A chemical probe to modulate human GID4 Pro/N-degron interactions.

The C-terminal to LisH (CTLH) complex is a ubiquitin ligase complex that recognizes substrates with Pro/N-degrons via its substrate receptor Glucose-Induced Degradation 4 (GID4), but its function and substrates in humans remain unclear. Here, we report PFI-7, a potent, selective and cell-active chemical probe that antagonizes Pro/N-degron binding to human GID4. Use of PFI-7 in proximity-dependent biotinylation and quantitative proteomics enabled the identification of GID4 interactors and GID4-regulated proteins. GID4 interactors are enriched for nucleolar proteins, including the Pro/N-degron-containing RNA helicases DDX21 and DDX50. We also identified a distinct subset of proteins whose cellular levels are regulated by GID4 including HMGCS1, a Pro/N-degron-containing metabolic enzyme. These data reveal human GID4 Pro/N-degron targets regulated through a combination of degradative and nondegradative functions. Going forward, PFI-7 will be a valuable research tool for investigating CTLH complex biology and facilitating development of targeted protein degradation strategies that highjack CTLH E3 ligase activity.

Discovery of PFI-6, a small-molecule chemical probe for the YEATS domain of MLLT1 and MLLT3.

Epigenetic proteins containing YEATS domains (YD) are an emerging target class in drug discovery. Described herein are the discovery and characterization efforts associated with PFI-6, a new chemical probe for the YD of MLLT1 (ENL/YEATS1) and MLLT3 (AF9/YEATS3). For hit identification, fragment-like mimetics of endogenous YD ligands (crotonylated histone-containing proteins), were synthesized via parallel medicinal chemistry (PMC) and screened for MLLT1 binding. Subsequent SAR studies led to iterative MLLT1/3 binding and selectivity improvements, culminating in the discovery of PFI-6. PFI-6 demonstrates good affinity and selectivity for MLLT1/3 vs. other human YD proteins (YEATS2/4) and engages MLLT3 in cells. Small-molecule X-ray co-crystal structures of two molecules, including PFI-6, bound to the YD of MLLT1/3 are also described. PFI-6 may be a useful tool molecule to better understand the biological effects associated with modulation of MLLT1/3.

Discovery of a Potent Deubiquitinase (DUB) Small-Molecule Activity-Based Probe Enables Broad Spectrum DUB Activity Profiling in Living Cells.

Deubiquitinases (DUBs) are a family of >100 proteases that hydrolyze isopeptide bonds linking ubiquitin to protein substrates, often leading to reduced substrate degradation through the ubiquitin proteasome system. Deregulation of DUB activity has been implicated in many diseases, including cancer, neurodegeneration and auto-inflammation, and several have been recognized as attractive targets for therapeutic intervention. Ubiquitin-derived covalent activity-based probes (ABPs) provide a powerful tool for DUB activity profiling, but their large recognition element impedes cellular permeability and presents an unmet need for small molecule ABPs which can account for regulation of DUB activity in intact cells or organisms. Here, through comprehensive chemoproteomic warhead profiling, we identify cyanopyrrolidine (CNPy) probe IMP-2373 (12) as a small molecule pan-DUB ABP to monitor DUB activity in physiologically relevant live cells. Through proteomics and targeted assays, we demonstrate that IMP-2373 quantitatively engages more than 35 DUBs across a range of non-toxic concentrations in diverse cell lines. We further demonstrate its application to quantification of changes in intracellular DUB activity during pharmacological inhibition and during MYC deregulation in a model of B cell lymphoma. IMP-2373 thus offers a complementary tool to ubiquitin ABPs to monitor dynamic DUB activity in the context of disease-relevant phenotypes.

The Kinase Chemogenomic Set (KCGS): An Open Science Resource for Kinase Vulnerability Identification.

We describe the assembly and annotation of a chemogenomic set of protein kinase inhibitors as an open science resource for studying kinase biology. The set only includes inhibitors that show potent kinase inhibition and a narrow spectrum of activity when screened across a large panel of kinase biochemical assays. Currently, the set contains 187 inhibitors that cover 215 human kinases. The kinase chemogenomic set (KCGS), current Version 1.0, is the most highly annotated set of selective kinase inhibitors available to researchers for use in cell-based screens.

(R)-PFI-2 is a potent and selective inhibitor of SETD7 methyltransferase activity in cells.

