Antinociceptive efficacy of lacosamide in rat models for tumor- and chemotherapy-induced cancer pain

The elusive Nav1.7: From pain to cancer

Voltage-gated sodium channels (Nav) are protein complexes that play fundamental roles in the transmission of signals in the nervous system, at the neuromuscular junction and in the heart. They are mainly present in excitable cells where they are responsible for triggering action potentials. Dysfunctions in Nav ion conduction give rise to a wide range of conditions, including neurological disorders, hypertension, arrhythmia, pain and cancer. Nav family 1 is composed of nine members, named numerically from 1 to 9. A Nax family also exists and is involved in body-fluid homeostasis. Of particular interest is Nav1.7 which is highly expressed in the sensory neurons of the dorsal root ganglions, where it is involved in the propagation of pain sensation. Gain-of-function mutations in Nav1.7 cause pathologies associated with increased pain sensitivity, while loss-of-function mutations cause reduced sensitivity to pain. The last decade has seen considerable effort in developing highly specific Nav1.7 blockers as pain medications, nonetheless, sufficient efficacy has yet to be achieved. Evidence is now conclusively showing that Navs are also present in many types of cancer cells, where they are involved in cell migration and invasiveness. Nav1.7 is anomalously expressed in endometrial, ovarian and lung cancers. Nav1.7 is also involved in Chemotherapy Induced Peripheral Neuropathy (CIPN). We propose that the knowledge and tools developed to study the role of Nav1.7 in pain can be exploited to develop novel cancer therapies. In this chapter, we illustrate the various aspects of Nav1.7 function in pain, cancer and CIPN, and outline therapeutic approaches.

Mechanisms of cancer pain

Personalised and targeted interventions have revolutionised cancer treatment and dramatically improved survival rates in recent decades. Nonetheless, effective pain management remains a problem for patients diagnosed with cancer, who continue to suffer from the painful side effects of cancer itself, as well as treatments for the disease. This problem of cancer pain will continue to grow with an ageing population and the rapid advent of more effective therapeutics to treat the disease. Current pain management guidelines from the World Health Organisation are generalised for different pain severities, but fail to address the heterogeneity of mechanisms in patients with varying cancer types, stages of disease and treatment plans. Pain is the most common complaint leading to emergency unit visits by patients with cancer and over one-third of patients that have been diagnosed with cancer will experience under-treated pain. This review summarises preclinical models of cancer pain states, with a particular focus on cancer-induced bone pain and chemotherapy-associated pain. We provide an overview of how preclinical models can recapitulate aspects of pain and sensory dysfunction that is observed in patients with persistent cancer-induced bone pain or neuropathic pain following chemotherapy. Peripheral and central nervous system mechanisms of cancer pain are discussed, along with key cellular and molecular mediators that have been highlighted in animal models of cancer pain. These include interactions between neuronal cells, cancer cells and non-neuronal cells in the tumour microenvironment. Therapeutic targets beyond opioid-based management are reviewed for the treatment of cancer pain.

The protective effect of chemical and natural compounds against vincristine-induced peripheral neuropathy (VIPN)

Vincristine, an alkaloid extracted from Catharanthus rosea, is a class of chemotherapy drugs that act by altering the function of the microtubules and by inhibiting mitosis. Despite its widespread application, a major adverse effect of vincristine that limits treatment duration is the occurrence of peripheral neuropathy (PN). PN presents with several symptoms including numbness, painful sensation, tingling, and muscle weakness. Vincristine-induced PN involves impaired calcium homeostasis, an increase of reactive oxygen species (ROS), and the upregulation of tumor necrosis factor-alpha (TNF-α), and interleukin 1 beta (IL-1β) expression. Several potential approaches to attenuate the vincristine-induced PN including the concomitant administration of chemicals with vincristine have been reported. These chemicals have a variety of pharmaceutical properties including anti-inflammation, antioxidant, and inhibition of calcium channels and calcineurin signaling pathways and increased expression of nerve growth factor (NGF). This review summarized several of these compounds and the mechanisms of action that could lead to effective options in improving vincristine-induced peripheral neuropathy (VIPN).

Chemical profiling of Justicia vahlii Roth. (Acanthaceae) using UPLC-QTOF-MS and GC-MS analysis and evaluation of acute oral toxicity, antineuropathic and antioxidant activities

ETHNOPHARMACOLOGICAL RELEVANCE

Justicia vahlii Roth. (Acanthaceae), also called as kodasoori and bhekkar is an annual therophyte erect or decumbent herb used traditionally in toothache, skin diseases (itching, topical inflammation) and for the treatment of various respiratory disorders.

