SAR & lead optimization
70 articles
Direct-to-Biology Screening Yields a GRP78 Inhibitor That Spares Other HSP70 Isoforms
- Isoform selectivity within the highly conserved HSP70 family is notoriously hard; the team targeted the peptide-binding pocket of GRP78's substrate-binding domain.
- A direct-to-biology workflow, testing crude library reactions without purification, pointed to compound 12.
- It engages GRP78 in biochemical, biophysical and cellular thermal shift assays, is selective over other tested HSP70s, and perturbs unfolded protein response signaling with selective killing of A549 cells.
Going after the substrate pocket rather than the ATP site is the sensible way to buy HSP70 selectivity, and D2B makes iterating on it cheap. The cell-line-selective killing is the part I'd treat cautiously: it could reflect UPR dependence or something off-target. Orthogonal engagement data like CETSA are encouraging; I'd want a close inactive analog next.
Development of Isoform-Selective GRP78 Inhibitors from a Direct-to-Biology Strategy ↗
DT-9081: Scaffold Hopping Delivers an Oral EP4 Antagonist That Has Cleared Phase I
- EP4 blockade is an immuno-oncology idea built on PGE2-driven immune suppression in tumors.
- Scaffold hopping gave a new chemical series with better activity and pharmacokinetics, and SAR work led to DT-9081.
- It combines potent antagonism, favorable ADME and a clean preclinical safety profile, and has completed a phase I monotherapy trial in solid cancers.
This paper is the full med-chem story behind a compound that already has human data, which is rarer and more useful than most 'discovery of' papers. EP4 is crowded, so the interesting part is how the new series differentiates on PK and safety against earlier antagonists. I'd read it for the scaffold-hop logic and watch whether phase I translates into combination activity with checkpoint blockade.
Aryl Sulfamates Get a Systematic SAR Look as Carbonic Anhydrase IX Binders
- Ortho- and meta-substituted aryl sulfamates were synthesized and profiled by thermal shift, enzyme inhibition and a live-cell competition assay against CA IX, the isozyme overexpressed in hypoxic solid tumors.
- The best compounds bound CA IX with very high affinity, and X-ray structures with several isozymes identified the groups driving affinity and selectivity.
- pH-dependent binding data indicate the deprotonated, negatively charged sulfamate nitrogen coordinates the active-site zinc.
CA inhibitors are dominated by sulfonamides, so a clean sulfamate SAR backed by crystal structures is useful chemotype diversification. Selectivity over the ubiquitous CA I and II is what sinks tumor-CA programs, and the co-crystals give a concrete handle on it. Live-cell competition data beat purely recombinant assays, but I'd want hypoxic-cell potency and physicochemical properties before calling these lead-like.
Structure-Affinity and Selectivity of Aryl-Sulfamates as Inhibitors of Carbonic Anhydrase IX ↗
Structure-Guided RXFP4 Agonists Stay in the Gut and Ease Constipation in Mice
- Guided by the cryo-EM structure of RXFP4, the authors built a tetrahydroisoquinoline agonist series aimed at two hurdles: close homology to RXFP3 and the need for gut-restricted exposure.
- Lead compound 44 was a potent agonist with strong selectivity over RXFP3 and a pharmacokinetic profile heavily skewed toward ileum over plasma.
- Oral dosing was effective in a loperamide-induced constipation mouse model.
Getting a small molecule onto a peptide-GPCR whose paralog looks nearly identical is the hard part, and using the cryo-EM structure to buy RXFP3 selectivity is the right play. The gut-over-plasma skew is what I'd look at first, since a locally acting agonist sidesteps systemic liabilities. I'd still want permeability, efflux and metabolic stability data behind that ileum exposure.
Reworking the DHIle Residue of α-Amanitin Yields Picomolar Trastuzumab–Amatoxin ADCs
- The team probed the δ-position of the 4,5-dihydroxyisoleucine residue in α-amanitin, a residue long assumed to drive RNA polymerase II inhibition.
- Two δ-modified analogs carry handles for direct linker attachment, so conjugation no longer has to go through other positions on the bicyclic peptide.
- Both were converted into trastuzumab conjugates that showed extremely high cytotoxicity on target-expressing cells, supporting these amatoxins as ADC payloads.
This is the kind of payload SAR I want more of. Amanitin's DHIle has been treated as untouchable, so finding a δ-position that tolerates substitution and doubles as a conjugation handle opens a cleaner attachment strategy than the usual lysine or Asn shuffles. I'd want to see plasma stability and bystander behaviour next, since transcription-arrest payloads live or die on therapeutic index.
