rel-AZ5576 is a selective CDK9 inhibitor with the activity of downregulating Mcl-1 and MYC mRNA transcription and protein expression in diffuse large B-cell lymphoma by inhibiting CDK9 , promoting MYC protein turnover, reducing MYC phosphorylation on the stable Ser62 residue and downregulating MYC transcriptional targets, inhibiting the growth of diffuse large B-cell lymphoma cell lines in vitro and in vivo and independent of the cell origin.