Chemical biology & target ID
22 articles
Electrophile-first screen yields covalent aminothiazole inhibitors of the E2 enzyme UBE2D2
- An electrophile-first screen, combined with X-ray crystallography, found a covalent hit that engages two cysteines (C85 and C111) of UBE2D2.
- Structure-guided SAR on the amide and ester groups removed binding to C111 while improving engagement of C85.
- The optimized analog inhibited UBE2D2 activity in vitro and suppressed proliferation of A549 lung cancer cells.
E2s have long been written off as undruggable, so seeing a crystal-supported covalent series is a real step. The interesting design move is dialing out the second cysteine, which is exactly what you need before calling anything a probe. I'd now ask how it behaves across other UBE2D family members, since the active-site cysteine is conserved and selectivity will be the hard part.
Much of the PROTAC target-engagement spread is exposure, not E3 recognition
- Twenty PROTACs with varied E3 ligands, linkers and target binders were profiled in intracellular NanoBRET competition assays against cereblon and VHL tracers.
- Apparent potency spread widely when referenced to applied concentration, and passive Caco-2 permeability explained little of it.
- Correcting for measured intracellular unbound exposure shrank the spread dramatically, matching values from permeabilized cells.
Before I read a PROTAC SAR table as E3 affinity, I'd now ask what the cell actually saw. If most of the shift is unbound exposure, linker tweaks that look like potency gains may just be permeability gains, and measuring exposure early keeps us from chasing the wrong variable.
A covalent ligand at cereblon's cryptic Cys287 locks the E3 ligase open and blocks IMiD-driven degradation
- Cysteine-directed chemoproteomic screening found covalent ligands for Cys287, an allosteric pocket far from the thalidomide-binding site.
- Lead VVD-105917 broadly blocks degradation of neosubstrates driven by IMiDs and CELMoDs.
- Cryo-EM shows it traps cereblon in its open, inactive state, and ligand order matters. A previously reported ligand at the same site promotes closure instead, so the pocket is 'sign-switchable'.
Every CRBN drug so far sits in one orthosteric pocket, so a covalent handle that controls the open/closed switch is a genuinely new knob. A pan-inhibitor is an excellent tool to dissect degrader mechanisms and rescue off-target degradation. A site that can push either way also means a degrader-enhancing ligand might be hiding in the same pocket. This is a preprint, so wait for review.
Allosteric covalent inhibition of cereblon through cryptic cysteine targeting ↗
A 5-azaindole TTBK1/2 probe with a matched negative control disrupts ciliogenesis
- The 5-azaindole inhibitor 13 is potent against tau tubulin kinases 1 and 2 and active in cells.
- In-cell kinome profiling showed few off-targets; follow-up NanoBRET work narrowed them to CDK11A/B, CK1δ and PIKfyve.
- A close analogue, compound 5, lacks in-cell TTBK affinity and serves as a negative control; compound 13 blocks TTBK2 autophosphorylation and impairs primary cilia formation in RPE-1 cells.
What I like here is the discipline: a kinome-wide in-cell selectivity map, honest naming of the CDK11 and PIKfyve liabilities, and a matched inactive control. That is what a probe should look like before anyone reads biology into a ciliogenesis phenotype. The CDK11 overlap is the caveat I'd test first, with an orthogonal chemotype.
Potent and Cell Active 5-Azaindole-based Tau Tubulin Kinase Inhibitors Disrupt Ciliogenesis ↗
Elevenostat is a multi-HDAC inhibitor biased to HDAC6, not an HDAC11-selective probe
- Re-testing Elevenostat (JB3-22) against recombinant HDAC isoforms with two orthogonal HDAC11 assays showed only weak HDAC11 inhibition.
- Full HDAC1–11 profiling found much stronger inhibition of HDAC6 and HDAC10, plus class I enzymes, with HDAC11 the least sensitive isoform.
- Cellular readouts (tubulin and histone acetylation, reduced viability) matched HDAC6 and class I engagement, so past HDAC11 conclusions drawn from this compound need re-reading.
This is the unglamorous but valuable kind of paper: a compound used as an HDAC11 tool turns out to hit HDAC6 hardest. Any phenotype published with Elevenostat now has an attribution problem. Before I reuse an inhibitor as a probe, I want full-panel selectivity and a matched inactive control, which this case argues for.
