Selective Senolysis: Clearing “Zombie Cells” in Humans – Evidence from Early Clinical Trials in Osteoarthritis, Chronic Kidney Disease, and Frailty

Senescent cells are often called “zombie cells” because they permanently stop dividing yet refuse to die. Instead, they accumulate with age and secrete a cocktail of inflammatory proteins, cytokines, and proteases known as the senescence-associated secretory phenotype (SASP). This chronic, low-grade inflammation—sometimes termed inflammaging—contributes to tissue dysfunction, organ decline, and multiple age-related diseases. In preclinical animal models, selective removal of these cells (senolysis) has produced striking improvements in healthspan and, in some cases, lifespan. These findings have generated considerable interest in translating senolytic therapies to humans. This article examines the biological mechanisms of cellular senescence, reviews the strongest available human clinical evidence—primarily from pilot and early-phase trials in osteoarthritis (OA), diabetic chronic kidney disease (CKD), and frailty-related conditions—and discusses practical implications, risks, and limitations. Emphasis is placed on randomized controlled trial (RCT) data and large cohort studies where they exist; animal and mechanistic work is noted only as context.

Biological Background

Cellular senescence is a stress response that halts cell proliferation to prevent the propagation of damaged cells. It is triggered by telomere shortening, DNA damage, oncogene activation, or oxidative stress. Key molecular hallmarks include activation of cyclin-dependent kinase inhibitors p16^INK4a^ and p21^CIP1^, leading to irreversible cell-cycle arrest, and upregulation of senescence-associated β-galactosidase (SA-β-gal). Critically, senescent cells remain metabolically active and develop the SASP, a pro-inflammatory secretome that includes interleukin-6 (IL-6), IL-8, tumor necrosis factor-α (TNF-α), matrix metalloproteinases (MMPs), and growth factors. The SASP can spread senescence to neighboring cells (bystander effect) and drive tissue remodeling, fibrosis, and chronic inflammation.

Senescent cells accumulate in virtually every tissue with advancing age and are enriched in sites of pathology such as osteoarthritic cartilage, fibrotic kidneys, and adipose tissue of individuals with metabolic disease. While transient senescence aids wound healing and tumor suppression, persistent accumulation is detrimental. Senolytics are a class of drugs that selectively induce apoptosis in senescent cells by transiently disabling their pro-survival networks (senescent cell anti-apoptotic pathways, or SCAPs). The most studied combination, dasatinib plus quercetin (D+Q), inhibits tyrosine kinases and BCL-2 family members, respectively. Fisetin, a flavonoid, and experimental agents such as UBX0101 (an MDM2-p53 disruptor) have also been tested. These agents are typically administered intermittently (“hit-and-run” dosing) to minimize off-target effects on healthy cells. In mice, such regimens reduce SASP factors, alleviate frailty-like phenotypes, and improve tissue function without eliminating all senescent cells—suggesting partial clearance can be beneficial.

Human Clinical Evidence

Human data remain early-stage. The first demonstrations that senolytics can reduce senescent cell burden in people came from small, open-label pilot studies conducted by the Mayo Clinic group.

In a 2019 open-label Phase 1 pilot (Hickson et al., *EBioMedicine*, 2019;47:446-456), nine adults with diabetic CKD (mean age 68.7 years, eGFR ~27 mL/min/1.73 m²) received oral dasatinib 100 mg/day plus quercetin 1,000 mg/day for three consecutive days. Adipose-tissue biopsies obtained 11 days later showed statistically significant reductions in senescent-cell markers (p16^INK4a^, p21^CIP1^, and SA-β-gal-positive cells) and decreased macrophage infiltration. Circulating and tissue SASP factors (including several inflammatory cytokines and MMPs) declined, indicating target engagement. The regimen was well tolerated, with no serious drug-related adverse events. This study provided the first direct evidence in humans that a short course of senolytics can lower senescent-cell burden and SASP activity in a clinically relevant tissue.

