STAT6 mRNA and protein knockdown using multiple siRNA sequences inhibits proliferation and induces apoptosis of the human colon adenocarcinoma cell line, HT-29

The transcription factor STAT6 is strongly expressed in various tumours and is most highly expressed in malignant lymphomas and pancreatic, colorectal, prostate and breast cancers. STAT6 expression in colorectal cancer is associated with an increased malignancy, poor prognosis and poor survival rates. Colorectal cancer has an incidence of approximately 1,361,000 patients per annum worldwide and approximately 60% of those cancers show STAT6 expression. Techniques aimed at reducing or blocking STAT6 expression may be useful in treating colorectal cancers. Celixir’s four proprietary STAT6 specific small interfering RNA (siRNA) sequences were tested in vitro using the human colon adenocarcinoma cell line, HT-29. The four sequences were introduced individually and in combination into HT-29 cells at different concentrations (10 to 200 nM). Decreases in STAT6 mRNA and protein levels were analysed to confirm the transfection was successful. STAT6 knockdown effects were measured by analysing cell proliferation and apoptosis. Results showed that 100nM siRNA concentration was the most effective and all four individual sequences knocked-down STAT6 mRNA and protein by more than 50%. Although all individual sequences were capable of significantly inhibiting cell proliferation, STAT6.1 and STAT6.4 were the best. STAT6 silencing also significantly induced late and total apoptotic events. In conclusion, these results demonstrate that STAT6 siRNA sequences are capable of inhibiting the proliferation, and inducing late apoptosis, of HT-29 colon cancer cells and, in some instances, halving the number of cancer cells. These experiments will be repeated using xenografts of STAT6-expressing colon cancer cells in immunocompromised mice and the STAT6 siRNA sequences will be tested in other cancers in which STAT6 is expressed. The STAT6 siRNA sequences therefore represent a potential treatment for the most serious colorectal cancers and a wide variety of STAT6-expressing cancers.