Tanezumab for the treatment of pain from osteoarthritis of the knee

Preliminary assessment of the safety and efficacy of tanezumab in Japanese patients with moderate to severe osteoarthritis of the knee: a randomized, double-blind, dose-escalation, placebo-controlled study

OBJECTIVE

To investigate the use of tanezumab, a humanized monoclonal antibody that inhibits nerve growth factor, for the treatment of moderate to severe osteoarthritis in Japanese patients.

DESIGN

Patients received tanezumab 10, 25, 50, 100, 200 μg/kg, or placebo and were followed for 92 or 120 days. Endpoints included the incidence of adverse events (AEs) and the change from baseline to week 8 in pain intensity and the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) subscales.

RESULTS

Patients (n = 83) were 69% female, age 44-73 years, with a Kellgren-Lawrence X-ray grade of 2-4. At week 8, compared with placebo, tanezumab 25, 100, and 200 μg/kg improved index knee pain during walking (-18.5, -14.3, and -27.6, respectively), index knee pain in the past 24 h (-19.1, -14.6, and -24.2, respectively), current index knee pain (-16.5, -10.9, and -22.8, respectively), and the WOMAC pain (-11.5, -9.6, and -18.8, respectively), physical function (-8.7, -9.5, and -17.6, respectively), and stiffness (-20.4, -11.2, and -10.2, respectively) subscales. Overall, seven patients reported AEs of abnormal peripheral sensation: allodynia (two in the tanezumab 200 μg/kg group); paresthesia (two in the tanezumab 200 μg/kg group), dysesthesia (one in the tanezumab 200 μg/kg group); thermohypoesthesia (one in the tanezumab 100 μg/kg group), and decreased vibratory sense (one in the placebo group). All of these AEs were mild to moderate in severity and transient in nature.

CONCLUSIONS

Tanezumab was safe and generally well tolerated and may improve pain symptoms in Japanese patients with moderate to severe osteoarthritis of the knee. CLINICALTRIALS.GOV IDENTIFIER: NCT00669409.

Pain and immunity

Chronic neuropathic and inflammatory pain is a major public health problem. Nociceptors undergo sensitization, first in peripheral tissues then in the central nervous sytem, via neuroimmune interactions linking neurons, glial cells (microglia and astrocytes), and immune cells. These interactions may either exacerbate or attenuate the pain and inflammation, which normally reach a state of equilibrium. With more powerful or longer lasting stimuli, specific profiles of microglial and, subsequently, astrocytic activation in the dorsal horn play a key role in neuronal plasticity and transition to chronic pain. Recent insights into the interactions between the nervous system and the immune system suggest a large number of potential therapeutic targets that could be influenced either by targeted inhibition or by directing the neuroimmune response toward the antiinflammatory and analgesic end of its spectrum.

Ultrasound-guided platelet-rich plasma injections for the treatment of osteoarthritis of the hip

OBJECTIVE

To assess the safety and symptomatic changes of IA injections of platelet-rich plasma (PRP) in patients with OA of the hip.

METHODS

Forty patients affected by monolateral severe hip OA were included in the study. Each joint received three IA injections of PRP, which were administered once a week. The primary end point was meaningful pain relief, which was described as a reduction in pain intensity of at least 30% from baseline levels as evaluated by the WOMAC subscale at 6-months post-treatment. The visual analogue scale (VAS) and Harris hip score subscale for pain were used to verify the results. Secondary end points included changes in the level of disability of at least 30% and the percentage of positive responders, i.e. the number of patients that achieved a >30% reduction in pain and disability.

RESULTS

Statistically significant reductions in VAS, WOMAC and Harris hip subscores for pain and function were reported at 7 weeks and 6 months (P < 0.05). Twenty-three (57.5%) patients reported a clinically relevant reduction of pain (45%, range 30-71%) as assessed by the WOMAC subscale. Sixteen (40%) of these patients were classified as excellent responders who showed an early pain reduction at 6-7 weeks, which was sustained at 6 months, and a parallel reduction of disability. Side effects were negligible and were limited to a sensation of heaviness in the injection site.

