Sorafenib, a multikinase inhibitor, is currently used as the normative treatment for advanced hepatocellular carcinoma (HCC). It can prolong survival for a few months however sorafenib insensitivity and resistance often develops in tumors hence a better understanding of resistance mechanisms is urgently needed. Tumor-initiating cells (T-ICs) have recently been implicated in the cause of treatment resistance. Recently, our group found that CD47 is preferentially expressed in liver T-ICs, which suggests a possibility of targeting CD47 in order to evade sorafenib resistance via elimination of liver T-ICs. To test this hypothesis, we have successfully developed sorafenib-resistant clones in HCC cell lines (BEL7402 and Huh-7 cells) and in vivo using patient-derived xenograft (PDTX #1) by continuous exposure to sorafenib. We found that sorafenib-resistant clones showed enhanced T-IC properties such as self-renewal, tumorigenicity and invasiveness, which is also accompanied by an increase in CD47 expression. We found increased NF-κB activation in sorafenib resistant clones indicated by upregulated levels of phosphorylated p65 and IkBα which is consistent to the bioinformatics analysis showing two putative NF-κB binding sites on the CD47 promoter. In addition, CD47 expression was found to be decreased upon treatment of NF-κB inhibitor IMD-0354 and increased upon treatment of TNF-α. These results suggested that NF-κB mediated CD47 upregulation promotes sorafenib resistance in HCC. To further confirm the role of CD47 in sorafenib resistance, we knocked down CD47 expression in CD47-high expressing HCC cells. Through annexin V staining, we found that knockdown of CD47 sensitized Huh-7 and MHCC-97L to sorafenib treatment at 10µM and 20µM respectively. Using patient derived xenograft model (PDTX #8) to investigate the effect of different treatment regimens, we found that mice treated with daily administration of sorafenib (100mg/Kg) showed tumor volume reduction by 3-fold upon 30 days of treatment and a similar effect was found in mice treated daily with and anti-CD47 antibody (500mg/Kg). Interestingly, sorafenib combined with anti-CD47 antibody exhibited maximal effect on tumor suppression. All in all, regulation of CD47 by NF-κB may enable the promotion of sorafenib resistance and anti-CD47 antibody in co-treatment with sorafenib may serve as a novel therapeutic regimen for the treatment of advanced stage HCC.
Citation Format: Jessica Lo, Eunice Yuen Ting Lau, Irene Oi Lin Ng, Terence Kin Wah Lee. NF-κB mediated CD47 upregulation promotes sorafenib resistance and its blockade synergizes the effect of sorafenib in hepatocellular carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1911. doi:10.1158/1538-7445.AM2014-1911