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: These data indicate that the adaptive response to ISO shows an early hypertrophic phase ( 1 - 4 days ) characterized by a substantial increase in RNA content and cardiac mass in the absence of changes in DNA .
### Output Text:
These data indicate that the adaptive response to <span class="chemical">ISO</span> shows an early hypertrophic phase ( 1 - 4 days ) characterized by a substantial increase in RNA content and cardiac mass in the absence of changes in DNA . 