A multivantaged behavioural method for measuring onset and sequence of the clinical actions of antidepressants

Design, Synthesis and Biological Evaluation of Novel Ketamine Derivatives as NMDAR Antagonists

Depression is a chronic, severe, and often life-threatening neurological disorder. It not only causes depression in patients and affects daily life but, in severe cases, may lead to suicidal behavior and have adverse effects on families and society. In recent years, it has been found that sub-anesthetic doses of ketamine have a rapid antidepressant effect on patients with treatment-resistant depression and can significantly reduce the suicidal tendencies of patients with major depressive disorder. Current studies suggest that ketamine may exert antidepressant effects by blocking NMDAR ion channels, but its anesthetic and psychotomimetic side effects limit its application. Here, we report efforts to design and synthesize a novel series of ketamine derivatives of NMDAR antagonists, among which compounds 23 and 24 have improved activity compared with ketamine, introducing a new direction for the development of rapid-acting antidepressant drugs.

Molecular and Cellular Mechanisms of Rapid-Acting Antidepressants Ketamine and Scopolamine

Major depressive disorder (MDD) is a prevalent neuropsychiatric disease that causes profound social and economic burdens. The impact of MDD is compounded by the limited therapeutic efficacy and delay of weeks to months of currently available medications. These issues highlight the need for more efficacious and faster-acting treatments to alleviate the burdens of MDD. Recent breakthroughs demonstrate that certain drugs, including ketamine and scopolamine, produce rapid and long-lasting antidepressant effects in MDD patients. Moreover, preclinical work has shown that the antidepressant actions of ketamine and scopolamine in rodent models are caused by an increase of extracellular glutamate, elevated BDNF, activation of the mammalian target of rapamycin complex 1 (mTORC1) cascade, and increased number and function of spine synapses in the prefrontal cortex (PFC). Here we review studies showing that both ketamine and scopolamine elicit rapid antidepressant effects through converging molecular and cellular mechanisms in the PFC. In addition, we discuss evidence that selective antagonists of NMDA and muscarinic acetylcholine (mACh) receptor subtypes (i.e., NR2B and M1-AChR) in the PFC produce comparable antidepressant responses. Furthermore, we discuss evidence that ketamine and scopolamine antagonize inhibitory interneurons in the PFC leading to disinhibition of pyramidal neurons and increased extracellular glutamate that promotes the rapid antidepressant responses to these agents. Collectively, these studies indicate that specific NMDA and mACh receptor subtypes on GABAergic interneurons are promising targets for novel rapid-acting antidepressant therapies.

Conflicting perspectives on neurobehavioral theories of the depressive disorders and drug actions

OBJECTIVE

A prominent theory of depression focusses on neural plasticity and stress as central issues in seeking to develop a pattern of identifiable biological markers for the depressive disorders. Relative neglect, however, of clinical factors in that theory limits the uncovering of markers and opens to question their methodological approach. A conflicting theory, the 'opposed neurobehavioral states', based on dimensional analysis of monoamine neurotransmitter systems and behavioural factors is presented. This perspectives paper contrasts the two approaches viewing the biomarkers theory as premature at this point in the progress of depression research.

METHOD

Studies developed to support the biomarkers theory and the opposed neurobehavioral states theory are examined for their strengths and limitations in explaining the nature of the disorder and the actions of therapeutic drugs. Reference is made to reviews of the many studies on biomarkers and the recent work that supports the opposed neurobehavioral states theory. Discussion Main issue: the biomarkers theory sets important goals, but despite the many advances in the neural investigations of factors underlying depression, is still not successful in specifying markers. Thus, it is believed to be applying the wrong methodologic approach and premature in its claims.

PERSPECTIVE

the 'opposed neurobehavioral' theory is limited in its breadth of research. It applies, however, the dimensional approach to the clinical side of the problem, a methodological approach more likely to be effective in selecting the best clinical treatment and open to a more productive path to understanding of the nature of the disorder in future research.

