Targeting V _1A-vasopressin receptors with [arg ⁶, D-Trp ^7,9, N ^mePhe ⁸]-substance P (6-11) identifies a strategy to develop novel anti-cancer therapies

Background and purpose: The anti-cancer agent [Arg ⁶, D-Trp ^7,9, N ^mePhe ⁸]-substance P (6-11) (SP-G) modulates gastrin releasing peptide (GRP) and arginine vasopressin signalling in small cell lung cancer cells leading to growth arrest and apoptosis. We have shown that SP-G acts as a biased agonist at GRP receptors. This work examines the hypothesis that SP-G acts as a biased agonist at the V _1A vasopressin receptor. Experimental approach: The human V _1A receptor was expressed in CHO-K1 cells. Extracellular regulated kinase (ERK) activation and intracellular Ca ²⁺ were measured using activation state-specific antibodies and Fura-2-AM respectively. The effect of SP-G on tumourigenicity was assessed by colony assay. Key results: In V _1A receptor expressing cells, SP-G caused a sustained activation of ERK via a stimulation of V _1A receptor coupling to G _i. Inhibition of G _i with Pertussis toxin attenuated the inhibition by SP-G of the growth of CHO-K1 cells stably expressing the V _1A receptor. Chimeric V _1A receptors containing the second or third intracellular loop of the V ₂ receptor were capable of binding vasopressin and SP-G but had altered ability to activate phospholipase C (PLC) and ERK. The second intracellular loop of the V _1A receptor was essential for vasopressin-stimulated PLC and ERK activation but not for SP-G-induced ERK activation. Conclusions and implications: This work provides mechanistic insight, for biased agonists at V _1A receptors and highlights a potential role for such agents as anti-cancer agents.