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: We conclude that mPGES - 1 - derived PGE ( 2 ) mediates lithium - induced polyuria likely via inhibition of AQP2 and NKCC2 expression .
### Output Text:
We conclude that mPGES - 1 - derived <span class="chemical">PGE ( 2 )</span> mediates <span class="chemical">lithium</span> - induced polyuria likely via inhibition of AQP2 and NKCC2 expression . 