Novel Tumor Growth Rate Analysis in the Randomized CLARINET Study Establishes the Efficacy of Lanreotide Depot/Autogel 120 mg with Prolonged Administration in Indolent Neuroendocrine Tumors.

INTRODUCTION: Tumor quantity while receiving cancer therapy is the sum of simultaneous regression of treatment-sensitive and growth of treatment-resistant fractions at constant rates. Exponential rate constants for tumor regression/decay (d) and growth (g) can be estimated. Previous studies established g as a biomarker for overall survival; g increases after treatment cessation, can estimate doubling times, and can assess treatment effectiveness in small cohorts by benchmarking to large reference data sets. Using this approach, we analyzed data from the clinical trial CLARINET, evaluating lanreotide depot/autogel 120 mg/4 weeks (LAN) for treatment of neuroendocrine tumors (NETs). METHODS AND MATERIALS: Computed tomography imaging data from 97 LAN- and 101 placebo-treated patients from CLARINET were analyzed to estimate g and d. RESULTS: Data from 92% of LAN- and 94% of placebo-treated patients could be fit to one of the equations to derive g and d (p < .001 in most data sets). LAN-treated patients demonstrated significantly slower g than placebo recipients (p = .00315), a difference of 389 days in doubling times. No significant difference was observed in d. Over periods of LAN administration up to 700 days, g did not change appreciably. Simulated analysis with g as the endpoint showed a sample size of 48 sufficient to detect a difference in median g with 80% power. CONCLUSION: Although treatment of NETs with LAN can affect tumor shrinkage, LAN primarily slows tumor growth rather than accelerates tumor regression. Evidence of LAN efficacy across tumors was identified. The growth-retarding effect achieved with LAN was sustained for a prolonged period of time. IMPLICATIONS FOR PRACTICE: The only curative treatment for neuroendocrine tumors (NETs) is surgical resection; however, because of frequent late diagnosis, this is often impossible. Because of this, treatment of NETs is challenging and often aims to reduce tumor burden and delay progression. A novel method of analysis was used to examine data from the CLARINET trial, confirming lanreotide depot/autogel is effective at slowing tumor growth and extending progression-free survival. By providing the expected rate and doubling time of tumor growth early in the course of treatment, this method of analysis has the potential to guide physicians in their management of patients with NETs.

Functional consequences of cocaine expectation: findings in a non-human primate model of cocaine self-administration.

Exposure to stimuli and environments associated with drug use is considered one of the most important contributors to relapse among substance abusers. Neuroimaging studies have identified neural circuits underlying these responses in cocaine-dependent subjects. But these studies are often difficult to interpret because of the heterogeneity of the participants, substances abused, and differences in drug histories and social variables. Therefore, the goal of this study was to assess the functional effects of exposure to cocaine-associated stimuli in a non-human primate model of cocaine self-administration, providing precise control over these variables, with the 2-[(14) C]deoxyglucose method. Rhesus monkeys self-administered 0.3 mg/kg/injection cocaine (n = 4) under a fixed-interval 3-minute (FI 3-min) schedule of reinforcement (30 injections/session) for 100 sessions. Control animals (n = 4) underwent identical schedules of food reinforcement. Sessions were then discontinued for 30 days, after which time, monkeys were exposed to cocaine- or food-paired cues, and the 2-[(14) C]deoxyglucose experiment was conducted. The presentation of the cocaine-paired cues resulted in significant increases in functional activity within highly restricted circuits that included portions of the pre-commissural striatum, medial prefrontal cortex, rostral temporal cortex and limbic thalamus when compared with control animals presented with the food-paired cues. The presentation of cocaine-associated cues increased brain functional activity in contrast to the decreases observed after cocaine consumption. Furthermore, the topography of brain circuits engaged by the expectation of cocaine is similar to the distribution of effects during the earliest phases of cocaine self-administration, prior to the onset of neuroadaptations that accompany chronic cocaine exposure.

Chronic methylphenidate treatment during early life is associated with greater ethanol intake in socially isolated rats.

