Design and synthesis of triarylacrylonitrile analogues of tamoxifen with improved binding selectivity to protein kinase C

PKC inhibition decreases amphetamine-maintained responding under a progressive-ratio schedule of reinforcement

Protein kinase C (PKC) is important for the mechanism of action of amphetamine (AMPH). Inhibiting PKC blocks AMPH-stimulated increases in extracellular dopamine levels and AMPH-stimulated locomotor activity. This study examined the effects of PKC inhibition on the reinforcing properties of AMPH. Male Sprague-Dawley rats were trained to respond for infusions of 0.032 mg/kg/infusion AMPH or for sucrose pellets under a progressive-ratio (PR) schedule of reinforcement. Number of infusions earned, breakpoints, and session duration were recorded over consecutive sessions. Once AMPH-maintained responding stabilized, rats were treated with 0, 10, or 30 pmol of enzastaurin, a PKCβ-selective inhibitor, or 6 mg/kg 6c, a brain-permeable PKC inhibitor, 18 hr prior to a self-administration session. Pretreatment with 30 pmol enzastaurin or 6 mg/kg 6c decreased the number of AMPH infusions earned and breakpoints without altering sucrose-maintained behaviors. These data suggest that PKC inhibition decreases motivation for AMPH and, therefore, is worth pursuing as a potential treatment for AMPH-use disorder. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Lithium as a Neuroprotective Agent for Bipolar Disorder: An Overview

Lithium (Li⁺) is a first option treatment for adult acute episodes of Bipolar Disorder (BD) and for the prophylaxis of new depressed or manic episodes. It is also the preferred choice as maintenance treatment. Numerous studies have shown morphological abnormalities in the brains of BD patients, suggesting that this highly heritable disorder may exhibit progressive and deleterious changes in brain structure. Since treatment with Li⁺ ameliorates these abnormalities, it has been postulated that Li⁺ is a neuroprotective agent in the same way atypical antipsychotics are neuroprotective in patients diagnosed with schizophrenia spectrum disorders. Li⁺'s neuroprotective properties are related to its modulation of nerve growth factors, inflammation, mitochondrial function, oxidative stress, and programmed cell death mechanisms such as autophagy and apoptosis. Notwithstanding, it is not known whether Li⁺-induced neuroprotection is related to the inhibition of its putative molecular targets in a BD episode: the enzymes inositol-monophosphatase, (IMPase), glycogen-synthase-kinase 3β (GSK3), and Protein kinase C (PKC). Furthermore, it is uncertain whether these neuroprotective mechanisms are correlated with Li⁺'s clinical efficacy in maintaining mood stability. It is expected that in a nearby future, precision medicine approaches will improve diagnosis and expand treatment options. This will certainly contribute to ameliorating the medical and economic burden created by this devastating mood disorder.

Neuropsychiatric effects of tamoxifen: Challenges and opportunities

Epidemiological, clinical, and basic research over the past thirty years have described the benefits of estrogen on cognition, mood, and brain health. Less is known about tamoxifen, a selective estrogen receptor modifier (SERM) commonly used in breast cancer which is able to cross the blood-brain barrier. In this article, we review the basic pharmacology of tamoxifenas well as its effects on cognition and mood. The literature reveals an overall impairing effect of tamoxifen on cognition in breast cancer patients, hinting at central antiestrogen activity. On the other hand, tamoxifen demonstrates promising effects in psychiatric disorders, like bipolar disorder, where its therapeutic action may be independent of interaction with estrogen receptors. Understanding the neuropsychiatric properties of SERMs like tamoxifen can guide future research to ameliorate unwanted side-effects and provide novel options for difficult to treat disorders.

Tamoxifen-induced acute mania: A case report

Introduction

Tamoxifen is widely used for the treatment of hormone-responsive breast cancer, osteoporosis, and post-menopausal symptoms. Also, tamoxifen is currently under investigation for its anti-manic properties. In this article, we report a case who developed manic episode following the initiation of tamoxifen and remitted with discontinuation of the medication.

