Biology subjects

Flaxman, H. A.

Publications and source records attributed to Flaxman, H. A..

4 recordsLinked to original sources

bioRxiv2023

The Cyclimids: Degron-inspired cereblon binders for targeted protein degradation

Cereblon (CRBN) is an E3 ligase substrate adapter widely exploited for targeted protein degradation (TPD) strategies. However, achieving efficient and selective target degradation is a preeminent challenge with ligands that engage CRBN. Here, we report that the cyclimids, ligands derived from the C-terminal cyclic imide degrons of CRBN, exhibit distinct modes of interaction with CRBN and offer a facile approach for developing potent and selective bifunctional degraders. Quantitative TR-FRET-based characterization of 60 cyclimid degraders in binary and ternary complexes across different substrates revealed that ternary complex binding affinities correlated strongly with cellular degradation efficiency. Our studies establish the unique properties of the cyclimids as versatile warheads in TPD and a systematic biochemical approach for quantifying ternary complex formation to predict their cellular degradation activity, which together will accelerate the development of degraders that engage CRBN.

biochemistry↗

bioRxiv2023

Sanglifehrin A mitigates multi-organ fibrosis in vivo by inducing secretion of the collagen chaperone cyclophilin B

Pathological deposition and crosslinking of collagen type I by activated myofibroblasts drives progressive tissue fibrosis. Therapies that inhibit collagen synthesis by myofibroblasts have clinical potential as anti-fibrotic agents. Lysine hydroxylation by the prolyl-3-hydroxylase complex, comprised of cartilage associated protein, prolyl 3-hydroxylase 1, and cyclophilin B, is essential for collagen type I crosslinking and formation of stable fibers. Here, we identify the collagen chaperone cyclophilin B as a major cellular target of the macrocyclic natural product sanglifehrin A (SfA) using photo-affinity labeling and chemical proteomics. Our studies reveal a unique mechanism of action in which SfA binding to cyclophilin B in the endoplasmic reticulum (ER) induces the secretion of cyclophilin B to the extracellular space, preventing TGF-{beta}1-activated myofibroblasts from synthesizing collagen type I in vitro without inhibiting collagen type I mRNA transcription or inducing ER stress. In addition, SfA prevents collagen type I secretion without affecting myofibroblast contractility or TGF-{beta}1 signaling. In vivo, we provide chemical, molecular, functional, and translational evidence that SfA mitigates the development of lung and skin fibrosis in mouse models by inducing cyclophilin B secretion, thereby inhibiting collagen synthesis from fibrotic fibroblasts in vivo. Consistent with these findings in preclinical models, SfA reduces collagen type I secretion from fibrotic human lung fibroblasts and precision cut lung slices from patients with idiopathic pulmonary fibrosis, a fatal fibrotic lung disease with limited therapeutic options. Our results identify the primary liganded target of SfA in cells, the collagen chaperone cyclophilin B, as a new mechanistic target for the treatment of organ fibrosis.

biochemistry↗

bioRxiv2021

Development of photo-lenalidomide for cellular target identification

The thalidomide analog lenalidomide is a clinical therapeutic that alters the substrate engagement of cereblon (CRBN), a substrate receptor for the CRL4 E3 ubiquitin ligase. Here, we report the development of photo-lenalidomide, a lenalidomide probe with a photo-affinity label and enrichment handle, for target identification by chemical proteomics. After evaluating a series of lenalidomide analogs, we identified a specific amide linkage to lenalidomide that allowed for installation of the desired functionality, while preserving the substrate degradation profile, phenotypic anti-proliferative and immunomodulatory properties of lenalidomide. Photo-lenalidomide maintains these properties by enhancing binding interactions with the thalidomide-binding domain of CRBN, as revealed by binding site mapping and molecular modeling. Using photo-lenalidomide, we captured the known targets IKZF1 and CRBN from multiple myeloma MM.1S cells, and further identified a new target, eukaryotic translation initiation factor 3 subunit i (eIF3i), from HEK293T cells. eIF3i is directly labeled by photolenalidomide and forms a complex with CRBN in the presence of lenalidomide, but is itself not ubiquitylated or degraded. These data point to the potentially broader array of substrates induced by ligands to CRBN that may or may not be degraded, which can be revealed by the highly translatable application of photo-lenalidomide and chemical proteomics in additional biological settings. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=85 SRC="FIGDIR/small/452075v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@1619364org.highwire.dtl.DTLVardef@113a07corg.highwire.dtl.DTLVardef@18d36acorg.highwire.dtl.DTLVardef@8e64_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2019

Discovery of a celecoxib binding site on PTGES with a cleavable chelation-assisted biotin probe

The coxibs are a subset of non-steroidal anti-inflammatory drugs (NSAIDs) that primarily target cyclooxygenase-2 (COX-2) to inhibit prostaglandin signaling and reduce inflammation. However, mechanisms to inhibit other members of the prostaglandin signaling pathway may improve selectivity and reduce off-target toxicity. Here, we report a novel binding site for celecoxib on prostaglandin E synthase (PTGES), an enzyme downstream of COX-2 in the prostaglandin signaling pathway, using a cleavable chelation-assisted biotin probe 6. Evaluation of the multi-functional probe 6 revealed significantly improved tagging efficiencies attributable to the embedded picolyl functional group. Application of the probe 6 within the small molecule interactome mapping by photo-affinity labeling (SIM-PAL) platform using photo-celecoxib as a reporter for celecoxib identified PTGES and other membrane proteins in the top eight enriched proteins from A549 cells. Carbonic anhydrase 12, a known protein target of celecoxib, was also enriched. Four binding sites to photo-celecoxib were additionally mapped by the probe 6, including a binding site with PTGES. The binding interaction with PTGES was validated by competitive displacement with celecoxib and known PTGES inhibitor licofelone. The binding site of photo-celecoxib on PTGES enabled the development of a structural model of the interaction and will inform the design of new selective inhibitors of the prostaglandin signaling pathway.

pharmacology and toxicology↗