Characterization and implication of the Orai3 channel and ABC type transporters in the phenomenon of chemoresistance to cisplatin and pemetrexed in lung cancer.

Orai3 channels have been associated with cell proliferation, survival and metastasis in several cancers. Previous studies have shown that Orai3 seems to be involved in the development of acquired chemo-resistance of cisplatin in non-small cell lung cancer via ABC transporters that transport certain chemotherapeutic agents, such as cisplatin, out of the cells. Based on these studies, we hypothesize that Orai3 may be involved in the development of acquired chemo-resistance of pemetrexed. By using MTT assay, we show that pemetrexed is efficient and signiftcantly decreases cell viability in a dose dependent manner. Furthermore, we demonstrate using siRNA-mediated Orai3 knockdown that Orai3 silencing has no effect on the chemoresistance against pemetrexed. Then, calcium imaging reveals that pemetrexed does not affect the activity of calcium channels like Orai3. As transcription factors are central to the regulation of gene expression, we wonder if pemetrexed could impact on Orai3 expression. To address the issue, Mn2+ -quench assays are performed in siOrai3 transfected A549 cells incubated with 1uM pemetrexed for 72h. Finally, RT-PCR is used in order to determine the mRNA expression proftle for Orai3 and ABC transporters in A549 cells. We demonstrate that pemetrexed increases Orai3 expression. Taken together, these results suggest that Orai3 is not involved in the development of acquired chemo-resistance of pemetrexed in non small cell lung cancer. Pemetrexed upregulates Orai3 expression but does not affect the activity of Orai3 channels. As Orai3 channels are known to be involved in the development of acquired chemoresistance of cisplatin in non-small cell lung cancer, pemetrexed could reduce the therapeutic efficacy of cisplatin if Orai3 protein levels are linked to Orai3 mRNA levels. Moreover, cisplatin has been shown to increase both expression and function of Orai3, resulting in increased chemoresistance. Therefore, our results show that Orai3 could constitute a robust therapeutic target in non-small cell lung cancer.