Targeting Orai1-mediated store-operated calcium entry by RP4010 for anti-tumor activity in esophagus squamous cell carcinoma

Esophageal cancer (EC) is the 6th leading cause of cancer mortality worldwide with poor prognosis, hence more effective chemotherapeutic drugs for this deadly disease are urgently needed. We previously reported that high expression of Orai1, a store-operated Ca²⁺entry (SOCE) channel, was associated with poor survival rate in EC patients and Orai1-mediated intracellular Ca²⁺ oscillations regulated cancer cell proliferation. Previous studies suggested that Orai1-mediated SOCE is a promising target for EC chemotherapy. Here, we evaluated the anti-cancer effect of a novel SOCE inhibitor, RP4010, in cultured EC cells and xenograft models. Compared to other previously reported SOCE channel inhibitors, RP4010 is more potent in blocking SOCE and inhibiting cell proliferation in EC and other cancer cells. Treatment with RP4010 resulted in reduction of intracellular Ca²⁺ oscillations, caused cell cycle arrest at G0/G1 phase in vitro, decreased nuclear translocation of nuclear factor kappa B (NF-κB) in vivo and in vitro, and inhibited tumor growth in vivo. Taken together, data demonstrated the therapeutic potential of RP4010 in EC patients via inhibition of SOCE-mediated intracellular Ca²⁺ signaling.

Acetylcholine induces intracellular Ca2+ oscillations and nitric oxide release in mouse brain endothelial cells

Basal forebrain neurons increase cortical blood flow by releasing acetylcholine (Ach), which stimulates endothelial cells (ECs) to produce the vasodilating gasotransmitter, nitric oxide (NO). Surprisingly, the mechanism whereby Ach induces NO synthesis in brain microvascular ECs is unknown. An increase in intracellular Ca²⁺ concentration recruits a multitude of endothelial Ca²⁺-dependent pathways, such as Ca²⁺/calmodulin endothelial NO synthase (eNOS). The present investigation sought to investigate the role of intracellular Ca²⁺ signaling in Ach-induced NO production in bEND5 cells, an established model of mouse brain microvascular ECs, by conventional imaging of cells loaded with the Ca²⁺-sensitive dye, Fura-2/AM, and the NO-sensitive fluorophore, DAF-DM diacetate. Ach induced dose-dependent Ca²⁺ oscillations in bEND5 cells, 300 μM being the most effective dose to generate a prolonged Ca²⁺ burst. Pharmacological manipulation revealed that Ach-evoked Ca²⁺ oscillations required metabotropic muscarinic receptor (mAchR) activation and were patterned by a complex interplay between repetitive ER Ca²⁺ release via inositol-1,4,5-trisphosphate receptors (InsP₃Rs) and store-operated Ca²⁺ entry (SOCE). A comprehensive real time-polymerase chain reaction analysis demonstrated the expression of the transcripts encoding for M3-mAChRs, InsP₃R1 and InsP₃R3, Stim1-2 and Orai2. Next, we found that Ach-induced NO production was hindered by L-NAME, a selective NOS inhibitor, and BAPTA, a membrane permeable intracellular Ca²⁺ buffer. Moreover, Ach-elicited NO synthesis was blocked by the pharmacological abrogation of the accompanying Ca²⁺ spikes. Overall, these data shed novel light on the molecular mechanisms whereby neuronally-released Ach controls neurovascular coupling in blood microvessels.