AIM OF THE STUDY

The current study aimed at exploring pain cessation potential of J. vahlii Roth. via murine model of neuropathic pain and its phytochemical, toxicological and antioxidant profiles.

MATERIALS AND METHODS

The hydro-alcoholic extract of J. vahlii (HAEJv) prepared by maceration technique was subjected to preliminary phytochemical screening, total bioactive content determination, UPLC-QTOF-MS and GC-MS analysis. Toxicity assessment was carried out by using brine shrimp lethality assay and acute oral toxicity test. Murine model of neuropathic pain was applied to assess the antineuropathic potential of the species. Furthermore effect of the extract on catalase, superoxide oxide dismutase (SOD), Glutathione (GSH), interleukin-1beta (IL-1β) and total necrosis factor-alpha (TNF-α) was also studied. In vitro antioxidant profile was explored by using four methods; 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azinobis(3-ethylbenothiazoline)-6-sulfonic acid (ABTS), CUPric reducing antioxidant capacity (CUPRAC) and Ferric reducing antioxidant power (FRAP) assay.

RESULTS

The phytochemical screening revealed the presence of phenols, flavonoids, coumarins, alkaloids and lignans as the major classes of secondary metabolites. The extract was found rich in total phenolics content (TPC) and total flavonoids content (TFC) with identification of total 59 bioactives in UPLC-QTOF-MS and 40 compounds in GC-MS analysis. The extract was found nontoxic up to 4000 mg/kg (p.o.) in mice and no mortality observed in brine shrimp lethality assay. The HAEJv significantly reduced number of acetic acid induced abdominal constrictions at 100 mg/kg (p < 0.01) and 200 mg/kg (p < 0.001) and increased paw withdrawal threshold p < 0.05 at 100 mg/kg and p < 0.001 at 200 mg/kg, and an increase in tail withdrawal latency time p < 0.001 at 200 mg/kg was observed. The extract significantly increased levels of catalase, SOD and GSH while decreased IL-1β and TNF-α levels in sciatic nerve tissue of mice. HAEJv showed highest antioxidant activity through CUPRAC method 121.32 ± 1.22 mg trolox equivalent per gram of dry extract (mg TE/g DE) followed by DPPH 81.334 ± 4.35 mg TE/g DE, FRAP 69.89 ± 3.05 mg TE/g DE and ABTS 38.17 ± 2.12 mg TE/g DE.

CONCLUSION

The current study back the traditional use of J. vahlii in pain cessation through antioxidant based antineuropathic pain activity and revealed the extract non-toxic with number of functional phytoconstituents and warrants further research on isolation of the compounds and sub-acute toxicity studies.

Druggability of CRMP2 for Neurodegenerative Diseases

Collapsin response mediator proteins (CRMPs) are ubiquitously expressed phosphoproteins that coordinate cytoskeletal formation and regulate cellular division, migration, polarity, and synaptic connection. CRMP2, the most studied of the five family members, is best known for its affinity for tubulin heterodimers and function in regulating the microtubule network. Accumulating evidence has also demonstrated a key role for CRMP2 in trafficking of voltage- and ligand-gated ion channels. These functions are tightly regulated by post-translational modifications including phosphorylation and SUMOylation (addition of a small ubiquitin like modifier). Over the past decade, it has become increasingly clear that dysregulated post-translational modifications of CRMP2 contribute to the pathomechanisms of diverse diseases, including cancer, neurodegenerative diseases, chronic pain, and bipolar disorder. Here, we review the discovery, functions, and current putative preclinical and clinical therapeutics targeting CRMP2. These potential therapeutics include CRMP2-based peptides that inhibit protein-protein interactions and small-molecule compounds. Capitalizing on the availability of structural information, we identify druggable pockets on CRMP2 and predict binding modes for five known CRMP2-targeting compounds, setting the stage for optimization and de novo drug discovery targeting this multifunctional protein.

Antinociceptive effectiveness of Tithonia tubaeformis in a vincristine model of chemotherapy-induced painful neuropathy in mice

BACKGROUND

Chemotherapy induced peripheral neuropathy (CIPN) is a painful side-effect of commonly used chemotherapeutic agents that profoundly impair the quality of life of patients as the current pharmacotherapeutic strategies are inefficient in providing adequate pain relief. Complementary and alternative medicine (CAM) therapies are preferred by patients with neuropathic pain as they experience insufficient control of pain with conventional medications. This study describes the antinociceptive effect of Tithonia tubaeformis (Jacq.) Cass. in a vincristine mouse model of established CIPN.

