Use of specific N-methyl-D-aspartate receptor antagonists in the prevention and treatment of neurodegeneration

Specific N-methyl-D-aspartate receptor antagonists are useful in the prevention and treatment of neurodegeneration in various pathological states.

SUMMARY OF THE INVENTION 
This invention is concerned with specific antagonists of 
N-methyl-D-aspartate (NMDA) receptors which are useful in the prevention 
and/or treatment of neurodegeneration in pathological conditions such as 
stroke, hypoglycaemia, cerebral palsy, transient cerebral ischaemic 
attack, cerebral ischaemia during cardiac pulmonary surgery or cardiac 
arrest, perinatal asphyxia, epilepsy, Huntington's chorea, Alzheimer's 
disease, Olivo-ponto-cerebellar atrophy, anoxia such as from drowning, 
spinal cord injury and poisoning by exogenous NMDA poisons (e.g. some 
forms of lathyrism). 
BACKGROUND OF THE INVENTION 
Excessive excitation by neurotransmitters can cause the degeneration and 
death of neurons. It is believed that this excitotoxic action is 
responsible for neuronal loss in stroke, cerebral palsy, cerebral 
ischaemia, perinatal asphyxia, epilepsy, ageing and Alzheimer's disease, 
Huntington's chorea and other chronic neurodegenerative disorders. 
There are no specific therapies for these neurodegenerative diseases, but 
compounds acting specifically to antagonise excitatory neurotransmission 
at NMDA receptors could offer a novel therapeutic approach to these 
disorders (Schwarcz, R and Meldrum B, The Lancet, 140 (1985)). 
Now with the present invention, there is provided a method of prevention 
and/or treatment of neurodegeneration in the aforementioned pathological 
conditions by the administration of specific, orally active NMDA receptor 
antagonists.

DETAILED DESCRIPTION OF THE INVENTION 
The novel method of treatment of neurodegeneration of this invention 
comprises the administration to a patient in need of such treatment with 
an effective amount of an N-methyl-D-aspartate (NMDA) receptor antagonist. 
The NMDA receptor antagonists useful in the novel method of treatment of 
this invention include compounds of the following structural formulae 
which are described in U.S. Pat. Nos. 4399141; 4374838 and 4064139, the 
disclosures of which are incorporated herein by reference: 
##STR1## 
or a pharmaceutically acceptable salt thereof, wherein R is (1) hydrogen, 
(2) C.sub.1-5 alkyl, preferably methyl or ethyl, 
(3) C.sub.2-5 alkenyl, preferably vinyl or allyl, 
(4) phenyl (or substituted phenyl)-(C.sub.1-3 alkyl)-, preferably benzyl or 
substituted benzyl wherein the substituent is halo such as fluoro, chloro 
or bromo, 
(5) C.sub.3-6 cycloalkyl, preferably cyclopropyl or cyclohexyl, 
(6) (C.sub.3-6 cycloalkyl)-(C.sub.1-3 alkyl), or 
(7) di(C.sub.1-5 alkyl)amino-(C.sub.1-5 alkyl), especially 
dimethylaminopropyl; 
R.sup.1 is 
(1) hydrogen, 
(2) C.sub.1-5 alkyl, preferably methyl or ethyl 
(3) C.sub.2-5 alkenyl, preferably vinyl or allyl 
(4) phenyl-(C.sub.1-3 alkyl), preferably benzyl, 
(5) C.sub.3-6 cycloalkyl, preferably cyclopropyl or cyclohexyl, or 
(6) (C.sub.3-6 cycloalkyl)-(C.sub.1-3 alkyl), 
R.sup.2 is 
(1) C.sub.1-5 alkyl, preferably methyl or ethyl 
(2) C.sub.3-5 alkenyl, preferably allyl, 
(3) phenyl-(C.sub.1-3 alkyl), preferably benzyl, 
(4) (C.sub.3-6 cycloalkyl)-(C.sub.1-3 alkyl), 
(5) di(C.sub.1-5 alkyl)amino-(C.sub.1-5 alkyl), especially 
dimethylaminopropyl; or 
(6) C.sub.2-3 hydroxyalkyl, preferably hydroxyethyl; and 
R.sup.3 and R.sup.4 are independently, 
(1) hydrogen 
(2) halogen, such as chloro, bromo, fluoro or iodo, 
(3) C.sub.1-5 alkoxy, preferably methoxy, 
(4) trifluoromethylthio, 
(5) cyano, 
(6) carboxy, or 
(7) hydroxy. 
A preferred group or compounds is that wherein R.sup.1 is hydrogen. 
Another preferred group of compounds is that wherein R.sup.1, R.sup.3 and 
R.sup.4 are hydrogen. 
Preferred definitions for R.sup.2 are C.sub.1-5 alkyl, especially methyl or 
ethyl, and hydroxyethyl. 
Preferred definitions for R are hydrogen, C.sub.1-5 alkyl or benzyl. 
A preferred species is 
5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (which is 
referred to below as "MK-801") or a pharmaceutically acceptable salt 
thereof. 