Neutral, CSF-Penetrant TTR Stabilizers Designed with Heterocyclic Linkers
- A new series of neutral, heterocyclic-linker-containing transthyretin (TTR) stabilizers is designed for improved brain and cerebrospinal fluid (CSF) penetration.
- Aims to address CNS/leptomeningeal manifestations of hereditary ATTR amyloidosis, where existing acidic stabilizers such as tafamidis show limited CNS exposure.
- Heterocyclic linker modifications reduced compound acidity relative to earlier chemotypes while reportedly preserving TTR tetramer-stabilizing potency and selectivity in vitro.
Finally—someone attacking the acidic-pharmacophore/P-gp efflux tradeoff head-on instead of just tolerating tafamidis's CNS blind spot. Ditching the carboxylic acid for heterocyclic linkers while holding onto tetramer-stabilizing potency is the hard part of this SAR, not the easy part. If CSF exposure holds up in vivo, leptomeningeal ATTR patients finally get a real option instead of an afterthought.
Fluorinated Isoxazolidinone Scaffold Delivers Apoptosis-Inducing Antiproliferative Leads
- A new series of fluorinated 4-methylideneisoxazolidin-5-one derivatives adds fluorine substituents onto the exocyclic methylidene-lactone-type isoxazolidinone core.
- The fluorinated analogs showed antiproliferative activity against cancer cell lines, with the reported cell-death mechanism attributed to induction of apoptosis.
- Structure-activity comparisons across the fluorinated series highlighted substitution patterns linked to improved potency and selectivity relative to non-fluorinated parent compounds.
An exocyclic methylidene lactone is a classic Michael acceptor shape — before crediting fluorination for the potency gain, I'd rule out plain thiol-reactive cytotoxicity masquerading as 'apoptosis.' Fluorination itself is a cheap, tractable SAR handle for potency/metabolic stability, but with no confirmed target, this stays a phenotypic hit until a pulldown or competition assay lands the binding site.
Imidazolium Amino Acids Proposed as Bioisosteres for Methylated Lysine and Arginine Residues
- Imidazolium amino acids are proposed as cationic bioisosteres mimicking the size and charge of trimethyllysine, dimethylarginine, and arginine side chains.
- Binding to methyl-lysine reader domains is evaluated to see how closely the surrogates reproduce native residue recognition and selectivity.
- Cell assays indicate the charged isosteres can still traverse membranes, and SAR trends tie ring substitution to the affinity-permeability tradeoff for reader ligands and CPPs.
A non-hydrolyzable Kme3/Rme2 mimic solves a genuine headache—native methylated peptides get erased by demethylases or clipped by proteases mid-assay, muddying SAR. If ring substitution tunes affinity without killing permeability, this is a genuine alternative scaffold for reader-domain PPI inhibitors and arginine-free CPPs, not just another quaternary-ammonium curiosity—worth testing against our own Kme3 reader panel.
New Dual-Acting Molecules Pair PARP Inhibition with Ferroptosis to Fight TNBC
- Medicinal chemists designed single small molecules combining PARP inhibition with GPX4 inhibition, pairing DNA-repair blockade with ferroptosis induction in one compound rather than as a drug combination.
- Structure-activity relationship work identified a new dual-acting chemotype optimized for potency against both targets.
- Lead compounds showed antitumor activity in triple-negative breast cancer models, supporting the dual-mechanism approach as a possible way to broaden PARP inhibitor efficacy.
Most TNBC is BRCA-wild-type, so PARP monotherapy has nowhere to go without synthetic lethality — pairing it with GPX4 inhibition to force ferroptosis is a real way around that, not just an add-on. The tougher ask is holding potency at two unrelated targets in one scaffold without MW/logP creeping past drug-like — if they pulled that off cleanly, it's more interesting than the biology.
Discovery of Dual PARP/GPX4 Inhibitors for the Treatment of Triple-Negative Breast Cancer ↗
Aminopyrazole Lead Optimization Yields Selective PLK4 Inhibitor EXEL-1855
- Exelixis researchers optimized an aminopyrazole hit series targeting PLK4, a kinase essential for centriole duplication, culminating in the advanced compound EXEL-1855.
- Structure-guided SAR and selectivity profiling addressed off-target kinase liabilities that had limited earlier aminopyrazole PLK4 inhibitors such as centrinone.
- In preclinical tumor models, EXEL-1855 showed strong antitumor activity, supporting its selection as a development candidate.
Selectivity was always the aminopyrazole scaffold's weak spot — centrinone's off-target kinase hits (PLK1/2/3, Aurora) made it a great chemical probe but a poor drug candidate. Getting EXEL-1855 to "development candidate" with a clean kinome profile is the real milestone here, not the potency number. PLK4's centrosome-duplication mechanism is also refreshingly uncrowded real estate next to the CDK/Aurora pileup.
