Atypical PKCiota Contributes to Poor Prognosis Through Loss of Apical-basal Polarity and Cyclin E Overexpression in Ovarian Cancer

We show that atypical PKCι, which plays a critical role in the establishment and maintenance of epithelial cell polarity, is genomically amplified and overexpressed in serous epithelial ovarian cancers. Furthermore, PKCι protein is markedly increased or mislocalized in all serous ovarian cancers. An increased PKCι DNA copy number is associated with decreased progression-free survival in serous epithelial ovarian cancers. In a Drosophila in vivo epithelial tissue model, overexpression of persistently active atypical PKC results in defects in apical-basal polarity, increased Cyclin E protein expression, and increased proliferation. Similar to the Drosophila model, increased PKCι proteins levels are associated with increased Cyclin E protein expression and proliferation in ovarian cancers. In nonserous ovarian cancers, increased PKCι protein levels, particularly in the presence of Cyclin E, are associated with markedly decreased overall survival. These results implicate PKCι as a potential oncogene in ovarian cancer regulating epithelial cell polarity and proliferation and suggest that PKCι is a novel target for therapy

An integrative genomic and proteomic analysis of PIK3CA, PTEN and AKT mutations in breast cancer

Phosphatidylinositol-3-kinase (PI3K)/AKT pathway aberrations are common in cancer. By applying mass spectroscopy-based sequencing and reverse phase protein arrays to 547 human breast cancers and 41 cell lines, we determined the subtype specificity and signaling effects of PIK3CA, AKT and PTEN mutations, and the effects of PIK3CA mutations on responsiveness to PI3K inhibition in-vitro and on outcome after adjuvant tamoxifen. PIK3CA mutations were more common in hormone receptor positive (33.8%) and HER2-positive (24.6%) than in basal-like tumors (8.3%). AKT1 (1.4%) and PTEN (2.3%) mutations were restricted to hormone receptor-positive cancers with PTEN protein levels also being significantly lower in hormone receptor-positive cancers. Unlike AKT1 mutations, PIK3CA (39%) and PTEN (20%) mutations were more common in cell lines than tumors, suggesting a selection for these but not AKT1 mutations during adaptation to culture. PIK3CA mutations did not have a significant impact on outcome in 166 hormone receptor-positive breast cancer patients after adjuvant tamoxifen. PIK3CA mutations, in comparison with PTEN loss and AKT1 mutations, were associated with significantly less and indeed inconsistent activation of AKT and of downstream PI3K/AKT signaling in tumors and cell lines, and PTEN loss and PIK3CA mutation were frequently concordant, suggesting different contributions to pathophysiology. PTEN loss but not PIK3CA mutations rendered cells sensitive to growth inhibition by the PI3K inhibitor LY294002. Thus, PI3K pathway aberrations likely play a distinct role in the pathogenesis of different breast cancer subtypes. The specific aberration may have implications for the selection of PI3K-targeted therapies in hormone receptor-positive breast cancer

Characterization of a Naturally Occurring Breast Cancer Subset Enriched in Epithelial-to-Mesenchymal Transition and Stem Cell Characteristics

Metaplastic breast cancers (MBC) are aggressive, chemoresistant tumors characterized by lineage plasticity. To advance understanding of their pathogenesis and relatedness to other breast cancer subtypes, 28 MBCs were compared with common breast cancers using comparative genomic hybridization, transcriptional profiling, and reverse-phase protein arrays and by sequencing for common breast cancer mutations. MBCs showed unique DNA copy number aberrations compared with common breast cancers. PIK3CA mutations were detected in 9 of 19 MBCs (47.4%) versus 80 of 232 hormone receptor–positive cancers (34.5%; P = 0.32), 17 of 75 HER-2–positive samples (22.7%; P = 0.04), 20 of 240 basal-like cancers (8.3%; P < 0.0001), and 0 of 14 claudin-low tumors (P = 0.004). Of 7 phosphatidylinositol 3-kinase/AKT pathway phosphorylation sites, 6 were more highly phosphorylated in MBCs than in other breast tumor subtypes. The majority of MBCs displayed mRNA profiles different from those of the most common, including basal-like cancers. By transcriptional profiling, MBCs and the recently identified claudin-low breast cancer subset constitute related receptor-negative subgroups characterized by low expression of GATA3-regulated genes and of genes responsible for cell-cell adhesion with enrichment for markers linked to stem cell function and epithelial-to-mesenchymal transition (EMT). In contrast to other breast cancers, claudin-low tumors and most MBCs showed a significant similarity to a “tumorigenic” signature defined using CD44+/CD24− breast tumor–initiating stem cell–like cells. MBCs and claudin-low tumors are thus enriched in EMT and stem cell–like features, and may arise from an earlier, more chemoresistant breast epithelial precursor than basal-like or luminal cancers. PIK3CA mutations, EMT, and stem cell-like characteristics likely contribute to the poor outcomes of MBC and suggest novel therapeutic targets

