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: A rat model was used to evaluate the general acute toxicity and the late cardiotoxicity of 4 mg / kg doxorubicin ( DOX ) given either as free drug or in the form of three N - ( 2 - hydroxypropyl ) methacrylamide ( HPMA ) copolymer conjugates .
### Output Text:
A rat model was used to evaluate the general acute toxicity and the late cardiotoxicity of 4 mg / kg <span class="chemical">doxorubicin</span> ( <span class="chemical">DOX</span> ) given either as free drug or in the form of three <span class="chemical">N - ( 2 - hydroxypropyl ) methacrylamide</span> ( <span class="chemical">HPMA</span> ) copolymer conjugates . 