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    Killing of Resistant Cancer Cells with Low Bak by a Combination of an Anti-mesothelin Immunotoxin and a TRAIL Receptor 2 Agonist Antibody.

    Clin Cancer Res. 2011 Aug 3;

    Authors: Du X, Xiang L, Mackall CL, Pastan I

    PURPOSE: Many solid tumors express cell surface mesothelin making them attractive targets for antibody-based therapies of cancer. SS1P (anti-mesothelin(Fv)PE38) is a recombinant immunotoxin (RIT) that has potent cytotoxic activity on several cancer cell lines and clinical activity in mesothelioma patients. Pancreatic cancers express mesothelin and are known to be resistant to most chemotherapeutic agents. The goal of the current study is to treat pancreatic cancer with RIT by targeting mesothelin. EXPERIMENTAL DESIGN: We measured the cytotoxic activity of an anti-mesothelin immunotoxin on pancreatic cancer cells. We also measured the levels of several pro- and anti-apoptotic proteins, as well as the ability of TRAIL or the anti-TRAIL receptor 2 agonist antibody (HGS-ETR2) to kill pancreatic cells and the cytotoxic activity of the two agents together in cell culture and against tumors in mice.RESULTS: In two pancreatic cancer cell lines immunotoxin treatment inhibited protein synthesis, but did not produce significant cell death. The resistant lines had low levels of the pro-apoptotic protein Bak. Increasing Bak expression enhanced the sensitivity to immunotoxins, while Bak knockdown diminished it. We also found that combining immunotoxin with TRAIL or HGS-ETR2 caused synergistic cell death, and together triggered caspase-8 recruitment and activation, Bid cleavage and Bax activation. Combining SS1P with HGS-ETR2 also acted synergistically to decrease tumor burden in a mouse model. CONCLUSIONS: Our data show that low Bak can cause cancer cells to be resistant to immunotoxin treatment, and that combining immunotoxin with TRAIL or a TRAIL agonist antibody can overcome resistance.

    PMID: 21813632 [PubMed - as supplied by publisher]

    www.ncbi.nlm.nih.gov


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    4T1 murine mammary carcinoma cells implanted in syngeneic Balb/c mice are increasingly being used in metastasis research, with some groups using this model to study tumor-induced accumulation of bone marrow–derived cells in metastatic target organs. Bone marrow–derived cells (including CD11b+Gr-1+ myelomonocytic cells) are thought to modify the local lung microenvironment to facilitate subsequent colonization by metastatic tumor cells. While quantification of metastatic 4T1 tumor cells in various tissues can be done using ex vivo colony-forming assays, detection of metastatic 4T1 cells is often facilitated by expressing fluorescent proteins in the tumor cells prior to implantation. We found that Balb/c mice mount a potent immune response against 4T1 cells expressing green fluorescent protein (GFP) that includes the generation of anti-GFP antibodies in the circulation. Importantly, the number of bone marrow–derived CD11b+Gr-1+ cells and metastatic tumor cells that accumulate in the lungs is significantly decreased in mice implanted with 4T1 cells expressing GFP compared with mice bearing wild-type 4T1 tumors. Taken together, our data caution against the use of GFP-expressing tumor cells in the Balb/c mouse strain, particularly for studying the influence of immunomodulatory cells on tumor cell metastasis. Cancer Res; 71(14); 5050–1. ©2011 AACR. cancerres.aacrjournals.org


