In vitro activity: BAY-958 is a lead compound for Atuveciclib (formerly known as BAY-1143572) which is novel, potent, oral and highly selective PTEFb/CDK9 inhibitor. It inhibits CDK9/CycT1 with an IC50 of 13 nM and is more than 100-fold more selective for CDK9 over CDK2. It also inhibits GSK3 kinase with IC50 values of 45 nM and 87 nM for GSK3α and GSK3β respectively. Atuveciclib is currently in Phase I clinical trial. Selective inhibition of exclusively transcription-regulating PTEFb/CDK9 is a promising new approach in cancer therapy. Starting from lead compound BAY-958, lead optimization efforts strictly focusing on kinase selectivity, physicochemical and DMPK properties finally led to the identification of the orally available clinical candidate atuveciclib (BAY 1143572). Structurally characterized by an unusual benzyl sulfoximine group, BAY 1143572 exhibited the best overall profile in vitro and in vivo, including high efficacy and good tolerability in xenograft models in mice and rats. BAY 1143572 is the first potent and highly selective PTEFb/CDK9 inhibitor to enter clinical trials for the treatment of cancer.

Kinase Assay: Merck Millipore CDK assays: Assays were performed according to the Merck Millipore KinaseProfilerTM standard protocols, with an ATP concentration of 10 μm..

Cell Assay: HeLa human cervical tumor cells (CCL‐2) were obtained from the American Type Culture Collection (Manassas, USA) and MOLM‐13 human acute myeloid leukemia cells (ACC 554) were obtained from the German Collection of Microorganisms and Cell Cultures (Braunschweig, Germany). Authentication of cell lines was conducted at the German Collection of Microorganisms and Cell Cultures via PCR‐ased DNA profiling of polymorphic short tandem repeats. Cells were propagated under the suggested growth conditions in a humidified 37 °C incubator. Proliferation assays were conducted in 96‐well plates at densities of 3000 (HeLa) and 5000 (MOLM‐13) cells per well in the growth medium containing 10 % fetal calf serum (FCS). Cells were treated in quadruplicate with serial dilutions of test compounds for 96 h. Relative cell numbers were quantified by crystal violet staining (HeLa) or CellTitre‐Glo Luminescent Cell Viability Assay (Promega) (MOLM‐13). IC50 values (inhibitory concentration at 50 % of maximal effect) were determined by means of a four‐parameter fit on measurement data which were normalized to vehicle (DMSO) treated cells (=100 %) and measurement readings taken immediately before compound exposure (=0 %).