The synthesis of SO-3, a conopeptide with high analgesic activity derived from Conus striatus

Animal Venom Peptides Cause Antinociceptive Effects by Voltage-gated Calcium Channels Activity Blockage

Pain is a complex phenomenon that is usually unpleasant and aversive. It can range widely in intensity, quality, and duration and has diverse pathophysiologic mechanisms and meanings. Voltage-gated sodium and calcium channels are essential to transmitting painful stimuli from the periphery until the dorsal horn of the spinal cord. Thus, blocking voltage-gated calcium channels (VGCCs) can effectively control pain refractory to treatments currently used in the clinic, such as cancer and neuropathic pain. VGCCs blockers isolated of cobra Naja naja kaouthia (α-cobratoxin), spider Agelenopsis aperta (ω-Agatoxin IVA), spider Phoneutria nigriventer (PhTx3.3, PhTx3.4, PhTx3.5, PhTx3.6), spider Hysterocrates gigas (SNX-482), cone snails Conus geographus (GVIA), Conus magus (MVIIA or ziconotide), Conus catus (CVID, CVIE and CVIF), Conus striatus (SO- 3), Conus fulmen (FVIA), Conus moncuri (MoVIA and MoVIB), Conus regularis (RsXXIVA), Conus eburneus (Eu1.6), Conus victoriae (Vc1.1.), Conus regius (RgIA), and spider Ornithoctonus huwena (huwentoxin-I and huwentoxin-XVI) venoms caused antinociceptive effects in different acute and chronic pain models. Currently, ziconotide is the only clinical used N-type VGCCs blocker peptide for chronic intractable pain. However, ziconotide causes different adverse effects, and the intrathecal route of administration also impairs its use in a more significant number of patients. In this sense, peptides isolated from animal venoms or their synthetic forms that act by modulating or blocking VGCCs channels seem to be a relevant prototype for developing new analgesics efficacious and well tolerated by patients.

Scalable Biosynthetic Production of Knotted Peptides Enables ADME and Thermodynamic Folding Studies

Knotted peptides present a wealth of structurally diverse, biologically active molecules, with the inhibitor cystine knot/knottin class among the most ecologically common ones. Many of these natural products interact with extracellular targets such as voltage-gated ion channels with exquisite selectivity and potency, making them intriguing therapeutic modalities. Such compounds are often produced in low concentrations by intractable organisms, making structural and biological characterization challenging, which is frequently overcome by various expression strategies. Here, we sought to test a biosynthetic route for the expression and study of knotted peptides. We screened expression constructs for a biosynthesized knotted peptide to determine the most influential parameters for successful disulfide folding and used NMR spectroscopic fingerprinting to validate topological structures. We performed pharmacokinetic characterization, which indicated that the interlocking disulfide structure minimizes liabilities of linear peptide sequences, and propose a mechanism by which knotted peptides are cleared. We then developed an assay to monitor solution folding in real time, providing a strategy for studying the folding process during maturation, which provided direct evidence for the importance of backbone organization as the driving force for topology formation.

A novel ω-conotoxin Bu8 inhibiting N-type voltage-gated calcium channels displays potent analgesic activity

ω-Conotoxins inhibit N-type voltage-gated calcium (Ca_V2.2) channels and exhibit efficacy in attenuating neuropathic pain but have a low therapeutic index. Here, we synthesized and characterized a novel ω-conotoxin, Bu8 from Conus bullatus, which consists of 25 amino acid residues and three disulfide bridges. Bu8 selectively and potently inhibits depolarization-activated Ba²⁺ currents mediated by rat Ca_V2.2 expressed in HEK293T cells (IC₅₀ = 89 nmol/L). Bu8 is two-fold more potent than ω-conotoxin MVIIA, a ω-conotoxin currently used for the treatment of severe chronic pain. It also displays potent analgesic activity in animal pain models of hot plate and acetic acid writhing but has fewer side effects on mouse motor function and lower toxicity in goldfish. Its lower side effects may be attributed to its faster binding rate and higher recovery ratios. The NMR structure demonstrates that Bu8 contains a small irregular triple β-strand. The structure-activity relationships of Bu8 Ala mutants and Bu8/MVIIA hybrid mutants demonstrate that the binding mode of Ca_V2.2 with the amino acid residues in loop 1 and loop 2 of Bu8 is different from that of MVIIA. This study characterizes a novel, more potent ω-conotoxin and provides new insights for designing Ca_V2.2 antagonists.

