For those men with a P53 mutation, It might be a good idea to start eating watercress
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Background
We reported previously that phenethyl isothiocyanate (PEITC, abundant in watercress), a dietary compound, can reactivate p53R175H mutant in vitro and in SK-BR-3 (p53R175H) breast xenograft model resulting in tumor inhibition. Because of the diversity of human cancers with p53 mutations, these findings raise important questions whether this mechanism operates in different cancer types with same or different p53 mutations. In this study, we investigated whether PEITC recuses mutant p53 in prostate cancer cells harboring different types of p53 mutants, structural and contact, in vitro and in vivo.
Methods
Cell proliferation, cell apoptosis and cell cycle arrest assays were performed to examine the effects of PEITC on prostate cancer cell lines with p53 mutation(s), wild-type p53, p53 null or normal prostate cells in vitro. Western blot analysis was used to monitor the expression levels of p53 protein, activation of ATM and upregulation of canonical p53 targets. Immunoprecipitation, subcellular protein fraction and qRT-PCR was performed to determine change in conformation and restoration of transactivation functions/ inhibition of gain-of-function (GOF) activities to p53 mutant(s). Mice xenograft models were established to evaluate the antitumor efficacy of PEITC and PEITC-induced reactivation of p53 mutant(s) in vivo. Immunohistochemistry of xenograft tumor tissues was performed to determine effects of PEITC on expression of Ki67 and mutant p53 in vivo.
Results
We demonstrated that PEITC inhibits the growth of prostate cancer cells with different “hotspot” p53 mutations (structural and contact), however, preferentially towards structural mutants. PEITC inhibits proliferation and induces apoptosis by rescuing mutant p53 in p53R248W contact (VCaP) and p53R175H structural (LAPC-4) mutant cells with differential potency. We further showed that PEITC inhibits the growth of DU145 cells that co-express p53P223L (structural) and p53V274F (contact) mutants by targeting p53P223L mutant selectively, but not p53V274F. The mutant p53 restored by PEITC induces apoptosis in DU145 cells by activating canonical p53 targets, delaying cells in G1 phase and phosphorylating ATM. Importantly, PEITC reactivated p53R175H and p53P223L/V274F mutants in LAPC-4 and DU145 prostate xenograft models, respectively, resulting in significant tumor inhibition.
Conclusions
In conclusion, this is the first report that via mutant p53 reactivation PEITC, a naturally-occurring compound derived from cruciferous vegetable, kills prostate cancer cells harboring different “hotspot” p53 mutants (structural and contact) to differential extents, but preferentially toward structural mutants. We also showed that PEITC inhibits the growth of prostate xenograft tumors harboring different p53 mutants and reactivates different p53 mutants in vivo. Previously, we have shown that PEITC reactivates mutant p53 in vitro as well as in a breast cancer SK-BR-3 xenograft mouse model, thus, inhibiting tumor growth. Collectively, these results suggest that the anticancer activity of PEITC is cancer type-independent, yet it acts in a p53 mutant type-dependent manner. These findings set stage for novel and practical personalized treatment / prevention strategies for human prostate cancers with p53 mutations. The results also support the potential of PEITC as a “basket trial” agent for human cancers harboring specific p53 mutant, irrespective of the organ-site-of-origin.
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