Yes, APOSTOLIC is a Scrabble word!

Letter values in Scrabble US: A 1, P 3, O 1, S 1, T 1, O 1, L 1, I 1, C 3.

Is it a valid word?

APOSTOLIC is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

of or relating to or deriving from the Apostles or their teachings
proceeding from or ordered by or subject to a pope or the papacy regarded as the successor of the Apostles

Not playable in Scrabble US: APOSTOLICAL.