Senolytics

Strong preclinical evidence; dasatinib + quercetin (D+Q) is the most-studied combination and multiple human trials are underway. Human translation remains indication-specific and early. In the first Phase 1 open-label trial in mild Alzheimer's disease (Neurotherapeutics 2025, n=5), D+Q confirmed CNS penetration of dasatinib and a favorable safety profile but produced no significant change in tau, amyloid, or neuroinflammatory fluid biomarkers and no cognitive/neuroimaging signal — senescent-cell clearance has not yet demonstrated a disease-modifying effect in the brain. A Phase 2 Alzheimer's RCT is underway. Unity Biotechnology and other companies continue clinical programs. UPDATE (August 2026): A peer-reviewed systematic review in Ageing Research Reviews 2026 (Lin, Altulea & Demaria) synthesized 29 articles covering 27 human interventional trials and 3,811 participants, and it constrains what nutritional and CR-mimetic approaches to senescence can currently claim. Calorie restriction produced the most recurrent reductions in circulating SASP-panel factors and senescence-associated transcriptomic signatures, but classical markers of senescent-cell ABUNDANCE (CDKN2A/p16, CDKN1A/p21) and telomere length were largely unchanged or highly variable. CR mimetics including metformin and rapamycin showed context-dependent effects, most evident under metabolic or physiological stress. The authors' key point: because SASP factors and circulating cytokines are heterogeneous and not specific to senescent cells, none of this establishes that any nutritional intervention reduces senescent-cell burden in humans. This complements - and reinforces - the null Phase 1 Alzheimer's fluid-biomarker result above: measured improvements in inflammatory panels should not be read as evidence of senescent-cell clearance. UPDATE (August 9, 2026): Nature Aging 2026 (Wang, Piccolantonio et al.; Demaria lab) reports a SENOMORPHIC rather than senolytic route: short-term CDK4/6 inhibition with abemaciclib suppressed the established NF-kB-associated SASP (NASP) in cells that were ALREADY senescent, in vitro and in vivo, reduced the pro-tumorigenic activity of chemotherapy-induced senescent cells, and improved physical function in mice after chemotherapy and in natural aging. Genetic CDK4/6 knockdown phenocopied it; mechanistically CDK4/6 inhibition suppresses retinoic acid signalling, with CDK4 and CDK6 binding NF-kB and CDK4 additionally binding RARalpha, and the RARalpha antagonist agn194310 reproducing the effect. Because abemaciclib is an approved oncology drug this is the most directly repurposable senomorphic lead in some time — but all aging data are murine and CDK4/6 inhibitors carry meaningful neutropenia, diarrhoea, hepatotoxicity, ILD and VTE risk. Not a basis for off-label geroprotective use. Alongside this, a Nature Aging 2026 Perspective (Schafer, Basisty & Baker) proposes classifying senescent cells into SENOTYPES by origin, molecular signature and effect — explicitly including adaptive, beneficial senescent states. That framework offers the clearest published explanation for why broad senolysis has produced inconsistent human results, including the null Phase 1 Alzheimer's biomarker data above: current agents do not distinguish maladaptive from beneficial senescent populations. The Perspective is a proposal, not new data, and is not yet operationalised into assays that could select patients. UPDATE (August 16, 2026): PEER-REVIEWED, PRECLINICAL. Nature Aging 2026 (Palikyras, Varamogiani-Mamatsi et al.; Papantonis lab) adds a third mechanistic route into the senescence phenotype, upstream of both senolysis and NF-kB-directed senomorphics. Senescence entry involves nuclear-speckle-associated clustering of CTCF, which coordinates chromatin rewiring and installs a senescence-associated ALTERNATIVE SPLICING programme; interventions countering that reorganisation delayed senescence entry in their models. Conceptually this nominates splicing control as a senomorphic axis distinct from the CDK4/6-RARalpha-NF-kB work above, and it fits the senotype framing - if senescent states are heterogeneous, splicing architecture is one of the features that could eventually distinguish them. Caveats are substantial: this is cell-based and preclinical, there is no in vivo healthspan or lifespan endpoint, no drug-like compound was identified, and splicing modulators as a drug class have historically had narrow therapeutic windows. It changes no clinical recommendation. UPDATE (August 23, 2026): Two developments, pulling in opposite directions. (1) PEER-REVIEWED, PRECLINICAL — a second CDK4/6 senomorphic paper. Nature Aging 2026 (Rajesh, Havas & Adams, 20 August 2026) reports that cyclin D1 and CDK6 regulate the inflammatory phenotype of senescent cells via DNA damage and cGAS–STING activation, and that blocking this axis with PALBOCICLIB improved motor function and reduced frailty in aged mice. This is a mechanistic complement to the abemaciclib work above, not a repeat: the two papers appeared together with a joint News & Views (Wang & Bernards) arguing that approved CDK4/6 inhibitors could be repurposed as senomorphics. Two independent laboratories converging on the same target through partly different mechanisms materially strengthens the CDK4/6 senomorphic hypothesis — while leaving it entirely murine, functional rather than survival-based, and constrained by real oncology toxicity. (2) CHALLENGED — a measurement problem underneath much of this literature. A research-integrity investigation reported in Nature News (21 August 2026) found at least 54 cell-aging papers, spanning Cell and Nature Aging down to low-impact titles, whose methods list an antibody raised against ESCHERICHIA COLI beta-galactosidase, apparently used to detect beta-galactosidase in MAMMALIAN cells as a senescence marker. Cross-kingdom reactivity of this kind is unsupported by theoretical or experimental evidence. The trail began with a 2016 Cell paper on in vivo partial reprogramming (Izpisua Belmonte laboratory) that listed an E. coli beta-gal antibody used on mouse liver; Cell says it is investigating and Springer Nature says it will assess. This is not proof that any specific conclusion