Abstract 2453: CD47 is a novel therapeutic target for hepatocellular carcinoma
Authors: Cheung Chi Ho , Lee Kin Wah , Ng Irene Oi-Lin 
Published: June 2012

Hepatocellular Carcinoma (HCC) is a deadly cancer which is chemoresistant and highly recurrent. Tumor-Initiating Cells (T-ICs), which is capable of tumor initiation, self-renewal, differentiation and chemoresistance, may account for the poor prognosis of HCC. Targeting liver T-ICs is hence critical for therapeutic intervention. Using gene expression profiling by cDNA microarray, we found significantly upregulation of CD47 in enriched liver T-ICs compared with their differentiated progenies. CD47 is a membrane protein involved in self-nonself discrimination in immune system. It is also reported to be T-IC markers in Acute Myeloid Leukemia and bladder cancer. The roles of CD47 in immune evasion and T-ICs identification imply CD47 as a potential therapeutic target in HCC.

To evaluate if CD47 is a possible liver T-IC marker, we compared CD47 expression in a panel of HCC cell line with non-tumorigenic normal liver cell line (MIHA) by flow cytometry. CD47 expression across HCC cell line panel ranged from 40.6% to 80.1%, with the highest expression in 97L cells. Notably, scanty expression was detected in MIHA. Oncogenomic analysis also documented over-expression of CD47 in HCC clinical samples, revealing the role of CD47 in hepatocarcinogensis. Further investigation of CD47 as T-IC marker was performed by FACS-sorting analysis. CD47+ HCC cells displayed higher tumorigenic ability and exhibited self-renewing phenotypes, including enhanced sphere-forming ability and preferential expression of “stemness’ genes.

As CD47+ cells possess T-IC properties, targeting CD47 may be a new therapeutic strategy against HCC. Lentiviral based knockdown was employed to examine effects of CD47 suppression. CD47 knockdown resulted in marked decrease in tumor forming, self-renewal and invasive abilities. To further investigate underlying mechanisms of CD47, cDNA microarray was performed by profiling between CD47 knockdown cells and control cells. Cathepsin S (CTSS), a cysteine protease which is crucial in chemoresistance, was identified as a downstream effecter in CD47 signalling. Interestingly, knockdown of CD47 increased chemo-sensitivity of HCC cells towards chemotherapeutic drugs. These, together with observation that chemoresistant HCC cells exhibited elevated levels of both CD47 and CTSS, suggests CD47 targeting combined with chemotherapy may be an effective treatment option for HCC. Using HCC xenograft tumor model, therapeutic role of CD47 and its combined effect with chemotherapy were assessed in vivo. Suppression of CD47 expression by vivo-morpholino alone caused tumor shrinkage while combination of CD47 targeting with doxorubicin exhibited a synergistic effect in tumor suppression.

In summary, our findings supported that CD47 inhibition suppressed self-renewal, tumor initiating ability and chemoresistance of dormant liver T-ICs. Our findings may have important ramifications in future therapeutics against this deadly disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2453. doi:10.1158/1538-7445.AM2011-2453