Dissection of PIM serine/threonine kinases in FLT3-ITD–induced leukemogenesis reveals PIM1 as regulator of CXCL12–CXCR4-mediated homing and migration

FLT3-ITD–mediated leukemogenesis is associated with increased expression of oncogenic PIM serine/threonine kinases. To dissect their role in FLT3-ITD–mediated transformation, we performed bone marrow reconstitution assays. Unexpectedly, FLT3-ITD cells deficient for PIM1 failed to reconstitute lethally irradiated recipients, whereas lack of PIM2 induction did not interfere with FLT3-ITD–induced disease. PIM1-deficient bone marrow showed defects in homing and migration and displayed decreased surface CXCR4 expression and impaired CXCL12–CXCR4 signaling. Through small interfering RNA–mediated knockdown, chemical inhibition, expression of a dominant-negative mutant, and/or reexpression in knockout cells, we found PIM1 activity to be essential for proper CXCR4 surface expression and migration of cells toward a CXCL12 gradient. Purified PIM1 led to the phosphorylation of serine 339 in the CXCR4 intracellular domain in vitro, a site known to be essential for normal receptor recycling. In primary leukemic blasts, high levels of surface CXCR4 were associated with increased PIM1 expression, and this could be significantly reduced by a small molecule PIM inhibitor in some patients. Our data suggest that PIM1 activity is important for homing and migration of hematopoietic cells through modification of CXCR4. Because CXCR4 also regulates homing and maintenance of cancer stem cells, PIM1 inhibitors may exert their antitumor effects in part by interfering with interactions with the microenvironment

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

The reaction of [Ir(IMes)(COD)Cl], [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene] with pyridazine (pdz) and phthalazine (phth) results in the formation of [Ir(COD)(IMes)(pdz)]Cl and [Ir(COD)(IMes)(phth)]Cl. These two complexes are shown by nuclear magnetic resonance (NMR) studies to undergo a haptotropic shift which interchanges pairs of protons within the bound ligands. When these complexes are exposed to hydrogen, they react to form [Ir(H)2(COD)(IMes)(pdz)]Cl and [Ir(H)2(COD)(IMes)(phth)]Cl, respectively, which ultimately convert to [Ir(H)2(IMes)(pdz)3]Cl and [Ir(H)2(IMes)(phth)3]Cl, as the COD is hydrogenated to form cyclooctane. These two dihydride complexes are shown, by NMR, to undergo both full N-heterocycle dissociation and a haptotropic shift, the rates of which are affected by both steric interactions and free ligand pKa values. The use of these complexes as catalysts in the transfer of polarisation from para-hydrogen to pyridazine and phthalazine via signal amplification by reversible exchange (SABRE) is explored. The possible future use of drugs which contain pyridazine and phthalazine motifs as in vivo or clinical magnetic resonance imaging probes is demonstrated; a range of NMR and phantom-based MRI measurements are reported

Crystal Structure of the PIM2 Kinase in Complex with an Organoruthenium Inhibitor

BACKGROUND: The serine/threonine kinase PIM2 is highly expressed in human leukemia and lymphomas and has been shown to positively regulate survival and proliferation of tumor cells. Its diverse ATP site makes PIM2 a promising target for the development of anticancer agents. To date our knowledge of catalytic domain structures of the PIM kinase family is limited to PIM1 which has been extensively studied and which shares about 50% sequence identity with PIM2. PRINCIPAL FINDINGS: Here we determined the crystal structure of PIM2 in complex with an organoruthenium complex (inhibition in sub-nanomolar level). Due to its extraordinary shape complementarity this stable organometallic compound is a highly potent inhibitor of PIM kinases. SIGNIFICANCE: The structure of PIM2 revealed several differences to PIM1 which may be explored further to generate isoform selective inhibitors. It has also demonstrated how an organometallic inhibitor can be adapted to the binding site of protein kinases to generate highly potent inhibitors. ENHANCED VERSION: This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1

Overcoming ABCG2-mediated drug resistance with imidazo-[1,2-b]-pyridazine-based Pim1 kinase inhibitors

Purpose Multidrug efflux pumps such as ABCG2 confer drug resistance to a number of cancer types, leading to poor prognosis and outcome. To date, the strategy of directly inhibiting multidrug efflux pumps in order to overcome drug resistance in cancer has been unsuccessful. An alternative strategy is to target proteins involved in the regulation of multidrug efflux pump activity or expression. Pim1 kinase has been demonstrated to phosphorylate ABCG2, promote its oligomerisation and contribute to its ability to confer drug resistance. Methods In the present manuscript, imidazo-pyridazine-based inhibitors of Pim1 were examined for their ability to overcome ABCG2-mediated drug resistance. Drug efficacy was measured as a cytotoxic response or an effect on transport by ABCG2. Protein expression patterns were assessed using western immuno-blotting. Results The two Pim1 inhibitors increased the potency of flavopiridol, mitoxantrone, topotecan and doxorubicin, specifically in ABCG2-expressing cells. This effect was associated with an increase in the cellular accumulation of [3H]-mitoxantrone, suggesting direct impairment of the transporter. However, prolonged pre-incubation with the studied inhibitors greatly enhanced the effect on mitoxantrone accumulation. The inhibitors caused a significant time-dependent reduction in the expression of ABCG2 in the resistant cells, an effect that would improve drug efficacy. Conclusion Consequently, it appears that the Pim1 inhibitors display a dual-mode effect on ABCG2-expressing cancer cells. This may provide a powerful new strategy in overcoming drug resistance by targeting proteins that regulate expression of efflux pumps