Characterization of a naturally occurring breast cancer subset enriched in epithelial-to-mesenchymal transition and stem cell characteristics

Metaplastic breast cancers (MBC) are aggressive, chemoresistant tumors characterized by lineage plasticity. To advance understanding of their pathogenesis and relatedness to other breast cancer subtypes, 28 MBCs were compared with common breast cancers using comparative genomic hybridization, transcriptional profiling, and reverse-phase protein arrays and by sequencing for common breast cancer mutations. MBCs showed unique DNA copy number aberrations compared with common breast cancers. PIK3CA mutations were detected in 9 of 19 MBCs (47.4%) versus 80 of 232 hormone receptor–positive cancers (34.5%; P = 0.32), 17 of 75 HER-2–positive samples (22.7%; P = 0.04), 20 of 240 basal-like cancers (8.3%; P less than 0.0001), and 0 of 14 claudin-low tumors (P = 0.004). Of 7 phosphatidylinositol 3-kinase/AKT pathway phosphorylation sites, 6 were more highly phosphorylated in MBCs than in other breast tumor subtypes. The majority of MBCs displayed mRNA profiles different from those of the most common, including basal-like cancers. By transcriptional profiling, MBCs and the recently identified claudin-low breast cancer subset constitute related receptor-negative subgroups characterized by low expression of GATA3-regulated genes and of genes responsible for cell-cell adhesion with enrichment for markers linked to stem cell function and epithelial-to-mesenchymal transition (EMT). In contrast to other breast cancers, claudin-low tumors and most MBCs showed a significant similarity to a “tumorigenic” signature defined using CD44+/CD24− breast tumor–initiating stem cell–like cells. MBCs and claudin-low tumors are thus enriched in EMT and stem cell–like features, and may arise from an earlier, more chemoresistant breast epithelial precursor than basal-like or luminal cancers. PIK3CA mutations, EMT, and stem cell-like characteristics likely contribute to the poor outcomes of MBC and suggest novel therapeutic targets. [Cancer Res 2009;69(10):4116–24

Synergistic induction of apoptosis by the Bcl-2 inhibitor ABT-737 and imatinib mesylate in gastrointestinal stromal tumor cells

Background: Although imatinib mesylate has revolutionized the management of patients with gastrointestinal stromal tumor (GIST), resistance and progression almost inevitably develop with long-term monotherapy. To enhance imatinib-induced cytotoxicity and overcome imatinib-resistance in GIST cells, we examined the antitumor effects of the pro-apoptotic Bcl-2/Bcl-x L inhibitor ABT-737, alone and in combination with imatinib. Methods: We treated imatinib-sensitive, GIST-T1 and GIST882, and imatinib-resistant cells with ABT-737 alone and with imatinib. We determined the anti-proliferative and apoptotic effects by cell viability assay, flow cytometric apoptosis and cell cycle analysis, immunoblotting, and nuclear morphology. Synergism was determined by isobologram analysis. Results: The IC 50 of single-agent ABT-737 at 72 h was 10 μM in imatinib-sensitive GIST-T1 and GIST882 cells, and 1 μM in imatinib-resistant GIST48IM cells. ABT-737 and imatinib combined synergistically in a time- and dose-dependent manner to inhibit the proliferation and induce apoptosis of all GIST cells, as evidenced by cell viability and apoptosis assays, caspase activation, PARP cleavage, and morphologic changes. Isobologram analyses revealed strongly synergistic drug interactions, with combination indices <0.5 for most ABT-737/imatinib combinations. Thus, clinically relevant in vitro concentrations of ABT-737 have single-agent antitumor activity and are synergistic in combination with imatinib. Conclusion: We provide the first preclinical evidence that Bcl-2/Bcl-x L inhibition with ABT-737 synergistically enhances imatinib-induced cytotoxicity via apoptosis, and that direct engagement of apoptotic cell death may be an effective approach to circumvent imatinib-resistance in GIST