DSPE-PEG Modification of α-Conotoxin TxID

In order to improve stability of a peptide marine drug lead, α-conotoxin TxID, we synthesized and modified TxID at the N-terminal with DSPE-PEG-NHS by a nucleophilic substitution reaction to prepare the DSPE-PEG-TxID for the first time. The reaction conditions, including solvent, ratio, pH, and reaction time, were optimized systematically and the optimal one was reacted in dimethyl formamide at pH 8.2 with triethylamine at room temperature for 120 h. The in vitro stabilities in serum, simulated gastric juice, and intestinal fluid were tested, and improved dramatically compared with TxID. The PEG-modified peptide was functionally tested on α3β4 nicotinic acetylcholine receptor (nAChR) heterologously expressed in Xenopus laevis oocytes. The DSPE-PEG-TxID showed an obvious inhibition effect on α3β4 nAChR. All in all, the PEG modification of TxID was improved in stability, resistance to enzymatic degradation, and may prolong the half-life in vivo, which may pave the way for the future application in smoking cessation and drug rehabilitation, as well as small cell lung cancer.

TAT-Modified ω-Conotoxin MVIIA for Crossing the Blood-Brain Barrier

As the first in a new class of non-opioid drugs, ω-Conotoxin MVIIA was approved for the management of severe chronic pains in patients who are unresponsive to opioid therapy. Unfortunately, clinical application of MVIIA is severely limited due to its poor ability to penetrate the blood-brain barrier (BBB), reaching the central nervous system (CNS). In the present study, we have attempted to increase MVIIA’s ability to cross the BBB via a fusion protein strategy. Our results showed that when the TAT-transducing domain was fused to the MVIIA C-terminal with a linker of varied numbers of glycine, the MVIIA-TAT fusion peptide exhibited remarkable ability to cross the bio-membranes. Most importantly, both intravenous and intranasal administrations of MVIIA-TAT in vivo showed therapeutic efficacy of analgesia. Compared to the analgesic effects of intracerebral administration of the nascent MVIIA, these systemic administrations of MVIIA-TAT require higher doses, but have much prolonged effects. Taken together, our results showed that TAT conjugation of MVIIA not only enables its peripheral administration, but also maintains its analgesic efficiency with a prolonged effective time window. Intranasal administration also rendered the MVIIA-TAT advantages of easy applications with potentially reduced side effects. Our results may present an alternative strategy to improve the CNS accessibility for neural active peptides.

Structure-Activity Analysis of N-Type Calcium Channel Inhibitor SO-3

As an ω-conopeptide originally discovered from Conus striatus, SO-3 contains 25 amino acid residues and three disulfide bridges. Our previous study has shown that this peptide possesses potent analgesic activity in rodent pain models (mouse and rat), and it specifically inhibits an N-type calcium ion channel (Cav2.2). In the study presented here, we investigated the key amino acid residues for their inhibitory activity against Cav2.2 expressed in HEK 293 cells and analgesic activity in mice. To improve the inhibitory activity of SO-3, we also evaluated the effects of some amino acid residues derived from the corresponding residues of ω-peptide MVIIA, CVID, or GVIA. Our data reveal that Lys6, Ile11, and Asn14 are the important functional amino acid residues for SO-3. The replacement of some amino acid residues of SO-3 in loop 1 with the corresponding residues of CVID and GVIA improved the inhibitory activity of SO-3. The binding mode of Cav2.2 with SO-3 amino acids in loop 1 and loop 2 may be somewhat different from that of MVIIA. This study expanded our knowledge of the structure-activity relationship of ω-peptides and provided a new strategy for improving the potency of Cav2.2 inhibitors.

