Barring any further restrictions/requirements as laserlight has asked, you can grab any parenthesized string with something like...
php > $regex = '/(?<=\()[^\)]+(?=\))/';
php > $text = 'asdb (ABC) fdafd (123) Foo (Bar)';
php > preg_match_all($regex, $text, $matches);
php > print_r($matches);
 => Array
 => ABC
 => 123
 => Bar
See https://www.php.net/manual/en/regexp.reference.assertions.php for info on the look-ahead/-behind assertions I used.