Abstract A30: Identifying microenvironment-dependent vulnerabilities in multiple myeloma using CRISPRi

Acquired drug resistance is a major clinical problem in a variety of cancer types and our understanding of the underlying mechanisms is insufficient. We lack a complete understanding of the interplay of factors between the tumor and its microenvironment controlling drug sensitivity. Several published studies and our preliminary results show that bone marrow microenvironment reduce the sensitivity of multiple myeloma cells to clinically approved proteasome inhibitor, carfilzomib, making it an ideal model system. Here we employ innovative CRISPR-interference (CRISPRi) based functional genomics platform to identify cell-intrinsic and microenvironment-dependent vulnerabilities in multiple myeloma. This platform utilizes a catalytically dead Cas9 (dCas9) fused to a transcriptional repressor domain to target and silence specific genes using single guide-RNAs (sgRNA). We have engineered the myeloma cells to express components of the CRISPRi system enabling us to perform genome-wide screens to identify factors that modulate sensitivity to carfilzomib. To identify microenvironment-dependent factors that alter carfilzomib sensitivity, we established a co-culture system where the CRISPRi expressing myeloma cells are grown in the presence of bone marrow stromal cells and subject to treatment with carfilzomib. We performed a pilot-screen using a library of sgRNAs targeted towards genes involved in the human proteostasis network and known cancer drug targets. The library expressing CRISPRi-myeloma cells were grown as mono- and co-culture in the presence or absence of carfilzomib. Through this screen we were able to identify several factors knockdown of which had differential effects in mono- and co-culture conditions on the growth of the cells and/or their drug response. Currently we are validating the identified factors using various biochemical assays and available pharmacological tools. This study will pave the way to better understand the crosstalk between the tumor and its microenvironment and enable rational design of combination therapies to overcome drug resistance. Citation Format: Poornima Ramkumar, Jaime Tawney, Diego Acosta-Alvear, Martin Kampmann. Identifying microenvironment-dependent vulnerabilities in multiple myeloma using CRISPRi [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr A30.