Structure-activity relationships of pyrazole derivatives as potential therapeutics for immune thrombocytopenias.

Idiopathic or immune thrombocytopenia (ITP) is a serious clinical disorder involving the destruction of platelets by macrophages. Small molecule therapeutics are highly sought after to ease the burden on current therapies derived from human sources. Earlier, we discovered that dimers of five-membered heterocycles exhibited potential to inhibit phagocytosis of human RBCs by macrophages. Here, we reveal a structure-activity relationship of the bis-pyrazole class of molecules with -C-C-, -C-N- and -C-O- linkers, and their evaluation as inhibitors of phagocytosis of antibody-opsonized human RBCs as potential therapeutics for ITP. We have uncovered three potential candidates, 37, 47 and 50, all carrying a different linker connecting the two pyrazole moieties. Among these compounds, hydroxypyrazole derivative 50 is the most potent compound with an IC50 of 14 ± 9 µM for inhibiting the phagocytosis of antibody-opsonized human RBCs by macrophages. None of the compounds exhibited significant potential to induce apoptosis in peripheral blood mononuclear cells (PBMCs). Current study has revealed specific functional features, such as up to 2-atom spacer arm and alkyl substitution at one of the N(1) positions of the bivalent pyrazole core to be important for the inhibitory activity.

Acute hemolysis after intravenous immunoglobulin amid host factors of ABO-mismatched bone marrow transplantation, inflammation, and activated mononuclear phagocytes.

BACKGROUND: Hemolysis may follow intravenous immunoglobulin (IVIG), with product, dosing, and host factors contributing. The importance of recipient features remains unclear. CASE REPORT: A 52-year-old obese woman, 10 years after ABO-mismatched (recipient O, donor A) marrow transplantation, presented with immune thrombocytopenia (ITP). IVIG at 100 g/day × 2 days was followed by hemoglobinuria and angina and dyspnea, with frank hemoglobinemia and anemia (hemoglobin 12.9 to 8.4 over 24 hr, to a nadir of 6.9 g/dL). STUDY DESIGN AND METHODS: Serologic methods established ABO, A1, Lewis, and Secretor type, while monocyte monolayer assay (MMA) examined erythrophagocytosis with control or patient monocytes, and the implicated IVIG lot to opsonize control (group A1, A2, B, O) or patient red blood cells (RBCs). Baseline, hemolytic, and convalescent markers (including cytokines) were assessed. RESULTS: Passive anti-A was identified on reverse type and eluted from sensitized RBCs (immunoglobulin G 1+, C3d-). Le(a-b+) typing and saliva confirmed H Secretor status. MMA revealed significant activity between patient RBCs, monocytes, and IVIG. However, normal A1 cells opsonized with IVIG were not significantly phagocytosed by either normal or patient monocytes. Proinflammatory markers were significantly elevated before and after IVIG. CONCLUSIONS: Synergizing host factors (including obesity-unadjusted dosing and existing inflammation) marked this severe post-IVIG hemolytic crisis. Group A antigen restriction to myeloid tissues, with H Secretor phenotype, may have contributed, rendering this bone marrow transplant chimera vulnerable to anti-A in a manner analogous to the idiosyncratic effect of therapeutic anti-D in certain D+ ITP recipients. However, MMA suggested a macrophage activation state as contributory, perhaps precipitated by existing inflammation.

Disulfide linked pyrazole derivatives inhibit phagocytosis of opsonized blood cells.

Immune thrombocytopenia (ITP) is caused by production of an autoantibody to autologous platelets. ITP can be treated either by reducing platelet destruction or by increasing platelet production. Fcγ receptor mediated phagocytosis of the opsonized blood cells is a well-accepted mechanism for the underlying pathogenesis of ITP and inhibition of this phagocytosis process with small molecules is a potential strategy for the development of drugs against ITP. A broad screen indicated that 4-methyl-1-phenyl-pyrazole derivative (1) could inhibit the phagocytosis of opsonized blood cells with weak potency. We reveal here the discovery of the polysulfide products, synthesis of various 1-phenyl-pyrazole derivatives, and the biological evaluation of pyrazole derivatives as inhibitors of phagocytosis for potential use as therapeutics for ITP. Substitution at C4 of the pyrazole moiety in the disulfide-bridged dimers influenced the potency in the increasing order of 10 ~/= 11~/= 16 < 19 < 20. A novel scaffold, 20 with an IC(50) of 100 nM inhibiting opsonized blood cell phagocytosis was identified as a potential candidate for further studies. Confirmation of the disulfide bridge additionally provides clues for the non-thiol or non-disulfide bridge carrying ligands targeting ITP and other similar disorders.