Validation of a Rodent Model of Chemotherapy-Induced Peripheral Neuropathy Using Oxaliplatin

poster abstractOxaliplatin (OXPL) is one of the most widely used and effective chemotherapeutic agents for colorectal cancer. However, the drug therapy is accompanied by severe dose-limiting off-target effects including tingling, burning pain and mechanical allodynia in the extremities of patients; together these symptomology is better known as chemotherapy-induced peripheral neuropathy (CIPN). The underlying pathophysiological mechanisms of CIPN are poorly understood and current therapeutic options only serve to alleviate the symptoms rather than prevent CIPN. To better understand mechanisms of OXPL-induced CIPN (OXPLN), we exposed adult female Sprague-Dawley rats to four intraperitoneal injections of vehicle or OXPL on alternative days. Behavioral results showed that thermal sensitivity failed to be affected by the OXPL. In contrast, the magnitude of mechanical allodynia increased such that the baseline withdrawal threshold for drug-treated animals was significantly lower than that for unprimed animals. Application of OXPL to afferent sensory neurons produced an increased amplitude and duration of compound action potentials that could be reversed with the voltage-gated sodium channel blocker, carbamazepine (CBZ). Astroglial and microglial markers glial fibrillary acidic protein (GFAP) and Iba-1 were imaged to examine glial reactivity in OXPLN at day 14. Microglia were not activated following OXPL whereas astrocytes exhibited increased GFAP fluorescence which paralleled OXPLN. Activation of astrocytes was prevented by co-administration of CBZ. These observations suggest that CBZ may serve to diminish OXPLN in the patient population. Oxaliplatin (OXPL) is one of the most widely used and effective chemotherapeutic agents for colorectal cancer. However, the drug therapy is accompanied by severe dose-limiting off-target effects including tingling, burning pain and mechanical allodynia in the extremities of patients; together these symptomology is better known as chemotherapy-induced peripheral neuropathy (CIPN). The underlying pathophysiological mechanisms of CIPN are poorly understood and current therapeutic options only serve to alleviate the symptoms rather than prevent CIPN. To better understand mechanisms of OXPL-induced CIPN (OXPLN), we exposed adult female Sprague-Dawley rats to four intraperitoneal injections of vehicle or OXPL on alternative days. Behavioral results showed that thermal sensitivity failed to be affected by the OXPL. In contrast, the magnitude of mechanical allodynia increased such that the baseline withdrawal threshold for drug-treated animals was significantly lower than that for unprimed animals. Application of OXPL to afferent sensory neurons produced an increased amplitude and duration of compound action potentials that could be reversed with the voltage-gated sodium channel blocker, carbamazepine (CBZ). Astroglial and microglial markers glial fibrillary acidic protein (GFAP) and Iba-1 were imaged to examine glial reactivity in OXPLN at day 14. Microglia were not activated following OXPL whereas astrocytes exhibited increased GFAP fluorescence which paralleled OXPLN. Activation of astrocytes was prevented by co-administration of CBZ. These observations suggest that CBZ may serve to diminish OXPLN in the patient population

Development of analgesic peptide therapeutics for AIDS-related neuropathic pain

poster abstractChronic neuropathic pain is a huge problem to the health and well-being of an increasingly ageing population in the US, as substantiated by the large unmet clinical need associated with this type of pain, with estimates of 30-50% of sufferers refractory to existing medication. Thus, there is an imperative to increase knowledge of mechanisms of action of the key proteins in nociceptive pathways in vitro and to extend this knowledge to in vivo models of neuropathy to advance therapeutic development in this area. N-type voltage-gated Ca2+ channels (CaV2.2) have emerged as potential novel targets for the treatment of chronic neuropathic pain. Funded, in part, by a FORCES grant, we have identified two novel derivatives of the parent 15 amino acid CBD3 peptide, derived from collapsin response mediator protein 2 (CRMP-2) that suppressed inflammatory and neuropathic hypersensitivity by inhibiting CRMP-2 binding to N-type voltage gated calcium channels (CaV2.2) [Brittain et al., Nature Medicine 17:822-829 (2011)]. Pharmacokinetic studies revealed nanogram levels of peptide in plasma of rats systemic administration consistent with relief of hypersensitivity. Furthermore, we observed improved and broader efficacy of the derivatized peptides in AIDS-therapy and nerve-injury related neuropathic pain models. Future studies regarding dosing and route of delivery optimization as well as identification of peptide-mimetics are ongoing to fully realize the commercial value of the peptides. Supported by the Startup program at the Indiana University Research & Technology Corporation (IURTC), we have setup Sophia Therapeutics LLC and together with IURTC are committed to the work proposed here

