¹Available from Allergan, Inc. or Irvine, Calif. under the tradename BOTOX®.

The success of BoNt/A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. A study of two commercially available BoNT/A preparations (BOTOX® and Dysport®) and preparations of BoNT/B and F (both obtained from Wako Chemicals, Japan) has been carried out to determine local muscle weakening efficacy, safety and antigenic potential. Botulinum toxin preparations were injected into the head of the right gastrocnemius muscle (0.5 to 200.0 units/kg) and muscle weakness was assessed using the mouse digit abduction scoring assay (DAS). ED₅₀ values were calculated from dose response curves. Additional mice were given intramuscular injections to determine LD₅₀ doses. The therapeutic index was calculated as LD₅₀/ED₅₀. Separate groups of mice received hind limb injections of BOTOX® (5.0 to 10.0 units/kg) or BoNt/B (50.0 to 400.0 units/kg), and were tested for muscle weakness and increased water consumption, the later being a putative model for dry mouth. Antigenic potential was assessed by monthly intramuscular injections in rabbits (1.5 or 6.5 ng/kg for BoNt/B or 0.15 ng/kg for BOTOX®). Peak muscle weakness and duration were dose related for all serotypes. DAS ED₅₀ values (units/kg) were as follows: BOTOX®: 6.7, Dysport®: 24.7, BoNt/B: 27.0 to 244.0, BoNT/F: 4.3. BOTOX® had a longer duration of action than BoNt/B or BoNt/F. Therapeutic index values were as follows: BOTOX®: 10.5, Dysport®: 6.3, BoNt/B: 3.2. Water consumption was greater in mice injected with BoNt/B than with BOTOX®, although BoNt/B was less effective at weakening muscles. After four months of injections 2 of 4 (where treated with 1.5 ng/kg) and 4 of 4 (where treated with 6.5 ng/kg) rabbits developed antibodies against BoNt/B. In a separate study, 0 of 9 BOTOX® treated rabbits demonstrated antibodies against BoNt/A. DAS results indicate relative peak potencies of BoNt/A being equal to BoNt/F, and BoNt/F being greater than BoNt/B. With regard to duration of effect, BoNt/A was greater than BoNt/B, and BoNt/B duration of effect was greater than BoNt/F. As shown by the therapeutic index values, the two commercial preparations of BoNt/A (BOTOX® and Dysport®) are different. The increased water consumption behavior observed following hind limb injection of BoNt/B indicates that clinically significant amounts of this serotype entered the murine systemic circulation. The results also indicate that in order to achieve efficacy comparable to BoNt/A, it is necessary to increase doses of the other serotypes examined. Increased dosage can comprise safety. Furthermore, in rabbits, serotype B was more antigenic than was BOTOX®, possibly because of the higher protein load injected to achieve an effective dose of BoNt/B.

The tetanus neurotoxin acts mainly in the central nervous system, while botulinum neurotoxin acts at the neuromuscular junction; both act by inhibiting acetylcholine release from the axon of the affected neuron into the synapse, resulting in paralysis. The effect of intoxication on the affected neuron is long-lasting and until recently has been thought to be irreversible. The tetanus neurotoxin is known to exist in one immunologically distinct serotype.

Acetylcholine

Typically only a single type of small molecule neurotransmitter is released by each type of neuron in the mammalian nervous system. The neurotransmitter acetylcholine is secreted by neurons in many areas of the brain, but specifically by the large pyramidal cells of the motor cortex, by several different neurons in the basal ganglia, by the motor neurons that innervate the skeletal muscles, by the preganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), by the postganglionic neurons of the parasympathetic nervous system, and by some of the postganglionic neurons of the sympathetic nervous system. Essentially, only the postganglionic sympathetic nerve fibers to the sweat glands, the piloerector muscles and a few blood vessels are cholinergic and most of the postganglionic neurons of the sympathetic nervous system secret the neurotransmitter norepinephine. In most instances acetylcholine has an excitatory effect. However, acetylcholine is known to have inhibitory effects at some of the peripheral parasympathetic nerve endings, such as inhibition of the heart by the vagal nerve.

