Babu Subramanyam

Lipoxins and novel 15-epi-lipoxin analogs display potent anti-inflammatory actions after oral administration

Lipoxins (LX) and aspirin‐triggered 15‐epi‐lipoxins (ATL) exert potent anti‐inflammatory actions. In the present study, we determined the anti‐inflammatory efficacy of endogenous LXA4 and LXB4, the stable ATL analog ATLa2, and a series of novel 3‐oxa‐ATL analogs (ZK‐996, ZK‐990, ZK‐994, and ZK‐142) after intravenous, oral, and topical administration in mice. LXA4, LXB4, ATLa2, and ZK‐994 were orally active, exhibiting potent systemic inhibition of zymosan A‐induced peritonitis at very low doses (50 ng kg−1–50 μg kg−1). Intravenous ZK‐994 and ZK‐142 (500 μg kg−1) potently attenuated hind limb ischemia/reperfusion‐induced lung injury, with 32±12 and 53±5% inhibition (P<0.05), respectively, of neutrophil accumulation in lungs. The same dose of ATLa2 had no significant protective action. Topical application of ATLa2, ZK‐994, and ZK‐142 (∼20 μg cm−2) prevented vascular leakage and neutrophil infiltration in LTB4/PGE2‐stimulated ear skin inflammation. While ATLa2 and ZK‐142 displayed approximately equal anti‐inflammatory efficacy in this model, ZK‐994 displayed a slower onset of action. In summary, native LXA4 and LXB4, and analogs ATLa2, ZK‐142, and ZK‐994 retain broad anti‐inflammatory effects after intravenous, oral, and topical administration. The 3‐oxa‐ATL analogs, which have enhanced metabolic and chemical stability and a superior pharmacokinetic profile, provide new opportunities to explore the actions and therapeutic potential for LX and ATL.

A novel P2Y12 adenosine diphosphate receptor antagonist that inhibits platelet aggregation and thrombus formation in rat and dog models

Irreversible platelet inhibitors, such as aspirin and clopidogrel, have limited anti-thrombotic efficacy in the clinic due to their bleeding risk. We have developed an orally active reversible P2Y(12) receptor antagonist, BX 667. The aim of this study was to determine if the reversible antagonist BX 667 had a greater therapeutic index than the irreversible P2Y(12) receptor antagonist clopidogrel. Since BX 667 is rapidly converted to its active metabolite BX 048 in rats, we first injected BX 048 intravenously (iv) in a rat arterial venous (A-V) shunt model of thrombosis. BX 048 dose- and concentration-dependently attenuated thrombosis. When administered orally, BX 667 and clopidogrel had similar efficacy, but BX 667 caused less bleeding than clopidogrel. In a rat model of a platelet-rich thrombus induced by vessel injury with FeCl(2), both BX 667 and clopidogrel exhibited higher levels of thrombus inhibition after oral administration compared to their potency in the A-V shunt model. Again, BX 667 caused less bleeding than clopidogrel. In a dog cyclic flow model, iv injection of either BX 667 or clopidogrel dose-dependently reduced thrombus formation with lower bleeding for BX 667 than clopidogrel. Inhibition of thrombosis was highly correlated with inhibition of ADP-induced platelet aggregation in these animal models. In dogs pre-treated with aspirin, BX 667 maintained its wider therapeutic index, measured by inhibition of platelet aggregation over bleeding, compared to the aspirin-clopidogrel combination. These data demonstrate that the reversible P2Y(12) receptor antagonist, BX 667, has a wider therapeutic index than clopidogrel in experimental models of thrombosis.

A novel inhibitor of activated thrombin-activatable fibrinolysis inhibitor (TAFIa) – Part I: Pharmacological characterization

We have discovered a novel small-molecule (3-phosphinoylpropionic acid) inhibitor of activated thrombin activatable fibrinolysis inhibitor (TAFIa), BX 528, which had an IC (50) of 2 nM in an enzymatic assay and 50 nM in an in-vitro clot lysis assay, with 3,500- to 35,000-fold selectivity against other carboxypeptidases, such as CPN, CPZ and CPD, and 5- and 12-fold selectivity against CPE (CPH) and CPB, respectively. At 10 micro M, BX 528 had no significant activity (<50% inhibition or antagonism) in a panel of 137 enzymes and receptors. It had no effects on blood coagulation and platelet aggregation up to 300 and 10 micro M, respectively. The plasma half-life following intravenous administration was 0.85 hours in rats and 4.5 hours in dogs. No significant metabolism was detected in human, dog or rabbit hepatic microsomes, and no significant inhibition of cytochrome P450 3A4 and 2D6 up to 30 micro M. No cytotoxic or cell proliferative effects were found in three hepatic and renal cell lines up to 300 micro M and no mutagenic activity was seen in the Ames II screen. There were no significant hemodynamic effects in rats and dogs up to 100 and 30 mg/kg with peak plasma drug concentrations of approximately 1,000 and 300 micro M, respectively. In an in-vivo complement activation model in guinea pigs, BX 528 showed minimal inhibition of plasma CPN activity up to 60 mg/kg with peak plasma concentrations up to 250 micro M. Thus, these data demonstrate that BX 528 is a novel, potent, selective and safe TAFIa inhibitor.

