The following should work:
ABC: *\([a-zA-Z]+\) *(.+)
Explanation:
ABC: # match literal characters 'ABC:'
* # zero or more spaces
\([a-zA-Z]+\) # one or more letters inside of parentheses
* # zero or more spaces
(.+) # capture one or more of any character (except newlines)
To get your desired grouping based on the comments below, you can use the following:
(ABC:) *(\([a-zA-Z]+\).+)