The efferent signals of the autonomic nervous system are transmitted to the body through either the sympathetic nervous system or the parasympathetic nervous system. The preganglionic neurons of the sympathetic nervous system extend from preganglionic sympathetic neuron cell bodies located in the intermediolateral horn of the spinal cord. The preganglionic sympathetic nerve fibers, extending from the cell body, synapse with postganglionic neurons located in either a paravertebral sympathetic ganglion or in a prevertebral ganglion. Since, the preganglionic neurons of both the sympathetic and parasympathetic nervous system are cholinergic, application of acetylcholine to the ganglia will excite both sympathetic and parasympathetic postganglionic neurons.

Acetylcholine activates two types of receptors, muscarinic and nicotinic receptors. The muscarinic receptors are found in all effector cells stimulated by the postganglionic neurons of the parasympathetic nervous system, as well as in those stimulated by the postganglionic cholinergic neurons of the sympathetic nervous system. The nicotinic receptors are found in the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic. The nicotinic receptors are also present in many membranes of skeletal muscle fibers at the neuromuscular junction.

Acetylcholine is released from cholinergic neurons when small, clear, intracellular vesicles fuse with the presynaptic neuronal cell membrane. A wide variety of non-neuronal secretory cells, such as, adrenal medulla (as well as the PC12 cell line) and pancreatic islet cells release catecholamines and insulin, respectively, from large dense-core vesicles. The PC12 cell line is a clone of rat pheochromocytoma cells extensively used as a tissue culture model for studies of sympathoadrenal development. Botulinum toxin inhibits the release of both types of compounds from both types of cells in vitro, permeabilized (as by electroporation) or by direct injection of the toxin into the denervated cell. Botulinum toxin is also known to block release of the neurotransmitter glutamate from cortical synaptosomes cell cultures.

Sanders et al. in U.S. Pat. No. 5,766,605 disclose that BoNT/A can be used to treat autonomic nervous system disorders, for example rhinorrhea, otitis media, excessive salivation, asthma, chronic obstructive pulmonary disease (COPD), excessive stomach acid secretion, spastic colitis and excessive sweating.

Furthermore, Binder U.S. Pat. No. 5,714,468 discloses that BoNT/A can be used to treat migraine headache pain that is associated with muscle spasm, vascular disturbances, neuralgia and neuropathy. Additionally, our laboratory data obtained from experiments with rats show that pain, particularly inflammation pain, may be reduced with an injection of botulinum serotype A, either spinally or peripherally.

One of the reasons that BoNT/A has been selected over the other serotypes, for example serotypes B, C₁, D, E, F, and G, for clinical use is that BoNT/A has a substantially longer lasting therapeutic effect. In other words, the inhibitory effect of BoNT/A is more persistent. Therefore, the other serotypes of botulinum toxins could potentially be effectively used in a clinical environment if their biological persistence could be enhanced. For example, parotid sialocele is a condition where the patient suffers from excessive salivation. Sanders et al. disclose in their patent that serotype D may be very effective in reducing excessive salivation. However, the biological persistence of serotype D botulinum toxin is relatively short and thus may not be practical for clinical use. If the biological persistence of serotype D may be enhanced, it may effectively be used in a clinical environment to treat, for example, parotid sialocele.

Another reason that BoNT/A has been a preferred neurotoxin for clinical use is, as discussed above, its superb ability to immobilize muscles through flaccid paralysis. For example, BoNT/A is preferentially used to immobilize muscles and prevent limb movements after a tendon surgery to facilitate recovery. However, for some minor tendon surgeries, the healing time is relatively short. It would be beneficial to have a BoNT/A without the prolonged persistence for use in such circumstances so that the patient can regain mobility at about the same time they recover from the surgery.

