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‐1α and activation of the EGFR‐MEK‐ERK, Wnt‐β‐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 β‐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 β‐hydroxybutyrate and carnitine while reducing l‐lactate content. The cellular content of phosphoinositide‐dependent 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, β‐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. What's new? Aerobic glycolysis is a multi‐component system that serves as the primary means of energy generation in cancer cells. As one of several interrelated processes associated with tumorigenesis, it is a key target in cancer therapy. A promising inhibitor is (R,R′)‐4‐methoxynaphthylfenoterol, or (R,R′)‐MNF, which targets the pro‐oncogenic G protein‐coupled receptor GPR55. This study shows that (R,R′)‐MNF effectively reduces glycolysis in both human PANC‐1 pancreatic cancer cells and a murine xenograft model. The inhibitor attenuated the expression and functi