Inhibition of mouse melanoma cell proliferation by corticotropin-releasing hormone and its analogs

Background: Observations that epidermal cells release both corticotropin-releasing hormone (CRH) and proopiome lanocortin (POMC) peptides has raised questions about the physiological relevance of this hypothalamo-pituitary-like system in mammalian skin. As CRH has shown anti-proliferative effects on cultured keratinocytes, we tested whether CRH can also regulate growth of melanoma cells. Materials and Methods. CRH, [D-Glu(20)]-CRH, [D-Pro(5)]-CRH, acetyl-cyclo(3033)[D-Phe(12),D-Glu(20),Nle(21),D-His(32),Lys(33),D-Nle(38)]-CRH(4-41), acetyl-cyclo(30-33)[D-Phe(12),Nle(18),D-Glu(20),Nle(21),D-Ala(32)]-urotensin 1(4-41), urocortin, and sauvagine were tested on Cloudman melanoma cell proliferation in culture and B16 melanoma tumor growth in C57B1/6 mice. Calcium-sensitive fluorescence measurements were used to examine the effect of CRH on intracellular Ca2+ signaling. The effects of CRH and CRH on intracellular Ca [D-Glu(20)]-CRH on blood pressure were compared by measuring mean arterial pressure in anesthetized rats. Results: CRH and si analogs were tested, and all demonstrated exceptional potency in inhibiting Cloudman cell proliferation in culture, with half-maximal effective concentrations ranging between 0.2 and 100pM. The amplitude of ionomycin-induced Ca2+ influx into Cloudman cells grown in suspension was reduced by 50% after 48-hr exposure to CRH. Daily injections of CRH or [D-Glu(20)]-CRH, 100 mug/kg.day s.c., for 5 days, reduced net B16 tumor volume in mice by 30-60% compared to control animals. [D-Glu(20)]-CRH was less hypotensive compared to CRH, despite having similar anti-proliferative potency. Conclusion: CRH, and various analogs thereof inhibit proliferation of Cloudman cells in culture, and inhibit B16 tumor-growth rate in vivo, most likely by activation of endogenous CRH1 receptors and subsequent altered intracellular Ca2+ signaling. CRH analogs, such as [D-Glu(20)]-CRH, with less hypotensive activity may provide new directions of therapy for melanoma.