Senolytics

A class of pharmacological agents that selectively kill senescent cells by disrupting the Senescent-Cell Anti-Apoptotic Pathways (SCAPs) that protect senescent cells from their own pro-apoptotic SASP environment. The concept and naming were established by Zhu, Tchkonia, Kirkland and colleagues at Mayo Clinic in 2015 ¹. Senolytics have moved from preclinical proof-of-concept to multiple Phase 2 human trials over a single decade — the most clinically-advanced anti-aging intervention class as of 2026.

This page covers the drug class as a whole. Specific compounds live in molecules/compounds/:

• fisetin (verified) — flavonol; cell-type-specific clearance; Phase 2 trials ongoing
• quercetin (verified) — flavonol; D+Q “Q”; HUVEC-active via BCL-xL / EFNB1 (not PI3Kδ, which is preadipocyte-selective per Zhu 2015)
• dasatinib (verified) — TKI; D+Q “D”; preadipocyte-active via ephrin/EPH receptors
• navitoclax (planned) — Bcl-2/Bcl-xL inhibitor; thrombocytopenia-limited
• a1331852 (planned) — selective Bcl-xL inhibitor

Definitional clarifications

The literature uses several overlapping terms; the distinctions matter:

Term	Meaning
Senolytic	Selectively kills senescent cells (induces apoptosis or other death)
Senomorphic	Suppresses SASP without killing senescent cells (e.g., rapamycin, JAK inhibitors, metformin, NF-κB inhibitors)
Senotherapeutic	Umbrella term covering both senolytics and senomorphics
Hit-and-run	Intermittent dosing strategy: senescent cells take days–weeks to repopulate after clearance, so continuous exposure isn’t required. Sublethal exposure carries a theoretical senescence-escape risk; the endogenous alternative is senescence-immune-surveillance

The SCAP framework

Zhu et al. 2015 (Aging Cell) ¹ is the foundational paper that established the SCAP concept and identified the first senolytic combination (dasatinib + quercetin). The key insight: senescent cells that resist their own pro-apoptotic SASP environment do so by upregulating specific anti-apoptotic networks, and these networks are distinct across cell types.

Cell-type-specific SCAPs identified (Zhu 2015 Fig 1D for preadipocytes; refined by Zhu 2016 + Yosef 2016 + Zhu 2017 across HUVECs and IMR90):

Cell type	SCAP nodes	Effective senolytics
Senescent HUVECs	BCL-xL, EFNB1	quercetin (Q); navitoclax; A1331852; fisetin (per Zhu 2017 — HUVECs only in that assay)
Senescent IMR90 fibroblasts	Multi-target Bcl-2 family — no single member sufficient (see note below)	navitoclax (hits BCL-2/BCL-xL/BCL-w); A1331852 (per Zhu 2017)
Senescent human preadipocytes	Ephrins (EFNB1/3); EPH receptors; PI3KCD; serpins (PAI-1/PAI-2); p21	dasatinib (D); D+Q combination

Note on IMR90 SCAP (corrected from earlier “BCL-2 + BCL-w dominant” framing per bcl-2 and bcl-xl verifier rounds):

• Zhu 2016 Fig 4A-B: BCL-xL siRNA alone or BCL-2 + BCL-xL together were insufficient for IMR90 senolysis; the full triple BCL-2 + BCL-xL + BCL-w combination was required.
• Yosef 2016: BCL-W + BCL-xL dual knockdown produced ~53% IMR90 viability reduction; each alone had only minor effect.
• Practical implication: IMR90 senescent cells require multi-target Bcl-2 family inhibition. Navitoclax (BCL-2/BCL-xL/BCL-w pan-inhibitor) is well-suited; single-target agents (e.g., venetoclax, BCL-2 only) are not.

Critical implication: no single senolytic clears all senescent cell types. D+Q was designed as a polypharmacological combination specifically to cover complementary cell-type populations. The clinical translation challenge is largely a cell-type-matching problem rather than a potency problem.

