Navitoclax
Navitoclax (ABT-263), oral BCL-2, BCL-xL and BCL-w inhibitor
Written by Aaron CuhaReviewed Sep 2026
Also known as: ABT-263, ABT263
The most-cited senolytic in mice, and the one that cannot be given to healthy people. In its first human trial, 29 of 55 patients with lymphoid cancers had grade 3 or 4 thrombocytopenia, because platelets survive on the same protein whose blockade kills senescent cells.
Overview
Navitoclax is an oral small molecule that binds and inhibits the anti-apoptotic proteins BCL-2, BCL-xL and BCL-w. Senescent cells raise these proteins to survive their own pro-apoptotic state, which is why blocking BCL-xL kills them. In mice this works: oral ABT-263 cleared senescent cells and rejuvenated haematopoietic and muscle stem cell compartments in irradiated and in normally aged animals, and cleared senescent glial cells in a tau model.
People have taken navitoclax, but only for cancer. The phase 1 dose-escalation study in 55 adults with relapsed or refractory lymphoid malignancy reported grade 3 or 4 thrombocytopenia in 29 of them, and the authors attributed it to high-affinity inhibition of BCL-xL, on which circulating platelets depend for survival. A single-arm phase 2 in 46 women with platinum-resistant ovarian cancer reported one partial response, 15 stable diseases, a median progression-free survival of 1.64 months, and grade 3 or 4 thrombocytopenia in 12 of 46. A phase 1/2 combination with trametinib in 91 patients with RAS-mutant tumours found partial responses in 8 of 49 evaluable patients at the recommended dose, with thrombocytopenia again among the most common adverse events.
The senolytic mechanism and the dose-limiting toxicity are the same mechanism. That is not a dosing problem to be solved by a better schedule, and it is the reason navitoclax has never been taken into an ageing trial. A live ClinicalTrials.gov query in September 2026 returned no registered navitoclax study in any ageing, senescence or geroscience indication. Navitoclax is not approved for anything, in any country. No senolytic has improved a clinical outcome in a randomised trial in humans, and navitoclax has not been tested for one.
Mechanism of action
Established in human cells and in mice: navitoclax is a BH3 mimetic that occupies the binding groove of BCL-2, BCL-xL and BCL-w, freeing pro-apoptotic BAX and BAK and triggering apoptosis in cells that depend on those proteins. In mice, that dependency is what makes senescent cells selectively vulnerable. In humans, the same dependency in platelets produces thrombocytopenia, verified in the oncology dose-escalation data. The senolytic selectivity demonstrated in mice has never been demonstrated in a person.
Human evidence
Substantial human data exist, all of it in cancer patients, none of it about ageing or senescence. Navitoclax has never been given to a person for a senolytic purpose, and no such trial is registered anywhere.
- Phase 1 dose escalation, 55 adults with relapsed or refractory lymphoid malignancy: grade 3 or 4 thrombocytopenia in 29 of 55, dose-limiting in both schedules. Funded by Abbott, Genentech and the National Cancer Institute.
- Phase 2 single-arm, 46 women with platinum-resistant ovarian cancer: median progression-free survival 1.64 months, one partial response, grade 3 or 4 thrombocytopenia in 12 of 46.
- Phase 1/2 with trametinib, 91 patients with RAS-mutant solid tumours: 8 of 49 evaluable patients responded at the recommended dose, all durable responses in gynaecologic cancers.
- ClinicalTrials.gov, checked September 2026: no navitoclax study registered in any ageing, senescence or geroscience indication. Every registered navitoclax trial is oncology or haematology.
What this does not tell you: Oncology data tell you what the drug does to platelets, T cells and tumours in people who are already ill and being treated for cancer. They tell you nothing about whether clearing senescent cells helps a healthy older adult, because that question has never been asked in a person with this drug. The thrombocytopenia is the reason it has not been asked.
Reading the research record
Navitoclax is the clearest case in the senolytic field of a compound whose mechanism defeats its own translation. BCL-xL keeps platelets alive; inhibiting BCL-xL kills senescent cells and drops the platelet count in the same stroke. The phase 1 authors named this explicitly in 2010. Every subsequent oncology trial has reported the same toxicity, which is tolerable when the alternative is progressive cancer and not tolerable as a preventive given to well people.
That is why DT2216, a degrader designed to route BCL-xL for destruction through an E3 ligase that platelets barely express, exists at all. It is also why the widely repeated claim that senolytics rejuvenate stem cells should always be read with its species label attached: the rejuvenation was in mice. No senolytic has improved a clinical outcome in a randomised trial in humans, and the drug with the strongest animal senolytic data is the one least likely to be tested for it.
