Spliceosome Inhibition in SF3B1-Mutated Uveal Melanoma

Treatment of uveal melanoma (UM) patients with metastatic disease is unfortunately limited. Twenty percent of UM harbor a mutation in splicing factor gene SF3B1, suggesting that aberrant spliceosome functioning plays a vital role in tumorigenesis. Splicing inhibitors exploit the preferential sensitivity of spliceosome compromised leukemic cells to these compounds. We have studied the effect of splicing inhibitor E7107 using two UM cell lines and ex vivo cultured SF3B1 and BAP1 mutated primary UM tumor slices. These UM cell lines and ex vivo tumor slices were exposed for 24h to different concentrations of E7107. Tumor slices were stained with H&E and incubated with BAP1, MelanA, MIB-1 and caspase-3 antisera. E7107 exposed UM cell lines showed decreased cell viability and increased apoptosis with the largest effect sizes in SF3B1-mutated UM. A similar effect was observed upon exposure of E7107 on UM tumor slices. Additionally, RNA was isolated for transcriptome analysis and the type and number of alternative and aberrant transcripts was evaluated. Ninety-seven transcripts had a decrease in aberrant transcripts in all samples after E7107 exposure, and this effect was mostly in intron retention. This study indicates / suggests that mutated SF3B1 UM cells are more sensitive to splicing inhibitor E7107 compared to wild-type SF3B1 UM cells. Simple SummaryUveal melanoma (UM) is an aggressive malignancy of the eye. UM prognosis varies and depends on mutational status. Mutations in spliceosome gene Splicing Factor 3b subunit 1 (SF3B1) are in UM associated with late onset metastasis. Also in other malignancies, such as breast cancer or leukemia, SF3B1 mutations have been implied as drivers for tumor formation. Targeting the spliceosome with inhibitors is possible and would make SF3B1-mutated UM amenable for treatment. We investigated and demonstrated using two cell lines and ex-vivo culturing of 3 SF3B1-mutated tumors and 17 SF3B1-wildtype tumors that spliceosome inhibitor E7107 decreased the cell viability of both SF3B1-mutated and SF3B1-wildtype UM cell line, but significantly more in SF3B1-mutated UM cell line. Therefore, inhibiting the spliceosome has the highest therapeutic potential in SF3B1-mutated UM, but further research is recommended to determine the best suited strategy to minimize risk and maximize efficacy in a therapeutic setting.