The trial including two stages. The first is an exploration stage to decide delivery frequency and dose of study drug. It is single-blinded, subjects will be randomly divided into 4 groups with a 2:2:2:1 ratio. Study drug given twice per week or 3 times per, dose of the drug are from 20μg to 40μg. The sample size is 105, duration is 12 to 18 months. Based on preliminary efficacy and safety, the better dosage regimen will decided for the second stage.The second stage is double-blinded,subject will be randomly divided into treatment group or placebo group with 2:1 ratio and sample size is 600.