Abstract:
A series of novel thyrotropin-releasing hormone analogs wherein the C-terminal prolineamide moiety has been preserved, the N-terminal moiety comprises one of five different ring structures and the histidyl moiety is substituted with CF 3 , NO 2  or a halogen. A method of use of the analog for the treatment of neurologic disorders is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 07/988,344, filed Dec. 9, 1992, now abandoned, which is a continuation of application Ser. No. 07/435,567, filed Nov. 13, 1989, now abandoned, which is a continuation-in-part of application Ser. No. 07/387,416, filed Jul. 31, 1989, now abandoned, which is a continuation of application Ser. No. 07/253,879, filed Oct. 5, 1988, now abandoned, which is a continuation of application Ser. No. 07/058,339, filed Jun. 5, 1987, now abandoned, and a continuation of application Ser. No. 07/400,189, filed Aug. 28, 1989, now abandoned, which is a continuation of application Ser. No. 07/253,880, filed Oct. 5, 1988, now abandoned, which is a continuation of application Ser. No. 07/058,380, filed June 5, 1987, now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a series of compounds and their use in the treatment of neurologic disorders, and more particularly relates to a series of novel thyrotropin-releasing hormone analogs for use in the treatment of brain and spinal cord trauma. 
     BACKGROUND OF THE INVENTION 
     Neurologic disorders are defined herein as any abnormal central nervous system conditions including, but not limited to, brain and spinal cord trauma; stroke; neurodegenerative disorders such as amyotropic lateral sclerosis or spinocerebellar degeneration; and coma or stupor due to anesthetics or an overdose of a drug. 
     Central nervous system trauma, caused by injuries such as spinal injuries and head injuries, are becoming increasingly prevalent. Many of these injuries are caused by automobile accidents. Other circumstances causing spinal or head injuries include serious falls, diving accidents, crushing industrial injuries, and gunshot or stab wounds. 
     Traumatic brain or spinal injuries cause tissue damage through both direct, or mechanical injury to the tissue, and indirect or secondary means. Secondary tissue damage is believed to be caused by the activation of endogenous, autodestructive, neurochemical substances. 
     Thyrotropin-releasing hormone (TRH), which has been identified as L-pyroglutamyl-L-histidyl-L-prolineamide, is a small peptide that has been found in various cells of the body, mainly the neural cells of the central nervous system. The structure of TRH is shown below: ##STR1## 
     The right portion of the molecule is known to those skilled in the art as the &#34;prolineamide&#34;, &#34;NH 2  &#34; or &#34;C-terminal&#34; portion; the center portion of the molecule is known as the &#34;histidyl&#34; portion; and the left portion of the molecule is known as the &#34;pyroglutamyl&#34;, &#34;COOH-terminal&#34; or &#34;N-terminal&#34; portion. 
     Endogenous TRH can act as either a neurotransmitter or a neuromodulator or both. A major percentage of this hormone is released from the hypothalamic nerve terminals in the median eminence to stimulate the secretion of thyroid stimulating hormone, the function for which TRH is named. TRH is also found in other areas of the central nervous system, and in tissues of the body such as the alimentary tract, pancreas, placenta and retina of the eye. 
     The function of TRH in these various areas of the body is largely unknown. However, numerous behavioral studies have shown that the peripheral or central administration of TRH induces arousal and counteracts the depressant effects of many drugs including neuroleptics, alcohol and anaesthetics. 
     TRH has recently been shown to antagonize many of the effects of the endogenous opiates including spinal cord injury. (Faden et al., Thyrotropin-releasing hormone improves neurologic recovery after spinal trauma in cats, N. Engl. J. Med., 305:1063-1067 (1981)). The advantage of TRH is that it acts as a physiological opiate antagonist without affecting nociception. 
     The major disadvantage of the use of TRH in central nervous system injury is that the hormone is very rapidly metabolized. Therefore, high doses or continuous infusions are necessary for effective treatment. The short plasma half-life (4-5 min) is most likely due to rapid degradation of the peptide at both the COOH-- and NH 2  terminals of the molecule. Cleavage of the pyroglutamyl moiety of TRH by peptidases causes formation of the metabolite cyclo-histidyl-proline-diketopiperazine. Deamidation of TRH results in the formation of the free acid TRH-OH. 
     A number of peptidase-resistant analogs of TRH have been synthesized, mainly for research purposes. They were developed initially as antidepressants. Most of these analogs have been found to have centrally active effects such as endocrine, analeptic and autonomic effects. 
     What is needed is a compound that is effective in treating neurologic disorders, especially a compound that is effective in reducing secondary brain and spinal injury in patients suffering from traumatic central nervous system injury, without affecting nociception, and without being rapidly metabolized. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a series of compounds and their use in the treatment of neurologic disorders. The series of compounds comprise novel thyrotropin-releasing hormone analogs. The neurologic disorder is treated by administering an effective amount of a compound to a patient. 
