Optimization of permeability in a series of pyrrolotriazine inhibitors of IRAK4.

We have developed a series of orally efficacious IRAK4 inhibitors, based on a scaffold hopping strategy and using rational structure based design. Efforts to tackle low permeability and high efflux in our previously reported pyrrolopyrimidine series (Scott et al., 2017) led to the identification of pyrrolotriazines which contained one less formal hydrogen bond donor and were intrinsically more lipophilic. Further optimisation of substituents on this pyrrolotriazine core culminated with the discovery of 30 as a promising in vivo probe to assess the potential of IRAK4 inhibition for the treatment of MyD88 mutant DLBCL in combination with a BTK inhibitor. When tested in an ABC-DLBCL model with a dual MyD88/CD79 mutation (OCI-LY10), 30 demonstrated tumour regressions in combination with ibrutinib.

AZD1208, a potent and selective pan-Pim kinase inhibitor, demonstrates efficacy in preclinical models of acute myeloid leukemia.

Upregulation of Pim kinases is observed in several types of leukemias and lymphomas. Pim-1, -2, and -3 promote cell proliferation and survival downstream of cytokine and growth factor signaling pathways. AZD1208 is a potent, highly selective, and orally available Pim kinase inhibitor that effectively inhibits all three isoforms at <5 nM or <150 nM in enzyme and cell assays, respectively. AZD1208 inhibited the growth of 5 of 14 acute myeloid leukemia (AML) cell lines tested, and sensitivity correlates with Pim-1 expression and STAT5 activation. AZD1208 causes cell cycle arrest and apoptosis in MOLM-16 cells, accompanied by a dose-dependent reduction in phosphorylation of Bcl-2 antagonist of cell death, 4EBP1, p70S6K, and S6, as well as increases in cleaved caspase 3 and p27. Inhibition of p4EBP1 and p-p70S6K and suppression of translation are the most representative effects of Pim inhibition in sensitive AML cell lines. AZD1208 inhibits the growth of MOLM-16 and KG-1a xenograft tumors in vivo with a clear pharmacodynamic-pharmacokinetic relationship. AZD1208 also potently inhibits colony growth and Pim signaling substrates in primary AML cells from bone marrow that are Flt3 wild-type or Flt3 internal tandem duplication mutant. These results underscore the therapeutic potential of Pim kinase inhibition for the treatment of AML.

Mechanism for the allosteric regulation of phosphodiesterase 2A deduced from the X-ray structure of a near full-length construct.

We report the X-ray crystal structure of a phosphodiesterase (PDE) that includes both catalytic and regulatory domains. PDE2A (215-900) crystallized as a dimer in which each subunit had an extended organization of regulatory GAF-A and GAF-B and catalytic domains connected by long alpha-helices. The subunits cross at the GAF-B/catalytic domain linker, and each side of the dimer contains in series the GAF-A and GAF-B of one subunit and the catalytic domain of the other subunit. A dimer interface extends over the entire length of the molecule. The substrate binding pocket of each catalytic domain is occluded by the H-loop. We deduced from comparisons with structures of isolated, ligand-bound catalytic subunits that the H-loop swings out to allow substrate access. However, in dimeric PDE2A (215-900), the H-loops of the two catalytic subunits pack against each other at the dimer interface, necessitating movement of the catalytic subunits to allow for H-loop movement. Comparison of the unliganded GAF-B of PDE2A (215-900) with previous structures of isolated, cGMP-bound GAF domains indicates that cGMP binding induces a significant shift in the GAF-B/catalytic domain linker. We propose that cGMP binding to GAF-B causes movement, through this linker region, of the catalytic domains, such that the H-loops no longer pack at the dimer interface and are, instead, free to swing out to allow substrate access. This increase in substrate access is proposed as the basis for PDE2A activation by cGMP and may be a general mechanism for regulation of all PDEs.

Structural basis for the catalytic mechanism of human phosphodiesterase 9.

The phosphodiesterases (PDEs) are metal ion-dependent enzymes that regulate cellular signaling by metabolic inactivation of the ubiquitous second messengers cAMP and cGMP. In this role, the PDEs are involved in many biological and metabolic processes and are proven targets of successful drugs for the treatments of a wide range of diseases. However, because of the rapidity of the hydrolysis reaction, an experimental knowledge of the enzymatic mechanisms of the PDEs at the atomic level is still lacking. Here, we report the structures of reaction intermediates accumulated at the reaction steady state in PDE9/crystal and preserved by freeze-trapping. These structures reveal the catalytic process of a PDE and explain the substrate specificity of PDE9 in an actual reaction and the cation requirements of PDEs in general.

Discovery of a Series of 5-Azaquinazolines as Orally Efficacious IRAK4 Inhibitors Targeting MyD88L265P Mutant Diffuse Large B Cell Lymphoma.

In this article, we report the discovery of a series of 5-azaquinazolines as selective IRAK4 inhibitors. From modestly potent quinazoline 4, we introduced a 5-aza substitution to mask the 4-NH hydrogen bond donor (HBD). This allowed us to substitute the core with a 2-aminopyrazole, which showed large gains in cellular potency despite the additional formal HBD. Further optimization led to 6-cyanomethyl-5-azaquinazoline 13, a selective IRAK4 inhibitor, which proved efficacious in combination with ibrutinib, while showing very little activity as a single agent up to 100 mg/kg. This contrasted to previously reported IRAK4 inhibitors that exhibited efficacy in the same model as single agents and was attributed to the enhanced specificity of 13 toward IRAK4.

Discovery and Optimization of Pyrrolopyrimidine Inhibitors of Interleukin-1 Receptor Associated Kinase 4 (IRAK4) for the Treatment of Mutant MYD88L265P Diffuse Large B-Cell Lymphoma.

Herein we report the optimization of a series of pyrrolopyrimidine inhibitors of interleukin-1 receptor associated kinase 4 (IRAK4) using X-ray crystal structures and structure based design to identify and optimize our scaffold. Compound 28 demonstrated a favorable physicochemical and kinase selectivity profile and was identified as a promising in vivo tool with which to explore the role of IRAK4 inhibition in the treatment of mutant MYD88L265P diffuse large B-cell lymphoma (DLBCL). Compound 28 was shown to be capable of demonstrating inhibition of NF-κB activation and growth of the ABC subtype of DLBCL cell lines in vitro at high concentrations but showed greater effects in combination with a BTK inhibitor at lower concentrations. In vivo, the combination of compound 28 and ibrutinib led to tumor regression in an ABC-DLBCL mouse model.