METHODS

Tithonia tubaeformis hydromethanolic extract was tested for preliminary qualitative phytochemical analysis and acute oral toxicity test in mice. The antinociceptive effect was investigated using the abdominal constriction (writhing) and tail immersion tests (25-200 mg/kg). The anti-neuropathic effect was determined in the vincristine mouse model, established by daily administration of vincristine (0.1 mg/kg/day, i.p) for consecutive 14 days. Acute treatment with Tithonia tubaeformis (100 and 200 mg/kg) and the positive control, gabapentin (75 mg/kg) was carried out on the 15th day of the last vincrsitine dose and the animals were tested for allodynia and thermal hyperalgesia at 30-120 min post extract/drug administration.

RESULTS

Vincristine produced significant temporal tactile allodynia and thermal hyperalgesia (P < 0.01 and P < 0.001 on day 7 and 14) and was maintained for the subsequent day (P < 0.001 during 30-120 min). Tithonia tubaeformis was effective in attenuating the vincristine-induced allodynia and thermal hyperalgesia at 100 mg/kg (P < 0.05, P < 0.01) and 200 mg/kg (P < 0.01, P < 0.001). Similarly, gabapentin also showed a robust antinociceptive effect in counteracting the vincristine associated behavioral alterations.

CONCLUSIONS

Tithonia tubaeformis can be an effective CAM therapeutic remedy for established CIPN due to its potential antinociceptive effect in attenuating vincristine-induced neuropathy.

Lacosamide diminishes dryness-induced hyperexcitability of corneal cold sensitive nerve terminals

Lacosamide is an anti-epileptic drug that is also used for the treatment of painful diabetic neuropathy acting through voltage-gated sodium channels. The aim of this work was to evaluate the effects of acute application of lacosamide on the electrical activity of corneal cold nerve terminals in lacrimo-deficient guinea pigs. Four weeks after unilateral surgical removal of the main lachrimal gland in guinea pigs, corneas were excised and superfused in vitro at 34°C for extracellular electrophysiological recording of nerve terminal impulse activity of cold thermosensitive nerve terminals. The characteristics of the spontaneous and the stimulus-evoked (cooling ramps from 34°C to 15°C) activity before and in presence of lacosamide 100µM and lidocaine 100µM were compared. Cold nerve terminals (n=34) recorded from dry eye corneas showed significantly enhanced spontaneous activity (8.0±1.1 vs. 5.2±0.7imp/s; P<0.05) and cold response (21.2±1.7 vs. 16.8±1.3imp/s; P<0.05) as well as reduced cold threshold (1.5±0.1 vs. 2.8±0.2 Δ°C; P<0.05) to cooling ramps compared to terminals (n=58) from control animals. Both lacosamide and lidocaine decreased spontaneous activity and peak response to cooling ramps significantly (P<0.05). Temperature threshold was increased by the addition of lidocaine (P<0.05) but not lacosamide (P>0.05) to the irrigation fluid. In summary, the application of lacosamide results in a significant decrease of the augmented spontaneous activity and responsiveness to cold of corneal sensory nerves from tear-deficient animals. Based on these promising results we speculate that lacosamide might be used to reduce the hyperexcitability of corneal cold receptors caused by prolonged ocular surface dryness due to hyposecretory or evaporative dry eye disease.

Randall Selitto pressure algometry for assessment of bone-related pain in rats

BACKGROUND

Deep pain is neglected compared with cutaneous sources. Pressure algometry has been validated in the clinic for assessment of bone-related pain in humans. In animal models of bone-related pain, we have validated the Randall Selitto behavioural test for assessment of acute and pathological bone pain and compared the outcome with more traditional pain-related behaviour measures.

METHODS

Randall Selitto pressure algometry was performed over the anteromedial part of the tibia in naïve rats, sham-operated rats, and rats inoculated with MRMT-1 carcinoma cells in the left tibia, and the effect of morphine was investigated. Randall Selitto measures of cancer-induced bone pain were supplemented by von Frey testing, weight-bearing and limb use test. Contribution of cutaneous nociception to Randall Selitto measures were examined by local anaesthesia.

RESULTS

Randall Selitto pressure algometry over the tibia resulted in reproducible withdrawal thresholds, which were dose-dependently increased by morphine. Cutaneous nociception did not contribute to Randall Selitto measures. In cancer-bearing animals, compared with sham, significant differences in pain-related behaviours were demonstrated by the Randall Selitto test on day 17 and 21 post-surgery. A difference was also demonstrated by von Frey testing, weight-bearing and limb use tests.

CONCLUSION

Our results indicate that pressure applied by the Randall Selitto algometer on a region, where the bone is close to the skin, may offer a way to measure bone-related pain in animal models and could provide a supplement to the traditional behavioural tests and a means to study deep pain.

