Use of conantokins

Details Use of conantokins Use of conantokins

2000-03-22

2002-06-04

Davenport, Avis M. (Department: 1653)

Drug, bio-affecting and body treating compositions

Designated organic active ingredient containing

Peptide containing doai

C514S002600, C514S013800, C530S300000, C530S326000, C530S324000, C530S325000, C424S185100

Reexamination Certificate

active

06399574

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to the use of relatively short peptides, about 10-30 residues in length, which are naturally available in minute amounts in the venom of the cone snails or analogous to the naturally available peptides, and which include preferably one to two or more &ggr;-carboxyglutamic acid residues for the treatment of neurologic and psychiatric disorders, such as anticonvulsant agents, as neuroprotective agents or for the management of pain.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated by reference, and for convenience are referenced in the following text by author and date and are listed alphabetically by author in the appended bibliography.
The predatory cone snails (Conus) have developed a unique biological strategy. Their venom contains relatively small peptides that are targeted to various neuromuscular receptors and may be equivalent in their pharmacological diversity to the alkaloids of plants or secondary metabolites of microorganisms. Many of these peptides are among the smallest nucleic acid-encoded translation products having defined conformations, and as such, they are somewhat unusual. Peptides in this size range normally equilibrate among many conformations. Proteins having a fixed conformation are generally much larger.
The cone snails that produce these peptides are a large genus of venomous gastropods comprising approximately 500 species. All cone snail species are predators that inject venom to capture prey, and the spectrum of animals that the genus as a whole can envenomate is broad. A wide variety of hunting strategies are used, however, every Conus species uses fundamentally the same basic pattern of envenomation.
Several peptides isolated from Conus venoms have been characterized. These include the &agr;-, &mgr;- and &ohgr;-conotoxins which target nicotinic acetylcholine receptors, muscle sodium channels, and neuronal calcium channels, respectively (Olivera et al., 1985). Conopressins, which are vasopressin analogs, have also been identified (Cruz et al., 1987). In addition, peptides named conantokins have been isolated from
Conus geographus
and
Conus tulipa
(Mena et al., 1990; Haack et al., 1990). These peptides have unusual age-dependent physiological effects: they induce a sleep-like state in mice younger than two weeks and hyperactive behavior in mice older than 3 weeks (Haack et al., 1990).
The conantokins are structurally unique. In contrast to the well characterized conotoxins from Conus venoms, most conantokins do not contain disulfide bonds. However, they contain 4-5 residues of the unusual modified amino acid &ggr;-carboxyglutamic acid. The occurrence of this modified amino acid, which is derived post-translationally from glutamate in a vitamin K-dependent reaction, was unprecedented in a neuropeptide. It has been established that the conantokins have N-methyl-D-aspartate (NMDA) antagonist activity, and consequently target the NMDA receptor. The conantokins reduce glutamate (or NMDA) mediated increases in intracellular Ca
2+
and cGMP without affecting kainate-mediated events (Chandler et al., 1993). Although these peptides have actions through polyamine responses of the NMDA receptors, the neurochemical profile of these polypeptides is distinct from previously described noncompetitive NMDA antagonists (Skolnick et al., 1992).
The previously identified conantokins are Conantokin G (Con G) and Conantokin T (Con T). Con G has the formula Gly-Glu-Xaa
1
-Xaa
1
-Leu-Gln-Xaa
2
-Asn-Gln-Xaa
2
-Leu-Ile-Arg-Xaa
2
-Lys-Ser-Asn (SEQ ID NO:1), wherein Xaa
1
and Xaa
2
are &ggr;-carboxyglutamic acid (Gla). The C-terminus preferably contains an amide group. Con T has the formula Gly-Glu-Xaa
1
-Xaa
1
-Tyr-Gln-Lys-Met-Leu-Xaa
2
-Asn-Leu-Arg-Xaa
2
-Ala-Glu-Val-Lys-Lys-Asn-Ala (SEQ ID NO:2), wherein Xaa
1
and Xaa
2
are &ggr;-carboxyglutamic acid. The C-terminus preferably contains an amide group. Analogues of Conantokin G have been synthesized and analyzed for their biological activity (Chandler et al., 1993; Zhou et al., 1996). It has been discovered that substitution of the Gla residue at position 4 of Con G destroys its NMDA antagonist properties. Substitution of the Gla residue at position 3 of Con G greatly reduces its NMDA antagonist activity. However, substitutions of the Gla residues at positions 7, 10 and 14 of Con G do not adversely affect potency of the peptide and may even enhance it. (Zhou et al., 1996).
Ischemic damage to the central nervous system (CNS) may result form either global or focal ischemic conditions. Global ischemia occurs under conditions in which blood flow to the entire brain ceases for a period of time, such as may result from cardiac arrest. Focal ischemia occurs under conditions in which a portion of the brain is deprived of its normal blood supply, such as may result from thromboembolytic occlusion of a cerebral vessel, traumatic head or spinal cord injury, edema or brain or spinal cord tumors. Both global and focal ischemic conditions have the potential for widespread neuronal damage, even if the global ischemic condition is transient or the focal condition affects a very limited area.
Epilepsy is a recurrent paroxysmal disorder of cerebral function characterized by sudden brief attacks of altered consciousness, motor activity, sensory phenomena or inappropriate behavior caused by abnormal excessive discharge of cerebral neurons. Convulsive seizures, the most common form of attacks, begin with loss of consciousness and motor control, and tonic or clonic jerking of all extremities but any recurrent seizure pattern may be termed epilepsy. The term primary or idiopathic epilepsy denotes those cases where no cause for the seizures can be identified. Secondary or symptomatic epilepsy designates the disorder when it is associated with such factors as trauma, neoplasm, infection, developmental abnormalities, cerebrovascular disease, or various metabolic conditions. Epileptic seizures are classified as partial seizures (focal, local seizures) or generalized seizures (convulsive or nonconvulsive). Classes of partial seizures include simple partial seizures, complex partial seizures and partial seizures secondarily generalized. Classes of generalized seizures include absence seizures, atypical absence seizures, myoclonic seizures, clonic seizures, tonic seizures, tonic-clonic seizures (grand mal) and atonic seizures. Therapeutics having anticonvulsant properties are used in the treatment of seizures. Most therapeutics used to abolish or attenuate seizures act at least through effects that reduce the spread of excitation from seizure foci and prevent detonation and disruption of function of normal aggregates of neurons. Traditional anticonvulsants that have been utilized include phenytoin, phenobarbital, primidone, carbamazepine, ethosuximide, clonazepam and valproate. Several novel and chemically diverse anticonvulsant medications recently have been approved for marketing, including lamotrigine, ferlbamate, gabapentin and topiramate. For further details of seizures and their therapy, see Rall & Schleifer (1985) and
The Merck Manual
(1992).
It has been shown that neurotransmission mediated through the NMDA receptor complex is associated with seizures (Bowyer, 1982; McNamara et al., 1988), ischemic neuronal injury (Simon et al., 1984; Park et al., 1988) and other phenomena including synaptogenesis (Cline et al., 1987), spatial learning (Morris et al., 1986) and long-term potentiation (Collinridge et al., 1983; Harris et al., 1984; Morris et al., 1986). Regulation of these neuronal mechanisms by NMDA-mediated processes may involve activation of a receptor-gated calcium ion channel (Nowak et al., 1984; Mayer et al., 1987; Ascher and Nowak, 1988).
The NMDA channel is regulated by glycine. This amino acid increases NMDA-evoked currents in various tissues [Johnson and Ascher, 1987; Kleckner and Dingledine, 1988] by increasing the opening

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