Case Report

A 58-year-old woman was diagnosed with breast cancer. Pathologic diagnosis was invasive ductal carcinoma. Following bilateral total mastectomy operation, trastuzumab was initiated with intervals of 21 days. Five days before the fourth application of trastuzumab, tamoxifen was added. On the sixth day following the initiation of tamoxifen, manic symptoms were developed and she was diagnosed as acute mania.

Management and Outcome

The oncology department suggested withdrawing tamoxifen due to a possible association between tamoxifen initiation and behavioral symptoms. Manic symptoms were rapidly (approximately 24 h) improved following cessation of tamoxifen. Psychiatric evaluation on the fifth day following cessation of tamoxifen revealed no manic symptoms. An aromatase inhibitor-exemestane was initiated and she showed no side effects with this medication since then.

Discussion

To our knowledge, this is the first case report of probable tamoxifen-induced mania. Our case report at least indicates that there were possibly some patients who were sensitive to the tamoxifen’s nervous system effects, mainly to manic effects. In conclusion, clinicians should be aware of these rare behavioral adverse effects of tamoxifen.

Development of a Semimechanistic Pharmacokinetic-Pharmacodynamic Model Describing Dextroamphetamine Exposure and Striatal Dopamine Response in Rats and Nonhuman Primates following a Single Dose of Dextroamphetamine

Acute central nervous system exposure to dextroamphetamine (d-amphetamine) elicits a multitude of effects, including dual action on the dopamine transporter (DAT) to increase extracellular dopamine, and induction of a negative feedback response to limit the dopamine increase. A semimechanistic pharmacokinetic and pharmacodynamic (PK/PD) model with consideration of these multiple effects as a basis was developed. Integrated pharmacokinetics of d-amphetamine in plasma, brain extracellular fluid (ECF) via microdialysis, and cerebrospinal fluid were characterized using a population approach. This PK model was then linked to an indirect-response pharmacodynamic model using as a basis the measurement of extracellular striatal dopamine, also via microdialysis. In both rats and nonhuman primates (NHPs), d-amphetamine stimulation of dopamine outflow (reverse transport) through DAT was primarily responsible for the dose-linear increase in dopamine. As well, in both species a moderator function was needed to account for loss of the dopamine response in the presence of a relatively sustained d-amphetamine ECF exposure, presumptive of an acute tolerance response. PK/PD model structure was consistent between species; however, there was a 10-fold faster return to baseline dopamine in NHPs in response to an acute d-amphetamine challenge. These results suggest preservation from rodents to NHPs regarding the mechanism by which amphetamine increases extracellular dopamine, but a faster system response in NHPs to tolerate this increase. This microdialysis-based PK/PD model suggests greater value in directing preclinical discovery of novel approaches that modify reverse transport stimulation to treat amphetamine abuse. General value regarding insertion of an NHP model in paradigm rodent-to-human translational research is also suggested.

Molecular Mechanisms of Amphetamines

There is a plethora of amphetamine derivatives exerting stimulant, euphoric, anti-fatigue, and hallucinogenic effects; all structural properties allowing these effects are contained within the amphetamine structure. In the first part of this review, the interaction of amphetamine with the dopamine transporter (DAT), crucially involved in its behavioral effects, is covered, as well as the role of dopamine synthesis, the vesicular monoamine transporter VMAT2, and organic cation 3 transporter (OCT3). The second part deals with requirements in amphetamine's effect on the kinases PKC, CaMKII, and ERK, whereas the third part focuses on where we are in developing anti-amphetamine therapeutics. Thus, treatments are discussed that target DAT, VMAT2, PKC, CaMKII, and OCT3. As is generally true for the development of therapeutics for substance use disorder, there are multiple preclinically promising specific compounds against (meth)amphetamine, for which further development and clinical trials are badly needed.