     In the preferred embodiments of the present invention, the compound comprises a TRH analog wherein the C-terminal prolineamide moiety has been preserved and the two remaining peptide components have been modified. The N-terminal portion of the analog comprises one of five different ring structures. The histidyl portion of the analog is modified by substitutions at the two and four carbon positions. The resulting preferred embodiments of the novel analog are shown below: ##STR2## 
     The histidyl portion of each compound is modified so that R═CF 3 , NO 2 , F, I or Br and R&#39;═H; or R═H and R&#39;═CF 3  ; or R and R&#39;═I or Br. 
     Accordingly, it is an object of the present invention to provide a novel TRH analog. 
     It is a further object of the present invention to provide a novel TRH analog that is effective in the treatment of central nervous system injury. 
     It is a further object of the present invention to provide a novel TRH analog that is not readily metabolized. 
     It is a further object of the present invention to provide a novel TRH analog having enhanced central nervous system penetration. 
     It is a further object of the present invention to provide an effective treatment for neurologic disorders. 
     It is a further object of the present invention to provide an effective treatment for brain and spinal cord trauma. 
     It is a further object of the present invention to provide an effective treatment for the secondary effects of central nervous system injury. 
     It is a further object of the present invention to provide an effective treatment for hypovolemic or anaphylactic shock. 
     It is a further object of the present invention to provide a compound that will increase the acceptance of a tissue transplant. 
     These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiment and the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention comprises a series of compounds and their use in the treatment of neurologic disorders. The compounds are novel thyrotropin-releasing hormone analogs which are preferably used in the treatment of brain and spinal cord trauma. The injury is treated by administering an effective amount of a compound to the patient wherein the compound preferably reduces the secondary effects of the trauma by optimally antagonizing the actions of autodestructive biochemical substances, such as endogenous opioids, without being rapidly metabolized. Preferably, the compound penetrates the central nervous system. 
     In a first preferred embodiment of the present invention, the compound is a TRH analog having the following structure: ##STR3## wherein R or R&#39; or both are halogens such as R═I and R&#39;═I or R═F and R&#39;═H, or R═I and R&#39;═H, or R═Br and R&#39;═Br, or R═Br and R&#39;═H. 
     Alternatively, R═CF 3  and R&#39;═H or the R and R&#39; are reversed so that R═H and R&#39;═CF 3 . In another alternative, R═NO 2  and R&#39;═H. 
     In a second preferred embodiment of the present invention, the compound is a TRH analog having the following structure: ##STR4## wherein R═NO 2  and R&#39;═H. 
     Alternatively, R═CF 3  and R&#39;═H or the R and R&#39; are reversed so that R═H and R&#39;═CF 3 . In another alternative, R or R&#39; or both are halogens such as R═F and R&#39;═H, or R═I and R&#39;═I, or R═I and R&#39;═H, or R═Br and R&#39;═Br, or R═Br and R&#39;═H. 
     In a third preferred embodiment of the present invention, the compound is a TRH analog having the following structure: ##STR5## wherein R═CF 3  and R&#39;═H. 
     Alternatively, the R and R&#39; are reversed so that R═H and R&#39;═CF 3 . In another alternative, R═NO 2  and R&#39;═H. In yet another alternative, R or R&#39; or both are halogens such as R═F and R&#39;═H, or R═I and R&#39;═I, or R═I and R&#39;═H, or R═Br and R&#39;═Br, or R═Br and R&#39;═H. 
     In a fourth preferred embodiment of the present invention, the compound is a TRH analog having the following structure: ##STR6## wherein R═CF 3  and R&#39;═H. 
     Alternatively, the R and R&#39; are reversed so that R═H and R&#39;═CF 3 . In another alternative, R═NO 2  and R&#39;═H. In yet another alternative, R or R&#39; or both are halogens such as R═F and R&#39;═H, or R═I and R&#39;═I, or R═I and R&#39;═H, or R═Br and R&#39;═Br, or R═Br and R&#39;═H. 
     In a fifth preferred embodiment of the present invention, the compound is a TRH analog having the following structure: ##STR7## wherein R═CF 3  and R&#39;═H. 
     Alteratively, the R and R&#39; are reversed so that R═H and R&#39;═CF 3 . In another alternative, R═NO 2  and R&#39;═H. In yet another alternative, R or R&#39; or both are halogens such as R═F and R&#39;═H, or R═I and R&#39;═I, or R═I and R&#39;═H, or R═Br and R&#39;═Br, or R═Br and R&#39;═H. 
