PDE4A and colonic neoplasm: To determine the effect of various PDEs on the anti-colon-cancer effect of EGCG, Caco-2 cells were pretreated with PDE1 inhibitor 8-Met-IBMX (10 mM), PDE2 inhibitor EHNA hydrochloride (5 μM), PDE4 inhibitor rolipram (10 μM), or PDE5 inhibitor VDN (5 μM), then treated or not with EGCG (5 μM) for 96 h.