5′-Deoxy-5′-(methylthio)adenosine (methylthioadenosine, MTA), the polyamine byproduct in the methionine salvage pathway that is reported to be a SAM-competitive inhibitor of PRMTs,50., 51., 52., 53., 54. and the PRMT5 inhibitor EPZ015666 (GSK3235025)50., 55. were used as ...