Amgen Inc. has opted out of a collaborative agreement with Bind Therapeutics Inc., a company developing tiny particles that adhere to medicines and help the drugs circulate longer in the bloodstream and enter cells. In December 2012, the Thousand Oaks pharmaceutical company entered into a 12-month agreement with Bind to combine its technology with an Amgen cancer drug. The agreement was extended until this month, but Bind announced both companies have decided to discontinue the arrangement. “The goal of this research collaboration was to optimize a specific therapeutic payload from Amgen. Despite achieving the objective of high tumor concentrations, the results were not sufficiently compelling to proceed forward,” Scott Minick, chief executive of Bind, said in a statement. In addition to its deal with Amgen, Bind has announced collaborations with Pfizer Inc., AstraZeneca and Roche. Since the announcement on July 2, Bind shares have lost $1.21 or 9.3 percent to close Monday at $11.68. Shares of Amgen have lost 82 cents or less than 1 percent to close at $120.16 on the Nasdaq.