Major senolytic drug families

BH3-mimetics (Bcl-2 family inhibitors)

The mechanistically cleanest senolytic class — directly inhibit anti-apoptotic Bcl-2/Bcl-xL/Bcl-w proteins, releasing the BAX/BAK-mediated mitochondrial apoptosis cascade in cells that are already primed for apoptosis (as senescent cells are, due to chronic SASP-driven stress). See apoptosis-pathway § BH3-mimetics for mechanism.

Agent	Target	Status	Key limitation
Navitoclax (ABT-263)	BCL-2 / BCL-xL / BCL-w	Oncology Phase 2; senolytic preclinical	Thrombocytopenia — BCL-xL is required for platelet survival; on-mechanism dose-limiting toxicity
A1331852	BCL-xL selective	Preclinical senolytic	Same platelet liability as navitoclax
ABT-737	BCL-2 / BCL-xL / BCL-w (tool compound)	Preclinical only	Poor oral bioavailability
UBX0101 (Unity Biotechnology)	MDM2 → p53/p21 axis (claimed)	Phase 2 failed for osteoarthritis (UNITY-OA-101, 2020)	Mechanism debated; may not act primarily as a clean senolytic
UBX1325 / foselutoclax (Unity Biotechnology)	BCL-xL-selective small molecule	Phase 2 positive trend (BEHOLD, NCT04857996) in diabetic macular edema 2; intravitreal route	Local-delivery design sidesteps systemic thrombocytopenia. First BCL-xL-axis senolytic to show positive Phase 2 RCT signal in humans; class proof-of-concept for local-delivery BH3-mimetics.

Navitoclax in aged-mouse studies improved hematopoietic stem cell function (Chang et al. 2016 Nat Med ³ — the primary finding per the paper’s title; lung/liver/bone marrow senescent-cell clearance data attributed to this paper cannot be confirmed from the PDF, which is unavailable in the archive no-fulltext-access — note: this is the correct attribution for the aged-mouse navitoclax data; it is NOT in Zhu 2016, which is in vitro only).

Tyrosine kinase inhibitors

Agent	Senolytic mechanism	Status
dasatinib	Disrupts ephrin/EPH SCAP arm in preadipocytes; complementary to BH3-mimetics	Phase 2 in D+Q regimen

Flavonoid / natural-product senolytics

Agent	Mechanism	Status
fisetin	PI3K/AKT/mTOR pathway disruption (proposed); cell-type-specific clearance; mechanism incompletely characterized	Phase 2 trials ongoing (NCT03675724, NCT03325322)
quercetin	BCL-xL / EFNB1 in HUVECs (PI3Kδ is preadipocyte-selective per Zhu 2015, not HUVEC); D+Q “Q” component	Phase 1/2 in D+Q regimen
Procyanidin C1 (grape seed)	Less-studied; preclinical evidence in mice (Xu 2021 Nat Metab)	Preclinical

Other / investigational

• Cardiac glycosides (digoxin, ouabain) — preclinical senolytic evidence (Triantafyllou 2019); narrow therapeutic index complicates translation
• HSP90 inhibitors (17-AAG, 17-DMAG) — preclinical only
• FOXO4-DRI peptide — disrupts FOXO4–p53 interaction in senescent cells; Baar 2017 preclinical evidence
• Galactose-conjugated prodrugs (lysosomal-targeting) — exploit elevated SA-β-galactosidase in senescent cells; preclinical / first-in-human trials beginning

Clinical evidence status (as of 2026)