Role of Protein Kinase C in Bipolar Disorder: A Review of the Current Literature

Bipolar disorder (BD) is a major health problem. It causes significant morbidity and imposes a burden on the society. Available treatments help a substantial proportion of patients but are not beneficial for an estimated 40-50%. Thus, there is a great need to further our understanding the pathophysiology of BD to identify new therapeutic avenues. The preponderance of evidence pointed towards a role of protein kinase C (PKC) in BD. We reviewed the literature pertinent to the role of PKC in BD. We present recent advances from preclinical and clinical studies that further support the role of PKC. Moreover, we discuss the role of PKC on synaptogenesis and neuroplasticity in the context of BD. The recent development of animal models of BD, such as stimulant-treated and paradoxical sleep deprivation, and the ability to intervene pharmacologically provide further insights into the involvement of PKC in BD. In addition, the effect of PKC inhibitors, such as tamoxifen, in the resolution of manic symptoms in patients with BD further points in that direction. Furthermore, a wide variety of growth factors influence neurotransmission through several molecular pathways that involve downstream effects of PKC. Our current understanding identifies the PKC pathway as a potential therapeutic avenue for BD.

Direct and Systemic Administration of a CNS-Permeant Tamoxifen Analog Reduces Amphetamine-Induced Dopamine Release and Reinforcing Effects

Amphetamines (AMPHs) are globally abused. With no effective treatment for AMPH addiction to date, there is urgent need for the identification of druggable targets that mediate the reinforcing action of this stimulant class. AMPH-stimulated dopamine efflux is modulated by protein kinase C (PKC) activation. Inhibition of PKC reduces AMPH-stimulated dopamine efflux and locomotor activity. The only known CNS-permeant PKC inhibitor is the selective estrogen receptor modulator tamoxifen. In this study, we demonstrate that a tamoxifen analog, 6c, which more potently inhibits PKC than tamoxifen but lacks affinity for the estrogen receptor, reduces AMPH-stimulated increases in extracellular dopamine and reinforcement-related behavior. In rat striatal synaptosomes, 6c was almost fivefold more potent at inhibiting AMPH-stimulated dopamine efflux than [3H]dopamine uptake through the dopamine transporter (DAT). The compound did not compete with [3H]WIN 35,428 binding or affect surface DAT levels. Using microdialysis, direct accumbal administration of 1 μM 6c reduced dopamine overflow in freely moving rats. Using LC-MS, we demonstrate that 6c is CNS-permeant. Systemic treatment of rats with 6 mg/kg 6c either simultaneously or 18 h prior to systemic AMPH administration reduced both AMPH-stimulated dopamine overflow and AMPH-induced locomotor effects. Finally, 18 h pretreatment of rats with 6 mg/kg 6c s.c. reduces AMPH-self administration but not food self-administration. These results demonstrate the utility of tamoxifen analogs in reducing AMPH effects on dopamine and reinforcement-related behaviors and suggest a new avenue of development for therapeutics to reduce AMPH abuse.

Microdialysis Coupled with LC-MS/MS for In Vivo Neurochemical Monitoring

Microdialysis is a powerful sampling technique used to monitor small molecules in vivo. Despite the many applications of microdialysis sampling, it is limited by the method of analyzing the resulting samples. An emerging technique for analysis of microdialysis samples is liquid chromatography-tandem mass spectrometry (LC-MS/MS). This technique is highly versatile, allowing multiplexed analysis of neurotransmitters, metabolites, and neuropeptides. Using LC-MS/MS for polar neurotransmitters is hampered by weak retention reverse phase LC columns. Several derivatization reagents have been utilized to enhance separation and resolution of neurochemicals in dialysate samples including benzoyl chloride (BzCl), dansyl chloride, formaldehyde, ethylchloroformate, and propionic anhydride. BzCl reacts with amine and phenol groups so that many neurotransmitters can be labeled. Besides improving separation on reverse phase columns, this reagent also increases sensitivity. It is available in a heavy form so that it can be used to make stable-isotope labeled internal standard for improved quantification. Using BzCl with LC-MS/MS has allowed for measuring as many as 70 neurochemicals in a single assay. With slightly different conditions, LC-MS/MS has also been used for monitoring endocannabinoids. LC-MS/MS is also useful for neuropeptide assay because it allows for highly sensitive, sequence specific measurement of most peptides. These advances have allowed for multiplexed neurotransmitter measurements in behavioral, circuit analysis, and drug effect studies.