OPRM1 and glioblastoma: To test for tumoricidal effects of methadone in glioblastoma, we first analyzed expression of the μ-opioid receptor (OPRM1) and the NMDA receptor subunit ζ1 (GRIN1) in our human glioblastoma cell lines A172, T98G and U251 by RT-PCR and in part, by western blotting.