The classic understanding of inhibitory small molecule drugs is a straightforward model in which they bind to their targets and prevent their function. However, it is now increasingly clear that the mechanisms of many small-molecule drugs require more complex models to explain their effects. For example, some possess neomorphic functions that modulate their targets beyond simple inhibition. Such cases have been demonstrated for molecular glues, protein degraders, and chromatin modulators. Crucially, a standard genetic knockout for target validation cannot recapitulate these modes of action. Therefore, understanding how to rationally design such molecules will require innovative and creative means for their discovery.
DNA damage tolerance mechanisms, including translesion synthesis (TLS) polymerases, promote cell survival under genotoxic stress and can contribute to cancer cell survival and chemoresistance. However, targeting TLS polymerases therapeutically has proven difficult. This is not due to a lack of chemical inhibitors but rather due to the redundancy within and across different classes of TLS polymerases. One approach to overcome this redundancy is to inhibit a target so that it sequesters the substrate, thereby preventing downstream pathways from ultimately eliminating the lesion. In the case of TLS polymerases, this could be achieved by trapping the TLS polymerase at sites of DNA damage in a manner similar to trapping PARP inhibitors such as Olaparib or topoisomerase poisons such as Topotecan.
To begin exploring how to trap these polymerases, the Hieter and Stirling groups will use their Mutational Target Mapping platform to screen for dominant gain-of-function mutations in TLS polymerases. The Mutational Target Mapping platform screens missense mutations that result in the dysfunction of therapeutic targets across the protein of interest. Here, the desired mutations will lead to TLS trapping at DNA damage sites. This project aims to identify such mutations and assess their synthetic lethality across various tumor types and genetic vulnerabilities, advancing both therapeutic strategies and biological understanding of TLS polymerases in cancer. Moreover, the mutations identified will guide the development of small molecule inhibitors with neomorphic trapping functions for TLS polymerases.