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Nuclear receptors SXR and CAR are possible master regulators of xenobiotic - inducible MDR1 expression in drug processing organs , but the mechanism of MDR1 regulation has yet to be directly demonstrated in vivo .
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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:
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