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: Transgenic mice overexpressing p300 in the heart and wild - type mice were subjected to doxorubicin treatment .
### Output Text:
Transgenic mice overexpressing p300 in the heart and wild - type mice were subjected to <span class="chemical">doxorubicin</span> treatment . 