A selective and orally bioavailable VHL-recruiting PROTAC achieves SMARCA2 degradation in vivo

Targeted protein degradation offers an alternative modality to classical inhibition and holds the promise of addressing previously undruggable targets to provide novel therapeutic options for patients. Heterobifunctional molecules co-recruit a target protein and an E3 ligase, resulting in ubiquitylation and proteosome-dependent degradation of the target. In the clinic, the oral route of administration is the option of choice but has only been achieved so far by CRBN- recruiting bifunctional degrader molecules. We aimed to achieve orally bioavailable molecules that selectively degrade the BAF Chromatin Remodelling complex ATPase SMARCA2 over its closely related paralogue SMARCA4, to allow in vivo evaluation of the synthetic lethality concept of SMARCA2 dependency in SMARCA4-deficient cancers. Here we outline structure- and property-guided approaches that led to orally bioavailable VHL-recruiting degraders. Our tool compound, ACBI2, shows selective degradation of SMARCA2 over SMARCA4 in ex vivo human whole blood assays and in vivo efficacy in SMARCA4-deficient cancer models. This study demonstrates the feasibility for broadening the E3 ligase and physicochemical space that can be utilised for achieving oral efficacy with bifunctional molecules

Synthesis and Testing of a Focused Phenothiazine Library for Binding to HIV-1 TAR RNA

SummaryWe have synthesized a series of phenothiazine derivatives, which were used to test the structure-activity relationship of binding to HIV-1 TAR RNA. Variations from our initial compound, 2-acetylphenothiazine, focused on two moieties: ring substitutions and n-alkyl substitutions. Binding characteristics were ascertained via NMR, principally by saturation transfer difference spectra of the ligand and imino proton resonance shifts of the RNA. Both ring and alkyl substitutions manifested NMR changes upon binding. In general, the active site, while somewhat flexible, has regions that can be capitalized for increased binding through van der Waals interactions and others that can be optimized for solubility in subsequent stages of development. However, binding can be nontrivially enhanced several-fold through optimization of van der Waals and hydrophilic sites of the scaffold

Direct NMR Probing of Hydration Shells of Protein Ligand Interfaces and Its Application to Drug Design

Fragment-based drug design exploits initial screening of low molecular weight compounds and their concomitant affinity improvement. The multitude of possible chemical modifications highlights the necessity to obtain structural information about the binding mode of a fragment. Herein we describe a novel NMR methodology (LOGSY titration) that allows the determination of binding modes of low affinity binders in the protein–ligand interface and reveals suitable ligand positions for the addition of functional groups that either address or substitute protein-bound water, information of utmost importance for drug design. The particular benefit of the methodology and in contrast to conventional ligand-based methods is the independence of the molecular weight of the protein under study. The validity of the novel approach is demonstrated on two ligands interacting with bromodomain 1 of bromodomain containing protein 4, a prominent cancer target in pharmaceutical industry