spliceostatin A (SSA) / Riken - LARVOL DELTA

High-throughput screen of 100 000 small molecules in C9ORF72 ALS neurons identifies spliceosome modulators that mobilize G4C2 repeat RNA into nuclear export and repeat associated non-canonical translation. (PubMed, Nucleic Acids Res) - "We screened 96 200 small molecules in C9ORF72 patient iPS neurons for modulation of nuclear G4C2 RNA foci and identified 82 validated hits, including the Brd4 inhibitor JQ1 as well as novel analogs of Spliceostatin-A, a known modulator of SF3B1, the branch point binding protein of the U2-snRNP. Our data (i) provide a new pharmacological entry point with novel as well as known, publicly available tool compounds for dissection of C9ORF72 pathobiology in C9ORF72 ALS models, (ii) allowing to differentially modulate RNA foci versus RAN translation, and (iii) suggest that therapeutic RNA foci elimination strategies warrant caution due to a potential storage function, counteracting translation into toxic dipeptide repeat polyproteins. Instead, our data support modulation of nuclear export via SRSF1 or SR protein kinases as possible targets for future pharmacological drug discovery."

Journal • Amyotrophic Lateral Sclerosis • CNS Disorders • BRD4 • SF3B1

Design and synthesis of 4-acetoxypentanamide derivatives of spliceostatin A and their biological evaluation towards prostate cancer treatment. (PubMed, Bioorg Med Chem Lett) - "We designed and synthesized novel 4-acetoxypentanamide derivatives of spliceostatin A, whose 4-acetoxypentenamide moiety is reduced (7), isomerized (8), or substituted with methyl at the α-position (9). The results of biological evaluation against AR-V7 and the docking analysis of each derivative suggest that the geometry of the 4-acetoxypentenamide moiety of spliceostatin A is important for its biological activity."

Journal • Genito-urinary Cancer • Oncology • Prostate Cancer • Solid Tumor • AR

Spliceostatin C, a component of a microbial bioherbicide, is a potent phytotoxin that inhibits the spliceosome. (PubMed, Front Plant Sci) - "The chemical structure of SPC closely resembles spliceostatin A (SPA) which was characterized as an anticancer agent and splicing inhibitor...Further proteomics data analysis revealed that spliceostatin C induces hormone-related responses in Arabidopsis seedlings. In silico binding studies showed that SPC binds to a pocket between the SF3B3 and PF5A of the spliceosome."

Journal • Oncology

Spliceostatin A stabilizes CDKN1B mRNA through the 3' UTR. (PubMed, Biochem Biophys Res Commun) - "Finally, we revealed that the 3' untranslated region of CDKN1B mRNA was involved in the stabilization. These results suggest that stabilization of CDKN1B mRNA is one of the reasons of upregulation of the p27 protein by SSA."

Journal • CDKN1B

CCNE1 and E2F1 Partially Suppress G1 Phase Arrest Caused by Spliceostatin A Treatment. (PubMed, Int J Mol Sci) - "The overexpression of CCNE1 and E2F1 in combination with CDKN1B knockout partially suppressed G1 phase arrest caused by SSA treatment. These results suggest that the downregulation of CCNE1 and E2F1 contribute to the G1 phase arrest induced by SSA treatment, although they do not exclude the involvement of other factors in SSA-induced G1 phase arrest."

Journal • CCNE1 • CDKN1B • E2F1

Splicing modulators elicit global translational repression by condensate-prone proteins translated from introns. (PubMed, Cell Chem Biol) - "Here, we identify a number of truncated proteins generated upon treatment with the splicing modulator spliceostatin A (SSA) via genome-wide ribosome profiling and bio-orthogonal noncanonical amino acid tagging (BONCAT) mass spectrometry...These findings indicate that creating an overburden of condensate-prone proteins derived from introns represses translation and prevents further production of harmful truncated proteins. This mechanism appears to contribute to the antiproliferative and proapoptotic activity of splicing modulators."

Clinical • Journal • Oncology • MAPK8

Structural basis of intron selection by U2 snRNP in the presence of covalent inhibitors. (PubMed, Nat Commun) - "Here we report crystal structures of the SF3B module of the U2 snRNP in complex with spliceostatin and sudemycin FR901464 analogs, and the cryo-electron microscopy structure of a cross-exon prespliceosome-like complex arrested with spliceostatin A. The structures reveal how modulators inactivate the branch site in a sequence-dependent manner and stall an E-to-A prespliceosome intermediate by covalent coupling to a nucleophilic zinc finger belonging to the SF3B subunit PHF5A. These findings support a mechanism of intron recognition by the U2 snRNP as a toehold-mediated strand invasion and advance an unanticipated drug targeting concept."

Journal • Oncology

Spliceostatin A interaction with SF3B limits U1 snRNP availability and causes premature cleavage and polyadenylation. (PubMed, Cell Chem Biol) - "Therefore, truncated transcripts are exported into the cytoplasm and translated, resulting in aberrant protein products. Our work demonstrates that active recycling of the splicing machinery maintains homeostasis of RNA processing beyond intron excision."

Journal • Oncology • MALAT1

Efficient RNA polymerase II pause release requires U2 snRNP function. (PubMed, Mol Cell) - "Multiomics analysis reveals that inhibition of U2 snRNP function increases the duration of Pol II pausing in the promoter-proximal region, impairs recruitment of the pause release factor P-TEFb, and reduces Pol II elongation velocity at the beginning of genes. Our results indicate that efficient release of paused Pol II into active transcription elongation requires the formation of functional spliceosomes and that eukaryotic mRNA biogenesis relies on positive feedback from the splicing machinery to the transcription machinery."

Journal

Rbm38 Reduces the Transcription Elongation Defect of the SMEK2 Gene Caused by Splicing Deficiency. (PubMed, Int J Mol Sci) - "This reduction was shown to require the N- and C-terminal regions of Rbm38, along with an important role being played by the RNA-recognition motif of Rbm38. These findings advance our understanding of the molecular mechanism of the transcription elongation defect caused by splicing deficiency."

Journal

Design and Synthesis of 1,2-Deoxy-pyranose Derivatives of Spliceostatin A toward Prostate Cancer Treatment. (PubMed, ACS Med Chem Lett) - "With respect to the biological activity, the 1,2-deoxy-pyranose analogue of spliceostatin A suppressed AR-V7 expression at the nano level (IC = 3.3 nM). In addition, the in vivo toxicity test showed that the 1,2-deoxy-pyranose analogue was able to avoid severe toxicity compared to spliceostatin A."

Journal • Genito-urinary Cancer • Oncology • Prostate Cancer • Solid Tumor

Dynamic Supraspliceosomes Are Assembled on Different Transcripts Regardless of Their Intron Number and Splicing State. (PubMed, Front Genet) - "Furthermore, splicing inhibition by spliceostatin A did not inhibit the assembly of supraspliceosomes on the E6 transcript, yet increased the percentage of E6 pre-mRNA supraspliceosomes...This assembly starts at the site of transcription and can continue during the life of the transcript in the nucleoplasm. This study further confirms the dynamic and universal nature of supraspliceosomes that package RNA polymerase II transcribed pre-mRNAs into complexes composed of four native spliceosomes connected by the transcript, independent of their length, number of introns, or splicing state."

Journal • SRSF2