Novel P2Y12 adenosine diphosphate receptor antagonists for inhibition of platelet aggregation (II): Pharmacodynamic and pharmacokinetic characterization

Antiplatelet drugs are used to prevent aberrant platelet activation in pathophysiologic conditions such as myocardial infarction and ischemic stroke. The key role that ADP plays in this process has led to the development of antiplatelet drugs that target the P2Y12 receptor. The aim of this study was to characterize the pharmacodynamic (PD) and pharmacokinetic (PK) properties of the novel P2Y12 receptor antagonists, BX 667 and BX 048. BX 667 blocks ADP-induced platelet aggregation in human, dog and rat blood (IC50=97, 317 and 3000 nM respectively). BX 667 had nominal effects on collagen-induced aggregation and weakly inhibited arachidonic acid-induced aggregation. BX 667 has an active metabolite, BX 048, that also potently inhibits ADP-induced aggregation (IC50=290 nM) in human blood. BX 667 was shown to have high oral bioavailability in both dog and rat unlike BX 048. Administration of BX 667 resulted in a rapid and sustained inhibition of platelet aggregation where the extent and duration of platelet inhibition was directly proportional to circulating plasma levels. This report describes the PK/PD properties of BX 667 showing that it has the properties required for a potential antiplatelet therapeutic agent.

Novel P2Y12 adenosine diphosphate receptor antagonists for inhibition of platelet aggregation (I): In vitro effects on platelets

ADP plays a key role in platelet aggregation which has led to the development of antiplatelet drugs that target the P2Y12 receptor. The aim of this study was to characterize the effects of two novel P2Y12 receptor antagonists, BX 667 and its active metabolite BX 048, on platelets. BX 667 and BX 048 block the binding of 2MeSADP to platelets and antagonize ADP-induced platelet aggregation in human, dog and rat washed platelets. Both compounds were shown to be reversible inhibitors of platelet aggregation. BX 048 prevents the decrease in cAMP induced by treatment of platelets with ADP. The specificity of BX 667 and BX 048 was demonstrated against cell lines expressing P2Y1 and P2Y6 as well as against a panel of receptors and enzymes. Taken all together these data show that both BX 048 and BX 667 are potent P2Y12 antagonists with high specificity which, in the accompanying paper are demonstrated to behave predictably in vivo.

Differential Inhibition of Inducible T Cell Cytokine Secretion by Potent Iron Chelators

Effector functions and proliferation of T helper (Th) cells are influenced by cytokines in the environment. Th1 cells respond to a synergistic effect of interleukin-12 (IL-12) and interleukin-18 (IL-18) to secrete interferon-gamma (IFN-γ). In contrast, Th2 cells respond to interleukin-4 (IL-4) to secrete IL-4, interleukin-13 (IL-13), interleukin-5 (IL-5), and interleukin-10 (IL-10). The authors were interested in identifying nonpeptide inhibitors of the Th1 response selective for the IL-12/IL-18-mediated secretion of IFN-γ while leaving the IL-4-mediated Th2 cytokine secretion relatively intact. The authors established a screening protocol using human peripheral blood mononuclear cells (PBMCs) and identified the hydrazino anthranilate compound 1 as a potent inhibitor of IL-12/IL-18-mediated IFN-γ secretion from CD3+ cells with an IC50 around 200 nM. The inhibitor was specific because it had virtually no effect on IL-4-mediated IL-13 release from the same population of cells. Further work established that compound 1 was a potent intracellular iron chelator that inhibited both IL-12/IL-18- and IL-4-mediated T cell proliferation. Iron chelation affects multiple cellular pathways in T cells. Thus, the IL-12/IL-18-mediated proliferation and IFN-γ secretion are very sensitive to intracellular iron concentration. However, the IL-4-mediated IL-13 secretion does not correlate with proliferation and is partially resistant to potent iron chelation

