Intrathecal ziconotide in the treatment of refractory pain in patients with cancer or AIDS: a randomized controlled trial

A perspective on toxicology of Conus venom peptides

The evolutionarily unique and ecologically diverse family Conidae presents fundamental opportunities for marine pharmacology research and drug discovery. The focus of this investigation is to summarize the worldwide distribution of Conus and their species diversity with special reference to the Indian coast. In addition, this study will contribute to understanding the structural properties of conotoxin and therapeutic application of Conus venom peptides. Cone snails can inject a mix of various conotoxins and these venoms are their major weapon for prey capture, and may also have other biological purposes, and some of these conotoxins fatal to humans. Conus venoms contain a remarkable diversity of pharmacologically active small peptides; their targets are an iron channel and receptors in the neuromuscular system. Interspecific divergence is pronounced in venom peptide genes, which is generally attributed to their species specific biotic interactions. There is a notable interspecific divergence observed in venom peptide genes, which can be justified as of biotic interactions that stipulate species peculiar habitat and ecology of cone snails. There are several conopeptides used in clinical trials and one peptide (Ziconotide) has received FDA approval for treatment of pain. This perspective provides a comprehensive overview of the distribution of cone shells and focus on the molecular approach in documenting their taxonomy and diversity with special reference to geographic distribution of Indian cone snails, structure and properties of conopeptide and their pharmacological targets and future directions.

Ziconotide Trialing by Intrathecal Bolus Injections: An Open-Label Non-Randomized Clinical Trial in Postoperative/Posttraumatic Neuropathic Pain Patients Refractory to Conventional Treatment

OBJECTIVES

The aim of this open-label, non-randomized, clinical trial was to evaluate the feasibility of trialing ziconotide by intrathecal bolus injections.

MATERIAL AND METHODS

Twenty-three patients, who had peripheral neuropathic pain refractory to pharmacological treatment and were under consideration for Spinal Cord Stimulation, received up to three ziconotide bolus injections according to a comprehensive algorithm. After a first injection of 2.5 μg, the patients progressed in the algorithm depending on the presence or absence of pain reduction and significant adverse events. A patient was considered a "responder" if experiencing pain reduction and no significant adverse event on two consecutive occasions at the same dosage.

RESULTS

We found a low proportion of responders (13%). However 30% of patients experienced ≥30% pain reduction on a least one injection, yielding a number needed to treat of ∼3 for clinically significant pain relief. Pain intensity changed significantly over time (0-6 h) (p = 0.047) after a mean ziconotide dose of 2.75 μg. Adverse events were as expected, and no serious adverse event occurred. We did not find any statistical association between response to Spinal Cord Stimulation and response to ziconotide.

CONCLUSIONS

Ziconotide bolus injection trialing seems feasible, but the proportion of responders in the present study was low. Adverse events were as expected, and no serious adverse event occurred. The predictive power of ziconotide bolus trialing remains unclear, and the pharmacological profile of ziconotide (slow tissue penetration due to high hydrophilicity) calls the rationale for bolus trialing into question.

Neurobiological studies of chronic pain and analgesia: Rationale and refinements

Chronic pain is a complex condition for which the need for specialized research and therapies has been recognized internationally. This review summarizes the context for the international call for expansion of pain research to improve our understanding of the mechanisms underlying pain in order to achieve improvements in pain management. The methods for conducting sensory assessment in animal models are discussed and the development of animal models of chronic pain is specifically reviewed, with an emphasis on ongoing refinements to more closely mimic a variety of human pain conditions. Pharmacological correspondences between pre-clinical pain models and the human clinical experience are noted. A discussion of the 3Rs Framework (Replacement, Reduction, Refinement) and how each may be considered in pain research is featured. Finally, suggestions are provided for engaging principal investigators, IACUC reviewers, and institutions in the development of strong partnerships to simultaneously expand our knowledge of the mechanisms underlying pain and analgesia while ensuring the humane use of animals in research.

Intrathecal Pharmacology Update: Novel Dosing Strategy for Intrathecal Monotherapy Ziconotide on Efficacy and Sustainability

INTRODUCTION

Intrathecal drug delivery is a well-defined strategy to treat malignant and nonmalignant pain. Ziconotide is a well-studied intrathecal medicine option that has many attractive qualities, as it is non-granulomagenic, overdose or underdose is not associated with cardiopulmonary compromise or death, and is a non-opoid analgesic. However, it has had slow adoption into pain care algorithms because it has been historically plagued with the connotation of having a narrow therapeutic window and a low sustainability rate. We introduce a novel dosing strategy to improve patient outcomes and sustainability.

METHODS

Patients were identified as being an intrathecal candidate and trialed with ziconotide based on the current standard of care. Patient demographics, diagnosis, previous treatment failures, and pre-implant visual analog scale (VAS) scores were recorded. Once the trial was deemed successful, based on the dual bolusing strategy, the patient underwent device implantation. Consecutive patients were prospectively followed. Ziconotide was then initiated with a flex dosing strategy, weighted during nocturnal dosing. Outcome endpoints included: reduction in VAS, side effects, durability of therapy, and systemic opioid use prior to implant and at last visit were noted (calculated to daily morphine equivalents). Primary endpoint was tolerability of ziconotide at three months following new dosing strategy. No industry support or funding was obtained for this project.

RESULTS

All enrolled patients met the endpoint of the study of tolerability of ziconotide at three months. Numbers declined to 75% of patients at four months, and 70% of patients at six months. The discontinuing side-effects were most commonly urinary retention and visual hallucinations. There were no serious adverse events and no unresolved complications reported. Numerical rating scale (NRS) decreased on average from 9.06 to 1.8. Opioid reduction in morphine equivalents averaged 91.5%

DISCUSSION

The efficacy and tolerability of monotherapy ziconotide may be improved by using a weighted bolus flex dosing strategy as compared with slow continuous infusions.

CONCLUSION

We present a novel strategy to deliver ziconotide using a unique continuous infusion flex dosing strategy. Further randomized, prospective, higher-powered studies are needed to critically evaluate the conclusions suggested by this limited prospective case series.