BACKGROUND: Methylphenidate (MPH) is a stimulant prescribed to treat attention-deficit/ hyperactivity disorder. Its primary mechanism of action is in the dopamine system, alterations of which are associated with vulnerability to alcohol abuse. There are concerns that juvenile MPH treatment may influence adult drinking behavior. This study examined the interaction of MPH treatment and environmental rearing conditions, which are known to independently influence ethanol (EtOH) drinking behavior, on anxiety-like behavior and vulnerability to alcohol abuse in a juvenile rodent model. METHODS: Male Sprague-Dawley rats were housed in enriched, standard, or isolated conditions for 4 weeks, starting at postnatal day 21. Rats were concurrently treated with 8 mg/kg/d MPH or saline, delivered via osmotic minipump. Anxiety-like behavior was determined at the end of the treatment session, and 5 weeks later. After MPH treatment, rats were exposed to a 2-bottle choice EtOH drinking procedure that lasted 3 weeks. RESULTS: Early life chronic MPH treatment was associated with greater EtOH intake and greater EtOH preference, but only in socially isolated animals. Isolated animals had greater levels of anxiety-like behavior than standard-housed or enriched animals after 4 weeks of exposure to the housing conditions, a difference that persisted even after all animals had been individually housed for an additional 5 weeks and exposed to EtOH. CONCLUSIONS: These results suggest that early life MPH treatment may increase vulnerability to EtOH drinking in adulthood in a subset of the population. Additionally, this study highlights the importance of early rearing condition for establishing long-lasting behavioral phenotypes. Environmental histories should be considered when prescribing MPH treatment to young children.

Withdrawal from extended-access cocaine self-administration results in dysregulated functional activity and altered locomotor activity in rats.

Much work has focused on determining the consequences of cocaine self-administration on specific neurotransmitter systems, thus neglecting the global changes that occur. Previous imaging studies have focused on the effects of cocaine self-administration in the presence of high blood levels of cocaine, but have not determined the functional effects of cocaine self-administration after cocaine has cleared. Extended-access cocaine self-administration, where animals administer cocaine for 6 h each day, results in escalation in the rate of cocaine intake and is believed to model the transition from recreational use to addiction in humans. We aimed to determine the functional changes following acute (48 h) withdrawal from an extended-access, defined-intake self-administration paradigm (5 days, 40 injections/day, 6 h/day), a time point when behavioral changes are present. Using the 2-[(14) C]deoxyglucose method to measure rates of local cerebral glucose metabolism, an indicator of functional activity, we found reductions in circuits related to learning and memory, attention, sleep, and reward processing, which have important clinical implications for cocaine addiction. Additionally, lower levels of functional activity were found in the dorsal raphe and locus coeruleus, suggesting that cocaine self-administration may have broader effects on brain function than previously noted. These widespread neurochemical reductions were concomitant with substantial behavioral differences in these animals, highlighted by increased vertical activity and decreased stereotypy. These data demonstrate that behavioral and neurochemical impairments following cocaine self-administration are present in the absence of drug and persist after cocaine has been cleared.

Prolonged exposure to cocaine self-administration results in a continued progression of alterations in functional activity in a nonhuman primate model.

Background: Studies of nonhuman primates with exposures of up to 100 days of cocaine self-administration (SA) have provided evidence that the central effects of cocaine progress over time. These durations of cocaine exposure, however, may be insufficient to capture the extent of the neurobiological alterations observed in cocaine users, many of whom use the drug for years. The goal of the present study was to determine whether 1.5 years of cocaine SA would result in further progression of alterations in functional brain activity. Methods: Adult male rhesus monkeys were exposed to 300 sessions of high-dose cocaine SA over 1.5 years. Following the final session rates of local cerebral glucose utilization (LCGU) were assessed with the 2-[14C]-deoxyglucose method and compared to rates of LCGU in control monkeys who responded for food reinforcement. In addition, LCGU in these animals was compared to a previously published group of monkeys that had self-administered cocaine or food for 100 sessions over a 4-5 month period. Results: Compared to 100 days of exposure, 300 days of cocaine SA further reduced LCGU in the post-commissural striatum and produced reductions in areas unaffected by the shorter duration of exposure, such as the hypothalamus, all of the amygdala, and large expanses of cortex. Conclusions: These findings demonstrate a clear progression of the impact of cocaine on functional activity with increasing durations of drug experience and have important implications for the development of potential strategies for the treatment of cocaine use disorder.

