meayamycin-b and Lung-Neoplasms

Therapeutic options for diffuse malignant peritoneal mesothelioma (DMPM) are limited to surgery and locoregional chemotherapy. Despite improvements in survival rates, patients eventually succumb to disease progression. We investigated splicing deregulation both as molecular prognostic factor and potential novel target in DMPM, while we tested modulators of SF3b complex for antitumor activity.. Tissue-microarrays of 64 DMPM specimens were subjected to immunohistochemical assessment of SF3B1 expression and correlation to clinical outcome. Two primary cell cultures were used for gene expression profiling and in vitro screening of SF3b modulators. Drug-induced splicing alterations affecting downstream cellular pathways were detected through RNA sequencing. Ultimately, we established bioluminescent orthotopic mouse models to test the efficacy of splicing modulation in vivo.. Spliceosomal genes are differentially upregulated in DMPM cells compared to normal tissues and high expression of SF3B1 correlated with poor clinical outcome in univariate and multivariate analysis. SF3b modulators (Pladienolide-B, E7107, Meayamycin-B) showed potent cytotoxic activity in vitro with IC50 values in the low nanomolar range. Differential splicing analysis of Pladienolide-B-treated cells revealed abundant alterations of transcripts involved in cell cycle, apoptosis and other oncogenic pathways. This was validated by RT-PCR and functional assays. E7107 demonstrated remarkable in vivo antitumor efficacy, with significant improvement of survival rates compared to vehicle-treated controls.. SF3B1 emerged as a novel potential prognostic factor in DMPM. Splicing modulators markedly impair cancer cell viability, resulting also in potent antitumor activity in vivo. Our data designate splicing as a promising therapeutic target in DMPM.

Topics: Aged; Animals; Antineoplastic Agents; Cell Line, Tumor; Cell Proliferation; Cell Survival; Epoxy Compounds; Female; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gene Regulatory Networks; Humans; Lung Neoplasms; Macrolides; Male; Mesothelioma; Mesothelioma, Malignant; Mice; Middle Aged; Morpholines; Peritoneal Neoplasms; Phosphoproteins; Pyrans; RNA Splicing; RNA Splicing Factors; Tissue Array Analysis; Xenograft Model Antitumor Assays

The myeloid cell leukemia-1 (MCL1) gene encodes antiapoptotic Mcl-1(L) and proapoptotic Mcl-1(S) proteins. In cancer, the Mcl-1(L)/Mcl-1(S) ratio is very high, accounting for the antiapoptotic nature of cancer cells. As such, reducing this ratio can render the cancer cells prone to apoptosis. The Mcl-1(L)/Mcl-1(S) ratio is determined in the alternative pre-mRNA splicing step that is regulated by splicing factor 3B1 (SF3B1). Here, we report that meayamycin B, a potent inhibitor of SF3B1, reversed the dominant isoform from Mcl-1(L) to Mcl-1(S) at the mRNA and protein levels. The resulting proapoptotic cellular environment was further exploited; when meayamycin B was combined with Bcl-x(L) inhibitor ABT-737, the combination treatment triggered apoptosis in nonsmall cell lung cancer A549 and H1299 cells that were otherwise resistant to ABT-737. These results demonstrate that perturbation of the MCL1 splicing with small molecule inhibitors of SF3B1 provides a means to sensitize cancer cells toward Bcl-x(L) inhibitors.

Topics: Alternative Splicing; Apoptosis; bcl-X Protein; Biphenyl Compounds; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Dose-Response Relationship, Drug; Epoxy Compounds; Humans; Lung Neoplasms; Morpholines; Myeloid Cell Leukemia Sequence 1 Protein; Nitrophenols; Phosphoproteins; Piperazines; Protein Isoforms; Pyrans; Ribonucleoprotein, U2 Small Nuclear; RNA Splicing Factors; Sulfonamides