PROJECT 1 – STRUCTURAL BIOLOGY OF DNA DEAMINASES IN CANCER

PROJECT 1 – STRUCTURAL BIOLOGY OF DNA DEAMINASES IN CANCER ABSTRACT The human APOBEC3 (A3) family of deaminases catalyze the conversion of cytosine to uracil in single- stranded DNA to elicit mutations and genome instability, which in turn promote tumor evolution and the development of therapy resistance and metastatic disease. However, despite the large overall impact of A3- mediated mutagenesis in human cancer and the likely benefits of inhibiting A3-mediated mutagenesis, targeting the A3 family of deaminases for catalytic inhibition and/or selective degradation has remained unfulfilled, challenging us to test the overarching hypothesis that blocking A3 mutagenesis will slow tumor evolution. In addition, several important questions regarding the mechanisms of A3-mediated DNA deamination remain unanswered. The goal of Project 1 – Structural Biology of DNA Deaminases in Cancer is to use the techniques of structural biology to reveal how small-molecule, oligonucleotide, and macromolecular antagonists interact with the A3 proteins to address specific mechanistic hypotheses about A3-mediated DNA deamination and its inhibition. We focus on APOBEC3A (A3A) and APOBEC3B (A3B), as they are the major drivers of tumor evolution. A3A/B antagonists include validated hit compounds from a high-throughput small-molecule inhibitor screen conducted by Core B, fragment binders identified in preliminary studies by this Project and Project 2, oligonucleotide-based inhibitors developed by Project 2, camelid-derived nanobodies, and natural A3 inhibitors from viruses. Not only will the structural information obtained in our studies be instrumental in the future development of targeted therapies, but these reagents will be invaluable in the specific detection of A3 proteins in cells and tissues as well as facilitating structural, biochemical, and cell biological studies to gain further insights into how A3 enzymes function inside normal and tumor cells. We will continue to work closely with all Projects/Cores to leverage the discoveries and novel reagents we develop to test both our overarching and specific, mechanistic hypotheses and, ultimately, help position the field for novel cancer treatments that include evolution-blocking agents.