Rule-Based SMILES Editing Tool Aids Fragment-to-Lead Optimization
- A new method systematically edits SMILES strings—swapping atom types, resizing or opening rings, and grafting fragments—to generate analog ideas for fragment-to-lead optimization.
- First implemented as a KNIME workflow tested on fragments from multiple programs, it's now also available as open-source Python code paired with AutoDock Vina docking.
- This non-learned, rule-based approach complements AI/ML generative design, offering a practical option when training data for a target is scarce.
Honestly this is what I'd do by hand anyway—ring contraction, bioisostere swaps, fragment grafting—just automated and exhaustive instead of me sketching ten ideas on a whiteboard. For a scarce-data fragment series, I'd trust this over a generative model I can't sanity-check. Free KNIME/Python beats begging IT for another SaaS license too.
Fragment Optimization─Simple SMILES String Manipulation Strategies to Optimize a Hit or Fragment ↗
Imidazole Scaffold Swap Delivers Selective, Oral CDK2 Inhibitor INCB127443
- An earlier pyrazole-based CDK2 inhibitor scaffold was computationally redesigned around an imidazole core to improve selectivity over CDK1.
- The new chemotype was optimized simultaneously for potency, CDK1/CDK2 selectivity, and physicochemical properties.
- This work yielded INCB127443, an orally bioavailable candidate with favorable CDK1 selectivity and a flat pharmacokinetic profile enabling sustained in vivo target coverage.
Swapping pyrazole for imidazole to fix CDK1 selectivity is a single-atom-position bet—when it works, it usually means the selectivity handle is a subtle H-bond vector difference in the near-identical ATP pockets, not a size mismatch, which is the harder kind to exploit on purpose. Imidazole is cheap, well-trodden SAR territory, and the flat PK is the real prize for sustained target coverage.
Discovery of INCB127443: A Potent and Orally Available Inhibitor of Cyclin-Dependent Kinase 2 ↗
Chemists Report New Allosteric SHP2 Inhibitors Built on an Azaindole Scaffold
- SHP2 is a cytosolic protein tyrosine phosphatase implicated in oncogenic RTK and immune checkpoint signaling, making it a closely watched cancer/immuno-oncology target.
- Earlier allosteric SHP2 inhibitors have reached clinical trials but can face resistance mutations or PK limitations, motivating further chemotype exploration.
- This preprint reports a new series of N-aryl-1H-azaindole-derived allosteric SHP2 inhibitors, shifting away from orthosteric (active-site) inhibition approaches.
That shallow, conserved catalytic pocket is exactly why orthosteric SHP2 programs never went anywhere in my hands—no surprise this moves allosteric. But the irony's real: clinical allosteric inhibitors like TNO155 already picked up resistance mutations right in that allosteric tunnel, so a new chemotype needs to show it escapes those hotspots, not just re-occupy the same pocket with a different scaffold.
TrmD as an Antibacterial Target: A Review of Small-Molecule Inhibitor Discovery Strategies
- TrmD, a SPOUT-family bacterial tRNA methyltransferase without a human counterpart, is highlighted as a validated antibacterial target amid rising antimicrobial resistance.
- The review catalogs strategies used to discover small-molecule TrmD inhibitors—fragment-based design, high-throughput and virtual screening, click-chemistry-enabled direct-to-biology methods, molecular hybridization, and prodrug approaches.
- It synthesizes structural features and structure-activity relationships across these diverse chemical scaffolds to inform future inhibitor optimization.
TrmD's lack of a human ortholog is the real selling point here — a wide therapeutic window without the usual off-target liability, which is rare enough in antibacterial discovery to justify the review's existence. The click-chemistry/direct-to-biology entries jump out as the underexploited lane: fast SAR turnaround without carrying every analog through full synthesis, exactly what a fragmented, scaffold-diverse target like this needs before someone finally nails spectrum and PK.
TrmD: A Promising Antibacterial Target and Its Small-Molecule Inhibitors ↗
Next-Gen AOH1996 Analogs Sharpen the Attack on Cancer's PCNA Isoform
- Second-generation analogs of the first-in-class caPCNA-selective inhibitor AOH1996, built by systematically modifying each of its four pharmacophoric regions.
- Explored substituent changes, bioisosteric swaps, linker adjustments, and scaffold hopping to improve on the parent compound.
- Lead analogs showed markedly improved cancer cell potency and better liver microsomal metabolic stability than AOH1996.