Early Symptom Improvement as a Predictor of Response to Extended Release Quetiapine in Major Depressive Disorder

The aim of this post-hoc analysis was to determine whether early symptom improvement with extended release quetiapine (quetiapine XR) may predict treatment outcome in patients with major depressive disorder. Data were from 6, double-blind, placebo-controlled studies of quetiapine XR (2 fixed-dose and 2 flexible-dose monotherapy and 2 adjunct studies) in adult patients with major depressive disorder. Montgomery-Åsberg Depression Rating Scale (MADRS) and Clinical Global Impression-Severity Score (CGI-S) were assessed at baseline, weeks 2, 4, and 6. Hamilton Rating Scale for Depression (HAM-D) was assessed at baseline and week 6. The MADRS improvement at week 2 (15%, 20%, 25%, 30%) was used to predict response and remission, based on MADRS (50% improvement; total score ≤ 12) or HAM-D (50% improvement; total score ≤ 7). The CGI-S improvement (1 point) at week 2 was used to predict final outcome (CGI-S score ≤ 2). The predictive value for early improvement with quetiapine XR was found to be "very strong" (Yule's Q coefficient, a combined measure of sensitivity and specificity) using 30% MADRS improvement as the threshold. This was relatively comparable for response and remission and for fixed-dose, flexible-dose, and adjunct studies. This was also observed for placebo. Exceptions were: adjunct studies (where predictivity was lower for ongoing antidepressant/placebo), and for remission (predictivity for remission appeared lower than for response with placebo). In conclusion, outcome at week 6 with quetiapine XR for a major depressive episode could be predicted by 30% improvement after 2 weeks, a finding that could give doctors confidence to continue treatment and may facilitate adherence in patients.

Evidence for shortening the duration of clinical trials of antidepressants and a proposed paradigm for such studies

The model for the clinical trial of putative antidepressants is older than 50 years. Recent failures resulted in several drug companies, citing excessive costs of lengthy multiweek trials, abandoning new drug development. Collateral problems include patients being maintained on ineffective drugs for 6 to 8 weeks, increasing the pain associated with the disorder. This study proposes an alternative model for testing new drugs that both shortens the clinical trial and broadens its aims to include a profile of the new drug's specific clinical actions. This alternative model makes it possible to uncover the drug's application to treatment of other mental disorders. It is based on recent findings that onset of action and a large proportion of an effective drug's positive effects, contrary to early reports, occur within the first 2 weeks. It uses an index of the 2-week "early improvement" to predict a 6-week outcome. Measuring effects on the dimensions of the disorder determined that effective antidepressants act on mood and behavioral components and that the Hamilton and new "multivantaged" methods can provide a profile of specific drug actions distinguished from nonspecific placebo effects, at 2 weeks. This early improvement is predictive of positive outcome of 6-week trials. Because of the implications of successful 2-week trials for reducing costs, providing data on specific clinical drug actions, potentially stimulating new drug development, and reducing patient suffering from extended treatment with ineffective drugs, a large sample, prospective study designed in accord with this test trial is recommended.

Neuropsychological correlates of symptom dimensions in inpatients with major depressive disorder

Symptoms of major depressive disorder (MDD) manifest variably across individuals. Accordingly, recent models of the disorder imply that MDD may be characterized according to independent symptom dimensions. In particular, several studies reveal that depression may be characterized along dimensions of negative affect, agitation and hostility, and lassitude and malaise. No research has examined the relationship between these dimensions and neuropsychological function. Towards this end, 133 in patients with unipolar MDD and 17 people without psychiatric illness were administered a brief battery of neuropsychological tests and the MMPI-2. Paralleling earlier research, principal component analysis of the MMPI-2 revealed symptom dimensions of negative affect, agitation, and lassitude and malaise. Multiple regression analyses showed that the negative affect and agitation dimensions accounted for significant variance on measures of executive function, speed of information processing, new learning, dexterity, and overall impairment. Lassitude and malaise failed to correspond with neuropsychological performance. Implications of these data for clinical practice and neural models of MDD are discussed.

