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To overcome this limitation , we have used adenoviral transfection to develop upgraded HepG2 cells ( ADV - HepG2 ) expressing the major P450 enzymes involved in drug metabolism ( CYP1A2 , CYP2D6 , CYP2C9 , CYP2C19 , and CYP3A4 ) at levels comparable to those of human hepatocytes .
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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