Inhibiting platelet-stimulated blood coagulation by inhibition of mitochondrial respiration.

Platelets are important mediators of blood coagulation that lack nuclei, but contain mitochondria. Although the presence of mitochondria in platelets has long been recognized, platelet mitochondrial function remains largely unaddressed. On the basis of a small amount of literature that suggests platelet mitochondria are functional, we hypothesized that the inhibition of platelet mitochondria disrupts platelet function and platelet-activated blood coagulation. To test this hypothesis, members of the tetrazole, thiazole, and 1,2,3-triazole families of small molecule heterocycles were screened for the ability to inhibit isolated mitochondrial respiration and coagulation of whole blood. The families of heterocycles screened were chosen on the basis of the ability of the heterocycle family to inhibit a biomimetic model of cytochrome c oxidase (CcO). The strength of mitochondrial inhibition correlates with each compound's ability to deter platelet stimulation and platelet-activated blood clotting. These results suggest that for this class of molecules, inhibition of blood coagulation may be occurring through a mechanism involving mitochondrial inhibition.

Isocitrate dehydrogenase 1 and 2 mutations induce BCL-2 dependence in acute myeloid leukemia.

Mutant isocitrate dehydrogenase (IDH) 1 and 2 proteins alter the epigenetic landscape in acute myeloid leukemia (AML) cells through production of the oncometabolite (R)-2-hydroxyglutarate (2-HG). Here we performed a large-scale RNA interference (RNAi) screen to identify genes that are synthetic lethal to the IDH1(R132H) mutation in AML and identified the anti-apoptotic gene BCL-2. IDH1- and IDH2-mutant primary human AML cells were more sensitive than IDH1/2 wild-type cells to ABT-199, a highly specific BCL-2 inhibitor that is currently in clinical trials for hematologic malignancies, both ex vivo and in xenotransplant models. This sensitization effect was induced by (R)-2-HG-mediated inhibition of the activity of cytochrome c oxidase (COX) in the mitochondrial electron transport chain (ETC); suppression of COX activity lowered the mitochondrial threshold to trigger apoptosis upon BCL-2 inhibition. Our findings indicate that IDH1/2 mutation status may identify patients that are likely to respond to pharmacologic BCL-2 inhibition and form the rational basis for combining agents that disrupt ETC activity with ABT-199 in future clinical studies.

Catalytic Activation of H(2) and C-H Bonds by Electron-Deficient Ruthenium(II) Porphyrins.

The Ru(2) and RuNi derivatives of 1,8-bis(10,15,20-trimesityl-5-porphyrinato)anthracene-a recently reported cofacial diporphyrin ligand comprising two hindered porphyrins spanned by an anthracene bridge-have been synthesized. Both Ru(2)(DPAHM) and RuNi(DPAHM) are extremely reactive species that apparently contain 14-electron Ru(II) centers and, as is the case for their monoporphyrin analog, (5,10,15,20-tetramesitylporphyrinato)ruthenium [Ru(TMP)], must be rigorously protected from oxygen, nitrogen, and other ligating agents. In addition, these electron-deficient Ru(II) porphyrins all appear to bind aromatic solvents such as benzene and toluene, the weakest ligating solvents in which these Ru(II) porphyrins have been found soluble. Ru(TMP) and its metallodiporphyrin analogs, Ru(2)(DPAHM) and RuNi(DPAHM), catalyze H(2)/D(2) exchange in benzene solution and as solids. When adsorbed on a particularly nonpolar carbon support, these Ru(II) porphyrins all manifest significant activity with respect to catalytic H(2)/D(2) exchange [approximately 40 turnovers s(-)(1), when normalized for Ru(II) content]. In addition, these molecules slowly catalyze the exchange of H(2) into deuterated aromatic hydrocarbons and, in the absence of solvent, the exchange of D(2) into CH(4). Kinetic studies of H(2)/D(2) exchange catalyzed by these Ru(II) porphyrins on carbon supports indicate that exchange is likely to be effected by one face of a single Ru(TMP) moiety. The activity of each supported catalyst was suppressed by the presence of ligands, either exogenous (CO irreversibly and N(2) reversibly) or from polar functionalities on the surface of the supporting matrix.