Physical-function outcomes were also explored in an idiopathic pulmonary fibrosis (IPF) pilot, a senescence-driven lung disease that shares frailty features. Justice et al. (*EBioMedicine*, 2019;40:554-563) treated 14 stable IPF patients with intermittent D+Q (dasatinib 100 mg + quercetin 1,250 mg daily for three days per week over three weeks). Retention was 100% and assessments were completed in 13/14 participants. Clinically meaningful improvements occurred in 6-minute walk distance, 4-meter gait speed, and chair-stand time (all p < 0.05). Pulmonary function tests and frailty index (FI-LAB) were unchanged. Circulating SASP markers showed variable responses, but changes in selected matrix-remodeling proteins and cytokines correlated with functional gains. A subsequent single-blind, placebo-controlled pilot in IPF patients (Nambiar et al., *eBioMedicine*, 2023) confirmed feasibility and tolerability but was not powered for efficacy.

Evidence in osteoarthritis has been less consistent. Unity Biotechnology’s UBX0101, delivered as a single intra-articular injection, showed dose-dependent improvements in pain and function plus SASP modulation in a Phase 1 study. However, the subsequent Phase 2 RCT (Lane et al., *Osteoarthritis and Cartilage*, 2021) in 183 patients with moderate-to-severe knee OA failed to meet its primary endpoint (WOMAC pain score at 12 weeks). Changes in pain were similar across UBX0101 doses and placebo, confounded by a large placebo response. A recent randomized, double-blind, placebo-controlled trial of oral fisetin (20 mg/kg/day for two days, repeated in cycles) in knee OA patients also reported no significant benefits for pain, physical function, or cartilage biomarkers (Tashman et al., *Osteoarthritis and Cartilage*, 2025 abstract). These null results in OA contrast with stronger preclinical cartilage data and highlight challenges in translating senolysis to weight-bearing joints where mechanical factors predominate.

Frailty and related geriatric syndromes have been secondary or exploratory outcomes in several trials. The CKD pilot noted above included frailty assessments, and functional gains in the IPF study occurred in a frail population. A 2025 single-arm pilot (Millar et al., *eBioMedicine*) administered intermittent D+Q to 12 older adults (≥65 years) with mild cognitive impairment and slow gait speed—hallmarks of physical frailty and Alzheimer’s risk. The regimen was feasible and safe; Montreal Cognitive Assessment scores rose modestly (especially in those with lower baseline scores), and reductions in TNF-α (a key SASP component) correlated with cognitive improvement. A Phase 2 RCT of intermittent D+Q in postmenopausal women (Farr et al., *Nature Medicine*, 2024;30:2605-2612) examined skeletal health (a frailty-related domain) and found no overall reduction in bone resorption but suggestive increases in bone-formation markers and bone-mineral density in participants with higher baseline senescent-cell burden. Larger, ongoing trials (e.g., NCT02848131 for CKD/frailty; trials in cancer survivors and osteoporosis) are testing these signals.

Collectively, human evidence consists of small (n < 20 in most cases), short-duration, often open-label or single-arm studies. Biomarker reductions (senescent cells and SASP) have been demonstrated in adipose tissue and, less consistently, systemically. Preliminary functional improvements appear in physical-performance measures relevant to frailty, but results in OA are negative or null. No large, long-term RCTs have yet reported hard clinical endpoints such as reduced incidence of major age-related diseases or improved survival. Animal-to-human extrapolation remains uncertain; doses achieving robust senolysis in mice may be lower than those needed in humans, and tissue-specific differences in senescent-cell biology matter.

Risk, Trade-offs, and Controversies

Intermittent D+Q has generally been safe in these short pilots, with mostly mild-to-moderate adverse events (gastrointestinal discomfort, skin irritation, transient respiratory symptoms). Dasatinib, used chronically at higher doses in oncology, carries known risks including pleural effusion, thrombocytopenia, and QT prolongation; quercetin is considered safe at the doses tested but can interact with medications via CYP3A4 inhibition. Long-term safety data are absent.

A fundamental trade-off concerns the beneficial roles of senescence. Transient senescent cells promote wound healing, embryonic development, and tumor suppression. Over-aggressive or chronic senolysis could theoretically impair tissue repair or increase cancer risk, although short-term human pilots have not shown such signals. Another controversy is whether complete or partial clearance is optimal and whether senomorphics (agents that suppress SASP without killing cells, e.g., JAK inhibitors or rapamycin analogs) might offer a safer profile. Finally, patient heterogeneity is high: baseline senescent-cell burden, comorbidities, and concomitant medications likely influence response. High placebo responses in OA trials underscore the need for rigorous controls.