Polytherapy with a combination of three repurposed drugs (PXT3003) down-regulates Pmp22 over-expression and improves myelination, axonal and functional parameters in models of CMT1A neuropathy

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited sensory and motor peripheral neuropathy. It is caused by PMP22 overexpression which leads to defects of peripheral myelination, loss of long axons, and progressive impairment then disability. There is no treatment available despite observations that monotherapeutic interventions slow progression in rodent models. We thus hypothesized that a polytherapeutic approach using several drugs, previously approved for other diseases, could be beneficial by simultaneously targeting PMP22 and pathways important for myelination and axonal integrity. A combination of drugs for CMT1A polytherapy was chosen from a group of authorised drugs for unrelated diseases using a systems biology approach, followed by pharmacological safety considerations. Testing and proof of synergism of these drugs were performed in a co-culture model of DRG neurons and Schwann cells derived from a Pmp22 transgenic rat model of CMT1A. Their ability to lower Pmp22 mRNA in Schwann cells relative to house-keeping genes or to a second myelin transcript (Mpz) was assessed in a clonal cell line expressing these genes. Finally in vivo efficacy of the combination was tested in two models: CMT1A transgenic rats, and mice that recover from a nerve crush injury, a model to assess neuroprotection and regeneration. Combination of (RS)-baclofen, naltrexone hydrochloride and D-sorbitol, termed PXT3003, improved myelination in the Pmp22 transgenic co-culture cellular model, and moderately down-regulated Pmp22 mRNA expression in Schwannoma cells. In both in vitro systems, the combination of drugs was revealed to possess synergistic effects, which provided the rationale for in vivo clinical testing of rodent models. In Pmp22 transgenic CMT1A rats, PXT3003 down-regulated the Pmp22 to Mpz mRNA ratio, improved myelination of small fibres, increased nerve conduction and ameliorated the clinical phenotype. PXT3003 also improved axonal regeneration and remyelination in the murine nerve crush model. Based on these observations in preclinical models, a clinical trial of PTX3003 in CMT1A, a neglected orphan disease, is warranted. If the efficacy of PTX3003 is confirmed, rational polytherapy based on novel combinations of existing non-toxic drugs with pleiotropic effects may represent a promising approach for rapid drug development.

Inhibition of breast cancer-cell glutamate release with sulfasalazine limits cancer-induced bone pain

Cancer in bone is frequently a result of metastases from distant sites, particularly from the breast, lung, and prostate. Pain is a common and often severe pathological feature of cancers in bone, and is a significant impediment to the maintenance of quality of life of patients living with bone metastases. Cancer cell lines have been demonstrated to release significant amounts of the neurotransmitter and cell-signalling molecule l-glutamate via the system xC(-) cystine/glutamate antiporter. We have developed a novel mouse model of breast cancer bone metastases to investigate the impact of inhibiting cancer cell glutamate transporters on nociceptive behaviour. Immunodeficient mice were inoculated intrafemorally with the human breast adenocarcinoma cell line MDA-MB-231, then treated 14days later via mini-osmotic pumps inserted intraperitoneally with sulfasalazine, (S)-4-carboxyphenylglycine, or vehicle. Both sulfasalazine and (S)-4-carboxyphenylglycine attenuated in vitro cancer cell glutamate release in a dose-dependent manner via the system xC(-) transporter. Animals treated with sulfasalazine displayed reduced nociceptive behaviours and an extended time until the onset of behavioural evidence of pain. Animals treated with a lower dose of (S)-4-carboxyphenylglycine did not display this reduction in nociceptive behaviour. These results suggest that a reduction in glutamate secretion from cancers in bone with the system xC(-) inhibitor sulfasalazine may provide some benefit for treating the often severe and intractable pain associated with bone metastases.

The application of support vector regression for prediction of the antiallodynic effect of drug combinations in the mouse model of streptozocin-induced diabetic neuropathy

Drug interactions are an important issue of efficacious and safe pharmacotherapy. Although the use of drug combinations carries the potential risk of enhanced toxicity, when carefully introduced it enables to optimize the therapy and achieve pharmacological effects at doses lower than those of single agents. In view of the development of novel analgesic compounds for the neuropathic pain treatment little is known about their influence on the efficacy of currently used analgesic drugs. Below we describe the preliminary evaluation of support vector machine in the regression mode (SVR) application for the prediction of maximal antiallodynic effect of a new derivative of dihydrofuran-2-one (LPP1) used in combination with pregabalin (PGB) in the streptozocin-induced neuropathic pain model in mice. Based on SVR the most effective doses of co-administered LPP1 (4mg/kg) and PGB (1mg/kg) were predicted to cause the paw withdrawal threshold at 6.7g in the von Frey test. In vivo for the same combination of doses the paw withdrawal was observed at 6.5g, which confirms good predictive properties of SVR.

