Nov 22 (Reuters) - Arrowhead Pharmaceuticals Inc (ARWR.O) on Monday entered a drug development deal with GlaxoSmithKline Plc (GSK.L) under which the British drugmaker will develop and market Arrowhead"s potential treatment for patients with fatty liver disease NASH. Under the pact, Arrowhead said it would get an upfront payment of $120 million and is eligible for additional milestone payments including up to $190 million at first commercial sale of the product, and up to $590 million in sales-related milestone payments. The drug candidate, ARO-HSD, is currently in an early-to-mid stage trial for nonalcoholic steatohepatitis (NASH), a fatty liver disease. It is based on RNA interference technology, where genes that contribute to disease are silenced. GSK will receive an exclusive license to develop and sell ARO-HSD in all territories except Greater China, which will be retained by Arrowhead. Pasadena, California-based Arrowhead said it is also eligible to receive tiered royalties on net product sales. Reporting by Manojna Maddipatla in Bengaluru; Editing by Amy Caren Daniel