Imprisoned dog to suffer (5)
I believe the answer is:
incur
'suffer' is the definition.
(to incur is to suffer or experience)
'imprisoned dog' is the wordplay.
'imprisoned' becomes 'in' (I am not sure about this - if you are sure you should believe this answer much more).
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'in'+'cur'='INCUR'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for incur that I've seen before include "Bring upon oneself - be liable for" , "Bring something unpleasant on oneself (5)" , "Meet" , "Become subject to (eg, taxes)" , "Become liable to (eg, a penalty)" .)