Construction of an immunotoxin, HN3-mPE24, targeting glypican-3 for liver cancer therapy
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Chunguang Wang1,2,*, Wei Gao1,3,*, Mingqian Feng1, Ira Pastan1, Mitchell Ho1
1Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892, USA
2Department of Thoracic Surgery, Second Hospital of Jilin University, Changchun, 130041, China
3Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Cell Biology, School of Basic Medical Science, Nanjing Medical University, Nanjing, Jiangsu, 210029, China
*These authors contributed equally to this work
Mitchell Ho, email: [email protected]
Keywords: glypican-3 or GPC3, hepatocellular carcinoma, recombinant immunotoxin, single-domain antibody fragment, mouse xenograft model
Received: May 06, 2016 Accepted: June 30, 2016 Published: July 13, 2016
Glypican-3 (GPC3) is overexpressed in hepatocellular carcinoma (HCC). We constructed a recombinant immunotoxin, HN3-mPE24, which contains a truncated form of Pseudomonas exotoxin A. The toxin portion lacks most of domain II and has seven point mutations in domain III to remove the B-cell epitopes thought to be responsible for causing off-target side effects and immunogenicity. We also fused a bivalent HN3 to mPE24. We tested these two molecules for GPC3 binding and cytotoxicity in HCC cell models. The KD values of HN3-mPE24 and HN3-HN3-mPE24 for GPC3-expressing tumor cells were 12 nM and 1.4 nM, respectively. The IC50 values of HN3-mPE24 and HN3-HN3-mPE24 for HCC cells were 0.2 nM and 0.4 nM, respectively. We also evaluated their toxicity and anti-tumor efficacy in mice. The maximum tolerated doses of HN3-mPE24 and HN3-HN3-mPE24 were 7 mg kg-1 and 3.6 mg kg-1, respectively. We treated mice with 5 mg kg-1 of HN3-mPE24 intravenously every other day for ten injections. The alpha-fetoprotein level of HN3-mPE24 treated group was approximately 700 fold less than that of the untreated group (1.1 μg ml-1 vs. 692.1 μg ml-1). In addition, 25% of the mice treated with HN3-mPE24 survived to the end of this study, which was 105 days after HCC tumor implantation. In conclusion, the HN3-mPE24 immunotoxin caused liver tumor regressions and extended survival with no significant side effects in mice. It is a promising candidate for the treatment of liver cancer that may be readily translated to humans.
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