Treatment Patterns of Long-Acting Somatostatin Analogs for Neuroendocrine Tumors.

Background: Long-acting somatostatin analog therapy (LA-SSA) is recommended as first-line therapy for treatment of unresectable or metastatic neuroendocrine tumors (NETs). Understanding treatment sequencing and dosing patterns of LA-SSA is essential for clinical decision-making to provide value-based management of NETs. Objective: To describe treatment patterns of LA-SSA among patients with NETs and subgroups with carcinoid syndrome (CS) in the United States. Methods: This retrospective study utilized claims data from MarketScan® databases to identify patients with NETs and newly treated with LA-SSA between January 1, 2015, and October 31, 2020. Patients were stratified by index LA-SSA (lanreotide and octreotide long-acting release [LAR]). Reported 28-day doses were based on claim fields for days' supply/drug quantity or units of service. Dose escalation was defined as increases in quantity or frequency. Continuous variables, categorical variables, and Kaplan-Meier estimated treatment durations were compared using t-tests, chi-square/Fisher's tests, and log-rank tests, respectively. Results: The study included 241 lanreotide and 521 octreotide LAR patients. Compared with octreotide LAR patients, treatment duration was longer for lanreotide patients (median, 41.3 vs 26.8 months; log-rank p=.004). Fewer lanreotide patients received rescue treatment with short-acting octreotide (7.9% vs 14.4%; p=.011), and a first (6.2% vs 27.3%) and second dose escalation (0.8% vs 5.2%; both p<.05). Among patients with doses reported, fewer lanreotide patients received above-label doses (2.5% [5/202] vs 14.4% [60/416]; p<.001). Among patients who ended treatment during follow-up, fewer lanreotide patients transitioned to another LA-SSA (18.9% [17/90] vs 33.6% [92/274]; p=.008). Similar treatment patterns were observed in CS subgroups. Results for switched treatment patterns were limited due to insufficient sample sizes. Discussion: Real-world treatment patterns of LA-SSA were assessed using more recent administrative claims data. Compared with octreotide LAR patients, lanreotide patients were more likely to remain longer on initial treatment and starting dose without dose escalations and less likely to use rescue treatment and transition to another LA-SSA after discontinuation of the index treatment. Conclusions: Findings from this claims study suggest a potential clinical benefit of lanreotide in NET management.

Residual deficits in functional brain activity after chronic cocaine self-administration in rhesus monkeys.

Previous studies in humans and in animals have shown dramatic effects of cocaine on measures of brain function that persist into abstinence. The purpose of this study was to examine the neurobiological consequences of abstinence from cocaine, using a model that removes the potential confound of cocaine cues. Adult male rhesus monkeys self-administered cocaine (0.3 mg/kg/injection; N = 8) during daily sessions or served as food-reinforcement controls (N = 4). Two times per week, monkeys were placed in a neutral environment and presented with a cartoon video for ~30 min, sometimes pre- and sometimes post-operant session, but no reinforcement was presented during the video. After ~100 sessions and when the cocaine groups had self-administered 900 mg/kg cocaine, the final experimental condition was a terminal 2-[14C]-deoxyglucose procedure, which occurred in the neutral (cartoon video) environment; for half of the monkeys in each group, this occurred after 1 day of abstinence and for the others after 30 days of abstinence. Rates of local cerebral glucose metabolism were measured in 57 brain regions. Global rates of cerebral metabolism were significantly lower in animals 1 day and 30 days post-cocaine self-administration when compared to those of food-reinforced controls. Effects were larger in 30- vs. 1-day cocaine abstinence, especially in prefrontal, parietal and cingulate cortex, as well as dorsal striatum and thalamus. Because these measures were obtained from monkeys while in a neutral environment, the deficits in glucose utilization can be attributed to the consequences of cocaine exposure and not to effects of conditioned stimuli associated with cocaine.

Chronic phenmetrazine treatment promotes D2 dopaminergic and α2-adrenergic receptor desensitization and alters phosphorylation of signaling proteins and local cerebral glucose metabolism in the rat brain.

Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2Thr202/Tyr204, GSK3ßTyr216, and DARPP-32Thr34. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[14C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [35S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D2 dopamine and α2-adrenergic, but not 5-HT1A, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3ß levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.

Long-term treatment with aripiprazole on the waking and postprandial urges to smoke in Chinese heavy smokers.

The central dopaminergic system plays a critical role in the reinforcing effects of nicotine, which are key determinants in the urge to smoke. Previous study has demonstrated that immediate administration of 10-mg aripiprazole significantly decreased various subjective responses to smoking. The present study investigated whether 2-week treatment with 10-mg aripiprazole could attenuate waking and postprandial urges to smoke in Chinese male and female heavy smokers. A randomized and placebo-controlled pilot clinical study was conducted to assess the effect of aripiprazole on various responses to smoking. The primary outcomes were subject's ratings on questionnaires of smoking urge, withdrawal syndromes, and cigarette evaluation. All participants were administered either placebo or 10-mg aripiprazole for 2 weeks. Throughout the experiment, participants were required to self-report (1) smoking urge and nicotine withdrawal symptoms before their first cigarette after awakening and after lunch and (2) subjective responses to the first cigarette smoked of the day and after lunch. Aripiprazole was associated with significantly decreased waking and postprandial urges to smoke. Aripiprazole failed to produce a significant effect on overall nicotine withdrawal symptoms after awakening and after lunch. However, waking, but not postprandial, withdrawal craving and syndromes were significantly reduced by aripiprazole. Aripiprazole had no effect on the overall subjective responses to the first cigarette of the day and after lunch. The attenuating effects of aripiprazole on waking and postprandial urges to smoke demonstrate the promising effect of aripiprazole in the treatment of nicotine dependence.

Regional elevations in microglial activation and cerebral glucose utilization in frontal white matter tracts of rhesus monkeys following prolonged cocaine self-administration.

It has been shown that exposure to cocaine can result in neuroinflammatory responses. Microglia, the resident CNS immune cells, undergo a transition to an activated state when challenged. In rodents, and possibly humans, cocaine exposure activates microglia. The goal of this study was to assess the extent and magnitude of microglial activation in rhesus monkeys with an extensive history of cocaine self-administration. Male rhesus monkeys (N = 4/group) were trained to respond on a fixed-interval 3-min schedule of food or 0.3 mg/kg/injection cocaine presentation (30 reinforcers/session) for 300 sessions. At the end of the final session, monkeys were administered 2-[14C]deoxyglucose intravenously and 45 min later euthanized. Brain sections were used for autoradiographic assessments of glucose utilization and for microglia activation with [3H]PK11195, a marker for the microglial 18-kDa translocator protein. There were no group differences in gray matter [3H]PK11195 binding, while binding was significantly greater in cocaine self-administration animals as compared to food controls in 8 of the 11 white matter tracts measured at the striatal level. Binding did not differ from control at other levels. There were also significant increases in white matter local cerebral glucose utilization at the striatal level, which were positively correlated with [3H]PK11195 binding. The present findings demonstrate an elevation in [3H]PK11195 binding in forebrain white matter tracts of nonhuman primates with a prolonged history of cocaine self-administration. These elevations were also associated with greater cerebral metabolic rates. These data suggest that white matter deficits may contribute to behavioral, motivational, and cognitive impairments observed in cocaine abusers.

Medical record review of transition to lanreotide following octreotide for neuroendocrine tumors.