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    Autologous peripheral blood progenitor cell (PBPC) transplantation is the treatment of choice for selected myeloma patients. However, tumor cells contaminating the apheresis product are a potential source of relapse. Here we report a sequential purging strategy targeting mature and immature clonogenic myeloma cell populations in the autograft. Thawed PBPC products of myeloma patients were treated with rituximab to kill CD138?20+ B cells (highly clonogenic immature cells), and bortezomib to target CD138+ cells (normal and differentiated myeloma plasma cells), followed by coculture with allogeneic mesenchymal stem cells (MSC) from normal donors. After 7 days of coculture, nonadherent cells were removed and cultured in the absence of MSC for an additional 7 days. Then, efficacy of purging (removal of CD138?20+ and CD138+ cells) was assessed by flow cytometry and PCR. We used our ex vivo purging strategy to treat frozen aphereses from 16 patients. CD138+ and CD138?20+(19+) cells present in the initial products were depleted more than 3 and 4 logs, respectively based on 106 flow-acquisition events, and to levels below the limit of detection by PCR. In contrast, total nucleated cell (TNC), CD34+ cell, and colony-forming cell numbers were increased by approximately 12 to 20, 8-, and 23-fold, respectively. Overall, ex vivo treatment of apheresis products with rituximab, bortezomib, and coculture with normal donor MSC depleted mature and immature myeloma cells from clinical aphereses while expanding the normal hematopoietic progenitor cell compartment. Cancer Res; 71(14); 5040–9. ©2011 AACR. cancerres.aacrjournals.org


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    Pluripotent stem cells, both human embryonic stem cells (hESC) and human-induced pluripotent stem cells (hiPSC), can give rise to multiple cell types and hence have tremendous potential for regenerative therapies. However, the tumorigenic potential of these cells remains a great concern, as reflected in the formation of teratomas by transplanted pluripotent cells. In clinical practice, most pluripotent cells will be differentiated into useful therapeutic cell types such as neuronal, cardiac, or endothelial cells prior to human transplantation, drastically reducing their tumorigenic potential. Our work investigated the extent to which these differentiated stem cell derivatives are truly devoid of oncogenic potential. In this study, we analyzed the gene expression patterns from three sets of hiPSC- and hESC-derivatives and the corresponding primary cells, and compared their transcriptomes with those of five different types of cancer. Our analysis revealed a significant gene expression overlap of the hiPSC- and hESC-derivatives with cancer, whereas the corresponding primary cells showed minimum overlap. Real-time quantitative PCR analysis of a set of cancer-related genes (selected on the basis of rigorous functional and pathway analyses) confirmed our results. Overall, our findings suggested that pluripotent stem cell derivatives may still bear oncogenic properties even after differentiation, and additional stringent functional assays to purify these cells should be done before they can be used for regenerative therapy. Cancer Res; 71(14); 5030–9. ©2011 AACR. cancerres.aacrjournals.org


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    The STAT3 transcription factor is an important regulator of stem cell self-renewal, cancer cell survival, and inflammation. In the pancreas, STAT3 is dispensable for normal development, whereas the majority of pancreatic ductal adenocarcinomas (PDAC) show constitutive activation of STAT3, suggesting its potential as a therapeutic target in this cancer. Here, we sought to define the mechanisms of STAT3 activation and its functional importance in PDAC pathogenesis. Large-scale screening of cancer cell lines with a JAK2 inhibitor that blocks STAT3 function revealed a more than 30-fold range in sensitivity in PDAC, and showed a close correlation of sensitivity with levels of tyrosine-phosphorylated STAT3 and of the gp130 receptor, an upstream signaling component. Correspondingly, upregulation of the IL6/LIF-gp130 pathway accounted for the strong STAT3 activation in PDAC subsets. To define functions of STAT3 in vivo, we developed mouse models that test the impact of conditional inactivation of STAT3 in KRAS-driven PDAC. We showed that STAT3 is required for the development of the earliest premalignant pancreatic lesions, acinar-to-ductal metaplasia (ADM) and pancreatic intraepithelial neoplasia (PanIN). Moreover, acute STAT3 inactivation blocked PDAC initiation in a second in vivo model. Our results show that STAT3 has critical roles throughout the course of PDAC pathogenesis, supporting the development of therapeutic approaches targeting this pathway. Moreover, our work suggests that gp130 and phospho-STAT3 expression may be effective biomarkers for predicting response to JAK2 inhibitors. Cancer Res; 71(14); 5020–9. ©2011 AACR. cancerres.aacrjournals.org


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