GPR55 receptor antagonist decreases glycolytic activity in PANC-1 pancreatic cancer cell line and tumor xenografts

The Warburg effect is a predominant metabolic pathway in cancer cells characterized by enhanced glucose uptake and its conversion to L-lactate and is associated with upregulated expression of HIF-1 alpha and activation of the EGFR-MEK-ERK, Wnt-beta-catenin, and PI3K-AKT signaling pathways. (R, R')-4'-methoxy-1-naphthylfenoterol ((R, R')-MNF) significantly reduces proliferation, survival, and motility of PANC-1 pancreatic cancer cells through inhibition of the GPR55 receptor. We examined (R, R')-MNF's effect on glycolysis in PANC-1 cells and tumors. Global NMR metabolomics was used to elucidate differences in the metabolome between untreated and (R, R')-MNF-treated cells. LC/MS analysis was used to quantify intracellular concentrations of beta-hydroxybutyrate, carnitine, and L-lactate. Changes in target protein expression were determined by Western blot analysis. Data was also obtained from mouse PANC-1 tumor xenografts after administration of (R, R')-MNF. Metabolomics data indicate that (R, R')-MNF altered fatty acid metabolism, energy metabolism, and amino acid metabolism and increased intracellular concentrations of b-hydroxybutyrate and carnitine while reducing (L)-lactate content. The cellular content of phosphoinositidedependent kinase-1 and hexokinase 2 was reduced consistent with diminished PI3K-AKT signaling and glucose metabolism. The presence of the GLUT8 transporter was established and found to be attenuated by (R, R')-MNF. Mice treated with (R, R')MNF had significant accumulation of L-lactate in tumor tissue relative to vehicle-treated mice, together with reduced levels of the selective L-lactate transporter MCT4. Lower intratumoral levels of EGFR, pyruvate kinase M2, beta-catenin, hexokinase 2, and p-glycoprotein were also observed. The data suggest that (R, R')-MNF reduces glycolysis in PANC-1 cells and tumors through reduced expression and function at multiple controlling sites in the glycolytic pathway.