Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48823, USA.
Molecular Genetics and Enzymology Department, National Research Centre, Dokki 12622, Egypt.
Int J Mol Sci. 2023 Sep 7;24(18):13785. doi: 10.3390/ijms241813785.
Cutaneous melanoma is the deadliest skin cancer. Most have Ras-MAPK pathway (BRAF or NRAS) mutations and highly effective targeted therapies exist; however, they and immune therapies are limited by resistance, in part driven by small GTPase (Rho and Rac) activation. To facilitate preclinical studies of combination therapies to provide durable responses, we describe the first mouse melanoma lines resistant to BRAF inhibitors. Treatment of mouse lines, YUMM1.7 and YUMMER, with vemurafenib (Vem), the BRAF-selective inhibitor, resulted in high-level resistance (IC shifts 20-30-fold). Resistant cells showed enhanced activation of Rho and the downstream transcriptional coactivator, myocardin-related transcription factor (MRTF). Resistant cells exhibited increased stress fibers, nuclear translocation of MRTF-A, and an increased MRTF-A gene signature. Pharmacological inhibition of the Rho/MRTF pathway using CCG-257081 reduced viability of resistant lines and enhanced sensitivity to Vem. Remarkably, co-treatment of parental lines with Vem and CCG-257081 eliminated resistant colony development. Resistant cells grew more slowly in vitro, but they developed highly aggressive tumors with a shortened survival of tumor-bearing mice. Increased expression of immune checkpoint inhibitor proteins (ICIs) in resistant lines may contribute to aggressive in vivo behavior. Here, we introduce the first drug-resistant mouse melanoma models for assessing combinations of targeted and immune therapies.
皮肤黑色素瘤是最致命的皮肤癌。大多数都存在 Ras-MAPK 通路（BRAF 或 NRAS）突变，并且存在高度有效的靶向治疗方法；然而，它们和免疫疗法受到耐药性的限制，部分原因是小 GTPase（Rho 和 Rac）的激活。为了促进联合治疗的临床前研究以提供持久的反应，我们描述了第一个对 BRAF 抑制剂具有抗性的小鼠黑色素瘤系。用 BRAF 选择性抑制剂 vemurafenib（vem）处理 YUMM1.7 和 YUMMER 小鼠系，导致高水平的耐药性（IC 移位 20-30 倍）。耐药细胞显示 Rho 和下游转录共激活因子心肌细胞相关转录因子（MRTF）的活性增强。耐药细胞表现出增加的应激纤维、MRTF-A 的核易位以及增加的 MRTF-A 基因特征。使用 CCG-257081 抑制 Rho/MRTF 通路的药理学抑制降低了耐药系的活力，并增强了对 vem 的敏感性。值得注意的是，vem 和 CCG-257081 联合处理亲本系可消除耐药集落的发展。耐药细胞在体外生长较慢，但它们形成了侵袭性更强的肿瘤，荷瘤小鼠的存活时间缩短。耐药系中免疫检查点抑制剂蛋白（ICIs）的表达增加可能导致体内行为的侵袭性。在这里，我们引入了第一个对药物有抗性的小鼠黑色素瘤模型，用于评估靶向和免疫治疗的联合应用。
