Nigakinone enhances FXR expression to synergize with irinotecan in suppressing colorectal cancer cells and xenografts.

The use of irinotecan (CPT-11), a first-line chemotherapeutic agent for colorectal cancer (CRC), is limited by acquired drug resistance and severe adverse effects. It has been found that activation of farnesoid X receptor (FXR) signaling reduced the growth of CRC. Here, we investigated the combination of obeticholic acid (OCA), a well-characterized FXR agonist, with CPT-11 as a potential therapeutic combination for CRC. In vitro experiments demonstrated that the OCA-CPT-11 synergistically inhibited proliferation and migration in FXR-high HT-29 and SW620 cells, but exhibited minimal synergy in FXR-low HCT116 and Caco-2 cells. Genetic knockdown of FXR in HT-29 cells attenuated the synergistic effects, whereas FXR overexpression in HCT116 cells enhanced them. These findings indicate that the synergistic effect of OCA-CPT-11 depends on basal FXR expression levels, highlighting the need to identify both FXR inducers and agonists. Through literature and database screening, silibinin (SB) and nigakinone (Nig) were identified to upregulate and activate FXR. Both SB-CPT-11 and Nig-CPT-11 exhibited strong synergistic anti-CRC effects in vitro, even under low FXR conditions. Nig achieved synergy with CPT‑11 at lower effective concentrations than SB, so it was prioritized as the lead candidate for in vivo evaluation. Consistently, the Nig-CPT‑11 combination synergistically inhibited the growth of HCT116 subcutaneous xenograft tumors in vivo. Notably. In summary, combining FXR inducers and agonists with CPT-11 offers a promising strategy for the treatment of CRC.