COMT and glioblastoma: However, it needs to be noted that the importance of estrogens in inhibiting COMT enzyme activity with a focus on mechanisms in the brain has been challenged by studies showing that estradiol does not affect (i) COMT activity in the rat brain and (ii) in a glioblastoma cell line (Cohn and Axelrod, 1971; Jiang et al., 2003; see also Harrison and Tunbridge, 2008 for an overview).