- Compounds were profiled across multiple cancer cell lines, including neuroblastoma and breast/colorectal cancer models.
Four pharmacophoric regions systematically walked — substituents, bioisosteres, linkers, and a scaffold hop — is a proper second-generation SAR campaign, not a token tweak. Pairing better cancer-cell potency with improved microsomal stability is what actually matters for a caPCNA-interaction disruptor, since these shallow, protein-interface-driven pockets are usually the first thing to fall apart metabolically.
Second-Generation AOH1996 Analogues with Enhanced Pharmacological Properties for Targeting PCNA ↗
Novel Dihydropyridine Series Delivers Potent Caspase-1 Antagonists
- A new series of dihydropyridine-derived small molecules is reported as antagonists of caspase-1, a cysteine protease central to inflammasome signaling.
- Caspase-1 activation drives maturation of the pro-inflammatory cytokines IL-1β and IL-18, making it a longstanding target in inflammation and inflammasome-related disease research.
- The dihydropyridine scaffold, more commonly associated with calcium-channel pharmacology, is explored here as a chemotype for caspase-1 antagonism.
- Compound activity was characterized using in vitro fluorescence-based enzymatic assays to gauge caspase-1 antagonism.
- Cell imaging was used alongside the biochemical assays to examine compound behavior and target engagement in a cellular context.
- The study, published in ChemMedChem, presents this dihydropyridine series as a structure-activity starting point for further caspase-1/inflammasome-directed medicinal chemistry.
First reaction: that's a nifedipine scaffold sitting in a caspase-1 SAR table. Bold, slightly nervy move — DHPs are about as pharmacologically 'loaded' as chemotypes get, so before getting excited about any hit here I'd want an L-type calcium-channel counter-screen and a broader Cav/hERG panel run immediately; that vasodilatory liability doesn't vanish just because you've redirected the scaffold at a protease. Caspase-1 itself is a reasonable target — druggable active-site cysteine, real precedent from peptidomimetic inhibitors — but selectivity across the caspase family, not potency, is the real hurdle here. The fluorescence assay plus cell imaging is the right combo methodologically: biochemical IC50s alone can't distinguish real antagonism from aggregation, chelation, or off-target channel hits, so imaging buys an early cellular engagement check before committing to a full selectivity panel.
Second-Generation AOH1996 Analogues Show Improved Potency Against Cancer-Associated PCNA
- PCNA supports at least 11 cellular pathways in DNA replication and repair; tumor cells express a distinct acidic isoform (caPCNA) not found in normal cells, creating a potential cancer-selective drug target.
- AOH1996 is City of Hope's first-in-class small-molecule PCNA inhibitor, which binds the PIP-box pocket to disrupt caPCNA protein interactions and selectively kill malignant cells.
- This paper describes second-generation AOH1996 analogues built through systematic structure-activity relationship work (substituent changes, bioisosteric replacement, linker and heteroatom modification, scaffold hopping) across all four pharmacophore regions.
- Lead analogues showed improved cellular potency against multiple cancer cell lines and better liver microsomal stability than first-generation AOH1996, supporting further lead optimization of this PCNA-targeted chemotype.
- The real headline isn't the potency bump — it's that the PIP-box pocket, a shallow PPI interface people wrote off as undruggable, actually supports systematic SAR across four independent pharmacophore regions. That's a proper chemotype, not a lucky HTS hit. - Getting better cellular potency AND better microsomal stability out of substituent/bioisostere/linker/scaffold-hop work is the signal I want at this stage — potency alone would leave me wondering if you'd just traded one metabolic liability for another. - "Selective for caPCNA" is a claim I'll hold loosely until I see a real therapeutic index — normal-cell counterscreens and in vivo tox, not just cancer-line IC50s. The acidic-isoform story is attractive but easy to oversell. - Still, beating first-gen AOH1996 on both axes is the right trajectory for a second-gen PPI series.
Second-Generation AOH1996 Analogues with Enhanced Pharmacological Properties for Targeting PCNA ↗
AI-Driven Lead Optimization Delivers 11B-6, a More Potent HBV Capsid Modulator
- Investigators describe a multi-objective lead-optimization campaign built on the sulfamoylbenzamide (SBA) chemotype exemplified by NVR 3-778, an earlier clinical-stage HBV capsid assembly modulator (CAM).
- An AI-guided computational workflow was integrated with iterative synthesis to simultaneously optimize antiviral potency alongside physicochemical and ADME/drug-like properties across the series.
- The campaign identified 11B-6 as the optimized lead, reported to combine stronger anti-HBV potency with improved drug-like characteristics relative to earlier series analogues.
