Pharmacological targeting of senescence with senolytics as a new therapeutic strategy for neurodegeneration

Cellular senescence is a state of permanent cell cycle arrest. Early in life, senescence has a physiological role in tumor suppression and wound healing. However, gradually, as these senescent cells accumulate over the lifespan of an organism, they contribute to inflammation and the progression of age-related diseases, including neurodegeneration. Targeting senescent cells using a class of drugs known as "senolytics" holds great promise for the management of Alzheimer's and Parkinson's disease. Already, several senolytic compounds have been shown to ameliorate cognitive deficits across several preclinical models of neurodegeneration. Most of these senolytics (e.g., dasatinib) are repurposed clinical or experimental anti-cancer drugs, which trigger apoptosis of senescent cells by interfering with pro-survival pathways. However, outside of their senolytic function, many first-generation senolytics also have other less appreciated neuroprotective effects such as potent antioxidant and anti-inflammatory activity. While these corollary properties of senolytics could be beneficial, in some cases, the effects may lead to negative dose-limiting toxicities, including thrombocytopenia. In this review, we discuss the various biological pathways targeted by the leading senolytic drugs, namely dasatinib, quercetin, fisetin, and navitoclax. We further evaluate the clinical transability of these compounds for neurodegeneration, assessing their adverse effects, pharmacokinetic properties, and chemical structure.