DUBLIN – Silence Therapeutics plc entered a wide-ranging siRNA-based drug discovery and development deal with Astrazeneca plc that has propelled it toward the front ranks of siRNA platform companies. It is banking an up-front payment of $60 million, another $20 million as an equity investment and up to $400 million in option fees and milestone payments per candidate drug, in an alliance that could entail up to five active programs within three years.