Trial	Agent(s)	Population	NCT	Status / key results
Justice 2019 4	D + Q	Idiopathic pulmonary fibrosis (n=14)	NCT02874989	Phase 1 pilot — primary endpoints feasibility (achieved); secondary 6MWT +21.5 m (p=0.012), gait speed +0.12 m/s (p=0.024), chair-stands −2.2 s (p=0.013); pulmonary function unchanged
Hickson 2019 5	D + Q	Diabetic kidney disease (n=9)	NCT02848131	Phase 1 — adipose biopsy: p16 −35% (p=0.001), p21 −17% (p=0.009), SA-βgal+ −62% (p=0.005); macrophages −28% (p=0.0001); circulating SASP factors (IL-1α, IL-6, MMPs-9/-12) reduced
Mayo Frailty Fisetin	Fisetin	Older women with frailty	NCT03675724	Phase 2 — ongoing as of 2026
DKD Fisetin	Fisetin	Patients with diabetic kidney disease	NCT03325322	Phase 2 — suspended (per ClinicalTrials.gov 2026-05-04; reason not posted)
UNITY-OA-101	UBX0101	Knee osteoarthritis	NCT04129944	Phase 2 failed — no improvement vs placebo; UBX0101 program subsequently abandoned. The first major senolytic clinical setback.
BEHOLD 2	UBX1325 (foselutoclax)	Diabetic macular edema (suboptimal anti-VEGF response)	NCT04857996	Phase 2 RCT — first positive BCL-xL-axis senolytic human trial. Single 10 µg intravitreal injection vs sham; n=65 (UBX1325 n=32, sham n=33); 48-wk follow-up. BCVA difference UBX1325 − sham at week 48 = +5.6 ETDRS letters (95% CI −1.5 to 12.7); no systemic safety signals (no platelet effects via local intravitreal route); 5 vs 4 Grade ≥3 TEAEs (UBX1325 vs sham; CI overlaps zero). UNITY pivoted to UBX1325/foselutoclax (a BCL-xL-selective small molecule) after UBX0101 failure; intravitreal local delivery sidesteps the systemic thrombocytopenia liability that has blocked navitoclax.
TROFFi 6	Fisetin	Postmenopausal breast cancer survivors with 6MWD <400 m	NCT05595499	Phase 2 RCT — protocol published 2026; 88 women; fisetin 20 mg/kg/day d1–3 of 14-day cycles × 4 cycles vs placebo; primary endpoint Δ6MWD baseline-to-end. Multicenter, double-blind, placebo-controlled. First placebo-controlled fisetin senolytic RCT with hard physical-function endpoint. Recruiting as of 2026-05.
Farr 2024 7	D + Q	Postmenopausal women (osteoporosis risk; n=60)	NCT04313634	First placebo-controlled D+Q RCT to report results; primary endpoint NEGATIVE. 20-week intermittent D+Q vs placebo; primary endpoint CTx (bone resorption): p=0.611 (NS). P1NP (formation) transiently elevated at 2 + 4 wk (NS at 20 wk). Exploratory high-senescent-burden tertile (highest T-cell p16 mRNA, n≈20): P1NP +34% (p=0.035) and CTx −11% (p=0.049) at 2 weeks post-dosing; radius BMD +2.7% (p=0.004) at 20 weeks. Materially qualifies the senolytic-for-bone framing: benefit appears NOT universal but stratifiable by senescent-cell burden. The biomarker-stratified follow-up is in progress (Farr 2025 Aging Cell). See bone for the bone-specific verification context.

needs-human-replication — All non-UBX1325 positive senolytic results in humans are from small open-label or pilot trials. No large randomized blinded outcome trials have completed. The UNITY-OA-101 failure is a cautionary signal that not all SCAP-targeting strategies translate; the UBX1325/BEHOLD result (Klier 2025) is the first BCL-xL-axis senolytic Phase 2 RCT to show a positive efficacy trend with a clean safety profile, vindicating the BCL-xL mechanism in a localized-delivery context.

