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Despite intensive studies of the secretase - mediated processing of the amyloid precursor protein ( APP ) to form the amyloid beta - peptide ( A beta ) , in relation to Alzheimer ' s disease ( AD ) , no new therapeutic agents have reached the clinics based on reducing A beta levels through the use of secretase inhibitors or immunotherapy .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None