Cyanoquinoline HIPK4 inhibitors open a route to non-hormonal male contraception
- HIPK4 is a spermatid-specific kinase needed for sperm head shaping, making it a candidate non-hormonal contraceptive target.
- A cyanoquinoline series gave potent, HIPK4-selective inhibitors, selective within the HIPK family and across the kinome.
- Some compounds also altered HIPK4 proteostasis in spermatids, causing insoluble aggregates and recruiting the autophagy receptor TAX1BP1.
A selective kinome-wide profile from a first series is what a probe needs, and the unexpected proteostasis effect is the intriguing bit: it hints at a degrader-like mode that could be tuned. For contraception the bar is brutal, though, with reversibility and long-term safety to prove.
Small-Molecule Modulators of HIPK4 Activity and Proteostasis ↗
Azide-bearing VEGFR2 inhibitors switch on under green light in the retina
- Azido-functionalized VEGFR2 inhibitors EYE1090 and EYE1118 bind the receptor in a light-triggered way while staying potent in the dark.
- Green light that reaches the human retina, including in older eyes, boosted their anti-angiogenic activity in vitro.
- Given orally, both suppressed VEGF-induced retinal leakage in rats and shrank lesions in a mouse choroidal neovascularization model without acute liver toxicity.
An azide as the photo-switch is a neat, small-footprint handle on a classic kinase scaffold. The appeal is spatial selectivity: systemic exposure with activity concentrated where light focuses. I'd probe how much dark activity remains, which matters for off-target VEGFR2 effects elsewhere, and the photoproduct's fate.
Three Nitrogen Atoms Turn Old Kinase Inhibitors Into New Targetable Remedy ↗
Azaphilone Probe Maps Reactive Lysines Across Live Bacterial Proteomes
- SCL-alkyne, a simplified azaphilone derived from the natural product sclerotiorin, was designed to profile lysine reactivity proteome-wide in bacteria.
- It was highly lysine-selective in vitro and in live E. coli; most engaged sites were lysines or protein N-termini, and only a small subset of reactive lysines sat in functional regions.
- Enrichment analysis pointed to bacterial chemotaxis as a major target pathway, which was then confirmed.
Covalent ligand discovery has been cysteine-centric, and lysine-directed scaffolds beyond sulfonyl fluorides and activated esters are scarce, so a natural-product-derived option is appealing. The observation that few reactive lysines are functional is a sober reminder that reactivity is cheap and function is not. As an E. coli preprint it is a starting point for covalent fragments, not a lead.
NanoBRET Assay Validates p53 Y220C Ligand Engagement in Living Cells
- Researchers built a live-cell NanoBRET assay to test whether reported p53 Y220C ligands truly engage the mutant protein inside intact cells.
- The BRET-based readout gives a cell-based engagement ranking for known Y220C stabilizer/reactivator compounds, complementing prior biochemical binding data.
- Such cellular validation checks permeability and intracellular target occupancy, a key hit-to-lead checkpoint for this hard-to-drug p53 cavity mutant.
Compounds that light up beautifully in DSF or ITC routinely stall out crossing a membrane into that buried, polar cavity — a cell-based BRET ranking is built to catch precisely that failure mode before a Y220C hit gets pushed into SAR. I'd still want it cross-referenced against a functional readout like p21 induction or apoptosis, and benchmarked directly against rezatapopt's (PC14586) cellular engagement window before trusting the ranking over biochemical Kd.
NanoBRET Target Engagement Enables Validation of p53 Y220C Ligands in a Cellular Context ↗
Better Linker Chemistry Lifts siRNA Antibody-Conjugate Delivery
- A new bioRxiv preprint investigates how the chemical architecture of antibody-oligonucleotide conjugates (AOCs) affects their performance as siRNA delivery vehicles.
- The work examines design variables such as linker composition, conjugation site on the antibody, and siRNA chemical modification pattern.
- Findings aim to clarify which structural choices most influence knockdown potency and delivery efficiency, informing rational AOC design.
Whether AOC chemists can transplant ADC lessons on conjugation-site control and linker stability wholesale — or oligo payloads demand their own rules — matters more than the siRNA payload itself. Locking down DAR and site-specificity is what turns AOCs into the extrahepatic answer GalNAc conjugates can't be, which is exactly why Alnylam, Avidity, and everyone else is racing to nail this chemistry first.
