Niclosamide prodrug enhances oral bioavailability and efficacy against hepatocellular carcinoma by targeting vasorin-TGFβ signalling.

[BACKGROUND AND PURPOSE] Hepatocellular carcinoma (HCC), the third leading cause of cancer-related deaths worldwide, has limited treatment options and high mortality rate. We previously used a bioinformatics approach to identify niclosamide (NIC) as a promising repurposed drug candidate for HCC. However, its poor water solubility and low bioavailability limit its clinical efficacy. It's mechanisms of action are not yet fully understood.

[EXPERIMENTAL APPROACH] We designed a water-soluble NIC prodrug (NIC-PS) and evaluated its efficacy (as single agent, or in combination with sorafenib or anti-PD-L1) and mechanisms using cell-based functional assays and HCC patient-derived xenograft (PDX) mouse models. We established vasorin knockout mouse tumour models and used RNA-seq to investigate the role of vasorin in mediating NIC-PS function. Western blotting and real-time PCR were used to validate the RNA-seq data and the biological effects of NIC-PS and vasorin.

[KEY RESULTS] NIC-PS exhibited a 10-fold increase in oral bioavailability and > 75% reduction in tumour volume in HCC PDX models. NIC binds to vasorin, and both NIC and NIC-PS suppressed vasorin expression, leading to suppression of TGFβ signalling and SMAD2/3 phosphorylation. NIC-PS enhanced the sensitivity of HCC cells and PDX to treatment with sorafenib or anti-PD-L1. Vasorin knockout results in similar effects as NIC-PS, suggesting that it partially mediates the actions of NIC-PS.

[CONCLUSION AND IMPLICATIONS] NIC-PS demonstrated improved bioavailability and antitumour efficacy compared with NIC and a potential for combination therapy with standard of care agents in HCC treatment. We also revealed its novel mechanism of action in targeting vasorin.