Ziconotide Combination Intrathecal Therapy for Noncancer Pain Is Limited Secondary to Delayed Adverse Effects: A Case Series With a 24-Month Follow-Up

OBJECTIVES

The efficacy and safety of ziconotide as a single agent has been evaluated in few short-term clinical trials and open-label studies. Ziconotide use is challenging given its adverse effect (AE) profile. The objective of this study is to describe the long-term efficacy and AEs of ziconotide used as an adjunct to other intrathecal (IT) agents in chronic noncancer pain patients.

MATERIALS AND METHODS

A case series of chronic noncancer pain patients who had suboptimal pain control from IT therapy. Ziconotide was introduced in the IT infusion mixture after a successful ziconotide trial. Pain scores, IT doses, as well as AEs were recorded and analyzed from trial to initial ziconotide infusion and up to 24 months.

RESULTS

Fifteen patients underwent ziconotide trials. Four subjects failed the trial, and 11 proceeded to continuous ziconotide treatment. Seven out of 11 patients experienced AEs resulting in ziconotide discontinuation. Two of the seven subjects who required discontinuation of ziconotide had improved pain. Four subjects were able to continue IT ziconotide through 24 months.

CONCLUSIONS

A high incidence of AEs limits the usefulness of IT ziconotide as adjunct therapy. Our results are limited by the size of our patient population; however, they represent a long follow-up period, which is limited in most current publications on this IT peptide. While ziconotide is a needed IT agent, more studies are necessary to better understand the factors that would improve the treatment to trial ratio as well as the long-term efficacy of IT ziconotide treatment.

The Relationship Between the Mechanisms of Action and Safety Profiles of Intrathecal Morphine and Ziconotide: A Review of the Literature

OBJECTIVE

To better characterize safety profiles associated with the intrathecal (IT) administration of morphine and ziconotide and discuss how they relate to mechanisms of action.

METHODS

Published data were evaluated to identify potential relationships between safety profiles of IT morphine and IT ziconotide and their mechanisms of action.

RESULTS

Potentially severe and clinically relevant adverse events (AEs) associated with IT morphine include respiratory depression, tolerance, and granuloma formulation, whereas IT ziconotide is associated with neuropsychiatric AEs, such as cognitive impairment, hallucinations, and changes in mood or consciousness, particularly with high doses and rapid titration. AEs associated with these IT therapies may result from spread of the medication out of the IT space into areas of the central and peripheral nervous systems and systemic circulation. AEs that occur usually can be managed and, in some cases, prevented. To mitigate risk, patients' histories should be reviewed to identify potential complicating factors (e.g., obesity or other risk factors for respiratory dysfunction in patients receiving IT morphine; a history of psychosis in patients receiving IT ziconotide). Also, treatment should be initiated at a low dose, titrated slowly, and patients should be closely monitored during treatment.

CONCLUSIONS

IT morphine and IT ziconotide are approved by the US Food and Drug Administration for patients who do not respond to less invasive treatments, but the safety profiles of each may make them more or less appropriate for certain patient populations.

Ziconotide-induced psychosis: a case report

Ziconotide is used intrathecally in the management of severe chronic pain that contains a warning against neuropsychiatric adverse events. The definition of psychiatric events is broad and management strategies are vague. This case report describes a 49-year-old female who was admitted to the acute psychiatric unit to address auditory hallucinations and paranoid ideation persisting for 3 weeks. Approximately 3 months ago, an intrathecal pump with ziconotide was implanted to treat pain. Upon hospital admission, the pump was infusing at a rate of 4.9 mcg/24 hours. Because the drug could not be immediately discontinued, risperidone 0.5 mg nightly was initiated and subsequently, the pump was drained of ziconotide, rinsed, and refilled with normal saline. The patient reported no hallucinations or apparent delusions several hours later and was eventually discharged with resolution of psychotic symptoms and continuation of risperidone for 10 days. Despite the identification of neuropsychiatric effects, limited information is available to characterize the presentation and guide specific management aside from recommendations to discontinue the infusion and possible use of psychotropic medications or necessity for hospitalization. This case report characterizes one presentation of hallucinations and paranoia associated with ziconotide intrathecal infusion. Clinicians should be aware of the management strategies to mediate these adverse effects, including expected time to adverse effect resolution, removal of ziconotide from the pump, and role for short-term use of antipsychotics.

Helminthes and insects: maladies or therapies

By definition, parasites cause harm to their hosts. But, considerable evidence from ancient traditional medicine has supported the theory of using parasites and their products in treating many diseases. Maggots have been used successfully to treat chronic, long-standing, infected wounds which failed to respond to conventional treatment by many beneficial effects on the wound including debridement, disinfection, and healing enhancement. Maggots are also applied in forensic medicine to estimate time between the death and discovery of a corpse and in entomotoxicology involving the potential use of insects as alternative samples for detecting drugs and toxins in death investigations. Leeches are segmented invertebrates, famous by their blood-feeding habits and used in phlebotomy to treat various ailments since ancient times. Leech therapy is experiencing resurgence nowadays in health care principally in plastic and reconstructive surgery. Earthworms provide a source of medicinally useful products with potential antimicrobial, antiviral, and anticancer properties. Lumbrokinases are a group of fibrinolytic enzymes isolated and purified from earthworms capable of degrading plasminogen-rich and plasminogen-free fibrin and so can be used to treat various conditions associated with thrombotic diseases. Helminth infection has been proved to have therapeutic effects in both animal and human clinical trials with promising evidence in treating many allergic diseases and can block the induction of or reduce the severity of some autoimmune disorders as Crohn's disease or ulcerative colitis. What is more, venomous arthropods such as scorpions, bees, wasps, spiders, ants, centipedes, snail, beetles, and caterpillars. The venoms and toxins from these arthropods provide a promising source of natural bioactive compounds which can be employed in the development of new drugs to treat diseases as cancer. The possibility of using these active molecules in biotechnological processes can make these venoms and toxins a valuable and promising source of natural bioactive compounds. The therapeutic use of helminthes and insects will be of great value in biomedicine and further studies on insect toxins will contribute extensively to the development of Biomedical Sciences.

