Cooperative Disengagement of Fas and Intercellular Adhesion Molecule-1 Function in Neoplastic Cells Confers Enhanced Colonization Efficiency

High mobility group box 1 antagonist limits metastatic seeding in the lungs via reduction of cell-cell adhesion

Metastatic spread is the leading cause for cancer-related mortality, with the lungs being a major site for metastatic seeding. Available therapies for patients with metastatic disease are extremely limited. Therefore, there is a desperate need for new strategies to prevent or limit metastatic dissemination and treat existing metastases. The metastatic cascade is highly complex and is affected by multiple factors related to both tumor cells themselves and the microenvironment in the future site of metastasis. We hypothesized that modifying the lung microenvironment by blocking central ubiquitous signals may affect metastatic seeding in the lungs. Given the high basal levels of the Receptor for Advanced Glycation End products (RAGE) in the pulmonary tissue, and its pro-inflammatory properties, we investigated the consequences of interfering with its ligand; High Mobility Group Box 1 (HMGB1). To this end, we tested the effect of Carbenoxolone, an HMGB1 antagonist, on primary tumor growth and metastatic progression in several murine tumor models. We show that antagonizing HMGB1 prevents the adhesion and colonization of cancer cells in the lungs through the reduction of their adhesion and cell–cell interaction both in vitro and in vivo. We demonstrated that these activities are mediated by downregulation of the adhesion molecule Intercellular Adhesion Molecule 1 (ICAM1) and ultimately result in reduced metastatic burden. Carbenoxolone decreases significantly lung metastases formation and can be used potentially as prophylactic therapy for metastatic diseases.

Cyclin Dependent Kinase 9 Inhibitors for Cancer Therapy

Cyclin dependent kinase (CDK) inhibitors have been the topic of intense research for nearly 2 decades due to their widely varied and critical functions within the cell. Recently CDK9 has emerged as a druggable target for the development of cancer therapeutics. CDK9 plays a crucial role in transcription regulation; specifically, CDK9 mediated transcriptional regulation of short-lived antiapoptotic proteins is critical for the survival of transformed cells. Focused chemical libraries based on a plethora of scaffolds have resulted in mixed success with regard to the development of selective CDK9 inhibitors. Here we review the regulation of CDK9, its cellular functions, and common core structures used to target CDK9, along with their selectivity profile and efficacy in vitro and in vivo.

Repression of IFN Regulatory Factor 8 by DNA Methylation Is a Molecular Determinant of Apoptotic Resistance and Metastatic Phenotype in Metastatic Tumor Cells

Apoptotic resistance is often associated with metastatic phenotype in tumor cells and is considered a hallmark of tumor progression. In this study, IFN regulatory factor 8 (IRF8) expression was found to be inversely correlated with an apoptotic-resistant and metastatic phenotype in human colon carcinoma cell lines in vitro. This inverse correlation was further extended to spontaneously arising primary mammary carcinoma and lung metastases in a mouse tumor model in vivo. Exogenous expression of IRF8 in the metastatic tumor cell line restored, at least partially, the sensitivity of the tumor cells to Fas-mediated apoptosis, and disruption of IRF8 function conferred the poorly metastatic tumors with enhanced apoptotic resistance and metastatic capability. DNA demethylation restored IRF8 expression and sensitized the metastatic tumor cells to Fas-mediated apoptosis. Analysis of genomic DNA isolated from both primary and metastatic tumor cells with methylation-sensitive PCR revealed hypermethylation of the IRF8 promoter in metastatic tumor cells but not in primary tumor cells. Taken together, our data suggest that IRF8 is both an essential regulator in Fas-mediated apoptosis pathway and a metastasis suppressor in solid tumors and that metastatic tumor cells use DNA hypermethylation to repress IRF8 expression to evade apoptotic cell death and to acquire a metastatic phenotype.