Abstract B062: Targeting Orai1-mediated store-operated Ca2+ entry by a novel compound RP4010 for antiproliferative activity against esophagus squamous cell carcinoma (2018)

Abstract Background: Esophageal cancer is the 6th leading cause of cancer mortality worldwide with poor prognosis and 5-year survival rate as low as 18%. It is an unmet need to develop more effective chemotherapeutic drugs to improve the treatment outcome. We previously reported that the expression of Orai1, a calcium channel, was elevated in esophageal squamous cell carcinoma (ESCC), a major form of esophageal cancer, and the high expression is associated with poor survival rate in patients. Orai1-mediated store-operated calcium entry (SOCE) has been demonstrated to contribute to cancer cell proliferation, migration, and invasion in ESCC and other cancers. RP4010 is a potent inhibitor for Orai1 channel (IC50=60 nM) with demonstrated efficacy across a range of cancer cell lines in vitro. Here we evaluated the anticancer effect of RP4010 in cultured ESCC cells and xenograft animals. Materials and Method: Orai channel inhibitory function was analyzed in ESCC cells loaded with fluorescent calcium indicator Fura-2. The antiproliferative effect was evaluated by MTT assay in various human ESCC cell lines, e.g., KYSE-30, KYSE-150, KYSE-790, and KYSE-70. Quantitative real-time RT-PCR, Western blot, and flow cytometry were used to analyze the changes in cell cycle, changes in mRNAs and proteins of some key molecules in calcium signaling pathway. The antitumor effects of RP4010 were monitored in ESCC xenografted nude mice. Result: Compared to commonly used Orai1 channel blockers, such as BTP-2, RP4010 is more potent in blocking Orai1-mediated SOCE and cell proliferation in ESCC cells. The IC50 in cell viability analysis for RP4010 were calculated as 1.2, 1.4, 1.4, and 5.5 μM for KYSE-30, KYSE-70, KYSE-150, and KYSE-790, respectively, while IC50 for BTP-2 was 17.7-17.8 μM for these cells. Treatment of RP4010 (10 μM) halted intracellular calcium oscillations, inhibited calcium-dependent activation of Akt/NF-κB and ERK1/2 pathways, and resulted in cell cycles arrested at G0/G1 phase. Interestingly, RP4010 did not induce significant cell death even at rather high concentrations. In vivo study revealed that the mice tolerated daily I.P. injection of 20 mg/kg RP4010 without body weight loss or noticeable adverse effects. At this dose, RP4010 significantly reduced tumor growth compared to vehicle treated control group. Conclusion: R4010 is a novel potent inhibitor for Orai1-mediated SOCE with demonstrated potential in animal models of esophageal cancer. Data indicate a therapeutic potential of the molecule in ESCC. Citation Format: Chaochu Cui, Yan Chang, Xiaoli Zhang, Kumar V. Penmetsa, Srikant Viswanadha, Liwu Fu, Zui Pan. Targeting Orai1-mediated store-operated Ca2+ entry by a novel compound RP4010 for antiproliferative activity against esophagus squamous cell carcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B062.