Melanoma prevention by MC1R selective small peptide analogs of alpha MSH

 描述（由申请人提供）：本修订后的申请将测试以下假设：作为黑皮质素 1 受体 (MC1R) 选择性激动剂的 α-黑皮质素 (α-MSH) 小肽类似物将通过增强紫外线辐射 (UV) 诱导的 DNA 损伤的修复和刺激黑素生成来预防转基因小鼠黑色素瘤模型中黑色素瘤的形成。我们率先对 MC1R 及其激动剂 α-黑素细胞刺激激素 (α-MSH) 进行了研究，并发现了它们通过激活 DNA 修复和抗氧化途径来减少紫外线诱导的 DNA 损伤程度的作用。这些发现阐明了 MC1R 如何作为黑色素瘤易感基因发挥作用，以及为什么与红发表型密切相关的功能丧失的 MC1R 等位基因变异的表达会增加黑色素瘤风险。我们对 MC1R/α-MSH 轴的研究使我们开始开发一种黑色素瘤化学预防策略，该策略基于通过高度选择性的 α-MSH 小类似物靶向 MC1R。我们设计并测试了一大组小型 α-MSH 类似物、三肽和四肽，它们是 MC1R 的完全激动剂，并模拟生理学 α-MSH 对人类黑素细胞的所有影响。在这个项目中，我们建议测试一种三肽 LK 514 和一种四肽 LK 467，这些肽是根据其对人类黑素细胞的效力而选择的，更重要的是，它们对 MC1R 的独特选择性、稳定性和亲脂性。在基于细胞和组织的测定中，这两种肽都没有任何细胞毒性作用。我们将测试这些类似物在与人类黑色素瘤相关的两种小鼠模型中预防黑色素瘤生成的功效，i) K14-SCF;Mc1r e/ 转基因小鼠，Mc1r 中隐性黄色突变的杂合子，红发 MC1R 变体杂合子的人类模型，代表美国和北欧白人的很大一部分，由于 MC1R 活性降低，患黑色素瘤的风险增加，以及； ii) HGF 转基因小鼠，紫外线诱导黑色素瘤模型。我们将研究这些类似物减少紫外线诱导的 DNA 损伤程度、刺激真黑素合成以及抑制黑素细胞增生、黑素瘤形成、进展和多样性的能力。这些体内实验对于将这些类似物推进一期临床试验至关重要。在无法治愈转移性黑色素瘤的情况下，这一应用具有重要意义，因为迫切需要有效的黑色素瘤预防策略，以降低与该疾病相关的死亡率和发病率，并阻止其发病率的持续增加。我们提出的策略是创新的，因为我们的类似物具有对 MC1R 高度选择性的独特特征，可减少由于与其他 MC 受体结合而导致的脱靶效应，此外它们的尺寸小、稳定性和亲脂性应允许局部递送和持久效果。这一策略应该会使数百万皮肤白皙且晒黑能力差的高风险个体受益，包括那些 MC1R 变异杂合子或携带其他黑色素瘤易感基因（如 p16）突变的人。

 DESCRIPTION (provided by applicant): This revised application will test the hypothesis that small peptide analogs of α-melanocortin (α-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 α-melanocyte stimulating hormone (α-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/α-MSH axis led us to begin developing a melanoma chemoprevention strategy based on targeting the MC1R by highly selective small analogs of α-MSH. We have designed and tested a large panel of small α-MSH analogs, tri- and tetrapeptides that are full agonists of the MC1R and mimic the physiological α-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.