BACKGROUND: Octreotide has been used for decades in the United States (US) and Europe to treat patients with advanced neuroendocrine tumors (NETs). Lanreotide was approved in 2014 to improve progression-free survival (PFS) in patients with unresectable, well- or moderately-differentiated, locally advanced or metastatic gastroenteropancreatic NETs. Therefore, clinicians and patients may consider sequencing therapy from octreotide to lanreotide. However, current real-world outcomes data on patients who have made this transition is limited. METHODS: We conducted a multicenter, noninterventional, retrospective medical record review of patients with locally advanced or metastatic gastroenteropancreatic NETs (NCT03112694). Included patients had been treated with long-acting octreotide monotherapy for ≥90 days before transitioning to lanreotide monotherapy and continued on lanreotide for ≥90 days. Abstractors entered patient demographic and clinical data into a customized, web-based case report form. We assessed clinically defined PFS and other tumor-related outcomes while patients were treated with lanreotide. Outcomes were analyzed according to level of response at the time of transition from octreotide to lanreotide: progressive disease, nonprogressive disease, or unknown. Statistical analyses were descriptive. Clinically defined PFS and duration of treatment with lanreotide were estimated using the Kaplan-Meier method. RESULTS: Data were abstracted for 91 patients with gastroenteropancreatic NETs who received long-acting octreotide followed by lanreotide at six US based sites. At initial diagnosis, 71.4% of patients had stage IV disease. Small intestine (63.7%) and pancreas (14.3%) were the most common primary tumor sites. Mean [standard deviation (SD)] duration of follow-up from diagnosis was 70.6 (41.3) months. Patients received long-acting octreotide for a mean (SD) of 38.4 (32.8) months. When patients transitioned to lanreotide, 57.1% had nonprogressive disease on octreotide, 30.8% had progressive disease, and the remainder had unknown disease status. The most common reasons for switching from octreotide to lanreotide were progressive disease (22.0%), formulary change (15.4%), and patient preference (9.9%). Patients received lanreotide for a median (95% CI) duration of 24.7 (16.7-59.9) months. At the end of follow-up, 74% of patients remained on lanreotide monotherapy. Progression occurred in 24.2% of patients during lanreotide treatment. Overall median (95% CI) clinician-defined PFS following the transition to lanreotide was estimated to be 23.7 months [20.2 months-NE (not estimable)]. Patients with nonprogressive disease when they transitioned to lanreotide experienced a median clinician-defined PFS of 24.7 (17.0-NE) months. Among patients reported to have progressive disease when they transitioned to lanreotide, median (95% CI) clinician-defined PFS was estimated to be 15.2 (11.4-NE) months. There were no material differences in adverse events recorded during the long-acting octreotide and lanreotide treatment periods. CONCLUSIONS: Our study suggests that lanreotide monotherapy is well tolerated and may contribute to stabilization of disease in a subset of patients with locally advanced or metastatic gastroenteropancreatic NETs previously treated with long-acting octreotide.

The effects of cocaine: a shifting target over the course of addiction.

Repeated exposure to psychostimulant drugs such as cocaine has been shown in numerous studies to produce significant neuroadaptations in both structure and function throughout the brain. Nonhuman primate models provide a way to systematically evaluate these adaptations engendered by cocaine self-administration and simulate the progressive nature of cocaine addiction in humans. Functional activity, measured using the 2-[14C]deoxyglucose method, was evaluated at selected critical time points over the course of chronic cocaine self-administration in rhesus monkeys. The effects of cocaine exposure in the initial stages of self-administration resulted in changes in functional activity in a highly restricted network of interconnected brain regions when compared to activity in food-reinforced controls. This pattern of changes was confined mainly to ventromedial prefrontal cortex and ventral striatum. Following chronic exposure to cocaine self-administration, however, the spatial extent and intensity of significant alterations in functional activity expanded considerably. The shift in topography of these changes was orderly, originating ventromedially in the prefrontal cortical-ventral striatal network and expanding dorsally to encompass the dorsal striatum. A strikingly similar progression occurred within the cortical areas that project to each of these striatal regions. Preliminary studies suggest that this pattern is maintained despite periods of abstinence from cocaine. The shifting patterns of cerebral metabolic function that accompany longer durations of cocaine self-administration may underlie many of the characteristics of chronic drug exposure, and may provide transitional mechanisms to more compulsive cocaine use.

The potential role of follicle-stimulating hormone in the cardiovascular, metabolic, skeletal, and cognitive effects associated with androgen deprivation therapy.