New frontiers in assessing pain and analgesia in laboratory animals

BACKGROUND

Translating promising analgesic compounds into reliable pain therapeutics in humans is made particularly challenging by the difficulty in measuring the pain quantitatively. This problem is manifest not only in clinical settings in which patient pain assessments involve mostly subjective measures but also in preclinical settings wherein laboratory animals, most commonly rodents, are typically evaluated in stimulus-evoked response tests.

OBJECTIVE

Given the limitations of traditional pain tests, we sought out new approaches to measure pain, and analgesia, in laboratory animals.

METHODS

We reviewed the peer reviewed literature to identify pain tests that could be utilized in preclinical settings to understand the effects of new and established analgesics.

RESULTS/CONCLUSIONS

The tests identified include weight bearing differential, suppression of feeding, reduction in locomotor activity, gait analysis, conditioning models and functional MRI. Although the pharmacology of known and new analgesics has not been broadly established in these models, they hold the promise of better predictive utility for the discovery of pain relievers.

Myoelectrical activity and muscle morphology in a rat model of myofascial trigger points induced by blunt trauma to the vastus medialis

OBJECTIVES

To explore myoelectrical activity and muscle morphology of myofascial trigger points (MTrPs) in an injury model of rats.

METHODS

A total of 24 male SD rats were randomly divided into a control group (group A) and model group (group B). A blunt striking injury and eccentric exercise were applied to the vastus medialis (VM) of rats in group B for 8 weeks. Later, the palpable taut band (TB), local twitch response, myoelectrical activities and morphology in the two groups were examined.

RESULTS

An average of 2.5 (30/12) palpable TBs were detected in the VM in group B compared with none in group A. The MTrPs had two types of abnormal potential. Their amplitudes were significantly higher than those in the control group (p<0.01) but their durations showed no significant differences. A series of reflex contractions appeared in groups A and B in response to external stimulation to the ear. Their amplitude and duration in group B were significantly lower than those in group A. A series of lower fibrillation potentials repeatedly occurred in model MTrPs in group B. The morphology of MTrPs showed abnormal muscle fibres with large round or ellipse shapes in cross-section and enlarged tapering shapes in longitudinal section.

CONCLUSIONS

Active MTrPs can be provoked by repeated blunt injury. Active MTrPs are a group of muscle fibres with abnormal shapes and abnormal myoelectrical potentials. External stimulation provokes low-voltage responses in MTrPs, which is different from the response of normal muscle fibres.

MRMT-1 rat breast carcinoma cells and models of bone metastases: improvement of an in vitro system to mimic the in vivo condition

Breast cancer frequently metastasizes to the skeleton thus interrupting the normal bone remodeling process and causing bone degradation. Having suitable in vitro and in vivo models is important for understanding the pathogenesis and developing treatment strategies for bone metastasis in humans. In order to improve and characterize an in vitro model of bone metastasis from breast cancer an MRMT-1 rat breast carcinoma cell line or their conditioned medium were directly co-cultured with rat monocytes. To confirm the in vitro results, an in vivo model, in which MRMT-1 cells were inoculated into the proximal surface of the tibia, was also adopted. Osteoclast viability, activity and differentiation showed a significant increase (p<0.05, p<0.0005, p<0.0005, respectively) between co-culture with MRMT-1 cells and the other culture conditions. Moreover, scanning electron microscopy analysis, phalloidin staining and 4'-6-diamidino-2-phenylindole (DAPI) nuclear acid staining confirmed that co-culture with MRMT-1 cells also induced a greater differentiation in osteoclast structure and morphology. Finally, the in vivo outcome at 3 weeks showed the presence of a severe osteolytic lesion, thus confirming the effectiveness of the present in vitro results. These results demonstrated an improvement of an in vitro model of bone metastases from breast cancer in which co-culture with MRMT-1 cells was shown to be a dynamic system that closely mimics the in vivo situation. The present study may help improve our understanding of the complex "vicious cycle" between osteoblasts, osteoclasts and tumor cells.

Neurological perspectives on voltage-gated sodium channels

The activity of voltage-gated sodium channels has long been linked to disorders of neuronal excitability such as epilepsy and chronic pain. Recent genetic studies have now expanded the role of sodium channels in health and disease, to include autism, migraine, multiple sclerosis, cancer as well as muscle and immune system disorders. Transgenic mouse models have proved useful in understanding the physiological role of individual sodium channels, and there has been significant progress in the development of subtype selective inhibitors of sodium channels. This review will outline the functions and roles of specific sodium channels in electrical signalling and disease, focusing on neurological aspects. We also discuss recent advances in the development of selective sodium channel inhibitors.

