Background: CB-839 is an oral, first-in-class glutaminase-1 (GLS1) inhibitor that targets the glutamine dependence of many solid and hematologic tumors. By selectively inhibiting the GAC and KGA isoforms of GLS1, it suppresses mitochondrial glutamine metabolism—a key energy and biosynthetic pathway in cancer cells. Early clinical studies show that CB-839 is well tolerated and can reduce tumor glutaminase activity by up to 96%. With its strong mechanistic rationale, favorable safety profile, and synergy with multiple anticancer agents, CB-839 is now advancing into combination therapy trials for advanced malignancies. GLS1-mediated glutaminolysis in the heart serves as an adaptive response to acute stress. BPTES (Bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide), the prototype compound of CB-839 and a selective GLS1 inhibitor, has been shown to attenuate pressure overload–induced cardiac hypertrophy. Acute ischemia–reperfusion (I/R) injury is characterized by mitochondrial dysfunction and excessive ROS generation, which further enhance glutaminolysis and aggravate myocardial injury. To determine whether pharmacologic inhibition of glutaminolysis by BPTES confers cardioprotection against I/R injury, we investigated its effects on mitochondrial function in the murine heart. Hypothesis: BPTES modulates cardiac mitochondrial bioenergetics and reduces oxidative stress by inhibiting glutaminolysis in vivo, conferring protection against acute myocardial ischemia-reperfusion injury. Methods: Adult mice received intraperitoneal BPTES (5 mg/kg/day) for 6 days. Cardiac mitochondria were isolated and assessed for oxygen consumption rate (OCR) and enzymatic activities of the electron transport chain (ETC). GLS1 activity was determined by measuring the kinetic conversion of glutamine to glutamate, and GLS1 protein expression in the myocardium was analyzed by Western blotting using an polyclonal antibody against GLS1. Data and Results: In vivo BPTES administration significantly impaired mitochondrial function in the murine heart. Cardiac mitochondria from BPTES-treated mice exhibited a marked reduction in state 3 (ADP-dependent) OCR and a decreased respiratory control ratio (state 3 OCR/state 4 OCR), consistent with diminished ATP-generating capacity and compromised mitochondrial integrity. Notably, state 4 (ADP-independent) OCR and FCCP-induced maximal OCR were significantly elevated, indicating that BPTES induces mitochondrial uncoupling in vivo. Immunoblotting analysis using a polyclonal antibody against UCP3 confirmed the above observation. However, GLS1 enzymatic activity in cardiac mitochondria did not differ between BPTES-treated and control mice, suggesting that BPTES did not inhibit myocardial GLS1 under these conditions. Conclusion: BPTES treatment uncouples cardiac mitochondria in vivo, as evidenced by decreased state 3 OCR, increased state 4 and FCCP-stimulated OCR, and upregulation of mitochondrial UCP3 in heart. Despite its known GLS1-inhibitory properties, BPTES did not significantly reduce cardiac GLS1 activity in vivo, suggesting that its mitochondrial effects bypass the glutaminolysis pathway and upregulate uncoupling mitochondria in vivo. These findings implicate a novel mechanism by which BPTES regulates cardiac mitochondrial function via dissipating proton back pressure with reduction of reactive oxygen species production and highlight the need for further investigation into its potential impact on myocardial energy metabolism during stress conditions such as I/R injury and heart failure. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Chen et al. (Fri,) studied this question.