Research activities in the Chen laboratory center on the development of technology and reagents for small-molecule-based drug discovery, and the application of these tools in the elucidation of signal transduction pathways in normal and diseased cellular systems. The laboratory focuses on 2 areas involving the regulation of transcription factors: regulation of pregnane X receptor (PXR) in drug metabolism and drug resistance; and regulation of PAX3-FKHR in alveolar rhabdomyosarcoma (ARMS).
In addition to cellular, molecular, biochemical, genomic, proteomic techniques and animal models, most of our projects depend on the development of high throughput biological assays and the use of automated instrumentation. Our technology development effort focuses on the development and miniaturization of biochemical and cell-based assays to screen large collections of small molecules to identify compounds with desirable bioactivity. We are also interested in developing and implementing high-content and multiplexing screening assays using automated imaging systems and specific algorisms for image analysis, to define mechanisms of action for selected compounds. Additionally, we have begun to integrate genome-wide RNAi technology into our current platforms.
PXR is a master regulator of CYP3A4, a major enzyme responsible for metabolizing more than 50% of clinically prescribed drugs, and multi-drug resistance 1 (MDR1), an ATP-binding cassette (ABC) transporter involved in drug resistance. Our hypothesis is that PXR activity is regulated not only by direct binding of agonist but also by crosstalk with other signaling pathways. Thus, drug metabolism is affected by the physiologic and pathologic conditions of patients - an important area that has not been adequately considered when evaluating drug metabolism. Our long term goal is to identify signaling pathways that modulate PXR function and understand the implication of these modulations in clinical drug metabolism and drug resistance. We currently focus on studying the regulation of PXR by cell cycle and phosphorylation.
Resistance of cancer to chemotherapy is a major cause of treatment failure. Tremendous efforts have been invested in inhibiting the activity of MDR1 as a salvage approach to reverse the drug-resistant phenotype of tumors. However, no significant clinical success has been achieved because of the toxicity of MDR1 inhibitors—undesired, yet expected because MDR1 plays essential physiologic roles in protecting the human body from toxic xenobiotics. MDR1 expression is regulated by many signaling pathways. Most notably, MDR1 expression is induced by PXR. Our hypothesis is that specific inhibition of the drug-induced upregulation of MDR1 will prevent drug-induced drug resistance. Antagonizing the drug-activated activity of PXR would provide a preventive approach to tackle drug resistance while decreasing undesired toxicity. Such a PXR antagonist has to be non-toxic, not interfere with constitutive PXR activity and MDR1 expression, only antagonize the agonist-induced activation of PXR, and be specific for PXR. We focus on developing PXR antagonists that meet our stringent criteria defined above. Our goal is to use these PXR antagonists as tools to study PXR antagonism and, ultimately, to develop them as co-drugs to attenuate the drug-induced activation of PXR and thus to prevent drug-induced drug resistance.
Rhabdomyosarcoma (RMS) is the most common cancer that originates in the soft tissues of the body in children. Two subtypes of RMS have been identified — embryonal (ERMS) and alveolar (ARMS) — each with distinct clinical and genetic characteristics. Children with ARMS have poorer response to conventional chemotherapy and radiation therapy, and much lower survival rates than those with ERMS. Once metastasizing, ARMS becomes resistant to conventional therapies, with a 5-year survival rate of lower than 30%.
A rearrangement between chromosomes #2 and #13 is present in >70% of ARMS cases. This rearrangement creates an abnormal fusion of genes known as PAX3-FKHR, a genetic marker of ARMS. The abnormal expression and activity of PAX3-FKHR contribute to its oncogenic behavior by modifying cell growth, differentiation and motility. We focus on developing PAX3-FKHR modulators and using them for target validation and, ultimately, for developing novel therapy for ARMS.
National Institute of General Medical Sciences
National Cancer Institute
American Lebanese Syrian Associated Charities
St. Jude Children's Research Hospital
St. Baldrick's Foundation