A painful peripheral neuropathy in the rat produced by the chemotherapeutic drug, paclitaxel

Pharmacokinetic drug interactions between apigenin, rutin and paclitaxel mediated by P-glycoprotein in rats

The aim of present study was to investigate the effects of apigenin and rutin on the pharmacokinetics of paclitaxel after oral administration of paclitaxel with apigenin and rutin to rats. Paclitaxel (40 mg/kg) was administered orally alone and in combination with apigenin and rutin (10, 20, and 40 mg/kg) for 15 consecutive days. In the single-dose pharmacokinetic study (SDS), blood samples were collected on 1st day whereas on 15th day in the multiple-dose pharmacokinetic study (MDS). The plasma concentrations of paclitaxel were increased dose-dependently in the combination of apigenin and rutin compared to that of paclitaxel control in SDS and MDS (p < 0.01). The areas under the plasma concentration-time curve (AUC) and the plasma peak concentrations (C max) of paclitaxel with apigenin and rutin were significantly higher (p < 0.01) than that of the control. The AUCs and C max of paclitaxel were increased with apigenin and rutin in the dose-dependent manner. The half-life (t 1/2) was significantly longer than that of the control. Non-everted sacs were filled with paclitaxel 100 μM in the presence and absence of verapamil (50 μM), apigenin, and rutin (50, 100 μM) and incubated at 37 ºC for 60 min. The absorption of paclitaxel was increased in the presence of apigenin, rutin, and verapamil, a typical P-glycoprotein and Cyp3A4 inhibitor. If these results are confirmed in humans in a clinical setting, the paclitaxel dose should be adjusted when it is given concomitantly with apigenin and rutin.

Toll-like receptor 4 signaling contributes to Paclitaxel-induced peripheral neuropathy

This paper tests the contribution of the toll-like receptors, TLR4 in particular, in the initiation and maintenance of paclitaxel-related chemotherapy-induced peripheral neuropathy. TLR4 and its immediate downstream signaling molecules-myeloid differentiation primary response gene 88 (MyD88) and toll/interleukin 1 receptor domain-containing adapter-inducing interferon-β (TRIF)-were found to be increased in the dorsal root ganglion (DRG) using Western blot by day 7 of paclitaxel treatment. The behavioral phenotype, the increase of both TLR4 and MyD88, was blocked by cotreatment with the TLR4 antagonist lipopolysaccharide-Rhodobacter sphaeroides during chemotherapy. A similar, but less robust, behavioral effect was observed using intrathecal treatment of MyD88 homodimerization inhibitory peptide. DRG levels of TLR4 and MyD88 reduced over the next 2 weeks, whereas these levels remained increased in spinal cord through day 21 following chemotherapy. Immunohistochemical analysis revealed TLR4 expression in both calcitonin gene-related peptide-positive and isolectin B4-positive small DRG neurons. MyD88 was only found in calcitonin gene-related peptide-positive neurons, and TRIF was found in both calcitonin gene-related peptide-positive and isolectin B4-positive small DRG neurons as well as in medium- and large-size DRG neurons. In the spinal cord, TLR4 was only found colocalized to astrocytes but not with either microglia or neurons. Intrathecal treatment with the TLR4 antagonist lipopolysaccharide-R. sphaeroides transiently reversed preestablished chemotherapy-induced peripheral neuropathy mechanical hypersensitivity. These results strongly implicate TLR4 signaling in the DRG and the spinal cord in the induction and maintenance of paclitaxel-related chemotherapy-induced peripheral neuropathy.

PERSPECTIVE

The toll-like receptor TLR4 and MyD88 signaling pathway could be a new potential therapeutic target in paclitaxel-induced painful neuropathy.

Prophylactic cannabinoid administration blocks the development of paclitaxel-induced neuropathic nociception during analgesic treatment and following cessation of drug delivery

Background

Chemotherapeutic treatment results in chronic pain in an estimated 30-40 percent of patients. Limited and often ineffective treatments make the need for new therapeutics an urgent one. We compared the effects of prophylactic cannabinoids as a preventative strategy for suppressing development of paclitaxel-induced nociception. The mixed CB₁/CB₂ agonist WIN55,212-2 was compared with the cannabilactone CB₂-selective agonist AM1710, administered subcutaneously (s.c.), via osmotic mini pumps before, during, and after paclitaxel treatment. Pharmacological specificity was assessed using CB₁ (AM251) and CB₂ (AM630) antagonists. The impact of chronic drug infusion on transcriptional regulation of mRNA markers of astrocytes (GFAP), microglia (CD11b) and cannabinoid receptors (CB₁, CB₂) was assessed in lumbar spinal cords of paclitaxel and vehicle-treated rats.

Results

Both WIN55,212-2 and AM1710 blocked the development of paclitaxel-induced mechanical and cold allodynia; anti-allodynic efficacy persisted for approximately two to three weeks following cessation of drug delivery. WIN55,212-2 (0.1 and 0.5 mg/kg/day s.c.) suppressed the development of both paclitaxel-induced mechanical and cold allodynia. WIN55,212-2-mediated suppression of mechanical hypersensitivity was dominated by CB₁ activation whereas suppression of cold allodynia was relatively insensitive to blockade by either CB₁ (AM251; 3 mg/kg/day s.c.) or CB₂ (AM630; 3 mg/kg/day s.c.) antagonists. AM1710 (0.032 and 3.2 mg/kg /day) suppressed development of mechanical allodynia whereas only the highest dose (3.2 mg/kg/day s.c.) suppressed cold allodynia. Anti-allodynic effects of AM1710 (3.2 mg/kg/day s.c.) were mediated by CB₂. Anti-allodynic efficacy of AM1710 outlasted that produced by chronic WIN55,212-2 infusion. mRNA expression levels of the astrocytic marker GFAP was marginally increased by paclitaxel treatment whereas expression of the microglial marker CD11b was unchanged. Both WIN55,212-2 (0.5 mg/kg/day s.c.) and AM1710 (3.2 mg/kg/day s.c.) increased CB₁ and CB₂ mRNA expression in lumbar spinal cord of paclitaxel-treated rats in a manner blocked by AM630.

Conclusions and implications

Cannabinoids block development of paclitaxel-induced neuropathy and protect against neuropathic allodynia following cessation of drug delivery. Chronic treatment with both mixed CB₁/CB₂ and CB₂ selective cannabinoids increased mRNA expression of cannabinoid receptors (CB₁, CB₂) in a CB₂-dependent fashion. Our results support the therapeutic potential of cannabinoids for suppressing chemotherapy-induced neuropathy in humans.

Paclitaxel alters the evoked release of calcitonin gene-related peptide from rat sensory neurons in culture

Peripheral neuropathy (PN) is a debilitating and dose-limiting side effect of treatment with the chemotherapeutic agent, paclitaxel. Understanding the effects of paclitaxel on sensory neuronal function and the signaling pathways which mediate these paclitaxel-induced changes in function are critical for the development of therapies to prevent or alleviate the PN. The effects of long-term administration of paclitaxel on the function of sensory neurons grown in culture, using the release of the neuropeptide calcitonin gene-related peptide (CGRP) as an endpoint of sensory neuronal function, were examined. Dorsal root ganglion cultures were treated with low (10 nM) and high (300 nM) concentrations of paclitaxel for 1, 3, or 5 days. Following paclitaxel treatment, the release of CGRP was determined using capsaicin, a TRPV1 agonist; allyl isothiocyanate (AITC), a TRPA1 agonist; or high extracellular potassium. The effects of paclitaxel on the release of CGRP were stimulant-, concentration-, and time-dependent. When neurons were stimulated with capsaicin or AITC, a low concentration of paclitaxel (10nM) augmented transmitter release, whereas a high concentration (300 nM) reduced transmitter release in a time-dependent manner; however, when high extracellular potassium was used as the evoking stimulus, all concentrations of paclitaxel augmented CGRP release from sensory neurons. These results suggest that paclitaxel alters the function of sensory neurons in vitro, and suggest that the mechanisms by which paclitaxel alters neuronal function may include functional changes in TRP channel activity. The described in vitro model will facilitate future studies to identify the signaling pathways by which paclitaxel alters neuronal sensitivity.

