Saikosaponin‑D triggers cancer cell death by targeting the PIM1/c-Myc axis to reprogram oncogenic alternative splicing.

Saikosaponins (SSs, including SSA, SSB, SSC, and SSD), the major bioactive compounds in the traditional medicine Radix Bupleuri, are emerging agents exhibiting anti-tumor efficacy in several cancers. However, the respective anti-tumor efficacy of these agents and mechanisms in cancers remains unclear. Here, we reported that SSD, among SSs, possessed a significant anti-tumor role across different cancer types in vivo and in vitro by downregulating alternative splicing factors and rewiring oncogenic alternative splicing events. Mechanistically, SSD directly targets PIM1 and blocks the interaction between PIM1 and Myc, and decreases PIM1-mediated Myc phosphorylation at serine 62 and Myc protein stability, resulting in global restraining of Myc-governed alternative splicing factors transcription and inducing oncogenic alternative splicing rewiring. Transcript-specific ablation of SSD-regulated alternative spliced products with CIRSPR-Cas13 or targeting PIM1/Myc with specific small inhibitors significantly desensitizes cancer cells and patient-derived organoids (PDOs) to SSD treatments. These studies demonstrated the potent anti-tumor efficacy of SSD and exposed a PIM1/Myc axis by which SSD modulates the expression of an oncogenic alternative splicing regulatory network that mediates SSD's anti-tumor role in cancers.