RSK2 is a serine/threonine kinase downstream signaling mediator in the RAS/ERK signaling pathway and may be a therapeutic target in mantle cell lymphoma (MCL). RSK2-Ser227 in the N-terminal kinase domain (NTKD) of RSK2 was found to be ubiquitously active in five MCL-derived cell lines and in tumor tissues derived from five MCL patients. BI-D1870, an inhibitor specific to RSK2-NTKD, caused RSK2-Ser227 dephosphorylation, and thereby, induced dose-dependent growth inhibition via G2/M cell cycle blockade and apoptosis. Comparative gene expression profiling of the MCL-derived cell lines showed that inhibition of RSK2-Ser227 by BI-D1870 caused downregulation of oncogenes, such c-MYC and MYB; anti-apoptosis genes, such as BCL2 and BCL2L1; genes for B cell development, including IKZF1, IKZF3 and PAX5; and genes constituting the B cell receptor signaling pathway, such as CD19, CD79B and BLNK. These findings show that targeting of RSK2-Ser227 enables concomitant blockade of pathways that are critically important in B cell tumorigenesis. Overall design: Mantle cell lymphoma-derivedcell lines (Jeko-1 and KPUM-YY1 cells) were treated with BI-D1870 at IC80 for each cell line. After 6 hours of culture, total RNA was isolated and hybridized on microarrays with Clariom S array (Affymetrix, Santa Clara, CA), a GeneChip WT Plus Reagent Kit (Thermo Fisher Scientific, Waltham, MA) and a GeneChip Scanner 7G (Affymetrix).