19783
The antitumor activity of these complexes against various tumor cells have been evaluated by MTT assay , and the results show that this type of arene Ru ( II ) complexes exhibit acceptable inhibitory effect against all of these tumor cells , especially osteosarcoma MG - 63 cells , but with low toxicity toward HK - 2 human normal cells .
 MTT, arene, Ru ( II )
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 MTT, arene, Ru ( II )