Inhibitory activity of luteinizing hormone-releasing hormone on tumor growth and progression

Luteinizing hormone-releasing hormone (LHRH) is the key hormone in the control of reproductive functions. In recent years, it has become evident that LHRH might act as a growth modulatory factor in tumors of the reproductive system. We have shown that in prostate cancer cells LHRH is expressed, together with its receptors, to negatively regulate cell proliferation. In these cells, LHRH acts as an antimitogenic factor through the activation of the Gi-cAMP intracellular signaling pathway. More recently, we investigated whether an LHRH-based autocrine system might also be expressed in tumors that are not classically related to the reproductive tract, such as melanoma. Malignant melanoma is known to be characterized not only by a high proliferation rate, but also by an aggressive metastatic behavior. We have demonstrated that both LHRH and LHRH receptors are expressed in human melanoma cells (BLM and Me15392). Activation of LHRH receptors by means of a potent LHRH agonist (Zoladex) significantly inhibited cell proliferation. The LHRH agonist also reduced the ability of melanoma cells to invade a reconstituted basement membrane (Matrigel) and to migrate in response to a chemotactic stimulus. These data indicate that: (a) in prostate cancer cells the LHRH receptor is coupled to a Gi-cAMP signal transduction pathway; (b) LHRH and LHRH receptors are also expressed in tumors that are not classically related to the reproductive system, such as melanoma; in melanoma cells, LHRH might act as an inhibitory factor on both cell proliferation and metastatic behavior. It is suggested that, in melanoma, LHRH receptors might represent a diagnostic marker and a possible molecular target for new therapeutic approaches for this pathology.