Enhancing the efficacy of siRNA Antibody Oligonucleotide Conjugates (AOCs) through chemical design ↗
New Selective HDAC4/HDAC7 Inhibitors Offer Chemical Probes for Th17 Biology
- HDAC4 and HDAC7 — two class IIa histone deacetylases with tissue-restricted expression — were recently identified as distinct transcriptional drivers of Th17 cell differentiation.
- Using the class IIa scaffold TMP269 as a starting point, researchers designed and synthesized a new series of HDAC4/7-targeted inhibitors.
- Structure-guided optimization of the metal-proximal and hydrophobic-binding regions yielded analogs with improved potency and greater isoform selectivity.
- Luciferase transcriptional assays, protein-binding studies, and docking analyses revealed distinct SAR patterns that separately govern selectivity for HDAC4 versus HDAC7.
- The resulting compounds offer selective chemical probes for dissecting HDAC4 and HDAC7 function in Th17 biology and a foundation for future therapies targeting Th17-driven inflammatory disease, including IBD.
Class IIa HDACs are pseudo-catalytic with shallow, promiscuous pockets — TMP269 already buys you pan-IIa selectivity over class I/IIb almost for free, so the real fight here is splitting HDAC4 from HDAC7, and that's the part I'd actually flag. Their catalytic domains are near-identical; selectivity has to come from second-shell/rim contacts in the hydrophobic channel, not the zinc-binding group, so decoupling the metal-chelating SAR from the selectivity-driving SAR (as they describe) is the right strategy and not trivial to execute. As probes, these look solid — potency plus genuine paralog discrimination is exactly what's needed to deconvolute Th17 phenotypes cleanly, though I'd want permeability/off-target data before trusting cellular calls. Going after Th17/IBD instead of the usual oncology playground is the smarter long game too: pan-HDACi toxicity is a dealbreaker for chronic dosing, and isoform-restricted engagement is the only realistic path to a tolerable chronic immunomodulator.
Chemists Engineer Isoform-Selective HDAC4/HDAC7 Probes to Dissect Th17 Inflammation
- HDAC4 and HDAC7 are class IIa histone deacetylases with limited tissue expression, making them attractive, more selective epigenetic drug targets than broadly expressed HDAC family members.
- Both enzymes help drive the transcriptional program behind Th17 cell differentiation, a pathway linked to inflammatory bowel disease and other Th17-associated inflammatory conditions.
- Chemists reworked the metal-binding and hydrophobic contact regions of TMP269, a known class IIa scaffold, to build a new series of HDAC4/7-directed analogs.
- Reporter-gene, binding, and docking studies uncovered distinct structural features that separately steer potency toward HDAC4 versus HDAC7.
- The work delivered isoform-selective, potent compounds usable as chemical probes to separately study HDAC4 and HDAC7 function, and as starting points for Th17-targeted therapeutics.
Class IIa HDACs are the pseudo-catalytic oddballs of the family — barely any intrinsic deacetylase activity, so their biology runs largely through protein contacts rather than a clean catalytic pocket, which is why generic HDAC pharmacophores rarely discriminate them well. Building off TMP269 instead of starting de novo is the pragmatic call: it's a validated class IIa binder, so tuning the metal-binding warhead plus the adjacent hydrophobic contacts is a much more tractable SAR exercise than blind discovery. Pulling HDAC4 vs HDAC7 selectivity out of that is the real win — these two are highly homologous, and clean separation is notoriously hard. Most clinical HDAC drugs are pan- or Class I-selective, so isoform-pure IIa probes are genuinely useful tool compounds for picking apart Th17 biology, well before anyone's thinking about a lead.
Photocrosslinking Probes Uncover New Nonhistone Partners of the TRIM24 Bromodomain
- TRIM24 is a dual-module epigenetic "reader" whose bromodomain binds acetylated histones and is an established cancer drug-discovery target, though its nonhistone binding partners have been poorly defined.
- Researchers installed genetically encoded photocrosslinkers, AzF and BzF, at residue L922 within the bromodomain's acetyllysine pocket, preserving histone binding while enabling UV-triggered covalent capture of interacting proteins.
