Abstract 2599: RP3035, a potent cytostatic anti-cancer agent, reduces NCI-H460 tumor growth in mice via inhibition of Orai1 (2011)

Abstract Background: Non-small cell lung cancer (NSCLC) is the most prevalent form of lung cancer and is one of the leading causes of cancer-related mortality across the globe. Majority of the NSCLC are characterized by the presence of ras mutation thereby rendering the subject relatively insensitive to treatment by known kinase inhibitors. Current treatment regimes for NSCLC are therefore limited to cytotoxic drugs besides surgery and radiation therapy. Herein, we describe the pharmacological profile of RP3035, a novel and potent cytostatic agent that inhibits tumor growth in xenograft models via a Calcium Release Activated Calcium (CRAC) channel pathway. Methods: Inhibition of thapsigargin induced calcium influx into Fluo-8 loaded NCI-H460 cells was determined fluorometrically. Viability assay (MTT) was conducted to determine the growth inhibitory effect of the compound on NCI-H460, a NSCLC cell line. Lactate dehydrogenase (LDH) release into the medium was determined colorimetrically. In vivo efficacy of the compound was determined using a mouse NCI-H460 xenograft model. Briefly, Balb/c mice were inoculated with NCI-H460 cells to induce tumor growth. Animals were treated with 30 mg/kg/po RP3035 BID for 15 d. Total RNA was extracted from tumors and evaluated for Orai1 expression by Real-Time PCR. Metabolic stability of the compound was evaluated in microsomes. Pharmacokinetic behaviour of RP3035 in plasma after single dose oral administration or IV injection was determined in female Balb/c mice and male Wistar rats. Results: RP3035 demonstrated remarkable potency at inhibiting thapsigargin-induced calcium influx into NCI-H460 cells (IC50 = 66.4 nM). Growth inhibition studies indicated that the compound suppressed proliferation in NCI-H460 cells with IC50 values of 230.4 nM without any noticeable cytotoxicity even at the highest dose. Xenograft studies, representative of NSCLC, demonstrated that RP3035 inhibited tumor growth by 42%, comparable with the reduction observed with paclitaxel. Real-time expression analysis revealed &amp;gt;90% reduction in Orai1 mRNA implicating its role in NSCLC progression and growth. Pharmacokinetic studies indicated good oral bioavailability of RP3035 with a favourable half-life and peak plasma concentrations in mouse and rat. Further, RP3035 was metabolically stable across species studied besides showing no significant CYP inhibition in human liver microsomes. Conclusions: Results demonstrate the efficacy and therapeutic potential of RP3035 in NCSLC. Targeting NSCLC through inhibition of Orai1 represents a novel approach primarily aimed at bypassing the resistance due to ras mutations besides alleviating the deleterious effects associated with cytotoxic agents. Dose-response studies for RP3035 are currently underway in NSCLC xenograft models. Besides lung cancer, studies are planned to test the efficacy of the compound in various other cancers as well. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2599. doi:10.1158/1538-7445.AM2011-2599