Investigating the role of Microhomology-Mediated End-Joining (MMEJ) in Mitosis and its impact on drug resistance

Sloan-Kettering Inst Can Research, New York NY

Investigators

Abstract

Project Summary Deregulation in DNA damage repair pathways can lead to genome instability, loss of genomic integrity, and ensuing chromosomal abnormalities, all of which are critical events driving the development of many cancers. A better understanding of DNA damage repair pathways and how these go awry in malignant transformation could form the basis for more efficacious therapeutic approaches for various cancers. Mammalian cells have evolved three major pathways to repair the highly toxic double-strand breaks (DSBs). Homologous Recombination (HR) is the preferred pathway, which fixes breaks without altering the original sequence. DSBs can also be repaired by Non-Homologous End-Joining (NHEJ) and Microhomology-Mediated End-Joining (MMEJ). MMEJ is the most mutagenic mode of DSB repair, mainly because of deletions and insertions that scar break sites following repair. In 2015, my lab attributed the source of the insertions to the activity of DNA polymerase theta (Pol coded by POLQ), a low-fidelity enzyme critical for MMEJ activity.Data from our group and others showed that tumor cells with defective HR highly depend on MMEJ to repair DSBs. These studies identified Pol as an attractive target for treating BRCA- mutated tumors with severe defects in HR-mediated repair. Several attempts to target Pol are underway, and inhibitors are currently in clinical trials as monotherapy and in combination with PARP inhibitors for treating tumors with BRCA mutations. Based on our previous findings and preliminary data, I propose in this application a set of experiments to address questions related to the underlying mechanism of MMEJ at different stages of the cell cycle. In addition, we will study the function of MMEJ in promoting resistance to targeted therapy, focusing on BRCA reversion mutations in response to PARP inhibition. Ultimately, uncovering the basis of MMEJ will provide a better understanding of the source of genomic instability as a function of malignancy and guide more effective treatment strategies for cancer.