- Quantitative proteomics identified the nonhistone proteins NPM1 (AzF-enriched) and CDK9 (BzF-enriched), plus candidates MAP4, RAN, and SND1.
- ChIP-seq showed TRIM24, CDK9, and NPM1 co-localize near transcription start sites of cancer-associated genes; KEGG analysis tied the hits to several signaling pathways.
- The approach shows photocrosslinking can extend reader-domain interactome mapping beyond histones, yielding new candidate leads for chemical-probe and target-discovery work on TRIM24.
"Selective bromodomain inhibitor" just got a harder definition. NPM1 and CDK9 turned up riding along at L922 — the acetyllysine pocket where any TRIM24 bromodomain probe or degrader warhead would sit — so selectivity now has to mean selective against displacing these too, not just against other BRD family members. Most bromodomain campaigns are still built structure-first off that pocket alone, chasing histone-mimetic potency; this says the pocket's biology extends past histones, so cellular phenotype from a TRIM24 chemical probe could be confounded by NPM1/CDK9 disruption rather than histone reading per se. No compound here, just a crosslinker — useful, but MAP4, RAN and SND1 are "candidates" in a proteomics list, not validated partners; I'd want co-IP/FP confirmation and dose-response competition before building any SAR narrative around them.
Bifunctional Pyridine Linker Enables Sequential, Stable Bioconjugation for ADCs and Peptides
- A programmable, bifunctional pyridine scaffold bearing a thianthrenium leaving group and a fluorine handle enables two sequential, chemoselective coupling reactions — first with alkylamines, then with cysteine thiols.
- The resulting aryl-cysteine linkage is non-chiral and stable, addressing limitations of existing bioconjugation approaches that often yield reversible linkages or stereochemical mixtures.
- Both coupling steps show high functional-group tolerance and chemoselectivity, making the chemistry compatible with complex peptides and proteins.
- The platform was applied to late-stage peptide diversification and stapling, as well as site-selective protein functionalization.
- Researchers also used the method to build an analog of the HER2-targeting antibody-drug conjugate MRG002 with a tunable drug-to-antibody ratio, reporting improved payload retention in serum relative to conventional linkage chemistry.
Maleimide-cysteine chemistry's dirty secret is retro-Michael instability — payload leaches back into circulation, and DAR isn't as fixed as the spec sheet claims. This bifunctional pyridine/thianthrenium scaffold attacks that head-on: the resulting aryl-thioether is non-chiral and hydrolytically stable, so no diastereomer mixtures and no slow linker exchange with serum thiols. Sequential chemoselectivity — amine coupling first, cysteine second, off one handle — is a real practical upgrade for installing orthogonal payloads/tags, not just another NHS-ester variant. What earns my attention is that they didn't stop at peptide-stapling demos: a tunable-DAR HER2 ADC analog of MRG002 with improved serum payload retention versus conventional linkage is the kind of proof point that actually moves a methodology from academic curiosity toward something worth piloting. Thianthrenium reagent scale-up and cost will decide if it ever displaces maleimide on a GMP line.
New Molecular Glue Degrader Targets WBP4, Debuts wTAG Degron-Tag Platform
- WBP4, a spliceosome-associated scaffold protein long considered undruggable, now has a first-in-class molecular glue degrader: dWBP4-1, which selectively eliminates it.
- The compound works through the CRBN E3 ligase, engaging WBP4 via a canonical G-loop interface to trigger rapid, highly potent degradation.
- Proteome-wide profiling showed the degrader was highly selective, with minimal off-target effects on gene expression or splicing patterns.
- The team pinpointed a compact 41-amino-acid region of WBP4 sufficient to serve as a degradation tag, naming the resulting chemical-genetic system "wTAG."
- When attached to other proteins of interest, wTAG enabled clean, dose-dependent degradation without the "hook effect" that limits many degrader tools, expanding its potential as a general research platform.
