Central Nervous System Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Central Nervous System Agents) - Volume 12, Issue 4, 2012

The effective anti-migraine drugs triptans, all bind with high affinity to three serotonin (5-HT) subtypes, the 5-HT1B, 5-HT1D and 5-HT1F. 5-HT1B mRNA is densely localized within smooth muscle, and less in the endothelium of cerebral blood vessels. This vascular distribution of 5-HT1B receptor has been shown to mediate the vasoconstrictive properties of the triptans, responsible for potential cardiac adverse events. Activation of 5-HT1D subtype, although effective in animal models of migraine, was not enough efficient to attenuate migraine attacks in clinical trials. The 5-HT1F receptor is located both in vessels and within the trigeminal ganglion (TG) and the trigeminal nucleus caudalis (Sp5C), but with the difference that the 5-HT1F receptor lack vasoconstrictive properties, making it an attractive target for new anti-migraine drugs. Selective activation of 5-HT1F receptor potently inhibited markers associated with electrical stimulation of the TG. Thus 5-HT1F receptor represents an ideal target for anti-migraine drugs. So far two selective 5-HT1F agonists have been tested in human trials for migraine: LY334370 and lasmiditan. Both molecules were efficient in attenuating migraine attacks with efficacy in the same range as oral sumatriptan 100mg, the gold standard for triptans. The LY334370 project withdrew because of toxicity in animals, while lasmiditan is still testing. In this review we present all the available preclinical and clinical data on the 5-HT1F agonists as a potential new class of anti-migraine drugs lacking vascular activity and we discuss related issues on the vascular and neuronal aspects of migraine pathogenesis.

Adverse side effects or toxicities of a drug were previously regarded as a manifestation of drug's own characterizations, such as the chemical structure and property of a drug. More recently, increasing experimental or clinical data and modern ideas suggest that human's genetic factors also play indispensable roles in resulting neural side effects of a drug, especially in antidepressant-induced suicide and antibiotics-induced hearing loss. However, there are many questions and technological obstacles (including high costs and limited samples) in these kinds of researches and this makes genetic study of drug toxicities in its initial stage. In this review, we in depth address and analysis of this matter from some new perspectives and propose some new initiatives to improve this type of researches in future. It is also highly needed to expedite the translation of these pharmacogenetic concepts from bench to bedside.

The synthesis of three series of novel 4-alkyl-5-(5'-chlorothiophen-2'-yl)-pyrazole-3-carbamoyl analogues of rimonabant with affinity for the CB1 cannabinoid receptor subtype is reported. Amongst the novel derivatives, compounds 21j, 22a, 22c, and 22f showed affinity values expressed as Ki ranging from 5.5 to 9.0 nM. Derivative 23e revealed a good CB1 affinity (Ki = 11.7 nM) and the highest CB1 selectivity of the whole series (KiCB2/KiCB1 = 384.6). These new compounds appeared to be able to pass the blood brain barrier and to counteract the activity of cannabinoid agonist. According to the results of mice vas deferens assays, as in the case of rimonabant, derivatives 21a, 22a, and 22b showed inverse agonist activity. In contrast, as a preliminary result to be confirmed, compound 23a exhibited neutral antagonist profile. According to the data obtained through an acute animal model, selected compounds 21a, 22a, and 23a evidenced the capability to significantly reduce food intake. At specific conditions, the effect of the novel compounds were higher than that induced by rimonabant. Amongst the novel CB1 antagonist compounds, 23a may represent a useful candidate agent for the treatment of obesity and its metabolic complications, with reduced side effects relative to those instead observed with rimonabant.

Several viruses may cause central nervous system infections that lead to a broad range of clinical manifestations. The course of the viral encephalitis can be acute, sub acute, or chronic. Some viruses have the ability to enter into the brain and cause direct injury, while others activate inflammatory cells that attack the central nervous system (CNS) secondarily. Some types of viral encephalitis occur in previously healthy individuals, while others affect immunocompromised patients. The epidemiology of viral encephalitis has undergone changes in recent years. Factors such as evolving lifestyles and ecological changes have had a considerable impact on the epidemiology of some types of viral encephalitis. The result is a change in the etiology spectrum of viral encephalitis, with new types of encephalitis arising or returning from time to time. Many scientific achievements in neuroimaging, molecular diagnosis, antiviral therapy, immunomodulatory treatments, and neurointensive care have allowed more precise and earlier diagnoses and more efficient treatments, resulting in improved outcomes. Despite these advances, there is still considerable morbidity and mortality related to these disorders. This aim of this article is to review the current knowledge of the current drugs used in the management of the most important viral encephalitis, focusing on the mechanisms of action, efficacy, and side effects of the drugs. In addition, future perspectives in this area will be addressed. Despite the technological advances, much effort has yet to be undertaken to reduce the impact of these potentially devastating diseases.