There is a need to have modified neurotoxins that are non serotype A botulinum toxins with enhanced biological persistence and modified neurotoxins that are BoNT/A with reduced biological persistence and methods for preparing such toxins.

SUMMARY OF THE INVENTION

The present invention meets this need and provides for non serotype A botulinum toxins with enhanced persistence and BoNT/A with reduced persistence and methods for preparing such toxins.

In one broad embodiment of the invention, a modified neurotoxin is formed from a neurotoxin which includes a structural modifcation. The structural modification is able to alter the biological persistence of the neurotoxin. In one embodiment, the structural modification includes fusing a biological persistence enhancing component with a neurotoxin. The biological persistence enhancing component increases the duration of the inhibitory effect of the modified neurotoxin intracellularly. Preferably, the biological persistence enhancing component is a leucine-based motif.

Without wishing to be limited by any particular theory or mechanism of operation, it is believed that the leucine-based motif enhances the persistence of a neurotoxin by increasing its biological half-life. For example, it is known that BoNT/A has a very long biological persistence. Keller et al., FEBS Letters, 456:137-142 (1999), investigated to determine whether the persistence of BoNT/A is due to a depressed synthesis of SNAP-25 to replace the cleaved ones, or is due to the stability of the light chain intracellularly. Keller et al. found that the major factor limiting cellular recovery is the prolonged stability of toxin, or prolonged half-life.

Furthermore, without wishing to be limited by any particular theory or mechanism of operation, it is believed that the leucine-based motif located on the light chain, or the third amino acid sequence region, of BoNT/A, and not on any other serotypes, is responsible for the prolonged half-life of BoNT/A.

A leucine-based motif is often found on the carboxyl termini of several membrane receptors and vesicular neurotransmitter transporter and it apparently plays a crucial role in vesicle/membrane trafficking. Liu et al. Trends Cell Biol, 9:356-363 (1999); Tan et al. J Biol Chem, 273:17351-17360 (1998); Dietrich et al. J. Cell Bio, 138:271-281 (1997); Shin et al. J Biol Chem, 266:10658-10665 (1991) and Geister et al. J Biol Chem, 273:21316-21323 (1998). More specifically, the leuine-based motif is found in a membrane-proximal, cytoplasmic, carboxylic terminal tail of a membrane-bound receptor or transporter protein. It has been demonstrated that adaptor proteins that are highly concentrated at clathrin coated pits bind to the leucine-based motif and that disruption of this motif disrupts endocytosis of the motif-containing protein. Tan et al. J Biol Chem, 273:17351-17360 (1998); Dietrich et al. J. Cell Bio, 138:271-281 (1997) and Shin et al. J Biol Chem, 266:10658-10665 (1991). Furthermore, addition of the leucine-based motif to the carboxyl terminus of the plasma membrane protein Tac resulted in endocytosis of the chimera, suggesting that the motif is sufficient for targeted endocytosis. Tan et al. Supra.

The leucine-based motif located on the light chain of BoNT/A may cause the light chain to localize at the membranes, similarly to how membrane-bound receptor or transporter protein are localized at the membranes described above. Localization of the light chain to the membrane may protect and preserve the light chain, and the heavy chain if it is still attached, from being removed and/or degraded by the intracellular cleaning processes, thereby rendering it a long biological half-life. For example, intracellular autophagosomes are responsible for cleaning the cytoplasm by engulfing, and thereafter degrading, free floating foreign substances in the cytoplasm. Erdal et al. Naunyn Schmiedebergs Acrch Phamacol, 351:67-78 (1995). Since the leucine-based motif provides an anchor for the light chain, and the heavy chain if it is still attached, it would be difficult for the autophagosomes to remove and engulf the light chain from the cytoplasm. Thus the light chain remains in the cytoplasm to continue exerting its inhibitory effects on vesicular exocytosis of neurotransmitters.

