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

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.

CRH, [D-Glu20]-CRH, [D-Pro5]-CRH, acetyl-cyclo(30-33)[D-Phe12,D-Glu20,Nle21,D-His32,Lys33,D-Nle38]-CRH(4-41), acetyl-cyclo(30-33)[D-Phe12,Nle18,D-Glu20,Nle21,D-Ala32]-urotensin I(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 [D-Glu20]-CRH on blood pressure were compared by measuring mean arterial pressure in anesthetized rats.

CRH and six 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 100 pM. 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-Glu20]-CRH, 100 micrograms/kg.day s.c., for 5 days, reduced net B16 tumor volume in mice by 30-60% compared to control animals. [D-Glu20]-CRH was less hypotensive compared to CRH, despite having similar anti-proliferative potency.

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-Glu20]-CRH, with less hypotensive activity may provide new directions of therapy for melanoma.