Characterization of bilateral trigeminal constriction injury using an operant facial pain assay

In order to better understand and treat neuropathic pain, scientific study must use methods that can assess pain processing at the cortical level where pain is truly perceived. Operant behavior paradigms can accomplish this. We used an operant task to evaluate changes following chronic constriction injury to the trigeminal nerves. We also relate these behavioral changes to immunohistochemistry of transient receptor potential channels vanilloid 1 and melastatin 8 (TRPV1 and TRPM8) in the trigeminal ganglia. Following nerve injury, successful performance of the operant task was reduced and aversive behaviors were observed with 10 and 37 °C stimulation, indicating cold allodynia and mechanical allodynia respectively. In contrast, while aversive behaviors were observed with 48 °C stimulation, successful performance of the operant task was not substantially hindered following injury. These behavioral changes were accompanied by an increase in TRPV1 positive cells and an increased intensity of TRPM8 staining at 2 weeks post-injury, when cold allodynia is maximal. These findings suggest that the incorporation of operant behavioral assessment in the study of pain may provide insight into the relationship among peripheral changes, motivational drive, and pain. Understanding this relationship will allow us to better treat and prevent chronic neuropathic pain.

The intrathecally administered kappa-2 opioid agonist GR89696 and interleukin-10 attenuate bone cancer-induced pain through synergistic interaction

BACKGROUND

Although bone cancer-related pain is one of the most disruptive symptoms in patients with advanced cancer, patients are often refractory to pharmacological treatments; thus, more effective treatments for bone cancer pain are needed. We evaluated the analgesic efficacy of and interaction between intrathecal GR89696, a κ(2)-opioid receptor agonist, and interleukin (IL)-10 in a rat model of bone cancer pain.

METHODS

The rat model of bone cancer pain was produced by right tibia intramedullary injection of rat breast cancer cells, and an intrathecal catheterization was performed. Ten days later, a paw-withdrawal threshold to mechanical stimulus by von Frey hairs was measured using the up-down method, after intrathecal administration of GR89696 and IL-10. The interaction between the 2 drugs was also evaluated using an isobolographic analysis.

RESULTS

Intrathecal GR89696 and IL-10 significantly increased the paw withdrawal threshold of the cancer cell-implanted rat, in a dose-dependent manner, with 50% effective dose values (95% confidence interval) of 50.78 μg (31.80-80.07μg) and 0.83 μg (0.59-1.15 μg), respectively. Isobolographic analysis revealed a synergistic interaction between intrathecal GR89696 and IL-10.

CONCLUSIONS

Intrathecally administered GR89696 and IL-10 attenuated bone cancer-induced pain, and the 2 drugs interacted synergistically in the spinal cord. These results raise the intriguing possibility of κ(2)-opioid receptor agonists and IL-10 as a new therapeutic approach for the management of bone cancer-associated pain.

VOLTAGE-GATED CALCIUM CHANNELS ARE NOT AFFECTED BY THE NOVEL ANTI-EPILEPTIC DRUG LACOSAMIDE

The novel anti-epileptic drug lacosamide targets two proteins - voltage-gated sodium channels and collapsin response mediator protein 2 (CRMP-2) - suggesting dual modes of action for lacosamide. We recently identified the neurite outgrowth and axonal guidance protein CRMP-2 as a novel partner and regulator of the presynaptic N-type voltage-gated Ca(2+) channel (CaV2.2) [Brittain et al., J. Biol. Chem. 284: 31375-31390 (2009)]. Here we examined the effects of lacosamide on voltage-gated Ba(2+) channels. Lacosamide did not affect Ba(2+) currents via N- and P/Q- channels in rat hippocampal neurons or L-type Ca(2+) channels in a mouse CNS neuronal cell line, respectively. N-type Ba(2+) currents, augmented by CRMP-2 expression, were also unaffected by acute or chronic lacosamide exposure. These results establish that the anti-epileptic mode of action of lacosamide does not involve these voltage-gated Ca(2+) channels.

Lacosamide for pain

IMPORTANCE OF THE FIELD

Neuropathic pain remains a condition that is difficult to treat and with which therapeutic failure is not uncommon. The need for new and effective drugs to treat neuropathic pain remains strong.

AREAS COVERED IN THIS REVIEW

The available preclinical and clinical data for the pain relieving effect of lacosamide have been examined using the papers published and referenced on Medline between 1990 and present.

