Glutamine serves as an important source of energy and building blocks for many tumor cells. The first step in glutamine utilization is its conversion to glutamate by the mitochondrial enzyme glutaminase. CB-839 is a potent, selective, and orally bioavailable inhibitor of both splice variants of glutaminase (KGA and GAC). CB-839 had antiproliferative activity in a triple-negative breast cancer (TNBC) cell line, HCC-1806, that was associated with a marked decrease in glutamine consumption, glutamate production, oxygen consumption, and the steady-state levels of glutathione and several tricarboxylic acid cycle intermediates. In contrast, no antiproliferative activity was observed in an estrogen receptor-positive cell line, T47D, and only modest effects on glutamine consumption and downstream metabolites were observed. Across a panel of breast cancer cell lines, GAC protein expression and glutaminase activity were elevated in the majority of TNBC cell lines relative to receptor positive cells. Furthermore, the TNBC subtype displayed the greatest sensitivity to CB-839 treatment and this sensitivity was correlated with (i) dependence on extracellular glutamine for growth, (ii) intracellular glutamate and glutamine levels, and (iii) GAC (but not KGA) expression, a potential biomarker for sensitivity. CB-839 displayed significant antitumor activity in two xenograft models: as a single agent in a patient-derived TNBC model and in a basal like HER2 þ cell line model, JIMT-1, both as a single agent and in combination with paclitaxel. Together, these data provide a strong rationale for the clinical investigation of CB-839 as a targeted therapeutic in patients with TNBC and other glutamine-dependent tumors. Mol Cancer Ther; 13(4); 890-901. Ó2014 AACR.
A mutant of Mycobacterium smegmatis has been isolated that is simultaneously resistant to both D-cycloserine (D-CS) and vancomycin. Genetic complementation with a PBP4 homolog restores sensitivity to both drugs. Resistance to D-CS and vancomycin in this mutant is most likely due to a novel mechanism involving peptidoglycan assembly at the cell surface.The emergence of antibiotic resistance is a growing problem among pathogenic bacteria. Of great concern is the increased prevalence of multidrug-resistant strains of Mycobacterium tuberculosis (4). To complicate this issue further, mycobacteria are intrinsically resistant to many drugs normally active on other gram-positive microorganisms, due to their distinctive lipid barriers composed of bound mycolic acid and free lipids, which render them impermeable to many substances (3).To gain greater insight into resistance mechanisms utilized by mycobacteria, we sought to create a laboratory mutant of Mycobacterium smegmatis that is resistant to the peptidoglycan biosynthesis inhibitor D-cycloserine (D-CS). To that end, a colony of wild-type M. smegmatis mc 2 155 was cultured in minimal medium with increasing concentrations of D-CS ranging from 10 to 150 g/ml. Aliquots of cells from each culture were plated onto 102 g of D-CS per ml, the concentration of D-CS that consistently kills wild-type cells. One of the mutants isolated from this selection was chosen for further characterization.The mutant was evaluated for resistance to other drugs affecting peptidoglycan biosynthesis, including fosfomycin and vancomycin. From these studies, it was determined that the mutant is resistant to low levels of vancomycin. Because the mutant displayed resistance to both D-CS and vancomycin, it was named Cvr-1 for D-cycloserine and vancomycin resistance. The D-CS MIC and minimum bactericidal concentration for wild-type M. smegmatis are both 105 g/ml, and those for Cvr-1 are 140 and 145 g/ml, respectively. The vancomycin MIC and minimum bactericidal concentration for wild-type M. smegmatis are 40 and 45 g/ml, respectively, and those for Cvr-1 are 65 and 70 g/ml, respectively.Resistance to both D-CS and vancomycin commonly maps to the D-alanine-D-alanine ligase (encoded by the gene ddlA) in many pathogenic bacterial species. The D-alanine-D-alanine ligase is responsible for catalyzing amide bond formation between two D-alanine molecules (16). The D-alanine-D-alanine dipeptides created by the ligase are then added onto the C termini of UDP-N-acetyl-muramic tripeptides to form peptidoglycan monomers that are eventually added to the peptidoglycan (16). David performed genetic fluctuation analyses on D-CS-resistant mutants of M. tuberculosis and concluded that drug resistance is primarily due to mutations in the Dalanine-D-alanine ligase gene (7). D-CS resistance mechanisms common to the ligase include changes in the specificity of the enzyme such that it is no longer able to recognize and interact with the drug.Resistance to vancomycin in other bacteria results from the replacement of the ter...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.