Practical considerations and patient selection for intrathecal drug delivery in the management of chronic pain

Chronic pain continues to pose substantial and growing challenges for patients, caregivers, health care professionals, and health care systems. By the time a patient with severe refractory pain sees a pain specialist for evaluation and management, that patient has likely tried and failed several nonpharmacologic and pharmacologic approaches to pain treatment. Although relegated to one of the interventions of "last resort", intrathecal drug delivery can be useful for improving pain control, optimizing patient functionality, and minimizing the use of systemic pain medications in appropriately selected patients. Due to its clinical and logistical requirements, however, intrathecal drug delivery may fit poorly into the classic pain clinic/interventional model and may be perceived as a "critical mass" intervention that is feasible only for large practices that have specialized staff and appropriate office resources. Potentially, intrathecal drug delivery may be more readily adopted into larger practices that can commit the necessary staff and resources to support patients' needs through the trialing, initiation, monitoring, maintenance, and troubleshooting phases of this therapy. Currently, two agents - morphine and ziconotide - are approved by the United States Food and Drug Administration for long-term intrathecal delivery. The efficacy and safety profiles of morphine have been assessed in long-term, open-label, and retrospective studies of >400 patients with chronic cancer and noncancer pain types. The efficacy and safety profiles of ziconotide have been assessed in three double-blind, placebo-controlled trials of 457 patients, and safety has been assessed in 1,254 patients overall, with severe chronic cancer, noncancer, and acquired immunodeficiency syndrome pain types. Both agents are highlighted as first-line intrathecal therapy for the management of neuropathic or nociceptive pain. The purpose of this review is to discuss practical considerations for intrathecal drug delivery, delineate criteria for the identification and selection of candidates for intrathecal drug delivery, and consider which agent may be more appropriate for individual patients.

Current perspectives on intrathecal drug delivery

Advances in intrathecal analgesia and intrathecal drug delivery systems have allowed for a range of medications to be used in the control of pain and spasticity. This technique allows for reduced medication doses that can decrease the side effects typically associated with oral or parenteral drug delivery. Recent expert panel consensus guidelines have provided care paths in the treatment of nociceptive, neuropathic, and mixed pain syndromes. While the data for pain relief, adverse effect reduction, and cost-effectiveness with cancer pain control are compelling, the evidence is less clear for noncancer pain, other than spasticity. Physicians should be aware of mechanical, pharmacological, surgical, and patient-specific complications, including possible granuloma formation. Newer intrathecal drug delivery systems may allow for better safety and quality of life outcomes.

Characterization of the triazine, T4, a representative from a novel series of CaV2 inhibitors with strong state-dependence, poor use-dependence, and distinctively fast kinetics

There is strong pharmacological, biological, and genetic evidence supporting the role of N-type calcium channels (CaV2.2) in nociception. There is also human validation data from ziconotide, the CaV2.2-selective peptidyl inhibitor used clinically to treat refractory pain. Unfortunately, ziconotide utility is limited by its narrow therapeutic window and required intrathecal route of administration. A major focus has been placed on identifying state-dependent CaV2.2 inhibitors to improve safety margins. Much less attention, however, has been given to characterizing the kinetics of CaV2.2 inhibitors as a means to further differentiate compounds and maximize therapeutic potential. Here we provide a detailed characterization of the CaV2.2 inhibitor T4 in terms of its state-dependence, use-dependence, kinetics, and mechanism of inhibition. Compound T4 displayed a >20-fold difference in potency when measured under inactivating conditions (IC50=1.1 μM) as compared to closed-state conditions (IC50=25 μM). At 3 μM, T4 produced a 15-fold hyperpolarizing shift in the inactivation curve for CaV2.2 while having no effect on channel activation. To assess the kinetic properties of T4 in a more physiological manner, its inhibition kinetics were assessed at 32°C using 2 mM Ca(2+) as the charge carrier. Surprisingly, the repriming rate for CaV2.2 channels at hyperpolarized potentials was similar in both the presence and absence of T4. This was in contrast to other compounds which markedly delayed repriming. Furthermore, T4 inhibited CaV2.2 channels more potently when channel inactivation was driven through a tonic sub-threshold depolarization rather than through a use-dependent protocol, despite similar levels of inactivation.

A pain research agenda for the 21st century

Chronic pain represents an immense clinical problem. With tens of millions of people in the United States alone suffering from the burden of debilitating chronic pain, there is a moral obligation to reduce this burden by improving the understanding of pain and treatment mechanisms, developing new therapies, optimizing and testing existing therapies, and improving access to evidence-based pain care. Here, we present a goal-oriented research agenda describing the American Pain Society's vision for pain research aimed at tackling the most pressing issues in the field.

PERSPECTIVE

This article presents the American Pain Society's view of some of the most important research questions that need to be addressed to advance pain science and to improve care of patients with chronic pain.

α9-nicotinic acetylcholine receptors contribute to the maintenance of chronic mechanical hyperalgesia, but not thermal or mechanical allodynia

Background

The current pharmacological treatments for chronic pain are limited. The first analgesic drug approved for clinical use in decades that has a novel molecular target is the synthetic version of a naturally occurring conotoxin. Several conotoxins that target ion channels have progressed to clinical trials for the relief of pain. Vc1.1 and RgIA are analgesic α-conotoxins that target α9-subunit-containing nicotinic acetylcholine receptors (α9-nAChR) as well as GABA_B receptor mechanisms. However, the evidence for the involvement of α9-nAChRs in pain is controversial. In the present study, the role of the α9-nAChR in pain was assessed using a battery of behavioural pain tests and pain models in α9-nAChR knockout (KO) mice.

Results

α9-nAChR KO mice showed normal responses to acute noxious thermal and mechanical stimuli, and developed normal chronic cold and mechanical allodynia in inflammatory and nerve injury pain models. However, KO animals developed mechanical hyperalgesia to a lesser extent than their wild type (WT) counterparts in both inflammatory and neuropathic pain models. Chronic neuropathic pain is sustained in WT mice for at least 21 days post injury, while KO mice show significant recovery by 14 days post injury. KO sham mice were also resistant to the repeated-measures effect of the noxious pain test that caused a gradual onset of mild mechanical hyperalgesia in WT sham animals.

Conclusions

The α9-nAChR is not involved in acute pain perception or chronic thermal or mechanical allodynia or thermal hyperalgesia but does contribute to the intensity and duration of chronic mechanical hyperalgesia, suggesting that pain-relieving actions of antagonists that target this site may be restricted to high threshold mechanosensation. The α9-nAChR appears to be a valid target for pharmacological compounds that alleviate long-term mechanical hyperalgesia and may be of use as a prophylactic drug to prevent the development of some symptoms of chronic pain.