Pathological pain and the neuroimmune interface

Reciprocal signalling between immunocompetent cells in the central nervous system (CNS) has emerged as a key phenomenon underpinning pathological and chronic pain mechanisms. Neuronal excitability can be powerfully enhanced both by classical neurotransmitters derived from neurons, and by immune mediators released from CNS-resident microglia and astrocytes, and from infiltrating cells such as T cells. In this Review, we discuss the current understanding of the contribution of central immune mechanisms to pathological pain, and how the heterogeneous immune functions of different cells in the CNS could be harnessed to develop new therapeutics for pain control. Given the prevalence of chronic pain and the incomplete efficacy of current drugs--which focus on suppressing aberrant neuronal activity--new strategies to manipulate neuroimmune pain transmission hold considerable promise.

Spinal changes of a newly isolated neuropeptide endomorphin-2 concomitant with vincristine-induced allodynia

Chemotherapy-induced neuropathic pain (CNP) is the major dose-limiting factor in cancer chemotherapy. However, the neural mechanisms underlying CNP remain unclear. There is increasing evidence implicating the involvement of spinal endomorphin-2 (EM2) in neuropathic pain. In this study, we used a vincristine-evoked rat CNP model displaying mechanical allodynia and central sensitization, and observed a significant decrease in the expression of spinal EM2 in CNP. Also, while intrathecal administration of exogenous EM2 attenuated allodynia and central sensitization, the mu-opioid receptor antagonist β-funaltrexamine facilitated these events. We found that the reduction in spinal EM2 was mediated by increased activity of dipeptidylpeptidase IV, possibly as a consequence of chemotherapy-induced oxidative stress. Taken together, our findings suggest that a decrease in spinal EM2 expression causes the loss of endogenous analgesia and leads to enhanced pain sensation in CNP.

Broad spectrum and prolonged efficacy of dimiracetam in models of neuropathic pain

Dimiracetam, a bicyclic 2-pyrrolidinone derivative originally developed as cognition enhancer, is a member of the nootropic family for which anecdotal efficacy in models of neuropathic pain has been reported. Its antineuropathic activity was evaluated in established models of neuropathic pain induced by nerve injury, chemotherapy or MIA-induced osteoarthritis. Acutely, dimiracetam was very effective in models of antiretroviral drug induced painful neuropathy, oxaliplatin-induced hyperalgesia and in the MIA-osteoarthritis. Chronic dimiracetam dosing in the MIA and ART- induced models completely reverted hyperalgesia back to the level of healthy controls. Once reached, the maximal effect was maintained despite dose diminution and increased inter-dose interval. The effect of the last dose outlasted dimiracetam half-life longer than 12 times. In synaptosomal preparations, dimiracetam counteracted the NMDA-induced release of glutamate with highest potency in the spinal cord, possibly via NMDA receptor isoforms containing pH-sensitive GluN1 and GluN2A subunits. Dimiracetam appears to be a promising and safe treatment for neuropathic pain conditions for which there are very limited therapeutic options.

The Self-administration of Analgesic Drugs in Experimentally Induced Chronic Pain

Systemically and centrally delivered opioids have been comprehensively studied for their effects both in analgesic and addiction models for many decades, primarily in subjects with presumptive normal sensory thresholds. The introduction of disease-based models of persistent hypersensitivity enabled chronic evaluation of opioid analgesic pharmacology under the specific state of chronic pain. These studies have largely (but not uniformly) reported reduced opioid analgesic potency and efficacy under conditions of chronic pain. A comparatively limited set of studies has evaluated the impact of experimentally induced chronic pain on self-administration patterns of opioid and non-opioid analgesics. Similarly, these studies have primarily (but not exclusively) found that responding for opioids is reduced under conditions of chronic pain. Additionally, such experiments have also demonstrated that the condition of chronic pain evokes self-administration or conditioned place preference for non-opioid analgesics. The consensus is that the chronic pain alters responding for opioid and non-opioid analgesics in a manner seemingly related to their respective antiallodynic/antihyperalgesic properties under the specific state of chronic pain.

Evaluation of chemotherapy-induced peripheral neuropathy using current perception threshold and clinical evaluations

PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is increasing with introduction of new and combination cancer pharmacotherapies. This study evaluated associations between clinical and self-report measurements and current perception threshold (CPT), a neuroselective measure of sensory nerve function that may detect asymptomatic CIPN damage.

METHODS

Data for this secondary analysis were from a prospective, observational study using CPT to evaluate CIPN. Bivariate mixed models, accounting for the intraclass correlation between repeated patient assessments, were used to assess the relationship between CPT at each frequency (5, 250, and 2,000 Hz) and each subjective measure (Neuropathic Pain Scale, FACT-GOGntx) and objective measurement (quantitative sensory testing, deep tendon reflexes, and grip strength).

RESULTS

A total of 29 chemotherapy-naïve subjects with various cancer types had a mean age of 56.7 (SD 10.4); nine subjects developed CIPN grade >1 using NCI CTC-AE criteria. Cold detection thresholds were inversely associated with CPT 5 [b(95 % CI) = -2.5(-4.5, -0.5)] and CPT 2,000 [-7.5(-11.8, -3.3)] frequencies. FACT GOG-ntx quality of life (QoL) scale and neurotoxicity and function subscales were inversely associated with CPT 2,000 [-1.8 (-3.5, -0.05), -2.2 (-4.2, -0.2), and -5.4 (-9.8, -0.9), respectively], indicating worsening QoL, impairment, and function as hypoesthesia increases.

CONCLUSIONS

CPT 2,000 may identify impending worsening of patient-reported outcomes such as QoL.

Pathobiology of cancer chemotherapy-induced peripheral neuropathy (CIPN)

Chemotherapy induced peripheral neuropathy (CIPN) is a type of neuropathic pain that is a major dose-limiting side-effect of potentially curative cancer chemotherapy treatment regimens that develops in a "stocking and glove" distribution. When pain is severe, a change to less effective chemotherapy agents may be required, or patients may choose to discontinue treatment. Medications used to alleviate CIPN often lack efficacy and/or have unacceptable side-effects. Hence the unmet medical need for novel analgesics for relief of this painful condition has driven establishment of rodent models of CIPN. New insights on the pathobiology of CIPN gained using these models are discussed in this review. These include mitochondrial dysfunction and oxidative stress that are implicated as key mechanisms in the development of CIPN. Associated structural changes in peripheral nerves include neuronopathy, axonopathy and/or myelinopathy, especially intra-epidermal nerve fiber (IENF) degeneration. In patients with CIPN, loss of heat sensitivity is a hallmark symptom due to preferential damage to myelinated primary afferent sensory nerve fibers in the presence or absence of demyelination. The pathobiology of CIPN is complex as cancer chemotherapy treatment regimens frequently involve drug combinations. Adding to this complexity, there are also subtle differences in the pathobiological consequences of commonly used cancer chemotherapy drugs, viz platinum compounds, taxanes, vincristine, bortezomib, thalidomide and ixabepilone, on peripheral nerves.

Current methods for the assessment and management of taxane-related neuropathy

Taxane-induced peripheral neuropathy (TIPN) affects a number of patients with breast cancer. To properly manage these patients, nurses must be able to identify and assess TIPN, as well as educate patients on TIPN as a side effect of taxane therapy. This article provides practical suggestions regarding how nurses can incorporate clinically feasible measurement approaches into practice and includes examples of grading TIPN that illustrate the limitations of the current tools and techniques for assessment. For example, a shortened and revised version of the Total Neuropathy Score and the Functional Assessment of Cancer Therapy/Gynecologic Oncology Group-Neurotoxicity subscale should be considered for future use. In addition, neuropathy-related results from numerous phase III trials in breast cancer are discussed, and the latest evidence regarding pharmacologic interventions for TIPN is briefly summarized.