A novel α-conopeptide Eu1.6 inhibits N-type (CaV2.2) calcium channels and exhibits potent analgesic activity

We here describe a novel α-conopeptide, Eu1.6 from Conus eburneus, which exhibits strong anti-nociceptive activity by an unexpected mechanism of action. Unlike other α-conopeptides that largely target nicotinic acetylcholine receptors (nAChRs), Eu1.6 displayed only weak inhibitory activity at the α3β4 and α7 nAChR subtypes and TTX-resistant sodium channels, and no activity at TTX-sensitive sodium channels in rat dorsal root ganglion (DRG) neurons, or opiate receptors, VR1, KCNQ1, L- and T-type calcium channels expressed in HEK293 cells. However, Eu1.6 inhibited high voltage-activated N-type calcium channel currents in isolated mouse DRG neurons which was independent of GABA_B receptor activation. In HEK293 cells expressing Ca_V2.2 channels alone, Eu1.6 reversibly inhibited depolarization-activated Ba²⁺ currents in a voltage- and state-dependent manner. Inhibition of Ca_V2.2 by Eu1.6 was concentration-dependent (IC₅₀ ~1 nM). Significantly, systemic administration of Eu1.6 at doses of 2.5–5.0 μg/kg exhibited potent analgesic activities in rat partial sciatic nerve injury and chronic constriction injury pain models. Furthermore, Eu1.6 had no significant side-effect on spontaneous locomotor activity, cardiac and respiratory function, and drug dependence in mice. These findings suggest α-conopeptide Eu1.6 is a potent analgesic for the treatment of neuropathic and chronic pain and opens a novel option for future analgesic drug design.

Molecular basis of toxicity of N-type calcium channel inhibitor MVIIA

MVIIA (ziconotide) is a specific inhibitor of N-type calcium channel, Cav2.2. It is derived from Cone snail and currently used for the treatment of severe chronic pains in patients unresponsive to opioid therapy. However, MVIIA produces severe side-effects, including dizziness, nystagmus, somnolence, abnormal gait, and ataxia, that limit its wider application. We previously identified a novel inhibitor of Cav2.2, ω-conopeptide SO-3, which possesses similar structure and analgesic activity to MVIIA's. To investigate the key residues for MVIIA toxicity, MVIIA/SO-3 hybrids and MVIIA variants carrying mutations in its loop 2 were synthesized. The substitution of MVIIA's loop 1 with the loop 1 of SO-3 resulted in significantly reduced Cav2.2 binding activity in vitro; the replacement of MVIIA loop 2 by the loop 2 of SO-3 not only enhanced the peptide/Cav2.2 binding but also decreased its toxicity on goldfish, attenuated mouse tremor symptom, spontaneous locomotor activity, and coordinated locomotion function. Further mutation analysis and molecular calculation revealed that the toxicity of MVIIA mainly arose from Met(12) in the loop 2, and this residue inserts into a hydrophobic hole (Ile(300), Phe(302) and Leu(305)) located between repeats II and III of Cav2.2. The combinative mutations of the loop 2 of MVIIA or other ω-conopeptides may be used for future development of more effective Cav2.2 inhibitors with lower side effects.

Bioactive marine drugs and marine biomaterials for brain diseases

Marine invertebrates produce a plethora of bioactive compounds, which serve as inspiration for marine biotechnology, particularly in drug discovery programs and biomaterials development. This review aims to summarize the potential of drugs derived from marine invertebrates in the field of neuroscience. Therefore, some examples of neuroprotective drugs and neurotoxins will be discussed. Their role in neuroscience research and development of new therapies targeting the central nervous system will be addressed, with particular focus on neuroinflammation and neurodegeneration. In addition, the neuronal growth promoted by marine drugs, as well as the recent advances in neural tissue engineering, will be highlighted.