- Mechanistically, 11B-6 functions as a capsid assembly modulator, engaging the HBV core (capsid) protein to misdirect nucleocapsid assembly and interfere with viral replication.
- The work positions 11B-6 as a candidate for further preclinical evaluation within the sulfamoylbenzamide CAM class for chronic hepatitis B treatment.
What actually catches my eye isn't the potency bump — it's that AI-guided optimization was wired into the synthesis loop, not run as a pre-filter before chemists took over. That's the difference between a screening deck and a real DMTA cycle. Going back to the SBA/NVR 3-778 chemotype rather than hunting a new capsid-binding scaffold is the pragmatic call: the pocket and assembly-misdirection mechanism are already de-risked clinically, so this campaign is buying SAR knowledge instead of paying discovery tax twice. That said, 'improved drug-like properties' is a claim I want backed by real microsomal stability, plasma protein binding, and hERG numbers before I get excited — potency plus a nicer cLogP on paper doesn't guarantee 11B-6 clears whatever tolerability hurdle likely sank NVR 3-778. Worth watching, not yet worth celebrating.
Dual-Acting M3/H1 Antagonists Designed for Long-Lasting Rhinitis Relief
- Rhinitis is a heterogeneous upper-airway inflammatory condition whose chronic symptoms, especially in mixed and nonallergic disease, often resist first-line intranasal antihistamines and corticosteroids.
- The authors designed bifunctional small molecules combining muscarinic M3 antagonism, which limits glandular hypersecretion and rhinorrhea, with histamine H1 antagonism, which limits itch, sneezing and vasodilation.
- A structure-activity relationship campaign balanced potency at both receptors within a single scaffold while extending duration of action, targeting once-daily control rather than short-acting relief.
- Lead compounds were profiled for pharmacokinetics, receptor selectivity and safety, distinguishing this dual-target strategy from conventional single-mechanism antihistamines or anticholinergics.
- This positions combined M3/H1 antagonism as a candidate approach for rhinitis, including mixed and nonallergic forms, poorly controlled by existing monotherapies.
Single scaffold, two GPCR pharmacophores, no PK penalty — that's the hard part, not the target rationale. Anyone who's tried to graft an M3 antagonist pharmacophore onto an H1 chemotype knows the tightrope: push affinity at one receptor and you drag the other's SAR along for the ride, or worse, the two optimize in opposite directions on logP/basicity. If they actually held balanced dual potency while stretching half-life toward once-daily dosing, that's real design work, not a screening accident. Target rationale is the more interesting sell, though — mixed/nonallergic rhinitis genuinely doesn't respond well to a single mechanism, so this isn't a me-too antihistamine with a longer half-life. Show me the selectivity margins before I get excited: M3 hits M2/M1 too easily, and dry mouth/blurred vision/urinary retention kill programs late. Therapeutic window on the anticholinergic side is the whole ballgame here.
Dual PARP-1/CK2α Inhibitors Aim Beyond HRD-Restricted Tumors
- Researchers designed a new class of small molecules built on a benzothieno[3,2-d]pyrimidin-4(1H)-one scaffold that simultaneously inhibits PARP-1 and casein kinase 2 alpha (CK2α).
- PARP-1 inhibitors typically benefit only tumors with homologous recombination deficiency (HRD); pairing PARP-1 blockade with CK2α inhibition, a kinase linked to DNA damage response and cell survival signaling, is proposed to extend efficacy to HRD-proficient tumors and limit metastatic spread.
- Structure-activity relationship exploration identified substituents on the tricyclic core that support potent, balanced binding at both targets.
- In cellular and tumor models, the dual inhibitors reportedly show antiproliferative and anti-metastatic activity independent of HRD status, supporting dual-target inhibition as a route beyond BRCA-mutant-restricted use.
Holding balanced dual-target SAR on one scaffold is the real difficulty here, not the headline claim — PARP-1's nicotinamide pocket and CK2α's ATP site are shaped nothing alike, so a substituent you add to hold potency at one target can quietly tank the other. I'd want the full SAR table, not just the lead actives, before believing that balance survives further optimization. The real payoff isn't PARP-1 potency itself, it's escaping the BRCA/HRD ceiling — another single-target PARP inhibitor chasing olaparib's lane is a hard sell, but HRD-independent activity actually opens new patient populations. The tricyclic benzothienopyrimidinone core gives usable vectors for dual substitution, though fusing two pharmacophores tends to inflate MW and logP fast. Next data I need: kinome-wide selectivity beyond CK2α, in vivo therapeutic window, and whether the anti-metastatic signal holds up against a PARP-1-only comparator.
