LONDON (Dow Jones)--Biotechnology company Silence Therapeutics PLC (SLN.LN) said Wednesday it extended a research deal with AstraZeneca PLC (AZN.LN) by another year. Silence specializes in RNA interference, an experimental branch of drug research which involves shutting off or silencing genes involved in disease by disrupting RNA "messages" in cells. The two companies are developing five potential drug candidates focused on respiratory diseases and cancer. If ultimately successful, Silence could earn up to GBP200 million in fees and milestone payments plus royalties on sales of any drugs that make it to market. The deal was originally signed in July 2007. The extension of this research deal in lung disease and cancer follows the extension in April of a second, 2008 collaboration between Silence and the Anglo-Swedish drug giant. The second collaboration is focused on developing methods of delivering drugs based on RNA interference to targets in the body. -By Jason Douglas, Dow Jones Newswires; 44-20-7842-9272; [email protected] (END) Dow Jones Newswires July 14, 2010 02:32 ET (06:32 GMT)