Practical Implications

The current human evidence base, while promising, does not yet support routine clinical use of senolytics for longevity or disease prevention. Target engagement has been shown in select tissues, and functional signals in frailty proxies are intriguing, but data are preliminary, derived from small studies, and sometimes conflicting. Larger, placebo-controlled, longer-duration RCTs are essential to establish efficacy, optimal dosing intervals, and safety.

Actionable Steps

1. Prioritize lifestyle interventions with the strongest evidence for reducing senescence burden and SASP: engage in regular aerobic and resistance exercise (≥150 minutes moderate activity weekly plus strength training 2–3 times weekly), which consistently lowers inflammatory markers and improves physical function in older adults.  
2. Adopt a Mediterranean-style or plant-rich diet high in polyphenols (berries, leafy greens, nuts) and maintain healthy body weight; these patterns are associated with lower systemic inflammation in large cohort studies.  
3. Optimize management of comorbidities known to accelerate senescence accumulation—control blood pressure, blood glucose, and lipids per current guidelines; treat sleep apnea and chronic infections.  
4. Maintain muscle mass and strength through progressive resistance training; sarcopenia and frailty share mechanistic overlap with senescence.  
5. Avoid self-experimentation with high-dose quercetin, fisetin, or off-label dasatinib. These compounds are not approved for aging indications, and unregulated supplements vary widely in purity and dosing accuracy.  
6. Participate in or support well-designed clinical trials if you meet eligibility criteria (many are listed on ClinicalTrials.gov under “senolytic” or “dasatinib quercetin”). 
7. Discuss with your physician any interest in emerging therapies; routine biomarker panels for senescence (e.g., p16 expression or composite SASP scores) are not yet validated for clinical decision-making.  
8. Monitor established biomarkers of aging and frailty (grip strength, gait speed, Short Physical Performance Battery) at annual health visits; these remain the most reliable, evidence-based indicators of healthspan.

In summary, selective senolysis represents a mechanistically rational approach to a core hallmark of aging. Early human trials have confirmed that senescent cells can be reduced and SASP attenuated in people, with encouraging signals in physical function. However, the transition from rodent proof-of-concept to robust clinical benefit is incomplete. Until larger, definitive trials report results, the most evidence-aligned strategy for healthspan optimization remains proven lifestyle measures that indirectly mitigate senescence-driven processes.

Bibliography

Hickson LTJ, Langhi Prata LGP, Bobart SA, et al. Senolytics decrease senescent cells in humans: Preliminary report from a clinical trial of Dasatinib plus Quercetin in individuals with diabetic kidney disease. *EBioMedicine*. 2019;47:446-456.  

Justice JN, Nambiar AM, Tchkonia T, et al. Senolytics in idiopathic pulmonary fibrosis: Results from a first-in-human, open-label, pilot study. *EBioMedicine*. 2019;40:554-563.  

Nambiar A, Kellogg DL III, Justice JN, et al. Senolytics dasatinib and quercetin in idiopathic pulmonary fibrosis: results of a phase I, single-blind, single-center, randomized, placebo-controlled pilot trial on feasibility and tolerability. *eBioMedicine*. 2023;90:104988.  

Lane NE, Corr M, Bolognese J, et al. A phase 2, randomized, double-blind, placebo-controlled study of intra-articular UBX0101, a p53/MDM2 interaction inhibitor, for the treatment of knee osteoarthritis. *Osteoarthritis Cartilage*. 2021;29(Suppl 1):S14-S15 (full results published 2021).  

Farr JN, Atkinson EJ, Achenbach SJ, et al. Effects of intermittent senolytic therapy on bone metabolism in postmenopausal women: a phase 2 randomized controlled trial. *Nat Med*. 2024;30(9):2605-2612.  

Millar CL, et al. A pilot study of senolytics to improve cognition and mobility in older adults at risk for Alzheimer’s disease. *eBioMedicine*. 2025 (published online February 2025).  

Tchkonia T, Kirkland JL. Aging, cell senescence, and chronic disease: emerging therapeutic strategies. *JAMA*. 2023