Novel Antibody Therapeutics Targeting Mesothelin In Solid Tumors

Abstract: Background Monoclonal antibodies have become attractive clinical anti-cancer drugs in the last 3 decades due to their targeting specificity and suitable pharmacokinetic properties. Mesothelin is a tumor-associated antigen with limited expression in normal tissues. It is frequently over-expressed on the cell membrane of a number of epithelial malignancies (e.g. mesothelioma, pancreatic, ovarian, lung, triple negative breast and gastric cancers). Methods Mesothelin is validated as a suitable antibody target for cancer therapy. A number of novel antibody therapeutics targeting mesothelin in development are compared and their mechanisms of action are also discussed. Both basic science and clinical data are provided to give a complete veiw of how an agent is developed from bench to bedside. Results Novel antibody therapeutics, including unconjugated monoclonal antibodies, recombinant immunotoxins and antibody-drug conjugates, targeting mesothelin exert anti-tumor activities by different mechanisms of action. Based on the convincing preclinical data generated with these molecules, the antibody therapeutics have been brought into early clinical evaluation where initial promising results were obtained. Conclusion These antibody therapeutics directed against mesothelin are expected to have different safety profiles, based on their different mechanism of action. Further clinical development will reveal which of these molecules shows the best efficacy and widest therapeutic window and thus is best suited to bring benefit to the patients.

Anti-tumor efficacy of the nucleoside analog 1-(2-deoxy-2-fluoro-4-thio-β-D-arabinofuranosyl) cytosine (4′-thio-FAC) in human pancreatic and ovarian tumor xenograft models

1‐(2‐Deoxy‐2‐fluoro‐4‐thio‐β‐D‐arabinofuranosyl) cytosine (4′‐thio‐FAC) is a deoxycytidine analog that has been shown previously to have impressive anti‐proliferative and cytotoxic effects in vitro and in vivo toward colorectal and gastric tumors. In our present studies, the pharmacokinetic behavior in nude mice and the effectiveness of 4′‐thio‐FAC against human pancreatic and ovarian tumor growth were assessed in comparison with standard chemotherapeutic agents. Potent in vitro anti‐proliferative effects were observed against pancreatic (Capan‐1, MIA‐PaCa‐2, BxPC‐3) and ovarian (SK‐OV‐3, OVCAR‐3, ES‐2) cancer cell lines with IC50 of 0.01–0.2 μM. In vivo anti‐tumor activity was evaluated in nude mice bearing subcutaneously (s.c.) implanted human pancreatic tumor xenografts or intraperitoneally (i.p.) disseminated human ovarian xenografted tumors. Oral daily administration of 4′‐thio‐FAC for 8–10 days significantly inhibited the growth of gemcitabine‐resistant BxPC‐3 pancreatic tumors and induced regression of gemcitabine‐refractory Capan‐1 tumors. 4′‐Thio‐FAC was also a highly effective inhibitor of ovarian peritoneal carcinomatosis. In the SK‐OV‐3 and ES‐2 ovarian cancer models, 4′‐thio‐FAC prolonged survival to a greater extent than that observed with gemcitabine. Furthermore, the superiority of 4′‐thio‐FAC to carboplatin and paclitaxel was demonstrated in the ES‐2 clear cell ovarian carcinoma model. Studies provide evidence that 4′‐thio‐FAC is a promising new alternative to gemcitabine and other chemotherapeutic drugs in the treatment of a variety of tumor indications, including pancreatic and ovarian carcinoma.

Design, synthesis, and biological activity of novel factor Xa inhibitors: 4-aryloxy substituents of 2,6-diphenoxypyridines.

A novel series of triaryloxypyridines have been designed to inhibit factor Xa, a serine protease strategically located in the coagulation cascade. Inhibitor 5e has a K(I) against factor Xa of 0.12nM and is greater than 8000- and 2000-fold selective over two related serine proteases, thrombin and trypsin, respectively. The 4-position of the central pyridine has been identified as a site that tolerates various substitutions without deleterious effects on potency and selectivity. This suggests that the 4-position of the pyridine ring is an ideal site for chemical modifications to identify inhibitors with improved pharmacokinetic characteristics. This investigation has resulted in inhibitor 5d, which has an oral availability of 6% in dogs. The synthesis, in vitro activity, and in vivo profile of this class of inhibitors is outlined.

Reversible, orally available ADP receptor (P2Y 12 ) antagonists Part I: Hit to lead process

A hit to lead process to identify reversible, orally available ADP receptor (P2Y12) antagonists lead compounds is described. High throughput screening afforded 1. Optimization of 1, using parallel synthesis methods, a methyl scan to identify promising regions for optimization, and exploratory SAR on these regions, provided 22 and 23. Compound 23 is an orally available, competitive reversible antagonist (KB = 94 nM for inhibition of ADP-induced platelet aggregation). It exhibits high metabolic stability in human, rat and dog liver microsomes and is orally absorbed. Although plasma level after oral dosing of 22 and 23 to rats is low, reasonable levels were achieved to merit extensive lead optimization of this structural class.