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: Pyrrolidine dithiocarbamate ( PDTC ) has a dual mechanism of action as an antioxidant and an inhibitor of the transcription factor kappa - beta .
### Output Text:
<span class="chemical">Pyrrolidine dithiocarbamate</span> ( <span class="chemical">PDTC</span> ) has a dual mechanism of action as an antioxidant and an inhibitor of the transcription factor kappa - beta . 