Uttroside B: A novel drug candidate against hepatocellular carcinoma

Introduction: Hepatocellular carcinoma (HCC) is associated with a high rate of mortality and exhibits inherent resistance to conventional chemotherapeutic agents. Our team has isolated a furostanol saponin, Uttroside B, from the leaves of Solanum nigrum Linn, which exhibits exceptional cytotoxicity towards liver cancer cells, compared to sorafenib, the only FDA approved drug against HCC.

Materials and Methods: Leaves of Solanum nigrum; liver cancer cell lines and normal hepatocytes; MTT assay, clonogenic assay, Western blotting, flow cytometry, EMSA, histopathology, immunocytochemistry, immunohistochemistry; toxicological studies in Swiss albino mice (IAEC/588/RUBY/2017); anti-tumor studies in NOD-SCID mice (IAEC/634/RUBY/2017); hemolysis studies in blood collected from healthy donors (IHEC No/1/2018/10).

Results and discussion

Uttroside B was isolated and characterized from the methanolic extract of the leaves of Solanum nigrum Linn. The compound is cytotoxic to all liver cancer cells, irrespective of their HBV status. It is more cytotoxic (IC50: 500nM) than sorafenib (IC50: 5.6 μM) in the HCC cell line, HepG2 and induces apoptosis, while being non-toxic to normal hepatocytes. Uttroside B drastically inhibited the growth of HepG2 liver cancer xenografts in NOD-SCID mice. It induces vacuolated structures, indicative of autophagy and activates autophagy markers such as LC3 II, Beclin 1 and Atgs. Uttroside B-mediated autophagy flux was confirmed using bafilomycin A1 and quantitated by RFP-GFP-LC3 tagged protein assay. Since the compound triggers autophagy followed by apoptosis, the interplay between autophagy and apoptosis was studied using bafilomycin A1 and 3-methyl adenine, the pharmacological inhibitors of autophagy. Beclin-siRNA transfection studies illustrated that inhibition of autophagy enhances uttroside B-mediated apoptosis. The mechanistic evaluation revealed that uttroside B inhibits mTOR and activates AMPK, two crucial signaling pathways regulating progression of HCC. A patent has been filed on the anti-cancer potential of uttroside B (Application No. 201641018401) and an MoU has been signed between RGCB and Oklahoma Medical Research Foundation, USA, for the clinical evaluation of the compound. Toxicological evaluation revealed that uttroside B is pharmacologically safe as indicated by serum biochemical and histopathological analysis. Unlike other saponins, uttroside B did not cause hemolysis. The pharmacokinetics and safety profile of uttroside B contained in the leaves of Solanum nigrum L is currently going on in patients (IHEC/01/2017/07), consuming the leaves as part of naturopathy treatment against liver disorders. A HepG2-xenograft study is being carried out to compare the efficacy of uttroside B and sorafenib against HCC.

Conclusion

The study authenticates uttroside B as a promising drug candidate against HCC.