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: Increased oxidative stress is a major factor implicated in the cardiotoxicity of doxorubicin ( DOX ) , a widely used antitumor anthracycline antibiotic .
### Output Text:
Increased oxidative stress is a major factor implicated in the cardiotoxicity of <span class="chemical">doxorubicin</span> ( <span class="chemical">DOX</span> ) , a widely used antitumor <span class="chemical">anthracycline</span> antibiotic . 