Effects of tanezumab on satellite glial cells in the cervicothoracic ganglion of cynomolgus monkeys: A 26-week toxicity study followed by an 8-week recovery period.

Tanezumab, a humanized monoclonal anti-NGF antibody, has demonstrated efficacy and safety profiles in Phase III clinical trials of chronic pain. In a 24-week study in non-human primates, morphological observations of sympathetic ganglia showed decreased ganglia volume, decreased neuronal size, and increased glial cell density compared with controls after 3 tanezumab treatments. Using stereological techniques to quantify glial cells, the present 26-week study found no significant difference after weekly treatments in total cervicothoracic ganglia satellite glial cell number between placebo- or tanezumab-treated cynomolgus monkeys. These findings suggest that tanezumab treatment does not result in a true gliosis in sympathetic ganglia.

Development of pain therapies targeting nerve growth factor signal transduction and the strategies used to resolve safety issues.

Therapeutic agents commonly used in the management of chronic pain have limited effectiveness and may be associated with issues of dependence and tolerability. Thus, a large unmet medical need exists for the development of safe and effective therapeutics for treatment of chronic pain. A novel approach includes identification of intracellular signals involved in the pain transduction pathway, such as nerve growth factor (NGF). Monoclonal antibodies targeting NGF, such as tanezumab, fulranumab and fasinumab, have been investigated for the treatment of chronic pain conditions. Due to unexpected joint adverse events in clinical studies and concerns about sympathetic nervous system toxicity in animals, these agents were placed on 2 separate partial clinical holds, which were subsequently lifted after rigorous evaluations were conducted to understand how inhibition of NGF impacts safety. To share learnings regarding the rigorous evaluation of clinical and nonclinical safety data which contributed to the removal of these partial clinical holds, this article reviews the rationale for developing agents that target NGF as potential treatments for chronic pain, describes nonclinical and clinical studies of these agents, and describes strategies used to evaluate whether inhibition of NGF has negative effects on joint or sympathetic nervous system safety.

From the Cover: Evaluation of the Effects of Tanezumab, a Monoclonal Antibody Against Nerve Growth Factor, on the Sympathetic Nervous System in Adult Cynomolgus Monkeys (Macaca fascicularis): A Stereologic, Histomorphologic, and Cardiofunctional Assessment.

Tanezumab, a humanized monoclonal antibody against nerve growth factor is in development for treatment of chronic pain. Three nonclinical studies assessed effects of clinically relevant and supratherapeutic doses of tanezumab on the sympathetic nervous system (SNS) of adult nonhuman primates. Study 1 evaluated potential effects of subcutaneous (SC) tanezumab (1.2 mg/kg every 8 weeks [Q8W]) on SNS in cynomolgus monkeys for 3 or 6 months and reversibility or persistence of any effects through a nondosing/recovery period. Study 2 evaluated whether neuronal cell death occurs shortly after a single SC tanezumab injection (1.2 mg/kg). Assessments for these two studies included evaluations of superior cervical and cervicothoracic ganglia for neuronal cell death and morphology. Study 3 evaluated effects of SC tanezumab (1.2 mg/kg Q8W and 30 mg/kg/week) over 6 months on sympathetic control of cardiovascular function. Tanezumab exposure was associated with stereologic changes in sympathetic ganglia, including smaller ganglion volume, and smaller average neuron size/area beginning at 2 weeks and reaching maximal levels by 1 month with no further progression through 6 months. These changes were not associated with clinical signs, completely reversed upon tanezumab withdrawal, and were not considered adverse. Tanezumab had no adverse effects on sympathetic control of cardiovascular function. These data support the conclusion that tanezumab administration for up to 6 months has no adverse effects on SNS morphology or function and does not cause neuronal cell death in adult nonhuman primates.

Effects of inducing physiological hyperglucagonemia on metabolic responses to exercise.

The purpose of the present study was to assess the effects of exogenously increasing the circulating levels of glucagon on the metabolic responses to exercise in rats. A total of six groups of rats were infused (iv) either with glucagon (20 or 50 ng x kg(-1) x min(-1)) or saline (0.9% NaCl), either in the resting state or during a bout of running exercise (45 min, 26 m x min(-1), 0% grade). Blood samples were taken at the end of the 45-min experiment. Animals infused with glucagon at 50 ng x kg(-1) x min(-1) showed significantly (P<0.01) higher mean plasma glucagon concentrations than animals infused with saline or glucagon at 20 ng x kg(-1) x min(-1). In addition, exercise resulted in significantly (P<0.05) higher mean plasma glucagon concentrations, compared to rest, in all groups. In spite of these differences in glucagon concentrations, there were no significant (P>0.05) effects of exercise and glucagon infusion on mean hepatic glycogen, plasma glucose, insulin, C-peptide, beta-hydroxybutyrate, or catecholamine concentrations. Although exercise resulted in a significant (P<0.01) increase in plasma glycerol and free fatty acid concentrations and a significant (P<0.05) decrease in glycogen in the soleus muscle, these responses were not affected by the glucagon infusion. These results suggest that the liver is non-responsive to physiological hyperglucagonemia in a short-term (45 min) exercise situation.

Effects of endurance training on the gluconeogenic capacity of periportal and perivenous hepatocytes.

This study was undertaken to assess the effect of 8 weeks of endurance training (treadmill, last 4 weeks: 60 min at 26 m/min, 8-10% grade) on the gluconeogenic capacity of periportal (PP-H) and perivenous (PV-H) hepatocytes of overnight fasted rats. Isolated PP-H and PV-H, obtained by selective destruction after liver perfusion with digitonin and collagenase, were incubated with saturating concentrations of a mixture of lactate and pyruvate (20:2 mM; Lac+Pyr) or alanine (20 mM; Ala) to determine the glucose production flux (J(glucose)) in the incubation medium. Endogenous J(glucose) as well as J(glucose) from substrates were significantly higher (P<.05) in PP-H than PV-H in the untrained state. Following training, a selective increase (P<.05) in J(glucose) from endogenous substrates and from Lac+Pyr was observed in PV-H only, resulting in the disappearance (P>.05) of the difference of J(glucose) between PP-H and PV-H. It is concluded that the increase in the gluconeogenic capacity of the liver following endurance training is first observed in PV-H.

Influence of prior exercise and liver glycogen content on the sensitivity of the liver to glucagon.

The purpose of the present study was to test the hypothesis that a prior period of exercise is associated with an increase in hepatic glucagon sensitivity. Hepatic glucose production (HGP) was measured in four groups of anesthetized rats infused with glucagon (2 microg. kg(-1). min(-1) iv) over a period of 60 min. Among these groups, two were normally fed and, therefore, had a normal level of liver glycogen (NG). One of these two groups was killed at rest (NG-Re) and the other after a period of exercise (NG-Ex; 60 min of running, 15-26 m/min, 0% grade). The two other groups of rats had a high hepatic glycogen level (HG), which had been increased by a fast-refed diet, and were also killed either at rest (HG-Re) or after exercise (HG-Ex). Plasma glucagon and insulin levels were increased similarly in all four conditions. Glucagon-induced hyperglycemia was higher (P < 0.01) in the HG-Re group than in all other groups. HGP in the HG-Re group was not, however, on the whole more elevated than in the NG-Re group. Exercised rats (NG-Ex and HG-Ex) had higher hyperglycemia, HGP, and glucose utilization than rested rats in the first 10 min of the glucagon infusion. HG-Ex group had the highest HGP throughout the 60-min experiment. It is concluded that hyperglucagonemia-induced HGP is stimulated by a prior period of exercise, suggesting an increased sensitivity of the liver to glucagon during exercise.