CONCLUSIONS

This preliminary non-controlled prospective study supported the safety, tolerability and efficacy of PRP injections for pain relief and improved function in a limited number of patients with OA of the hip.

Pharmacological modulation of central nociception in the management of chronic musculoskeletal pain

SUMMARY Chronic musculoskeletal pain, defined as pain lasting beyond the usual healing time of 6 weeks to 3 months, is a very common condition. It adversely affects the quality of life of patients and has a significant economic impact on our society. There is an ever increasing understanding of the pathophysiology of chronic pain. This has resulted in the effective use of various medications aimed at modulating both central and peripheral sensitizations. There are also new agents being developed based on fundamental research. The pharmacological agents used in the modulation of central nociception in chronic musculoskeletal pain are reviewed in this article.

Perineural invasion and associated pain in pancreatic cancer

Perineural invasion (PNI) is a prominent characteristic of pancreatic cancer. PNI is a process whereby cancer cells invade the surrounding nerves, thus providing an alternative route for metastatic spread and pain generation. PNI is thought to be an indicator of aggressive tumour behaviour and has been shown to correlate with poor prognosis of patients with pancreatic cancer. Recent studies demonstrated that some signalling molecules and pathways that are involved in PNI are also involved in pain generation. Targeting these signalling pathways has shown some promise in alleviating pain and reducing PNI, which could potentially improve treatment outcomes for patients with pancreatic cancer.

A variant in MCF2L is associated with osteoarthritis

Osteoarthritis (OA) is a prevalent, heritable degenerative joint disease with a substantial public health impact. We used a 1000-Genomes-Project-based imputation in a genome-wide association scan for osteoarthritis (3177 OA cases and 4894 controls) to detect a previously unidentified risk locus. We discovered a small disease-associated set of variants on chromosome 13. Through large-scale replication, we establish a robust association with SNPs in MCF2L (rs11842874, combined odds ratio [95% confidence interval] 1.17 [1.11-1.23], p = 2.1 × 10(-8)) across a total of 19,041 OA cases and 24,504 controls of European descent. This risk locus represents the third established signal for OA overall. MCF2L regulates a nerve growth factor (NGF), and treatment with a humanized monoclonal antibody against NGF is associated with reduction in pain and improvement in function for knee OA patients.

Preventive or late administration of anti-NGF therapy attenuates tumor-induced nerve sprouting, neuroma formation, and cancer pain

Early, preemptive blockade of nerve growth factor (NGF)/tropomyosin receptor kinase A (TrkA) attenuates tumor-induced nerve sprouting and bone cancer pain. A critical unanswered question is whether late blockade of NGF/TrkA can attenuate cancer pain once NGF-induced nerve sprouting and neuroma formation has occurred. By means of a mouse model of prostate cancer-induced bone pain, anti-NGF was either administered preemptively at day 14 after tumor injection when nerve sprouting had yet to occur, or late at day 35, when extensive nerve sprouting had occurred. Animals were humanely killed at day 70 when, in vehicle-treated animals, significant nerve sprouting and neuroma formation was present in the tumor-bearing bone. Although preemptive and sustained administration (days 14-70) of anti-NGF more rapidly attenuated bone cancer nociceptive behaviors than late and sustained administration (days 35-70), by day 70 after tumor injection, both preemptive and late administration of anti-NGF significantly reduced nociceptive behaviors, sensory and sympathetic nerve sprouting, and neuroma formation. In this model, as in most cancers, the individual cancer cell colonies have a limited half-life because they are constantly proliferating, metastasizing, and undergoing necrosis as the parent cancer cell colony outgrows its blood supply. Similarly, the sensory and sympathetic nerve fibers that innervate the tumor undergo sprouting at the viable/leading edge of the parent tumor, degenerate as the parent cancer cell colony becomes necrotic, and resprout in the viable, newly formed daughter cell colonies. These results suggest that preemptive or late-stage blockade of NGF/TrkA can attenuate nerve sprouting and cancer pain.

