Hepatocellular carcinoma (HCC) is the most prevalent malignancy in liver and a leading cause of cancer-related deaths. Despite the pressing need for treatment options, patients with HCC develop significant resistance and adverse side effects to current approved drugs that becomes a major barrier to effective treatment. A natural product Tetrandrine (TET) is a potential alternative treatment option for HCC, with demonstrated effectiveness and low toxicity. However, the mechanisms by which Tetrandrine inhibits HCC are unclear. In the current study, we identify Ca2+/calmodulin-dependent protein kinase II delta (CaMKII delta) as a potential TET drug target through structural modeling. Screening of a panel of HCC cell lines reveal differential sensitivities toward TET treatment. Interestingly, IC50 of TET inhibition of HCC cell proliferation is positively correlated with CaMKII delta expression level in these distinct HCC cells. Furthermore, TET treatment resulted in a marked reduction of CaMKII delta phosphorylation level, and knockdown of CaMKII delta reduced the sensitivity of HCC cells to TET. Most importantly, CaMKII delta protein levels in high-grade human HCC samples were significantly elevated as compared to normal liver tissues. Taken together, our studies demonstrate that the natural compound TET targets CaMKII delta in HCC cells, and that CaMKII delta level is a potential biomarker to identify HCC patient populations sensitive to Tetrandrine treatment. (C) 2018 Elsevier Inc. All rights reserved.