The therapies of mood and anxiety disorders are not solved, because current antidepressants have delayed onset of therapeutic action and a significant number of patients are non-responsive. Research on the field was leaning towards neuropeptides as therapeutic targets. Vasopressin (VP) is a hot candidate, as beyond its peripheral actions VP is implicated in interneuronal communication and modulates the hypothalamo-pituitary-adrenal (HPA), the key stress axis, as well as behavioural functions. Affective disorders are stress related disorders and the most frequently occurring abnormality in depressed subjects is hyperactivity of the HPA. VP with nucleus paraventricularis hypothalami origin is a direct adrenocorticotrophin secretagogue through its V1b receptor. VP seems to have special importance under prolonged stress conditions, which are known to be strong predictive factor of depressive disorder and can induce depressive-like symptoms. Preclinical and clinical data summarized in this review underline the importance of VP in the development of anxiety- and depressive-like symptoms. Orally active nonpeptiderg V1b antagonists were developed and seemed to have effective anxiolytic and antidepressant profile in preclinical studies, which was not fully confirmed by clinical observations. It seems that V1a receptors on special brain areas could have same importance. Taken together current knowledge strongly implies an importance of vasopressinergic regulation in affective disorders and consider VP as endogenous anxiogenic/depressogenic substance. However, wide range of side effects could develop as a result of an intervention on the VP system; therefore there is a need for area-specific targeting of VP receptors (e.g. with modified nanoparticles).

Neuropathic pain, pain arising as a direct consequence of a lesion or disease affecting the somatosensory system, is relatively common, occurring in about 1% of the population. Studies in animal models describe a number of peripheral and central pathophysiological processes after nerve injury that would be the basis of underlying neuropathic pain mechanism. Additionally, neuro-imaging (positron emission tomography and functional magnetic resonance imaging) provides insights in brain mechanisms corresponding with mechanistic processes including allodynia, hyperalgesia, altered sensation, and spontaneous pain. A change in function, chemistry, and structures of neurons (neural plasticity) underlie the production of the altered sensitivity characteristics of neuropathic pain. Peripheral processes in neuropathic pain involve production of mediators (cytokines, protons, nerve growth factor), alterations in calcium channels, sodium channels, hyperpolarisation-activated nucleotide-gated ion channels, and potassium channels, phenotypic switches and sprouting of nerves endings, and involvement of the sympathetic nervous system. Stimulation of the N-Methyl-DAspartate receptor, activation of microglia, oligodendrocytes, and astrocytes, increased production of nerve growth factor and brain-derived neurotrophic factor together with loss of spinal inhibitory control are responsible for central neuron hyperexcitability and maintenance of neuropathic pain. Recent advances, including functional imaging techniques, in identification of peripheral and central sensitization mechanisms related to nervous system injury have increased potential for affecting pain research from both diagnostic as well as therapeutic view. Key brain regions involved in generating pharmacologically induced analgesia may be identified. Despite the progress in pain research, neuropathic pain is challenge to manage. Although numerous treatment options are available for relieving neuropathic pain, there is no consensus on the most appropriate treatment. However, recommendations can be proposed for first-line, second-line, and third-line pharmacological treatments based on the level of evidence for the different treatment strategies. Available therapies shown to be effective in managing neuropathic pain include opioids and tramadol, anticonvulsants, antidepressants, topical treatments (lidocaine patch, capsaicin), and ketamine. Tricyclic antidepressants are often the first drugs selected to alleviate neuropathic pain (first-line pharmacological treatment). Although they are very effective in reducing pain in several neuropathic pain disorders, treatment may be compromised (and outweighed) by their side effects. In patients with a history of cardiovascular disorders, glaucoma, and urine retention, pregabalin and gabapentine are emerging as first-line treatment for neuropathic pain. In addition these anti-epileptic drugs have a favourable safety profile with minimal concerns regarding drug interactions and showing no interference with hepatic enzymes. Alternatively, opioids (oxycodone and methadone) and tramadol may alleviate nociceptive and neuropathic pain. Despite the numerous treatment options available for relieving neuropathic pain, no more than half of patients experience clinically meaningful pain relief, which is almost always partial but not complete relief. In addition, patients frequently experience burdensome adverse effects and as a consequence are often unable to tolerate the treatment. In the remaining patients, combination therapies using two or more analgesics with different mechanisms of action may also offer adequate pain relief. Although combination treatment is clinical practice and may result in greater pain relief, trials regarding different combinations of analgesics (which combination to use, occurrence of additive or supra-additive effects, sequential or concurrent treatment, adverse-event profiles of these analgesics, alone and in combination) are scarce. If medical treatments have failed, invasive therapies such as intrathecal drug administration and neurosurgical stimulation techniques (spinal cord stimulation, deep brain stimulation, and motor cortex stimulation) may be considered.

The nervous system is a primary target for animal venoms as the impairment of its function results in the fast and efficient immobilization or death of a prey. There are numerous evidences about effects of crude snake venoms or isolated toxins on peripheral nervous system. However, the data on their interactions with the central nervous system (CNS) are not abundant, as the blood-brain barrier (BBB) impedes penetration of these compounds into brain. This updated review presents the data about interaction of snake venom polypeptides with CNS. Such data will be described according to three main modes of interactions: - Direct in vivo interaction of CNS with venom polypeptides either capable to penetrate BBB or injected into the brain. - In vitro interactions of cell or sub-cellular fractions of CNS with crude venoms or purified toxins. - Indirect effects of snake venoms or their components on functioning of CNS under different conditions. Although the venom components penetrating BBB are not numerous, they seem to be the most suitable candidates for the leads in drug design. The compounds with other modes of action are more abundant and better studied, but the lack of the data about their ability to penetrate BBB may substantially aggravate the potentials for their medical perspectives. Nevertheless, many such compounds are used for research of CNS in vitro. These investigations may give invaluable information for understanding the molecular basis of CNS diseases and thus lay the basis for targeted drug design. This aspect also will be outlined in the review.