Active senolytic trials count (ClinicalTrials.gov, 2026-05-08): 14 RECRUITING + ACTIVE_NOT_RECRUITING + ENROLLING_BY_INVITATION (excludes oncology-only navitoclax/venetoclax monotherapy trials). Fisetin dominates the senolytic-aging trial roster (17 active/enrolling fisetin trials, several spanning aging-relevant indications: PAD, mild Alzheimer’s [NCT07279714], healthy aging [NCT07195318], breast-cancer-survivor frailty [NCT06113016, NCT05595499], multimorbidity [NCT06431932], cancer-survivor fatigue [NCT06819254]).

Cell-type specificity and clinical translation challenges

The cell-type-specific SCAP framework has direct clinical-design implications:

• D+Q clears preadipocytes, mesenchymal stem cells, and some stromal populations — well-suited for fibrotic diseases (where mesenchymal senescent cells drive pathology) and metabolic syndromes (preadipocyte senescence drives adipose dysfunction).
• Navitoclax / A1331852 are most effective on HUVECs and other Bcl-xL-dependent senescent cells — well-suited for vascular and hematologic contexts, but the dose-limiting thrombocytopenia restricts use to cancer indications where the risk/benefit profile permits.
• Fisetin shows broader cell-type activity than pure Bcl-2-family targeting would predict — its mechanism remains incompletely characterized, which is both its appeal (broader spectrum) and its limitation (harder to design rational combinations).

Trial design implication: the indication should be chosen for the senescent-cell type most relevant to the disease, not just for the most easily-recruited patient population. This is a partial explanation for the UNITY-OA-101 failure (osteoarthritis senescent cells may not have been the right SCAP profile for UBX0101’s mechanism).

SENS / hallmark mapping

• SENS strategy: ApoptoSENS (death-resistant cells) — senolytics are the canonical ApoptoSENS intervention
• Hallmark targets: cellular-senescence (direct clearance), chronic-inflammation (indirect via SASP reduction)

Related approaches

• Genetic senescent-cell clearance — INK-ATTAC and p16-3MR transgenic mouse models (Baker 2011 ⁸; Baker 2016 ⁹) — preclinical proof-of-principle that motivated senolytic drug development. Baker 2016 demonstrated 27% (mixed background) / 24% (C57BL/6) lifespan extension from p16+ cell clearance in naturally-aged mice (per p21 verification round; tissue-selective effect).
• Senomorphics (suppress SASP without killing): rapamycin, JAK inhibitors (ruxolitinib), metformin (partial), NF-κB inhibitors, BET inhibitors — see sasp for mechanism details
• CAR-T senolytic approaches (preclinical) — uPAR-targeted CAR-T cells that clear senescent cells (Amor 2020 Nature) — an early-stage cellular-immunotherapy translation of the senolytic concept

Limitations and open questions

• Cell-type specificity is the dominant unsolved problem. No single agent or combination clears all senescent cells; tissue-level efficacy depends on which senescent populations dominate.
• Long-term safety in humans is unknown for all senolytics — acute trials (single or short courses) have favorable safety; chronic intermittent exposure data is accumulating but limited. long-term-unknown
• Optimal dosing schedule remains debated — “hit-and-run” intermittent (D+Q 3-day courses, weekly cycles per Justice 2019) vs continuous low-dose. Mechanistic basis for hit-and-run is solid but timing optimization is empirical. dose-response-unclear
• Trial enrollment biomarkers — no validated way to identify patients with high senescent-cell burden a priori. Trials enroll on disease state. needs-replication for biomarker validation
• Senolytic vs senomorphic comparative efficacy — head-to-head clinical comparisons are scarce.
• Off-target toxicity at therapeutic doses — D+Q dosing is short and intermittent partly to minimize TKI cardiotoxicity (D) and bioavailability concerns (Q).
• Cardiac-glycoside senolytic activity — promising preclinical signal but interpretation complicated by their narrow therapeutic index and existing clinical use in heart failure.
• UBX0101 failure interpretation — was the failure due to wrong cell-type targeting? Wrong indication? Wrong mechanism (UBX0101 may not act as a senolytic at all)? The post-mortem is incomplete and matters for the next generation of senolytic trials.

