Senomorphic preconditioning with rapamycin enhances senolytic efficacy via lysosomal priming and reduces off-target toxicity

Background

The convergence of senolytic and metabolic interventions has shown synergistic lifespan extension in mice, exemplified by rapamycin plus acarbose achieving up to 36.6% median lifespan increase [2]. However, clinical translation is hampered by off-target toxicity of potent senolytics such as navitoclax, which causes thrombocytopenia [1]. Emerging strategies use senomorphics to suppress the senescence-associated secretory phenotype (SASP) before senolytic exposure to reduce inflammatory toxicity [1].

Hypothesis

We propose that short-term pretreatment with rapamycin acts as a senomorphic that remodels lysosomal function and increases the expression of specific endocytic receptors on senescent cells, thereby enhancing the uptake and cytotoxic efficiency of subsequently administered senolytics while permitting lower drug doses and reducing off-target effects.

Testable Predictions

1. In vitro, human fibroblasts rendered senescent by irradiation will show increased lysosomal activity (measured by LysoTracker fluorescence) and upregulated expression of the mannose-6-phosphate receptor (M6PR) after 24 h rapamycin treatment (10 nM).
2. Co‑culture of these pre‑treated senescent cells with navitoclax will result in a ≥2‑fold increase in Annexin V‑positive cells compared with navitoclax alone, an effect blocked by chloroquine pretreatment.
3. In aged mice, intermittent rapamycin (5 mg/kg, i.p., 3 days/week) administered 48 h prior to a sub‑therapeutic dose of navitoclax (25 mg/kg) will achieve senescent cell clearance comparable to full‑dose navitoclax (50 mg/kg) in liver and adipose tissue, as measured by p16^Ink4a^ immunostaining, without causing a significant drop in platelet count (>15 % reduction).
4. Transcriptomic analysis of sorted senescent cells from rapamycin‑pretreated mice will reveal enrichment of genes involved in endocytosis and lysosomal acidification, correlating with improved senolytic efficacy.

Mechanistic Rationale

Rapamycin inhibits mTORC1, leading to TFEB nuclear translocation and a lysosomal biogenesis program. Senescent cells already exhibit altered lysosomal metabolism; amplifying this pathway may increase their propensity to sequester and activate pro‑drug senolytics that rely on lysosomal trapping. Additionally, mTOR inhibition reduces platelet production, potentially offsetting navitoclax‑induced thrombocytopenia when dosing is staggered. This sequential senomorphic‑senolytic approach leverages metabolic priming to widen the therapeutic window of senolysis, addressing a key barrier in clinical translation.