Splicing modulation as novel therapeutic strategy against diffuse malignant peritoneal mesothelioma

Introduction:Therapeutic options for diffuse malignant peritoneal mesothelioma (DMPM) are limited to surgeryand locoregional chemotherapy. Despite improvements in survival rates, patients eventually succumb to diseaseprogression. We investigated splicing deregulation both as molecular prognostic factor and potentialnovel targetin DMPM, while we tested modulators of SF3b complex for antitumor activity.Methods:Tissue-microarrays of 64 DMPM specimens were subjected to immunohistochemical assessment ofSF3B1 expression and correlation to clinical outcome. Two primary cell cultures were used for gene expressionprofiling andin vitroscreening of SF3b modulators. Drug-induced splicing alterations affecting downstream cel-lular pathways were detected through RNA sequencing. Ultimately, we established bioluminescent orthotopicmouse models to test the efficacy of splicing modulationin vivo.Results:Spliceosomal genes are differentially upregulated in DMPM cells compared to normal tissues and highexpression of SF3B1 correlated with poor clinical outcome in univariate and multivariate analysis. SF3b modula-tors (Pladienolide-B, E7107, Meayamycin-B) showed potent cytotoxic activityin vitrowith IC50 values in the lownanomolar range. Differential splicing analysis of Pladienolide-B-treated cells revealed abundant alterations oftranscripts involved in cell cycle, apoptosis and other oncogenic pathways. This was validated by RT-PCR andfunctional assays. E7107 demonstrated remarkablein vivoantitumor efficacy, with significant improvement ofsurvival rates compared to vehicle-treated controls.Conclusions:SF3B1 emerged as a novel potential prognostic factor in DMPM. Splicing modulators markedly im-pair cancer cell viability, resulting also in potent antitumor activityin vivo. Our data designate splicing as a prom-ising therapeutic target in DMPM.