SOUTH SAN FRANCISCO, Calif., June 12 /PRNewswire-FirstCall/ -- Sunesis Pharmaceuticals, Inc. (Nasdaq: SNSS - News) today announced that it has earned a $4.25 million payment from Merck & Co., Inc. for meeting certain preclinical milestones in the companies' collaboration to develop oral small molecule inhibitors of beta-amyloid converting enzyme (BACE), which is believed to play a key role in Alzheimer's disease.