Pharmacological management of central post-stroke pain: a practical guide

Pain is one of the most troublesome sequelae of stroke. Some of this post-stroke pain is caused by the brain lesion itself; this is called central post-stroke pain (CPSP). Although the prevalence of CPSP is low (1-8 %), persistent, often treatment-resistant, painful sensations are a major problem for stroke patients. The pathogenesis of CPSP remains unknown, but suggested underlying causes include hyperexcitation in the damaged sensory pathways, damage to the central inhibitory pathways, or a combination of the two. For pharmacological treatment, amitriptyline, an adrenergic antidepressant, is currently the first-line drug for CPSP. However, its effect is frequently incomplete and a high dose is commonly not tolerated in stroke patients. Lamotrigine, an antiepileptic, was also found to be effective in a controlled trial and can be used as an alternative or additive therapy. GABAergic drugs with potential calcium channel-blocking effects, such as gabapentin or pregabalin, have recently emerged as a potentially useful therapy. These drugs are effective in various neuropathic pain syndromes, but their effect on CPSP remains to be proven. Pregabalin may improve pain-related anxiety and sleep disturbances. Fluvoxamine and mexiletine may be used adjunctively in some patients. Non-pharmacological treatments such as motor cortex stimulation or deep brain stimulation are used in some centers, but are not proven to be effective. Further well designed clinical trials as well as basic research should be performed to improve our understanding of the pathophysiology of CPSP and to develop better treatment strategies.

Pain in the cancer patient: different pain characteristics CHANGE pharmacological treatment requirements

Twenty years ago, the main barriers to successful cancer pain management were poor assessment by physicians, and patients' reluctance to report pain and take opioids. Those barriers are almost exactly the same today. Cancer pain remains under-treated; in Europe, almost three-quarters of cancer patients experience pain, and almost a quarter of those with moderate to severe pain do not receive any analgesic medication. Yet it has been suggested that pain management could be improved simply by ensuring that every consultation includes the patient's rating of pain, that the physician pays attention to this rating, and a plan is agreed to increase analgesia when it is inadequate. After outlining current concepts of carcinogenesis in some detail, this paper describes different methods of classifying and diagnosing cancer pain and the extent of current under-treatment. Key points are made regarding cancer pain management. Firstly, the pain may be caused by multiple different mechanisms and therapy should reflect those underlying mechanisms - rather than being simply based on pain intensity as recommended by the WHO three-step ladder. Secondly, a multidisciplinary approach is required which combines both pharmacological and non-pharmacological treatment, such as psychotherapy, exercise therapy and electrostimulation. The choice of analgesic agent and its route of administration are considered, along with various interventional procedures and the requirements of palliative care. Special attention is paid to the treatment of breakthrough pain (particularly with fast-acting fentanyl formulations, which have pharmacokinetic profiles that closely match those of breakthrough pain episodes) and chemotherapy-induced neuropathic pain, which affects around one third of patients who receive chemotherapy. Finally, the point is made that medical education should place a greater emphasis on pain therapy, both at undergraduate and postgraduate level.

Phα1β, a peptide from the venom of the spider Phoneutria nigriventer shows antinociceptive effects after continuous infusion in a neuropathic pain model in rats

BACKGROUND

Neuropathic pain is a severe painful pathology that is difficult to treat. One option for its management is the continuous intrathecal (i.t.) infusion of ziconotide (the Conus magnus peptide ω-conotoxin MVIIA), which, in addition to being effective, produces serious adverse effects at analgesic doses. Single i.t. administration of Phα1β, a peptide purified from the venom of the spider Phoneutria nigriventer, has antinociceptive effects with a greater therapeutic window than ziconotide in rodents. To further evaluate its analgesic potential, we investigated the antinociceptive and toxic effects of Phα1β after single or continuous i.t. infusion in a rat model of neuropathic pain.

METHODS

Adult male Wistar rats (200-300 g) bred in-house were used. Chronic constriction injury (CCI) of the sciatic nerve was used as the neuropathic pain model. Nociception was assessed by detecting mechanical hyperalgesia, considering a significant reduction in 50% paw withdrawal threshold values after CCI compared with baseline values. First, we assessed the antinociceptive effect of a single i.t. injection of Phα1β (10, 30, or 100 pmol/site) in a model of neuropathic pain 8 days after nerve injury. In a different experiment, we delivered Phα1β (60 pmol/μL/h) or vehicle (phosphate-buffered saline, 1.0 μL/h) through continuous infusion using an osmotic pump by spinal catheterization for 7 days in rats submitted to nerve injury. Behavioral adverse effects were evaluated after single or continuous Phα1β i.t. administration, and histopathological analysis of spinal cord, brainstem, and encephalon was performed after continuous Phα1β i.t. injection.

RESULTS

We observed that CCI of the sciatic nerve but not sham surgery caused intense (reduction of approximately 2.5 times in mechanical withdrawal threshold) and persistent (up to 14 days) nociception in rats. The single i.t. injection of Phα1β (30 or 100 pmol/site) reduced neuropathic nociception from 1 to 6 hours after administration, without showing detectable side effects. Similarly, the continuous infusion of Phα1β (60 pmol/μL/h for 7 days) was also able to reverse nerve injury-induced nociception from 1 to 7 days, but did not cause either behavioral side effects or histopathological changes in the central nervous system.

CONCLUSIONS

Thus, we have shown for the first time that the continuous i.t. delivery of Phα1β produces analgesia disconnected from toxicity in a relevant model of neuropathic pain, indicating that it is an effective and safe drug with a great potential to treat pain.

Intrathecal pain pumps: indications, patient selection, techniques, and outcomes

Intrathecal drug delivery represents an advanced modality for refractory chronic pain patients as well as intractable spasticity. This article reviews the advantages and indications for intrathecal therapy, as well as recommendations for proper patient selection using a multidisciplinary team to provide a global assessment of the impact of chronic pain on the patient's well-being. The goals and expectations of trialing are discussed alongside advantages and disadvantages of several trialing techniques. A discussion of outcomes is presented for patients with chronic pain due to both malignant and nonmalignant causes.

