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Epigenetic silencing of the tumor suppressor RASSF4 favors multiple myeloma progression

ABSTRACT: RAS is frequently mutated in multiple myeloma (MM) leading to aberrant signaling. Next to their classical oncogenic effects, RAS proteins also mediate anti-tumor effects through the Ras-Association Domain Family (RASSF) proteins. Currently, no data about the role of RASSF proteins in MM disease is available. Here we report that RASSF4 is downregulated during MM progression, correlating with a bad prognosis. Epigenetic modulating agents significantly increased RASSF4 expression, indicating that the RASSF4 downregulation is due to epigenetic silencing. Forced RASSF4 expression induced a G2-phase arrest and caspase-3 mediated apoptosis in human MM cell lines, strongly reduced viability of primary CD138+ MM cells and significantly reduced in vivo tumor growth. Moreover, we demonstrated RASSF4-MST1 binding and the involvement of the downstream signaling pathways JNK/Jun, p38 and p53. RASSF4 overexpression sensitized MM cells to the proteasome inhibitor bortezomib, the specific MEK1/2 inhibitor trametinib and the ROS inducer Prima-1Met. Consequently, combining trametinib with histone deacetylase inhibitors (HDACi) revealed very strong synergistic anti-MM activity. In conclusion, our study identified RASSF4 as a new potent tumor suppressor in MM that is epigenetically silenced during MM progression and provides the basis for novel therapeutic strategies enhancing RASSF4 expression (using HDACi) in combination with MEK/ERK inhibitors and bortezomib.

ORGANISM(S): Homo sapiens

PROVIDER: GSE85020 | GEO | 2017/07/31

SECONDARY ACCESSION(S): PRJNA335945

REPOSITORIES: GEO

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Project description:The first clinical trial testing the combination of targeted therapy with a BRAF inhibitor vemurafenib and immunotherapy with a CTLA-4 antibody ipilimumab was terminated early due to significant liver toxicities, possibly due to paradoxical activation of the MAPK pathway by BRAF inhibitors in tumors with wild type BRAF. MEK inhibitors can potentiate the MAPK inhibition in tumor, while potentially alleviating the unwanted paradoxical MAPK activation. With a mouse model of syngeneic BRAFV600E driven melanoma (SM1), we tested whether the addition of the MEK inhibitor trametinib would enhance the immunosensitization effects of the BRAF inhibitor dabrafenib. Combination of dabrafenib and trametinib with pmel-1 adoptive cell transfer (ACT) showed complete tumor regression. Bioluminescent imaging and tumor infiltrating lymphocyte (TIL) phenotyping showed increased effector infiltration to tumors with dabrafenib, trametinib or dabrafenib plus trametinib with pmel-1 ACT combination. Intracellular IFN gamma staining of the TILs and in vivo cytotoxicity studies showed trametinib was not detrimental to the effector functions in vivo. Dabrafenib increased tumor associated macrophages and T regulatory cells (Tregs) in the tumors, which can be overcome by addition of trametinib. Microarray analysis revealed increased melanoma antigen, MHC expression, and global immune-related gene upregulation with the triple combination therapy. Given the up-regulation of PD-L1 seen with dabrafenib and/or trametinib combined with antigen specific ACT, we tested the triple combination of dabrafenib, trametinib with anti-PD1 therapy, and observed superior anti-tumor effect to SM1 tumors. Our findings support the testing of these combinations in patients with BRAFV600E mutant metastatic melanoma. SM1 tumors were implanted into C57BL/6 mice. Mice were treated by ACT of pmel-1 splenocytes or C57BL/6 splenocytes as control. Pmel-1 treated mice were additionally treated with either vehicle, dabrafenib, trametinib, or combination of both drugs and control mice were treated with vehicle or combination of both drugs.

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Epigenetic silencing of the tumor suppressor RASSF4 favors multiple myeloma progression

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