Molecular profiling of malignant peritoneal mesothelioma identifies the ubiquitin-proteasome pathway as a therapeutic target in poor prognosis tumors

Abstract

9549 Background: Malignant peritoneal mesothelioma (MPM) is an aggressive neoplasm derived from cells lining serosal membranes. The characteristics of the epithelial (E) type MPM are distinct from those of the biphasic and sarcomatous (BS) type tumors. The goal of our study was to examine the molecular basis for this distinction. Methods: We used global molecular profiling with DNA microarrays to identify pathways associated with histologic subtype of 16 MPM tumor specimens acquired from patients entered into pilot multimodality protocols at our Institution. We performed immunohistochemistry on a tissue microarray and quantitative-real time PCR to validate the microarray results. Results: We performed average linkage agglomerative hierarchical clustering using microdissected MPM specimens and normal peritoneal tissue. The tumors segregated into two clades associated with histological subtype, which were distinct from the controls. 476 genes were differentially expressed between E and BS histologic classes (P < .001, with permutation test P value of .001). To identify biologically important differentially expressed genes and pathways, we examined the functional annotation of mesothelioma histologic subtype classifiers using the Pathway Comparison tool of BRB-Array. Among the differentially expressed categories was the ubiquitin-proteasome (UP) pathway, which was upregulated in BS tumors. Cytoxicity experiments by MTS assay indicated that, by the computation of combination indexes of activity, cells derived from BS tumors were exquisitely sensitive to sequential combination regimens containing the proteasome inhibitor (PI) bortezomib and oxaliplatin. The mechanism of this synergistic response, which was not detected in cells of E tumor origin, was apoptosis. Conclusions: Together, our results identify the ubiquitin-proteasome pathway as a biomarker of poor prognosis biphasic and sarcomatous malignant peritoneal mesothelioma tumors and suggest that proteasome inhibitors could increase the effectiveness of cytotoxic chemotherapy in this subset of patients. No significant financial relationships to disclose.