Small-molecule CaVα1⋅CaVβ antagonist suppresses neuronal voltage-gated calcium-channel trafficking

Extracellular calcium flow through neuronal voltage-gated CaV2.2 calcium channels converts action potential-encoded information to the release of pronociceptive neurotransmitters in the dorsal horn of the spinal cord, culminating in excitation of the postsynaptic central nociceptive neurons. The CaV2.2 channel is composed of a pore-forming α1 subunit (CaVα1) that is engaged in protein-protein interactions with auxiliary α2/δ and β subunits. The high-affinity CaV2.2α1⋅CaVβ3 protein-protein interaction is essential for proper trafficking of CaV2.2 channels to the plasma membrane. Here, structure-based computational screening led to small molecules that disrupt the CaV2.2α1⋅CaVβ3 protein-protein interaction. The binding mode of these compounds reveals that three substituents closely mimic the side chains of hot-spot residues located on the α-helix of CaV2.2α1 Site-directed mutagenesis confirmed the critical nature of a salt-bridge interaction between the compounds and CaVβ3 Arg-307. In cells, compounds decreased trafficking of CaV2.2 channels to the plasma membrane and modulated the functions of the channel. In a rodent neuropathic pain model, the compounds suppressed pain responses. Small-molecule α-helical mimetics targeting ion channel protein-protein interactions may represent a strategy for developing nonopioid analgesia and for treatment of other neurological disorders associated with calcium-channel trafficking

Decoy peptide targeted to Toll-IL-1R domain inhibits LPS and TLR4-active metabolite morphine-3 glucuronide sensitization of sensory neurons

Accumulating evidence indicates that Toll-like receptor (TLR) signaling adapter protein interactions with Toll/Interleukin-1 Receptor (TIR) domains present in sensory neurons may modulate neuropathic pain states. Following ligand interaction with TLRs, TIR serves to both initiate intracellular signaling and facilitate recruitment of signaling adapter proteins to the intracytoplasmic domain. Although TLR TIR is central to a number of TLR signaling cascades, its role in sensory neurons is poorly understood. In this study we investigated the degree to which TLR TIR decoy peptide modified to include a TAT sequence (Trans-Activator of Transcription gene in HIV; TAT-4BB) affected LPS-induced intracellular calcium flux and excitation in sensory neurons, and behavioral changes due to TLR4 active metabolite, morphine-3-glucuronide (M3G) exposure in vivo. TAT-4BB inhibited LPS-induced calcium changes in a majority of sensory neurons and decreased LPS-dependent neuronal excitability in small diameter neurons. Acute systemic administration of the TAT-4BB reversed M3G-induced tactile allodynia in a dose-dependent manner but did not affect motor activity, anxiety or responses to noxious thermal stimulus. These data suggest that targeting TLR TIR domains may provide novel pharmacological targets to reduce or reverse TLR4-dependent pain behavior in the rodent

Identification of a functional interaction of HMGB1 with Receptor for Advanced Glycation End-products in a model of neuropathic pain