In another embodiment, the leucine-based motif located on the light chain of BoNT/A is removed in its entirety or in parts. This modified neurotoxin effectively has a shortened the biological persistence. Preferably, this modified neurotoxin has a decreased half-life.

This invention also provide for methods of producing modified neurotoxins. Additionally, this invention provide for methods of using the modified neurotoxins to treat biological disorders.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based upon the discovery that the biological persistence of a neurotoxin may be altered by structurally modifying the neurotoxin. In other words, a modified neurotoxin with an altered biological persistence may be formed from a neurotoxin containing or including a structural modification. In one embodiment, the structural modification includes the fusing a biological persistence enhancing component to the primary structure of a neurotoxin to enhance its biological persistence. In a preferred embodiment, the biological persistence enhancing component is a leucine-based motif. Preferably, the biological persistence enhancing component enhances the biological half-life of the modified neurotoxin. More preferably, the biological half-life of the modified neurotoxin is enhanced by about 10%. Even more preferably, the biological half-life of the modified neurotoxin is enhanced by about 100%. Generally speaking, the modified neurotoxin has a biological persistence of about 20% to 300% more than an identical neurotoxin without the structural modification. That is, for example, the modified neurotoxin including the biological persistence enhancing component is able to cause a substantial inhibition of acetylcholine release from a nerve terminal for about 20% to about 300% longer than a neurotoxin that is not modified.

In a broad embodiment of the present invention, a leucine-based motif is an oligomer of seven amino acids. The oligomer is organized in to two groups. The first five amino acids starting from the amino terminal of the leucine-based motif form a "quintet of amino acids." The two amino acids immediately following the quintet of amino acids form a "duplet of amino acids." In a preferred embodiment, the duplet of amino acids is located at the carboxyl terminal region of the leucine-based motif. In another preferred embodiment, the quintet of amino acids includes at least one acidic amino acid selected from a group consisting of a glutamate and an aspartate.

The duplet of amino acid includes at least one hydrophobic amino acid, for example leucine, isoleucine, methionine, alanine, phenylalanine, tryptophan, valine or tyrosine. Preferably, the duplet of amino acid is a leucine-leucine, a leucine-isoleucine, an isoleucine-leucine or an isoleucine-isoleucine. Even more preferably, the duplet is a leucine-leucine.

In one embodiment, the leucine-based motif is xDxxxLL, SEQ ID#1, wherein x and may be any amino acids. In another embodiment, the leucine-based motif is xExxxLL, SEQ ID#2, wherein E is glutamic acid. In another embodiment, the duplet of amino acids may include an isoleucine or a methionine, forming xDxxxLI, SEQ ID#3 or xDxxxLM, SEQ ID#4, respectively. Additionally, the aspartic acid, D, may be replaced by a glutamic acid, E, to form xExxxLI, SEQ ID# 5, and xExxxLM, SEQ ID#6. In a preferred embodiment, the leucine-based motif is phenylalanine-glutamate-phenylalanine-tyrosine-lycine-leucine-leucine, SEQ ID #7.

In another embodiment, the quintet of amino acids comprises at least one hydroxyl containing amino acid, for example a serine, a threonine or a tyrosine. Preferably, the hydroxyl containing amino acid can be phosphorylated. More preferably, the hydroxyl containing amino acid is a serine which can be phosphorylated to allow for the binding of adaptor proteins.

Although non-modified amino acids are provided as examples, a modified amino acid is also contemplated to be within the scope of this invention. For example, leucine-based motif may include a halogenated, preferably, fluorinated leucine.

Various leucine-based motif are found in various species. A list of possible leucine-based motif derived from the various species that may be used in accordance with this invention is shown in Table 1. This list is not intended to be limiting.

VMAT is vesicular monoamine transporter; VACht is vesicular acetylcholine transporter. Italicized serine residues are potential sites of phosphorylation.