     The first preferred novel TRH analog of the present invention is synthesized by starting with the compound N-  (5)-4-oxo-2-azetidinyl!carbonyl!-L-histadyl-L-prolineamide dihydrate known in the industry as YM-14673, which is available through Yamanouchi Pharmaceutical Co. LTD (Tokyo, Japan). The various substitutions are created in accordance with the method of Labroo, V. M., Feurerstein, G., and Cohen, L. A., in &#34;Peptides: Structure and Function&#34; Proceedings of the Ninth American Peptide Symposium, Deber, Hruby and Kopple, eds., pp. 703-706, 1985, which is incorporated herein by reference. The second preferred novel TRH analog is synthesized by starting with the compound orotyl-L-histidyl-L-prolineamide, known in the industry as CG 3703, which is available through Chemie Grunenethal (Stolberg, West Germany). The various substitutions are created in accordance with the method of Labroo cited above. The third preferred novel TRH analog of the present invention is synthesized by starting with the thryotropin releasing hormone and modifying it in accordance with method known to those skilled in the art. The various substitutions are created in accordance with the method of Labroo cited above. The fourth preferred novel TRH analog of the present invention is synthesized by starting with the compound known in the industry as CG 3509, which is available through Chemie Grunenethal (Stolberg, West Germany). The various substitutions are created in accordance with the method of Labroo cited above. The fifth preferred novel TRH analog of the present invention is synthesized by starting with the compound γ-butyrolactone-γ-carbonyl-L-histidyl-L-proline amide citrate, known in the industry as DN 1417, which is available through Takeda Chemical Industries, Ltd. (Osaka, Japan). The various substitutions are created in accordance with the method of Labroo cited above. 
     An effective dose of the TRH analog of the present invention comprises an amount of the analog sufficient to reduce secondary injury by blocking or reducing the release of injurious endogenous substances. Preferably, the effective dose is from approximately 0.1 to 10.0 mg/kg body weight of the patient. This dose is preferably administered every 4-6 hours for approximately 24 hours to treat trauma. It will be understood by those skilled in the art that the compound is administered chronically for the treatment of other neurologic disorders such as stroke; systic, hypovolemic or anaphylactic shock; neurodegenerative disorders such as amyotropic lateral sclerosis or spinocerebellar degeneration; and unconsciousness or subconsciousness due to anesthetics or overdoses. 
     Most preferably the effective dose of the TRH analog of the present invention is approximately 1.0 mg/kg body weight of the patient administered every 4-6 hours within the first 24 hours after trauma. 
     Although not wanting to be bound by the following hypothesis, it is believed that the preferred embodiments of the TRH analog of the present invention increase neurologic recovery by blocking the actions of several injury factors including opioids, leukotrienes, and platelet activating factor released as a consequence of the trauma. The analog may also inhibit lipid membrane breakdown, i.e. reduce the release of polyunsaturated fatty acids and eicosanoids which are toxic to central nervous system tissue. The TRH analog may also act by maintaining magnesium homeostasis. Furthermore, halogenation of the histidyl portion of the analog may enhance blood-brain barrier penetration. 
     The therapeutic route of administration of the compound of the present invention includes, but is not limited to, intravenous, intramuscular, subcutaneous, and oral administration. Preferably, the compound is administered intravenously. 
     The compound of the present invention can be administered as a liquid or gel by any of the above described routes of administration or orally in the form of a solid tablet. Preferably, the compound is administered to the patient in the form of a liquid solution, the solution comprising an effective amount of active ingredient compound and a pharmaceutically acceptable solution. 
     The pharmaceutically acceptable solution includes any solution that is safe for injection or ingestion and is biologically inert so that it does not interfere with the active ingredient. The preferred pharmaceutically acceptable solution comprises an isotonic solution suitable for injection into a patient. For example, the isotonic solution may contain water, salt, and conventional ingredients such as glucose. The pharmaceutically acceptable solution may also contain purified water mixed with preservatives, flavors, colorants, flavor enhancing agents, and other additives such as sodium benzoate, methyl paraben, propylene glycol, glycerin, sorbitol, alcohol, sucrose, saccharin, menthol and citric acid. 
     As described above, the TRH analog of the present invention is preferably used to treat brain and spinal cord injuries caused by central nervous system trauma. However, the TRH analog of the present invention can also be administered to a patient undergoing a tissue transplant by reducing secondary traumatic injury associated with the transplant process. 
     The following specific examples will illustrate the invention as it applies in particular to improving neurologic function. It will be appreciated that other examples will be apparent to those of ordinary skill in the art and that the invention is not limited to these specific illustrative examples. 
     EXAMPLE 1 
     An experiment is described to illustrate the effect of the following TRH analog on neurological function: ##STR8## wherein R and R&#39;═I. 
