系统性研究肿瘤耐药性的新方法

作者：吕顺

众所周知，许多抗肿瘤药物能有效地抑制肿瘤的生长，但最常见的挑战是随后的复发。以黑色素瘤为例，大约50％的肿瘤发现BRAF基因突变，靶向BRAF突变基因通路的药物起初能有效地治疗黑色素瘤，但是大约9个月以后通常开始复发，并且产生耐药性。以劳伦•所罗门（Levi Garranway）为首的麻省理工学院研究团队最近在《自然》杂志报道一种新型系统性地研究肿瘤耐药机制的方法。采用这个新方法，该研究团队成功发现黑色素瘤的耐药机理，并且找到克服黑色素瘤耐药的新途径。

该团队表达了超过15,000个基因，并采用能启动单个基因表达的ORF（Open Reading Frame）基因表达库，以便系统地模拟细胞产生耐药的机制。随后课题组在BRAF突变的黑色素瘤细胞中一个个地激活每一个基因，而后观察细胞对治疗BRAF突变的黑色素瘤常见药物的敏感性。由此发现不同基因突变对可能发生耐药的一个完整列表。结果发现，负责正常皮肤细胞生长的一个关键通路是黑色素瘤耐药的最常见机制。

【原文摘要】

A melanocyte lineage program confers resistance to MAP kinase pathway inhibition

Malignant melanomas harbouring point mutations (Val600Glu) in the serine/threonine-protein kinase BRAF (BRAF(V600E)) depend on RAF–MEK–ERK signalling for tumour cell growth1. RAF and MEK inhibitors show remarkable clinical efficacy in BRAF(V600E) melanoma2, 3; however, resistance to these agents remains a formidable challenge2, 4. Global characterization of resistance mechanisms may inform the development of more effective therapeutic combinations. Here we carried out systematic gain-of-function resistance studies by expressing more than 15,500 genes individually in a BRAF(V600E) melanoma cell line treated with RAF, MEK, ERK or combined RAF–MEK inhibitors. These studies revealed a cyclic-AMP-dependent melanocytic signalling network not previously associated with drug resistance, including G-protein-coupled receptors, adenyl cyclase, protein kinase A and cAMP response element binding protein (CREB). Preliminary analysis of biopsies from BRAF(V600E) melanoma patients revealed that phosphorylated (active) CREB was suppressed by RAF–MEK inhibition but restored in relapsing tumours. Expression of transcription factors activated downstream of MAP kinase and cAMP pathways also conferred resistance, including c-FOS, NR4A1, NR4A2 and MITF. Combined treatment with MAPK-pathway and histone-deacetylase inhibitors suppressed MITF expression and cAMP-mediated resistance. Collectively, these data suggest that oncogenic dysregulation of a melanocyte lineage dependency can cause resistance to RAF–MEK–ERK inhibition, which may be overcome by combining signalling- and chromatin-directed therapeutics.

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