Abstract LB-109: Pharmacological evaluation of RP3042, a cytostatic calcium release activated calcium (CRAC) channel inhibitor, in non-small cell lung cancer
Authors: Viswanadha Srikant , Varanasi Kanthikiran V. , Muthuppalniappan Meyyappan , Kuppireddi Sumalatha , Veeraraghavan Sridhar , Merikapudi Gayatri Swaroop , Vakkalanka Swaroop 
Published: February 2011

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 biological and pharmacokinetic parameters of RP3042, a novel and potent cytostatic agent that inhibits proliferation in NSCLC cell lines 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 NSCLC cell lines such as A549, NCI-H460, and NCI-H522. Lactate dehydrogenase (LDH) release into the medium was determined colorimetrically. Expression of Orai1 and Stim1 in NSCLC cells was confirmed by RT-PCR. hERG inhibitory potential and selectivity over voltage operated channels (VOC) were estimated by radioligand binding assays. Metabolic stability of the compound was evaluated in microsomes obtained from mouse, rat, dog, monkey, and human. Pharmacokinetic behaviour of RP3042 in plasma after single dose oral administration or IV injection was determined in female Balb/c mice and male Wistar rats.

Results: RP3042 demonstrated remarkable potency at inhibiting thapsigargin-induced calcium influx into NCI-H460 cells (IC50 = 72.65 nM). All cell lines tested displayed high expression levels of Orai1 and Stim1, two key proteins responsible for calcium signalling via CRAC channels. Growth inhibition studies indicated that the compound suppressed proliferation in NCI-H460, A549, and NCI-H522 cells with IC50 values of 164, 152, and 206 nM respectively without any noticeable cytotoxicity even at the highest dose. Radioligand binding assays demonstrated the selectivity of RP3042 over VOC with no apparent hERG channel inhibition. Pharmacokinetic studies indicated good oral bioavailability of RP3042 with a maximum plasma concentration of 16.5 and 7.6 µM and an elimination half-life of 2.5 and 1.6 h respectively in mouse and rat. Further, RP3042 was metabolically stable across the species studied besides showing no significant CYP inhibition in human liver microsomes.

Conclusions: Results demonstrate the efficacy, safety, and therapeutic potential of RP3042 in NCSLC. Targeting NSCLC through inhibition of CRAC channels represents a novel approach primarily aimed at bypassing the resistance due to ras mutations besides alleviating the deleterious effects associated with cytotoxic agents. RP3042 is currently being tested for its effects on lung cancer biomarkers besides in vivo efficacy in xenograft models.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-109.