WBP4 is a spliceosome scaffold with no ligandable pocket — this isn't a kinase-with-a-degron-tail story, it's proof CRBN can be steered onto a genuinely undruggable surface via a G-loop contact. That binding hypothesis is worth stealing for other scaffold targets sitting in my own tractability triage pile. The selectivity data is the real flex: clean proteome-wide profile AND minimal splicing perturbation, exactly where glues usually get you in trouble (neosubstrate promiscuity, cryptic RBM39-style splicing hits). Getting both together is rare. wTAG might matter more than the degrader itself — a 41-residue portable degron with no hook effect is a cleaner dTAG-class tool, and I'd rather have that in my assay toolbox than another single-target lead.
ER-Targeted NIR Probe Enables High-Throughput Discovery of hCES2A Inhibitors
- PA-HDCI, a near-infrared fluorogenic probe built on the HDCI fluorophore scaffold, localizes to the endoplasmic reticulum and reports on human carboxylesterase 2A (hCES2A) activity in living cells and animals.
- The probe combines a large Stokes shift, high metabolic stability, and reliable ER targeting, enabling in situ, real-time imaging of hCES2A function across multiple biological systems.
- Using PA-HDCI in a high-throughput screening assay, the team identified compound A4, a highly potent covalent inhibitor of hCES2A.
- hCES2A is the intestinal enzyme that converts the chemotherapy drug irinotecan into its toxic active metabolite, driving irinotecan-induced intestinal toxicity (IIT).
- In tumor-bearing mouse models, A4 showed a favorable safety profile and reduced irinotecan-associated intestinal toxicity while therapeutic efficacy was maintained.
- Together, the work delivers both a new imaging tool and a validated drug-discovery platform for hCES2A-targeted therapeutics.
Solid probe engineering, not just a screening reagent: coaxing ER-selective localization and a large Stokes shift out of the HDCI scaffold gives clean signal separation in situ — photophysics that holds up in cells, not just a cuvette. The real value-add is methodological. A mechanistic imaging tool doubling as an HTS readout turns hCES2A activity into a screenable phenotype in living systems, closing the usual gap between biochemical assays and cellular reality. Target-wise, nothing novel here — hCES2A is a known off-target liability that bioactivates irinotecan into its gut-toxic metabolite, so this is a 'fix the side effect' play, not a new mechanism. A4 is an HTS-derived covalent hit with encouraging mouse data, but still needs the standard covalent-hit workup: reactivity profiling, esterase-family selectivity, and SAR.
Machine-Learning Screen of 5M Candidates Yields Light-Activated PARP1 Inhibitors
- Combined protein–ligand docking, ML force fields, quantum chemistry, and free-energy perturbation (FEP) to screen roughly 5 million hypothetical photoactive PARP1 ligands.
- Docking identified candidates with differential PARP1 binding between light-exposed and dark states; ML force fields and QM calculations predicted pKa, absorption spectra, and thermal half-lives, while graph-based surrogate models screened the remaining library.
- Excited-state nonadiabatic dynamics simulations (with ML force fields) estimated photoswitching quantum yields; FEP refined binding-affinity predictions for top hits.
- Prioritized a small set of synthetically accessible candidates combining red-shifted absorption (favoring deeper tissue penetration), therapeutically suitable thermal half-lives, and light/dark-selective PARP1 binding.
- Predictions were experimentally validated, demonstrating an end-to-end computational-to-experimental pipeline for designing light-activated (photopharmacological) cancer therapeutics.
Five million virtual candidates funneled down to a handful that actually work is the real story — that pipeline (docking → ML force fields → QM → nonadiabatic dynamics → FEP) is doing what a med chem team's SAR intuition used to do by hand, just faster and across chemical space no bench chemist would ever hand-explore. The binding-mode hypothesis is straightforward: a photoswitch appended to (presumably) a nicotinamide-mimetic PARP1 pharmacophore toggles pocket occupancy between light and dark isomers, so "selectivity" here means spatiotemporal control over tumor tissue, not isoform selectivity against PARP2/tankyrases — a different axis entirely from what olaparib or niraparib were ever optimized for. Red-shifted absorption for tissue penetration plus a therapeutically workable thermal half-life are the tractability bottlenecks that usually kill photopharmacology leads, so getting synthetically accessible hits past both, and into validated wet-lab data, is the genuinely notable part.
Computational Design and Experimental Validation of Photoactive PARP1 Inhibitors ↗
Covalent Metal-Complex Platform Maps Proteome-Wide Cysteines, Nets a PRMT1 Inhibitor
- Introduces reactive metallo-scaffolds (r-mS), a new class of covalent metal complexes bearing a chloroacetamide electrophile designed to engage ligandable cysteines across the proteome.
