Mala Mani

A novel Aurora-A kinase inhibitor MLN8237 induces cytotoxicity and cell-cycle arrest in multiple myeloma

Aurora-A is a mitotic kinase that regulates mitotic spindle formation and segregation. In multiple myeloma (MM), high Aurora-A gene expression has been correlated with centrosome amplification and proliferation; thus, inhibition of Aurora-A in MM may prove to be therapeutically beneficial. Here we assess the in vitro and in vivo anti-MM activity of MLN8237, a small-molecule Aurora-A kinase inhibitor. Treatment of cultured MM cells with MLN8237 results in mitotic spindle abnormalities, mitotic accumulation, as well as inhibition of cell proliferation through apoptosis and senescence. In addition, MLN8237 up-regulates p53 and tumor suppressor genes p21 and p27. Combining MLN8237 with dexamethasone, doxorubicin, or bortezomib induces synergistic/additive anti-MM activity in vitro. In vivo anti-MM activity of MLN8237 was confirmed using a xenograft-murine model of human-MM. Tumor burden was significantly reduced (P = .007) and overall survival was significantly increased (P < .005) in animals treated with 30 mg/kg MLN8237 for 21 days. Induction of apoptosis and cell death by MLN8237 were confirmed in tumor cells excised from treated animals by TdT-mediated dUTP nick end labeling assay. MLN8237 is currently in phase 1 and phase 2 clinical trials in patients with advanced malignancies, and our preclinical results suggest that MLN8237 may be a promising novel targeted therapy in MM.

Targeting the β-catenin/TCF transcriptional complex in the treatment of multiple myeloma

Multiple myeloma (MM) is an invariably fatal form of cancer characterized by clonal proliferation of malignant plasma cells in the bone marrow. The canonical Wnt signaling pathway is activated in MM cells through constitutively active β-catenin, a messenger molecule relevant to growth, survival, and migration of MM cells. The identification of a number of small molecular compounds, such as PKF115–584, which disrupt the interaction of the transcriptionally active β-catenin/TCF protein complex, provides valuable new therapeutic tools to target an alternative pathway in MM independent of the proteasome. Here we evaluated the transcriptional, proteomic, signaling changes, and biological sequelae associated with the inhibition of Wnt signaling in MM by PKF115–584. The compound blocks expression of Wnt target genes and induces cytotoxicity in both patient MM cells and MM cell lines without a significant effect in normal plasma cells. In xenograft models of human MM, PKF115–584 inhibits tumor growth and prolongs survival. Taken together, these data demonstrate the efficacy of disrupting the β-catenin/TCF transcriptional complex to exploit tumor dependence on Wnt signaling as a therapeutic approach in the treatment of MM.

Targeted Disruption of the BCL9/β-Catenin Complex Inhibits Oncogenic Wnt Signaling

Blocking BCL9/β-catenin interaction with a stapled peptide inhibits Wnt-dependent transcription and suppresses growth and metastasis in colon cancer and multiple myeloma. Stapling Down Oncogenic Wnt Signaling The Wnt signaling pathway plays ancient and essential roles—it’s required for embryonic development in all animals and for key functions in adult tissues. Dysregulation of the pathway, however, underlies multiple human cancers. The development of Wnt pathway inhibitors has received considerable attention, but to be useful, such inhibitors must not disrupt vital pathway functions. To address this issue, Takada and colleagues now target an interaction between two Wnt pathway proteins, one of which (BCL9) is highly expressed in tumors but not in the cells of tumor origin. Wnt signaling ultimately increases nuclear levels of the transcriptional activator β-catenin, which promotes the expression of genes involved in cell survival and division. Certain coactivators, including BCL9, can form a complex with β-catenin and increase such gene expression. Takada et al. aimed to disrupt the BCL9–β-catenin interaction with a structured peptide mimicking the BCL9 binding interface. BCL9 binds to a site on β-catenin that differs from those of other binding partners; contact occurs via an α-helical domain of BCL9. The authors stabilized peptides representing that domain by using hydrocarbon stapling, in which chemical restraints reinforce the α-helical structure. These peptides, unlike the unmodified version, were taken up by cancer cells. Additionally, one stabilized α helix of BCL9 (SAH-BCL9) bound β-catenin, selectively dissociating BCL9/β-catenin complexes and inhibiting Wnt-dependent transcription. SAH-BCL9, but not a mutant control peptide, reduced the proliferation of Wnt-dependent colorectal cancer and multiple myeloma cell lines. (SAH-BCL9 did not affect cell lines that do not express BCL9 or depend on Wnt signaling.) Furthermore, in mouse xenograft models of Wnt-driven colon cancer and multiple myeloma, SAH-BCL9 suppressed tumor growth, invasion into nearby tissues, and metastasis, as well as local formation of new blood vessels, in an apparently nontoxic manner. Thus, targeting the BCL9–β-catenin interaction may represent a useful approach for treating Wnt-dependent cancers. Additional experiments will be required to further optimize the drug-like properties of SAH-BCL9. Deregulated Wnt/β-catenin signaling underlies the pathogenesis of a broad range of human cancers, yet the development of targeted therapies to disrupt the resulting aberrant transcription has proved difficult because the pathway comprises large protein interaction surfaces and regulates many homeostatic functions. Therefore, we have directed our efforts toward blocking the interaction of β-catenin with B cell lymphoma 9 (BCL9), a co-activator for β-catenin–mediated transcription that is highly expressed in tumors but not in the cells of origin. BCL9 drives β-catenin signaling through direct binding mediated by its α-helical homology domain 2. We developed a stabilized α helix of BCL9 (SAH-BCL9), which we show targets β-catenin, dissociates native β-catenin/BCL9 complexes, selectively suppresses Wnt transcription, and exhibits mechanism-based antitumor effects. SAH-BCL9 also suppresses tumor growth, angiogenesis, invasion, and metastasis in mouse xenograft models of Colo320 colorectal carcinoma and INA-6 multiple myeloma. By inhibiting the BCL9–β-catenin interaction and selectively suppressing oncogenic Wnt transcription, SAH-BCL9 may serve as a prototype therapeutic agent for cancers driven by deregulated Wnt signaling.