Emerging drugs for osteoarthritis

INTRODUCTION

Osteoarthritis (OA), the most prevalent form of joint disease, affects as much as 13% of the world's population. In the USA, it is the leading cause of disability in people over age 65 and is characterized by progressive cartilage loss, bone remodeling, osteophyte formation and synovial inflammation with resultant joint pain and disability. There are no treatments marketed for structural disease modification; current treatments mainly target symptoms, with > 75% of patients reporting need for additional symptomatic treatment.

AREAS COVERED

Drugs in later development (Phase II - III) for OA pain and joint structural degeneration are reviewed. Topics that are not covered in this article are procedural-based (e.g., arthrocentesis, physical therapy), behavioral-based (e.g., weight loss, pain coping techniques) or device-based (e.g., knee braces, surgical implants) treatments.

EXPERT OPINION

More in-depth understanding of the pathophysiology of the disease, as well as elucidation of the link between clinical symptomatology and structural changes in the joint will likely lead to the development of novel target classes with promising efficacy in the future. Efficacy notwithstanding, there remain significant hurdles to overcome in clinical development of these therapeutics, inherent in the progression pattern of the disease as well as challenges with readouts for both pain and structure modification trials.

New molecules for the treatment of pain

PURPOSE OF REVIEW

To inform on preclinical and early clinical advances in the effort to identify novel classes of analgesic drugs.

RECENT FINDINGS

Human genetic and animal preclinical studies have identified several mechanisms that appear to make important contributions to abnormal pain states. From human genetics, a small number of patients with mutations in the genes encoding nerve growth factor/TrkA signaling and in a particular sodium channel subunit (SCN9a, encoding Nav1.7) show congenital analgesia with limited other effects. There are, therefore, considerable hopes that pharmacological manipulation of these systems in chronic pain patients might be an effective analgesic strategy. A substantial body of preclinical work has focussed on interactions between the immune and the nervous system and this has led to the identification of a number of novel putative inflammatory mediators and receptors, which are being explored as potential analgesic targets. A recent preclinical effort has studied intracellular signaling cascades recruited in the transition from acute to chronic pain states - the analgesic opportunities on offer here are being pursued in early clinical trials.

SUMMARY

Existing analgesic drugs are small in number, limited in efficacy and associated with significant side-effects. There is, therefore, a need for new pain medications. In the last decade or so, clinical and preclinical research have progressed rapidly and this work has identified multiple plausible drug targets, which are currently being evaluated. We review here the rationale of some of the most promising mechanisms and report on progress in drug development.

Non-surgical treatment of osteoarthritis-related pain in the elderly

Osteoarthritis (OA), the third most common diagnosis in the elderly [1], causes significant pain leading to disability and decreased quality of life in subjects 65 years and older [2]. Traditionally, clinicians have relied heavily on the use of non-steroidal anti-inflammatory drugs (NSAIDs) to treat the pain of OA, as numerous studies have proven these agents to be effective. The cardiovascular, gastrointestinal, renal and hepatic toxicities of NSAIDs have limited their use, particularly in the elderly. Acetaminophen has been recommended as initial therapy due to relative safety. Several other topical, oral and intra-articular agents are available today, with use limited by efficacy and side effect profiles. Many non-pharmacologic approaches are available but underused, and may be attractive choices to avoid poly-pharmacy in older patients. We will attempt to highlight the evidence behind available non-surgical therapies for OA while paying specific attention to issues in geriatric patients.

