Two pivotal trials testing the ability of a topical suspension of silver particles to improve the efficacy of laser therapy for acne have both failed to surface additional benefit from the candidate, SNA-001, sending shares of the regimen's developer, Sienna Biopharmaceuticals Inc. (NASDAQ:SNNA) down as far as $12.77 before ending the day at $15 Monday, down 70 cents. The probability of success in a soon-to-finish third pivotal trial with a different laser now seems lower, Sienna's president and CEO, Frederick Beddingfield, said.