Oncogenic KRAS G12C: Kinetic and Redox Characterization of Covalent Inhibition

Minh V. Huynh, Derek Parsonage, Tom E. Forshaw, Venkat R. Chirasani, G. Aaron Hobbs, Hanzhi Wu, Jingyun Lee, Cristina M. Furdui, Leslie B. Poole, Sharon L. Campbell

Journal of Biological Chemistry, 2022

https://doi.org/10.1016/j.jbc.2022.102186

The recent development of mutant-selective inhibitors for the oncogenic KRASG12C allele has generated considerable excitement. These inhibitors covalently engage the mutant C12 thiol located within the phosphoryl binding loop of RAS, locking the KRASG12C protein in an inactive state. While clinical trials of these inhibitors have been promising, mechanistic questions regarding the reactivity of this thiol remain. Here, we show by NMR and an independent biochemical assay that the pKa of the C12 thiol is depressed (pKa ∼7.6), consistent with susceptibility to chemical ligation. Using a validated fluorescent KRASY137W variant amenable to stopped-flow spectroscopy, we characterized the kinetics of KRASG12C fluorescence changes upon addition of ARS-853 or AMG 510, noting that at low temperatures, ARS-853 addition elicited both a rapid first phase of fluorescence change (attributed to binding, Kd = 36.0 ± 0.7 μM), and a second, slower pH-dependent phase, taken to represent covalent ligation. Consistent with the lower pKa of the C12 thiol, we found that reversible and irreversible oxidation of KRASG12C occurred readily both in vitro and in the cellular environment, preventing the covalent binding of ARS-853. Moreover, we found that oxidation of the KRASG12C Cys12 to a sulfinate altered RAS conformation and dynamics to be more similar to KRASG12D in comparison to the unmodified protein, as assessed by molecular dynamics simulations. Taken together, these findings provide insight for future KRASG12C drug discovery efforts, as well as identifying the occurrence of G12C oxidation with currently unknown biological ramifications.

Discovery and Characterization of a Novel Series of Chloropyrimidines as Covalent Inhibitors of the Kinase MSK1

Adrian Hall, Jan Abendroth, Madison J. Bolejack, Tom Ceska, Sylvie Dell’Aiera, Victoria Ellis, David Fox, Cyril François, Muigai M. Muruthi, Camille Prével, Karine Poullennec, Sergei Romanov, Anne Valade, Alain Vanbellinghen, Jason Yano, and Martine Geraerts

ACS Medicinal Chemistry Letters 2022

DOI: 10.1021/acsmedchemlett.2c00134

We describe the identification and characterization of a series of covalent inhibitors of the C-terminal kinase domain (CTKD) of MSK1. The initial hit was identified via a high-throughput screening and represents a rare example of a covalent inhibitor which acts via an SNAr reaction of a 2,5-dichloropyrimidine with a cysteine residue (Cys440). The covalent mechanism of action was supported by in vitro biochemical experiments and was confirmed by mass spectrometry. Ultimately, the displacement of the 2-chloro moiety was confirmed by crystallization of an inhibitor with the CTKD. We also disclose the crystal structures of three compounds from this series bound to the CTKD of MSK1, in addition to the crystal structures of two unrelated RSK2 covalent inhibitors bound to the CTKD of MSK1.

Nucleophilic covalent ligand discovery for the cysteine redoxome

Fu, L.; Jung, Y.; Tian, C.; Ferreira, R.; He, F.; Yang, J.; Carroll, K. ChemRxiv 2022.

https://chemrxiv.org/engage/chemrxiv/article-details/62ab096604a3a9469c48d4ec

The convergence of reactive cysteine-targeted electrophilic fragments and chemoproteomics have dramatically accelerated the discovery of ligandable sites in the proteome. Our genome encodes 214,000 cysteine residues, at least 20% of which are estimated to be redox-active. Oxidation blunts sulfur reactivity toward electrophiles but opens the door to a new class of nucleophilic covalent ligands that target cysteinyl sulfenic acids, which are widespread post-translational modifications. Here we report a quantitative analysis of nucleophilic fragments screened against the human sulfenome. Ligands were discovered for >500 sulfenated cysteines in >400 proteins, including sites not targeted by electrophiles with the same scaffold. Among these were compounds that preferentially react with hepatoma-derived growth factor (HDGF)-related proteins (HRPs) one of which was able to block nuclear transport of this oncoprotein. Nucleophilic fragments provide a rich resource for chemical biology and drug discovery, where ligandability in the human proteome extends beyond protein thiols.