WHAT THE READER WILL GAIN

It is hoped that readers will gain an insight into the use of this novel analgesic agent in human clinical pain.

TAKE HOME MESSAGE

The data relating to the pain relieving effect of lacosamide are sparse. The majority of the published human data relate to the use of lacosamide for the treatment of painful diabetic neuropathy where the extent of pain relief produced has not been deemed sufficient to warrant an application for a product license for this indication. That said, it is suggested that there remains merit in further investigation of this drug for other neuropathic pain conditions.

Antinociceptive effect of intrathecal cannabinoid receptor agonist WIN 55,212-2 in a rat bone tumor pain model

Bone tumor pain is a poorly controlled pain comprising background and severe pain on moving or weight-bearing postures that decreases the quality of life for cancer patients; thus, more effective analgesics are clearly needed. This study evaluated the efficacy of a cannabinoid (CB) receptor agonist (WIN 55,212-2) on bone tumor pain in the spinal cords of rats, and clarified the roles of the CB1 and CB2 receptors in WIN 55,212-2-induced antinociception at the spinal level. Bone tumor pain was induced by injecting MRMT-1 tumor cells (1×10(5)) into the right tibias of female Sprague-Dawley rats under sevoflurane anesthesia. Bone tumor development was monitored radiologically. Under sevoflurane anesthesia, a polyethylene catheter was inserted into the intrathecal space for drug administration. To assess pain, the withdrawal threshold was measured by applying a von Frey filament to the tumor cell inoculation site. The effect of intrathecal WIN 55,212-2 was investigated. Next, the WIN 55,212-2-mediated antinociception was reversed using CB1 (AM 251) and CB2 (AM 630) receptor antagonists. The intratibial injection of MRMT-1 tumor cells produced radiologically confirmed bone tumors. The paw withdrawal threshold decreased significantly (mechanical allodynia) with tumor development; however, intrathecal WIN 55,212-2 dose-dependently increased the withdrawal threshold. The antinociceptive effect of WIN 55,212-2 was reversed by both CB1 and CB2 receptor antagonists. Intrathecal WIN 55,212-2 reduced bone tumor-related pain behavior mediated via spinal CB1 and CB2 receptors. Therefore, spinal CB receptor agonists may be novel analgesics in the treatment of bone tumor pain.

Behavioral, medical imaging and histopathological features of a new rat model of bone cancer pain

Pre-clinical bone cancer pain models mimicking the human condition are required to respond to clinical realities. Breast or prostate cancer patients coping with bone metastases experience intractable pain, which affects their quality of life. Advanced monitoring is thus required to clarify bone cancer pain mechanisms and refine treatments. In our model of rat femoral mammary carcinoma MRMT-1 cell implantation, pain onset and tumor growth were monitored for 21 days. The surgical procedure performed without arthrotomy allowed recording of incidental pain in free-moving rats. Along with the gradual development of mechanical allodynia and hyperalgesia, behavioral signs of ambulatory pain were detected at day 14 by using a dynamic weight-bearing apparatus. Osteopenia was revealed from day 14 concomitantly with disorganization of the trabecular architecture (µCT). Bone metastases were visualized as early as day 8 by MRI (T₁-Gd-DTPA) before pain detection. PET (Na¹⁸F) co-registration revealed intra-osseous activity, as determined by anatomical superimposition over MRI in accordance with osteoclastic hyperactivity (TRAP staining). Pain and bone destruction were aggravated with time. Bone remodeling was accompanied by c-Fos (spinal) and ATF3 (DRG) neuronal activation, sustained by astrocyte (GFAP) and microglia (Iba1) reactivity in lumbar spinal cord. Our animal model demonstrates the importance of simultaneously recording pain and tumor progression and will allow us to better characterize therapeutic strategies in the future.

