ReACp53

Backgrounds:p53 is a tumor suppressor that prevents cancer onset and progression, and mutations in the p53 gene cause loss of the tumor suppressor function of the protein. The mutant p53 protein in tumor cells can form aggregates which contribute to the dominant-negative effect over the wild-type p53 protein, causing loss of p53 tumor suppression or gain of novel oncogenic functions. Mutations in p53 have been implicated in the pathogenesis of primary prostate cancer (PCa), and are often detected in recurrent and metastatic disease. Thus, targeting mutant p53 may constitute an alternative therapeutic strategy for advanced PCa for which there are no other viable options.Methods:In this study, we used immunoprecipitation, immunofluorescence, clonogenic survival, and cell proliferation assays, flow cytometric analysis and in vivo xenograft to investigate the biological effects of ReACp53, a cell-permeable peptide inhibitor of p53 aggregation, on mutant p53-carrying PCa cells.Results:Our results show that ReACp53 targets amyloid aggregates of mutant p53 protein and restores the p53 nuclear function as transcriptional factor, induces mitochondrial cell death and reduces DNA synthesis of mutant p53-carrying PCa cells; ReACp53 also inhibits xenograft tumor growth in vivo.Conclusions:The data presented here suggest a therapeutic potential of targeting mutant p53 protein in advanced PCa setting, which has a clinical impact for aggressive PCa with transforming how such tumors are managed.

Half of all human cancers lose p53 function by missense mutations, with an unknown fraction of these containing p53 in a self-aggregated amyloid-like state. Here we show that a cell-penetrating peptide, ReACp53, designed to inhibit p53 amyloid formation, rescues p53 function in cancer cell lines and in organoids derived from high-grade serous ovarian carcinomas (HGSOC), an aggressive cancer characterized by ubiquitous p53 mutations. Rescued p53 behaves similarly to its wild-type counterpart in regulating target genes, reducing cell proliferation and increasing cell death. Intraperitoneal administration decreases tumor proliferation and shrinks xenografts in vivo. Our data show the effectiveness of targeting a specific aggregation defect of p53 and its potential applicability to HGSOCs.

Mutation of the TP53 gene represents a prevalent genetic alteration in human cancers, and a subset of p53 mutants may form amyloid-like aggregates that contribute to the gain of oncogenic functions (GOFs) and chemoresistance. Here we identify the pathways that may mediate the aggregation-associated GOF by using combined proteomic analysis and genome-wide recruitment profiling. Mass spectrometry revealed activation of unfolded protein response (UPR) pathway and upregulation of endoplasmic reticulum protein 29 (ERp29) inR282WTP53-expressing cells that were exposed to cisplatin stress. Chromatin immunoprecipitation sequencing identified a significant 'CCCASS' binding motif of Arg282Trp, which is present in the promoter region of ERP29 gene. The mutant p53 upregulated ERP29 mRNA and protein expression levels, whereas targeting ERP29 by specific small interfering RNAs suppressed the chemoresistant effect of Arg282Trp. The anti-aggregation peptide ReACp53 significantly decreased ERP29 expression and suppressed the chemoresistant effect. These findings highlight a role of ERP29 in the acquired chemoresistance of cancer cells expressing the aggregating p53 mutant Arg282Trp. Our results also suggest that ERP29-mediated GOF can be targeted by the anti-aggregation peptide ReACp53.