A Monoclonal Antibody (MCPR3-7) Interfering with the Activity of Proteinase 3 by an Allosteric Mechanism

Proteinase 3 (PR3) is an abundant serine protease of neutrophil granules and a major target of autoantibodies (PR3 anti-neutrophil cytoplasmic antibodies) in granulomatosis with polyangiitis. Some of the PR3 synthesized by promyelocytes in the bone marrow escapes the targeting to granules and occurs on the plasma membrane of naive and primed neutrophils. This membrane-associated PR3 antigen may represent pro-PR3, mature PR3, or both forms. To discriminate between mature PR3 and its inactive zymogen, which have different conformations, we generated and identified a monoclonal antibody called MCPR3-7. It bound much better to pro-PR3 than to mature PR3. This monoclonal antibody greatly reduced the catalytic activity of mature PR3 toward extended peptide substrates. Using diverse techniques and multiple recombinant PR3 variants, we characterized its binding properties and found that MCPR3-7 preferentially bound to the so-called activation domain of the zymogen and changed the conformation of mature PR3, resulting in impaired catalysis and inactivation by α₁-proteinase inhibitor (α₁-antitrypsin). Noncovalent as well as covalent complexation between PR3 and α₁-proteinase inhibitor was delayed in the presence of MCPR3-7, but cleavage of certain thioester and paranitroanilide substrates with small residues in the P1 position was not inhibited. We conclude that MCPR3-7 reduces PR3 activity by an allosteric mechanism affecting the S1′ pocket and further prime side interactions with substrates. In addition, MCPR3-7 prevents binding of PR3 to cellular membranes. Inhibitory antibodies targeting the activation domain of PR3 could be exploited as highly selective inhibitors of PR3, scavengers, and clearers of the PR3 autoantigen in granulomatosis with polyangiitis.     

ALCAPs induce mitochondrial apoptosis and activate DNA damage response by generating ROS and inhibiting topoisomerase I enzyme activity in K562 leukemia cell line

Endemic Alkanna cappadocica was used to isolate novel antitumor molecules from Turkish landscapes in our previous studies. In this study, deoxyalkannin (ALCAP1), β,β-dimethylacrylalkannin (ALCAP2), acetylalkannin (ALCAP3), and alkannin (ALCAP4) as well as the novel isolated compounds 5-methoxydeoxyalkannin (ALCAP5), 8-methoxydeoxyalkannin (ALCAP6), 5-methoxyacetylalkannin (ALCAP7), 5-methoxy-β,β-dimethylacrylalkannin (ALCAP8) were characterized. The topoisomerase I (topo I) inhibitory activity of ALCAPs was investigated using in vitro plasmid relaxation assay and found that ALCAP2, 3, 4 and 7 were potent inhibitors at 2–6 μM concentrations. Further, DNA damage response to ALCAP treatments was also studied by measuring the H2AX^(S139) and ATM^(S1981) phosphorylations. ALCAP2, 7 and 8 induced the DNA damage and apoptosis, consistently resulted in PARP cleavage at nanomolar concentrations in K562 leukemia cells. Moreover, when the free radical (ROS) generating capacity of the compounds was studied by 2′,7′-dichlorofluorescein-diacetate assay using flow cytometry, we found that a known antioxidant N-acetyl-cysteine almost completely abrogated the H2AX^(S139) phosphorylations and the caspase 3 cleavage and activation. Thus, γH2AX^(S139) foci formation remained higher than the control, and an increase in CHK2^(T68) phosphorylation was observed by ALCAP2 and 7 treatments suggested that, these compounds can be potential therapeutics against tumor cell growth because of their unique DNA damaging abilities additional to enzyme inhibition similar to those of doxorubicin.     

Toxoplasma gondii RH Ankara: production of evolving tachyzoites using a novel cell culture method

Nitric oxide (NO) and NO-derived reactive nitrogen species (RNS) are present in the food vacuole (FV) of Plasmodium falciparum trophozoites. The product of PFL1555w, a putative cytochrome b₅, localizes in the FV membrane, similar to what was previously observed for the product of PF13_0353, a putative cytochrome b₅ reductase. These two gene products may contribute to NO generation by denitrification chemistry from nitrate and/or nitrite present in the erythrocyte cytosol. The possible coordination of NO to heme species present in the food vacuole was probed by resonance Raman spectroscopy. The spectroscopic data revealed that in situ generated NO interacts with heme inside the intact FVs to form ferrous heme nitrosyl complexes that influence intra-vacuolar heme solubility. The formation of heme nitrosyl complexes within the FV is a previously unrecognized factor that could affect the equilibrium between soluble and crystallized heme within the FV in vivo.     

Ring A structural modified derivatives of withaferin A and the evaluation of their cytotoxic potential

Regio-/stereoselective Michael addition to ring A of withaferin-A was performed using an optimized reaction procedure to synthesise a library of 2,3-dihydro,3-β-substituted withaferin-A derivatives. The analogues thus obtained were evaluated for in vitro cytotoxicity against various human cancer cell lines. 3-Azido analogue exhibited 35-fold increase (IC(50)=0.02-1.9 μM) in cytotoxicity against almost the entire cell lines tested when compared to the parent molecule. However, further modifications of 3-azido analogue with various alkynes under Husigen's cycloaddition conditions generated a variety of triazole derivatives with reduced cytotoxicity.