is wrong — several affected experiments were ancillary and at least one author states the error did not affect the paper's conclusions — and it is journalism reporting a post-publication audit rather than a peer-reviewed re-analysis. But it lands on the single most widely used senescence readout, and it compounds a pre-existing dispute over whether SA-beta-gal staining identifies senescent cells at all. UPDATE (September 6, 2026): Two additions that move the debate from WHICH molecule to WHEN, HOW OFTEN, and WHETHER KILLING IS EVEN THE RIGHT VERB. (1) Timing - a peer-reviewed multitissue single-cell study of dasatinib + quercetin in aged mice (Nature Aging, June 17 2026; Hou et al.) found D+Q remodelled immunity, reduced tissue inflammation and improved metabolic profiles, but strictly in a tissue- and cell-type-specific way, with incomplete senescent-cell clearance. Its practically important result: intervention initiated during EARLY aging and continued long term mitigated aging readouts more than short, late-stage courses - which cuts against the intermittent late-life hit-and-run schedule most clinics inherited from the original mouse work. This is preclinical and framed by the authors as a tendency, not a powered head-to-head schedule trial. (2) Mechanism - a peer-reviewed Science paper (July 16 2026; Tan et al., Andreasson lab, Stanford) shows that a large share of age-associated senescent-cell accumulation is a CLEARANCE failure: aged tissue-resident macrophages stop performing efferocytosis of senescent neutrophils because of prostaglandin E2 receptor EP2 signalling, and pharmacologic EP2 inhibition in aged mice restored youthful clearance and prevented cognitive decline, frailty, sarcopenia, adiposity, cardiac impairment and systemic inflammation. Elevated TRM EP2 expression and senescent-neutrophil accumulation were also present in aged and diseased human tissue, though the human data are expression-level and cross-sectional. Neither result changes what can be offered today: both are mouse intervention studies, EP2 antagonists have no aging indication or chronic-dosing safety record in older adults, and the completed human senolytic brain trial remains biomarker-null. UPDATE (September 13, 2026): Two peer-reviewed preclinical papers shift the mechanistic frame from "kill senescent cells" toward "restore their clearance." In Cell Metabolism (Chaib, Langhi Prata, Suda et al., Cedars-Sinai/Mayo, 10 Sep 2026), PD-L2 was identified as a senescence-associated immune checkpoint: it is upregulated on senescent human cells and with age, aged PD-L2 knockout mice accumulate fewer senescent cells and have better insulin sensitivity and grip strength, and anti-PD-L2 antibody therapy restored insulin sensitivity in aged wild-type mice. Senolytics preferentially removed high-PD-L2 senescent cells, and soluble PD-L2 is proposed as a candidate circulating burden marker — the human data, however, are correlative, not interventional, and checkpoint blockade has never been trialled for an aging indication. Separately, in Neuron (Liu, Gan et al., Weill Cornell, 11 Aug 2026), senescent microglia with shortened telomeres were shown to secrete soluble DLK1, which impairs oligodendrocyte function and alters neuronal activity; CSF sDLK1 rose with age in mice and was abolished by microglial depletion, and DLK1 rises with age in human brain single-cell data. That nominates a specific secreted mediator for the brain-aging arm where the one completed human senolytic brain trial (D+Q in mild Alzheimer's) was biomarker-null. Both are preclinical; neither supports a change in senolytic practice today. UPDATE (September 20, 2026): Two peer-reviewed additions, both bearing on the field's unresolved definitional and biomarker problem rather than on any compound. (1) A PROTEOSTASIS SIGNATURE. Nature Communications 2026 (Da Silva Fernandes, Kielisch, Fulzele, Behl & Ulrich, 16 Sept 2026) used mass-spectrometry proteomics to track the proteome through the progression of replicative senescence and found the changes are COORDINATED rather than piecemeal: widespread protein depletion on chromatin, depletion of the cytoplasmic translation machinery, increased insolubility of mitochondrial proteins, compromised autophagic and proteasome activity, remodelled ubiquitin linkages and depletion of ubiquitin E3 ligases. Benchmarked against other pathophysiological cellular states, this yields a distinctive senescent signature shaped by the proteostasis network. That matters directly to the definitional problem documented here previously - where only 173 of 1,250 genes across the four standard senescence gene sets were corroborated by two or more resources, and only IL6 and JUN by all four - because a proteostasis-level signature is a candidate discriminator that transcript panels have not delivered. Strict limits: in vitro replicative senescence in cultured cells only, no in vivo or human tissue data, replicative senescence may not represent therapy-induced or oncogene-induced states, and it is a descriptive resource, not evidence that any senolytic or senomorphic acts through this axis. (2) THE FIELD'S OWN ACCOUNTING. Nature Aging 2026 (Cerrato, Farsetti & Demaria, Meeting Report, 3 Sept 2026) publishes the SENESCENCE2030 consensus roadmap from the network's Coimbra conference and industry-academia workshop (May 2026). Researchers, clinicians, industry and policy stakeholders named what must be solved before senescence biology reaches practice: functional classifications of senescent states, standardised and clinically actionable biomarkers, precision senescence medicine, translational and regulatory frameworks, and international collaboration. The clinically useful signal is what the consensus does NOT claim - there is no agreed biomarker to select patients, no agreed definition of the target cell population, and no regulatory pathway for an aging indication. A consensus document carries no experimental weight of its own and reflects the composition of the participating group, which included industry representatives; treat it as an honest statement of where the bottlenecks sit, not as evidence about any compound.

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