Channelrhodopsin-2-expressed dorsal root ganglion neurons activates calcium channel currents and increases action potential in spinal cord

STUDY DESIGN

We used optogenetic techniques in spinal cord and dorsal root ganglion (DRG) neuron studies.

OBJECTIVE

This study investigated changes in channelrhodopsin-2 (ChR2) expression in the spinal cord and DRG neurons using optogenetic techniques. The results show the possibility of using optogenetics to treat neuropathic pain.

SUMMARY OF BACKGROUND DATA

Previous studies have shown that activated ChR2 induces an increase in DRG neuron action potential.

METHODS

Western blot analysis was used to measure ChR2 protein levels in the spinal cord and DRG neurons or rats intrathecally injected with ChR2 lentivirus. Electrophysiology recording was used to detect differences in action potential levels in the spinal cord and calcium channel currents in the DRG neurons.

RESULTS

Our studies showed that ChR2 expression increased the action potential in the spinal cord and increased calcium channel currents in DRG neurons.

CONCLUSION

We successfully expressed the ChR2 protein in the spinal cord and DRG neurons. We also found that ChR2 increased the action potential in the spinal cord and activated the calcium channel in DRG neurons. These findings support the research possibilities of using optogenetic studies to improve treatment for neuropathic pain.

LEVEL OF EVIDENCE

N/A.

N-type calcium current, Cav2.2, is enhanced in small-diameter sensory neurons isolated from Nf1+/- mice

Major aspects of neuronal function are regulated by Ca(2+) including neurotransmitter release, excitability, developmental plasticity, and gene expression. We reported previously that sensory neurons isolated from a mouse model with a heterozygous mutation of the Nf1 gene (Nf1+/-) exhibited both greater excitability and evoked release of neuropeptides compared to wildtype mice. Furthermore, augmented voltage-dependent sodium currents but not potassium currents contribute to the enhanced excitability. To determine the mechanisms giving rise to the enhanced release of substance P and calcitonin gene-related peptide in the Nf1+/- sensory neurons, the potential differences in the total voltage-dependent calcium current (ICa) as well as the contributions of individual Ca(2+) channel subtypes were assessed. Whole-cell patch-clamp recordings from small-diameter capsaicin-sensitive sensory neurons demonstrated that the average peak ICa densities were not different between the two genotypes. However, by using selective blockers of channel subtypes, the current density of N-type (Cav2.2) ICa was significantly larger in Nf1+/- neurons compared to wildtype neurons. In contrast, there were no significant differences in L-, P/Q- and R-type currents between the two genotypes. Quantitative real-time polymerase chain reaction measurements made from the isolated but intact dorsal root ganglia indicated that N-type (Cav2.2) and P/Q-type (Cav2.1) Ca(2+) channels exhibited the highest mRNA expression levels although there were no significant differences in the levels of mRNA expression between the genotypes. These results suggest that the augmented N-type (Cav2.2) ICa observed in the Nf1+/- sensory neurons does not result from genomic differences but may reflect post-translational or some other non-genomic modifications. Thus, our results demonstrate that sensory neurons from Nf1+/- mice, exhibit increased N-type ICa and likely account for the increased release of substance P and calcitonin gene-related peptide that occurs in Nf1+/- sensory neurons.

The use of combined spinal-epidural technique to compare intrathecal ziconotide and epidural opioids for trialing intrathecal drug delivery

SUMMARY Choosing the initial medications for intrathecal delivery is often confusing and not standardized. We describe a novel way for using a combined spinal-epidural technique to compare two first-line medications for intrathecal delivery; ziconotide and morphine (or hydromorphone). Five patients with intractable chronic or cancer pain were elected to have an intrathecal drug delivery system implanted for pain management. Each patient was given a 3-day inpatient trial with the combined spinal-epidural technique. The Visual Analog Scale, Numerical Rating Scale, short-term McGill questionnaire and opioid consumption were monitored daily. The results were used to develop a paradigm to describe how ziconotide can be used in practice.

Neuropathic cancer pain: What we are dealing with? How to manage it?

Cancer pain is a serious health problem, and imposes a great burden on the lives of patients and their families. Pain can be associated with delay in treatment, denial of treatment, or failure of treatment. If the pain is not treated properly it may impair the quality of life. Neuropathic cancer pain (NCP) is one of the most complex phenomena among cancer pain syndromes. NCP may result from direct damage to nerves due to acute diagnostic/therapeutic interventions. Chronic NCP is the result of treatment complications or malignancy itself. Although the reason for pain is different in NCP and noncancer neuropathic pain, the pathophysiologic mechanisms are similar. Data regarding neuropathic pain are primarily obtained from neuropathic pain studies. Evidence pertaining to NCP is limited. NCP due to chemotherapeutic toxicity is a major problem for physicians. In the past two decades, there have been efforts to standardize NCP treatment in order to provide better medical service. Opioids are the mainstay of cancer pain treatment; however, a new group of therapeutics called coanalgesic drugs has been introduced to pain treatment. These coanalgesics include gabapentinoids (gabapentin, pregabalin), antidepressants (tricyclic antidepressants, duloxetine, and venlafaxine), corticosteroids, bisphosphonates, N-methyl-D-aspartate antagonists, and cannabinoids. Pain can be encountered throughout every step of cancer treatment, and thus all practicing oncologists must be capable of assessing pain, know the possible underlying pathophysiology, and manage it appropriately. The purpose of this review is to discuss neuropathic pain and NCP in detail, the relevance of this topic, clinical features, possible pathology, and treatments of NCP.

Action of Phα1β, a peptide from the venom of the spider Phoneutria nigriventer, on the analgesic and adverse effects caused by morphine in mice

Opioids are standard therapy for the treatment of pain; however, adverse effects limit their use. Voltage-gated calcium channel blockers may be used to increase opioid analgesia, but their effect on opioid-induced side effects is little known. Thus, the goal of this study was to evaluate the action of the peptide Phα1β, a voltage-gated calcium channel blocker, on the antinociceptive and adverse effects produced by morphine in mice. A single administration of morphine (3-10 mg/kg) was able to reduce heat nociception as well as decrease gastrointestinal transit. The antinociception caused by a single injection of morphine was slightly increased by an intrathecal injection of Phα1β (30 pmol/site). Repeated treatment with morphine caused tolerance, hyperalgesia, withdrawal syndrome, and constipation, and the Phα1β (.1-30 pmol/site, intrathecal) was able to reverse these effects. Finally, the effects produced by the native form of Phα1β were fully mimicked by a recombinant version of this peptide. Taken together, these data show that Phα1β was effective in potentiating the analgesia caused by a single dose of morphine as well as in reducing tolerance and the adverse effects induced by repeated administration of morphine, indicating its potential use as an adjuvant drug in combination with opioids.