General and comparative efficacy and effectiveness of antidepressants in the acute treatment of depressive disorders: a report by the WPA section of pharmacopsychiatry

Current gold standard approaches to the treatment of depression include pharmacotherapeutic and psychotherapeutic interventions with social support. Due to current controversies concerning the efficacy of antidepressants in randomized controlled trials, the generalizability of study findings to wider clinical practice and the increasing importance of socioeconomic considerations, it seems timely to address the uncertainty of concerned patients and relatives, and their treating psychiatrists and general practitioners. We therefore discuss both the efficacy and clinical effectiveness of antidepressants in the treatment of depressive disorders. We explain and clarify useful measures for assessing clinically meaningful antidepressant treatment effects and the types of studies that are useful for addressing uncertainties. This includes considerations of methodological issues in randomized controlled studies, meta-analyses, and effectiveness studies. Furthermore, we summarize the differential efficacy and effectiveness of antidepressants with distinct pharmacodynamic properties, and differences between studies using antidepressants and/or psychotherapy. We also address the differential effectiveness of antidepressant drugs with differing modes of action and in varying subtypes of depressive disorder. After highlighting the clinical usefulness of treatment algorithms and the divergent biological, psychological, and clinical efforts to predict the effectiveness of antidepressant treatments, we conclude that the spectrum of different antidepressant treatments has broadened over the last few decades. The efficacy and clinical effectiveness of antidepressants is statistically significant, clinically relevant, and proven repeatedly. Further optimization of treatment can be helped by clearly structured treatment algorithms and the implementation of psychotherapeutic interventions. Modern individualized antidepressant treatment is in most cases a well-tolerated and efficacious approach to minimize the negative impact of otherwise potentially devastating and life-threatening outcomes in depressive disorders.

Rethinking depression and the actions of antidepressants: uncovering the links between the neural and behavioral elements

Despite major strides in the understanding of mechanisms of antidepressant drug action, few, if any, widely applicable drug treatments with new mechanisms have been developed since the selective serotonin reuptake inhibitors in the late 1970's. One factor that may contribute to this lack of advance is reliance on a set of flawed assumptions that have guided most new drug development over the past quarter century. These assumptions have been particularly deleterious to the development of treatments with mechanisms distinctly different from currently approved treatments. One such assumption is that antidepressant actions on clinical aspects are delayed for several weeks. We review the results of studies on time to improvement and describe two collaborative, multidisciplinary studies during this period which employed a behavioral component model for assessment of change, as an alternative to the conventional "diagnostic-specific" research model. These studies incorporated a novel neurobehavioral framework for describing depressive episodes. The studies indicated that (1) depressive states are comprised of relatively independent and somewhat opposed behavioral and emotional components of anxiety-agitation and depression-retardation, coexisting with a third dimension, hostility, all of which might indicate some degree of mixed state phenomenology, (2) drugs selectively targeted at serotonergic and noradrenergic systems have differing profiles of impact on the behavioral dimensions of depressive states and (3) the sequence of behavioral improvements initiated by pharmacodynamically different drugs also differ. In the aggregate these consistent observations provide the basis for a new paradigm on the nature of major depression. The proposition links drug-induced neural and behavioral changes of antidepressants with prediction of clinical outcome based on early response. We submit that the proposed approach may bring about a new paradigm for improving behavioral technology and design of studies capable of identifying drugs with novel properties and rapid onset of improvement, while avoiding some problematic constructs in past biological research on depression.

