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: Earlier observations that ADR interacts with mitochondrial cytochrome c oxidase ( COX ) and suppresses its enzyme activity led us to investigate ADR ' s action on the cardiovascular functions and heart mitochondrial morphology in Balb - c mice i . p . treated with ADR for several weeks .
### Output Text:
Earlier observations that <span class="chemical">ADR</span> interacts with mitochondrial cytochrome c oxidase ( COX ) and suppresses its enzyme activity led us to investigate <span class="chemical">ADR</span> ' s action on the cardiovascular functions and heart mitochondrial morphology in Balb - c mice i . p . treated with <span class="chemical">ADR</span> for several weeks . 