Poly ADP-ribose polymerase inhibitor (PARP) inhibitors are a highly effective therapy in widespread clinical use for breast and ovarian cancer. PARP inhibitors act by trapping PARP1 on DNA. In cancers with homologous recombination (HR) DNA repair defects (eg BRCA1 mutations) trapping causes replication fork collapse, overwhelming alternative repair pathways. The failure of these alternative pathways leads to exposed ssDNA, mitotic catastrophe and cell death.
Resistance to PARP inhibitors occurs when PARP1 acquires mutations that releive the allosteric force of the inhibitor binding that causes trapping or interfere with binding of the HPF1 protein that controls automodification of PARP1. We are characterising all possible mutations in the PARP1 catalytic and HPF1 binding domains for their impact on inhibitor resistance using multiplex high throughput genomics techniques. Through testing of multiple PARP inhibitors, we are determining the mutations that are specific to an individual drug. This will provide clinical annotation with the potential for making patient care decisions and to improve our fundamental understanding of PARP inhibitor function and resistance.
Using MAVEDB (mavedb.org) and its integration into the SHARIANT database (shariant.org.au) this data will be rapidly available to directly support clinical decision making where clinical sequencing is available.
Futhermore, data from our Deep Mutational Scan (DMS) of PARP1 variants will be used to construct a computational molecular dynamics model of PARP1-HPF1 interaction. This model will be validated by making computational predictions of additional inhibitors prior to testing these inhibitors experimentally. This model will then be applied to compound mutations, including patients that carry rare population mutations to allow accurate variant interpretation in understudied minorities.
Combined, these studies will provide detailed variant annotations for this important cancer gene and provide variant specific recommendations for overcoming resistance in clinical sequencing, with direct translation to clinical care through linkages from MAVEDB to clinical annotation databases.