ABSTRACT: (R,S′)-4'-Methoxy-1-naphthylfenoterol, (R,S′)-MNF, suppresses cellular growth of various cancer cell types. To assess the potency and mechanism of action of (R,S′)-MNF, we performed in vitro assays of cell proliferation, signal transduction via the G-protein-coupled atypical cannabinoid receptor GPR55, and expression of pro-oncogenic proteins in cultured human PANC-1 pancreatic cancer cells, followed by in vivo studies on the growth of PANC-1 cells in a nude mouse xenograft model. In addition to tumor growth, the tumor tissues were analyzed using multiplatform non-targeted and targeted metabolomics, global RNA microarray, and Western immunoblotting. (R,S′)-MNF significantly inhibited cell proliferation in these cells and blocked GPR55-mediated ERK activation without affecting mitochondrial bioenergetics. Moreover, (R,S′)-MNF was effective at reducing PANC-1 tumor growth in vivo, an outcome associated with altered lipid metabolism and metabolic reprogramming. Many of the metabolome changes in cysteine/methionine metabolism and associated oxidative stress, protein degradation, and pyrimidine nucleotide synthesis were validated using a targeted metabolomics approach. Transcriptomics analysis of PANC-1 xenograft tumors of (R,S′)-MNF-treated vs. vehicle-treated mice revealed striking downmodulation of genes involved in Hippo/YAP and Wnt/beta-catenin pathways, and coincided with reduced expression of YAP, beta-catenin, HIF-1alpha, and c-Myc proteins in response to (R,S′)-MNF administration. The contribution of Hippo and beta-catenin signaling pathways in GPR55 pro-oncogenic signaling provides insight into the mechanisms that drive tumorigenesis. The ability of (R,S′)-MNF to inhibit GPR55 may represent a novel anti-cancer treatment.