PURPOSE: To explore how follicle-stimulating hormone (FSH) may contribute to cardiovascular, metabolic, skeletal, and cognitive events in men treated for prostate cancer, with various forms of androgen deprivation therapy (ADT). MATERIALS AND METHODS: A colloquium of prostate cancer experts was convened in May 2015, to discuss the role of FSH in the development of unwanted effects associated with ADT. Subsequently, a literature review (Medline, PubMed, and relevant congress abstract databases) was performed to further explore and evaluate the collected evidence. RESULTS: It has become evident that, in the setting of ADT, FSH can promote the development of atherosclerotic plaque formation, metabolic syndrome, and insulin resistance. Data also suggest that FSH is an important mediator of bone remodeling, particularly bone resorption, and thereby increases the risk for bone fracture. Additional evidence implicates a role for FSH in bone metastasis as well. The influence of FSH on ADT-induced cognitive deficits awaits further elucidation; however, the possibility that FSH may be involved therein cannot be ruled out. CONCLUSIONS: The widespread molecular and physiological consequences of FSH system activation in normal and pathological conditions are becoming better understood. Progress in this area has been achieved by the development of additional investigative and clinical measures to better evaluate specific adverse effects. More research is needed on FSH function in the development of cancer as well as its association with cardiovascular, metabolic, musculoskeletal, and cognitive effects in ADT.

Psychostimulants and monoamine transporters: upsetting the balance.

Monoamine transporters were originally associated simply with the termination of synaptic monoamine function. In addition to amine reuptake, however, the transporters can act as ion channels that affect exocytotic neurotransmitter release and can operate in reverse mode, mediating non-exocytotic amine release. Activity at the plasma membrane is controlled by trafficking, which is modulated by interaction with both substrates and inhibitors and by cytosolic kinases and phosphatases. Monoamine transporters also constitute the principal sites of action of many psychoactive drugs, including amphetamines and cocaine, as well as therapeutic drugs for the treatment of depression, addiction and attention deficit hyperactivity disorder, each modifying the balance of presynaptic neurotransmitter function.

Effects of abstinence from chronic cocaine self-administration on nonhuman primate dorsal and ventral noradrenergic bundle terminal field structures.

Repeated exposure to cocaine is known to dysregulate the norepinephrine system, and norepinephrine has also been implicated as having a role in abstinence and withdrawal. The goal of this study was to determine the effects of exposure to cocaine self-administration and subsequent abstinence on regulatory elements of the norepinephrine system in the nonhuman primate brain. Rhesus monkeys self-administered cocaine (0.3 mg/kg/injection, 30 reinforcers/session) under a fixed-interval 3-min schedule of reinforcement for 100 sessions. Animals in the abstinence group then underwent a 30-day period during which no operant responding was conducted, followed by a final session of operant responding. Control animals underwent identical schedules of food reinforcement and abstinence. This duration of cocaine self-administration has been shown previously to increase levels of norepinephrine transporters (NET) in the ventral noradrenergic bundle terminal fields. In contrast, in the current study, abstinence from chronic cocaine self-administration resulted in elevated levels of [(3)H]nisoxetine binding to the NET primarily in dorsal noradrenergic bundle terminal field structures. As compared to food reinforcement, chronic cocaine self-administration resulted in decreased binding of [(3)H]RX821002 to α2-adrenoceptors primarily in limbic-related structures innervated by both dorsal and ventral bundles, as well as elevated binding in the striatum. However, following abstinence from responding for cocaine binding to α2-adrenoceptors was not different than in control animals. These data demonstrate the dynamic nature of the regulation of norepinephrine during cocaine use and abstinence, and provide further evidence that the norepinephrine system should not be overlooked in the search for effective pharmacotherapies for cocaine dependence.

The individual and combined effects of phenmetrazine and mgluR2/3 agonist LY379268 on the motivation to self-administer cocaine.

