Physapubescin I from husk tomato suppresses SW1990 cancer cell growth by targeting kidney-type glutaminase

Kidney-type glutaminase (KGA), catalyzing the hydrolysis of glutamine to glutamate for energy supply, is over-expressed in many cancers and has been regarded as a new therapeutic target for cancers. Physapubescin I was isolated from the fruits of the edible herb Physalis pubescens L., commonly named as "husk tomato or hairy groundcherry", and was predicted to be a potential KGA inhibitor through structure-based virtual ligand screening. Enzyme inhibition assays, microscale thermophoresis (MST) and cellular thermal shift assay (CETSA) experiments have demonstrated the high efficiency and specificity of physapubescin I targeting KGA. EdU proliferation, Hoechst 33258 staining and cytotoxicity assays indicated that physapubescin I could inhibit cancer cell proliferation and promote apoptosis more effectively than the known KGA inhibitor, BPTES. Knockdown of KGA by siRNA reduced the inhibition of physapubescin I to SW1990 cells. Meanwhile, physapubescin I impaired glutamine metabolism in SW1990 cells with increasing intracellular level of glutamine, and correspondingly decreasing glutamate and its downstream metabolites, which may account for its inhibition of cancer cell proliferation and proapoptosis. Physapubescin I also showed significant tumor growth inhibition and low toxicity in a SW1990 xenograft mouse model. Collectively, physapubescin I may serve as a potential drug candidate or lead compound for cancer therapy by targeting KGA.