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

Abstract 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.