Suzane L. Um

p38 mitogen-activated protein kinase phosphorylates cytosolic phospholipase A2 (cPLA2) in thrombin-stimulated platelets. Evidence that proline-directed phosphorylation is not required for mobilization of arachidonic acid by cPLA2

The Ca2+-sensitive 85-kDa cytosolic phospholipase A2 (cPLA2) is responsible for thrombin-stimulated mobilization of arachidonic acid for the synthesis of thromboxane A2 in human platelets. We have previously shown that thrombin activates p38 kinase, a recently discovered new member of the mitogen-activated protein kinase family (Kramer, R. M., Roberts, E. F., Strifler, B. A., and Johnstone, E. M. (1995) J. Biol. Chem. 270, 27395-27398) and also induces phosphorylation of cPLA2, thereby increasing its intrinsic catalytic activity. In the present study we have examined the role of p38 kinase in the phosphorylation and activation of cPLA2 in stimulated platelets. We have observed that activation of p38 kinase accompanies receptor-mediated events in platelets and coincides with cPLA2 phosphorylation. Furthermore, in the presence of inhibitors of p38 kinase, the proline-directed phosphorylation of cPLA2 was completely blocked in platelets stimulated with the thrombin receptor agonist peptide SFLLRN and was suppressed during the early (up to 2 min) phase of platelet stimulation caused by thrombin. Unexpectedly, we found that prevention of proline-directed phosphorylation of cPLA2 in stimulated platelets did not attenuate its ability to release arachidonic acid from platelet phospholipids. We conclude that: 1) cPLA2 is a physiological target of p38 kinase; 2) p38 kinase is involved in the early phosphorylation of cPLA2 in stimulated platelets; and 3) proline-directed phosphorylation of cPLA2 is not required for its receptor-mediated activation.

New insights into the protein C pathway: potential implications for the biological activities of drotrecogin alfa (activated)

It has been hypothesized that the protein C pathway is a pivotal link between the inflammation and coagulation cascades. The demonstration that a survival benefit is associated with administration of drotrecogin alfa (activated) (recombinant human activated protein C [APC]) in severe sepsis patients has provided new insights into the protein C pathway. APC was originally identified based on its antithrombotic properties, which result from the inhibition of activated Factors V and VIII. In the early 1990s, any potential anti-inflammatory properties of APC were thought to relate primarily to its inhibition of thrombin generation. However, the mid-1990s saw the identification of the endothelial protein C receptor (EPCR), which has subsequently been shown to be neither endothelial specific nor protein C specific, but has a primary function as a cofactor for enhancing the generation of APC or behaving as an APC receptor. Thus, the potential biologic activities of APC can be classed into two categories related either to the limiting of thrombin generation or to cellular effects initiated by binding to the EPCR. Intracellular signaling initiated by binding of APC to its receptor appears to be mediated by interaction with an adjacent protease-activated receptor (PAR), or by indirect activation of the sphingosine 1-phosphate pathway. Based mostly on in vitro studies, binding of APC to its receptor on endothelial cells leads to a decrease in thrombin-induced endothelial permeability injury, while such binding on blood cells, epithelial cells, and neurons has been shown to inhibit chemotaxis, be anti-apoptotic, and be neuroprotective, respectively. In the Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) study, drotrecogin alfa (activated) was associated with improved cardiovascular function, respiratory function, and a prevention of hematologic dysfunction. This article discusses the way in which the interactions of APC may alter the microcirculation.

Circulating endothelial and endothelial progenitor cells in patients with severe sepsis

