Validation of Potential Chemosensitivity Genes in Multiple Myeloma

Abstract 1818

Chemotherapy agents are extremely important in the treatment of liquid malignancies, such as multiple myeloma (MM). Unfortunately, chemotherapy resistance in MM therapy is the most significant cause of treatment failure. The ability to predict, treat, or circumvent resistance is extremely likely to improve clinical outcomes. Thus, identification of novel genes that play a crucial role in MM progression and chemosensitivity is necessary to understand this disease better at the molecular level. Moreover, these genes and their products may serve as new therapeutic targets for MM, whose expression could improve patient outcomes or served as a predictor for chemotherapy outcome. To identify potential chemosensitivity genes, establishing a high-throughput method for validation of targets becomes urgently needed. Toward this purpose, we have successfully developed a high-throughput siRNA based functional target validation approach and identified 34 potential chemosensitivity genes.

Our preliminary studies focusing on one of the candidate gene, TJP1 (tight junction protein 1), suggested that targeting TJP1 led to tumor cell resistant to several chemotherapy agents, including doxorubicin (Dox), cisplatin (Cis), methotrexate (MTX), and bortezomib. Further analysis with 264 bortezomib treated MM patients indicated that expression level of TJP1 correlated with patient response to bortezomib. Two clones and pooled RPMI 8226 MM cell line, which were developed against bortezomib treatment in our lab, showed loss of TJP1 expression, suggesting a role of TJP1 may play in bortezomib resistance development. More importantly, TJP1 targeting in myeloma cells resulted in cell resistance to bortezomib treatment.

Protein tyrosine phosphatase, receptor type, O1 (PTRPO) was identified in our screening as well. We first examined the expression of PTPRO in a panel of myeloma cell lines, and found that PTPRO expression was dramatically decreased in several drug resistant lines compared to their parental sensitive cells. Moreover, using a Lentiviral cDNA expression system to overexpress PTPRO, we observed that PTPRO significantly inhibited cell growth and sensitized drug sensitivity of several drug lines by triggering apoptosis. Finally, evaluation of the publicly available gene expression profiling data gathered from primary plasma cells on the Multiple Myeloma Genomics Portal, and the linked clinical annotation describing patient outcomes, has shown that over-expression of PTPRO is associated with a superior overall survival compared to patients whose myeloma show low levels of PTRPO expression, suggesting this may be a prognostic marker as well.

Together, we have successfully identified a group of potential chenmosensitivity genes, in which two of the genes (TJP1 and PTPRO) have been further validated to sensitize the drug treatment in multiple myeloma cells.