Abstract 6131: Extracellular vesicles containing p53 of xenogeneic origin as a therapeutic strategy
Authors: Tendler Alex , Shalev Gil , Kasuto Harel , Volokh Lana , Lin Albina , Tendler Yevgeny , Sidransky David 
Published: April 2023

Abstract
Introduction: It was recently discovered that extracellular vesicles (EVs) containing p53 are actively secreted by corneal epithelial cells into the corneal extracellular space and tear film. These EVs are re-captured by neighboring epithelial cells and play a pivotal role in local anti-cancer defense because the corneal epithelium (As an immuno-privileged tissue site), lacks classic critical pathways of innate and adaptive immunity. We took advantage of the local corneal mechanism of anti-cancer defense to develop a novel therapeutic approach based on EVs delivery of WT p53 protein to tumors. In order to avoid the inhibition of newly delivered WT p53 through the known dominant negative effect of mutant p53, we utilized p53 containing EVs produced by corneal epithelial cells of chicken origin. The C-terminal domain responsible for oligomerization is sufficiently diverse between chicken and human p53 to preventing suppression of the delivered WT p53.
Methods: The functional consequences of chicken tissue derived p53 containing EVs in human malignancies was assessed in vitro in variety of p53 mutated panels through the Annexin/PI potency assay, cell cycle arrest assessment, cell counting and IncuCyte. Confirmation of the p53 driven mechanism of action (MoA) was achieved using RT-PCR of p53 downstream responsive genes such as p21, YPEL3, BAX and PIDD. In vivo testing was performed using the Colo320 DM human colon cancer xenograft model in nude mice.
Results: Following treatment with avian p53 containing EVs multiple tested human malignant cell lines exhibited cell cycle arrest and/or massive apoptosis within 24h. Transcription levels of the YPEL3 and BAX genes were increased significantly in human LN18 cells (p53 mut GBM) post treatment. Moreover transcription levels of the YPEL3 and PIDD genes were increased significantly in human HCT116 p53wt cells (p53 WT colorectal carcinoma) while BAX and PIDD genes are increased significantly in human HCT116 p53ko cells (p53 KO colorectal carcinoma) after treatment. In vivo results showed significant inhibition of growth in Colo320DM xenografts with further histopathological findings of reduced proliferation (Ki-67) and increased apoptosis (TUNEL) in treated group.
Conclusions: Upregulation of key p53 responsive genes is direct evidence of p53-driven response in human cancer cells triggered by p53-containing avian EVs. Further functional evidence of activity was observed through documented apoptosis and cell cycle arrest in multiple cell lines and in-vivo model. Additional relevant in-vivo models are being treated and assessed for tumor growth inhibition and functional p53 downstream activity. These preliminary preclinical results show promise for this novel therapeutic concept in targeting a hallmark genetic alteration that poses a major challenge in human cancer therapy.
Citation Format: Alex Tendler, Gil Shalev, Harel Kasuto, Lana Volokh, Albina Lin, Yevgeny Tendler, David Sidransky. Extracellular vesicles containing p53 of xenogeneic origin as a therapeutic strategy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6131.