Analgesic effect of highly reversible ω-conotoxin FVIA on N type Ca2+ channels

Background

N-type Ca²⁺ channels (Ca_v2.2) play an important role in the transmission of pain signals to the central nervous system. ω-Conotoxin (CTx)-MVIIA, also called ziconotide (Prialt^®), effectively alleviates pain, without causing addiction, by blocking the pores of these channels. Unfortunately, CTx-MVIIA has a narrow therapeutic window and produces serious side effects due to the poor reversibility of its binding to the channel. It would thus be desirable to identify new analgesic blockers with binding characteristics that lead to fewer adverse side effects.

Results

Here we identify a new CTx, FVIA, from the Korean Conus Fulmen and describe its effects on pain responses and blood pressure. The inhibitory effect of CTx-FVIA on N-type Ca²⁺ channel currents was dose-dependent and similar to that of CTx-MVIIA. However, the two conopeptides exhibited markedly different degrees of reversibility after block. CTx-FVIA effectively and dose-dependently reduced nociceptive behavior in the formalin test and in neuropathic pain models, and reduced mechanical and thermal allodynia in the tail nerve injury rat model. CTx-FVIA (10 ng) also showed significant analgesic effects on writhing in mouse neurotransmitter- and cytokine-induced pain models, though it had no effect on acute thermal pain and interferon-γ induced pain. Interestingly, although both CTx-FVIA and CTx-MVIIA depressed arterial blood pressure immediately after administration, pressure recovered faster and to a greater degree after CTx-FVIA administration.

Conclusions

The analgesic potency of CTx-FVIA and its greater reversibility could represent advantages over CTx-MVIIA for the treatment of refractory pain and contribute to the design of an analgesic with high potency and low side effects.

cDNA cloning of conotoxins with framework XII from several Conus species

In our efforts for cloning novel I(2)-superfamily conotoxins using the signal peptide sequence, we identified a novel conotoxin Lt12.4 from Conus litteratus. This gene has a framework XII (-C-C-C-C-CC-C-C-), which is distinct from the cysteine pattern I(2)-superfamily conotoxin (-C-C-CC-CC-C-C-). Subsequently, we found the signal peptide sequence of Lt12.4 by 5'-RACE. Using this new sequence, we identified another five novel conotoxins with this cysteine pattern from four Conus species (Conus eburneus, Conus imperialis, Conus marmoreus, and C. litteratus). These novel conotoxins have the same cysteine pattern as the reported Gla-TxX and Gla-MII, and may contain Gla residues. Furthermore, they have the highly conserved signal peptide and hypervariable mature peptide sequences, and widely exist in Conus species. Therefore, it could be defined as a new superfamily of E-conotoxins.

Identification of novel I-superfamily conopeptides from several clades of Conus species found in the South China Sea

The I-superfamily of Conus peptides represents a new class of peptides with four disulfide bridges (-C-C-CC-CC-C-C-) that falls into three (I1, I2 and I3) categories according to the different signal peptide sequences. The I-superfamily has received increasing attention because it targets K+ ion channels, a function that is relatively rare in conotoxins. Herein we report 11 novel I-superfamily conotoxins from the venom ducts of five Cone snails (Conus eburneus, Conus imperialis, Conus vitulinus, Conus emaciatus and Conus litteratus) native to the South China Sea using a primer designed according to the N-terminus of the signal sequence of I2-superfamily conotoxins. The alignment of sequences revealed that signal regions exhibited moderate conservation with the exception of Eb11.3 from C. eburneus with homologies of 21.1%, 38.5% and 30.0% to the signal peptides of I1, I2 and I3 superfamily conotoxins, respectively. The mature peptides ranged from almost identical to highly divergent between species. Analyses of the evolutionary trees of these peptides with those of reported I-superfamily conotoxins showed that nine of them fall in I2 superfamily clades, but two of them were neither I1- and I2- nor I3-superfamily clades. Notably, some peptides exhibited significantly different amino acid residues in the intercysteine loops compared with group A, B and C of I-superfamily conopeptides, suggesting that they may have different bioactivities and functions.