Managing pain in inflammatory bowel disease

Pain is a common complaint in inflammatory bowel disease, and it has significant consequences for patients' quality of life. A thorough evaluation to determine the source of patients' pain should include clinical, laboratory, radiologic, and endoscopic assessments as indicated. Differentiating among active inflammation, secondary complications, and functional pain can be complicated. Even when all active disease is adequately treated, clinicians are often left with the difficulty of managing chronic pain. This paper will review the benefits and limitations of several commonly used treatments and promising future therapies. A suggested treatment algorithm will provide some guidance in this challenging area of inflammatory bowel disease management.

Potential mechanisms for hypoalgesia induced by anti-nerve growth factor immunoglobulin are identified using autoimmune nerve growth factor deprivation

Nerve growth factor (NGF) antagonism has long been proposed as a chronic pain treatment. In 2010, the FDA suspended clinical trials using tanezumab, a humanized monoclonal anti-NGF antibody, to treat osteoarthritis due to worsening joint damage in 16 patients. Increased physical activity in the absence of acute pain which normally prevents self-harm was purported as a potential cause. Such an adverse effect is consistent with an extension of tanezumab's primary mechanism of action by decreasing pain sensitivity below baseline levels. In animal inflammatory pain models, NGF antagonism decreases intraepidermal nerve fiber (IENF) density and attenuates increases in expression of nociception-related proteins, such as calcitonin gene-related peptide (CGRP) and substance P (SP). Little is known of the effects of NGF antagonism in noninflamed animals and the hypoalgesia that ensues. In the current study, we immunized rats with NGF or cytochrome C (cytC) and examined (1) nocifensive behaviors with thermal latencies, mechanical thresholds, the hot plate test, and the tail flick test, (2) IENF density, and (3) expression of CGRP, SP, voltage-gated sodium channel 1.8 (Nav1.8), and glutaminase in subpopulations of dorsal root ganglion (DRG) neurons separated by size and isolectin B4 (IB4) labeling. Rats with high anti-NGF titers had delayed responses on the hot plate test but no other behavioral abnormalities. Delayed hot plate responses correlated with lower IENF density. CGRP and SP expression was decreased principally in medium (400-800 μm(2)) and small neurons (<400 μm(2)), respectively, regardless of IB4 labeling. Expression of Nav1.8 was only decreased in small and medium IB4 negative neurons. NGF immunization appears to result in a more profound antagonism of NGF than tanezumab therapy, but we hypothesize that decreases in IENF density and nociception-related protein expression are potential mechanisms for tanezumab-induced hypoalgesia.

Perioperative nerve blockade: clues from the bench

Peripheral and neuraxial nerve blockades are widely used in the perioperative period. Their values to diminish acute postoperative pain are established but other important outcomes such as chronic postoperative pain, or newly, cancer recurrence, or infections could also be influenced. The long-term effects of perioperative nerve blockade are still controversial. We will review current knowledge of the effects of blocking peripheral electrical activity in different animal models of pain. We will first go over the mechanisms of pain development and evaluate which types of fibers are activated after an injury. In the light of experimental results, we will propose some hypotheses explaining the mitigated results obtained in clinical studies on chronic postoperative pain. Finally, we will discuss three major disadvantages of the current blockade: the absence of blockade of myelinated fibers, the inappropriate duration of blockade, and the existence of activity-independent mechanisms.

The effects of radiofrequency hyperthermia on pain and function in patients with knee osteoarthritis: a preliminary report

BACKGROUND

The clinical evidence of the efficacy of hyperthermia on osteoarthritis (OA) has not yet been clearly established. In addition, the application of a modality that can control the temperature inside the joints has not been reported. The purpose of this study was to investigate the effect of percutaneous radiofrequency hyperthermia, which could safely raise the temperature of the body core, in patients with OA knees.

METHODS

Temperature changes inside the knee joint without OA were measured during exposure to radiofrequency. Radiofrequency hyperthermia was performed on 12 OA knees by exposure to 8 MHz and 200 W for 20 min, 3 times, at 1-week intervals. The clinical outcome was evaluated by use of the Lequesne index (LI) and the Japan Orthopaedic Association (JOA) scale. The osteoarthritis research society international (OARSI) responder criteria were also analyzed.

