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 cardiomyopathy ( CM ) produced by the anticancer drug doxorubicin ( DXR ) ( Adriamycin ) provides a unique opportunity to analyze dose - effect and structure - function relationships during development of myocardial disease .
### Output Text:
The cardiomyopathy ( CM ) produced by the anticancer drug <span class="chemical">doxorubicin</span> ( <span class="chemical">DXR</span> ) ( <span class="chemical">Adriamycin</span> ) provides a unique opportunity to analyze dose - effect and structure - function relationships during development of myocardial disease . 