Abstract (R,R')-4′-methoxy-1-naphtylfenoterol (MNF) inhibits proliferation of 1321N1 astrocytoma cell line in a β2-adrenergic receptor (β2AR)-dependent manner, while reducing rat C6 glioma growth in a xenograft mouse model. MNF interferes also with pro-oncogenic signaling induced by the orphan G-protein-linked receptor, GPR55, in human HepG2 hepatocarcinoma and PANC-1 pancreatic carcinoma cells. Here, we utilized a number of cellular and biochemical techniques to investigate the anti-tumorigenic potential of MNF in a panel of human melanoma cell lines. Cell migration, which was performed using scratch wound healing assay, demonstrated the ability of MNF to dose-dependently reduce the motility of EGFR-expressing UACC-647 and M93-047 cell lines in a biphasic (IC50 = 0.32 nM and 1.48 µM) and sigmoidal (IC50 = 7.14 nM) fashion, respectively. In contrast, EGFR-negative UACC-903 cells were unresponsive to MNF. The proliferation rate of UACC-647 cells was diminished by 38 ± 3.7% in the presence of MNF, with an IC50 of 136 nM. Pharmacological inhibition of β2AR with the selective antagonist ICI-118,551 (50 nM) did not confer protection against the actions of MNF on cell motility and proliferation. U-shaped dose-response curves, with a nadir at 1 nM, were observed when the levels of phosphorylated MEK and ERK were determined in MNF-treated UACC-647 cells. A similar dose-response relationship was observed with the β2AR agonists, epinephrine and (R,R')-fenoterol, and cell pretreatment with 50 nM ICI-118,551 abolished MNF-evoked drop in phospho-ERK levels. However, MNF markedly increased inhibitory phosphorylation of eukaryotic elongation factor 2 (eEF2) on Thr56, which was accompanied by global defect in protein biosynthesis as revealed by pulse-labeling experiments with [35S]-methionine. We conclude that the anti-tumorigenic functions of MNF most likely reflect dual effects of MNF through interaction with different receptors in melanoma. This work was supported entirely by the Intramural Research Program of the National Institute on Aging/NIH and NIA/NIH contract N01-AG31009, and the Foundation for Polish Science (TEAM 2009-4/5 programme). Citation Format: Artur Wnorowski, Rajib K. Paul, Lucita Jimenez, Lawrence Toll, Abdelmohsen Kotb, Michel Bernier, Irving W. Wainer. (R,R')-4′-methoxy-1-naphtylfenoterol inhibits pro-survival signaling, proliferation and motility of select human melanoma cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3680. doi:10.1158/1538-7445.AM2014-3680