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: The mechanism of doxorubicin ( DOX ) - induced cardiotoxicity remains controversial .
### Output Text:
The mechanism of <span class="chemical">doxorubicin</span> ( <span class="chemical">DOX</span> ) - induced cardiotoxicity remains controversial . 