- Chemoproteomic profiling of a focused r-mS series in HEK293T cell lysate mapped novel cysteine engagement proteome-wide.
- Metal identity, arene substituents, and overall scaffold topography together tune cysteine reactivity and targeting selectivity.
- Lead compound r-mS-2 engages a cysteine within the functionally relevant SAM-binding domain of the methyltransferase PRMT1, confirmed by intact-protein LC-MS.
- That engagement functionally inhibits PRMT1 activity, tying a covalent hit directly to modulation of a validated target.
- Positions the platform as a generalizable route to target discovery for rational, next-generation metallodrug design.
The SAM-pocket cysteine hit on PRMT1 is the part I trust most here — that's a genuinely druggable site, and confirming occupancy by intact-protein LC-MS rather than an activity readout alone is the right bar. Where I'd slow down is selectivity: tuning reactivity through metal identity and arene substituents is a real lever, but it's one more variable than iodoacetamide/chloroacetamide fragment libraries already juggle, and a lysate screen doesn't tell me the off-target cysteine load in cells. Chemically, this is genuinely unfamiliar ground for most of us — ligand exchange, redox lability, and batch-to-batch reproducibility are liabilities organic warheads simply don't have. Against established cysteine-directed chemoproteomic platforms, r-mS adds an interesting third tuning axis, not yet a clear win. Metallodrugs as a class still carry that same tractability tax relative to organic small molecules — worth watching, not yet worth reaching for.
Photocrosslinking Probes Reveal Nonhistone Partners of the TRIM24 Bromodomain
- Genetic code expansion installed site-specific photocrosslinkers (AzF and BzF) at residue L922, within the acetyllysine-binding pocket of the TRIM24 bromodomain.
- Both crosslinker variants retained recognition of acetylated histones and crosslinked efficiently under UV, enabling interaction-based protein profiling (IBPP) in a native context.
- Quantitative proteomics of the two complementary probes gave differing capture profiles: AzF enriched for NPM1, BzF enriched for CDK9, with MAP4, RAN, and SND1 as additional candidates.
- ChIP-seq showed TRIM24, CDK9, and NPM1 co-occupying regions near transcription start sites of cancer-associated genes.
- Together the results suggest the TRIM24 bromodomain reads acetylation on nonhistone proteins as well as histones, broadening its reader function and informing chemical-probe design against this pocket.
The crosslinker sits inside the acetyllysine pocket itself, at L922 — that's not a fortuitous surface hit, it's evidence TRIM24 reads acetylated lysine on NPM1 and CDK9 through the same pocket it uses on histones, not a peripheral contact. That reframes TRIM24 as an acetyl-lysine reader with a broader substrate scope, and it means any inhibitor competing for that pocket is also competing off a nonhistone binding event, not just a histone mark. Practically, TRIM24 probe programs need NPM1/CDK9 engagement counter-screens now, and the TSS co-occupancy by ChIP-seq suggests that off-target isn't background noise but transcriptionally active. Worth flagging: this is GCE-based interactome mapping, not medicinal chemistry — no chemotype, no SAR, just a map of what a pocket-directed probe will also touch. BET programs learned this same lesson with nonhistone acetyl-lysine substrates years ago; TRIM24 is only now catching up to that complexity.
Tideglusib Identified as First Chemical Probe for NatA Acetyltransferase via Novel Covalent Mechanism
- NatA catalyzes a large share of eukaryotic Nα-acetylation, a co-translational modification important for protein stability, localization and function; no validated small-molecule NatA probe had previously been reported.
- Screening an in-house ~700-compound library and optimizing a thiadiazolidinedione scaffold identified tideglusib (YD3139) — a clinical-stage GSK-3β inhibitor — as a hit, repurposing a known drug toward NatA.
- Mechanistic studies showed tideglusib first binds NatA allosterically, after which CoA released during catalysis chemically modifies it into a reversible covalent adduct, a previously undescribed catalysis-dependent inhibition mechanism.
- The compound showed low-micromolar potency against yeast and human NatA with good selectivity over other NAT family members, and proteomics confirmed on-target activity in yeast cells, validating it as a mechanistic chemical probe.
