Anales RANF

P.72 EFFECT OF WEAK BASE DRUGS ON LYSOSOMAL CAPACITY OF CANCER CELLS: POSSIBLE INVOLVEMENT OF P2X4 RECEPTOR. Skoupa N., Dolezel P., and Mlejnek P. Department of Anatomy, Faculty of Medicine and Dentistry, Palacky University Olomouc, Hnevotinska 3, Olomouc 77515, Czech Republic. It is believed that lysosomal sequestration of hydrophobic weak base chemotherapeutic drugs prevents these drugs to reach their target sites, resulting in a significantly reduced cytotoxic effect. In addition, recent results suggested that lysosomal sequestration of hydrophobic weak base drugs triggers lysosomal biogenesis mediated by activation of transcription factor EB (TFEB), which in turn further increases lysosomal sequestration of hydrophobic weak base anticancer drugs and thus enhance resistance against these drugs. Here we addressed the question whether lysosomal biogenesis is the only mechanism that increases lysosomal sequestration capacity. We observed that lysosomal sequestration of some tyrosine kinase inhibitors (TKIs) induced expansion of lysosmal compartment. However, expression analysis of lysosomal genes, including LAMP1, LAMP2, vacuolar ATPase subunit B2, ACP, and GLB controlled by TFEB did not indicate increased expression. Instead, we found that high concentrations of TKIs induced lysosomal fusion. Our results further suggested that lysosomal fusion is Ca 2+ dependent and that P2X4 receptor contributed to this process significantly. In conclusion, we demonstrated that lysosomal sequestration capacity can be significantly enlarged due to the lysosomal fusion with apparent participation of P2X4 receptor in cancer cells. Acknowledgement: This work was supported by the Grant Agency of the Czech Republic, GACR 17-16614S