     Models 
     Traumatic Brain Injury 
     Following anesthesia with pentobarbital (60 mg/kg, i.p.) male, Sprague-Dawley rats (400±25 g) are subjected to traumatic brain injury utilizing a lateral, fluid-percussion. 
     The fluid-percussion device used to produce experimental brain injury is a Plexiglas cylindrical reservoir, 60 cm long and 4.5 cm in diameter, bounded at one end by a Plexiglas, cork-covered piston mounted on O rings. The opposite end of the reservoir is fitted with a 2-cm-long metal housing on which a transducer (Gould) is mounted and connected to a 5-mm tube (2 mm ID) that terminates with a male Luer Lok fitting. At the time of injury, the tube is connected to a female Luer Lok fitting that has been chronically implanted over the exposed cortex of the rat. After the entire system is filled with 37° C. isotonic saline, injury is induced by a metal pendulum, which strikes the piston of the device from a predetermined height. The device produces a pulse of increased intracranial pressure of fairly constant duration (21-23 ms) by injecting varying volumes of saline into the closed cranial cavity. Brief displacement and deformation of neural tissue results from the rapid epidural injection of saline, and increased magnitude of tissue deformation is associated with an increased magnitude of brain injury. The magnitude of injury is regulated by varying the height of the pendulum, which results in corresponding variations in intracranial pressure pulses expressed in atmospheres. These pressure pulses are measured extracranially by a transducer (housed in the injury device) at the time of injury, recorded on a storage oscilloscope, and photographed with a Polaroid camera. 
     Spinal Cord Injury 
     Male, Sprague-Dawley rats (300±25 g are anesthetized with sodium pentobarbital (60 mg/kg, i.p.) and laminectomy is performed at T 9 . The spinal cord is injured using a modification of the weight-drop method in which a 10 g weight is dropped a distance of 5 cm through a guide tube onto a Teflon impounder plate that strikes the exposed spinal cord. This 50 g-cm impact force causes severe, reproducible, but incomplete tissue injury (control animals show moderately severe spastic paraparesis 4 weeks after trauma). A catheter is inserted into the jugular vein for drug administration. 
     Drug Treatment 
     Traumatic Brain Injury 
     At 30 min following a 2.5 atmosphere level injury, animals are randomly assigned to one of two treatment groups (each n=8): the above-described TRH analog (1.0 mg/kg) or equal volume (1 cc) physiological saline, each administered as a slow intravenous bolus injection over 60 sec. 
     Traumatic Spinal Cord Injury 
     At 15 min following spinal cord trauma, animals are randomly assigned to one of two treatment groups: the above-described TRH analog (n=17) or equal volume (1 cc) physiological saline (n=15), each administered as a slow intravenous bolus injection over 60 sec. 
     Neurological Evaluation 
     Traumatic Brain Injury 
     Neurological function is evaluated daily over a 2-week period by an individual unaware of treatment group. Animals are evaluated separately for five tests of motor function, each scored on an ordinal scale from 0 (severely impaired) to 4 (normal function). Tests include: (a) ability to maintain position on an inclined plane in either the vertical or horizontal position for 5 sec; (b) forelimb flexion following suspension by the tail; (c) the degree of resistance to lateral pulsion; and (d) activity monitored in a computerized Opto-Varimex activity chamber (Columbus Instruments). Each of the five individual scores--vertical angle, horizontal angle, forelimb flexion, lateral pulsion, and activity--are added to yield a composite neurological score that ranges from 0 to 20. Animals are maintained for 2 weeks. 
     Spinal Cord Injury 
     Animals are scored blindly over a 4-week period after trauma utilizing an 8-point ordinal scale based on motor function: 0=no spontaneous movements; 1=spontaneous movements but unable to support weight; 2=supports weight only briefly; 3=stands, but unable to walk; 4=walks, but with severe spasticity and ataxia; 5=walks, but with moderate marked spasticity; 6=walks with minimal spasticity; 7=normal motor function. Animals are also graded as either walkers (score=4-7) or nonwalkers (score=0-3). In addition, rats are scored on their ability to maintain themselves on an inclined plane in the vertical and horizontal positions for 5 sec, with the maximal angle noted. 
     Results 
     Composite neurological scores at 2 weeks after traumatic brain injury are significantly higher in the treatment group animals than in controls. TRH analog treatment also improves neurological outcome at 4 weeks after traumatic spinal cord injury. 
     The present study shows that the above-described TRH analog, administered as a single bolus intravenous injection after trauma, significantly improves neurological outcome following fluid-percussion-induced lateral brain injury and impact spinal cord trauma in rats. 
     It should be understood, of course, that the foregoing relates only to preferred embodiments of the present invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.