Locally expressed LHRH receptors mediate the oncostatic and antimetastatic activity of LHRH agonists on melanoma cells

Malignant melanoma is a tumor known for its uncontrollable growth and aggressive metastatic behavior. The mean survival time for patients with a metastatic melanoma is estimated to be less than 6 months, tumor cells being refractory to the conventional chemotherapy. A better understanding of the mechanisms regulating melanoma growth and progression might help increase the number of therapeutic options for this pathology. In this paper, we have shown that LHRH receptors are present in the BLM melanoma cell line, both at mRNA and at protein level; a potent LHRH agonist (LHRH-A; Zoladex) binds to these receptors with high affinity. BLM cells also express the mRNA for LHRH, indicating the presence of an autocrine LHRH-based system in melanoma cells. The treatment of BLM cells with LHRH-A dose-dependently inhibited cell proliferation; this effect was found to be specific because it was completely abrogated by the simultaneous treatment of the cells with a LHRH antagonist. Similar observations could be obtained in another melanoma cell line (Me15392). The activation of LHRH receptors, by means of LHRH-A, also reduced the ability of melanoma cells to invade a reconstituted basement membrane (Matrigel) and to migrate through a Boyden's chamber in response to a chemotactic stimulus. These data represent the first report that 1) LHRH and LHRH receptors are expressed in melanoma tumor cells; and 2) the activation of tumor LHRH receptors reduces both the proliferation and the metastatic potential of melanoma cells. It is suggested that the expression of LHRH receptors might represent a new diagnostic marker for the detection and progression of melanoma. These receptors might also be considered as a possible molecular target for a hormone-based therapeutic approach to this tumor.