Neurosteroid 3α-androstanediol efficiently counteracts paclitaxel-induced peripheral neuropathy and painful symptoms

Painful peripheral neuropathy belongs to major side-effects limiting cancer chemotherapy. Paclitaxel, widely used to treat several cancers, induces neurological symptoms including burning pain, allodynia, hyperalgesia and numbness. Therefore, identification of drugs that may effectively counteract paclitaxel-induced neuropathic symptoms is crucial. Here, we combined histopathological, neurochemical, behavioral and electrophysiological methods to investigate the natural neurosteroid 3α-androstanediol (3α-DIOL) ability to counteract paclitaxel-evoked peripheral nerve tissue damages and neurological symptoms. Prophylactic or corrective 3α-DIOL treatment (4 mg/kg/2days) prevented or suppressed PAC-evoked heat-thermal hyperalgesia, cold-allodynia and mechanical allodynia/hyperalgesia, by reversing to normal, decreased thermal and mechanical pain thresholds of PAC-treated rats. Electrophysiological studies demonstrated that 3α-DIOL restored control values of nerve conduction velocity and action potential peak amplitude significantly altered by PAC-treatment. 3α-DIOL also repaired PAC-induced nerve damages by restoring normal neurofilament-200 level in peripheral axons and control amount of 2’,3’-cyclic-nucleotide-3’-phosphodiesterase in myelin sheaths. Decreased density of intraepidermal nerve fibers evoked by PAC-therapy was also counteracted by 3α-DIOL treatment. More importantly, 3α-DIOL beneficial effects were not sedation-dependent but resulted from its neuroprotective ability, nerve tissue repairing capacity and long-term analgesic action. Altogether, our results showing that 3α-DIOL efficiently counteracted PAC-evoked painful symptoms, also offer interesting possibilities to develop neurosteroid-based strategies against chemotherapy-induced peripheral neuropathy. This article shows that the prophylactic or corrective treatment with 3α-androstanediol prevents or suppresses PAC-evoked painful symptoms and peripheral nerve dysfunctions in rats. The data suggest that 3α-androstanediol-based therapy may constitute an efficient strategy to explore in humans for the eradication of chemotherapy-induced peripheral neuropathy.

An overview of animal models of pain: disease models and outcome measures

Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model.

PERSPECTIVE

Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic.

Effect of ω-conotoxin MVIIA and Phα1β on paclitaxel-induced acute and chronic pain

The treatment with the chemotherapeutic agent paclitaxel produces a painful peripheral neuropathy, and is associated with an acute pain syndrome in a clinically significant number of patients. However, no standard therapy has been established to manage the acute pain or the chronic neuropathic pain related to paclitaxel. In the present study, we evaluated the analgesic potential of two N-type voltage-gated calcium channel (VGCC) blockers, ω-conotoxin MVIIA and Phα1β, on acute and chronic pain induced by paclitaxel. Adult male rats were treated with four intraperitoneal injections of paclitaxel (1+1+1+1mg/kg, in alternate days) and the development of mechanical hyperalgesia was evaluated 24h (acute painful stage) or 15days (chronic painful stage) after the first paclitaxel injection. Not all animals showed mechanical hyperalgesia 24h after the first paclitaxel injection, but those that showed developed a more intense mechanical hyperalgesia at the chronic painful stage. Intrathecal administration (i.t.) of ω-conotoxin MVIIA (3-300pmol/site) or Phα1β (10-300pmol/site) reduced the mechanical hyperalgesia either at the acute or at the chronic painful stage induced by paclitaxel. When administered at the acute painful stage, ω-conotoxin MVIIA (300pmol/site, i.t.) and Phα1β (300pmol/site, i.t.) prevented the worsening of chronic mechanical hyperalgesia. Furthermore, Phα1β (30-300pmol/site, i.t.) elicited less adverse effects than ω-conotoxin MVIIA (10-300 pmol/site, i.t.). Taken together, our data evidence the involvement of N-type VGCC in pain sensitization induced by paclitaxel and point out the potential of Phα1β as a safer alternative than ω-conotoxin MVIIA to treat the pain related to paclitaxel.

T-type Ca2+ channels in normal and abnormal brain functions

Low-voltage-activated T-type Ca(2+) channels are widely expressed in various types of neurons. Once deinactivated by hyperpolarization, T-type channels are ready to be activated by a small depolarization near the resting membrane potential and, therefore, are optimal for regulating the excitability and electroresponsiveness of neurons under physiological conditions near resting states. Ca(2+) influx through T-type channels engenders low-threshold Ca(2+) spikes, which in turn trigger a burst of action potentials. Low-threshold burst firing has been implicated in the synchronization of the thalamocortical circuit during sleep and in absence seizures. It also has been suggested that T-type channels play an important role in pain signal transmission, based on their abundant expression in pain-processing pathways in peripheral and central neurons. In this review, we will describe studies on the role of T-type Ca(2+) channels in the physiological as well as pathological generation of brain rhythms in sleep, absence epilepsy, and pain signal transmission. Recent advances in studies of T-type channels in the control of cognition will also be briefly discussed.

Assessment of paclitaxel induced sensory polyneuropathy with "Catwalk" automated gait analysis in mice

Neuropathic pain as a symptom of sensory nerve damage is a frequent side effect of chemotherapy. The most common behavioral observation in animal models of chemotherapy induced polyneuropathy is the development of mechanical allodynia, which is quantified with von Frey filaments. The data from one study, however, cannot be easily compared with other studies owing to influences of environmental factors, inter-rater variability and differences in test paradigms. To overcome these limitations, automated quantitative gait analysis was proposed as an alternative, but its usefulness for assessing animals suffering from polyneuropathy has remained unclear. In the present study, we used a novel mouse model of paclitaxel induced polyneuropathy to compare results from electrophysiology and the von Frey method to gait alterations measured with the Catwalk test. To mimic recently improved clinical treatment strategies of gynecological malignancies, we established a mouse model of dose-dense paclitaxel therapy on the common C57Bl/6 background. In this model paclitaxel treated animals developed mechanical allodynia as well as reduced caudal sensory nerve action potential amplitudes indicative of a sensory polyneuropathy. Gait analysis with the Catwalk method detected distinct alterations of gait parameters in animals suffering from sensory neuropathy, revealing a minimized contact of the hind paws with the floor. Treatment of mechanical allodynia with gabapentin improved altered dynamic gait parameters. This study establishes a novel mouse model for investigating the side effects of dose-dense paclitaxel therapy and underlines the usefulness of automated gait analysis as an additional easy-to-use objective test for evaluating painful sensory polyneuropathy.

Bioenergetic deficits in peripheral nerve sensory axons during chemotherapy-induced neuropathic pain resulting from peroxynitrite-mediated post-translational nitration of mitochondrial superoxide dismutase

Many of the widely used anticancer drugs induce dose-limiting peripheral neuropathies that undermine their therapeutic efficacy. Animal models of chemotherapy-induced painful peripheral neuropathy (CIPN) evoked by a variety of drug classes, including taxanes, vinca alkaloids, platinum-complexes, and proteasome-inhibitors, suggest that the common underlying mechanism in the development of these neuropathies is mitotoxicity in primary nerve sensory axons (PNSAs) arising from reduced mitochondrial bioenergetics [eg adenosine triphosphate (ATP) production deficits due to compromised respiratory complex I and II activity]. The causative mechanisms of this mitotoxicity remain poorly defined. However, peroxynitrite, an important pro-nociceptive agent, has been linked to mitotoxicity in several disease states and may also drive the mitotoxicity associated with CIPN. Our findings reveal that the development of mechano-hypersensitivity induced by paclitaxel, oxaliplatin, and bortezomib was prevented by administration of the peroxynitrite decomposition catalyst Mn(III) 5,10,15,20-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)) without interfering with their anti-tumor effects. Peak CIPN was associated with the nitration and inactivation of superoxide dismutase in the mitochondria, but not in the cytosol, as well as a significant decrease in ATP production within the PNSAs; all of these events were attenuated by MnTE-2-PyP(5+). Our results provide continued support for the role of mitotoxicity in the development of CIPN across chemotherapeutic drug classes, and identify peroxynitrite as a key mediator in these processes, thereby providing the rationale towards development of "peroxynitrite-targeted" therapeutics for CIPN.