SET domain containing (lysine methyltransferase) 7 (SETD7) is implicated in multiple signaling and disease related pathways with a broad diversity of reported substrates. Here, we report the discovery of (R)-PFI-2-a first-in-class, potent (Ki (app) = 0.33 nM), selective, and cell-active inhibitor of the methyltransferase activity of human SETD7-and its 500-fold less active enantiomer, (S)-PFI-2. (R)-PFI-2 exhibits an unusual cofactor-dependent and substrate-competitive inhibitory mechanism by occupying the substrate peptide binding groove of SETD7, including the catalytic lysine-binding channel, and by making direct contact with the donor methyl group of the cofactor, S-adenosylmethionine. Chemoproteomics experiments using a biotinylated derivative of (R)-PFI-2 demonstrated dose-dependent competition for binding to endogenous SETD7 in MCF7 cells pretreated with (R)-PFI-2. In murine embryonic fibroblasts, (R)-PFI-2 treatment phenocopied the effects of Setd7 deficiency on Hippo pathway signaling, via modulation of the transcriptional coactivator Yes-associated protein (YAP) and regulation of YAP target genes. In confluent MCF7 cells, (R)-PFI-2 rapidly altered YAP localization, suggesting continuous and dynamic regulation of YAP by the methyltransferase activity of SETD7. These data establish (R)-PFI-2 and related compounds as a valuable tool-kit for the study of the diverse roles of SETD7 in cells and further validate protein methyltransferases as a druggable target class.

Epigenetic drugs that do not target enzyme activity.

While the installation and removal of epigenetic post-translational modifications or 'marks' on both DNA and histone proteins are the tangible outcome of enzymatically catalyzed processes, the role of the epigenetic reader proteins looks, at first, less obvious. As they do not catalyze a chemical transformation or process as such, their role is not enzymatic. However, this does not preclude them from being potential targets for drug discovery as their function is clearly correlated to transcriptional activity and as a class of proteins, they appear to have binding sites of sufficient definition and size to be inhibited by small molecules. This suggests that this third class of epigenetic proteins that are involved in the interpretation of post-translational marks (as opposed to the creation or deletion of marks) may represent attractive targets for drug discovery efforts. This review mainly summarizes selected publications, patent literature and company disclosures on these non-enzymatic epigenetic reader proteins from 2009 to the present.

Chemical tools for the Gid4 subunit of the human E3 ligase C-terminal to LisH (CTLH) degradation complex.

We have developed a novel chemical handle (PFI-E3H1) and a chemical probe (PFI-7) as ligands for the Gid4 subunit of the human E3 ligase CTLH degradation complex. Through an efficient initial hit-ID campaign, structure-based drug design (SBDD) and leveraging the sizeable Pfizer compound library, we identified a 500 nM ligand for this E3 ligase through file screening alone. Further exploration identified a vector that is tolerant to addition of a linker for future chimeric molecule design. The chemotype was subsequently optimized to sub-100 nM Gid4 binding affinity for a chemical probe. These novel tools, alongside the suitable negative control also identified, should enable the interrogation of this complex human E3 ligase macromolecular assembly.

A Second-Generation Oral SARS-CoV-2 Main Protease Inhibitor Clinical Candidate for the Treatment of COVID-19.

Despite the record-breaking discovery, development and approval of vaccines and antiviral therapeutics such as Paxlovid, coronavirus disease 2019 (COVID-19) remained the fourth leading cause of death in the world and third highest in the United States in 2022. Here, we report the discovery and characterization of PF-07817883, a second-generation, orally bioavailable, SARS-CoV-2 main protease inhibitor with improved metabolic stability versus nirmatrelvir, the antiviral component of the ritonavir-boosted therapy Paxlovid. We demonstrate the in vitro pan-human coronavirus antiviral activity and off-target selectivity profile of PF-07817883. PF-07817883 also demonstrated oral efficacy in a mouse-adapted SARS-CoV-2 model at plasma concentrations equivalent to nirmatrelvir. The preclinical in vivo pharmacokinetics and metabolism studies in human matrices are suggestive of improved oral pharmacokinetics for PF-07817883 in humans, relative to nirmatrelvir. In vitro inhibition/induction studies against major human drug metabolizing enzymes/transporters suggest a low potential for perpetrator drug-drug interactions upon single-agent use of PF-07817883.

Discovery of High-Affinity Small-Molecule Binders of the Epigenetic Reader YEATS4.

A series of small-molecule YEATS4 binders have been discovered as part of an ongoing research effort to generate high-quality probe molecules for emerging and/or challenging epigenetic targets. Analogues such as 4d and 4e demonstrate excellent potency and selectivity for YEATS4 binding versus YEATS1,2,3 and exhibit good physical properties and in vitro safety profiles. A new X-ray crystal structure confirms direct binding of this chemical series to YEATS4 at the lysine acetylation recognition site of the YEATS domain. Multiple analogues engage YEATS4 with nanomolar potency in a whole-cell nanoluciferase bioluminescent resonance energy transfer assay. Rodent pharmacokinetic studies demonstrate the competency of several analogues as in vivo-capable binders.

Target 2035 - an update on private sector contributions.

Target 2035, an international federation of biomedical scientists from the public and private sectors, is leveraging 'open' principles to develop a pharmacological tool for every human protein. These tools are important reagents for scientists studying human health and disease and will facilitate the development of new medicines. It is therefore not surprising that pharmaceutical companies are joining Target 2035, contributing both knowledge and reagents to study novel proteins. Here, we present a brief progress update on Target 2035 and highlight some of industry's contributions.

