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: Doxorubicin depletes cardiac p300 , a transcriptional coactivator that is required for the maintenance of the differentiated phenotype of cardiac myocytes .
### Output Text:
<span class="chemical">Doxorubicin</span> depletes cardiac p300 , a transcriptional coactivator that is required for the maintenance of the differentiated phenotype of cardiac myocytes . 