Substance P Antagonist in the Treatment of Posttraumatic Stress Disorder

Posttraumatic Stress Disorder (PTSD) is a common chronic anxiety disorder that is often debilitating and follows exposure to an overwhelming traumatic event. The burden of PTSD on individuals and society is significant. The majority of PTSD sufferers also meet the diagnostic criteria for several other psychiatric disorders and many attempt suicide. Despite the devastating impact of PTSD on the lives of millions worldwide, little is known about the etiology or pathophysiology of this disorder. Although disruptions in the hypothalamic-pituitary adrenal (HPA) Axis, noradrenergic, serotonergic systems have been proposed as neurobiological substrates in the development of PTSD, the exact underpinnings of the neurobiology of PTSD remain to be fully elucidated. PTSD is responsive to treatment with selective serotonin reuptake inhibitors, but response rates rarely exceed 60%, and even fewer patients (20%-30%) experience improvement that could be characterized as remission. Thus, there is a clear need to develop novel and improved therapeutics for PTSD. A growing body of preclinical evidence suggests that activation of the Substance P (SP) and its receptor NK1 is anxiogenic and that NK1 antagonists, upon chronic administration, exert significant dampening (albeit complex) effects on the SP-NP system. Furthermore, several stress paradigms are believed to exert many of their deleterious effects on hippocampal structures via enhancement of SP-NK1 system. Overall, excess activity of the SP-NK1 system stands as a prime candidate for involvement in the pathophysiology of anxiety disorders such as PTSD. In this study, we propose to investigate the potential antianxiety efficacy of the highly specific NK1 antagonist GR205171 in PTSD. Furthermore, we propose to, in a preliminary fashion, longitudinally investigate whether neuroendocrine surrogate markers are predictive of treatment response. This is an 8-week double-blind placebo-controlled study that will examine the efficacy and safety of an NK1 antagonist in patients with PTSD. Patients, ages 18 to 65 years with a diagnosis of PTSD, will in this pilot study be randomized to double-blind treatment to receive either the NK1 antagonist, GR205171 (5 mg/day) or placebo for a period of 8 weeks. Approximately 52 patients will enter the study to obtain 40 subjects who complete the 8 weeks of acute NK1 antagonist treatment.