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: We investigated the diagnostic value of cTnI and cTnT for the diagnosis of myocardial damage in a rat model of doxorubicin ( DOX ) - induced cardiomyopathy , and we examined the relationship between serial cTnI and cTnT with the development of cardiac disorders monitored by echocardiography and histological examinations in this model .
### Output Text:
We investigated the diagnostic value of cTnI and cTnT for the diagnosis of myocardial damage in a rat model of <span class="chemical">doxorubicin</span> ( <span class="chemical">DOX</span> ) - induced cardiomyopathy , and we examined the relationship between serial cTnI and cTnT with the development of cardiac disorders monitored by echocardiography and histological examinations in this model . 