In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: p53 inhibition blocked transient DOX - induced STAT3 activation in MHC - CB7 mice , which was associated with enhanced induction of the DNA repair proteins Ku70 and Ku80 .
### Output Text:
p53 inhibition blocked transient <span class="chemical">DOX</span> - induced STAT3 activation in MHC - CB7 mice , which was associated with enhanced induction of the DNA repair proteins Ku70 and Ku80 . 