Splicing inhibition hampers pancreatic cancer cell viability by disrupting DNA repair proficiency and mitotic checkpoint integrity

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with a remarkably poor prognosis. Splicing dysregulation is emerging as a hallmark of cancer, influencing multiple aspects of tumor development. To evaluate the impact of its dysregulation we employed three splicing-targeting drugs: Pladienolide B (PdB), Thailanstatin A (Th.A) and Indisulam (Ind.), all involved in the recognition of 3’ splice site. Transcriptome analyses in PDAC cell lines and PDOs revealed that splicing inhibition negatively affects the DDR pathway (BRCA1, CHEK1, CHEK2) in homologous recombination-proficient (HRP) PDAC models, representing a promising strategy to enhance their sensitivity to PARP inhibitor (Talazoparib) treatment. Moreover, among the genes that are altered by all three drugs, we observe an enrichment of genes involved in the mitotic checkpoint genes (AURKA, AURKB, CDC25B, KIF21, EZH2). Indeed, splicing inhibitors induced severe mitotic defects with a strong enrichment in the G2/M phase of the cycle, leading to the accumulation of condensed chromosomes on monopolar spindles and misaligned chromosomes on bipolar spindles; which lead to the formation of multinucleated cells. The high expression of AURKA, AURKB and CHEK1 were correlated with poor prognosis in PDAC; furthermore, CHEK1 expression was also significantly correlated with AURKA and AURKB. Indeed, combined treatments with CHEK1i (AZD7762) and AURKAi (Alisertib) have an additive effect on both PDAC cell lines and PDOs, suggesting promising new therapeutic strategies that may be used in PDAC patients.