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: The findings suggest that NIK - 247 may be a useful drug for the treatment of Alzheimer ' s disease .
### Output Text:
The findings suggest that <span class="chemical">NIK - 247</span> may be a useful drug for the treatment of Alzheimer ' s disease . 