Connecting DNA Replication Fork Instability with Novel Chemotherapeutic Strategies for Breast Cancer
Abstract
Mutations in the BRCA1 and BRCA2 genes account for the vast majority of familial breast cancer cases. Breast cancer patients carrying BRCA1/2 gene mutations are often treated with chemotherapeutics that damage the cancer cell’s DNA in an attempt to stop replication and induce cancer cell death. Unfortunately, current treatment regimens for breast cancer are hindered by the development of resistance to mainstay drugs. Our goal is to determine how breast cancers carrying BRCA1/2 gene mutations cope with chemotherapy treatment and to ultimately develop a new, more effective strategy for chemotherapy. To achieve this goal, we have extensively characterized a key mechanism used by cancer cells to confront chemotherapy-induced DNA lesions and prevent replication forks from colliding with replication obstacles. This mechanism is termed replication fork reversal. Our lab found that BRCA proteins, which are well known for their roles in repairing double-strand breaks, also play an important role in protecting reversed replication forks by preventing their degradation. When BRCA proteins are missing, the reversed DNA forks are unprotected, and nucleases can easily degrade the DNA. This degradation phenotype provides important clues to explain why BRCA-deficient tumors are susceptible to chemotherapeutic drugs that damage DNA and stall replication. As part of our original Breast Cancer Research Program (BCRP) award, we discovered that BRCA-mutant cells use a fork recovery pathway as a last resort to save the extensively degraded replication forks and to withstand DNA-damaging chemotherapy. We also found that these fork recovery pathways are different between BRCA1- and BRCA2-mutant cells. In particular, fork recovery relies on a specialized nuclease called MUS81 in BRCA2-deficient, but not in BRCA1-deficient cells. Notably, two other proteins, RAD18 and UBC13, are required for fork recovery in BRCA1-deficient, but not BRCA2-deficient cells. Aim 1 of this project will define how the MUS81 pathway works in BRCA2-mutant cells, and Aim 2 will focus on the RAD18/UBC13 pathway in BRCA1-mutants. This project will tackle two overarching challenges: (a) it will revolutionize treatment regimens by replacing them with ones that are more effective and less toxic and (b) it will identify novel determinants for breast cancer initiation, risk, or susceptibility. By identifying cellular factors that promote recovery of degraded forks in BRCA-mutated cells, our data will provide a strategy to further sensitize BRCA-mutated breast tumors to DNA-damaging therapies. Moreover, we are developing novel tissue microarrays from BRCA1- and BRCA2-mutated breast tumors that will be used to screen for mutations or alterations in the mRNA/protein levels of fork recovery factors. We will systematically interrogate whether mutations or alterations in mRNA/protein levels correlate with reduced risk of disease recurrence in patients with early-stage BRCA-mutated breast cancer treated with (neo)adjuvant chemotherapy. These studies will advance a novel, more effective, and highly targeted treatment strategy that therapeutically exploits these molecular alterations in breast cancer. The identification of factors required for fork recovery in BRCA1/2-mutated cells will also identify novel determinants for breast cancer initiation, and it will define the molecular basis of the incomplete penetrance of BRCA1 and BRCA2 mutations. The current treatments for BRCA-mutant breast cancer patients with DNA-damaging chemotherapeutics are often accompanied by significant collateral damage and unwanted side effects. Thus, there is a strong need to develop treatments that preferentially kill cancer cells while minimizing the impact on normal cells. The knowledge that will emerge from this study has the potential to augment and improve current chemotherapeutic regimens based on DNA-damaging agents by targeting replication fork recovery pathways, which are selectiv
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010893
Entities
People
- Alessandro Vindigni
Organizations
- United States Army
- Washington University in St. Louis