X. Xu1,2, Z. Liu1, Q. Tao1, L. Wei1, S. Ma1, Y. Huang1, M. Chen1, X. Xie1, X. Sun1, X. Li1, R. Liu1, Q. Wang1, M. Wu1, D. Chen1, and J. Yu1; 1Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, 2The Second Affiliated Hospital of Shandong First Medical University, Taian, Shandong, China
Purpose/Objective(s): Radiotherapy efficacy relies not only on the direct tumor cells induced by irradiation but also on the anti-tumor immunity. It’s well recognized that high glycolytic states of tumor cells could contribute to tumor progression, metastasis, invasion and therapy resistance, which is mainly attributed to extensive consumption of glucose and amino acids and production of the metabolite lactate in the tumor microenvironments. SLC16A3, which mediates lactate efflux, plays an important role in immunotherapy resistance. Thus in our study, we aimed to explore whether inhibition of SLC16A3 could reverse glycolysis and overcome radiotherapy resistance. Materials/
Methods: Public databases and retrospective analysis of clinical data were executed to determine the association between expression of SLC16A3 and serum lactate dehydrogenase (LDH) level and radiotherapy prognosis. Glycolysis state of tumor cells after radiotherapy in the presence or absence of SLC16A3/Slc16a3 inhibitor VB124 was analyzed using O2k-FluoRespirometer, real-time qPCR, western blotting and lactate assay. And Slc16a3 knockout cell lines were established in MC38, B16F10 and E0771 cells using CRISPR-Cas9 technology. Subcutaneous murine tumor models established with Slc16a3 knockout tumor cells or wildtype tumor cells were subjected to radiotherapy with or without SLC16A3 inhibitor lonidamine to validate whether inhibiting Slc16a3 can enhance the anti-tumor effects of radiotherapy. Tumor immune microenvironments were analyzed subsequently using flow cytometry. Results: Analysis of TCGA database showed that expression of SLC16A3 was negatively correlated with the prognosis of NSCLC patients subjected to radiotherapy. Further retrospective analysis of SCLC patients from our hospital demonstrated negative correlation between serum LDH levels and prognosis after radiotherapy. Using in vitro system, it’s found that radiotherapy could boost glycolysis in both murine and human tumor cells, demonstrated as increased expression of glycolysis pathway related genes and proteins, enhanced efflux of lactate in culture supernatants, and elevated extracellular acidification rate, which could be partly reversed by inhibition of Slc16a3, as validated by both Slc16a3 knockout cell lines and VB124. Using Slc16a3-deficient MC38 and B16F10 tumor mouse models, it’s illustrated that the absence of tumor cell intrinsic Slc16a3 could enhance the anti-tumor effects of radiotherapy. And lonidamine also showed synergistical anti-tumor effects in combination with radiotherapy in E0771 tumors. And further analysis of tumor immune microenvironments showed increased infiltration of CD8+ T cells, CD4+T cells and M1-TAMs in the absence of tumor cell intrinsic Slc16a3 after radiotherapy. Conclusion: Inhibition of tumor cell intrinsic SLC16A3 can enhance radiotherapy efficacy via improving the tumor immune microenvironment.
