PO-227 Sensitising glioma cells to fatty acid oxidation inhibitor by modulation of SLC22A5 transporter activity

Abstract

IntroductionGliomas are the most common primary malignant brain tumour in adults, but current treatment for glioblastoma multiforme (GBM) is insufficient. It was shown that primary-cultured human GBM cells depend on fatty acid oxidation (FAO) for proliferation, and that FAO inhibition in vivo by etomoxir prolongs survival in the mouse model of malignant glioma. Etomoxir, an inhibitor of FAO rate-limiting enzyme – carnitine palmitoylotransferase 1 (CPT1), was tested in clinical trials, which were terminated due to high toxicity. Carnitine is a CPT1 substrate, and SLC22A5 is the only high-affinity carnitine transporter in the plasma membrane expressed in the central nervous system. Moreover, HEK293 cells overexpressing SLC22A5 show increased transport of several chemotherapeutics, the process that may inhibit carnitine transport into the cell. This study is aimed at establishing the role of SLC22A5 in glioma cells and at assessing its potential for sensitising them to lower, less toxic doses of etomoxir.Material and methodsData from REMBRANDT and a Western Blot analysis of non-transformed astrocytes and several glioma cell lines were used to assess SLC22A5 expression both on the mRNA level and the protein level, respectively. Transport of radiolabeled carnitine was measured to verify whether anti-cancer drugs transported by SLC22A5 are able to inhibit carnitine transport in U87-MG, LN229 and T89G glioma cells. MTT assay and BrdU staining were used to test the viability and proliferation of glioma cells after administering SLC22A5-transported drugs alone and combined with etomoxir.Results and discussionsStatistical analysis of data from REMBRANDT showed significantly higher SLC22A5 expression in glioma patient-derived tissues when compared to normal tissues, an observation confirmed by a Western Blot analysis of astrocytes and several glioma cell lines. Out of several tested drugs, vinorelbine and vincristine are most efficient in carnitine transport inhibition in all of the tested lines. The viability and proliferation are significantly reduced when the foregoing are used in combination with etomoxir.ConclusionProper carnitine delivery by SLC22A5 transporter is important for glioblastoma metabolism and SLC22A5-transported chemotherapeutics may induce cell death both by their regular mechanism of action and by inhibition of carnitine delivery to glioma cells, thus sensitising them to lower, less toxic doses of CPT1 inhibitors.This project is financed by grant 2016/23/N/NZ3/02430 from National Science Centre in Poland.