PARP inhibitors attenuate chemotherapy-induced painful neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major toxicity of chemotherapy treatment for which no therapy is approved. Poly(ADP-ribose) polymerase (PARP)1/2 are nuclear enzymes activated upon DNA damage, and PARP1/2 inhibition provides resistance against DNA damage. A role for PARP inhibition in sensory neurotransmission has also been established. PARP inhibitors attenuate pain-like behaviors and neuropathy-associated decreased peripheral nerve function in diabetic models. The hypothesis tested was that PARP inhibition protects against painful neuropathy. The objective of this study was to investigate whether the novel, selective PARP1/2 inhibitors (ABT-888 and related analogues) would attenuate development of mechanical allodynia in vincristine-treated rats. PARP inhibitors were dosed for 2 days, and then co-administered with vincristine for 12 days. Mechanical allodynia was observed in rats treated with vincristine. PARP1/2 inhibition significantly attenuated development of mechanical allodynia and reduced poly ADP-ribose (PAR) activation in rat skin. The data presented here show that PARP inhibition attenuates vincristine-induced mechanical allodynia in rats, and supports that PARP inhibition may represent a novel therapeutic approach for CIPN.

Induction of monocyte chemoattractant protein-1 (MCP-1) and its receptor CCR2 in primary sensory neurons contributes to paclitaxel-induced peripheral neuropathy

The use of paclitaxel (Taxol), a microtubule stabilizer, for cancer treatment is often limited by its associated peripheral neuropathy (chemotherapy-induced peripheral neuropathy [CIPN]), which predominantly results in sensory dysfunction, including chronic pain. Here we show that paclitaxel CIPN was associated with induction of chemokine monocyte chemoattractant protein-1 (MCP-1) and its cognate receptor CCR2 in primary sensory neurons of dorsal root ganglia. Immunostaining revealed that MCP-1 was mainly expressed in small nociceptive neurons whereas CCR2 was expressed in large and medium-sized myelinated neurons. Direct application of MCP-1 consistently induced intracellular calcium increases in dorsal root ganglia large and medium-sized neurons but not in small neurons mainly dissociated from paclitaxel-treated but not vehicle-treated animals. Paclitaxel also induced increased expression of MCP-1 in spinal astrocytes, but no CCR2 signal was detected in the spinal cord. Local blockade of MCP-1/CCR2 signaling by anti-MCP-1 antibody or CCR2 antisense oligodeoxynucleotides significantly attenuated paclitaxel CIPN phenotypes including mechanical hypersensitivity and loss of intraepidermal nerve fibers in hindpaw glabrous skin. These results suggest that activation of paracrine MCP-1/CCR2 signaling between dorsal root ganglion neurons plays a critical role in the development of paclitaxel CIPN, and targeting MCP-1/CCR2 signaling could be a novel therapeutic approach.

PERSPECTIVE

CIPN is a severe side effect accompanying paclitaxel chemotherapy and lacks effective treatments. The current study suggests that blocking MCP-1/CCR2 signaling could be a new therapeutic strategy to prevent or reverse paclitaxel CIPN. This preclinical evidence encourages future clinical evaluation of this strategy.

Topical combinations aimed at treating microvascular dysfunction reduce allodynia in rat models of CRPS-I and neuropathic pain

Growing evidence indicates that various chronic pain syndromes exhibit tissue abnormalities caused by microvasculature dysfunction in the blood vessels of skin, muscle, or nerve. We tested whether topical combinations aimed at improving microvascular function would relieve allodynia in animal models of complex regional pain syndrome type I (CRPS-I) and neuropathic pain. We hypothesized that topical administration of either α(2)-adrenergic (α(2)A) receptor agonists or nitric oxide (NO) donors combined with either phosphodiesterase (PDE) or phosphatidic acid (PA) inhibitors would effectively reduce allodynia in these animal models of chronic pain. Single topical agents produced significant dose-dependent antiallodynic effects in rats with chronic postischemia pain, and the antiallodynic dose-response curves of PDE and PA inhibitors were shifted 2.5- to 10-fold leftward when combined with nonanalgesic doses of α(2)A receptor agonists or NO donors. Topical combinations also produced significant antiallodynic effects in rats with sciatic nerve injury, painful diabetic neuropathy, and chemotherapy-induced painful neuropathy. These effects were shown to be produced by a local action, lasted up to 6 hours after acute treatment, and did not produce tolerance over 15 days of chronic daily dosing. The present results support the hypothesis that allodynia in animal models of CRPS-I and neuropathic pain is effectively relieved by topical combinations of α(2)A or NO donors with PDE or PA inhibitors. This suggests that topical treatments aimed at improving microvascular function may reduce allodynia in patients with CRPS-I and neuropathic pain.

PERSPECTIVE

This article presents the synergistic antiallodynic effects of combinations of α(2)A or NO donors with PDE or PA inhibitors in animal models of CRPS-I and neuropathic pain. The data suggest that effective clinical treatment of chronic neuropathic pain may be achieved by therapies that alleviate microvascular dysfunction in affected areas.

Neuropathy-inducing effects of eribulin mesylate versus paclitaxel in mice with preexisting neuropathy

Eribulin mesylate (E7389, INN:eribulin mesilate Halaven(®)) is a non-taxane microtubule dynamics inhibitor currently in clinical use for advanced breast cancer. Other microtubule-targeting agents for breast cancer, including paclitaxel and ixabepilone, display a common treatment dose-limiting toxicity of peripheral neuropathy (PN). In an earlier study, we found eribulin mesylate had a lower propensity to induce PN in mice than either paclitaxel or ixabepilone. In the current study, we compared additional PN induced by paclitaxel versus eribulin mesylate when administered to mice with preexisting paclitaxel-induced PN. Initially, paclitaxel at 0.75 × its maximum tolerated dose (MTD; 22.5 mg/kg) was given on a Q2Dx3 regimen for 2 weeks. The second chemotherapy was 0.5 MTD eribulin mesylate (0.875 mg/kg) or paclitaxel (15 mg/kg) on a similar regimen, starting 2 weeks after the first. Initial paclitaxel treatment produced significant decreases in caudal nerve conduction velocity (NCV; averaging 19.5 ± 1 and 22.2 ± 1.3 %, p < 0.001) and amplitude (averaging 53.2 ± 2.6 and 72.4 ± 2.1 %, p < 0.001) versus vehicle when measured 24 h or 2 weeks after dosing cessation, respectively. Additional 0.5 MTD paclitaxel further reduced caudal NCV and amplitude relative to immediately before initiation of the second regimen (by 11 ± 2.1 and 59.2 ± 5 %, p < 0.01, respectively). In contrast, 0.5 MTD eribulin mesylate caused no further decrease in caudal NCV. In conclusion, unlike additional paclitaxel treatment, eribulin mesylate administered to mice with preexisting paclitaxel-induced PN had limited additional deleterious effects at 6 weeks. These preclinical data suggest that eribulin mesylate may have reduced tendency to exacerbate preexisting paclitaxel-induced PN in clinical settings.

Spinal astrocytic activation contributes to mechanical allodynia in a rat chemotherapy-induced neuropathic pain model

Chemotherapy-induced neuropathic pain (CNP) is the major dose-limiting factor in cancer chemotherapy. However, the neural mechanisms underlying CNP remain enigmatic. Accumulating evidence implicates the involvement of spinal glia in some neuropathic pain models. In this study, using a vincristine-evoked CNP rat model with obvious mechanical allodynia, we found that spinal astrocyte rather than microglia was dramatically activated. The mechanical allodynia was dose-dependently attenuated by intrathecal administratration of L-α-aminoadipate (astrocytic specific inhibitor); whereas minocycline (microglial specific inhibitor) had no such effect, indicating that spinal astrocytic activation contributes to allodynia in CNP rat. Furthermore, oxidative stress mediated the development of spinal astrocytic activation, and activated astrocytes dramatically increased interleukin-1β expression which induced N-methyl-D-aspartic acid receptor (NMDAR) phosphorylation in spinal neurons to strengthen pain transmission. Taken together, our findings suggest that spinal activated astrocytes may be a crucial component of the pathophysiology of CNP and “Astrocyte-Cytokine-NMDAR-neuron” pathway may be one detailed neural mechanisms underlying CNP. Thus, inhibiting spinal astrocytic activation may represent a novel therapeutic strategy for treating CNP.