PERSPECTIVE

This article presents preclinical evidence for a useful adjuvant drug in opioid treatment. Phα1β, a peptide calcium channel blocker, could be used not only to potentiate morphine analgesia but also to reduce the adverse effects caused by repeated administration of morphine.

Calcium-permeable ion channels in pain signaling

The detection and processing of painful stimuli in afferent sensory neurons is critically dependent on a wide range of different types of voltage- and ligand-gated ion channels, including sodium, calcium, and TRP channels, to name a few. The functions of these channels include the detection of mechanical and chemical insults, the generation of action potentials and regulation of neuronal firing patterns, the initiation of neurotransmitter release at dorsal horn synapses, and the ensuing activation of spinal cord neurons that project to pain centers in the brain. Long-term changes in ion channel expression and function are thought to contribute to chronic pain states. Many of the channels involved in the afferent pain pathway are permeable to calcium ions, suggesting a role in cell signaling beyond the mere generation of electrical activity. In this article, we provide a broad overview of different calcium-permeable ion channels in the afferent pain pathway and their role in pain pathophysiology.

Brief review: Neuraxial analgesia in refractory malignant pain

PURPOSE

This narrative review aims to inform health care practitioners of the current literature surrounding the use of intrathecal (IT) and epidural analgesia in cancer patients with refractory pain at end of life. Topics discussed and reviewed include: patient selection, treatment planning, procedure, equipment, medications, complications, policies and procedures, as well as directions for future research.

PRINCIPAL FINDINGS

Cancer pain is inadequately treated in an estimated 10% of patients with malignant pain despite the implementation of the World Health Organization three-step analgesic ladder. This has prompted some to advocate for the addition of a fourth step that would include neuraxial interventions. There is moderate evidence supporting the safety and efficacy of IT drug therapy in cancer patients with refractory pain. A detailed assessment and interdisciplinary team approach is necessary to develop and implement care plans for patients requiring neuraxial analgesia. Neuraxial analgesia can significantly improve pain and reduce side effects, but this must be balanced against the increased complexity of care and the risk of uncommon but serious complications.

CONCLUSION

Neuraxial drug delivery gives clinicians more options to manage refractory pain at end of life and should be offered to patients with intractable cancer pain. Teams should be interprofessional with clear delineation of roles and responsibilities. They should discuss advanced discharge planning with the patient prior to implantation as well as provide on-call support.

Ziconotide: a new nonopioid intrathecal analgesic for the treatment of chronic pain

Ziconotide is a new nonopioid intrathecal agent recently approved for the treatment of chronic pain. Ziconotide is indicated for the management of severe chronic pain in patients for whom intrathecal therapy is warranted and who are intolerant of or refractory to other treatment, such as systemic analgesics, adjunctive therapies or intrathecal morphine. Ziconotide blocks the N-type calcium channels located in the superficial dorsal horn of the spinal cord, resulting in potent analgesia. The efficacy of ziconotide has been demonstrated in three randomized, placebo-controlled trials in over 500 patients. In addition, its safety has been demonstrated in over 1200 subjects. Ziconotide is a potent analgesic with a narrow therapeutic window. The drug requires a slow titration in order to achieve analgesia while avoiding dose-limiting side effects. This review examines the currently available information on this new analgesic.

Ziconotide

Questions from patients about pain conditions and analgesic pharmacotherapy and responses from authors are presented to help educate patients and make them more effective self-advocates. The topics addressed in this issue are ziconotide, a novel approach to pain management that is derived from a snail toxin, its uses and possible side effects.

Modulation of TRP ion channels by venomous toxins

Venoms are evolutionarily fine-tuned mixtures of small molecules, peptides, and proteins-referred to as toxins-that have evolved to specifically modulate and interfere with the function of diverse molecular targets within the envenomated animal. Many of the identified toxin targets are membrane receptors and ion channels. Due to their high specificity, toxins have emerged as an invaluable tool set for the molecular characterization of ion channels, and a selected group of toxins even have been developed into therapeutics. More recently, TRP ion channels have been included as targets for venomous toxins. In particular, a number of apparently unrelated peptide toxins target the capsaicin receptor TRPV1 to produce inflammatory pain. These toxins have turned out to be invaluable for structural and functional characterizations of the capsaicin receptor. If toxins will serve similar roles for other TRP ion channels, only future will tell.

Spinal morphine but not ziconotide or gabapentin analgesia is affected by alternative splicing of voltage-gated calcium channel CaV2.2 pre-mRNA

Presynaptic voltage-gated calcium Ca_V2.2 channels play a privileged role in spinal level sensitization following peripheral nerve injury. Direct and indirect inhibitors of Ca_V2.2 channel activity in spinal dorsal horn are analgesic in chronic pain states. Ca_V2.2 channels represent a family of splice isoforms that are expressed in different combinations according to cell-type. A pair of mutually exclusive exons in the Ca_V2.2 encoding Cacna1b gene, e37a and e37b, differentially influence morphine analgesia. In mice that lack exon e37a, which is enriched in nociceptors, the analgesic efficacy of intrathecal morphine against noxious thermal stimuli is reduced. Here we ask if sequences unique to e37a influence: the development of abnormal thermal and mechanical sensitivity associated with peripheral nerve injury; and the actions of two other classes of analgesics that owe part or all of their efficacy to Ca_V2.2 channel inhibition. We find that: i) the analgesic efficacy of morphine, but not ziconotide or gabapentin, is reduced in mice lacking e37a, ii) the induction and maintenance of behaviors associated with sensitization that accompany peripheral nerve injury, do not require e37a-specific sequence, iii) intrathecal morphine, but not ziconotide or gabapentin analgesia to thermal stimuli is significantly lower in wild-type mice after peripheral nerve injury, iv) the analgesic efficacy of ziconotide and gabapentin to mechanical stimuli is reduced following nerve injury, and iv) intrathecal morphine analgesia to thermal stimuli in mice lacking e37a is not further reduced by peripheral nerve injury. Our findings show that the analgesic action of morphine, but not ziconotide or gabapentin, to thermal stimuli is linked to which Cacna1b exon, e37a or e37b, is selected during alternative pre-mRNA splicing.