The administration in the novel method of treatment of this invention may 
conveniently be oral, rectal, or parenteral at a dosage level of, for 
example, about 0.01 to 50 mg/kg, preferably about 0.05 to 10 mg/kg and 
especially about 0.05 to 0.5 mg/kg/day and may be administered on a 
regimen of 1 to 4 times per day. 
The pharmaceutical formulations comprising the NMDA receptor antagonists of 
this invention may conveniently be tablets, pills, capsules, powders, or 
granules for oral administration; sterile parenteral solutions or 
suspensions for parenteral adminstration; or as suppositories for rectal 
administration. 
The compounds useful in the novel method of treatment of this invention 
bind with a high affinity and in a reversible and saturable manner to 
membranes from rat brain cortex. In addition these useful compounds 
potently and selectively block responses to NMDA in a brain slice from 
rate cortex, the antagonism apparently being non-competitive. 
BINDING STUDIES 
Binding of [.sup.3 H]-MK-801 to rat brain in vitro was conducted in a crude 
synaptosomal membrane fraction (P2) prepared from rat cerebral cortex 
according to a modified method of Hulme et al, Molecular Pharmocology 14, 
737-750 (1978). A large number of excitatory and inhibitory drugs failed 
to displace [.sup.3 H]-MK-801 up to a concentration of 10.sup.-4 M. 
However, analogs of MK-801 displaced the [.sup.3 H]-MK-801 binding in a 
dose-dependent manner as shown in Tables I, II and III. 
TABLE I 
__________________________________________________________________________ 
Displacement potencies 
of 
Analogs of MK-801 
##STR2## 
Compound 
R R.sup.1 
R.sup.2 R.sup.3 
R.sup.4 
Ki (.mu.M) 
__________________________________________________________________________ 
L-640,689 
(+)H H CH.sub.3 
H H 0.04 
L-637,939 
H H CH.sub.3 
H H 0.56 
L-638,275 
CH.sub.3 H CH.sub.3 
H H 0.830 
L-638,276 
CH.sub.3 H H H H 11.900 
L-639,015 
CH.sub.2 CHCH.sub.2 
H CH.sub.3 
H H 3.40 
L-639,057 
H H CH.sub.2 CH.sub.3 
H H 0.05 
L-639,442 
H H CH.sub.3 
7-Br H 0.18 
L-639,470 
H H (CH.sub.2).sub.2 CH.sub.3 
H H 8.60 
L-639,902 
H H CH.sub.2 CH.sub.2 OH 
H H 0.26 
L-640,690 
(-) H H CH.sub.3 
H H 0.32 
L-641,042 
CH.sub.2 CH.sub.2 OH 
H CH.sub.3 
H H 12.800 
L-641,074 
H H CH.sub.3 
H 2-OCH.sub.3 
0.605 
L-641,086 
H H CH.sub.3 
8-OCH.sub.3 
H 0.040 
L-641,285 
H H CH.sub.3 
8-OH H 0.05 
L-641,368 
H H CH.sub.3 
7-Cl H 0.08 
L-645,114 
CH.sub.3 H CH.sub.3 
H H 0.509 
L-645,156 
(CH.sub.2).sub.2 CH.sub.3 
H CH.sub.3 
H H 0.450 
L-665,039 
H H CH.sub.3 
7-OH H 0.02 
L-639,441 
H H CH.sub.3 
H 3-Br 0.02 
L-640,688 
CH.sub.3 CH.sub.3 
CH.sub.3 
H H 0.71 
L-641,291 
H H CH.sub.3 
H 2-OH 0.34 
L-641,294 
H H CH.sub.3 
H 3-Cl 0.01 
__________________________________________________________________________ 
TABLE II 
______________________________________ 
Displacement Potencies 
of 
Analogs of MK-801 
##STR3## 
Compound R R.sup.2 R.sup.3 
Ki (.mu.M) 
______________________________________ 
L-639,420 H CH.sub.2 CH.sub.3 
H 0.12 
L-638,204 H CH.sub.3 H 0.14 
L-637,686 CH.sub.3 CH.sub.3 H 1.20 
L-639,450 H H 3-Cl 0.15 
______________________________________ 
TABLE III 
______________________________________ 
##STR4## 
Com- 
pound R R.sup.1 R.sup.2 
R.sup.3 
R.sup.4 
Ki (.mu.M) 
______________________________________ 
L-633,239 
CH.sub.3 CH.sub.3 
CH.sub.3 
2-CN H 31.300 
L-633,170 
(CH.sub.2).sub.2 CH.sub.3 
CH.sub.3 
CH.sub.3 
H H 0.35 
L-631,922 
CH.sub.3 CH.sub.3 
CH.sub.3 
2-CF.sub.3 
H 109.400 
L-631,876 
CH.sub.3 CH.sub.3 
H H H 6.930 
L-627,891 
CH.sub.3 CH.sub.3 
CH.sub.3 
H H 0.22 
L-632,938 
##STR5## CH.sub.3 
CH.sub.3 
H H 4.00 
L-633,744 
(CH.sub.2).sub.3 CH.sub.3 
CH.sub.3 
CH.sub.3 
H H 0.39 
______________________________________ 
CORTICAL SLICE STUDIES 
The effects of MK-801 and its analogs on responses to NMDA and quisqualate 
were assessed using the rat cortical slice as described by Harrison et 
al., Brit. J. Pharmacol, 84, 381-391 (1985). Cortical neurons in this 
preparation are depolarized by bath applications of NMDA. MK-801 produces 
a dose dependent depression of NMDA responses with a threshold dose of 
about 100 nM and complete suppression of responses at 1 .mu.M. In 
contrast, responses to kainate and quisqualate are totally unaffected by 
MK-801 at doses of up to 30 .mu.M. 
