Kalita_2021_Mol.Pharm_18_451

Glycosaminoglycans (GAGs) such as heparan sulfate and chondroitin sulfate decorate all mammalian cell surfaces. These mucopolysaccharides act as coreceptors for extracellular ligands, regulating cell signaling, growth, proliferation, and adhesion. In glioblastoma, the most common type of primary malignant brain tumor, dysregulated GAG biosynthesis results in altered chain length, sulfation patterns, and the ratio of contributing monosaccharides. These events contribute to the loss of normal cellular function, initiating and sustaining malignant growth. Disruption of the aberrant cell surface GAGs with small molecule inhibitors of GAG biosynthetic enzymes is a potential therapeutic approach to blocking the rogue signaling and proliferation in glioma, including glioblastoma. Previously, 4-azido-xylose-alpha-UDP sugar inhibited both xylosyltransferase (XYLT-1) and beta-1,4-galactosyltransferase-7 (beta-GALT-7)-the first and second enzymes of GAG biosynthesis-when microinjected into a cell. In another study, 4-deoxy-4-fluoro-beta-xylosides inhibited beta-GALT-7 at 1 mM concentration in vitro. In this work, we seek to solve the enduring problem of drug delivery to human glioma cells at low concentrations. We developed a library of hydrophobic, presumed prodrugs 4-deoxy-4-fluoro-2,3-dibenzoyl-(alpha- or beta-) xylosides and their corresponding hydrophilic inhibitors of XYLT-1 and beta-GALT-7 enzymes. The prodrugs were designed to be activatable by carboxylesterase enzymes overexpressed in glioblastoma. Using a colorimetric MTT assay in human glioblastoma cell lines, we identified a prodrug-drug pair (4-nitrophenyl-alpha-xylosides) as lead drug candidates. The candidates arrest U251 cell growth at an IC(50) = 380 nM (prodrug), 122 microM (drug), and U87 cells at IC(50) = 10.57 microM (prodrug). Molecular docking studies were consistent with preferred binding of the alpha- versus beta-nitro xyloside conformer to XYLT-1 and beta-GALT-7 enzymes.