Mechanistic insights into the analgesic efficacy of A-1264087, a novel neuronal Ca(2+) channel blocker that reduces nociception in rat preclinical pain models

Voltage-gated Ca(2+) channels play an important role in nociceptive transmission. There is significant evidence supporting a role for N-, T- and P/Q-type Ca(2+) channels in chronic pain. Here, we report that A-1264087, a structurally novel state-dependent blocker, inhibits each of these human Ca(2+) channels with similar potency (IC50 = 1-2 μM). A-1264087 was also shown to inhibit the release of the pronociceptive calcitonin gene-related peptide from rat dorsal root ganglion neurons. Oral administration of A-1264087 produces robust antinociceptive efficacy in monoiodoacetate-induced osteoarthritic, complete Freund adjuvant-induced inflammatory, and chronic constrictive injury of sciatic nerve-induced, neuropathic pain models with ED50 values of 3.0, 5.7, and 7.8 mg/kg (95% confidence interval = 2.2-3.5, 3.7-10, and 5.5-12.8 mg/kg), respectively. Further analysis revealed that A-1264087 also suppressed nociceptive-induced p38 and extracellular signal-regulated kinase 1/2 phosphorylation, which are biochemical markers of engagement of pain circuitry in chronic pain states. Additionally, A-1264087 inhibited both spontaneous and evoked neuronal activity in the spinal cord dorsal horn in complete Freund adjuvant-inflamed rats, providing a neurophysiological basis for the observed antihyperalgesia. A-1264087 produced no alteration of body temperature or motor coordination and no learning impairment at therapeutic plasma concentrations.

PERSPECTIVE

The present results demonstrate that the neuronal Ca(2+) channel blocker A-1264087 exhibits broad-spectrum efficacy through engagement of nociceptive signaling pathways in preclinical pain models in the absence of effects on psychomotor and cognitive function.

N-type voltage gated calcium channels mediate excitatory synaptic transmission in the anterior cingulate cortex of adult mice

Voltage gated calcium channels (VGCCs) are well known for its importance in synaptic transmission in the peripheral and central nervous system. However, the role of different VGCCs in the anterior cingulate cortex (ACC) has not been studied. Here, we use a multi-electrode array recording system (MED64) to study the contribution of different types of calcium channels in glutamatergic excitatory synaptic transmission in the ACC. We found that only the N-type calcium channel blocker ω-conotoxin-GVIA (ω-Ctx-GVIA) produced a great inhibition of basal synaptic transmission, especially in the superficial layer. Other calcium channel blockers that act on L-, P/Q-, R-, and T-type had no effect. We also tested the effects of several neuromodulators with or without ω-Ctx-GVIA. We found that N-type VGCC contributed partially to (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid- and (R)-Baclofen-induced synaptic inhibition. By contrast, the inhibitory effects of 2-Chloroadenosine and carbamoylcholine chloride did not differ with or without ω-Ctx-GVIA, indicating that they may act through other mechanisms. Our results provide strong evidence that N-type VGCCs mediate fast synaptic transmission in the ACC.

Recent advances in select interventional approaches to cancer-related pain

SUMMARY Interventional approaches for cancer-related pain have demonstrated utility and safety as a component of multimodal pain management. A number of techniques have been developed and implemented to manage the variety of cancer pain conditions and syndromes that exist as a result of the underlying malignant process and its associated oncologic treatment. These procedural pain modalities continue to evolve with advances in experience, understanding and technology in the field. Neurostimulation, vertebral augmentation with stabilization and intrathecal drug delivery, are prime examples of innovative approaches in interventional pain medicine for cancer pain with continued improvement in design to better achieve adequate analgesia and reduce risk. The intent of this article is to describe the aforementioned interventions and recent developments pertaining to them.

Intrathecal ziconotide: a review of its use in patients with chronic pain refractory to other systemic or intrathecal analgesics

Ziconotide (Prialt(®)) is a synthetic conopeptide analgesic that acts by selectively antagonizing N-type voltage-gated calcium channels. Intrathecal ziconotide is the only non-opioid intrathecal analgesic that is FDA-approved for use in patients with treatment-refractory, chronic pain. The efficacy of intrathecal ziconotide was demonstrated in randomized, double-blind, placebo-controlled trials in patients with treatment-refractory noncancer-related pain or cancer- or AIDS-related pain. Across trials, ziconotide recipients had significantly greater reductions in pain intensity during ziconotide treatment than those receiving placebo (primary endpoint). At the end of the titration period, approximately one-sixth to one-third of patients with noncancer chronic pain and one-half with cancer- or AIDS-related pain who received ziconotide reached a pain response threshold (≥30 % reduction in the pain intensity score). In ziconotide responders, analgesic effects were enduring, with some patients continuing treatment over extended periods. Across trials, the chief tolerability concerns in ziconotide recipients during the titration phase and during extended treatment were related to CNS adverse events. These were mostly of mild to moderate intensity, although serious adverse events were commonly attributed to ziconotide treatment, especially in trials with rapid ziconotide titration and that permitted higher dosages. In general, clinically important non-CNS adverse events were infrequent, and during the ziconotide titration phase, relatively few patients discontinued treatment because of adverse events. Ongoing research will assess various strategies for selecting patients for ziconotide treatment and for enhancing its efficacy and tolerability. At the present time, intrathecal ziconotide provides a treatment option for patients with severe, unremitting pain who have failed to respond to other intensive analgesic regimens.

