6697
The in vitro cytotoxicity of compounds 1 - 4 and 6 against human carcinoma A549 , MCF - 7 , and HeLa cell lines were evaluated using the MTT colourimetric assay .
 MTT
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 MTT