This revised application will test the hypothesis that small peptide analogs of ¿-melanocortin (¿-MSH) that are selective agonists of the melanocortin 1 receptor (MC1R) will prevent melanoma tumor formation in transgenic mouse melanoma models by enhancing repair of ultraviolet radiation (UV)-induced DNA damage and stimulating melanogenesis. We have pioneered the research on the MC1R and its agonist ¿-melanocyte stimulating hormone (¿-MSH), and discovered their role in reducing the extent of UV-induced DNA damage by activating DNA repair and antioxidant pathways. These findings illuminated how the MC1R functions as a melanoma predisposition gene, and why expression of loss-of-function MC1R allelic variants that are strongly associated with red hair phenotype increases melanoma risk. Our research on MC1R/¿-MSH axis led us to begin developing a melanoma chemoprevention strategy based on targeting the MC1R by highly selective small analogs of ¿-MSH. We have designed and tested a large panel of small ¿-MSH analogs, tri- and tetrapeptides that are full agonists of the MC1R and mimic the physiological ¿-MSH in all its effects on human melanocytes. In this project, we are proposing to test one tripeptide, LK 514, and one tetrapeptide, LK 467, that were selected based on their potency on human melanocytes, and importantly, for their unique selectivity for the MC1R, stability, and lipophilicity. Neither peptide had any cytotoxic effects in cell- and tissue-based assays. We will test the efficacy of these analogs to prevent melanomagenesis in two mouse models that are relevant to human melanoma, i) K14- SCF;Mc1r e/+ transgenic mice, heterozygous for the recessive yellow mutation in Mc1r, a model for humans heterozygous for a red hair MC1R variant who represent a large sector of the white population in the U.S.A. and Northern Europe and have increased risk for melanoma due to reduced MC1R activity, and; ii) HGF transgenic mice, a model for UV-inducible melanoma. We will investigate the ability of these analogs to reduce the extent of UV-induced DNA damage, stimulate eumelanin synthesis, and inhibit melanocytic hyperplasia, melanoma formation, progression and multiplicity. These in vivo experiments are crucial in order to advance these analogs towards a Phase I Clinical Trial. In the absence of a cure for metastatic melanoma, this application is significant due to the critical need for effective melanoma prevention strategies that will reduce the mortality and morbidity associated with the disease, and halt the continuous increase in its incidence. Our proposed strategy is innovative, since our analogs have the unique feature of being highly selective to MC1R, which reduces off-target effects due to binding to other MC receptors, in addition to their small size, stability and lipophilicity that should allow for topical delivery and long lasting effcts. This strategy should benefit millions of high risk individuals with fair skin and poor tanning ability, including those heterozygous for MC1R variant, or harboring mutations in other melanoma predisposition genes, such as p16.