OPRM1 and neuroblastoma: In human neuroblastoma SK-N-SH and SH-SY5Y cells, chronic exposure to the selective MOR agonist, [D-Ala(2), N-Me-Phe(4), Gly(5)-ol] enkephalin (DAMGO) (0.1–10 μM, 48 h) results in enhanced binding of Sp1/Sp3 to the OPRM1 promoter, which is attenuated by the pretreatment with the MOR antagonist, naloxone [173].