New Benzimidazole-Tetrahydrofuran Series Delivers Potent, Selective NaV1.8 Inhibitor Lead for Pain
- NaV1.8 inhibition is a clinically validated non-opioid strategy for pain, with the marketed drug VX-548 (Journavx) serving as the benchmark; its metabolic pathways in humans and rats are well characterized.
- Researchers designed a new chemotype, 2-(2-benzimidazole)-substituted tetrahydrofurans, and applied structure-based optimization to circumvent VX-548's known metabolic liabilities while retaining nanomolar NaV1.8 potency and subtype selectivity.
- The resulting lead, compound 31, showed favorable oral bioavailability in rats, with plasma AUC more than 10-fold higher than VX-548, alongside potent in vivo analgesic efficacy.
- Pharmacokinetic behavior was consistent across species, with favorable profiles also seen in beagle dogs and cynomolgus monkeys.
- Compound 31 exhibited a favorable early safety profile, including no genotoxicity and weak hERG inhibition, supporting its status as a metabolically optimized preclinical lead for further evaluation.
Call this a metabolism play more than a new-target story. With VX-548's clearance liabilities already mapped in human and rat, swapping to a 2-benzimidazole-tetrahydrofuran scaffold reads as targeted scaffold-hopping around known soft spots rather than blind SAR exploration. That's the efficient way to run a fast-follower program: let the first approved drug's ADME data write your design brief. A >10x jump in rat AUC is the number that matters here — that's the difference between a compound needing frequent dosing with exposure gaps and one you can actually push into efficacy studies with margin. Clean hERG and no genotox flags this early derisks the biggest attrition risks before you've spent tox budget. The THF-benzimidazole core isn't exotic chemistry, nothing hard to scale — this looks like a real backup/second-gen candidate, not just a paper compound.
Wild-Type-Sparing PI3Kα H1047R Inhibitors Identified from Quinazolinone Series
- Approved PI3Kα inhibitors for HR+/HER2− PIK3CA-mutated breast cancer cause dose-limiting hyperglycemia and other adverse effects linked to inhibition of wild-type PI3Kα.
- Researchers designed a series of tetrasubstituted quinazolin-4(3H)-one compounds intended to selectively inhibit the oncogenic PI3Kα H1047R mutant.
- Selectivity for the mutant enzyme over wild-type PI3Kα is proposed to stem from a slow-on, slow-off binding mechanism.
- Lead compound 34 showed potent, mutant-selective activity in vitro along with a favorable ADME profile.
- In a T47D xenograft mouse model, compound 34 produced significant tumor growth inhibition without affecting blood glucose or serum insulin levels, unlike a benchmark approved PI3Kα inhibitor.
- The authors note that further optimization of compound 34 is needed to lower the efficacious dose and improve tolerability.
Alpelisib's hyperglycemia problem is the elephant in every PI3Kα SAR discussion — it's the reason dose reductions dog that drug in clinic, tracing straight back to wild-type inhibition in normal insulin signaling. A slow-on, slow-off kinetic selectivity mechanism here is more interesting than a static pocket-shape argument: if H1047R's altered conformational dynamics let this quinazolinone linger on mutant enzyme while it washes out of WT, that's a residence-time story I'd want kinITC and washout kinetics to confirm before fully believing. Tetrasubstituted quinazolinones aren't an exotic scaffold to make, which helps for a program needing heavy analoging around that pocket. Clean xenograft efficacy without glucose/insulin perturbation is the proof-of-concept that matters — but the authors' own admission that compound 34 needs a lower efficacious dose and better tolerability is the real tell: promising probe, not yet a candidate.
Novel Plant Metabolites Show Isoform-Selective Inhibition of Cav3.1 Calcium Channels
- Five new natural products, hyreptaones A-E (1-5), were isolated from the plant Hypericum reptans, defining a novel class of 1,2-seco-bicyclic polyprenylated acylphloroglucinols (BPAPs).
- Compounds 1-3 are the first 1,2-seco-BPAPs shown to derive from rare 3,3-diisoprenylated BPAP precursors, while 4 and 5 feature an unusual spirocyclic 6/5/5 ring system formed by further cyclization of the 1,2-seco-BPAP core.
- Structures were established using spectroscopic analysis together with X-ray crystallography.
- All five compounds preferentially inhibited the Cav3.1 T-type calcium channel over other T-type channel subtypes, indicating isoform selectivity.
- Compounds 4 and 5 additionally showed state-dependent modulation of Cav3.1 gating, marking them as a new class of Cav3.1 allosteric modulators.