The evidence, charted
Fig. 1 · evidence composition
4of 7 citations (57%) are in people
Counted from the citation list on this page. The Human count is the same number shown in the badge at the top. Both understate any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 7 distinct years, 2010 to 2026, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Approved
AU
Approved
CA
Not approved
Approved in 2 of 4, prescription route in 0, not approved in 2. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 4 · dose response
No human dose response curve exists
We draw this figure where the data supports it. For this compound in humans it does not, so the panel stays empty rather than borrowing an animal curve and implying it transfers.
Key studies & citations
- Human2010
Navitoclax, a targeted high-affinity inhibitor of BCL-2, in lymphoid malignancies: a phase 1 dose-escalation study of safety, pharmacokinetics, pharmacodynamics, and antitumour activity
55 adults with relapsed or refractory lymphoid malignancy, median age 59, treated at seven United States sites. Grade 3 or 4 thrombocytopenia in 29 patients, lymphocytopenia in 18, neutropenia in 18. Dose-limiting toxicities on both schedules included grade 4 thrombocytopenia. The authors describe a novel mechanism of peripheral thrombocytopenia and T-cell lymphopenia attributable to high-affinity inhibition of BCL-xL and BCL-2. Funded by Abbott Laboratories, Genentech and the National Cancer Institute.
The Lancet Oncology - Human2022
A phase II study of Navitoclax (ABT-263) as single agent in women heavily pretreated for recurrent epithelial ovarian cancer
46 women with platinum-resistant high-grade serous ovarian cancer, median four prior lines, single-arm. Three-month progression-free survival 22.7 percent, median progression-free survival 1.64 months, one partial response and 15 stable diseases. Grade 3 or 4 thrombocytopenia in 12 of 46, causing dose reduction in 8 and discontinuation in 3. The authors concluded activity was poor.
Gynecologic Oncology - Human2024
Phase I/II Study of Combined BCL-xL and MEK Inhibition with Navitoclax and Trametinib in KRAS or NRAS Mutant Advanced Solid Tumors
91 patients with RAS-mutant tumours. At the recommended phase 2 dose, 8 of 49 evaluable patients had a partial response, 7 of them among the 21 with gynaecologic cancers. No responses in colorectal, lung or pancreatic cancer. Thrombocytopenia was among the most common adverse events.
Clinical Cancer Research - Human2026
A Study of ABT-263 in Subjects With Relapsed or Refractory Lymphoid Malignancies
Registry record for the phase 1/2 programme above. Sponsor AbbVie, enrolment 81, status COMPLETED, verified live September 2026. No results are posted on the registry record.
ClinicalTrials.gov - Animal2016
Clearance of senescent cells by ABT263 rejuvenates aged hematopoietic stem cells in mice
Mouse. Oral ABT-263 in sublethally irradiated and in normally aged mice depleted senescent cells, including senescent haematopoietic and muscle stem cells, and rejuvenated those compartments. This is the load-bearing senolytic result for navitoclax and it is entirely in mice.
Nature Medicine - Animal2018
Clearance of senescent glial cells prevents tau-dependent pathology and cognitive decline
Mouse tau model. Clearing senescent astrocytes and microglia prevented tau deposition and cognitive decline. Mouse only; no human neurodegeneration trial of navitoclax exists.
Nature - Animal2023
Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progression
Mouse. Clearing senescent cells, including with ABT-263, worsened pulmonary hypertension in several models. A senolytic harm signal in animals, reported here because the benefit signals in animals are quoted constantly and this one is not.
Circulation
Frequently asked questions
Has navitoclax been tested as an anti-ageing drug in people?
No. As of September 2026 there is no registered navitoclax trial in any ageing, senescence or geroscience indication anywhere in ClinicalTrials.gov. All human navitoclax data come from oncology and haematology trials.
Why is the thrombocytopenia such a problem?
Because it is the same mechanism as the senolytic effect. Platelets depend on BCL-xL to survive, and so do senescent cells. In the phase 1 study, 29 of 55 patients had grade 3 or 4 thrombocytopenia and it was dose-limiting on both dosing schedules. A better schedule does not separate the two effects, because there is only one effect.
What did navitoclax actually do in mice?
Oral ABT-263 depleted senescent cells in irradiated and normally aged mice and rejuvenated haematopoietic and muscle stem cell compartments, and in a separate tau model it cleared senescent glial cells and prevented cognitive decline. Both results are in mice. Neither has a human counterpart.
Is clearing senescent cells always beneficial?
Not in animals. A 2023 Circulation paper reported that eliminating senescent cells, including with ABT-263, promoted the development and progression of pulmonary hypertension in mouse models. Harm signals of this kind are part of the record and are rarely quoted alongside the benefit signals.