drug congener, gilvocarcin V, against human lung cancer (H460), murine lung cancer (LL/2), and breast cancer (MCF-7) cell lines. Our findings demonstrate GilGT to be a moderately flexible C-glycosyltransferase able to transfer both D- and L-hexopyranose moieties to the unique angucyclinone-derived benzo[D]naphtho[1,2b]pyran-6-one backbone of the gilvocarcins.