Hypothesis

Combining low‑dose HDAC inhibition with transient OSKM expression produces a synergistic senolytic effect that clears senescent cells while limiting tumorigenic risk.

Mechanistic Rationale

Senolytics such as quisinostat (an HDAC inhibitor) already reduce epigenetic age by restoring heterochromatin marks1. Transient OSKM reprogramming opens chromatin during the TRA‑1‑60+ window (days 7‑11) and lowers epigenetic age proportionally2. We propose that a brief HDAC inhibitor pulse sensitizes chromatin to OSKM‑driven remodeling, allowing lower OSKM doses and shorter exposure to achieve the same age‑reset. This dual action should (1) amplify removal of senescent cells via heightened BCL2/MCL1/TP53 stress, and (2) prevent accumulation of partially reprogrammed cells that could drive aneuploidy or SASP‑mediated inflammation3.

Testable Predictions

1. In human fibroblast cultures induced to senesce by irradiation, treatment with quisinostat (0.5 µM) plus a doxycycline‑inducible OSKM pulse (24 h) will increase senescent cell clearance to >70 % (vs ~45 % for quisinostat alone or OSKM alone) measured by SA‑β‑gal and p16 loss.
2. The combined treatment will reduce epigenetic age (Horvath clock) by ≥2.0 years after 3 days, exceeding the ~1.2‑year drop seen with either monotherapy.
3. Tumoroid formation in soft‑agar assays will remain at baseline levels, indicating no increase in tumorigenic potential compared with OSKM alone.
4. RNA‑seq will show synergistic up‑regulation of pro‑apoptotic BAX and down‑regulation of SASP cytokines (IL6, IL8) relative to single agents.

Experimental Design

• Cell model: IMR‑90 fibroblasts rendered senescent by 10 Gy γ‑irradiation; confirm SA‑β‑gal positivity >80 %.
• Treatment groups: (a) vehicle, (b) quisinostat 0.5 µM, (c) OSKM inducible (24 h doxycycline), (d) quisinostat + OSKM, (e) high‑dose OSKM (48 h) as tumorigenicity control.
• Readouts: flow cytometry for p16/p21, SA‑β‑gal fluorescence, Horvath methylation array, colony formation assay, cytokine multiplex, apoptosis (caspase‑3/7).
• Analysis: two‑way ANOVA with post‑hoc Tukey; significance set at p<0.05.

If predictions hold, the data would support a mechanistic synergy where HDAC inhibition primes chromatin for OSKM, enabling senolytic clearance at lower reprogramming stress and mitigating cancer risk—a directly falsifiable claim that can be validated in vitro before moving to organoid or murine models.