Acta Pharmacologica Sinica 2008 May; 29 (5): 606-613; doi: 10.1111/j.1745-7254.2008.00779.x

Aim: To construct a recombinant adenovirus that can express human spermidine/spermine N¹-acetyltransferase (SSAT) and detect its inhibitory effect on colorectal cancer cell growth in vitro.

Methods: A 516 bp cDNA of SSAT was amplified and cloned into a pGL3-hTERT plasmid. The pGL3-hTERT-SSAT recombinant was digested, and the small fragment was cloned into the shuttle vector pAdTrack. The pAdTrack-hTERT-SSAT plasmids were recombined with pAdEasy-1 vectors in AdEasy-1 cells. Positive clones were selected and transfected into the HEK293 packaging cells (transformed human embryonic kidney cells) after they were linearized by PacI. The process of adenovirus packaging and amplification was monitored by green fluorescent protein (GFP) expression. The SSAT protein levels were determined by Western blotting, and the intracellular polyamine content was detected by reverse-phase high performance liquid chromatography. The MTS (3-(4, 5-dimethylthiaol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(-4-sulfophenyl)-2H-tetrazolium, inner salt) and colony-forming assays were used to analyze the gene transduction efficiency and effect on the growth of HT-29 and LoVo cells. A viable cell count was used to determine the cell growth with or without exogenous polyamines.

Results: The GFP expression in 293 cells during virus packing and amplification was observed by fluorescence microscopy. Western blotting results demonstrated that Ad-hTERT-SSAT could increase the expression of SSAT, and consequently, spermidine and spermine were reduced to low levels. The MTS and colony-forming assay results showed that HT-29 and LoVo cell growth were significantly inhibited, and the inhibitory effect could be partially reversed by exogenous spermidine and spermine.

Conclusion: The successfully constructed recombinant adenovirus Ad-hTERT-SSAT could accelerate polyamine catabolism and inhibit the colorectal cell growth in vitro. It also has therapeutic potential in the treatment of colorectal cancer.

Keywords: spermidine/spermine N¹-acetyltransferase; adenovirus; colorectal cancer