Development of novel site-selective chemical strategies to conjugate PROTACS to antibodies

The mechanism is based on inhibition of protein by inducing molecular proximity between protein of interest and ubiquitin E3 ligase using heterobifunctional molecule (PROTAC), this induces proteasomal degradation of the protein targets. Thus, PROTACs allows the elimination of any protein targets including those considered “undruggable”. However, PROTACs approach lacks of cell-specificity raises toxicity concerns for application. This project aim to develop new chemical strategies to conjugate PROTACs in a site- selective manner to antibody for targeting PROTACs to specific diseased cells. Optimization of molecular design is proposed to further improve the extent of knock-down level of the diseased cell only by PROTACs-antibody conjugate. This molecular construction can bring to close proximity the target protein and an E3 ubiquitin ligase, leading to ubiquitination and subsequent proteasomal degradation of the target protein4.

Notably, PROTACs also have catalytic turnover, meaning that one small-molecule PROTAC can induce the degradation of multiple target protein subunits5. Since PROTACs possess the advantage of small molecules, especially ability to access a wide range of sites of action, yet has the ability to also target any disease-causing protein and exhibits catalytic mode of action allowing low exposure to be efficacious, it offers a great potential to medicine discovery. However, PROTACs lack cell-specificity which raises toxicity concerns for in vivo applications. Therefore, there is an ongoing need for a potent method to specifically direct PROTACs delivery to diseased cell that contains target protein. Statement of Problem/Project Objectives. The overall aim of this project is to develop high quality antibody-PROTAC conjugate for facilitating selective intracellular degradation of target protein.

The specific aims are: (1) To develop protein modification technique that allows construction of homogenous antibody-PROTAC conjugate molecules; (2) To evaluate the activity and selectivity of antibody-PROTAC conjugate in cellular assays; (3) To further refine the antibody-PROTAC conjugate molecules for potency, selectivity, stability, and activity through linker optimization. Proposed Plan of Investigation. 1 Designing linker reagents for Lysine modification. The conjugate product will be subjected to enzymatic degradation to identify of the exact residue(s) where the modification occurred as a validation of the regio- and chemo-selectivity of the reaction. 3 Construction of homogenous antibody-PROTAC conjugate. Utilizing the established protein modification method, the antibody-PROTAC conjugate will then be constructed. First, the antibody (e. g. Proposed Outcomes. Despite the emerging importance of PROTACs and their intense therapeutic interest, its inherent lack of cell-specificity has limited their potential for in vivo application.

This work represents a novel and promising approach to target PROTACs to specific diseased cell through antibody conjugation. We propose that this project will generate important starting strategy to validate the therapeutic potential of antibody-PROTAC conjugate molecules in cells. References. A. & McClendon, C. L. Reaching for high-hanging fruit in drug discovery at protein–protein interfaces. Nature 450, 1001–1009 (2007). M. Small-Molecule PROTACS: New Approaches to Protein Degradation. Angew. Chem. Int. , Dumontet, C. & Corvaïa, N. Strategies and challenges for the next generation of antibody–drug conjugates. Nat. Rev. J. Am. Chem. Soc. Freedy, A. Nat. Commun. Figure 1. Schematic diagram of PROTAC. A PROTAC molecule consists of a ligand binding with an E3-ubiquitin ligase, a ligand binding with target protein, and a linker to link the two ligands.