Frontal electroencephalogram changes in early phase antidepressant treatment predict clinical response in major depressive disorder

Evaluation of: Leuchter AF, Cook IA, Marangell LB et al.: Comparative effectiveness of biomarkers and clinical indicators for predicting outcomes of SSRI treatment in major depressive disorder: results of the BRITE-MD study. Psychiatry Res. 169, 124–131 (2009) and Leuchter AF, Cook IA, Marangell LB et al.: Effectiveness of a quantitative electroencephalographic biomarker for predicting differential response or remission with escitalopram and bupropion in major depressive disorder. Psychiatry Res. 169, 132–138 (2009). The investigators of the Biomarkers for Rapid Identification of Treatment Effectiveness in Major Depression (BRITE-MD) study calculated the Antidepressant Treatment Response (ATR) index, a biomarker of frontal quantitative electroencephalogram changes, after 1 week of escitalopram treatment and examined whether the ATR had utility as a predictor of outcome after a further 7 weeks of treatment. The ATR index predicted response and remission at week 7, whereas the symptom reduction in Hamilton Depression Rating Scale scores by week 1 only predicted response at week 7. Other markers, such as genetic polymorphisms (5-HTTLPR and 5HT2A), the clinician-rated global impression of improvement and serum drug concentrations, did not provide significant predictive utility. Notably, high ATR values predicted response to escitalopram, while low ATR values predicted response to bupropion. The findings provocatively suggest that the ATR index may be a useful predictor for short-term antidepressant outcome. These results may encourage the future work that will be necessary to evaluate the role of the ATR index and clinical measures as predictors of both short- and long-term antidepressant treatment outcomes.

Assessing activity onset time and efficacy for clinically effective antidepressant and antimanic drugs in animal models based on dominant-submissive relationships

There is confusion in the literature on the measurement of the drug activity onset time (AOT) for both clinical and non-clinical studies of antidepressant and antimanic drugs. The questions asked are: How often and at which time points should drug effects be measured? At what level of a drug effect should AOT be determined? Is the placebo (control) effect important for consideration of drug AOT? This paper reviews approaches taken to answer these questions and to assess drug therapeutic AOT. The first part of the paper is devoted to a review of methods used in clinical trials with depression as an indication. The second part is focused on approaches taken in animal models of depression and how they could help in assessing drug AOT. Finally, a summary of pharmacological values on which the AOT depends is presented and a new statistical approach to data analysis method proposed. The allied experimental design for pre-clinical and clinical studies may help to characterize and differentiate AOT for available and new generation of antidepressants and antimanic drugs.

A panic experimental model: Validation of a complex operant behavioral method in undernourished rats, with desipramine to provide a template effect profile

INTRODUCTION

Clinical studies have shown that some antidepressants may be more efficient than benzodiazepines to alleviate anxiety associated with panic disorders; however, operant conflict procedures in rats developed so far seem not particularly able to model human anxiety sensitive to antidepressant treatments. Previous panic models with learned responses did not statistically subtract the effect of confounding factors from the variable of interest.

METHODS

Undernourished rats were selected due to their behavioral and neurobiological resemblance to human patients suffering from panic disorder. The Geller-Seifter paradigm represented the stressful environmental condition in adult life. Desipramine (10 mg/kg/day) or saline were administered IP during 7 days under a cross over design (N=10). Five daily 15 min-operant sessions were carried out on each experiment. Unpunished, unrewarded and punished operant behavioral periods were identical both in their duration and in their reward system (the FR1 schedule) in order to measure response suppression, which has not been considered in previous studies with the Geller-Seifter paradigm. The dependent variable was the difference between comparable unpunished and punished periods.

RESULTS

A significant Diet x Drug interaction was observed in the dependent variable, which represented the level of "suppression/suppression release" induced by treatments.

DISCUSSION

Compared to control rats, deprived rats showed a significant and selective anticonflict effect of desipramine on the stressful and complex operant performance. The animal model of perinatally protein-deprived rats along with the Geller-Seifter's operant behavioral paradigm may represent a more sensitive approach to model human anxiety sensitive to antidepressant treatments by considering the combined impact of both early biological trauma and adult learned experiences under the same design.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.