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Few nanocarriers have been proposed to address the challenge of ATP / AZT - TP cellular delivery , but the loading efficiency , preparation complexity , and efficient cellular delivery remain important barriers to their development .
 ATP, AZT - TP
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ATP, AZT - TP