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: METHODS AND RESULTS : Two - week - old MHC - CB7 mice ( which express dominant - interfering p53 in cardiomyocytes ) and their non - transgenic ( NON - TXG ) littermates received weekly DOX injections for 5 weeks ( 25 mg / kg cumulative dose ) .
### Output Text:
METHODS AND RESULTS : Two - week - old MHC - CB7 mice ( which express dominant - interfering p53 in cardiomyocytes ) and their non - transgenic ( NON - TXG ) littermates received weekly <span class="chemical">DOX</span> injections for 5 weeks ( 25 mg / kg cumulative dose ) . 