Members of the RAS family of oncogenes are the most frequently mutated in human cancer. KRAS mutations are present in 95% of pancreas, 35% of colon and 20% of lung cancers. Decades of research failed to develop effective KRAS-directed therapies. As an alternative, current work aims at targeting crucial KRAS downstream effectors. Some of these proteins, such as MEK, belong to the MAP-Kinase pathway and are critical regulators of cell proliferation and survival. Cellular resistance mechanisms have hampered the efficacy of MEK inhibitors. However, combination therapies may be more effective by targeting two pathways simultaneously. We used data generated from genome-scale CRISPR-Cas9 Project Achilles screens to discover vulnerabilities in KRAS-mutant cancer cell lines, and identified the Rho GTPase RAC1 as a key signaling node supporting proliferation and survival of KRAS-mutant cancers. In tumors, RAC1 is usually hyper-activated and RAC1 inhibitors such as EHop-016 aim at blocking the interaction of RAC1 with several of its known guanine nucleotide exchange factors (GEFs). In this project, we validated RAC1 dependency in KRAS-mutant lines. We evaluated cell lines that were predicted by CRISPR-Cas9 screening to be preferentially dependent on RAC1 as well as lines that did not show this dependency. Response to drug treatment was measured using Cell Titer GloR. To investigate the potential for combination therapy, we also performed combination treatment studies with EHop-016 and the MEK inhibitor Trametinib, to determine if the combination resulted in better antiproliferative effects than either drug alone. We further distinguished synergistic from additive effects using the Bliss Independence Model. We present data supporting RAC1 dependency in KRAS mutant cell lines and demonstrate synergistic interactions with MEK inhibition. In the future, improved understanding of downstream players will provide a better ground for combination therapies to support a path forward for clinical implementation of this strategy.
PROJECT: Validation of RAC1 dependency and combination therapy for KRAS cancer cells
I came to the Broad Institute feeling certain that my expectations for the summer experience could not be set too high, and this was indeed the case. There are many things about the Broad Institute that exceeded my expectations, but most prominent was the strong culture of collaboration and learning. I felt truly respected not only by my cohort, lab mates and mentors, but also by scientists working at the forefront of their respective fields. This summer was a golden opportunity to grow and challenge myself intellectually and personally, as SRPG connected us with amazing scientists, mentors and other students. Thank you SRPG!