Effect of ethyl pyruvate on Paclitaxel-induced neuropathic pain in rats

Background

Although paclitaxel is a widely used chemotherapeutic agent for the treatment of solid cancers, side effects such as neuropathic pain lead to poor compliance and discontinuation of the therapy. Ethyl pyruvate (EP) is known to have analgesic effects in several pain models and may inhibit apoptosis. The present study was designed to investigate the analgesic effects of EP on mechanical allodynia and apoptosis in dorsal root ganglion (DRG) cells after paclitaxel administration.

Methods

Rats were randomly divided into 3 groups: 1) a control group, which received only vehicle; 2) a paclitaxel group, which received paclitaxel; and 3) an EP group, which received EP after paclitaxel administration. Mechanical allodynia was tested before and at 7 and 14 days after final paclitaxel administration. Fourteen days after paclitaxel treatment, DRG apoptosis was determined by activated caspase-3 immunoreactivity (IR).

Results

Post-treatment with EP did not significantly affect paclitaxel-induced allodynia, although it tended to slightly reduce sensitivities to mechanical stimuli after paclitaxel administration. After paclitaxel administration, an increase in caspase-3 IR in DRG cells was observed, which was co-localized with NF200-positive myelinated neurons. Post-treatment with EP decreased the paclitaxel-induced caspase-3 IR. Paclitaxel administration or post-treatment with EP did not alter the glial fibrillary acidic protein IRs in DRG cells.

Conclusions

Inhibition of apoptosis in DRG neurons by EP may not be critical in paclitaxel-induced mechanical allodynia.

Effect of paclitaxel on transient receptor potential vanilloid 1 in rat dorsal root ganglion

Peripheral neuropathy is a common adverse effect of paclitaxel treatment. To analyze the contribution of transient receptor potential vanilloid 1 (TRPV1) in the development of paclitaxel-induced thermal hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after paclitaxel treatment. Behavioral assessment using the tail-flick test showed that intraperitoneal administration of 2 and 4 mg/kg paclitaxel induced thermal hyperalgesia after days 7, 14, and 21. Paclitaxel-induced thermal hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Paclitaxel (2 and 4 mg/kg) treatment increased the expression of TRPV1 mRNA and protein in DRG neurons. Immunohistochemistry showed that paclitaxel (4 mg/kg) treatment increased TRPV1 protein expression in small and medium DRG neurons 14 days after treatment. Antibody double labeling revealed that isolectin B4-positive small DRG neurons co-expressed TRPV1. TRPV1 immunostaining was up-regulated in paw skin day 14 after paclitaxel treatment. Moreover, in situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small or medium in size. These results suggest that paclitaxel treatment increases TRPV1 expression in DRG neurons and may contribute to functional peripheral neuropathic pain.

Inflammation and cancer-related fatigue: mechanisms, contributing factors, and treatment implications

Fatigue is one of the most common and distressing side effects of cancer and its treatment, and may persist for years after treatment completion in otherwise healthy survivors. Guided by basic research on neuro-immune interactions, a growing body of research has examined the hypothesis that cancer-related fatigue is driven by activation of the pro-inflammatory cytokine network. In this review, we examine the current state of the evidence linking inflammation and cancer-related fatigue, drawing from recent human research and from experimental animal models probing effects of cancer and cancer treatment on inflammation and fatigue. In addition, we consider two key questions that are currently driving research in this area: what are the neural mechanisms of fatigue, and what are the biological and psychological factors that influence the onset and/or persistence of inflammation and fatigue in cancer patients and survivors? Identification of the mechanisms driving cancer-related fatigue and associated risk factors will facilitate the development of targeted interventions for vulnerable patients.

Topical application of disodium isostearyl 2-O-L-ascorbyl phosphate, an amphiphilic ascorbic acid derivative, reduces neuropathic hyperalgesia in rats

BACKGROUND AND PURPOSE

Ca(v) 3.2 T-type calcium channels, targeted by H(2) S, are involved in neuropathic hyperalgesia in rats and ascorbic acid inhibits Ca(v) 3.2 channels. Therefore, we evaluated the effects of intraplantar (i.pl.) administration of ascorbic acid or topical application of disodium isostearyl 2-O-L-ascorbyl phosphate (DI-VCP), a skin-permeable ascorbate derivative on hyperalgesia induced by NaHS, an H(2) S donor, and on neuropathic hyperalgesia.

EXPERIMENTAL APPROACH

In rats mechanical hyperalgesia was evoked by i.pl. NaHS, and neuropathic hyperalgesia was induced by L5 spinal nerve cutting (L5SNC) or by repeated administration of paclitaxel, an anti-cancer drug. Dermal ascorbic acid levels were determined colorimetrically.

KEY RESULTS

The NaHS-evoked Ca(v) 3.2 channel-dependent hyperalgesia was inhibited by co-administered ascorbic acid. Topical application of DI-VCP, but not ascorbic acid, prevented the NaHS-evoked hyperalgesia, and also increased dermal ascorbic acid levels. Neuropathic hyperalgesia induced by L5SNC or paclitaxel was reversed by i.pl. NNC 55-0396, a selective T-type calcium channel blocker, ascorbic acid or DI-VCP, and by topical DI-VCP, but not by topical ascorbic acid. The effects of i.pl. ascorbic acid and topical DI-VCP in the paclitaxel-treated rats were characterized by the faster onset and greater magnitude, compared with their effects in the L5SNC rats. Dermal ascorbic acid levels in the hindpaw significantly decreased after paclitaxel treatment, but not L5SNC, which was reversed by topical DI-VCP.

CONCLUSIONS AND IMPLICATIONS

Ascorbic acid, known to inhibit Ca(v) 3.2 channels, suppressed neuropathic hyperalgesia. DI-VCP ointment for topical application may be of benefit in the treatment of neuropathic pain.

The glial modulatory drug AV411 attenuates mechanical allodynia in rat models of neuropathic pain

Controlling neuropathic pain is an unmet medical need and we set out to identify new therapeutic candidates. AV411 (ibudilast) is a relatively nonselective phosphodiesterase inhibitor that also suppresses glial-cell activation and can partition into the CNS. Recent data strongly implicate activated glial cells in the spinal cord in the development and maintenance of neuropathic pain. We hypothesized that AV411 might be effective in the treatment of neuropathic pain and, hence, tested whether it attenuates the mechanical allodynia induced in rats by chronic constriction injury (CCI) of the sciatic nerve, spinal nerve ligation (SNL) and the chemotherapeutic paclitaxel (Taxol). Twice-daily systemic administration of AV411 for multiple days resulted in a sustained attenuation of CCI-induced allodynia. Reversal of allodynia was of similar magnitude to that observed with gabapentin and enhanced efficacy was observed in combination. We further show that multi-day AV411 reduces SNL-induced allodynia, and reverses and prevents paclitaxel-induced allodynia. Also, AV411 cotreatment attenuates tolerance to morphine in nerve-injured rats. Safety pharmacology, pharmacokinetic and initial mechanistic analyses were also performed. Overall, the results indicate that AV411 is effective in diverse models of neuropathic pain and support further exploration of its potential as a therapeutic agent for the treatment of neuropathic pain.

The maintenance of cisplatin- and paclitaxel-induced mechanical and cold allodynia is suppressed by cannabinoid CB₂ receptor activation and independent of CXCR4 signaling in models of chemotherapy-induced peripheral neuropathy

Background

Chemotherapeutic agents produce dose-limiting peripheral neuropathy through mechanisms that remain poorly understood. We previously showed that AM1710, a cannabilactone CB₂ agonist, produces antinociception without producing central nervous system (CNS)-associated side effects. The present study was conducted to examine the antinociceptive effect of AM1710 in rodent models of neuropathic pain evoked by diverse chemotherapeutic agents (cisplatin and paclitaxel). A secondary objective was to investigate the potential contribution of alpha-chemokine receptor (CXCR4) signaling to both chemotherapy-induced neuropathy and CB₂ agonist efficacy.

