Pittsburgh, PA, United States
Pittsburgh, PA, United States

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Chen D.,UPCI Research Pavilion | Wei L.,UPCI Research Pavilion | Wei L.,University of Pittsburgh | Yu J.,UPCI Research Pavilion | And 2 more authors.
Clinical Cancer Research | Year: 2014

Purpose: Regorafenib, a multikinase inhibitor targeting the Ras/Raf/MEK/ERK pathway, has recently been approved for the treatment of metastatic colorectal cancer. However, the mechanisms of action of regorafenib in colorectal cancer cells have been unclear. We investigated how regorafenib suppresses colorectal cancer cell growth and potentiates effects of other chemotherapeutic drags. Experimental Design: We determined whether and how regorafenib induces the expression of PUMA, a p53 target and a critical mediator of apoptosis in colorectal cancer cells. We also investigated whether PUMA is necessary for the killing and chemosensitization effects of regorafenib in colorectal cancer cells. Furthermore, xenograft tumors were used to test if PUMA mediates the in vivo antitumor, antiangiogenic, and chemosensitization effects of regorafenib. Results: We found that regorafenib treatment induces PUMA in colorectal cancer cells irrespective of p53 status through the NF-κB pathway following ERK inhibition and glycogen synthase kinase 3β activation. Upregulation of PUMA is correlated with apoptosis induction in different colorectal cancer cell lines. PUMA is necessary for regorafenib-induced apoptosis in colorectal cancer cells. Chemosensitization by regorafenib is mediated by enhanced PUMA induction through different pathways. Furthermore, deficiency in PUMA abrogates the in vivo antitumor, antiangiogenic, and chemosensitization effects of regorafenib. Conclusions: Our results demonstrate a key role of PUMA in mediating the anticancer effects of regorafenib in colorectal cancer cells. They suggest that PUMA induction can be used as an indicator of regorafenib sensitivity, and also provide a rationale for manipulating the apoptotic machinery to improve the therapeutic efficacy of regorafenib and other targeted drags. © 2014 American Association for Cancer Research.

Andrade Filho P.A.,University of Pittsburgh | Ito D.,University of Pittsburgh | Deleo A.B.,University of Pittsburgh | Ferris R.L.,University of Pittsburgh | Ferris R.L.,UPCI Research Pavilion
Cancer Immunology, Immunotherapy | Year: 2010

The TP53 tumor suppressor gene contains a well-studied polymorphism that encodes either proline (P) or arginine (R) at codon 72, and over half of the world's population is homozygous for R at this codon. The wild-type sequence (wt) p53 peptide, p5365-73, has been identified as a CD8+ T cell-defined tumor antigen for use in broadly applicable cancer vaccines. However, depending on the TP53 codon 72 polymorphism of the recipient, the induced responses to the peptides incorporating R (p5372R) or P (p5372P) can be "self" or "non-self." Thus, we sought to determine which wt p5365-73 peptide should be used in wt p53-based cancer vaccines. Despite similar predicted HLA-A2-binding affinities, the p5372P peptide was more efficient than the p5372R peptide in HLA-A2 stabilization assays. In vitro stimulation (IVS) of CD8+ T cells obtained from healthy HLA-A2+ donors with these two peptides led to the generation of CD8+ T cell effectors in one-third of the samples tested, at a frequency similar to the responsiveness to other wt p53 peptides. Interestingly, regardless of their p53 codon 72 genotype, CD8+ T cells stimulated with either p5372P or p5372R peptide were cross-reactive against T2 cells pulsed with either peptide, as well as HLA-A2+ head and neck cancer (HNC) cell lines presenting p53 72P and/or p5372R peptides for T cell recognition. Therefore, the cross-reactivity of CD8+ T cells for the polymorphic wt p53 65-73 peptides, irrespective of their p53 codon 72 polymorphism, suggests that employing either peptide in wt p53-based vaccines can result in efficient targeting of this epitope. © 2010 Springer-Verlag.

Leibowitz M.S.,University of Pittsburgh | Andrade Filho P.A.,University of Pittsburgh | Ferrone S.,University of Pittsburgh | Ferris R.L.,University of Pittsburgh | Ferris R.L.,UPCI Research Pavilion
Cancer Immunology, Immunotherapy | Year: 2011

Squamous cell carcinoma of the head and neck (SCCHN) cells can escape recognition by tumor antigen (TA)-specific cytotoxic T lymphocytes (CTL) by downregulation of antigen processing machinery (APM) components, such as the transporter associated with antigen processing (TAP)-1/2 heterodimer. APM component upregulation by interferon gamma (IFN-γ) restores SCCHN cell recognition and susceptibility to lysis by CTL, but the mechanism underlying TAP1/2 downregulation in SCCHN cells is not known. Because IFN-γ activates signal transducer and activator of transcription (STAT)-1, we investigated phosphorylated (p)-STAT1 as a mediator of low basal TAP1/2 expression in SCCHN cells. SCCHN cells were found to express basal total STAT1 but low to undetectable levels of activated STAT1. The association of increased pSTAT1 levels and APM components likely reflects a cause-effect relationship, since STAT1 knockdown significantly reduced both IFN-γ-mediated APM component expression and TA-specific CTL recognition of IFN-γ-treated SCCHN cells. On the other hand, since oncogenic pSTAT3 is overexpressed in SCCHN cells and was found to heterodimerize with pSTAT1, we also tested whether pSTAT3 and pSTAT1:pSTAT3 heterodimers inhibited IFN-γ-induced STAT1 activation and APM component expression. First, STAT3 activation or depletion did not affect basal or IFN-γ-induced expression of pSTAT1 and APM components or recognition of SCCHN cells by TA-specific CTL. Second, pSTAT1:pSTAT3 heterodimers did not interfere with IFN-γ-induced STAT1 binding to the TAP1 promoter or APM protein expression. These findings demonstrate that APM component downregulation is regulated primarily by an IFN-γ-pSTAT1- mediated signaling pathway, independent of oncogenic STAT3 overexpression in SCCHN cells. © 2011 Springer-Verlag.

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