The apparent potencies of MK-801 and its analogs are shown in Table IV; 
they correlate closely with results from [.sup.3 H]-MK-801 binding 
studies. 
TABLE IV 
______________________________________ 
Apparent Potency as 
NMDA Antagonist 
Compound Kb (.mu.M) 
______________________________________ 
L-640,689 (MK-801) 
0.08 
L-639,057 0.50 
L-641,285 0.10 
L-640,690 0.30 
L-627,891 1.13 
L-639,470 3.00 
L-637,686 2.00 
L-632,938 0.64 
L-633,170 0.30 
L-633,744 0.47 
L-637,939 0.09 
L-638,204 0.31 
L-639,015 3.10 
L-639,420 0.20 
L-639,441 1.00 
L-639,442 0.40 
L-639,902 0.20 
L-640,688 0.87 
L-641,291 0.51 
L-641,294 0.05 
L-641,368 1.00 
L-665,039 0.13 
______________________________________ 
The responses to NMDA and quisqualate were examined on cortical slices from 
4 rats which had been pretreated with MK-801 (1 mg/kg, i.p) 2 hours before 
they were sacrificed. Responses to NMDA were markedly depressed resulting 
in a shift to the right of the NMDA dose-response curve of approximately 
2.4 fold when compared to the mean NMDA dose-response curved from 
untreated animals. The responses to quisqualate were much less affected 
with only the highest dose slightly depressed. 
These results show that MK-801, when administered peripherally in 
reasonable doses, blocks NMDA receptor mediated events on central neurons. 
NEUROPROTECTION STUDIES 
(a) Ischaemia was induced in gerbils by 10 or 30 minute unilateral 
occlusion of the carotid artery. Restoration of blood flow after occlusion 
was checked visually and the animals were allowed to survive for 4 days. 
The extent of neuronal degeneration in the hippocampus was assessed. Test 
animals were treated by administering MK-801 at doses of 1 and 10 mg/kg 
(i.p.) one hour prior to artery occulsion. The results are given in Table 
V. 
TABLE V 
______________________________________ 
1 mg/kg 
Control 
MK-801 10 mg/kg MK-801 
______________________________________ 
(A) 10 min occlusion 
Number of animals 
12 4 3 
showing damage 
Number undamaged 
8 11 12 
(B) 30 min occlusion 
Number of animals 
8 11 14 
surviving 
Number dead 7 4 1 
______________________________________ 
(b) The right carotid artery of gerbils was occluded for 10 minutes and 
MK-801 at a dose of 1 mg/kg (i.p.) administered one hour before, then 1, 
3, 5, 10 and 15 hours following occlusion. The animals were allowed to 
survive for 4 days and the extent of neuronal damage in the hippocampus 
was assessed. The results are given in Table VI. 
TABLE VI 
______________________________________ 
Control MK-801 - treated 
______________________________________ 
Number of animals showing 
7 1 
damage 
Number undamaged 1 8 
______________________________________ 
(c) Ischaemia was induced in gerbils by 5 minute occlusion of both carotid 
arteries. Restoration of blood flow after occlusion was checked visually 
and the animals allowed to survive for 4 days. The extent of neuronal 
degeneration in the hippocampus was measured. Test animals were treated by 
administering MK-801 at doses of 1, 3 and 10 mg/kg (i.p.) one hour prior 
to occlusion. The results are given in Table VII 
TABLE VII 
______________________________________ 
Percentage of 
Area of neuronal 
anaimals with 
(No.) degeneration (mm.sup.2) 
full protection 
______________________________________ 
Control (10) 7.70 .+-. 0.25 
0 
1 mg/kg MK-801 
(5) 0.47 .+-. 0.33 
60 
3 mg/kg MK-801 
(5) 0.14 .+-. 0.16 
80 
10 mg/kg MK-801 
(10) 0.84 .+-. 0.52 
70 
______________________________________ 
(d) The neuroprotective activity of compounds for use in accordance with 
the invention has also been determined by measuring the ability of the 
compounds to prevent increases in calcium levels in the gerbil hippocampus 
following bilateral artery occlusion. The results obtained are shown in 
Table VIII. 
TABLE VII 
______________________________________ 
Depression of Hippocampal [Ca.sup.2+ ] 
Compound Relative Potency (MK-801 = 1) 
______________________________________ 
MK-801 (L-640,689) 
1 (IC.sub.50 .about. 0.1 mg/kg) 
L-665,039 0.8 
L-641,291 1 
______________________________________