Results

AM1710 (0.1, 1 or 5 mg/kg i.p.) suppressed the maintenance of mechanical and cold allodynia in the cisplatin and paclitaxel models. Anti-allodynic effects of AM1710 were blocked by the CB₂ antagonist AM630 (3 mg/kg i.p.), but not the CB₁ antagonist AM251 (3 mg/kg i.p.), consistent with a CB₂-mediated effect. By contrast, blockade of CXCR4 signaling with its receptor antagonist AMD3100 (10 mg/kg i.p.) failed to attenuate mechanical or cold hypersensitivity induced by either cisplatin or paclitaxel. Moreover, blockade of CXCR4 signaling failed to alter the anti-allodynic effects of AM1710 in the paclitaxel model, further suggesting distinct mechanisms of action.

Conclusions

Our results indicate that activation of cannabinoid CB₂ receptors by AM1710 suppresses both mechanical and cold allodynia in two distinct models of chemotherapy-induced neuropathic pain. By contrast, CXCR4 signaling does not contribute to the maintenance of chemotherapy-induced established neuropathy or efficacy of AM1710. Our studies suggest that CB₂ receptors represent a promising therapeutic target for the treatment of toxic neuropathies produced by cisplatin and paclitaxel chemotherapeutic agents.

Effect of synthetic eel calcitonin, elcatonin, on cold and mechanical allodynia induced by oxaliplatin and paclitaxel in rats

Oxaliplatin and paclitaxel are commonly used anti-cancer drugs, but they frequently cause peripheral neuropathic pain. In this study, we investigated the effect of elcatonin, a synthetic eel calcitonin, on oxaliplatin- and paclitaxel-induced neuropathy in rats. The rats were treated with a single dose of oxaliplatin (6 mg/kg, i.p.) or repeated doses of paclitaxel (2 mg/kg, i.p.) on 4 alternate days. Both treatments resulted in cold and mechanical allodynia. We assessed the anti-allodynic effects of subcutaneously administered elcatonin (20 U/kg/day) by using a newly developed method to provide cold stimulation (8°C) directly to the hind paw of the rats and by using the von Frey test. Elcatonin almost completely reversed the effects of both cold and mechanical allodynia. To determine the mechanism of this anti-allodynic effect, we examined the effect of elcatonin on neuropathy induced by intraplantar injection of two organic compounds: allyl isothiocyanate (1 nmol/paw), which activates transient receptor potential ankyrin-1 channels, and menthol (1.28 μmol/paw), which activates transient receptor potential ankyrin-1 and melastatin-8. Pre-administration of elcatonin almost completely prevented cold and mechanical allodynia from being induced by both compounds. These results suggest that elcatonin attenuates oxaliplatin- and paclitaxel-induced neuropathic pain by inhibiting the cellular signaling related to transient receptor potential ankyrin-1 and melastatin-8. Thus, we conclude that administration of elcatonin may improve the quality of life of cancer patients receiving chemotherapy.

Neuropathic pain and reactive gliosis are reversed by dialdehydic compound in neuropathic pain rat models

The role of the purinergic system in the modulation of pain mechanisms suggests that it might be promising target for treating neuropathic pain. In this study we evaluated the effects of two different dialdehydic compounds: a modified stable adenosine (2-[1-(6-amminopurin-9-il)-2-osso-etossi]prop-2-enale, named MED1101), and oxidized ATP (Ox-ATP), in two different neuropathic pain rat models: the sciatic spared nerve injury (SNI) and paclitaxel evoked painful peripheral neuropathy (pPPN). Neuropathic animals were divided in groups as follows: (a) treated with intraperitoneal (i.p.) MED1101 or Ox-ATP for 21 days; (b) receiving vehicle (VEH) and (c) control (CTR) rats. The allodynic and hyperalgesic behavior was investigated by Von Frey filament test and thermal Plantar test, respectively. We evaluated by immunocytochemistry the astrocytic (GFAP) and microglial (Iba1) response on lumbar spinal cord sections. In either experimental models and using either substances, treated animals showed reduced allodynia and thermal hyperalgesia paralleled by a significant reduction of glial reaction in the spinal cord. These data prompt to hypothesize a potential role of dialdehydes as analgesic agent in chronic neuropathic pain and a possible role as anti-gliotic molecules.

Etodolac, a cyclooxygenase-2 inhibitor, attenuates paclitaxel-induced peripheral neuropathy in a mouse model of mechanical allodynia

The effect of the cyclooxygenase-2 (COX-2) inhibitor etodolac on the mechanical allodynia induced by paclitaxel was investigated in mice and compared with the effects of the nonselective COX inhibitors indomethacin and diclofenac, the selective COX-2 inhibitor celecoxib, the calcium channel α(2)δ subunit inhibitor pregabalin, the sodium channel blocker mexiletine, and the serotonin-norepinephrine reuptake inhibitor duloxetine. The decrease in the paw-withdrawal threshold induced by paclitaxel was reversed by oral administration of etodolac at 10 mg/kg but was not affected by indomethacin, diclofenac, or celecoxib. The antiallodynic effect of etodolac gradually increased during repeated administration, and after 2 weeks the paw-withdrawal threshold at the preadministration point was significantly increased. Pregabalin, duloxetine, and mexiletine also showed an antiallodynic effect in this model. Whereas pregabalin had a preadministration effect similar to that of etodolac during repeated administration, mexiletine or duloxetine had no such effect. There was almost no difference in the distribution of etodolac and diclofenac in nervous tissue, indicating that COX inhibition is unlikely to be involved in the antiallodynic effect of etodolac. Etodolac did not show a neuroprotective effect against morphological transformations such as the axonal degeneration induced by paclitaxel. Instead, etodolac probably acts at the level of functional changes accompanying paclitaxel treatment, such as alterations in the activation state of components of the pain transmission pathway. Our findings suggest that etodolac attenuates paclitaxel-induced peripheral neuropathy by a COX-independent pathway and that it might be useful for the treatment of paclitaxel-induced peripheral neuropathy.

Targeting the overproduction of peroxynitrite for the prevention and reversal of paclitaxel-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) accompanied by chronic neuropathic pain is a major dose-limiting side effect of a large number of antitumoral agents including paclitaxel (Taxol). Thus, CIPN is one of most common causes of dose reduction and discontinuation of what is otherwise a life-saving therapy. Neuropathological changes in spinal cord are linked to CIPN, but the causative mediators and mechanisms remain poorly understood. We report that formation of peroxynitrite (PN) in response to activation of nitric oxide synthases and NADPH oxidase in spinal cord contributes to neuropathological changes through two mechanisms. The first involves modulation of neuroexcitatory and proinflammatory (TNF-α and IL-1β) and anti-inflammatory (IL-10 and IL-4) cytokines in favor of the former. The second involves post-translational nitration and modification of glia-derived proteins known to be involved in glutamatergic neurotransmission (astrocyte-restricted glutamate transporters and glutamine synthetase). Targeting PN with PN decomposition catalysts (PNDCs) not only blocked the development of paclitaxel-induced neuropathic pain without interfering with antitumor effects, but also reversed it once established. Herein, we describe our mechanistic study on the role(s) of PN and the prevention of neuropathic pain in rats using known PNDCs (FeTMPyP(5+) and MnTE-2-PyP(5+)). We also demonstrate the prevention of CIPN with our two new orally active PNDCs, SRI6 and SRI110. The improved chemical design of SRI6 and SRI110 also affords selectivity for PN over other reactive oxygen species (such as superoxide). Our findings identify PN as a critical determinant of CIPN, while providing the rationale toward development of superoxide-sparing and "PN-targeted" therapeutics.

