Profitable cure vital to be developed (9)
I believe the answer is:
lucrative
'profitable' is the definition.
('lucrative' can be similar in meaning to 'profitable')
'cure vital to be developed' is the wordplay.
'to be developed' indicates an anagram.
'cure'+'vital'='curevital'
'curevital' is an anagram of 'LUCRATIVE'.
(Other definitions for lucrative that I've seen before include "Producing a sizeable profit" , "Making money" , "Revictual (anag.)" , "rewarding" , "Highly profitable" .)