SO-3, a new O-superfamily conopeptide derived from Conus striatus, selectively inhibits N-type calcium currents in cultured hippocampal neurons

Whole-cell currents in cultured hippocampal neurons were recorded to investigate the effects of SO-3, a new O-superfamily conopeptide derived from Conus striatus, on voltage-sensitive channels. SO-3 had no effect on voltage-sensitive sodium currents, delayed rectifier potassium currents, and transient outward potassium currents. Similar to the selective N-type calcium channel blocker omega-conotoxin MVIIA (MVIIA), SO-3 could concentration-dependently inhibit the high voltage-activated (HVA) calcium currents (I(Ca)). MVIIA(3 microM), 10 microM nimodipine, and 0.5 microM omega-agatoxin IVA (Aga) could selectively block the N-, L-, and P/Q-type I(Ca), which contributed approximately 32, approximately 38, and approximately 21% of the HVA currents in hippocampal neurons, respectively. About 31% of the total HVA currents were inhibited by 3 microM SO-3. SO-3 (3 microM) and 3 microM MVIIA inhibited the overlapping components of HVA currents, whereas no overlapping component was inhibited by 3 microM SO-3 and 10 microM nimodipine, or by 3 microM SO-3 and 0.5 microM Aga. Also, 3 microM SO-3 had no effect on R-type currents. SO-3 had less inhibitory effects on non-N-type HVA currents than MVIIA at higher concentrations (30 and 100 microM). The inhibitory effects of SO-3 and MVIIA on HVA currents were almost fully reversible. However, the recovery from block by MVIIA was more rapid than recovery from block by SO-3. It is concluded that SO-3 is a new omega-conotoxin selectively targeting N-type voltage-sensitive calcium channels. Considering the significance of N-type calcium channels for pain transduction, SO-3 may have therapeutic potential as a novel analgesic agent.

Emerging analgesics in cancer pain management

Cancer pain is one of the most frequent symptoms in malignant disease, severely impairing the patients' quality of life. The recommendations of the World Health Organization will provide adequate pain relief for the vast majority of cancer patients. However, some patients will suffer from inadequate analgesia or intolerable side effects. Cyclooxygenase-2 (COX-2)-selective non-steroidal anti-inflammatory drugs (NSAIDs), new anticonvulsants, cannabinoids and NMDA receptor antagonists are being developed for these patients. NSAIDs with nitric oxide-releasing moieties are an interesting addition, as this new class of analgesics combines improved analgesic efficacy with higher tolerability. Conotoxins and other drugs such as nicotinic acetylcholinergic receptor agonists will be advantageous only for a few patients in the near future, as side-effect profile and risk of complications, as well as the burden on the patient, often are not worth the additional analgesic benefit.

Biologic poisons for pain

Pain therapies from natural sources date back thousands of years to the use of plant and animal extracts for a variety of painful conditions and injuries. We certainly are all familiar with modern uses of plant-derived analgesic compounds such as opium derivatives from papaverum somniferum and salicylates from willow bark (Salix species). Local anesthetics were isolated from coca leaves in the late 1800s. Sarapin, derived from carnivorous pitcher plants, has been injected for regional analgesia in human and veterinary medicine, but efficacy is controversial. Biologic organisms can play important roles in developing an understanding of pain mechanisms, either from isolation of compounds that are analgesic or of compounds that produce pain, hyperalgesia, and allodynia.