CNS response to a thermal stressor in human volunteers and rats may predict the clinical utility of analgesics

Role of Brain Imaging in Drug Development for Psychiatry

Background:

Over the last decades, many brain imaging studies have contributed to new insights in the pathogenesis of psychiatric disease. However, in spite of these developments, progress in the development of novel therapeutic drugs for prevalent psychiatric health conditions has been limited.

Objective:

In this review, we discuss translational, diagnostic and methodological issues that have hampered drug development in CNS disorders with a particular focus on psychiatry. The role of preclinical models is critically reviewed and opportunities for brain imaging in early stages of drug development using PET and fMRI are discussed. The role of PET and fMRI in drug development is reviewed emphasizing the need to engage in collaborations between industry, academia and phase I units.

Conclusion:

Brain imaging technology has revolutionized the study of psychiatric illnesses, and during the last decade, neuroimaging has provided valuable insights at different levels of analysis and brain organization, such as effective connectivity (anatomical), functional connectivity patterns and neurochemical information that may support both preclinical and clinical drug development. Since there is no unifying pathophysiological theory of individual psychiatric syndromes and since many symptoms cut across diagnostic boundaries, a new theoretical framework has been proposed that may help in defining new targets for treatment and thus enhance drug development in CNS diseases. In addition, it is argued that new proposals for data-mining and mathematical modelling as well as freely available databanks for neural network and neurochemical models of rodents combined with revised psychiatric classification will lead to new validated targets for drug development.

Targeting migraine treatment with neuroimaging-Pharmacological neuroimaging in headaches

PURPOSE

The current review provides a recapitulation of recent advances in pharmacological neuroimaging in headache, a promising tool to understanding of how a drug works in the brain and how it may lead to new insights of disease mechanisms of headache.

RESULTS

Pharmacological positron emission tomography with radioligand-labeled medication may provide evidence whether and where a medication binds in the brain but is still mostly restricted to animal work. Pharmacological functional MRI using task-specific approaches identified central modulation patterns as a consequence of attack and preventative headache medication, which may be distinct to a specific drug mechanism. Pharmacological neuroimaging and specifically in combination with functional imaging is a promising tool to better understand not only certain medications but also certain disease mechanisms.

SUMMARY

Pharmacological imaging techniques have advanced over the last few years and showed great potential of providing new insights into drug pharmacodynamics and disease mechanism. There are still limitations and challenges to be overcome.

Lost but making progress--Where will new analgesic drugs come from?

There is a critical need for effective new pharmacotherapies for pain. The paucity of new drugs successfully reaching the clinic calls for a reassessment of current analgesic drug discovery approaches. Many points early in the discovery process present significant hurdles, making it critical to exploit advances in pain neurobiology to increase the probability of success. In this review, we highlight approaches that are being pursued vigorously by the pain community for drug discovery, including innovative preclinical pain models, insights from genetics, mechanistic phenotyping of pain patients, development of biomarkers, and emerging insights into chronic pain as a disorder of both the periphery and the brain. Collaborative efforts between pharmaceutical, academic, and public entities to advance research in these areas promise to de-risk potential targets, stimulate investment, and speed evaluation and development of better pain therapies.

Transferring morality to human-nonhuman chimeras

Human-nonhuman chimeras have been the focus of ethical controversies for more than a decade, yet some related issues remain unaddressed. For example, little has been said about the relationship between the origin of transferred cells and the morally relevant capacities to which they may give rise. Consider, for example, a developing mouse fetus that receives a brain stem cell transplant from a human and another that receives a brain stem cell transplant from a dolphin. If both chimeras acquire morally relevant capacities as a result of transplantation, and if those capacities are indistinguishable, should the difference in cell origin matter to how we classify these creatures? I argue that if morally relevant capacities are easy to detect, cell origin is irrelevant to how the chimera ought to be treated. However, if such capacities are hard to detect, cell origin should play a role in considerations about how to treat the chimera.

Pharmacological neuroimaging in headache and pain

PURPOSE OF REVIEW

The current review gives an overview about recent advances in neuroimaging studies with specific emphasis on pharmacological modulation of pain and headache. Further, we want to highlight how imaging methods have changed our understanding of chronic pain and discuss how pharmacological MRI could lead to new insights into underlying mechanisms of headache and pain.

RECENT FINDINGS

Several studies from different imaging laboratories have highlighted the outstanding role of imaging in getting a deeper insight regarding the central mechanisms of drugs. Neuroimaging techniques start to unravel how analgesic drugs, antidepressants or NSAIDs act on pain perception and in particular on central pain processes. Furthermore, the studies included in this review show how context dependent drugs act and how differently they reveal their action in the human brain.

SUMMARY

Imaging techniques give us the opportunity to gain a better understanding of drug processes in the central nervous system and help to understand where drugs reveal their therapeutic effect. While some substances work on the emotional-affective component of pain, others modulate sensory-discriminative pain pathways. Especially in the field of headache research, still a lot has to be done to understand how preventatives and acute medication modulate the human brain. Future studies should also replicate and extend recent findings.

Use of functional imaging across clinical phases in CNS drug development

The use of novel brain biomarkers using nuclear magnetic resonance imaging holds potential of making central nervous system (CNS) drug development more efficient. By evaluating changes in brain function in the disease state or drug effects on brain function, the technology opens up the possibility of obtaining objective data on drug effects in the living awake brain. By providing objective data, imaging may improve the probability of success of identifying useful drugs to treat CNS diseases across all clinical phases (I-IV) of drug development. The evolution of functional imaging and the promise it holds to contribute to drug development will require the development of standards (including good imaging practice), but, if well integrated into drug development, functional imaging can define markers of CNS penetration, drug dosing and target engagement (even for drugs that are not amenable to positron emission tomography imaging) in phase I; differentiate objective measures of efficacy and side effects and responders vs non-responders in phase II, evaluate differences between placebo and drug in phase III trials and provide insights into disease modification in phase IV trials.

