Occasionally, cell buddies escape (5)
I believe the answer is:
elude
'escape' is the definition.
(synonyms)
'occasionally cell buddies' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'cell'+'buddies'='cellbuddies'
The alternate letters of 'cellbuddies' are 'ELUDE'.
(Other definitions for elude that I've seen before include "Escape - avoid" , "Avoid; slip one's mind" , "Avoid first" , "Avoid (e.g. capture)" , "Get round" .)