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: Five days after DOX administration , left ventricular performance was significantly depressed in PARP - 1 + / + mice , but only to a smaller extent in PARP - 1 - / - ones .
### Output Text:
Five days after <span class="chemical">DOX</span> administration , left ventricular performance was significantly depressed in PARP - 1 + / + mice , but only to a smaller extent in PARP - 1 - / - ones . 