BCL9 Promotes Tumor Progression by Conferring Enhanced Proliferative, Metastatic, and Angiogenic Properties to Cancer Cells

Several components of the Wnt signaling cascade have been shown to function either as tumor suppressor proteins or as oncogenes in multiple human cancers, underscoring the relevance of this pathway in oncogenesis and the need for further investigation of Wnt signaling components as potential targets for cancer therapy. Here, using expression profiling analysis as well as in vitro and in vivo functional studies, we show that the Wnt pathway component BCL9 is a novel oncogene that is aberrantly expressed in human multiple myeloma as well as colon carcinoma. We show that BCL9 enhances beta-catenin-mediated transcriptional activity regardless of the mutational status of the Wnt signaling components and increases cell proliferation, migration, invasion, and the metastatic potential of tumor cells by promoting loss of epithelial and gain of mesenchymal-like phenotype. Most importantly, BCL9 knockdown significantly increased the survival of xenograft mouse models of cancer by reducing tumor load, metastasis, and host angiogenesis through down-regulation of c-Myc, cyclin D1, CD44, and vascular endothelial growth factor expression by tumor cells. Together, these findings suggest that deregulation of BCL9 is an important contributing factor to tumor progression. The pleiotropic roles of BCL9 reported in this study underscore its value as a drug target for therapeutic intervention in several malignancies associated with aberrant Wnt signaling.

Aurora kinase A is a target of Wnt/β-catenin involved in multiple myeloma disease progression

Multiple myeloma (MM) is a cancer of plasma cells with complex molecular characteristics that evolves from monoclonal gammopathy of undetermined significance, a highly prevalent premalignant condition. MM is the second most frequent hematologic cancer in the United States, and it remains incurable, thereby highlighting the need for new therapeutic approaches, particularly those targeting common molecular pathways involved in disease progression and maintenance, shared across different MM subtypes. Here we report that Wnt/beta-catenin is one such pathway. We document the involvement of beta-catenin in cell-cycle regulation, proliferation, and invasion contributing to enhanced proliferative and metastatic properties of MM. The pleiotropic effects of beta-catenin in MM correlate with its transcriptional function, and we demonstrate regulation of a novel target gene, Aurora kinase A, implicating beta-catenin in G2/M regulation. beta-catenin and Aurora kinase A are present in most MM but not in normal plasma cells and are expressed in a pattern that parallels progression from monoclonal gammopathy of undetermined significance to MM. Our data provide evidence for a novel functional link between beta-catenin and Aurora kinase A, underscoring a critical role of these pathways in MM disease progression.

β-catenin is dynamically stored and cleared in multiple myeloma by the proteasome–aggresome–autophagosome–lysosome pathway

β-catenin is dynamically stored and cleared in multiple myeloma by the proteasome–aggresome–autophagosome–lysosome pathway

TRIM13 (RFP2) downregulation decreases tumour cell growth in multiple myeloma through inhibition of NF Kappa B pathway and proteasome activity.

Multiple myeloma (MM) is an incurable neoplasm caused by proliferation of malignant plasma cells in the bone marrow (BM). MM is characterized frequently by a complete or partial deletion of chromosome 13q14, seen in more than 50% of patients at diagnosis. Within this deleted region the tripartite motif containing 13 (TRIM13, also termed RFP2) gene product has been proposed to be a tumour suppressor gene (TSG). Here, we show that low expression levels of TRIM13 in MM are associated with chromosome 13q deletion and poor clinical outcome. We present a functional analysis of TRIM13 using a loss‐of‐function approach, and demonstrate that TRIM13 downregulation decreases tumour cell survival as well as cell cycle progression and proliferation of MM cells. In addition, we provide evidence for the involvement of TRIM13 downregulation in inhibiting the NF kappa B pathway and the activity of the 20S proteasome. Although this data does not support a role of TRIM13 as a TSG, it substantiates important roles of TRIM13 in MM tumour survival and proliferation, underscoring its potential role as a novel target for therapeutic intervention.