RESULTS

Radiofrequency hyperthermia of 8 MHz and 200 W for 20 min increased the temperature inside the joint from 34.4 to 39.4°C. The LI decreased by 3.55 points from baseline during the 3 weeks. The JOA scale improved significantly during the period, reaching 86.25 points at the final examination from baseline of 67.5 points. 67% of patients had a response to the therapy according to OARSI criteria. No side effects were observed.

CONCLUSIONS

Radiofrequency hyperthermia can safely increase the temperature inside the knee joint. Radiofrequency hyperthermia on OA knees provides a remarkable pain relief effect and can improve the patients' daily life. In the future, clinical studies should be performed with a protocol containing more cases, with appropriate control groups.

Antagonism of nerve growth factor-TrkA signaling and the relief of pain

Nerve growth factor (NGF) was originally discovered as a neurotrophic factor essential for the survival of sensory and sympathetic neurons during development. However, in the adult NGF has been found to play an important role in nociceptor sensitization after tissue injury. The authors outline mechanisms by which NGF activation of its cognate receptor, tropomyosin-related kinase A receptor, regulates a host of ion channels, receptors, and signaling molecules to enhance acute and chronic pain. The authors also document that peripherally restricted antagonism of NGF-tropomyosin-related kinase A receptor signaling is effective for controlling human pain while appearing to maintain normal nociceptor function. Understanding whether there are any unexpected adverse events and how humans may change their behavior and use of the injured/degenerating tissue after significant pain relief without sedation will be required to fully appreciate the patient populations that may benefit from these therapies targeting NGF.

Efficacy and safety of tanezumab in the treatment of chronic low back pain

Increased nerve growth factor levels are associated with chronic pain conditions, including chronic low back pain (LBP). This study examined safety and analgesic efficacy of tanezumab, a humanized anti-nerve growth factor antibody, in adults with chronic LBP. Patients received intravenous tanezumab 200 μg/kg plus oral placebo (n=88), intravenous placebo plus oral naproxen 500 mg twice a day (n=88), or intravenous placebo plus oral placebo (n=41). Primary outcome was average LBP intensity (aLBPI) at Week 6. Secondary outcomes were proportion of patients with ≥30% or ≥50% reduction in aLBPI, Roland-Morris Disability Questionnaire and Brief Pain Inventory-short form scores, Patients' Global Assessment of LBP, Patients' Global Evaluation of study medication, and rescue medication use. Mean aLBPI change from baseline to Week 6 was greater with tanezumab vs naproxen (P=0.004) and placebo (P<0.001). Greater proportions of patients reported ≥30% and ≥50% reduction in aLBPI with tanezumab vs naproxen (P≤0.013) and placebo (P<0.001), and greater improvements in Roland-Morris Disability Questionnaire (P<0.001) and other secondary outcomes except rescue medication use. Tanezumab was associated with adverse events (AEs) of abnormal peripheral sensation that were generally mild and resolved before study completion; however, there were no serious AEs. Nine patients (4 of whom were tanezumab-treated) discontinued due to AEs. In conclusion, tanezumab resulted in analgesic efficacy that was clinically and statistically superior to placebo and naproxen in patients with chronic LBP. Tanezumab clinical development is on regulatory hold due to AEs in osteoarthritis patients.

Treatment options for osteoarthritis: considerations for older adults

Osteoarthritis (OA) is the most common form of arthritis and the leading cause of disability among older adults in the United States. Treatment options such as acetaminophen and nonsteroidal anti-inflammatory drugs are the most widely used agents to manage mild-to-moderate pain. Treatment with tramadol or opioids is usually reserved for severe pain associated with OA. These agents do not come without risk, especially for older adults. Patient-specific parameters and comorbid conditions must be considered when evaluating treatment options for older adults. This article reviews pharmacological and nonpharmacological approaches to the management of OA in older adults.

