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: However , the maximal reduction in body weight seen in animals that received polymer - bound DOX ( 4 mg / kg ) was significantly lower than that observed in those that received free DOX ( 4 mg / kg ) or a mixture of the unmodified parent HPMA copolymer and free DOX ( 4 mg / kg ; P less than 0 . 01 ) .
### Output Text:
However , the maximal reduction in body weight seen in animals that received polymer - bound <span class="chemical">DOX</span> ( 4 mg / kg ) was significantly lower than that observed in those that received free <span class="chemical">DOX</span> ( 4 mg / kg ) or a mixture of the unmodified parent <span class="chemical">HPMA</span> copolymer and free <span class="chemical">DOX</span> ( 4 mg / kg ; P less than 0 . 01 ) . 