Isoform selectivity within the T-type family (Cav3.1 vs 3.2/3.3) is exactly what's been missing from this space — most T-type blockers I've seen are promiscuous pore-blockers with narrow therapeutic windows, so five compounds hitting Cav3.1 preferentially is worth a second look. The state-dependent gating modulation in 4/5 is the more interesting story mechanistically: allosteric, conformation-selective action tends to buy better selectivity and fewer off-target liabilities than brute-force channel block. That said, I'm skeptical this scaffold is a med-chem starting point rather than a probe — a spirocyclic 6/5/5 BPAP that needed X-ray to nail down stereochemistry screams synthetic bottleneck, and five compounds isolated from one plant is not a supply chain, it's a bottleneck waiting to happen. I'd want SAR against simplified, truncated analogs before believing this is optimizable rather than just interesting.
Structural Survey Reveals How Kinase Inhibitors Engage Conserved Catalytic Residues
- More than 300 X-ray cocrystal structures spanning diverse kinase-inhibitor complexes were analyzed to catalog recurring non-covalent contact patterns.
- The study highlights a set of conserved Lys, Asp, and Glu residues near the ATP pocket, dubbed "Catalytic Cluster Residues" (CCRs), that support catalysis and frequently contact bound inhibitors.
- Across most inhibitor chemotypes, these polar residues form non-covalent interactions rather than covalent bonds, making them broadly relevant handles for ligand design.
- Side-chain orientation of the CCRs tracks with the kinase's active or inactive conformational state, linking binding geometry to structural dynamics.
- The authors argue this conformation-coupled behavior can guide rational, structure-based inhibitor design aimed at improving potency and tuning selectivity across the kinome.
"Catalytic Cluster Residues" is new branding for something most kinase chemists already lean on informally — the Lys-Glu ion pair, DFG-Asp contacts. The real value here is systematizing it: 300+ structures gives a statistical backbone for deciding when to actually chase these polar contacts instead of hinge binding or a back-pocket selectivity vector. If CCR geometry really tracks active/inactive state, that's a usable lever — bias type-I vs type-II engagement via salt bridges and H-bonds instead of reaching for a covalent warhead, attractive when cysteine liabilities or covalent reversibility are a concern. I'm skeptical the conformational-coupling claim generalizes cleanly across the kinome, though — 300 structures sounds like a lot until you split it by subfamily, and PDB deposition bias means scaffolds like EGFR, ABL, and CDKs are almost certainly overrepresented relative to understudied kinases.
A Structural Perspective on Non-covalent Targeting of Conserved Polar Residues in Protein Kinases ↗
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.
New "Scope" Chemical Space Yields Ligand-Efficient Hits Across Three Targets
- "Scope" describes a mid-sized (10k-50k compound) chemical space positioned between minimal fragments and fully elaborated low-molecular-weight libraries, designed to maximize ligand efficiency and medicinal chemistry tractability.
- The authors introduce "Scope ring systems" (ring-X-ring) as a core organizing concept for building libraries and guiding functionalization toward sufficient potency.
- A 10k-compound Scope screening set — evaluated by SPR, native mass spectrometry, DSF, and biochemical assays — matches general diversity sets' primary hit rates even at higher screening concentrations, while showing superior ligand efficiency and higher hit rates after counter-screening.
- Case studies on trypanosomal CLK1 kinase, a 14-3-3/estrogen receptor-alpha molecular glue project, and SARS-CoV-2 main protease show the set yields diverse, tractable, ligand-efficient hits across varied binding sites.
The "sweet spot between fragments and full libraries" pitch isn't new — DEL, FBDD, and house libraries have all claimed it before. What's actually new in Scope is the ring-X-ring organizing logic: forcing vectors off two ring systems rather than one flat scaffold gives a built-in growth vector for SAR from hit one, the part fragment campaigns usually bolt on later. The number that matters to me isn't the hit rate, it's "higher hit rate after counter-screening" — that's fewer SPR artifacts and aggregators wasting my week. The real test is the 14-3-3/ERα glue case: PPI/glue targets chew up conventional libraries because there's no deep pocket to reward LE. If a rigid, moderately-sized scaffold set can seed a glue hit, that's the transferability claim worth watching, not the Mpro or CLK1 wins.
Flavonoid Scaffold Redesigned via Bioisosteric Replacement to Target Aromatase in ER+ Breast Cancer
- Aromatase (CYP19A1) catalyzes the final step converting androgens to estrogens, and its activity drives tumor proliferation in estrogen receptor-positive (ER+) breast cancer, making it a long-validated target for hormonal therapy.
- Existing steroidal and nonsteroidal aromatase inhibitors (AIs) are effective as first-line treatments but face limitations from acquired resistance and off-target/tolerability issues, motivating a search for new chemical starting points.
