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.

Initial biological qualification of SBDP-145 as a biomarker of compound-induced neurodegeneration in the rat.

Detection of compound-related neurodegeneration is currently limited to brain histopathology in veterinary species and functional measurements such as electroencephalography and observation of clinical signs in patients. The objective of these studies was to investigate whether concentrations of spectrin breakdown product 145 (SBDP-145) in cerebrospinal fluid (CSF) correlate with the severity of neurodegeneration in rats administered neurotoxic agents, as part of a longer term objective of developing in vivo biomarkers of neurotoxicity for use in non-clinical and clinical safety studies. Non-erythroid alpha-II spectrin is a cytoskeletal protein cleaved by the protease calpain when this enzyme is activated by dysregulation of calcium in injured cells. Calcium dysregulation is also associated with some toxicological responses in animals, and may be sufficient to activate neuronal calpain and produce SBDPs that can be released into CSF. Neurotoxicants (kainic acid, 2-chloropropionic acid, bromethalin, and pentylenetetrazole) known to affect different portions of the brain were administered to rats in dose-response and time-course studies in which neurodegeneration was measured by histopathology and SBDP-145 concentrations in CSF were measured by ELISA. We consistently observed >3-fold increases in SBDP-145 concentration in rats with minimal to slight neurodegenerative lesions, and 20 to 150-fold increases in animals with more severe lesions. In contrast, compounds that caused non-degenerative changes in central nervous system (CNS) did not increase SBDP-145 in CSF. These data support expanded use of SBDP-145 as a biomarker for monitoring compound-induced neurodegeneration in pre-clinical studies, and support the investigation of clinical applications of this biomarker to promote safe dosing of patients with compounds that have potential to cause neurodegeneration.

LY2875358, a neutralizing and internalizing anti-MET bivalent antibody, inhibits HGF-dependent and HGF-independent MET activation and tumor growth.

PURPOSE: MET, the receptor for hepatocyte growth factor (HGF), has been implicated in driving tumor proliferation and metastasis. High MET expression is correlated with poor prognosis in multiple cancers. Activation of MET can be induced either by HGF-independent mechanisms such as gene amplification, specific genetic mutations, and transcriptional upregulation or by HGF-dependent autocrine or paracrine mechanisms. EXPERIMENTAL DESIGN/RESULTS: Here, we report on LY2875358, a novel humanized bivalent anti-MET antibody that has high neutralization and internalization activities, resulting in inhibition of both HGF-dependent and HGF-independent MET pathway activation and tumor growth. In contrast to other bivalent MET antibodies, LY2875358 exhibits no functional agonist activity and does not stimulate biologic activities such as cell proliferation, scattering, invasion, tubulogenesis, or apoptosis protection in various HGF-responsive cells and no evidence of inducing proliferation in vivo in a monkey toxicity study. LY2875358 blocks HGF binding to MET and HGF-induced MET phosphorylation and cell proliferation. In contrast to the humanized one-armed 5D5 anti-MET antibody, LY2875358 induces internalization and degradation of MET that inhibits cell proliferation and tumor growth in models where MET is constitutively activated. Moreover, LY2875358 has potent antitumor activity in both HGF-dependent and HGF-independent (MET-amplified) xenograft tumor models. Together, these findings indicate that the mechanism of action of LY2875358 is different from that of the one-armed MET antibody. CONCLUSIONS: LY2875358 may provide a promising therapeutic strategy for patients whose tumors are driven by both HGF-dependent and HGF-independent MET activation. LY2875358 is currently being investigated in multiple clinical studies.