Deplorably shifty about publicity (5)
I believe the answer is:
sadly
'deplorably' is the definition.
(thesaurus)
'shifty about publicity' is the wordplay.
'shifty' becomes 'sly' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' is an insertion indicator.
'publicity' becomes 'ad' (advert).
'sly' placed around 'ad' is 'SADLY'.
Can you help me to learn more?
(Other definitions for sadly that I've seen before include "Regrettably" , "With sorrow" , "Alas" , "Lamentably, unfortunately" , "Mournfully" .)