Abstract LB-C13: Selective GPR55 antagonism attenuates EGFR-PKM2-β-catenin signaling and reduces chemoresistance in PANC-1 pancreatic cancer cells

Abstract

Abstract G protein-coupled receptor GPR55 possesses pro-oncogenic activity, but the nature of GPR55 signaling pathways in mammalian tumor cells remain unclear. The effect of (R,R')-4'-methoxy-1-naphthylfenoterol (MNF), a potent GPR55 competitive inhibitor, on the expression of cancer biomarkers, such as EGFR, PKM2, β-catenin and HIF-1A, was investigated in human pancreatic cancer cell line, PANC-1. We also examined the modulation in expression of P-glycoprotein (Pgp) and other multidrug resistance drug exporters (MDR) in response to MNF. Incubation of PANC1 cells with MNF (1 μM) for 24h significantly decreased EGFR (∼2-fold), PKM2 (∼2.5-fold) and β-catenin (∼2-fold) protein levels and was accompanied by significant reduction in nuclear accumulation of HIF-1A(∼1.5-fold) and phospho-active forms of PKM2 (∼3-fold) and B-catenin (∼2-fold). MNF and the GPR55 antagonist CID16020046 consistently reduced the expression of Pgp (∼2-fold), BCRP (∼2-fold), MRP1 (∼1.5-fold) and MRP5 (∼1.5-fold) in total cellular extracts while diminishing the nuclear expression of Pgp (∼2.5-fold) and BCRP (∼4.5-fold). Further, a significant increase in the nuclear accumulation of doxorubicin was observed in MNF-treated PANC-1 cells using laser scanning confocal microscopy. Importantly, a 24-h preincubation with MNF increased the cytotoxicity of doxorubicin (IC50 reduced from 170nM to 24nM) and gemcitabine (IC50 reduced from 486nM to 157nM) in PANC-1 cells. In the mouse xenograft model, daily MNF treatment (10mg.kg-1, i.p.) for 21 days led to a ∼2-fold reduction in the expression of EGFR, PKM2, β-catenin and Pgp in PANC-1 tumor tissue relative to vehicle-treated controls (P < 0.001). These data suggest that MNF exerts its antitumor effects by inhibiting GPR55-mediated activation of select cancer biomarkers, and suppressing multidrug resistance to chemotherapeutic agents in pancreatic cancer cells. Citation Format: Nagendra Singh, Michel Bernier, Irving W. Wainer. Selective GPR55 antagonism attenuates EGFR-PKM2-β-catenin signaling and reduces chemoresistance in PANC-1 pancreatic cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-C13.