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: PURPOSE : The anthracyclines daunorubicin and doxorubicin and the epipodophyllotoxin etoposide are potent DNA cleavage - enhancing drugs that are widely used in clinical oncology ; however , myelosuppression and cardiac toxicity limit their use .
### Output Text:
PURPOSE : The <span class="chemical">anthracyclines</span> <span class="chemical">daunorubicin</span> and <span class="chemical">doxorubicin</span> and the <span class="chemical">epipodophyllotoxin</span> <span class="chemical">etoposide</span> are potent DNA cleavage - enhancing drugs that are widely used in clinical oncology ; however , myelosuppression and cardiac toxicity limit their use . 