Elevated circulating endothelial cell (CEC) and circulating endothelial progenitor cell (CEPC) counts may indicate vascular damage and disease status, but data on these cell populations in patients with severe sepsis are limited. This study compared CEC and CEPC counts in patients with and without severe sepsis following intensive care unit (ICU) admission. Venous blood samples were collected within 24 h, 48-72 h, and 120-144 h. Baseline demographics, 28-day mortality, ICU and hospital days, and Sequential Organ Failure Assessment (SOFA) scores were recorded. Patients with (n=18) and without (n=28) severe sepsis were balanced for mean age (63.7 and 61.3 years, respectively) and gender. There were no differences in 28-day mortality, ICU days, or hospital days. Baseline SOFA scores were higher in the sepsis group. At 48-72 h, patients with severe sepsis had significantly higher median CEC counts (51.5 vs. 28.0 cells/4 ml of blood, P=0.02). CEC values for all ICU patients were significantly (P<0.05) higher than in healthy volunteers. CEPC counts in both cohorts ranged from 0 to >21 colonies/4 ml blood (mean=1.13±2.25; median=0) without significant differences at any time point. This study demonstrates the ability to quantify CECs and CEPCs using consensus methodology. Understanding the relationship between CEC/CEPC counts and outcomes may provide insight into the mechanisms of endothelial cell changes in severe sepsis.

Fused bicyclic Gly-Asp β-turn mimics with potent affinity for GPIIb-IIIa. Exploration of the arginine isostere

6-[4-Amidinobenzoyl]amino]-tetralone-2-acetic acid is a potent antagonist of GPIIb-IIIa. Substitution in the meta position of the benzamidine, or replacement with a heteroaryl amidine was tolerated in this series. Use of an acyl-linked 4-alkyl piperidine as an arginine isostere also provided active compounds. Compounds from this series provided substantial systemic exposure in the rat following oral administration.

Dihydroisoquinolone RGD mimics. Exploration of the aspartate isostere

Abstract Disubstituted 3,4-dihydroisoquinolones that contain an ether-linked benzamidine at C6 and a β-substituted aspartate mimic at C2 offer enhanced affinity for GPIIb–IIIa relative to the non-substituted isoquinolone propionate. Alkyl substituents afforded a 10-fold increase in intrinsic activity while aryl substituents yielded a 40-fold improvement.

An acyliminium ion approach towards the synthesis of β-substituted 3,4-dihydroisoquinolone propionates

A variety of α-methoxy amides were prepared either by selective reduction of the exocyclic carbonyl of a 2-acyl-3,4-dihydroisoquinolone and subsequent trapping of the resultant α-hydroxy amide with acidic methanol or by reacting the sodium salt of 3,4-dihydroisoquinolone with a functionalized α-chloro ether. These intermediates were reacted with 1-tert-butoxy-1-tert-butyldimethylsiloxy ethene in the presence of BF3·Et2O providing access to β-substituted isoquinolone propionates in good yield.

Quantitative detection of platelet GPIIb‐IIIa receptor antagonist activity using a flow cytometric method

Platelet‐membrane surface receptors are important targets for pharmacologic intervention in cardiovascular disease. Among these, glycoprotein (GP) IIb‐IIIa is dominant and integrally involved in platelet aggregation and thrombus formation. When activated, GPIIb‐IIIa binds soluble fibrinogen (Fb) in a key, early step of this process. New drugs are under development that block Fb binding to GPIIb‐IIIa and inhibit platelet aggregation. A thorough understanding of the relationship between circulating drug levels and the extent of GPIIb‐IIIa receptor occupancy in humans is crucial for safe and efficacious use of these agents. Described here is the development of a new technique for measurement of GPIIb‐IIIa receptor occupancy. In this assay, activated human platelets are incubated with biotinylated fibrinogen (Fb‐biotin) followed by antibiotin‐FITC. The extent of Fb binding is determined using flow cytometric analysis. Our results indicate that Fb‐biotin binds rapidly to activated platelets and its detection is dependent on incubation temperature. Platelets that were pre‐incubated with the GPIIb‐IIIa antagonist echistatin were inhibited from binding Fb‐biotin in a concentration‐dependent manner. The fluorescence of processed samples was stable for two weeks in the cold. The assay described here is simple, cost effective, and can be adapted for use in clinical evaluations of these new drugs. J. Clin. Lab. Anal. 12:191–196, 1998.

