Resin glycosides from Ipomoea wolcottiana as modulators of the multidrug resistance phenotype in vitro

Recycling liquid chromatography was used for the isolation and purification of resin glycosides from the CHCl3-soluble extracts prepared using flowers of Ipomoea wolcottiana Rose var. wolcottiana. Bioassay-guided fractionation, using modulation of both antibiotic activity against multidrug-resistant strains of Gram-negative bacteria and vinblastine susceptibility in breast carcinoma cells, was used to isolate the active glycolipids as modulators of the multidrug resistance phenotype. An ester-type dimer, wolcottine I, one tetra- and three pentasaccharides, wolcottinosides I-IV, in addition to the known intrapilosin VII, were characterized by NMR spectroscopy and mass spectrometry. In vitro assays established that none of these metabolites displayed antibacterial activity (MIC>512 μg/mL) against multidrug-resistant strains of Escherichia coli, and two nosocomial pathogens: Salmonella enterica serovar Typhi and Shigella flexneri; however, when tested (25 μg/mL) in combination with tetracycline, kanamycin or chloramphenicol, they exerted a potentiation effect of the antibiotic susceptibility up to eightfold (64 μg/mL from 512 μg/mL). It was also determined that these non-cytotoxic (CI50>8.68 μM) agents modulated vinblastine susceptibility at 25 μg/mL in MFC-7/Vin(+) cells with a reversal factor (RFMCF-7/Vin(+)) of 2-130 fold.