Platform for Orthogonal N-Cysteine-Specific Protein Modification Enabled by Cyclopropenone Reagents

 Alena Istrate, Michael B. Geeson, Claudio D. Navo, Barbara B. Sousa, Marta C. Marques, Ross J. Taylor, Toby Journeaux, Sebastian R. Oehler, Michael R. Mortensen, Michael J. Deery, Andrew D. Bond, Francisco Corzana, Gonzalo Jiménez-Osés, and Gonçalo J. L. Bernardes

Journal of the American Chemical Society 2022

DOI: 10.1021/jacs.2c02185

Protein conjugates are valuable tools for studying biological processes or producing therapeutics, such as antibody–drug conjugates. Despite the development of several protein conjugation strategies in recent years, the ability to modify one specific amino acid residue on a protein in the presence of other reactive side chains remains a challenge. We show that monosubstituted cyclopropenone (CPO) reagents react selectively with the 1,2-aminothiol groups of N-terminal cysteine residues to give a stable 1,4-thiazepan-5-one linkage under mild, biocompatible conditions. The CPO-based reagents, all accessible from a common activated ester CPO-pentafluorophenol (CPO-PFP), allow selective modification of N-terminal cysteine-containing peptides and proteins even in the presence of internal, solvent-exposed cysteine residues. This approach enabled the preparation of a dual protein conjugate of 2×cys-GFP, containing both internal and N-terminal cysteine residues, by first modifying the N-terminal residue with a CPO-based reagent followed by modification of the internal cysteine with a traditional cysteine-modifying reagent. CPO-based reagents enabled a copper-free click reaction between two proteins, producing a dimer of a de novo protein mimic of IL2 that binds to the β-IL2 receptor with low nanomolar affinity. Importantly, the reagents are compatible with the common reducing agent dithiothreitol (DTT), a useful property for working with proteins prone to dimerization. Finally, quantum mechanical calculations uncover the origin of selectivity for CPO-based reagents for N-terminal cysteine residues. The ability to distinguish and specifically target N-terminal cysteine residues on proteins facilitates the construction of elaborate multilabeled bioconjugates with minimal protein engineering.

A direct high-throughput protein quantification strategy facilitates discovery and characterization of a celastrol-derived BRD4 degrader

N. Connor Payne, Semer Maksoud, Bakhos A. Tannous, Ralph Mazitschek

Cell Chemical Biology, 2022

DOI: https://doi.org/10.1016/j.chembiol.2022.05.003

We describe a generalizable time-resolved Förster resonance energy transfer (TR-FRET)-based platform to profile the cellular action of heterobifunctional degraders (or proteolysis-targeting chimeras [PROTACs]) that is capable of both accurately quantifying protein levels in whole-cell lysates in less than 1 h and measuring small-molecule target engagement to endogenous proteins, here specifically for human bromodomain-containing protein 4 (BRD4). The detection mix consists of a single primary antibody targeting the protein of interest, a luminescent donor-labeled anti-species nanobody, and a fluorescent acceptor ligand. Importantly, our strategy can readily be applied to other targets of interest and will greatly facilitate the cell-based profiling of small-molecule inhibitors and PROTACs in a high-throughput format with unmodified cell lines. We furthermore validate our platform in the characterization of celastrol, a p-quinone methide-containing pentacyclic triterpenoid, as a broad cysteine-targeting E3 ubiquitin ligase warhead for potent and efficient targeted protein degradation.