Mesothelin: a malignant factor and novel therapeutic vaccine target for pancreatic cancer Free

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Background: Mesotheline (MSLN) is a GPI-linked glycoprotein, which is overexpressed in several cancer types including mesothelioma, ovarian cancer, and pancreatic cancer, but very little or no expression of MSLN is seen in normal tissues and other cancer types. In this study, we investigated the expression and functions of MSLN in human pancreatic cancer cells, and further determined the effect and mechanism of chimeric virus-like particle (VLP)-hMSLN as a potent candidate for vaccine and immune therapy for pancreatic cancer.

Methods: The expression of MSLN in human pancreatic cancer cell lines, HPDE cells, clinical specimens of human pancreatic adenocarcinoma were determined by real-time RT-PCR and western blot. MSLN stable overexpression and silencing cells were selected in MIA PaCa-2, and BxPC-3 cells using retrovirus vectors. In vitro cell proliferation, migration, and cell cycle were performed by MTS, modified Boyden chamber assay, and flow cytometry analysis, respectively. In vivo tumor growth was performed in subcutaneous and orthotopic nude mice model. Chimeric VLP-hMSLN was constructed, and C57BL/6J mice were immunized by VLP-hMSLN to treat preexisting pancreatic tumor. MSLN-specific T cells and antibodies were assessed by ELISPOT and ELISA, respectively.

Results: The MSLN expression levels were significantly increased in all four pancreatic cancer cell lines tested, compared with that in HPDE cells (p<0.05). In 10 clinical pancreatic carcinoma samples, MSLN was found to be substantially over-expressed compared with the surrounding normal tissues (p<0.05). Forced expression of MSLN boosts tumor cell proliferation, and migration in vitro by 90% and 300% compared with the vector control cells (p<0.05), and contributes to tumor progression in nude mouse xenograft model through effects on the STAT3 pathway. Silencing of MSLN decreased cell proliferation, and migration in pancreatic cancer cells by 50% and 70% compared with the vector control cells (p<0.05), and ablated tumor progression in vivo. Immunization with chimeric VLP which contains surface protein MSLN (VLP-hMSLN) significantly regressed tumor progression in C57BL/6J mice. The elevated levels of MSLN specific CD8+ T cell responses and down regulated T regulatory cells were found to be responsible for controlling tumor growth and correlated with prolonged survival.

Conclusions: These data demonstrate that MSLN is overexpressed, and is a malignant factor in pancreatic cancer. VLP-hMSLN immunization in C57BL/6J mice significantly regressed the preexisting pancreatic tumor, and can be used as a novel therapeutic vaccine. This study may provide a new treatment strategy for therapeutic intervention in pancreatic cancer.