title: Structural analysis identifies imidazo[1,2-b]pyridazines as PIM kinase inhibitors with in vitro antileukemic activity.
abstract: Much attention has recently been focused on PIM kinases as potential targets for the treatment of hematopoietic malignancies and some solid cancers. Using protein stability shift assays, we identified a family of imidazo[1,2-b]pyridazines to specifically interact with and inhibit PIM kinases with low nanomolar potency. The high-resolution crystal structure of a PIM1 inhibitor complex revealed that imidazo[1,2-b]pyridazines surprisingly interact with the NH(2)-terminal lobe helix alphaC rather than with the kinase hinge region. Thus, the identified inhibitors are ATP competitive but not ATP mimetic compounds, explaining their enhanced selectivity with respect to conventional type I kinase inhibitors. One of the identified imidazo[1,2-b]pyridazines (K00135) was further tested in several hematopoietic cellular systems. First, K00135 dose-dependently impaired survival of murine Ba/F3 cells that have been rendered cytokine independent by overexpression of human PIMs. Second, K00135 impaired survival and clonogenic growth of a panel of human acute leukemia cells. Third, exposure of K00135 significantly suppressed in vitro growth of leukemic blasts from five acute myelogenous leukemia patients but not of normal umbilical cord blood mononuclear cells. In vitro kinase assays and immunoblotting using lysates from human MV4;11 leukemic cells showed inhibition of phosphorylation of known PIM downstream targets, such as BAD and eukaryotic translation initiation factor 4E-binding protein 1, by K00135. Taken together, we report a family of small molecules that selectively interact and block PIM kinases and could serve as a lead to develop new targeted antileukemic therapeutics.
authors.affiliation: Department of Research and the Hematology Clinic, University Hospital Basel, Hebelstrasse 20, CH-4031 Basel, Switzerland.
authors.forename: Vanda
authors.initials: V
authors.lastname: Pogacic
authors.forename: Alex N
authors.initials: AN
authors.lastname: Bullock
authors.forename: Oleg
authors.initials: O
authors.lastname: Fedorov
authors.forename: Panagis
authors.initials: P
authors.lastname: Filippakopoulos
authors.forename: Christelle
authors.initials: C
authors.lastname: Gasser
authors.forename: Andrea
authors.initials: A
authors.lastname: Biondi
authors.forename: Sandrine
authors.initials: S
authors.lastname: Meyer-Monard
authors.forename: Stefan
authors.initials: S
authors.lastname: Knapp
authors.forename: Juerg
authors.initials: J
authors.lastname: Schwaller
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002626:Chemistry, Pharmaceutical / Q000379:methods; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D020128:Inhibitory Concentration 50; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors*; D051573:Proto-Oncogene Proteins c-pim-1; D011724:Pyridazines / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D011724:Pyridazines; D017346:Protein Serine-Threonine Kinases; D051573:Proto-Oncogene Proteins c-pim-1; C406031:proto-oncogene proteins pim