BACKGROUND: The US Food and Drug Administration has not approved a treatment for cocaine addiction, possibly due in part to the fact that repeated cocaine use results in dysregulation of multiple neurotransmitter systems, including glutamate and dopamine, and an emergence of increased negative affective states and heightening motivation to take cocaine despite negative consequences. We used a combination therapy approach to assess whether modulation of both glutamate and dopamine transmission would reduce the motivation to self- administer cocaine compared to modulation of either system alone. METHODS: The metabotropic glutamate 2/3 receptor agonist, LY379268, and the monoamine releaser, phenmetrazine, were used to assess their individual and combined ability to decrease the reinforcing efficacy of cocaine because they modulate glutamate and dopamine levels, respectively. Cocaine breakpoints and cocaine intake was assessed, using a progressive ratio schedule, at baseline in three groups based on dose of cocaine (0.19, 0.38, 0.75mg/kg/infusion), and following LY379268 (0.03 or 0.30mg/kg; i.p.), phenmetrazine (25mg/kg/day; osmotic minipump), and a combination of the two drugs. RESULTS: LY379268 and phenmetrazine alone reduced breakpoints for all doses of cocaine. The combination of the two drugs showed a concerted effect in reducing breakpoints for all doses of cocaine, with the lowest dose of cocaine reduced by as much as 70%. CONCLUSIONS: These data support combination therapy of dopamine and glutamate systems as an effective means to reduce the motivation to take cocaine since a combination of drugs can address neurobiological dysfunction in multiple neurotransmitter systems compared to therapies using single drugs.

Effects of chronic cocaine self-administration on norepinephrine transporters in the nonhuman primate brain.

RATIONALE: While cocaine blocks dopamine and serotonin transporters, considerably less emphasis has been placed on its effects following blockade of the norepinephrine transporter (NET). To date, no studies have made a systematic investigation of the effects of chronic cocaine on primate NET density. OBJECTIVE: We previously reported increases in NET density in portions of the monkey bed nucleus of stria terminalis after 100 days of cocaine self-administration. In the present study we extend these findings and assess the changes in [3H]nisoxetine binding in additional brain regions of rhesus monkeys chronically self-administrating cocaine. RESULTS: [3H]Nisoxetine binding sites in the A1 noradrenergic cell group were significantly higher after 5 days of cocaine exposure. One hundred days of self-administration also induced a higher density of NET binding within the A1 cell group; however, in addition, the effects extended to the nucleus prepositus, as well as forebrain regions such as hypothalamic nuclei, basolateral amygdala, parasubiculum, and entorhinal cortex. CONCLUSIONS: These data demonstrate that cocaine self-administration alters the noradrenergic system of nonhuman primates. Although cocaine affected NET binding sites in the forebrain projections of both the ventral (VNAB) and dorsal (DNAB) noradrenergic bundles, the alteration in the A1 cell group at the early time-point suggests that the VNAB appears to be more sensitive than the DNAB to the effects of cocaine. Given the role of norepinephrine in arousal and attention, as well as mediating responses to stress, long-term exposure to cocaine is likely to result in significant changes in the way in which information is perceived and processed by the central nervous system of long-term cocaine users.

Effects of the dopamine/norepinephrine releaser phenmetrazine on cocaine self-administration and cocaine-primed reinstatement in rats.

RATIONALE: Like other monoamine releasers such as D-amphetamine, chronic treatment with phenmetrazine can attenuate cocaine self-administration in monkeys. OBJECTIVES: The present studies extended this finding to rodents and to cocaine-primed reinstatement, a putative laboratory animal model of relapse. METHODS: In experiment 1, rats self-administered food pellets or injections of 0.19 mg/kg cocaine (i.v.) under a progressive-ratio schedule. When responding was stable, subcutaneous osmotic pumps were implanted containing saline or (+)-phenmetrazine (25 or 50 mg/kg per day). In experiment 2, rats self-administered injections of 0.75 mg/kg cocaine under a fixed-ratio 1 schedule in daily 6-h sessions. When responding was stable, rats were removed from the self-administration environment for 7 days and treated continuously with saline, 5 mg/kg per day D-amphetamine or phenmetrazine (25 or 50 mg/kg per day) via osmotic pumps. Rats were then returned to the self-administration context while treatment continued, and responding was extinguished by removing response-contingent stimulus changes and cocaine injections. Once responding was extinguished, reinstatement tests were conducted using cocaine injections (10 mg/kg i.p.). RESULTS: Phenmetrazine decreased self-administration of cocaine, but not food pellets, during the 14-day treatment period; effects persisted for several days after treatment was discontinued. Moreover, cocaine-induced increases in responding during the reinstatement test were attenuated by D-amphetamine and both phenmetrazine doses. CONCLUSIONS: These results extend the study of the effects of phenmetrazine on cocaine self-administration to a rodent model, and provide further support for the use of monoamine releasers as agonist medications for cocaine abuse.