Novel ω-conotoxins from C. catus reverse signs of mouse inflammatory pain after systemic administration

Background

Antagonists of N-type voltage-gated calcium channels (VGCC), Ca_v2.2, can manage severe chronic pain with intrathecal use and may be effective systemically. A series of novel ω-conotoxins that selectively inhibit N-type VGCCs was isolated from Conus catus. In the present study, the potency and reversibility of ω-conotoxins CVID, CVIE and CVIF to inhibit N-type calcium currents were investigated in mouse isolated dorsal root ganglion (DRG) neurons. The systemic potency of each ω-conotoxin to reverse signs of mouse chronic inflammatory pain was also compared.

Results

In DRG neurons, the rank order of potency to inhibit N-type calcium currents was CVIE > CVIF > CVID. After subcutaneous administration, CVID and CVIE, but not CVIF, partially reversed impaired weight bearing in mice injected with Freund’s complete adjuvant (CFA) three days prior to testing. No side-effects associated with systemic administration of ω-conotoxins were observed.

Conclusions

The present study indicates a potential for CVID and CVIE to be developed as systemically active analgesics with no accompanying neurological side-effects.

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.

Continuous Intrathecal Infusion of Ziconotide for Treatment of Chronic Malignant and Nonmalignant Pain Over 12 Months: A Prospective, Open-label Study

Objectives.  This study aims to assess the safety and efficacy of long-term intrathecal (IT) ziconotide infusion. Materials and Methods.  In this prospective study, 155 patients with severe chronic pain (48 with malignant pain, 107 with nonmalignant pain) who had been responsive to short-term IT ziconotide in a double-blind, placebo-controlled study received long-term, open-label IT ziconotide monotherapy. Efficacy assessments included the mean percentage change on the visual analog scale of pain intensity from baseline in the study of origin; safety was monitored by adverse event (AE) reports, periodic laboratory tests, and vital sign measurements. Results.  At the last available observation, the visual analog scale of pain intensity scores had decreased by a mean of 36.9% from baseline in the short-term trial (N = 144; 95% CI: 30.1-43.7%; p < 0.0001). The mean IT ziconotide dose remained stable over 12 months in the 31 patients who participated in the study for ≥ one year. Ziconotide-related AEs were reported in 147 out of 155 patients (94.8%); 39.4% of patients discontinued treatment because of AEs, the majority of which were considered ziconotide related. Conclusions.  Ziconotide IT monotherapy provided patients with analgesia for 12 months in this open-label study, with an acceptable benefit/risk profile and no evidence of tolerance.

Intrathecal drug administration in chronic pain syndromes

Chronic pain may recur after initial response to strong opioids in both patients with cancer and patients without cancer or therapy may be complicated by intolerable side effects. When minimally invasive interventional pain management techniques also fail to provide satisfactory pain relief, continuous intrathecal analgesic administration may be considered. Only 3 products have been officially approved for long-term intrathecal administration: morphine, baclofen, and ziconotide. The efficacy of intrathecal ziconotide for the management of patients with severe chronic refractory noncancer pain was illustrated in 3 placebo-controlled trials. A randomized study showed this treatment option to be effective over a short follow-up period for patients with pain due to cancer or AIDS. The efficacy of intrathecal opioid administration for the management of chronic noncancer pain is mainly derived from prospective and retrospective noncontrolled trials. The effect of intrathecal morphine administration in patients with pain due to cancer was compared with oral or transdermal treatment in a randomized controlled trial, which found better pain control and fewer side effects with intrathecal opioids. Other evidence is derived from cohort studies. Side effects of chronic intrathecal therapy may either be technical (catheter or pump malfunction) or biological (infection). The most troublesome complication is, however, the possibility of granuloma formation at the catheter tip that may induce neurological damage. Given limited studies, the evidence for intrathecal drug administration in patients suffering from cancer-related pain is more compelling than that of chronic noncancer pain.

Voltage-gated calcium channel antagonists and traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in the United States. Despite more than 30 years of research, no pharmacological agents have been identified that improve neurological function following TBI. However, several lines of research described in this review provide support for further development of voltage gated calcium channel (VGCC) antagonists as potential therapeutic agents. Following TBI, neurons and astrocytes experience a rapid and sometimes enduring increase in intracellular calcium ([Ca²⁺]_i). These fluxes in [Ca²⁺]_i drive not only apoptotic and necrotic cell death, but also can lead to long-term cell dysfunction in surviving cells. In a limited number of in vitro experiments, both L-type and N-type VGCC antagonists successfully reduced calcium loads as well as neuronal and astrocytic cell death following mechanical injury. In rodent models of TBI, administration of VGCC antagonists reduced cell death and improved cognitive function. It is clear that there is a critical need to find effective therapeutics and rational drug delivery strategies for the management and treatment of TBI, and we believe that further investigation of VGCC antagonists should be pursued before ruling out the possibility of successful translation to the clinic.

Spider peptide Phα1β induces analgesic effect in a model of cancer pain

The marine snail peptide ziconotide (ω-conotoxin MVIIA) is used as an analgesic in cancer patients refractory to opioids, but may induce severe adverse effects. Animal venoms represent a rich source of novel drugs, so we investigated the analgesic effects and the side-effects of spider peptide Phα1β in a model of cancer pain in mice with or without tolerance to morphine analgesia. Cancer pain was induced by the inoculation of melanoma B16-F10 cells into the hind paw of C57BL/6 mice. After 14 days, painful hypersensitivity was detected and Phα1β or ω-conotoxin MVIIA (10-100 pmol/site) was intrathecally injected to evaluate the development of antinociception and side-effects in control and morphine-tolerant mice. The treatment with Phα1β or ω-conotoxin MVIIA fully reversed cancer-related painful hypersensitivity, with long-lasting results, at effective doses 50% of 48 (32-72) or 33 (21-53) pmol/site, respectively. Phα1β produced only mild adverse effects, whereas ω-conotoxin MVIIA induced dose-related side-effects in mice at analgesic doses (estimated toxic dose 50% of 30 pmol/site). In addition, we observed that Phα1β was capable of controlling cancer-related pain even in mice tolerant to morphine antinociception (100% of inhibition) and was able to partially restore morphine analgesia in such animals (56 ± 5% of inhibition). In this study, Phα1β was as efficacious as ω-conotoxin MVIIA in inducing analgesia in a model of cancer pain without producing severe adverse effects or losing efficacy in opioid-tolerant mice, indicating that Phα1β has a good profile for the treatment of cancer pain in patients.