Recent studies indicate that the release of high mobility group box 1 (HMGB1) following nerve injury may play a central role in the pathogenesis of neuropathic pain. HMGB1 is known to influence cellular responses within the nervous system via two distinct receptor families; the Receptor for Advanced Glycation End-products (RAGE) and Toll-like receptors (TLRs). The degree to which HMGB1 activates a receptor is thought to be dependent upon the oxidative state of the ligand, resulting in the functional isoforms of all-thiol HMGB1 (at-HMGB1) acting through RAGE, and disufide HMGB1 (ds-HMGB1) interacting with TLR4. Though it is known that dorsal root ganglia (DRG) sensory neurons exposed to HMGB1 and TLR4 agonists can influence excitation, the degree to which at-HMGB1 signaling through neuronal RAGE contributes to neuropathic pain is unknown. Here we demonstrate that at-HMGB1 activation of nociceptive neurons is dependent on RAGE and not TLR4. To distinguish the possible role of RAGE on neuropathic pain, we characterized the changes in RAGE mRNA expression up to one month after tibial nerve injury (TNI). RAGE mRNA expression in lumbar dorsal root ganglion (DRG) is substantially increased by post-injury day (PID) 28 when compared with sham injured rodents. Protein expression at PID28 confirms this injury-induced event in the DRG. Moreover, a single exposure to monoclonal antibody to RAGE (RAGE Ab) failed to abrogate pain behavior at PID 7, 14 and 21. However, RAGE Ab administration produced reversal of mechanical hyperalgesia on PID28. Thus, at-HMGB1 activation through RAGE may be responsible for sensory neuron sensitization and mechanical hyperalgesia associated with chronic neuropathic pain states

Bone pain induced by multiple myeloma is reduced by targeting V-ATPase and ASIC3

Multiple myeloma (MM) patients experience severe bone pain (MMBP) that is undertreated and poorly understood. In this study, we studied MMBP in an intratibial mouse xenograft model which employs JJN3 human MM cells. In this model, mice develop MMBP associated in bone with increased sprouting of calcitonin gene-related peptide-positive (CGRP+) sensory nerves and in dorsal root ganglia (DRG) with upregulation of phosphorylated ERK1/2 (pERK1/2) and pCREB, two molecular indicators of neuron excitation. We found that JJN3 cells expressed a vacuolar proton pump (V-ATPase) that induced an acidic bone microenvironment. Inhibition of JJN3-colonized bone acidification by a single injection of the selective V-ATPase inhibitor, bafilomycin A1, decreased MMBP, CGRP+ SN sprouting, and pERK1/2 and pCREB expression in DRG. CGRP+ sensory nerves also expressed increased levels of the acid-sensing nociceptor ASIC3. Notably, a single injection of the selective ASIC3 antagonist APETx2 dramatically reduced MMBP in the model. Mechanistic investigations in primary DRG neurons co-cultured with JJN3 cells showed increased neurite outgrowth and excitation inhibited by bafilomycin A1 or APETx2. Further, combining APETx2 with bafilomycin A1 reduced MMBP to a greater extent than either agent alone. Lastly, combining bafilomycin A1 with the osteoclast inhibitor zoledronic acid was sufficient to ameliorate MMBP which was refractory to zoledronic acid. Overall, our results show that osteoclasts and MM cooperate to induce an acidic bone microenvironment that evokes MMBP as a result of the excitation of ASIC3-activated sensory neurons. Further, they present a mechanistic rationale for targeting ASIC3 on neurons along with the MM-induced acidic bone microenvironment as a strategy to relieve MMBP in patients

Delayed functional expression of neuronal chemokine receptors following focal nerve demyelination in the rat: a mechanism for the development of chronic sensitization of peripheral nociceptors