Recent class-level developments (2024–2026)

The 2024–2026 senolytic literature has shifted from generic “BH3-mimetic monotherapy” toward:

1. Local-delivery BCL-xL inhibition — UBX1325/foselutoclax’s intravitreal route (Klier 2025 ²) demonstrates that the systemic-thrombocytopenia barrier can be bypassed for tissue-localized senescent-cell pathology (retina, CNS, joint). This is the first BCL-xL-axis senolytic to clear Phase 2 with a positive efficacy trend.
2. Tissue-specific PROTAC degraders (DT2216, PZ15227-class; recent reviews ¹⁰) — recruit organ-restricted E3 ligases (VHL, CRBN) to degrade BCL-xL selectively in nucleated senescent cells while sparing platelets. Reviewed as one of three “next-generation” senotherapy strategies in Zhang 2026.
3. Immune-based senolysis — uPAR-targeted CAR-T (Amor 2020), NK cell senotherapy approaches (Front Immunol 2025), and immune-checkpoint-modulated SnC clearance.
4. Microbiome-senolysis crosstalk — SCFAs (butyrate) modulate drug-transporter expression and SASP; emerging gut-liver axis modifiers of senolytic efficacy ¹⁰.
5. Indication-specific cell-type matching — community-wide rethinking of trial design (Nature Aging 2025 perspective “Towards a personalized approach in senolytic trials”) in light of UBX0101-OA failure vs UBX1325-DME positive signal.

long-term-unknown — long-term effects of repeated intravitreal BCL-xL inhibition (UBX1325) not yet characterized; BEHOLD followed for 48 wk.

Cross-references

• fisetin — verified senolytic compound page
• quercetin — verified senolytic compound page
• dasatinib — verified senolytic compound page
• cellular-senescence — hallmark page (target)
• sasp — senescence secretome (downstream of senolytic clearance; verified)
• apoptosis-pathway — verified mechanism page
• caloric-restriction — adjacent intervention with senomorphic effects
• sens-damage-categories — ApoptoSENS section is the SENS-framing of this drug class

Footnotes

Footnotes

1. doi:10.1111/acel.12344 · in-vitro + in-vivo (mouse) · transcriptomic SCAP identification + first senolytic combination · model: human cells (HUVECs, IMR90, preadipocytes) + Ercc1-/Δ progeroid mice · Aging Cell — the foundational senolytic paper ↩ ↩²

2. doi:10.1056/EVIDoa2400009 · Klier S et al. (UNITY Biotechnology) · NEJM Evidence 2025 May;4(5):EVIDoa2400009 · Phase 2 randomized sham-controlled · n=65 (UBX1325 32, sham 33) DME patients with prior suboptimal anti-VEGF response · single 10 µg intravitreal injection vs sham; 48-week follow-up · BCVA Δ at week 48: UBX1325 − sham +5.6 ETDRS letters (95% CI −1.5 to +12.7) · 5 vs 4 Grade ≥3 TEAEs UBX1325 vs sham; no apparent between-group differences in vital signs, ECG, or routine chemistries · NCT04857996 · UBX1325/foselutoclax is a BCL-xL-selective small-molecule senolytic; local intravitreal delivery sidesteps systemic platelet toxicity. Verifier note: abstract-level extraction; full-text not yet end-to-end verified. ↩ ↩² ↩³

3. doi:10.1038/nm.4010 · in-vivo (mouse) · navitoclax (ABT-263) in naturally-aged mice · Nature Medicine · confirmed title: “Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice” — HSC rejuvenation is the primary finding; lung/liver/bone marrow senescent-cell clearance claims no-fulltext-access (DOI lookup failed after retry) ↩