An inhibitor of neuronal exocytosis (DD04107) displays long-lasting in vivo activity against chronic inflammatory and neuropathic pain

Small peptides patterned after the N terminus of the synaptosomal protein of 25 kDa, a member of the protein complex implicated in Ca(2+)-dependent neuronal exocytosis, inhibit in vitro the release of neuromodulators involved in pain signaling, suggesting an in vivo analgesic activity. Here, we report that compound DD04107 (palmitoyl-EEMQRR-NH(2)), a 6-mer palmitoylated peptide that blocks the inflammatory recruitment of ion channels to the plasma membrane of nociceptors and the release of calcitonin gene-related peptide from primary sensory neurons, displays potent and long-lasting in vivo antihyperalgesia and antiallodynia in chronic models of inflammatory and neuropathic pain, such as the complete Freund's adjuvant, osteosarcoma, chemotherapy, and diabetic neuropathic models. Subcutaneous administration of the peptide produced a dose-dependent antihyperalgesic and antiallodynic activity that lasted ≥24 h. The compound showed a systemic distribution, characterized by a bicompartmental pharmacokinetic profile. Safety pharmacology studies indicated that the peptide is largely devoid of side effects and substantiated that the in vivo activity is not caused by locomotor impairment. Therefore, DD04107 is a potent and long-lasting antinociceptive compound that displays a safe pharmacological profile. These findings support the notion that neuronal exocytosis of receptors and neuronal algogens pivotally contribute to chronic inflammatory and neuropathic pain and imply a central role of peptidergic nociceptor sensitization to the pathogenesis of pain.

Controlling murine and rat chronic pain through A3 adenosine receptor activation

Clinical management of chronic neuropathic pain is limited by marginal effectiveness and unacceptable side effects of current drugs. We demonstrate A(3) adenosine receptor (A(3)AR) agonism as a new target-based therapeutic strategy. The development of mechanoallodynia in a well-characterized mouse model of neuropathic pain following chronic constriction injury of the sciatic nerve was rapidly and dose-dependently reversed by the A(3)AR agonists: IB-MECA, its 2-chlorinated analog (Cl-IB-MECA), and the structurally distinct MRS1898. These effects were naloxone insensitive and thus are not opioid receptor mediated. IB-MECA was ≥1.6-fold more efficacious than morphine and >5-fold more potent. In addition, IB-MECA was equally efficacious as gabapentin (Neurontin) or amitriptyline, but respectively >350- and >75-fold more potent. Besides its potent standalone ability to reverse established mechanoallodynia, IB-MECA significantly increased the antiallodynic effects of all 3 analgesics. Moreover, neuropathic pain development in rats caused by widely used chemotherapeutics in the taxane (paclitaxel), platinum-complex (oxaliplatin), and proteasome-inhibitor (bortezomib) classes was blocked by IB-MECA without antagonizing their antitumor effect. A(3)AR agonist effects were blocked with A(3)AR antagonist MRS1523, but not with A(1)AR (DPCPX) or A(2A)AR (SCH-442416) antagonists. Our findings provide the scientific rationale and pharmacological basis for therapeutic development of A(3)AR agonists for chronic pain.

Discovering cytokines as targets for chemotherapy-induced painful peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN), a dose-limiting neurotoxic effect of chemotherapy, is the most common reason for early cessation of cancer treatment. This can result in an increased risk of recurrence and decreased survival rate. Inflammatory cascade activation, proinflammatory cytokine upregulation, and neuro-immune communication pathways play essential roles in the initiation and progression of CIPN. Most notably, TNF-α, IL-1β, IL-6, and CCL2 are involved in neuropathic pain. Further elucidation of the role of these cytokines could lead to their development and use as biomarkers for predicting the onset of painful peripheral neuropathy and early axonal damage. In this review, we provide evidence for the involvement of cytokines in CIPN, the possible underlying mechanisms, and their use as potential therapeutic targets and biomarkers to prevent and improve the painful peripheral neuropathy related to chemotherapeutic agents.

Animal models of peripheral neuropathies

Peripheral neuropathies are common neurological diseases, and various animal models have been developed to study disease pathogenesis and test potential therapeutic drugs. Three commonly studied disease models with huge public health impact are diabetic peripheral neuropathy, chemotherapy-induced peripheral neuropathy, and human immunodeficiency virus-associated sensory neuropathies. A common theme in these animal models is the comprehensive use of pathological, electrophysiological, and behavioral outcome measures that mimic the human disease. In recent years, the focus has shifted to the use of outcome measures that are also available in clinical use and can be done in a blinded and quantitative manner. One such evaluation tool is the evaluation of epidermal innervation with a simple skin biopsy. Future clinical trials will be needed to validate the translational usefulness of this outcome measure and validation against accepted outcome measures that rely on clinical symptoms or examination findings in patients.

Evaluation of lercanidipine in Paclitaxel-induced neuropathic pain model in rat: a preliminary study

Objective. To demonstrate the antinociceptive effect of lercanidipine in paclitaxel-induced neuropathy model in rat. Materials and Methods. A total of 30 rats were divided into five groups of six rats in each group as follows: Gr I: 0.9% NaCl, Gr II: paclitaxel + 0.9% NaCl, Gr III: paclitaxel + lercanidipine 0.5 μg/kg, Gr IV: paclitaxel + lercanidipine 1 μg/kg, and Gr V: paclitaxel + lercanidipine 2.5 μg/kg. Paclitaxel-induced neuropathic pain in rat was produced by single intraperitoneal (i.p.) injection of 1 mg/kg of paclitaxel on four alternate days (0, 2, 4, and 6). The tail flick and cold allodynia methods were used for assessing the pain threshold, and the assessments were done on days 0 (before first dose of paclitaxel) and on days 7, 14, 21, and 28. Results. There was a significant decrease (P < 0.001) in the tail flick and cold allodynia latency in the paclitaxel-alone group from day 14 onward when compared with day 0. In the lercanidipine groups, the decrease in the tail flick and cold allodynia latency was not observed in 1.0 and 2.5 μg/kg groups and it was statistically significant (P < 0.01) when compared with paclitaxel-alone group.

Anti-nociceptive effect of kinin B₁ and B₂ receptor antagonists on peripheral neuropathy induced by paclitaxel in mice

BACKGROUND AND PURPOSE

In the current study, we investigated the role of both kinin B₁ and B₂ receptors in peripheral neuropathy induced by the chronic treatment of mice with paclitaxel a widely used chemotherapeutic agent.

EXPERIMENTAL APPROACH

Chemotherapy-evoked hyperalgesia was induced by i.p. injections of paclitaxel (2 mg·kg⁻¹) over 5 consecutive days. Mechanical and thermal hyperalgesia were evaluated between 7 and 21 days after the first paclitaxel treatment.

KEY RESULTS

Treatment with paclitaxel increased both mechanical and thermal hyperalgesia in mice (C57BL/6 and CD1 strains). Kinin receptor deficient mice (B₁, or B₂ receptor knock-out and B₁B₂ receptor, double knock-out) presented a significant reduction in paclitaxel-induced hypernociceptive responses in comparison to wild-type animals. Treatment of CD1 mice with kinin receptor antagonists (DALBK for B₁ or Hoe 140 for B₂ receptors) significantly inhibited both mechanical and thermal hyperalgesia when tested at 7 and 14 days after the first paclitaxel injection. DALBK and Hoe 140 were also effective against paclitaxel-induced peripheral neuropathy when given intrathecally or i.c.v. A marked increase in B₁ receptor mRNA was observed in the mouse thalamus, parietal and pre-frontal cortex from 7 days after the first paclitaxel treatment.

CONCLUSIONS AND IMPLICATIONS

Kinins acting on both B₁ and B₂ receptors, expressed in spinal and supra-spinal sites, played a crucial role in controlling the hypernociceptive state caused by chronic treatment with paclitaxel.

Prevention of paclitaxel-induced neuropathy through activation of the central cannabinoid type 2 receptor system

BACKGROUND

Peripheral neuropathy is a major dose-limiting toxicity of chemotherapy, especially after multiple courses of paclitaxel. The development of paclitaxel-induced neuropathy is associated with the activation of microglia followed by the activation and proliferation of astrocytes, and the expression and release of proinflammatory cytokines in the spinal dorsal horn. Cannabinoid type 2 (CB(2)) receptors are expressed in the microglia in neurodegenerative disease models.

