BCL2 amplicon loss and super-enhancer remodeling drives ABT-199 resistance

ABSTRACT: Drug-tolerant “persister” tumor cells underlie the emergence of drug-resistant clones contribute to relapse and disease progression; thus, identifying actionable targets that disable persisters and mitigate relapse are a high priority need. Although the BCL2-targeting agent venetoclax (ABT-199) has shown promising responses in mantle cell and double hit B cell lymphomas, resistance often arises, yet mechanistically how this occurs is unclear. Here we report that ABT-199 resistance can evolve from persister clones that have selective deletions at 18q21 that involve the drug target BCL2 and the apoptotic regulators Noxa (PMAIP1) and TCF4. Notably, reprogramming of super enhancers (SE) in persisters contributes to resistance, where there is a selection for SE-directed overexpression of the apoptotic regulator BCL2A1 and oncogenic transcription factors IKZF1 and FOXC1. At the same time, the SE reprogramming confers an opportunity for overcoming ABT-199 resistance. An unbiased drug screen on a platform that recapitulates the lymphoma microenvironment revealed that persisters are vulnerable to inhibitors of transcription initiation and elongation, and especially so to inhibitors of cyclin-dependent kinase 7 (CDK7) that is essential for transcription initiation. Specifically, CDK7 loss or inhibition eliminated the persister phenotype by disabling SE-driven expression of BCL2A1, IKZF1 and FOXC1. Thus, the co-treatment of ABT-199 with CDK7 inhibitors blocked the evolution of drug resistance, and provoked tumor regression in models of mantle cell lymphoma (MCL) and double hit lymphomas (DHL) that overexpress both MYC and BCL2. Together, these findings establish loss of apoptotic regulators and an adaptive transcriptional response as drug resistance mechanisms in lymphoma, more importantly, establish a rationale for transcription inhibition-based combination strategies to prevent and overcome drug resistance in B cell malignancies toward BCL2 inhibitor.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): B Cell

DISEASE(S): Lymphoma

SUBMITTER: John Koomen  

LAB HEAD: Jianguo Tao MD/PhD

PROVIDER: PXD010193 | Pride | 2020-05-26

REPOSITORIES: Pride