Long-term open-label study of tanezumab for moderate to severe osteoarthritic knee pain

OBJECTIVE

This study was designed to evaluate the long-term safety and effectiveness of repeated doses of the humanized anti-nerve growth factor antibody, tanezumab, during open-label treatment of patients with OA knee pain.

DESIGN

The current study (clinicaltrials.gov identifier: NCT00399490) was a multicenter, phase II, open-label, multiple-dose extension of an earlier randomized clinical trial. All patients (N=281) received infusions of tanezumab 50μg/kg on Days 1 and 56 with subsequent doses administered at 8-week intervals (up to a total of eight infusions). The primary endpoint of this study was safety. Effectiveness evaluations included overall knee pain, Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index subscales, and subject global assessment (SGA) of response to therapy on 0-100 point visual analog scales.

RESULTS

Repeated administration of tanezumab resulted in a low incidence of treatment-related adverse events (AEs; 7.5%). The rate of serious AEs was also low (2.8%) with none considered treatment-related. Few AEs of abnormal peripheral sensation were reported; hypoesthesia was reported by nine patients (3.2%), paresthesia by seven patients (2.5%), and hyperesthesia, peripheral neuropathy, and sensory disturbance were each reported by one patient (0.4% for each). Most AEs of abnormal peripheral sensation were rated as mild (95%) and the majority (65%) resolved before study completion. At Week 8, overall knee pain and SGA improved from baseline by a mean (± standard error) of -12.8 (±1.78) and 8.0 (±1.66), respectively. Similar improvements occurred for WOMAC subscales.

CONCLUSIONS

Repeated injections of tanezumab in patients with moderate to severe knee OA provide continued pain relief and improved function with a low incidence of side effects. Additional studies to define the efficacy and duration of pain reduction and to provide a more complete assessment of long-term safety are warranted.

New targets, new drugs for metastatic bone pain: a new philosophy

Bone pain is a common symptom in bone metastases. The therapies that are currently available include nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, steroids and gabapentin which have been demonstrated to improve neuropathic pain. In addition, preclinical studies indicate that agents such as transient receptor potential vanilloid 1 antagonists and cannabinoid 2 receptor agonist could be considered as adjuncts in ameliorating opioid side effects. New drugs are in the clinical phase of development, among which the most promising molecules seem to be anti-nerve growth factor (NGF) antibodies. Anti-NGF antibody therapy may be particularly effective in blocking bone cancer pain because NGF appears to be integrally involved in the upregulation, sensitization and disinhibition of multiple neurotransmitters, ion channels and receptors in the primary afferent nerve. The best way to treat bone metastases pain is to improve the control of skeletal disease burden. Recently, denosumab, a noncytotoxic IgG2 monoclonal antibody with high affinity for human RANKL, has been demonstrated to significantly prevent clinically relevant increase in pain compared with zoledronic acid across the tumor types. Based on these data, it has been suggested that denosumab has the potential to become a new standard of treatment in bone metastases management.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.

Mitochondrial dependence of nerve growth factor-induced mechanical hyperalgesia

Mitochondria are present at high concentration at the site of sensory transduction in the peripheral terminals of nociceptors. Because nerve growth factor (NGF), which induces nociceptor sensitization by acting on the high-affinity tropomyosin receptor kinase A (TrkA) receptor, also produces local recruitment of mitochondria in DRG neurons, we evaluated the role of mitochondria in NGF-induced mechanical hyperalgesia. Inhibition of 3 major mitochondrial functions-oxidation of nutrients, adenosine triphosphate (ATP) production, and generation of reactive oxygen species--markedly attenuated NGF-induced mechanical hyperalgesia in the rat. Disruption of microtubules, which are required for the trafficking and subcellular localization of mitochondria, also attenuated NGF-induced hyperalgesia. Our results suggest a contribution of mitochondrial localization and function to NGF-dependent pain syndromes.