What earns this a second look is the mechanism: an allosteric binder that stays non-covalent until the enzyme's own turnover releases CoA to staple it in place — a genuinely new trick, not just another warhead. Whether it generalizes beyond NatA's odd CoA-release chemistry is unclear, but it's worth filing away as a template for other CoA- or cofactor-dependent enzymes. The selectivity over other NATs despite a conserved active site is the more actionable lesson: skip the catalytic pocket, go allosteric, and you dodge the conservation problem for free. As probe discovery, repurposing tideglusib beats de novo synthesis for speed, but it also means every existing GSK-3β dataset on this molecule is now confounded — nobody should read across to NatA biology from tideglusib phenotypes without new chemical matter. NatA itself looks like a legitimate, underexplored target; this is a probe paper, not a drug paper, but it's the right first step.
Direct-to-Biology Approach Delivers a Selective GRP78 Inhibitor Probe
- GRP78 (BiP/HSPA5) is a chaperone in the highly conserved HSP70 family, making isoform-selective inhibitors difficult to design.
- Using a Direct-to-Biology (D2B) strategy — synthesizing and screening compounds without intermediate purification — researchers identified compound 12 as a selective GRP78 inhibitor.
- Compound 12 binds the peptide-binding pocket in GRP78's substrate-binding domain and is selective for GRP78 over other tested HSP70 isoforms.
- It potently and selectively kills A549 lung cancer cells while showing minimal activity in other tested lung cancer cell lines.
- Cellular thermal shift assay (CETSA) confirmed cellular target engagement, and compound 12 modulates GRP78-linked unfolded protein response (UPR) stress signaling.
- The authors present compound 12 as a chemical probe for studying GRP78 biology and a starting point for GRP78-targeted therapeutics.
Substrate-binding domain, not the ATPase pocket — that's the harder but more selective play, since most HSP70-family programs chase the nucleotide site and inherit its cross-reactivity problem. Getting selectivity for GRP78 over other HSP70 isoforms out of a peptide-binding groove is a real medicinal chemistry win; those pockets are shallow and promiscuous by design. What I'd want to see next: the SAR trail from D2B — crude-plate hits jumping straight to CETSA-confirmed engagement is fast, but I'd want a clean resynthesis and dose-response before trusting potency off unpurified reactions. Still, as a probe-grade starting point with A549-selective killing, compound 12 is a legitimate template for follow-on optimization, not another ATPase-site me-too.
Development of Isoform-Selective GRP78 Inhibitors from a Direct-to-Biology Strategy ↗
New Conjugate Chemistry Releases Payload on Target Binding, Bypassing Endocytosis
- Researchers introduce a binding-to-release (BTR) strategy that triggers drug-conjugate payload release directly upon target binding, rather than requiring receptor-mediated endocytosis.
- The approach uses a new bioconjugation reaction, phosphorus(V)-phenol exchange (PhoPEx) — inspired by SuFEx click chemistry — engineered so that chemistry within the binding pocket itself cleaves the drug free once the conjugate engages its target.
- Because only a minority of drug targets support efficient endocytosis, this binding-triggered release could extend conjugate-based therapies to otherwise poorly internalizing targets.
- The authors describe proof-of-concept work with a conjugate targeting fibroblast activation protein (FAP), evaluated from in vitro settings through patient-derived tissue specimens.
The clever bit is topological: you need a nucleophilic residue (Ser/Tyr/Lys) sitting close enough to the P(V) center once the conjugate is bound, so this only works when pocket geometry cooperates — not a universal fix, more a case-by-case design problem per target. SuFEx proved robust and bioorthogonal enough to become a real click-chemistry platform; whether PhoPEx's release kinetics and selectivity hold up outside FAP is the real open question — proof-of-concept in patient tissue is promising but still one target. What I like: it decouples release from endocytosis and lysosomal processing entirely, which is the actual bottleneck for most ADC-style approaches against non-internalizing or slowly-trafficking surface receptors (GPCRs, some ion channels, stromal markers like FAP itself). If the chemistry generalizes, it's a genuine expansion of addressable target space for conjugates, not just a linker tweak.
A binding-to-release strategy for targeted anticancer drug delivery ↗