Brief Article
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World J Gastroenterol. Jun 7, 2013; 19(21): 3300-3308
Published online Jun 7, 2013. doi: 10.3748/wjg.v19.i21.3300
Anticancer effects of sweet potato protein on human colorectal cancer cells
Peng-Gao Li, Tai-Hua Mu, Le Deng
Peng-Gao Li, Tai-Hua Mu, Le Deng, Key Laboratory of Agro-products Processing, Ministry of Agriculture, Institute of Agro-products Processing Science and Technology, Chinese Academy of Agricultural Sciences, Beijing 100193, China
Peng-Gao Li, School of Public Health and Family Medicine, Capital Medical University, Beijing 100069, China
Peng-Gao Li, Beijing Municipal Key Laboratory of Clinical Epidemiology, Beijing 100069, China
Author contributions: Li PG and Mu TH designed the research; Li PG and Deng L carried out the laboratory experiments and analyzed the data; Li PG prepared the manuscript.
Supported by The Earmarked Fund for China Agriculture Research System, No. CARS-11-B-19; “Technique of Processing and Utilization for Plant Proteins” from China-Argentina Science and Technology Cooperation Program, No. 2010DFA32690; Grant from the Capital Medical University, No. 2009ZR03 and No. 2012ZR17; the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions
Correspondence to: Dr. Tai-Hua Mu, Key Laboratory of Agro-products Processing, Ministry of Agriculture, Institute of Agro-products Processing Science and Technology, Chinese Academy of Agricultural Sciences, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100193, China. mutaihuacaas@126.com
Telephone: +86-10-62815541 Fax: +86-10-62815541
Received: December 28, 2012
Revised: March 25, 2013
Accepted: April 27, 2013
Published online: June 7, 2013
Processing time: 158 Days and 2.9 Hours
Abstract

AIM: To investigate the effects of proteins purified from sweet potato storage roots on human colorectal cancer cell lines.

METHODS: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Hoechst 33258 nuclear staining and Boyden transwell chamber methods were used to determine whether purified sweet potato protein (SPP) from fresh sweet potato roots affected proliferation, migration and invasion, respectively, of human colorectal cancer SW480 cells in vitro. The inhibitory effects of SPP on growth of human colorectal cancer HCT-8 cells intraperitoneally xenografted in nude mice and spontaneous lung metastasis of murine Lewis lung carcinoma 3LL cells subcutaneously transplanted in C57 BL/6 mice were also investigated in vivo.

RESULTS: SPP inhibited the proliferation of SW480 cells in a dose-dependent manner, with an IC50 value of 38.732 μmol/L (r2 = 0.980, P = 0.003) in the MTT assay. Hoechst 33258 nuclear staining further revealed inhibition of cell viability and induction of apoptosis by SPP. The transwell assay disclosed significant reduction in migrated cells/field by 8 μmol/L SPP (8.4 ± 2.6 vs 23.3 ± 5.4, P = 0.031) and invaded cells/field through the ECMatrix by 0.8 μmol/L SPP, compared with the control (25.2 ± 5.2 vs 34.8 ± 6.1, P = 0.038). Both intraperitoneal (ip) and intragastric (ig) administration of SPP led to significant suppression of growth of intraperitoneally inoculated HCT-8 cells in nude mice to 58.0% ± 5.9% (P = 0.037) and 43.5% ± 7.1% (P = 0.004) of the controls, respectively, after 9 d treatment. Bloody ascites additionally disappeared after ip injection of trypsin inhibitor. Notably, ig and ip administration of SPP induced a significant decrease in spontaneous pulmonary metastatic nodule formation in C57 BL/6 mice (21.0 ± 12.3 and 27.3 ± 12.7 nodules/lung vs 42.5 ± 4.5 nodules/lung in controls, respectively, P < 0.05) after 25 d treatment. Moreover, the average weight of primary tumor nodules in the hind leg of mice decreased from 8.2 ± 1.3 g/mice in the control to 6.1 ± 1.4 g/mice in the ip group (P = 0.035).

CONCLUSION: SPP exerts significant antiproliferative and antimetastatic effects on human colorectal cancer cell lines, both in vitro and in vivo.

Keywords: Sweet potato protein; Colorectal cancer; Cell proliferation; Cell invasion; Metastasis

Core tip: Sweet potato protein (SPP) is a type of serine protease inhibitor that suppresses the activity of trypsin. The current study showed that SPP significantly inhibited proliferation, migration and invasion of human colorectal cancer SW480 cells in vitro. Moreover, the protein significantly suppressed the growth of intraperitoneally xenografted human colorectal cancer HCT-8 cells and volume of bloody ascites formed in nude mice. Spontaneous lung metastasis of a murine lung carcinoma cell line was significantly inhibited by SPP in mice. Notably, both intragastric infusion and intraperitoneal injection of SPP were effective in animal models.