Identifying Combinatorial Drug Targets for Ras Pathway-Driven Melanomas

melanoma;cancer;therapeutics;CRISPR;CRISPR screen;small molecules;BET;HDAC;USP7;Ras pathway

Manchester, Haley Ellen ; Hemann, Michael,Fisher, David,Polyak, Kornelia,Haigis, Kevin

University:Havard University

Department:Medical Sciences

关键词: melanoma;    cancer;    therapeutics;    CRISPR;    CRISPR screen;    small molecules;    BET;    HDAC;    USP7;    Ras pathway;   

Others  :  https://dash.harvard.edu/bitstream/handle/1/37365790/MANCHESTER-DISSERTATION-2020.pdf?sequence=1&isAllowed=y

美国|英语

来源: Digital Access to Scholarship at Harvard

【 摘 要 】

Cutaneous melanoma is a highly metastatic skin cancer, with ~100,000 new cases estimated to occur in 2020 in the US. Melanomas are defined by oncogenic “driver” mutations that constitutively activate the Ras/Raf/MEK/ERK signaling (henceforth called Ras/ERK) pathway. Clinical agents that target various components of this pathway have been developed, although they are not typically curative.For BRAF-mutant melanomas, combined BRAF and MEK inhibitors prolong survival, although patients still relapse within ~11 months. Unfortunately, Ras/ERK pathway inhibitors are even less effective in NRAS-mutant tumors, with MEK inhibitors stimulating only partial responses in 15-20% of patients. Thus, NRAS mutations are associated with poor overall survival, and there is a great need for improved therapies. The goal of my thesis has been to identify agents that potentiate the effects of Ras/ERK pathway inhibitors as a means of developing more effective therapies for NRAS and other Ras pathway-driven melanomas. This dissertation describes three promising therapeutic combinations. In one approach, we discovered a new combinatorial therapy for NRAS-mutant melanomas by performing an unbiased negative selection CRISPR-Cas9 screen.Specifically, we identified the de-ubiquitinase USP7 as a target that when suppressed, sensitizes NRAS-mutant melanomas to MEK inhibitors. Further genetic and mechanistic analysis revealed USP7 interacts with two other hits from our screen and together form a complex that regulates H2B ubiquitination, a marker of transcriptional elongation. Through epigenetic and transcriptional studies, we found that this complex regulates the expression of CABLES1, which is required for triggering cell death and tumor regression.Using candidate-based approaches, we also identified two additional combination therapies that target BRAF-, NRAS-, and NF1-mutant melanomas. Specifically, we discovered that histone de-acetylase (HDAC) inhibitors potentiate responses to Ras/ERK signaling pathway inhibitors in BRAF-, NRAS-, and NF1-mutant melanomas by suppressing DNA repair pathways (Maertens et al. 2019). Additionally, we demonstrated that the combination of Ras/ERK signaling pathway and bromodomain and extraterminal domain (BET) inhibitors represents a promising new therapeutic approach to reduce acquired and intrinsic resistance in BRAF-mutant melanomas (Katherine R. Singleton 2017). In summary, this dissertation details three promising combination therapies for Ras/ERK pathway-driven melanomas and describes the distinct mechanisms by which they function.