Target 2035 - update on the quest for a probe for every protein.

Twenty years after the publication of the first draft of the human genome, our knowledge of the human proteome is still fragmented. The challenge of translating the wealth of new knowledge from genomics into new medicines is that proteins, and not genes, are the primary executers of biological function. Therefore, much of how biology works in health and disease must be understood through the lens of protein function. Accordingly, a subset of human proteins has been at the heart of research interests of scientists over the centuries, and we have accumulated varying degrees of knowledge about approximately 65% of the human proteome. Nevertheless, a large proportion of proteins in the human proteome (∼35%) remains uncharacterized, and less than 5% of the human proteome has been successfully targeted for drug discovery. This highlights the profound disconnect between our abilities to obtain genetic information and subsequent development of effective medicines. Target 2035 is an international federation of biomedical scientists from the public and private sectors, which aims to address this gap by developing and applying new technologies to create by year 2035 chemogenomic libraries, chemical probes, and/or biological probes for the entire human proteome.

Optimisation of a novel series of selective CNS penetrant CB(2) agonists.

A series of benzimidazole CB(2) receptor agonists were prepared and their properties investigated. Optimisation of the three benzimidazole substituents led to the identification of compound 23, a potent CB(2) full agonist (EC(50) 2.7nM) with excellent selectivity over the CB(1) receptor (>3000-fold). Compound 23 demonstrated good CNS penetration in rat. Further optimisation led to the identification of compound 34 with improved selectivity over hERG and excellent CNS penetration in rat.

Synthesis and evaluation of heteroarylalanine diacids as potent and selective neutral endopeptidase inhibitors.

Heteroarylalanine derivatives 4 were designed as potential inhibitors of neutral endopeptidase (NEP EC 3.4.24.11). Selectivity over other zinc metalloproteinases was explored through occupation of the S2' subsite within NEP. Structural optimisation led to the identification of 5-phenyl oxazole 4f, a potent and selective NEP inhibitor. A crystal structure of the inhibitor bound complex is reported.

Structure and Inhibitor Binding Characterization of Oncogenic MLLT1 Mutants.

Dysfunction of YEATS-domain-containing MLLT1, an acetyl/acyl-lysine dependent epigenetic reader domain, has been implicated in the development of aggressive cancers. Mutations in the YEATS domain have been recently reported as a cause of MLLT1 aberrant reader function. However, the structural basis for the reported alterations in affinity for acetylated/acylated histone has remained elusive. Here, we report the crystal structures of both insertion and substitution mutants present in cancer, revealing significant conformational changes of the YEATS-domain loop 8. Structural comparison demonstrates that not only did such alteration alter the binding interface for acetylated/acylated histones, but the sequence alterations in the loop in T1 mutant may enable dimeric assembly consistent with inducing self-association behavior. Nevertheless, we show that also the MLLT1 mutants can be targeted by developed acetyllysine mimetic inhibitors with affinities similarly to wild-type. Our report provides a structural basis for the altered behaviors and a potential strategy for targeting oncogenic MLLT1 mutants.

Investigating 3,3-diaryloxetanes as potential bioisosteres through matched molecular pair analysis.

Oxetanes have received increasing interest in medicinal chemistry as attractive polar and low molecular weight motifs. The application of oxetanes as replacements for methylene, methyl, gem-dimethyl and carbonyl groups has been demonstrated to often improve chemical properties of target molecules for drug discovery purposes. The investigation of the properties of 3,3-diaryloxetanes, particularly of interest as a benzophenone replacement, remains largely unexplored. With recent synthetic advances in accessing this motif we studied the effects of 3,3-diaryloxetanes on the physicochemical properties of 'drug-like' molecules. Here, we describe our efforts in the design and synthesis of a range of drug-like compounds for matched molecular pair analysis to investigate the viability of the 3,3-diaryloxetane motif as a replacement group in drug discovery. We conclude that the properties of the diaryloxetanes and ketones are similar, and generally superior to related alkyl linkers, and that diaryloxetanes provide a potentially useful new design element.

Preclinical characterization of an intravenous coronavirus 3CL protease inhibitor for the potential treatment of COVID19.

COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. PF-00835231, a 3CL protease inhibitor, has exhibited potent in vitro antiviral activity against SARS-CoV-2 as a single agent. Here we report, the design and characterization of a phosphate prodrug PF-07304814 to enable the delivery and projected sustained systemic exposure in human of PF-00835231 to inhibit coronavirus family 3CL protease activity with selectivity over human host protease targets. Furthermore, we show that PF-00835231 has additive/synergistic activity in combination with remdesivir. We present the ADME, safety, in vitro, and in vivo antiviral activity data that supports the clinical evaluation of PF-07304814 as a potential COVID-19 treatment.