METHODS

To explore the potential of CB(2) agonists for preventing paclitaxel-induced neuropathy, we designed and synthesized a novel CB(2)-selective agonist, namely, MDA7. The effect of MDA7 in preventing paclitaxel-induced allodynia was assessed in rats and in CB(2)(+/+) and CB(2)(-/-) mice. We hypothesized that the CB(2) receptor functions in a negative-feedback loop and that early MDA7 administration can blunt the neuroinflammatory response to paclitaxel and prevent mechanical allodynia through interference with specific signaling pathways.

RESULTS

We found that MDA7 prevents paclitaxel-induced mechanical allodynia in rats and mice in a dose- and time-dependent manner without compromising paclitaxel's antineoplastic effect. MDA7's neuroprotective effect was absent in CB(2)(-/-) mice and was blocked by CB(2) antagonists, suggesting that MDA7's action directly involves CB(2) receptor activation. MDA7 treatment was found to interfere with early events in the paclitaxel-induced neuroinflammatory response as evidenced by relatively reduced toll-like receptor and CB(2) expression in the lumbar spinal cord, reduced levels of extracellular signal-regulated kinase 1/2 activity, reduced numbers of activated microglia and astrocytes, and reduced secretion of proinflammatory mediators in vivo and in in vitro models.

CONCLUSIONS

Our findings suggest an innovative therapeutic approach to prevent chemotherapy-induced neuropathy and may permit more aggressive use of active chemotherapeutic regimens with reduced long-term sequelae.

Cannabinoid agonist WIN 55,212-2 prevents the development of paclitaxel-induced peripheral neuropathy in rats. Possible involvement of spinal glial cells

Spinal glial activation contributes to the development and maintenance of chronic pain states, including neuropathic pain of diverse etiologies. Cannabinoid compounds have shown antinociceptive properties in a variety of neuropathic pain models and are emerging as a promising class of drugs to treat neuropathic pain. Thus, the effects of repeated treatment with WIN 55,212-2, a synthetic cannabinoid agonist, were examined throughout the development of paclitaxel-induced peripheral neuropathy. Painful neuropathy was induced in male Wistar rats by intraperitoneal (i.p.) administration of paclitaxel (1mg/kg) on four alternate days. Paclitaxel-treated animals received WIN 55,212-2 (1mg/kg, i.p.) or minocycline (15 mg/kg, i.p.), a microglial inhibitor, daily for 14 days, simultaneous with the antineoplastic. The development of hypersensitive behaviors was assessed on days 1, 7, 14, 21 and 28 following the initial administration of drugs. Both the activation of glial cells (microglia and astrocytes) at day 29 and the time course of proinflammatory cytokine release within the spinal cord were also determined. Similar to minocycline, repeated administration of WIN 55,212-2 prevented the development of thermal hyperalgesia and mechanical allodynia in paclitaxel-treated rats. WIN 55,212-2 treatment also prevented spinal microglial and astrocytic activation evoked by paclitaxel at day 29 and attenuated the early production of spinal proinflammatory cytokines (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α). Our results confirm changes in the reactivity of glial cells during the development of peripheral neuropathy induced by paclitaxel and support a preventive effect of WIN 55,212-2, probably via glial cells reactivity inactivation, on the development of this neuropathy.

Evidence that spinal astrocytes but not microglia contribute to the pathogenesis of Paclitaxel-induced painful neuropathy

Paclitaxel often induces persistent painful neuropathy as its most common treatment-limiting side effect. Little is known concerning the underlying mechanisms. Given the prominent role of glial cells in many types of neuropathic pain, we investigated here the morphological and functional changes of spinal astrocytes and microglia in a rat model of paclitaxel-induced neuropathy. Immunohistochemistry, western blotting, and real-time polymerase chain reaction were performed with samples from 109 rats up to 28 days after paclitaxel treatment. Paclitaxel (2 mg/kg, i.p.) induced a rapid and persistent activation of spinal astrocytes assessed using glial fibrillary acidic protein, but not apparent activation of microglia assessed using OX42, Iba-1, and phosphorylated p38. In the context of astocyte activation, there was a significant downregulation of glial glutamate transporters GLAST and GLT-1 in spinal dorsal horn. The activation of spinal astrocytes by paclitaxel was not associated with expression of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, or interleukin-6 in spinal dorsal horn. Systemic treatment with minocycline (50 mg/kg, i.p.) prevented activation of astrocytes and downregulation of glial glutamate transporters in spinal dorsal horn induced by paclitaxel. These data suggest the involvement of spinal astrocytes but not microglia in the pathogenesis of paclitaxel-induced neuropathy.

PERSPECTIVE

Spinal astrocytes and/or glial glutamate transporters could be new therapeutic targets for paclitaxel-induced painful neuropathy.

Gender differences in paclitaxel-induced neuropathic pain behavior and analgesic response in rats

BACKGROUND

Females show greater sensitivity than males to several modalities of experimental pain. However, the gender differences in paclitaxel-induced neuropathic pain have not been studied. The current study examined the gender differences in neuropathic pain behavior and the effect of analgesics in a paclitaxel-induced neuropathic pain model in rats.

METHODS

Neuropathic pain was induced by intraperitoneal injection of paclitaxel (2 mg/kg) on 4 alternate days in Sprague-Dawley rats of both genders. Mechanical allodynia was measured using a von Frey filament. The gender differences in analgesic responses were determined after administration of morphine (2 or 5 mg/kg), ketamine (2 or 5 mg/kg), or combined morphine (2 mg/kg) and ketamine (2 mg/kg).

RESULTS

Paclitaxel induced mechanical allodynia, which began to manifest on day 4, peaked within 10 days, and plateaued for at least 2 months after the first paclitaxel injection. No gender difference in the manifestation of mechanical allodynia was observed. A 2 mg/kg dose of ketamine increased the mechanical threshold only in males. The 5 mg/kg dose of ketamine significantly increased the mechanical threshold in both genders. Morphine (2 and 5 mg/kg) dose-dependently increased the mechanical thresholds in both genders. The 2 mg/kg dose of ketamine enhanced the antinociceptive effect of 2 mg/kg morphine only in females.

CONCLUSIONS

No gender difference in paclitaxel-induced neuropathic pain or analgesic response to ketamine or morphine was observed in Sprague-Dawley rats. Low dose ketamine enhanced the analgesic effect of morphine on paclitaxel-induced mechanical allodynia but only in female rats.

Effects of mitochondrial poisons on the neuropathic pain produced by the chemotherapeutic agents, paclitaxel and oxaliplatin

The dose-limiting side effect of taxane, platinum-complex, and other kinds of anticancer drugs is a chronic, distal, bilaterally symmetrical, sensory peripheral neuropathy that is often accompanied by neuropathic pain. Work with animal models of these conditions suggests that the neuropathy is a consequence of toxic effects on mitochondria in primary afferent sensory neurons. If this is true, then additional mitochondrial insult ought to make the neuropathic pain worse. This prediction was tested in rats with painful peripheral neuropathy due to the taxane agent, paclitaxel, and the platinum-complex agent, oxaliplatin. Rats with established neuropathy were given 1 of 3 mitochondrial poisons: rotenone (an inhibitor of respiratory Complex I), oligomycin (an inhibitor of adenosine triphosphate synthase), and auranofin (an inhibitor of the thioredoxin-thioredoxin reductase mitochondrial antioxidant defense system). All 3 toxins significantly increased the severity of paclitaxel-evoked and oxaliplatin-evoked mechano-allodynia and mechano-hyperalgesia while having no effect on the mechano-sensitivity of chemotherapy-naïve rats. Chemotherapy-evoked painful peripheral neuropathy is associated with an abnormal spontaneous discharge in primary afferent A fibers and C fibers. Oligomycin, at the same dose that exacerbated allodynia and hyperalgesia, significantly increased the discharge frequency of spontaneously discharging A fibers and C fibers in both paclitaxel-treated and oxaliplatin-treated rats, but did not evoke any discharge in naïve control rats. These results implicate mitochondrial dysfunction in the production of chemotherapy-evoked neuropathic pain and suggest that drugs that have positive effects on mitochondrial function may be of use in its treatment and prevention.