Abstract 19: Targeting Delta133p53 isoform with small-molecule compounds to modulate cellular senescence

Cellular senescence (CS) and senescence-associated secretory phenotype (SASP) contribute to aging and age-related diseases. Mechanistically, the stress sensor p53 plays a pivotal role in the initiation and maintenance of CS. In humans, TP53 is expressed as 12 isoforms that contribute to the fine-tuning of p53 activity. Delta133p53 is generated from an alternative promoter located in intron 4 and is therefore devoid of both the transactivation domain and part of the DNA binding domain. Delta133p53 is predominantly located in the nucleus and is largely regulated at the protein level through chaperone-assisted selective autophagic degradation. Delta133p53 counteracts p53-mediated replicative CS and reduces the secretion of SASP cytokines. Delta133p53 is expressed in most normal tissues, but its expression is deregulated in age-associated diseases such as cancer, neurodegenerative diseases, and premature aging disorders. Delta133p53 is downregulated in exhausted CD8+ T cells, nearly senescent fibroblasts from Hutchinson-Gilford progeria syndrome patients, and astrocytes from irradiated brains and Alzheimer’s disease and amyotrophic lateral sclerosis patients. Delta133p53 overexpression extends the replicative lifespan in normal cells but does not cause immortalization or malignant transformation. Hence, delta133p53 appears to be a safe, novel therapeutic target to regulate CS. The present study aims at identifying small-molecule compounds that stabilize or prevent the degradation of delta133p53 protein and inhibit CS. To screen for activators of delta133p53, we developed two cell-based high-throughput screening (HTS) assays using an inducible vector for the expression of an eGFP-tag recombinant protein, and a luminescent peptide tag (HiBiT) appended onto the endogenous gene. The biologic activity of the fusion proteins was confirmed by evaluating the i) nuclear localization, ii) autophagic degradation during CS, and iii) ability to delay replicative CS. In collaboration with the National Center for Advancing Translational Sciences (NCATS), we screened a collection of ~8,350 compounds that includes all drugs that have been approved for use by the US Food and Drug Administration. Selected compounds were then screened in a secondary assay to evaluate their efficacy at reducing SASP cytokines secretion. Several candidate compounds are currently being investigated to confirm their effect on endogenous delta133p53 expression and CS. We have established robust cell-based HTS assays to screen for activators of delta133p53 and identified candidate compounds that could potentially develop into novel therapeutic leads to treat major life-threatening diseases. Citation Format: Delphine Lissa, Kyra Ungerleider, Izumi Horikawa, Patricia Dranchak, Erin Oliphan, Jessica Beck, Sebastien Jo, James Inglese, Curtis C. Harris. Targeting Delta133p53 isoform with small-molecule compounds to modulate cellular senescence [abstract]. In: Proceedings of the AACR Special Conference on Advancing Precision Medicine Drug Development: Incorporation of Real-World Data and Other Novel Strategies; Jan 9-12, 2020; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_1):Abstract nr 19.