- Researchers applied bioisosteric replacement strategies to a flavonoid-derived scaffold, a plant-derived chemotype structurally distinct from current AI drug classes, to generate a series of novel candidate inhibitors.
- The substitutions were assessed computationally for how they might alter predicted binding within the CYP19A1 active site, alongside their effects on physicochemical and ADME-relevant properties.
- The overall goal is a lead series that suppresses estradiol biosynthesis while addressing some of the structural liabilities associated with existing AI chemotypes.
A flavonoid core is a bold starting point — it's structurally miles from the triazole-based nonsteroidal AIs (letrozole, anastrozole) and steroidal exemestane, but that novelty cuts both ways. First question: what's actually coordinating the heme iron? Nonsteroidal AIs work because that triazole/imidazole nitrogen chelates Fe3+ — if the bioisosteric swaps didn't install an equivalent, the "improved binding" predictions may be modeling the wrong interaction entirely. Second, flavonoids are notorious for glucuronidation, poor solubility, and promiscuous CYP inhibition (isoform selectivity is the whole AI liability story, not just CYP19A1 potency) — bioisosteric replacement can just relocate those ADME problems rather than fix them. And this is docking/property prediction only; no IC50s, no CYP19A1/CYP3A4 selectivity ratios, no cell data. Promising scaffold idea, but until there's a measured Ki, I'm filing this under "watch, don't chase."
Large-Scale Virtual Screen Delivers Potent New TAAR1 Agonists for Schizophrenia
- TAAR1 is a G protein-coupled receptor pursued as a non-dopaminergic drug target for schizophrenia and antipsychotic therapy.
- A structure-based virtual screen docked about 65 million candidate molecules against an active-state model of TAAR1.
- Of 55 top-ranked hits tested experimentally, 14 showed genuine TAAR1 agonist activity, ranging from mid-nanomolar to micromolar potency.
- Hit optimization then yielded agonists with nanomolar potency, and cryo-EM structures confirmed the binding poses the docking had predicted.
- Three optimized agonists showed high brain exposure and potency described as exceeding that of ulotaront, a clinical-stage TAAR1 antipsychotic candidate.
- In mice, all three normalized amphetamine-induced disruption of pre-pulse inhibition, a schizophrenia-relevant behavioral measure, without causing catalepsy, a common antipsychotic side effect.
A 25% experimental hit rate (14/55) out of 65 million docked molecules is the number that jumps out — that's an unusually clean confirmation rate for an active-state GPCR model, and it's real validation for structure-based virtual screening on TAAR1, not just a docking-score exercise. Better still, cryo-EM backs up the predicted binding poses, so the model isn't just getting lucky on affinity. The pharmacology is the real prize: brain-penetrant, potency beating ulotaront, and no catalepsy in the PPI assay — that's the non-dopaminergic promise actually paying off, not just a slogan. Ulotaront is now the bar every TAAR1 agonist has to clear, and these three cleared it. Worth watching whether the SAR generalizes beyond these three chemotypes.
Structure based discovery of antipsychotic-like TAAR1 agonists ↗
Researchers Advance Quinoline CYP8B1 Inhibitor as Lead for Metabolic Disease
- CYP8B1 is a liver enzyme in the bile-acid synthesis pathway now being explored as a drug target for metabolic disorders such as nonalcoholic fatty liver disease and type 2 diabetes.
- The project started from compound 1, a CYP8B1 inhibitor identified by high-throughput screening, which broke down too quickly to be tested in live animals.
- Chemists used structure-based design and metabolite identification to learn how the molecule degraded, then ran DMPK-guided analog synthesis to explore structure-activity relationships.
- That work produced compound 9, a quinoline analog with markedly improved metabolic stability.
- In mice, compound 9 showed robust in vivo CYP8B1 inhibition, providing a validated lead for further optimization.
This is textbook DMPK-guided lead optimization done right: compound 1 degrades too fast for in vivo work, so instead of abandoning it, they identify the metabolite, figure out exactly where the molecule is falling apart, and redesign around that liability. That's the disciplined way to do hit-to-lead, and it's refreshing to see it laid out explicitly rather than glossed over. Landing on a quinoline is a plus for tractability — cheap chemistry, well-understood SAR space, easy to riff on for follow-up analogs. CYP8B1/bile-acid signaling is also a nice change of scenery from the overworked FXR and GLP-1 real estate in NAFLD/T2D. My one nagging question: going from compound 1 to a stable, in vivo-active compound 9 reads suspiciously clean for a single campaign — what substituent or ring modification actually killed the metabolic soft spot? That's the detail I'd want in the SAR table before believing this fully.
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.