UBX1325

UBX1325 (foselutoclax) is a soluble phosphate prodrug that is cleaved rapidly in ocular tissues by ubiquitous phosphatases to yield the active parent molecule UBX0601, a potent inhibitor of the B-cell lymphoma-extra large (Bcl-xL) anti-apoptotic protein and related Bcl-2 family members. The compound was developed by Unity Biotechnology as the first senolytic therapeutic candidate designed for intravitreal administration in ophthalmologic indications, principally diabetic macular edema (DME), diabetic retinopathy (DR), and neovascular (wet) age-related macular degeneration (AMD). The senolytic mechanism is fundamentally distinct from the anti-vascular endothelial growth factor (anti-VEGF) agents that constitute the current standard of care for these conditions: rather than neutralizing a single cytokine to reduce vascular permeability, UBX1325 selectively induces apoptosis in senescent retinal vascular endothelial cells that have accumulated in areas of disease activity, thereby removing a persistent source of pro-inflammatory and pro-permeability signaling and potentially modifying the underlying disease process rather than managing its downstream consequences.

The compound originated from a 2016 strategic licensing arrangement between Unity Biotechnology and Ascentage Pharma, under which Unity screened Ascentage's Bcl-2 family compound library for candidates with senolytic activity against age-related disease targets. The selected molecule, BM-962, was optimized as a phosphate prodrug (UBX1325/foselutoclax) to improve aqueous solubility for ophthalmic formulation. Preclinical studies demonstrated that intravitreal administration of UBX1325 in oxygen-induced retinopathy and streptozotocin-induced diabetic retinopathy mouse models selectively eliminated senescent cells from diseased retinal vasculature while sparing healthy tissue, reduced retinal vascular permeability, and improved retinal function as measured by electroretinography. A Phase 1 single ascending dose study in 12 patients with advanced DME and wet AMD (NCT04537884) established safety and tolerability at doses up to 10 micrograms, with no dose-limiting toxicities, no treatment-related serious adverse events, and encouraging signals of visual acuity improvement and retinal thickness reduction persisting through 12 weeks. The Phase 2 BEHOLD trial (NCT04857996) enrolled 65 patients with DME who had suboptimal response to prior anti-VEGF therapy and randomized them to a single intravitreal injection of 10 micrograms UBX1325 or sham; at 48 weeks, UBX1325-treated patients gained a mean of 6.2 ETDRS letters from baseline (5.6 letters over sham), with 53 percent of treated patients requiring no anti-VEGF rescue through the full study duration compared to 22 percent in the sham arm. These results, published in Nature Medicine in 2024, represent the first clinical demonstration of senolytic therapy in ophthalmology. The Phase 2 ENVISION trial (NCT05275205) in wet AMD did not meet its primary non-inferiority endpoint versus aflibercept at 24 weeks, though 40 percent of UBX1325-treated patients required no anti-VEGF rescue through 48 weeks. The Phase 2b ASPIRE trial (NCT06011798) evaluated repeat dosing of UBX1325 every 8 weeks versus aflibercept every 8 weeks in 52 DME patients; at 36 weeks, UBX1325 produced mean gains of 5.5 ETDRS letters, achieving non-inferiority to aflibercept at most time points except the pre-specified primary endpoint (average of weeks 20 and 24), with superior performance in a pre-specified subgroup of patients with baseline central subfield thickness below 400 microns.

This monograph reviews the chemistry, prodrug design, and molecular pharmacology of UBX1325; the senolytic mechanism of action through Bcl-xL inhibition; the preclinical pharmacology in retinal disease models; the complete clinical evidence base across Phase 1, BEHOLD, ENVISION, and ASPIRE trials; reconstitution and handling considerations for intravitreal formulation; stack interactions with anti-VEGF agents and corticosteroids; the adverse-event and safety profile; and a structured comparative assessment of five alternative approaches to DME therapy (aflibercept, faricimab, ranibizumab, navitoclax, and dasatinib plus quercetin) against UBX1325 on five competency standards. The compound is not approved by any regulatory authority as of the monograph revision date. Unity Biotechnology is advancing development toward registrational trials.