MYB and mantle cell lymphoma: BI-D1870 is a specific inhibitor of the N-terminal kinase domain of the MAPK-downstream serine/threonine kinase ribosomal protein S6 kinase 2 (RSK2), and BI-D1870-mediated RSK2 inhibition led to suppression of MYB and MYC accompanied by G2/M cell cycle arrest and apoptosis induction in MCL/mantle cell lymphoma cells (Jeko-1, KPUM-YY1, MINO, and Z-138 cell lines).