Chronic baclofen desensitizes GABA(B)-mediated G-protein activation and stimulates phosphorylation of kinases in mesocorticolimbic rat brain.

The GABAB receptor is a therapeutic target for CNS and neuropathic disorders; however, few preclinical studies have explored effects of chronic stimulation. This study evaluated acute and chronic baclofen treatments on GABAB-activated G-proteins and signaling protein phosphorylation as indicators of GABAB signaling capacity. Brain sections from rats acutely administered baclofen (5 mg/kg, i.p.) showed no significant differences from controls in GABAB-stimulated GTPγS binding in any brain region, but displayed significantly greater phosphorylation/activation of focal adhesion kinase (pFAK(Tyr397)) in mesocorticolimbic regions (caudate putamen, cortex, hippocampus, thalamus) and elevated phosphorylated/activated glycogen synthase kinase 3-ß (pGSK3ß(Tyr216)) in the prefrontal cortex, cerebral cortex, caudate putamen, nucleus accumbens, thalamus, septum, and globus pallidus. In rats administered chronic baclofen (5 mg/kg, t.i.d. for five days), GABAB-stimulated GTPγS binding was significantly diminished in the prefrontal cortex, septum, amygdala, and parabrachial nucleus compared to controls. This effect was specific to GABAB receptors: there was no effect of chronic baclofen treatment on adenosine A1-stimulated GTPγS binding in any region. Chronically-treated rats also exhibited increases in pFAK(Tyr397) and pGSK3ß(Tyr216) compared to controls, and displayed wide-spread elevations in phosphorylated dopamine- and cAMP-regulated phosphoprotein-32 (pDARPP-32(Thr34)) compared to acutely-treated or control rats. We postulate that those neuroadaptive effects of GABAB stimulation mediated by G-proteins and their sequelae correlate with tolerance to several of baclofen's effects, whereas sustained signaling via kinase cascades points to cross-talk between GABAB receptors and alternative mechanisms that are resistant to desensitization. Both desensitized and sustained signaling pathways should be considered in the development of pharmacotherapies targeting the GABA system.

The effects of GSK-3ß blockade on ketamine self-administration and relapse to drug-seeking behavior in rats.

RATIONALE: The role of glycogen synthase kinase-3 (GSK-3) has recently been implicated in the neurochemical mechanism underlying ketamine-induced neuronal toxicity and behavioral disturbance. OBJECTIVES: The primary goal of the present study was to determine the role of GSK-3ß in ketamine self-administration (SA) and relapse to drug-seeking behavior after abstinence. METHODS: In Experiment 1, the level of phosphorylated GSK-3ß (p-GSK-3ß) and total GSK-3ß (t-GSK-3ß) was determined in various brain areas following 14 days of ketamine SA. In Experiments 2 and 3, the effects of a GSK-3ß inhibitor, SB216763 (2 and 4 mg/kg) and a GSK-3 inhibitor, lithium (LiCl, 100mg/kg) on the responding maintained by 0.5mg/kg/infusion ketamine SA were evaluated. In Experiments 4 and 5, rats underwent ketamine SA for 14 days followed by a 10-day abstinence period. The animals were treated with 2 or 4 mg/kg GSK-3ß inhibitor, or 100mg/kg LiCl during the cue-induced relapse test. Seven days later, animals received the same drug treatment and underwent the drug-induced relapse test. Finally, the effect of saline and DMSO on locomotor activity was evaluated in Experiment 6. RESULTS: Ketamine SA significantly decreased the ratio p-GSK-3ß and t-GSK-3ß (p-GSK-3ß:t-GSK-3ß) in the caudate putamen, nucleus accumbens, and ventral tegmental area. Both SB216763 and LiCl decreased responding on a progressive ratio schedule, but not on a fixed ratio schedule. Cue-induced relapse was suppressed only by 4mg/kg SB216763, whereas drug-induced relapse was inhibited by 2, 4 mg/kg SB216763 and LiCl. However, inactive responses were also suppressed by LiCl during progressive ratio and drug-induced relapse testing. CONCLUSIONS: SB216763 was effective at decreasing ketamine SA under the PR schedule and reducing drug-seeking behavior after abstinence.