The modified neurotoxin may be formed from any neurotoxin. Preferably, the neurotoxin used is a Clostridial neurotoxin. A Clostridial neurotoxin comprises a polypeptide having three amino acid sequence regions. The first amino acid sequence region includes a neuronal binding moiety which is substantially completely derived from a neurotoxin selected from a group consisting of beratti toxin; butyricum toxin; tetani toxin; BoNT/A, B. C₁, D, E, F, and G. Preferably, the first amino acid sequence region is derived from the carboxyl terminal region of a toxin heavy chain, H_C.

The second amino acid sequence region is effective to translocate the polypeptide or a part thereof across an endosome membrane into the cytoplasm of a neuron. In one embodiment, the second amino acid sequence region of the polypeptide comprises an amine terminal of a heavy chain, H_N, derived from a neurotoxin selected from a group consisting of beratti toxin; butyricum toxin; tetani toxin; BoNT/A, B, C₁, D, E, F, and G.

The third amino acid sequence region has therapeutic activity when it is released into the cytoplasm of a target cell or neuron. In one embodiment, the third amino acid sequence region of the polypeptide comprises a toxin light chain, L, derived from a neurotoxin selected from a group consisting of beratti toxin; butyricum toxin; tetani toxin; BoNT/A, B, C₁, D, E, F, and G.

The Clostridial neurotoxin may be a hybrid neurotoxin. For example, each of the neurotoxin's amino acid sequence regions may be derived from a different Clostridial neurotoxin serotype. For example, in one embodiment, the polypeptide comprises a first amino acid sequence region derived from the H_C of the tetani toxin, a second amino acid sequence region derived from the H_N of BoNt/B, and a third amino acid sequence region derived from the L chain of botulinum serotype E. All other possible combinations are included within the scope of the present invention.

Alternatively, all three of the amino acid sequence regions of the Clostridial neurotoxin may be from the same species and same serotype. If all three amino acid sequence regions of the neurotoxin are from the same Clostridial neurotoxin species and serotype, the neurotoxin will be referred to by the species and serotype name. For example, a neurotoxin polypeptide may have its first, second and third amino acid sequence regions derived from BoNT/E. In which case, the neurotoxin is referred as BoNT/E.

Additionally, each of the three amino acid sequence regions may be modified from the naturally occurring sequence from which they are derived. For example, the amino acid sequence region may have at least one or more amino acid may be added or deleted as compared to the naturally occurring sequence.

The biological persistence enhancing component, preferably the leucine-based motif, may be fused with any of the above described neurotoxin to form a modified neurotoxin with an enhanced biological persistence. "Fusing" as used in the context of this invention includes covalently adding to or covalently inserting in between a primary structure of a neurotoxin. Preferably, the biological persistence enhancing component is added to a Clostridial neurotoxin which does not have a leucine-based motif in its primary structure. For example, in one embodiment, the leucine-based motif is fused with a hybrid neurotoxin, wherein the third amino acid sequence is not derived from botulinum serotype A. In another embodiment, the leucine-based motif is fused with a BoNt/E.

In one embodiment, the leucine-based motif is fused with the third amino acid sequence region of the neurotoxin. In a preferred embodiment, the leucine-based motif is fused with the region towards the carboxylic terminal of the third amino acid sequence region. More preferably, the leucine-based motif is fused with the carboxylic terminal of the third region of a neurotoxin. Even more preferably, the leucine-based motif is fused with the carboxylic terminal of the third region of BoNt/E.

In another embodiment, the structural modification of a neurotoxin which has a preexisting leucine-based motif includes deleting one or more amino acids from the leucine-based motif. Alternatively, a modified neurotoxin includes a structural modification which results in a neurotoxin with one or more amino acids absent from the leucine-based motif. The removal of one or more amino acids from the preexisting leucine-based motif is effective to reduce the biological persistence of a modified neurotoxin. More preferably, the deletion of one or more amino acids from the leucine-based motif of BoNT/A reduces the biological half-life of the modified neurotoxin.