4. doi:10.1016/j.ebiom.2018.12.052 · open-label Phase 1 pilot · n=14 IPF · D 100 mg + Q 1250 mg/day, 3 consec days/week × 3 weeks (9 dosing days) · primary endpoints feasibility; secondary 6MWT +21.5 m (p=0.012), gait speed +0.12 m/s (p=0.024), chair-stands −2.2 s (p=0.013) · model: humans ↩

5. doi:10.1016/j.ebiom.2019.08.069 · open-label Phase 1 · n=9 DKD · 3-day oral course: D 100 mg/day + Q 1000 mg twice daily · adipose biopsy: p16 −35% (p=0.001), p21 −17% (p=0.009), SA-βgal+ −62% (p=0.005); macrophages −28% (p=0.0001); circulating SASP factors reduced (IL-1α, IL-2, IL-6, IL-9, MMP-2, -9, -12 all decreased) · model: humans ↩

6. doi:10.1177/17588359261424668 · Ji J, Crespi CM, Yee L, Zekster YA, Al-Saleem A, Petersen L, Lee C, Son N, Smith C, Evans T, Tchkonia T, Kirkland JL, Kuchel GA, Cohen HJ, Sedrak MS · Ther Adv Med Oncol 2026 Mar 11;18:17588359261424668 · TROFFi study rationale and trial design publication (not yet results) · Phase 2 multicenter randomized double-blind placebo-controlled trial · planned n=88 postmenopausal early-stage breast cancer survivors with 6MWD <400 m, completed neo/adjuvant chemotherapy within 12 mo · 1:1 randomization to fisetin 20 mg/kg/day d1–3 of 14-day cycle × 4 cycles vs placebo · primary endpoint Δ6MWD baseline-to-end-of-treatment · NCT05595499 · status: recruiting as of 2026-05. ↩

7. doi:10.1038/s41591-024-03096-2 · Farr JN et al. · Nature Medicine 2024;30(9):2605-2612 · randomized placebo-controlled · n=60 postmenopausal women · 20-week intermittent D+Q (D 100 mg + Q 1000 mg × 3 consecutive days monthly × 6 cycles) vs placebo · primary endpoint CTx Δ at 20 wk: NS (p=0.611) · exploratory high-T-cell-p16 tertile (n≈10/arm): P1NP +34% (p=0.035) and CTx −11% (p=0.049) at 2 weeks post-dosing; radius BMD +2.7% (p=0.004) at 20 weeks · NCT04313634 · the first placebo-controlled D+Q clinical bone trial; established the need for senescent-burden stratification in trial design (added 2026-05-23 via bone verifier pass; timing-split corrected 2026-05-23 via osteoporosis verifier pass — initial single-timepoint framing was wrong) ↩

8. doi:10.1038/nature10600 · in-vivo (mouse) · INK-ATTAC transgenic; p16+ cell genetic clearance · model: BubR1 progeroid mice · proof-of-principle for senescent-cell clearance benefit. Note: green OA but DOI lookup has failed; full PDF unverified — #gap/no-fulltext-access ↩

9. doi:10.1038/nature16932 · in-vivo (mouse) · INK-ATTAC; naturally-aged mice · 27% (mixed bg) / 24% (C57BL/6) median lifespan extension from p16+ cell clearance (range 17–35% by sex); tissue-selective · per p21 verification round — values directly read from PDF ↩

10. doi:10.1038/s41514-026-00355-z · Zhang W, Song S et al. · NPJ Aging 2026 Mar 10 · review · model: literature synthesis · catalogues three next-generation senotherapy strategies — (1) immune-based senolysis (CAR-T uPAR, GD3-blocking, ferroptosis sensitization); (2) tissue-precision PROTACs (VHL, CRBN E3-ligase recruiters degrading BCL-xL in nucleated cells but sparing platelets); (3) microbiome-epigenetic interplay (SCFAs/butyrate modulating drug transporters + SASP) · review-level claims; not a primary-source experiment. ↩ ↩²