Involvement of inflammatory mediators in neuropathic pain caused by vincristine

Elucidation of the mechanism of neuropathic pain caused by vincristine is required because long-term treatment with this anticancer agent often causes neuropathic pain. We refer to the involvement of inflammatory mediators in vincristine-induced neuropathic pain in this review. Several reports using rodents have shown that long-lasting neuropathic pain (mechanical allodynia) is caused by repeated systemic injection of vincristine. Vincristine damaged Schwann cells and DRG neurons in this model. Vincristine-induced macrophage infiltration in the peripheral nervous system (PNS) and macrophage-derived IL-6 elicited mechanical allodynia. These findings proved that inhibition of IL-6 function prevented neuropathic pain caused by vincristine. In the central nervous system (CNS), activation of microglia and astrocytes in the spinal cord were demonstrated after long-term vincristine treatment. TNF-alpha was upregulated in activated microglia and astrocytes, and inhibition of TNF-alpha function attenuated neuropathic pain caused by vincristine. These results suggest that vincristine induces macrophage infiltration to the damaged PNS, and that macrophage-derived inflammatory cytokines such as IL-6 elicits neuroinflammation. Signal transduction of pain from the PNS to the CNS activates microglia and astrocytes, and these activated glial cells release inflammatory cytokines such as TNF-alpha. In the CNS, these inflammatory cytokines have an important role in the neuropathic pain caused by vincristine. Immune-modulating agents that prevent activation of immune cells and/or the inhibitory agents of inflammatory cytokines could prevent the neuropathic pain caused by vincristine. These agents could increase the tolerability of vincristine when used for the treatment of leukemia and lymphoma.

Lacosamide

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Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The June 2009 monograph topics are everolimus; Japanese encephalitis vaccine, inactivated; inhaled insulin; pitavastatin; and dabigatran etexilate. The DUE is on plerixafor.

Lacosamide: a new approach to target voltage-gated sodium currents in epileptic disorders

The mechanism of action of several antiepileptic drugs (AEDs) rests on their ability to modulate the activity of voltage-gated sodium currents that are responsible for fast action potential generation. Recent data indicate that lacosamide (a compound with analgesic and anticonvulsant effects in animal models) shares a similar mechanism. When compared with other AEDs, lacosamide has the unique ability to interact with sodium channel slow inactivation without affecting fast inactivation. This article reviews these findings and discusses their relevance within the context of neuronal activity seen during epileptiform discharges generated by limbic neuronal networks in the presence of chemical convulsants. These seizure-like events are characterized by sustained discharges of sodium-dependent action potentials supported by robust depolarizations, thus providing synchronization within neuronal networks. Generally, AEDs such as phenytoin, carbamazepine and lamotrigine block sodium channels when activated. In contrast, lacosamide facilitates slow inactivation of sodium channels both in terms of kinetics and voltage dependency. This effect may be relatively selective for repeatedly depolarized neurons, such as those participating in seizure activity in which the persistence of sodium currents is more pronounced and promotes neuronal excitation. The clinical effectiveness of lacosamide has been demonstrated in randomized, double-blind, parallel-group, placebo-controlled, adjunctive-therapy trials in patients with refractory partial seizures. Further studies should determine whether the effects of lacosamide in animal models and in clinical settings are fully explained by its selective action on sodium current slow inactivation or whether other effects (e.g. interactions with the collapsin-response mediator protein-2) play a contributory role.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Sensory neuron voltage-gated sodium channels as analgesic drug targets

Voltage-gated sodium channels are crucial determinants of neuronal excitability and signalling; some specific channel subtypes have been implicated in a number of chronic pain conditions. Human genetic studies show gain-of-function or loss-of-function mutations in Na(V)1.7 lead to an enhancement or lack of pain, respectively, whilst transgenic mouse and knockdown studies have implicated Na(V)1.3, Na(V)1.8 and Na(V)1.9 in peripheral pain pathways. The development of subtype-specific sodium channel blockers, though clearly desirable, has been technically challenging. Recent advances exploiting both natural products and small molecule selective channel blockers have demonstrated that this approach to pain control is feasible. These observations provide a rationale for the development of new analgesics without the side effect profile of broad spectrum sodium channel blockers.

Intrathecal morphine suppresses immune function in rats with inflammatory-induced pain

Acute and chronic systemic administration of morphine is known to suppress immune function; however, the effect of chronic intrathecal (IT) morphine on immune function in inflammatory-induced pain is still unclear. This study examined the effects on the immune system of IT morphine in rats with formalin-induced pain. Lumbar IT catheters were implanted in rats and saline or 2.5, 5.0 or 10.0 microg/h morphine were administered for 7 days. On the last day, formalin-induced inflammatory pain was induced in rat hind paws and pain intensity was assessed. Rat spleens were then harvested for immune function assay. The IT morphine induced a dose-dependent analgesic effect and lactic acid dehydrogenase release assay showed dose-dependent suppression of natural killer cell activity. Concanavalin-A-induced splenocyte proliferation assay showed IT morphine to suppress T lymphocyte function in a dose-dependent manner. Flow cytometry showed IT morphine significantly to decrease T lymphocyte function and the percentages of T lymphocyte subsets in a dose-dependent manner. Hence, in inflammatory-induced pain IT morphine was found to suppress immune function. Chronic IT morphine should be used cautiously to treat chronic pain in immunocompromised cases.