488 Abstract withdrawn

<h3>Background</h3> Lactate serves as a key metabolite that regulates the metabolic reprogramming of cancer cells, a hallmark of tumor physiology. Beyond its role in metabolism, lactate exerts a modulatory effect within the tumor microenvironment; it is utilized by stromal cells and has been implicated in the suppression of the immune response against the tumor. The impact of lactate dehydrogenase inhibitors (LDHIs) on melanoma cell metabolism and their therapeutic potential in combination with immune checkpoint inhibitors (ICIs) was investigated in this study. <h3>Methods</h3> Cellular proliferation and apoptosis rates were monitored in real-time using the IncuCyte live-cell imaging system. Metabolic profiles of the cancer cells were assessed using the Seahorse XFe96 Analyzer to measure extracellular fluxes indicative of metabolic activity. Intracellular metabolite quantifications were conducted via liquid chromatography-mass spectrometry (LC-MS). The distribution of cell cycle phases, overall cell viability, and the profile of intratumoral immune cells were determined through flow cytometry. For in vivo assessments, the B78-D14 melanoma tumor model was established in C57BL/6 mice. Statistical analyses were performed using one-way ANOVA, complemented by Tukey’s post-hoc test to discern between group differences. <h3>Results</h3> A potent anti-proliferative effect (via both cell cycle alterations and enhanced apoptosis) of LDHIs, Oxamate (Oxa) and methyl 1-hydroxy-6-phenyl-4-(trifluoromethyl)-1H-indole-2-carboxylate (NHI-2), was found upon treatment of melanoma cell lines. Using a combination of Oxa and NHI-2, a synergistic effect to inhibit proliferation, glycolysis, and ATP production was observed. Metabolic analysis revealed significant alteration in glycolysis and oxidative phosphorylation, while metabolite profiling emphasized consequential effects on lactate metabolism and caused energy depletion by LDHIs. Detection of increased RANTES and MCP-1, with Oxa and NHI-2 treatment, prompted the consideration of combining LDHIs with ICIs. In vivo studies using a murine B78 melanoma tumor model revealed a significant improvement in treatment efficacy when LDHIs were combined with ICIs. <h3>Conclusions</h3> The combination therapy of LDHIs and ICIs not only directly disrupted the metabolism of melanoma cells but also regulated the immune response, resulting in improved outcomes in a murine tumor model. These findings suggest the potential of targeting lactate metabolism to enhance the efficacy of ICI treatments in patients with melanoma. <h3>Acknowledgements</h3> The authors express their gratitude to Professors Paul Sondel and Zachary Morris from the University of Wisconsin-Madison for their generous contribution of melanoma cell lines and the aCTLA-4 monoclonal antibody. <h3>Ethics Approval</h3> All mouse procedures were conducted in accordance with the Institutional Animal Care and Use Committee at the University of Wisconsin-Madison.