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Background: We reported previously that phenethyl isothiocyanate (PEITC), 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. Conclusion: Our studies provide the first evidence that PEITC's anti-cancer activity is cancer cell type-independent, but p53 mutant-type dependent. [ABSTRACT FROM AUTHOR]

Summary: Most developmentally programmed cell death in metazoans is mediated by caspases. During Drosophila metamorphosis, obsolete tissues, including the midgut and salivary glands, are removed by programmed cell death . The initiator caspase Dronc and its activator Ark are required for the death of salivary glands, but not for midgut removal . In addition to caspases, complete removal of salivary glands requires autophagy . However, the contribution of autophagy to midgut cell death has not been explored. Examination of combined mutants of the main initiator and effector caspases revealed that the canonical apoptotic pathway is not required for midgut cell death. Further analyses revealed that the caspase Decay is responsible for most of the caspase activity in dying midguts, yet inhibition of this activity has no effect on midgut removal. By contrast, midgut degradation was severely delayed by inhibition of autophagy, and this occurred without a decrease in caspase activity. Surprisingly, the combined inhibition of caspases and autophagy did not result in an additional delay in midgut removal. Together, our results indicate that autophagy, not caspases, is essential for midgut programmed cell death, providing the first in vivo evidence of caspase-independent programmed cell death that requires autophagy despite the presence of high caspase activity. [Copyright &y& Elsevier]