Abstract 1776: Antitumor activity of Chk1 inhibitor LY2606368 as a single agent in SW1990 human pancreas orthotopic tumor model

ChK1 is a key kinase in the DNA damage response signaling network, including cell cycle checkpoints, DNA repair, apoptosis and transcription, thus emerging as an attractive target in anti-cancer therapy. LY2606368, a potent and selective ATP competitive inhibitor of the Chk1 protein kinase, is currently in clinical development. LY2606368 has been reported to inhibit Chk1 auto-phosphorylation activated by DNA damaging agents, and induce phosphorylation of H2AX, a DNA damage maker in multiple cancer cell lines in vitro. In addition, LY2606368 has demonstrated potent single agent activity and potentiates the anti-tumor activity of DNA damaging agents in vivo. Pancreatic cancer is one of the least curable cancers, with an approximate 5% overall 5-year survival for all patients. In the current study, we evaluated the efficacy of LY2606368 (as its methanesulfonate salt, hydrate; LY2606368.MeSO3H.H2O = LY2940930) in pancreatic cancer cell lines in vitro and xenograft tumors (including subcutaneous and orthotopic models) in vivo. LY2606368 alone significantly inhibited the cell proliferation in a variety of pancreatic cell lines (SW1990, SU86.86, Bx-PC3, AsPC-1, CFPAC-1, Capan-2, HPAF-II) with SW1990 being the most sensitive (IC50=1.5 nM). In SW1990 subcutaneous xenograft model, LY2606368 showed substantial dose-dependent inhibition of tumor growth. In SW1990 pancreas orthotopic model, which represents the local and metastatic growth pattern seen in pancreas cancer patients, LY2606368 treatment resulted in over 92% inhibition of primary tumor growth as well as 100% inhibition of metastasis to lymph node, spleen and intestine. The anti-tumor effect of LY2606368 treatment was further demonstrated in comparing with gemcitabine (the standard of care for pancreas cancer patient) in SW1990 orthotopic model. The anti-tumor and/or anti-metastasis mechanism of LY2606368 was also investigated, including phosphorylation of H2AX, cell proliferation, cell survival, and soft agar anchorage-independent growth. Together, our findings demonstrate the therapeutic potential of LY2606368 as a single agent in the treatment of pancreatic cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1776. doi:1538-7445.AM2012-1776

Platelet glycoprotein IIb–IIIa receptor (GPIIb–IIIa) antagonists derived from amidinoindoles

Abstract A series of substituted amidinoindoles have been prepared as mimics of the RGD sequence and were studied as antagonists of the platelet glycoprotein IIb–IIIa receptor (GPIIb–IIIa). The agents were potent and selective antagonists of GPIIb–IIIa. Compared to their acyclic counterparts, the amidinoindole series bound with 10- to 20-fold greater affinity, indicating the advantages of added conformational restriction and/or hydrophobicity in the basic region of RGD mimics.

Merestinib (LY2801653) inhibits neurotrophic receptor kinase (NTRK) and suppresses growth of NTRK fusion bearing tumors

Merestinib is an oral multi-kinase inhibitor targeting a limited number of oncokinases including MET, AXL, RON and MKNK1/2. Here, we report that merestinib inhibits neurotrophic receptor tyrosine kinases NTRK1/2/3 which are oncogenic drivers in tumors bearing NTRK fusion resulting from chromosomal rearrangements. Merestinib is shown to be a type II NTRK1 kinase inhibitor as determined by x-ray crystallography. In KM-12 cells harboring TPM3-NTRK1 fusion, merestinib exhibits potent p-NTRK1 inhibition in vitro by western blot and elicits an anti-proliferative response in two- and three-dimensional growth. Merestinib treatment demonstrated profound tumor growth inhibition in in vivo cancer models harboring either a TPM3-NTRK1 or an ETV6-NTRK3 gene fusion. To recapitulate resistance observed from type I NTRK kinase inhibitors entrectinib and larotrectinib, we generated NIH-3T3 cells exogenously expressing TPM3-NTRK1 wild-type, or acquired mutations G595R and G667C in vitro and in vivo. Merestinib blocks tumor growth of both wild-type and mutant G667C TPM3-NTRK1 expressing NIH-3T3 cell-derived tumors. These preclinical data support the clinical evaluation of merestinib, a type II NTRK kinase inhibitor (NCT02920996), both in treatment naïve patients and in patients progressed on type I NTRK kinase inhibitors with acquired secondary G667C mutation in NTRK fusion bearing tumors.