Update on peripheral mechanisms of pain: beyond prostaglandins and cytokines

The peripheral nociceptor is an important target of pain therapy because many pathological conditions such as inflammation excite and sensitize peripheral nociceptors. Numerous ion channels and receptors for inflammatory mediators were identified in nociceptors that are involved in neuronal excitation and sensitization, and new targets, beyond prostaglandins and cytokines, emerged for pain therapy. This review addresses mechanisms of nociception and focuses on molecules that are currently favored as new targets in drug development or that are already targeted by new compounds at the stage of clinical trials--namely the transient receptor potential V1 receptor, nerve growth factor, and voltage-gated sodium channels--or both.

Osteoarthritis year 2010 in review: pharmacological therapies

This review highlights a selection of original studies related to the treatment of osteoarthritis in 2010.

Proof of concept trial of tanezumab for the treatment of symptoms associated with interstitial cystitis

PURPOSE

In this randomized, double-blind, placebo controlled phase 2 study we investigated tanezumab, a humanized monoclonal antibody that specifically inhibits nerve growth factor as a treatment for interstitial cystitis pain.

MATERIALS AND METHODS

Patients with interstitial cystitis received a single intravenous dose of 200 μg/kg tanezumab or placebo. Patients recorded daily pain scores (on an 11-point numerical rating scale) 7 days before attending study visits and completed a urinary symptom diary for 3 of those days. Patients also completed the Interstitial Cystitis Symptom Index questionnaire and a global response assessment. The primary end point was change in average daily numerical rating scale pain score from baseline to week 6. Secondary end points included global response assessment, Interstitial Cystitis Symptom Index score, micturition and urgency episode frequency per 24 hours, and mean voided volume per micturition. The incidence of adverse events was also assessed.

RESULTS

A total of 34 patients received tanezumab and 30 received placebo. At week 6 tanezumab produced a significant reduction from baseline in average daily pain score vs placebo (treatment difference [LS mean, 90% CI] was -1.4 [-2.2, -0.5]). A significantly higher proportion of patients on tanezumab responded as improved in the global response assessment and tanezumab also significantly reduced urgency episode frequency vs placebo. Tanezumab had no significant effect on Interstitial Cystitis Symptom Index score, micturition frequency or mean voided volume per micturition. The most common adverse events were headache (tanezumab 20.6%, placebo 16.7%) and paresthesia (tanezumab 17.6%, placebo 3.3%).

CONCLUSIONS

Tanezumab has shown preliminary efficacy in the treatment of pain associated with interstitial cystitis.

Interview: Key questions in pain research: clinical observations informing research and vice versa

Dr David Bennett received his MB PhD qualification from the United Medical and Dental Schools of Guy’s and St Thomas’ London (UK) in 1999. He undertook an intercalated PhD studying the role of neurotrophic factors in sensory neuronal development and plasticity in the department of physiology under the supervision of Steven McMahon and John Priestley. Subsequent work investigated the importance of neurotrophic factors in the response to nerve injury. Subspecialty training in neurology took place principally in London at the National Hospital for Neurology and Neurosurgery, King’s College Hospital, and Guy’s and St Thomas’ NHS Trust. Since 2009, Dr Bennett has been a consultant neurologist at King’s College Hospital and provides a specialist clinical service for the investigation and treatment of peripheral neuropathy and neuropathic pain. He is currently a Wellcome clinical scientist and his research focuses on understanding the neurobiology of nerve injury and the development of neuropathic pain. He is a member of the Wellcome Trust-funded London Pain Consortium and Vice-Director of the ‘Europain’ Investigational Medicines Initiative. He is also an Associate Editor of Pain Management.

