Adam Hedger  | Watts Research Group  | PhRMA Foundation Predoctoral Fellowship in Drug Discovery

The apolipoprotein-B mRNA-editing catalytic polypeptide-like 3 (APOBEC3, or A3) family of cytosine deaminase enzymes forms part of the innate immune system - hypermutating cytosine (C) to uracil (U) in single-stranded DNA (ssDNA), as a first response to invading viruses. Specific A3 enzymes, including A3G, were first shown to potently restrict human immunodeficiency virus (HIV). However, expression of these enzymes is a delicate balance – low level deamination of the HIV genome provides a constant source of viral mutation, contributing to high viral fitness and rapid resistance to anti-viral drugs. Moreover, upregulation of other A3 enzymes, like A3A and A3B, is linked to many cancers, helping to expand genetic diversity in tumors to supercharge progression, metastasis, recurrence, and drug resistance. Abolishing activity of specific A3 enzymes may slow viral evolution and prevent tumor recurrence.

Structural examination of A3 active sites reveal their close homology to that of human cytidine deaminase (CDA), which converts C to U in single nucleosides. Introducing CDA inhibitors (transition state analogues, or TSAs) in place of the target C in ssDNA enables delivery to the A3 active site. Yet, development of selective inhibitors against individual A3 family members remains a challenge. Recently, our lab solved the co-crystal structures for A3A-ssDNA and A3G-ssDNA, and have also discovered that both the tertiary structure and DNA sequence flanking the target cytosine confer specificity to different A3 enzymes. I hypothesize that by exploiting these preferences – through manipulation of DNA sequence, oligonucleotide tertiary structure, and rational placement of chemical modifications – I can create potent and selective A3 inhibitors. Leveraging the Watts lab’s expertise in nucleic acid chemistry and the Schiffer lab’s extensive experience with A3G, I will first develop A3G-selective inhibitors, and then A3A and A3B inhibitors.