Purpose:To assess the safety and tolerability, pharmacokinetics, and early evidence of antitumor activity of escalating doses of lexatumumab (HGS-ETR2), a fully human agonistic monoclonal antibody which targets and activates the tumor necrosis factor^related apoptosis-inducing ligand receptor 2 (TRAIL-R2) in patients with advanced solid malignancies. Experimental Design: In this phase 1, open label study, patients with advanced solid malignancies were treated with escalating doses of lexatumumab administered i.v. over 30 to120 min every 21days. A cohort of four patients, which could be expanded to six patients, was studied at each dose level. The dose-limiting toxicity (DLT) dose was defined as the dose at which the incidence of DLT in the first two cycles was z33%.The maximum tolerated dose was defined as the highest dose at which <33% of subjects experienced DLT. The pharmacokinetics and immunogenicity of lexatumumab were also characterized. Tumor specimens from historical or current biopsies, when available, were stained forTRAIL-R2 using immunohistochemistry techniques. Results: Thirty-seven patients received 120 cycles of lexatumumab at doses ranging from 0.1to 20 mg/kg every 21 days as of May 2006. The 20 mg/kg dose was identified as the DLT dose based on DLTs in three of seven patients treated with this dose; DLTs included asymptomatic elevations of serum amylase, transaminases, and bilirubin. The 10 mg/kg dose cohort was expanded to 12 patients and the 10 mg/kg dose was identified as the maximum tolerated dose. The mean (FSD) clearance and apparent terminal half-life values at the 10 mg/kg dose averaged 6.0 (2.9) mL/d/kg and 16.4 (10.9) days, respectively. Twelve patients had durable stable disease that lasted a median of 4.5 months, including three patients with sarcoma having prolonged stable disease (z6.7 months). Immunohistochemistry forTRAIL-R2 showed specific staining in >10% of tumor cells for 16 of the 20 evaluable specimens submitted (80%). Conclusions: Lexatumumab was safe and well tolerated at doses up to and including 10 mg/kg every 21 days. Lexatumumab was associated with sustained stable disease in several patients. Pharmacokinetics were linear over the dose range studied, and consistent with a two-compartment model with first-order elimination from the central compartment. Additional evaluation of this novel apoptosis-inducing agent, particularly in combination with chemotherapy agents, is warranted and ongoing.

Cells must sense extracellular signals and transfer the information contained about their environment reliably to make appropriate decisions. To perform these tasks, cells use signal transduction networks that are subject to various sources of noise. Here, we study the effects on information transfer of two particular types of noise: basal (leaky) network activity and cell-to-cell variability in the componentry of the network. Basal activity is the propensity for activation of the network output in the absence of the signal of interest. We show, using theoretical models of protein kinase signaling, that the combined effect of the two types of noise makes information transfer by such networks highly vulnerable to the loss of negative feedback. In an experimental study of ERK signaling by single cells with heterogeneous ERK expression levels, we verify our theoretical prediction: In the presence of basal network activity, negative feedback substantially increases information transfer to the nucleus by both preventing a near-flat average response curve and reducing sensitivity to variation in substrate expression levels. The interplay between basal network activity, heterogeneity in network componentry, and feedback is thus critical for the effectiveness of protein kinase signaling. Basal activity is widespread in signaling systems under physiological conditions, has phenotypic consequences, and is often raised in disease. Our results reveal an important role for negative feedback mechanisms in protecting the information transfer function of saturable, heterogeneous cell signaling systems from basal activity.cell sensing | MAPK signaling | mutual information | ultrasensitivity | biomolecular networks C ells must sense extracellular concentrations and transfer the information contained about their environment reliably to make appropriate decisions. Understanding the process of information transfer from the biological environment to the nucleus (1) and studying quantitatively how information about the signal is lost along the way are essential in understanding cellular decision-making (2, 3). The signal transduction networks used by cells are subject to various sources of noise, and we are only beginning to explore how these affect the process of information transfer (4, 5). Here we focus, in the context of protein kinase (PK) signaling, on the little-studied effects of two important types of biological noise: cell-to-cell variability in the componentry of the network and basal network activity. The effect on information transfer of cell-to-cell variation (heterogeneity) in the protein componentry of signaling networks remains largely unexplored. Such variation is expected under physiological conditions (6) and underlies the variable responses observed for genetically identical cells exposed to the same stimulus or drug treatment (7-9). By basal activity, we mean the propensity for activation of the signaling system in the absence of the stimulus or signal of interest. Basal activity is widespread in signaling system...

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In Parkinson’s disease, misfolded α-synuclein accumulates, often in a ubiquitinated form, in neuronal inclusions termed Lewy bodies. An important outstanding question is whether ubiquitination in Lewy bodies is directly relevant to α-synuclein trafficking or turnover and Parkinson’s pathogenesis. By comparative analysis in human postmortem brains, we found that ubiquitin immunoreactivity in Lewy bodies is largely due to K63-linked ubiquitin chains and markedly reduced in the substantia nigra compared with the neocortex. The ubiquitin staining in cells with Lewy bodies inversely correlated with the content and pathological localization of the deubiquitinase Usp8. Usp8 interacted and partly colocalized with α-synuclein in endosomal membranes and, both in cells and after purification, it deubiquitinated K63-linked chains on α-synuclein. Knockdown of Usp8 in the Drosophila eye reduced α-synuclein levels and α-synuclein–induced eye toxicity. Accordingly, in human cells, Usp8 knockdown increased the lysosomal degradation of α-synuclein. In the dopaminergic neurons of the Drosophila model, unlike knockdown of other deubiquitinases, Usp8 protected from α-synuclein–induced locomotor deficits and cell loss. These findings strongly suggest that removal of K63-linked ubiquitin chains on α-synuclein by Usp8 is a critical mechanism that reduces its lysosomal degradation in dopaminergic neurons and may contribute to α-synuclein accumulation in Lewy body disease.