In one broad aspect of the present invention, a method is provided for treating a biological disorder using a modified neurotoxin. The treatments may include treating neuromuscular disorders, autonomic nervous system disorders and pain.

The neuromuscular disorders and conditions that may be treated with a modified neurotoxin include: for example, strabismus, blepharospasm, spasmodic torticollis (cervical dystonia), oromandibular dystonia and spasmodic dysphonia (largyngeal dystonia).

For example, Borodic U.S. Pat. No. 5,053,005 discloses methods for treating juvenile spinal curvature, i.e. scoliosis, using BoNT/A. The disclosure of Borodic is incorporated in its entirety herein by reference. In one embodiment, using substantially similar methods as disclosed by Borodic, a modified neurotoxin is administered to a mammal, preferably a a human, to treat spinal curvature. In a preferred embodiment, a modified neurotoxin comprising BoNT/E fused with a leucine-based motif is administered. Even more preferably, a modified neurotoxin comprising BoNT/E with a leucine-based motif fused to the carboxyl terminal of its light chain is administered to the mammal, preferably a human, to treat spinal curvature. The modified neurotoxin may be administered to treat other neuromuscular disorders using well known techniques that are commonly performed with BoNT/A.

Autonomic nervous system disorders may also be treated with a modified neurotoxin. For example, glandular malfunctioning is an autonomic nervous system disorder. Glandular malfunctioning includes excessive sweating and excessive salivation. Respiratory malfunctioning is another example of an autonomic nervous system disorder. Respiratory malfunctioning includes chronic obstructive pulmonary disease and asthma. Sanders et al. discloses methods for treating the autonomic nervous system, such as excessive sweating, excessive salivation, asthma, etc., using naturally existing botulinum toxins. The disclosure of Sander et al. is incorporated in its entirety by reference herein. In one embodiment, substantially similar methods to that of Sanders et al. may be employed, but using a modified neurotoxin, to treat autonomic nervous system disorders such as the ones discussed above. For example, a modified neurotoxin may be locally applied to the nasal cavity of the mammal in an amount sufficient to degenerate cholinergic neurons of the autonomic nervous system that control the mucous secretion in the nasal cavity.

Pain that may be treated by a modified neurotoxin include pain caused by muscle tension, or spasm, or pain that is not associated with muscle spasm. For example, Binder in U.S. Pat. No. 5,714,468 discloses that headache caused by vascular disturbances, muscular tension, neuralgia and neuropathy may be treated with a naturally occurring botulinum toxin, for example BoNT/A. The disclosures of Binder is incorporated in its entirety herein by reference. In one embodiment, substantially similar methods to that of Binder may be employed, but using a modified neurotoxin, to treat headache, especially the ones caused by vascular disturbances, muscular tension, neuralgia and neuropathy. Pain caused by muscle spasm may also be treated by an administration of a modified neurotoxin. For example, a BoNT/E fused with a leucine-based motif, preferably at the carboxyl terminal of the BoNT/E light chain, may be administered intramuscularly at the pain/spasm location to alleviate pain.

Furthermore, a modified neurotoxin may be administered to a mammal to treat pain that is not associated with a muscular disorder, such as spasm. In one broad embodiment, methods of the present invention to treat non-spasm related pain include central administration or peripheral administration of the modified neurotoxin.

For example, Foster et al. in U.S. Pat. No. 5,989,545 discloses that a botulinum toxin conjugated with a targeting moiety may be administered centrally (intrathecally) to alleviate pain. The disclosures of Foster et al. is incorporated in its entirety by reference herein. In one embodiment, substantially similar methods to that of Foster et al. may be employed, but using the modified neurotoxin according to this invention, to treat pain. The pain to be treated may be an acute pain, or preferably, chronic pain.

