Conversion of Small-Molecule Inhibitors into Heterobifunctional Compounds in the Discovery of Novel Chemotherapeutics

Abstract

Heterobifunctional polypharmacologic agents are compounds that have individual pharmacophores for at least two separate biological targets. Our work spans two distinct sets of heterobifunctional molecules: 1. Polypharmacologic agents that inhibit two proteins known to contribute to the disease state, and 2. Protein degraders: Proteolysis targeting chimeras (PROTACs) and molecular glues. Both types of protein degraders function through recruiting an E3 ligase to the protein of interest, resulting in a hijacking of the ubiquitin-proteasome system, and the subsequent destruction of the target protein. The use of type 1 compounds is rapidly growing as such polypharmacologic agents are postulated to exhibit distinct advantages over the monovalent, parent drug compounds from which they are constructed, including the ability to increase therapeutic effect, lower effective dosage, and circumvent treatment resistance. Type 2 compounds – the protein degraders – can eliminate a target of interest, requiring the cell to resynthesize the protein to regain its cellular function. These compounds may have a catalytic mechanism of action wherein the compounds are recycled after mediating the degradation of the target protein, thereby requiring non-stoichiometric amounts of drug while also directly countering resistance that manifests through target protein upregulation. Moreover, such degraders retain activity with resistant proteins where traditional, non-covalent small-molecule drugs fail. Due to these advantages, there is increasing enthusiasm that targeted protein degraders may herald a new class of anti-cancer therapeutics. Herein, our efforts towards the discovery of heterobifunctional pharmaceuticals for the treatment of drug-resistant hematological malignancies are described.