Abstract

   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.

   Subject terms: Drug development, Cancer

Introduction

   Radix Bupleuri (Chaihu) has been a widely used traditional medicine in
   Asian countries such as China, Japan, and Korea for over two thousand
   years for its properties, including anti-inflammation, antitumor,
   antifebrile, antibacterial, antiviral, and neuroprotective effects
   [[44]1]. Phytochemical studies have demonstrated that Saikosaponins,
   especially SSA, SSB2, SSC, and SSD, are the main bioactive compounds
   [[45]2, [46]3], highlighting their critical roles in Radix Bupleuri in
   clinical settings. Many studies have reported that Saikosaponins
   possess potent pharmacological effects such as sedation, antipyretic,
   antiviral, anti-inflammation, and antitumor properties, consistent with
   the clinical benefits of Radix Bupleuri [[47]4, [48]5]. Saikosaponins
   in Radix Bupleuri are complex compounds composed of triterpene aglycone
   and a carbohydrate part containing 1–13 monosaccharides [[49]6].
   Accumulating studies have reported the anti-tumor efficacy of the main
   Saikosaponins in Radix Bupleuri [[50]7–[51]9], while the individual
   anti-tumor effects and direct targets remain unclear. Additionally, the
   different structural characteristics of various Saikosaponins may
   result in distinct pharmacological activities. Currently, no studies
   have been reported comparing the differences in anti-tumor effects and
   cancer type-specific preferences of different Saikosaponins.