<p>Abstract</p> <p>Background</p> <p>Animal and clinical studies have revealed that focal peripheral nerve axon demyelination is accompanied by nociceptive pain behavior. C-C and C-X-C chemokines and their receptors have been strongly implicated in demyelinating polyneuropathies and persistent pain syndromes. Herein, we studied the degree to which chronic nociceptive pain behavior is correlated with the neuronal expression of chemokines and their receptors following unilateral lysophosphatidylcholine (LPC)-induced focal demyelination of the sciatic nerve in rats.</p> <p>Results</p> <p>Focal nerve demyelination increased behavioral reflex responsiveness to mechanical stimuli between postoperative day (POD) 3 and POD28 in both the hindpaw ipsilateral and contralateral to the nerve injury. This behavior was accompanied by a bilateral increase in the numbers of primary sensory neurons expressing the chemokine receptors CCR2, CCR5, and CXCR4 by POD14, with no change in the pattern of CXCR3 expression. Significant increases in the numbers of neurons expressing the chemokines monocyte chemoattractant protein-1 (MCP-1/CCL2), Regulated on Activation, Normal T Expressed and Secreted (RANTES/CCL5) and interferon γ-inducing protein-10 (IP-10/CXCL10) were also evident following nerve injury, although neuronal expression pattern of stromal cell derived factor-1α (SDF1/CXCL12) did not change. Functional studies demonstrated that acutely dissociated sensory neurons derived from LPC-injured animals responded with increased [Ca²⁺]_ifollowing exposure to MCP-1, IP-10, SDF1 and RANTES on POD 14 and 28, but these responses were largely absent by POD35. On days 14 and 28, rats received either saline or a CCR2 receptor antagonist isomer (CCR2 RA-<b>[R]</b>) or its inactive enantiomer (CCR2 RA-<b>[S]</b>) by intraperitoneal (i.p.) injection. CCR2 RA-[<b>R</b>] treatment of nerve-injured rats produced stereospecific bilateral reversal of tactile hyperalgesia.</p> <p>Conclusion</p> <p>These results suggest that the presence of chemokine signaling by both injured and adjacent, uninjured sensory neurons is correlated with the maintenance phase of a persistent pain state, suggesting that chemokine receptor antagonists may be an important therapeutic intervention for chronic pain.</p

Effect of the Phosphodiesterase-5 Inhibitor Zaprinast on Ischemia-Reperfusion Injury in Rats

The cardiac and renal protective effects of phosphodiesterase-5 (PDE-5) inhibitors against ischemia-reperfusion injury have recently been demonstrated in animal studies. We evaluated the effect of pretreatment with the PDE-5 inhibitor zaprinast on warm renal ischemia in a rat model

Merging Structural Motifs of Functionalized Amino Acids and α-Aminoamides Results in Novel Anticonvulsant Compounds with Significant Effects on Slow and Fast Inactivation of Voltage-Gated Sodium Channels and in the Treatment of Neuropathic Pain

We recently reported that merging key structural pharmacophores of the anticonvulsant drugs lacosamide (a functionalized amino acid) with safinamide (an α-aminoamide) resulted in novel compounds with anticonvulsant activities superior to that of either drug alone. Here, we examined the effects of six such chimeric compounds on Na+-channel function in central nervous system catecholaminergic (CAD) cells. Using whole-cell patch clamp electrophysiology, we demonstrated that these compounds affected Na+ channel fast and slow inactivation processes. Detailed electrophysiological characterization of two of these chimeric compounds that contained either an oxymethylene ((R)-7) or a chemical bond ((R)-11) between the two aromatic rings showed comparable effects on slow inactivation, use-dependence of block, development of slow inactivation, and recovery of Na+ channels from inactivation. Both compounds were equally effective at inducing slow inactivation; (R)-7 shifted the fast inactivation curve in the hyperpolarizing direction greater than (R)-11, suggesting that in the presence of (R)-7 a larger fraction of the channels are in an inactivated state. None of the chimeric compounds affected veratridine- or KCl-induced glutamate release in neonatal cortical neurons. There was modest inhibition of KCl-induced calcium influx in cortical neurons. Finally, a single intraperitoneal administration of (R)-7, but not (R)-11, completely reversed mechanical hypersensitivity in a tibial-nerve injury model of neuropathic pain. The strong effects of (R)-7 on slow and fast inactivation of Na+ channels may contribute to its efficacy and provide a promising novel therapy for neuropathic pain, in addition to its antiepileptic potential