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

Background: Observations that epidermal cells release both corticotropin-re leasing hormone (CRH) and proopiome lanocortin (POMC) peptides has raised q uestions about the physiological relevance of this hypothalamo-pituitary-li ke 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 m elanoma cell proliferation in culture and B16 melanoma tumor growth in C57B 1/6 mice. Calcium-sensitive fluorescence measurements were used to examine the effect of CRH on intracellular Ca2+ signaling. The effects of CRH and C RH on intracellular Ca [D-Glu(20)]-CRH on blood pressure were compared by m easuring mean arterial pressure in anesthetized rats. Results: CRH and si a nalogs were tested, and all demonstrated exceptional potency in inhibiting Cloudman cell proliferation in culture, with half-maximal effective concent rations ranging between 0.2 and 100pM. The amplitude of ionomycin-induced C a2+ 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% co mpared to control animals. [D-Glu(20)]-CRH was less hypotensive compared to CRH, despite having similar anti-proliferative potency. Conclusion: CRH, a nd various analogs thereof inhibit proliferation of Cloudman cells in cultu re, and inhibit B16 tumor-growth rate in vivo, most likely by activation of endogenous CRH1 receptors and subsequent altered intracellular Ca2+ signal ing. CRH analogs, such as [D-Glu(20)]-CRH, with less hypotensive activity m ay provide new directions of therapy for melanoma.