Decision-making using fMRI in clinical drug development: revisiting NK-1 receptor antagonists for pain

Substance P (SP) and neurokinin-1 receptors (NK-1R) are localized within central and peripheral sensory pain pathways. The roles of SP and NK-1R in pain processing, the anatomical distribution of NK-1R and efficacy observed in preclinical pain studies involving pain and sensory sensitization models, suggested that NK-1R antagonists (NK-1RAs) would relieve pain in patient populations. Despite positive data available in preclinical tests for a role of NK-1RAs in pain, clinical studies across several pain conditions have been negative. In this review, we discuss how functional imaging-derived information on activity in pain-processing brain regions could have predicted that NK-1RAs would have a low probability of success in this therapeutic domain.

A procedural framework for good imaging practice in pharmacological fMRI studies applied to drug development #1: processes and requirements

There is increasing interest in the application of quantitative magnetic resonance imaging (MRI) methods to drug development, but as yet little standardization or best practice guidelines for its use in this context. Pharmaceutical trials are subject to regulatory constraints and sponsor company processes, including site qualification and expectations around study oversight, blinding, quality assurance and quality control (QA/QC), analysis and reporting of results. In this article, we review the processes on the sponsor side and also the procedures involved in data acquisition at the imaging site. We then propose summary recommendations to help guide appropriate imaging site qualification, as part of a framework of 'good imaging practice' for functional (f)MRI studies applied to drug development.

Can Functional Magnetic Resonance Imaging Improve Success Rates in CNS Drug Discovery?

INTRODUCTION: The bar for developing new treatments for CNS disease is getting progressively higher and fewer novel mechanisms are being discovered, validated and developed. The high costs of drug discovery necessitate early decisions to ensure the best molecules and hypotheses are tested in expensive late stage clinical trials. The discovery of brain imaging biomarkers that can bridge preclinical to clinical CNS drug discovery and provide a 'language of translation' affords the opportunity to improve the objectivity of decision-making. AREAS COVERED: This review discusses the benefits, challenges and potential issues of using a science based biomarker strategy to change the paradigm of CNS drug development and increase success rates in the discovery of new medicines. The authors have summarized PubMed and Google Scholar based publication searches to identify recent advances in functional, structural and chemical brain imaging and have discussed how these techniques may be useful in defining CNS disease state and drug effects during drug development. EXPERT OPINION: The use of novel brain imaging biomarkers holds the bold promise of making neuroscience drug discovery smarter by increasing the objectivity of decision making thereby improving the probability of success of identifying useful drugs to treat CNS diseases. Functional imaging holds the promise to: (1) define pharmacodynamic markers as an index of target engagement (2) improve translational medicine paradigms to predict efficacy; (3) evaluate CNS efficacy and safety based on brain activation; (4) determine brain activity drug dose-response relationships and (5) provide an objective evaluation of symptom response and disease modification.

CNS animal fMRI in pain and analgesia

Animal imaging of brain systems offers exciting opportunities to better understand the neurobiology of pain and analgesia. Overall functional studies have lagged behind human studies as a result of technical issues including the use of anesthesia. Now that many of these issues have been overcome including the possibility of imaging awake animals, there are new opportunities to study whole brain systems neurobiology of acute and chronic pain as well as analgesic effects on brain systems de novo (using pharmacological MRI) or testing in animal models of pain. Understanding brain networks in these areas may provide new insights into translational science, and use neural networks as a "language of translation" between preclinical to clinical models. In this review we evaluate the role of functional and anatomical imaging in furthering our understanding in pain and analgesia.

A fMRI evaluation of lamotrigine for the treatment of trigeminal neuropathic pain: pilot study

Using functional magnetic resonance imaging (fMRI) methods, we evaluated the effects of lamotrigine vs placebo in a double-blind 1:1 randomized trial. Six patients with neuropathic pain were recruited for the study. All subjects had baseline pain >4/10 on a visual analog scale (VAS) and allodynia to brush as inclusion criteria for the study. Patients underwent two fMRI sessions, with half of the subjects receiving placebo first and half receiving drug first (based on the blinding protocol). Lamotrigine decreased their average pain intensity level from 5.6 to 3.5 on a VAS. All subjects had brush, cold, and heat applied to the affected and mirror-unaffected sides of their face. The results show: 1) in a small cohort, lamotrigine had a significant effect on heat VAS but not on the other stimuli; and 2) contrast analysis of fMRI results for heat stimuli applied to the affected face for lamotrigine vs placebo produced an overall decrease in blood oxygen dependent level signal, suggesting a potential inhibitory effect of the drug on predominantly cortical regions (frontal, parietal, and temporal).

Studying the brain-gut axis with pharmacological imaging

Pharmacological imaging provides great potential both for evaluating the efficacy of new candidate compounds in the treatment of gastrointestinal symptom-based disorders, and for furthering our understanding of the underlying pathophysiology of such disorders. By combining evaluation of symptoms, behavior, and brain responses to relevant stimuli, use of neuroimaging is able to move the study of brain-gut disorders away from more subjective outcomes and emphasize the underlying neural networks involved in symptom generation and treatment. This chapter reviews the state of the art in pharmacological imaging studies, both in human subjects and in animal models of brain-gut interactions.