An acute or chronic pain that is not associated with a muscle spasm may also be alleviated with a local, peripheral administration of the modified neurotoxin to an actual or a perceived pain location on the mammal. In one embodiment, the modified neurotoxin is administered subcutaneously at or near the location of pain, for example at or near a cut. In another embodiment, the modified neurotoxin is administered intramuscularly at or near the location of pain, for example at or near a bruise location on the mammal. In another embodiment, the modified neurotoxin is injected directly into a joint of a mammal, for treating or alleviating pain cause arthritis conditions. Also, frequent repeated injections or infusion of the modified neurotoxin to a peripheral pain location is within the scope of the present invention. However, given the long lasting therapeutic effects of the present invention, frequent injections or infusion of the neurotoxin may not be necessary. For example, practice of the present invention can provide an analgesic effect, per injection, for 2 months or longer, for example 27 months, in humans.

Without wishing to limit the invention to any mechanism or theory of operation, it is believed that when the modified neurotoxin is administered locally to a peripheral location, it inhibits the release of neuro-substances, for example substance P, from the peripheral primary sensory terminal. Since the release of substance P by the peripheral primary sensory terminal may cause or at least amplify pain transmission process, inhibition of its release at the peripheral primary sensory terminal will dampen the transmission of pain signals from reaching the brain.

In addition to having pharmacologic actions at the peripheral location, the modified neurotoxin of the present invention may also have inhibitory effects in the central nervous system. Presumably the retrograde transport is via the primary afferent. This hypothesis is supported by our experimental data which shows that BoNT/A is retrograde transported to the dorsal horn when the neurotoxin is injected peripherally. Moreover, work by Weigand et al, Nauny-Schmiedeberg's Arch. Pharmacol. 1976; 292, 161-165, and Habermann, Nauny-Schmiedeberg's Arch. Pharmacol. 1974; 281, 47-56, showed that botulinum toxin is able to ascend to the spinal area by retrograde transport. As such, a modified neurotoxin, for example BoNt/A with one or more amino acids deleted from the leucine-based motif, injected at a peripheral location, for example intramuscularly, may be retrograde transported from the peripheral primary sensory terminal to the central primary sensory terminal.

The amount of the modified neurotoxin administered can vary widely according to the particular disorder being treated, its severity and other various patient variables including size, weight, age, and responsiveness to therapy. Generally, the dose of modified neurotoxin to be administered will vary with the age, presenting condition and weight of the mammal, preferably a human, to be treated. The potency of the modified neurotoxin will also be considered.

Assuming a potency which is substantially equivalent to LD₅₀=2,730 U in a human patient and an average person is 75 kg, a lethal dose would be about 36 U/kg of a modified neurotoxin. Therefore, when a modified neurotoxin with such an LD₅₀ is administered, it would be appropriate to administer less than 36 U/kg of the modified neurotoxin into human subjects. Preferably, about 0.01 U/kg to 30 U/kg of the modified neurotoxin is administered. More preferably, about 1 U/kg to about 15 U/kg of the modified neurotoxin is administered. Even more preferably, about 5 U/kg to about 10 U/kg modified neurotoxin is administered. Generally, the modified neurotoxin will be administered as a composition at a dosage that is proportionally equivalent to about 2.5 cc/100 U. Those of ordinary skill in the art will know, or can readily ascertain, how to adjust these dosages for neurotoxin of greater or lesser potency.

Although examples of routes of administration and dosages are provided, the appropriate route of administration and dosage are generally determined on a case by case basis by the attending physician. Such determinations are routine to one of ordinary skill in the art (see for example, Harnson's Principles of Internal Medicine (1998), edited by Anthony Fauci et al., 14^th edition, published by McGraw Hill). For example, the route and dosage for administration of a modified neurotoxin according to the present disclosed invention can be selected based upon criteria such as the solubility characteristics of the modified neurotoxin chosen as well as the types of disorder being treated.

