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: BACKGROUND : Doxorubicin induces a self - perpetuating nephropathy characterized by early glomerular and late - onset tubular lesions in rats .
### Output Text:
BACKGROUND : <span class="chemical">Doxorubicin</span> induces a self - perpetuating nephropathy characterized by early glomerular and late - onset tubular lesions in rats . 