8167
The most active compound exhibited potent COX - 2 inhibition , some selectivity for COX - 2 over COX - 1 , only slight cytotoxicity towards healthy cells ( HaCaT skin cells ) , and no mutagenic potential ( as determined by an Ames assay ) .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 None