Targeting the Melanocortin 1 Receptor by Selective Small Analogs of α-Melanocortin for Melanoma Prevention

太阳紫外线辐射（UV）是黑色素瘤的主要病因，黑色素瘤是最致命的皮肤癌， 也是退伍军人中第五大癌症黑色素瘤的发病率在退伍军人中比在 平民，特别是肤色浅和晒黑能力差的人。超过65%的退伍军人 这个phenotype。伊拉克和阿富汗等地理区域部署数百万士兵 由于不可避免的每日过度阳光照射而没有最佳保护，增加了患黑色素瘤的风险。 鉴于黑色素瘤的先进治疗选择的局限性，重要的是要专注于开发新的 化学预防策略，以减少其发病率。我们的目标是开发一种黑色素瘤预防策略 基于黑皮质素1受体（MC 1 R）的靶向作用， 已知该基因是人类色素沉着和黑素细胞对太阳紫外线反应的主要调节因子。我们 是第一个报道了开创性的发现，MC 1 R的激活，一种膜结合的Gs蛋白偶联的 受体通过其激动剂α-黑素细胞刺激激素（α-黑皮质素; α-MSH）表达于黑素细胞上 通过增强DNA修复和抗氧化能力减少紫外线诱导的DNA损伤， 刺激光保护性真黑素的合成。另一些人则表示， MC 1 R的功能变体与增加的UV特征突变和常见的体细胞突变相关。 BRAF中的V600 E突变，其驱动黑色素瘤发生。约50%的白色高加索人，包括约7 100万退伍军人是MC 1 R变异的杂合子携带者，这种基因型与增加的风险有关。 黑素瘤这些人将特别受益于我们的预防战略， 激活MC 1 R。我们已经开发了α-MSH的四肽和三肽类似物， α-MSH对人黑素细胞的作用是稳定的，亲脂性的，其独特之处在于对人黑素细胞的高选择性。 MC1R这些肽的美容用途由已公布的专利申请涵盖。四肽是 在激活MC 1 R信号传导方面，三肽的效力仅比α-MSH低10倍 及其在培养的人类黑素细胞中的下游效应。这些肽增强了UV诱导的细胞损伤的修复。 DNA光产物，并增加色素沉着的培养人类皮肤替代品（CSS）没有任何紫外线 exposure.与α-MSH不同，这些小肽不应引起免疫抑制，因为它们缺乏 α-MSH的羧基端11-13个氨基酸残基（Lys-Pro-瓦尔）负责其抗- 炎症和免疫抑制作用。我们提出我们的α-MSH的三肽和四肽类似物 对MC 1 R具有选择性的药物将被开发为局部药物，以刺激皮肤色素沉着并减少 紫外线诱导的DNA损伤，为了维持黑素细胞基因组的稳定性， 退伍军人患黑色素瘤的风险。我们的具体目标是：I：开发MC 1 R选择性的局部制剂 四肽和三肽，证明它们通过表皮的渗透，定量它们的 在皮肤层中的浓度，并验证其在体外对完整的人类皮肤或CSS的光保护作用 当局部应用时。二.为了测试两种肽对临床前动物模型的作用，包括 将移植到免疫缺陷小鼠身上的人类CSS，以及皮肤与之相似的小型猪模型， 人类终点将包括测量DNA损伤、色素沉着、增殖和 角质形成细胞和黑素细胞的凋亡。将采集血液样本用于初步药代动力学研究 将检查试验和组织样本的总体毒理学效应。该项目的成果应 推动我们更接近申请研究性新药和进行临床试验。

Solar ultraviolet radiation (UV) is the main etiological factor for melanoma, the deadliest form of skin cancer, and the fifth most diagnosed cancer in veterans. The incidence of melanoma is higher in veterans than in civilians, particularly in individuals with light skin color and poor tanning ability. Over 65% of all veterans have this phenotype. Deployment of millions of soldiers in geographical areas such as Iraq and Afghanistan increases their risk for melanoma due to unavoidable daily excessive sun exposure without optimal protection. Given the limitations of advanced therapeutic options for melanoma, it is important to focus on developing new chemoprevention strategies to reduce its incidence. Our goal is to develop a melanoma prevention strategy based on targeting the melanocortin 1 receptor (MC1R), the product of a bona fide melanoma predisposition gene known to be a major regulator of human pigmentation and the response of melanocytes to solar UV. We were the first to report the seminal findings that activation of the MC1R, a membrane-bound Gs protein-coupled receptor expressed on melanocytes, by its agonist α-melanocyte stimulating hormone (α-melanocortin; α-MSH) reduces UV-induced DNA damage by enhancing DNA repair and antioxidant capacities, in addition to stimulating the synthesis of photoprotective eumelanin. Others have shown that expression of a loss-of- function variant of MC1R is associated with increased UV signature mutations and the common somatic V600E mutation in BRAF, that drive melanomagenesis. About 50% of all White Caucasians, including about 7 million veterans, are heterozygous carriers of a MC1R variant, a genotype associated with increased risk for melanoma. These individuals will particularly benefit from our prevention strategy that will enhance the activation of the MC1R. We have developed tetra- and tripeptide analogs of α-MSH that mimic the effects of α-MSH on human melanocytes, and are stable and lipophilic, and unique in their high selectivity for the MC1R. The cosmetic use of these peptides is covered by a published patent application. The tetrapeptides are 100 fold more potent, and the tripeptides are only 10 fold less potent than α-MSH in activating MC1R signaling and its downstream effects in cultured human melanocytes. These peptides enhanced repair of UV-induced DNA photoproducts, and increased pigmentation of cultured human skin substitutes (CSS) without any UV exposure. These small peptides, unlike α-MSH, should not cause immunosuppression, since they lack the COOH-terminal 11-13 amino acid residues (Lys-Pro-Val) of α-MSH that are responsible for its anti- inflammatory and immunosuppressive effects. We propose that our tri- and tetrapeptide analogs of α-MSH that are selective for the MC1R will be developed as topical agents to stimulate skin pigmentation and reduce UV-induced DNA damage, in order to maintain the genomic stability of melanocytes, and therefore reduce the risk for melanoma in veterans. Our Specific Aims are: I: To develop topical formulations of MC1R-selective tetrapeptide and tripeptidepeptide, demonstrate their permeation through the epidermis, quantify their concentrations in the skin layers, and validate their photoprotective effects on intact human skin or CSS in vitro when applied topically. II. To test the effects of the two peptides on pre-clinical animal models, including human CSS that will be grafted onto immunodeficient mice, and a miniature pig model with skin similar to that of humans. Endpoints will include measurement of DNA damage, changes in pigmentation, proliferation and apoptosis of keratinocytes and melanocytes. Blood samples will be obtained for preliminary pharmacokinetics testing and tissue samples will be examined for gross toxicological effects. The outcome of this project should advance us closer towards application for Investigational New Drug and conducting clinical trials.