Nerve growth factor in cancer cell death and survival

One of the major challenges for cancer therapeutics is the resistance of many tumor cells to induction of cell death due to pro-survival signaling in the cancer cells. Here we review the growing literature which shows that neurotrophins contribute to pro-survival signaling in many different types of cancer. In particular, nerve growth factor, the archetypal neurotrophin, has been shown to play a role in tumorigenesis over the past decade. Nerve growth factor mediates its effects through its two cognate receptors, TrkA, a receptor tyrosine kinase and p75NTR, a member of the death receptor superfamily. Depending on the tumor origin, pro-survival signaling can be mediated by TrkA receptors or by p75NTR. For example, in breast cancer the aberrant expression of nerve growth factor stimulates proliferative signaling through TrkA and pro-survival signaling through p75NTR. This latter signaling through p75NTR promotes increased resistance to the induction of cell death by chemotherapeutic treatments. In contrast, in prostate cells the p75NTR mediates cell death and prevents metastasis. In prostate cancer, expression of this receptor is lost, which contributes to tumor progression by allowing cells to survive, proliferate and metastasize. This review focuses on our current knowledge of neurotrophin signaling in cancer, with a particular emphasis on nerve growth factor regulation of cell death and survival in cancer.

Ion channels in inflammation

Most physical illness in vertebrates involves inflammation. Inflammation causes disease by fluid shifts across cell membranes and cell layers, changes in muscle function and generation of pain. These disease processes can be explained by changes in numbers or function of ion channels. Changes in ion channels have been detected in diarrhoeal illnesses, pyelonephritis, allergy, acute lung injury and systemic inflammatory response syndromes involving septic shock. The key role played by changes in ion transport is directly evident in inflammation-induced pain. Expression or function of all major categories of ion channels like sodium, chloride, calcium, potassium, transient receptor potential, purinergic receptor and acid-sensing ion channels can be influenced by cyto- and chemokines, prostaglandins, leukotrienes, histamine, ATP, reactive oxygen species and protons released in inflammation. Key pathways in this interaction are cyclic nucleotide, phosphoinositide and mitogen-activated protein kinase-mediated signalling, direct modification by reactive oxygen species like nitric oxide, ATP or protons and disruption of the cytoskeleton. Therapeutic interventions to modulate the adverse and overlapping effects of the numerous different inflammatory mediators on each ion transport system need to target adversely affected ion transport systems directly and locally.

The majority of myelinated and unmyelinated sensory nerve fibers that innervate bone express the tropomyosin receptor kinase A

Although skeletal pain is a leading cause of chronic pain and disability, relatively little is known about the specific populations of nerve fibers that innervate the skeleton. Recent studies have reported that therapies blocking nerve growth factor (NGF) or its cognate receptor, tropomyosin receptor kinase A (TrkA) are efficacious in attenuating skeletal pain. A potential factor to consider when assessing the analgesic efficacy of targeting NGF-TrkA signaling in a pain state is the fraction of NGF-responsive TrkA+ nociceptors that innervate the tissue from which the pain is arising, as this innervation and the analgesic efficacy of targeting NGF-TrkA signaling may vary considerably from tissue to tissue. To explore this in the skeleton, tissue slices and whole mount preparations of the normal, adult mouse femur were analyzed using immunohistochemistry and confocal microscopy. Analysis of these preparations revealed that 80% of the unmyelinated/thinly myelinated sensory nerve fibers that express calcitonin gene-related peptide (CGRP) and innervate the periosteum, mineralized bone and bone marrow also express TrkA. Similarly, the majority of myelinated sensory nerve fibers that express neurofilament 200 kDa (NF200) which innervate the periosteum, mineralized bone and bone marrow also co-express TrkA. In the normal femur, the relative density of CGRP+, NF200+ and TrkA+ sensory nerve fibers per unit volume is: periosteum>bone marrow>mineralized bone>cartilage with the respective relative densities being 100:2:0.1:0. The observation that the majority of sensory nerve fibers innervating the skeleton express TrkA+, may in part explain why therapies that block NGF/TrkA pathway are highly efficacious in attenuating skeletal pain.