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: As TNF and PAF are thought to be involved in the development of septic shock and adult respiratory distress syndrome , we hypothesize that high - dose Ara - C may be associated with cytokine release .
### Output Text:
As TNF and PAF are thought to be involved in the development of septic shock and adult respiratory distress syndrome , we hypothesize that high - dose <span class="chemical">Ara - C</span> may be associated with cytokine release . 