P2‐177: TARGETING DELTA133P53 ISOFORM WITH SMALL MOLECULE COMPOUNDS TOWARDS THE TREATMENT OF CELLULAR SENESCENCE‐ASSOCIATED DISEASES

Abstract

Cellular senescence (CS) is an important contributor to aging and age-related diseases such as Alzheimer's Disease (AD). Senescent cells are characterized by a durable cell cycle arrest and the acquisition of a senescence-associated secretory phenotype (SASP). Clearance of senescent astrocytes and microglia in an AD mouse model prevented tau-dependent pathology and cognitive decline suggesting pharmacological agents targeting CS might provide novel therapeutic approaches for AD. The tumor suppressor gene p53 plays a pivotal role in the initiation and maintenance of CS. Upregulation of p53 induces tau phosphorylation and inhibition of p53 has been shown to attenuate amyloid-beta mediated neuronal death. Our lab has shown delta133p53 regulates replicative CS by acting as a dominant-negative to full-length p53. We observe high levels of delta133p53 in proliferative cells, while conversely senescent cells, such as astrocytes from AD patients, have decreased levels of the isoform. Overexpression of delta133p53 restores the replicative capacity of near-senescent astrocytes and decreases the secretion of several SASP factors including interleukin 6 (IL-6). Our study aims at identifying small molecule compounds that increase delta133p53 expression to counteract CS. We developed a cell-based high-throughput screening assay using cell lines generated to express a translational reporter system, where the delta133p53 cDNA sequence is cloned in frame with the GFP. The biological activity of the fusion protein was confirmed by evaluating its nuclear localization, autophagic degradation and ability to inhibit CS. In collaboration with the National Center for Advancing Translational Sciences (NCATS), we screened two large chemical libraries consisting of approximately 8,500 compounds. Following the fluorescent-based primary screening assay, 95 compounds were screened in a secondary assay to evaluate their efficacy at reducing astrocyte secretion of IL-6 following irradiation. We are currently confirming the activity of 13 compounds on endogenous delta133p53 levels. We will further validate the candidate compounds by assessing their effect on DNA damage, cell proliferation, SASP and CS. Additionally, we plan to screen the Genesis Chemical Library (95,744 compounds), that contains novel chemotypes which have the potential to form new drugs. This first drug discovery program to target delta133p53 could potentially lead to the development of a first-in-class drug.