Altered calcium-homeostasis of cisplatin-resistant non small cell (NSLC) and small cell lung (SCLC) cancer cells

Abstract

22185 Background: Chemotherapy in advanced lung cancer often leads to encouraging responses, but, in the course of the treatment, resistance to chemotherapy ultimately limits the life expectancy of the patient. The mechanisms of resistance to cisplatin, which is one of the most effective and most frequently used chemotherapeutics in lung cancer, are still not understood. We aimed at investigating if the intracellular Ca2+-homeostasis may be related to cisplatin resistance. Methods: The squamous cell lung carcinoma cell line EPLC and the small cell lung cancer cell line H1339 were exposed to cisplatin analogue to the in vivo pharmacokinetics. Changes in the cytoplasmic Ca2+-concentration ([Ca2+]c) were recorded using fluorescence microscopy and protein expression was quantified using Western Blot analysis and immuno-fluorescence. Results: Four “cycles” of cisplatin led to partial resistance in EPLC and H1339 cells. The partial resistance could be mimicked by buffering [Ca2+]c using BAPTA. In the resistant clones of both cell types, the Ca2+-content of the endoplasmic reticulum (ER) was decreased. In EPLC cells, this was correlated with an increased expression of the inositol-1,4,5-trisphosphate receptor (IP3R). In H1339 cells, the decrease Ca2+-content of the ER was correlated with a decreased expression of sarco/endoplasmic reticulum Ca2+-ATPases (SERCA). Using the siRNA technique, we could show that the modified expression of the respective proteins in fact altered the cisplatin sensitivity. Conclusions: We conclude that a decreased Ca2+- content of the ER contributes to cisplatin resistance and show for the first time that upregulation of the IP3R and decreased expression of SERCA are involved in cisplatin-resistance. No significant financial relationships to disclose.