The modified neurotoxin may be produced by chemically linking the leucine-based motif to a neurotoxin using conventional chemical methods well known in the art. The neurotoxin may be obtained from a harvesting neurotoxins. For example, BoNt/E can be obtained by establishing and growing cultures of Clostridium botulinum in a fermenter and then harvesting and purifying the fermented mixture in accordance with known procedures. All the botulinum toxin serotypes are initially synthesized as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C₁, D and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the BoNt/B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the BoNt/B toxin is likely to be inactive, possibly accounting for the known significantly lower potency of BoNt/B as compared to BoNt/A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy. Additionally, it is known that BoNt/B has, upon intramuscular injection, a shorter duration of activity and is also less potent than BoNt/A at the same dose level.

The modified neurotoxin may also be produced by recombinant techniques. Recombinant techniques are preferable for producing a neurotoxin having amino acid sequence regions from different Clostridial species or having modified amino acid sequence regions. Also, the recombinant technique is preferable in producing BoNT/A with the leucine-based motif being modified by deletion. The technique includes steps of obtaining genetic materials from natural sources, or synthetic sources, which have codes for a neuronal binding moiety, an amino acid sequence effective to translocate the neurotoxin or a part thereof, and an amino acid sequence having therapeutic activity when released into a cytoplasm of a target cell, preferably a neuron. In a preferred embodiment, the genetic materials have codes for the biological persistence enhancing component, preferably the leucine-based motif, the H_C, the H_N and the L chain of the Clostridial neurotoxins and fragments thereof. The genetic constructs are incorporated into host cells for amplification by first fusing the genetic constructs with a cloning vectors, such as phages or plasmids. Then the cloning vectors are inserted into hosts, preferably E. coli 's. Following the expressions of the recombinant genes in host cells, the resultant proteins can be isolated using conventional techniques.

There are many advantages to producing these modified neurotoxins recombinantly. For example, to form a modified neurotoxin, a modifying fragment must be attached or inserted into a neurotoxin. The production of neurotoxin from anaerobic Clostridium cultures is a cumbersome and time-consuming process including a multi-step purification protocol involving several protein precipitation steps and either prolonged and repeated crystallization of the toxin or several stages of column chromatography. Significantly, the high toxicity of the product dictates that the procedure must be performed under strict containment (BL-3). During the fermentation process, the folded single-chain neurotoxins are activated by endogenous clostridial proteases through a process termed nicking to create a dichain. Sometimes, the process of nicking involves the removal of approximately 10 amino acid residues from the single-chain to create the dichain form in which the two chains remain covalently linked through the intrachain disulfide bond.

The nicked neurotoxin is much more active than the unnicked form. The amount and precise location of nicking varies with the serotypes of the bacteria producing the toxin. The differences in single-chain neurotoxin activation and, hence, the yield of nicked toxin, are due to variations in the serotype and amounts of proteolytic activity produced by a given strain. For example, greater than 99% of Clostridial botulinum serotype A single-chain neurotoxin is activated by the Hall A Clostridial botulinum strain, whereas serotype B and E strains produce toxins with lower amounts of activation (0 to 75% depending upon the fermentation time). Thus, the high toxicity of the mature neurotoxin plays a major part in the commercial manufacture of neurotoxins as therapeutic agents.

The degree of activation of engineered clostridial toxins is, therefore, an important consideration for manufacture of these materials. It would be a major advantage if neurotoxins such as botulinum toxin and tetanus toxin could be expressed, recombinantly, in high yield in rapidly-growing bacteria (such as heterologous E. coli cells) as relatively non-toxic single-chains (or single chains having reduced toxic activity) which are safe, easy to isolate and simple to convert to the fully-active form.

With safety being a prime concern, previous work has concentrated on the expression in E. coli and purification of individual H and L chains of tetanus and botulinum toxins; these isolated chains are, by themselves, non-toxic; see Li et al., Biochemistry 33:7014-7020 (1994); Zhou et al., Biochemistry 34:15175-15181 (1995), hereby incorporated by reference herein. Following the separate production of these peptide chains and under strictly controlled conditions the H and L chains can be combined by oxidative disulphide linkage to form the neuroparalytic di-chains.