Abstract:
The invention provides a compound having formula X 1 -Arg-Xaa-Arg-X 2  in which X 1  and X 2  are up to 30 amino acid residues and Xaa is an amino acid residue. A preferred compound is the tripeptide Arg-Glu-Arg which corresponds to amino acid residues 328 to 330 of human amyloid precursor protein. The invention further provides a derivative of a polypeptide having the formula: X 1 -Arg-Xaa-Arg-X 2  wherein X 1  and X 2 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof and Xaa represents a natural or synthetic amino acid residue or derivative thereof, at least one functional group of at least one said amino acid residue or derivative thereof being protected by a protective group. The compounds of the invention are believed to be useful in the treatment of Alzheimer&#39;s disease and as cognitive enhancers.

Description:
FIELD OF THE INVENTION 
     The present invention relates to polypeptide compounds, to compounds derived therefrom and to the use of such compounds in medicine. Compounds according to the invention are believed to be potentially useful as cognitive enhancers and in the treatment of neurodegenerative diseases such as Alzheimer&#39;s disease. 
     BACKGROUND TO THE INVENTION 
     Alzheimer&#39;s disease is a degenerative brain disease which is characterised by progressive loss of memory and subsequently most other cognitive functions in an irreversible decline over a period of years. It represents a substantial health problem, particularly in an ageing population. 
     The amyloid precursor protein (“APP”) is a multifunctional transmembrane protein and is known to have important functions in normal brain tissue. The human form of APP is known to consist of 695 amino acid residues (SEQ ID No: 1) in a sequence which is also known (see Kang et al, Nature 325, 733-736 (1987), the contents of which are incorporated herein by reference). The chick form of APP is known to consist of 534 amino acid residues (SEQ ID No: 2) and to resemble the human form closely, being approximately 95% homologous therewith (see the paper by Kang et al just mentioned and Barnes et al, J Neurosci, 18 (15) 5869-5880 (1998), contents of which are also incorporated herein by reference). The amino acid sequences of the human and chick forms of APP are reproduced in  FIG. 1  of the drawings of this specification. 
     Two effects which have been noted to take place in the brain of a person suffering from Alzheimer&#39;s disease are the build up outside the nerve cells of the brain of tangled masses of protein and the build up inside the brain cells of a different protein. The extracellular proteins are known to be aggregates of polypeptides having amino acid sequences corresponding to portions of the extracellular part of APP. The tangled masses of these proteins are known as amyloid plaques. The intracellular proteins are known as tau proteins. It is however not known whether either or both of the extracellular accumulation of amyloid plaques and the intracellular accumulation of tau proteins are the causes or the symptoms of Alzheimer&#39;s and related neurodegenerative diseases of the Alzheimer type. 
     The amino acid sequence of the β-amyloid polypeptide fragment (1-42) is identical in the human and chick forms of APP and consists of amino acid residues 597 to 638 in the human form and residues 436 to 477 in the chick form, (see the papers by Kang et al and Barnes et al referred to hereinbefore). 
     DEFINITIONS 
     The following expressions are used in this specification and have the following meanings, except where the context indicates otherwise: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 APP 
                 means “amyloid precursor 
               
               
                   
                 protein”; 
               
               
                 human APP 
                 means the human form of APP; 
               
               
                 chick APP 
                 means the chick form of APP; 
               
               
                 RERMS 
                 means the pentapeptide Arg-Glu- 
               
               
                   
                 Arg-Met-Ser (SEQ ID No.:3); 
               
               
                 APP 328-332 
                 also means the pentapeptide Arg- 
               
               
                   
                 Glu-Arg-Met-Ser (SEQ ID No.:3) 
               
               
                   
                 which corresponds to amino acid 
               
               
                   
                 residues 328 to 332 of human APP; 
               
               
                 SMRER 
                 means the pentapeptide Ser-Met- 
               
               
                   
                 Arg-Glu-Arg (SEQ ID No.:4); 
               
               
                 APP 332-328 
                 means the same as SMRER; 
               
               
                   
                 (SEQ ID NO.:4) 
               
               
                 Aβ domain 
                 means the domain of APP which 
               
               
                   
                 forms β-amyloid plaques; 
               
               
                 β-amyloid 12-28 
                 means the sequence of amino acid 
               
               
                   
                 residues which constitute part of 
               
               
                   
                 the Aβ domain of human APP, the 
               
               
                   
                 sequence being Val-His-His-Gln- 
               
               
                   
                 Lys-Leu-Val-Phe-Phe-Ala-Glu-Asp- 
               
               
                   
                 Val-Gly-Ser-Asn-Lys (SEQ ID No: 
               
               
                   
                 8) which corresponds to amino 
               
               
                   
                 acid residues 608 to 624 of human 
               
               
                   
                 APP and amino acids 447 to 463 of 
               
               
                   
                 chick APP; 
               
               
                 RSAER 
                 means the pentapeptide Arg-Ser- 
               
               
                   
                 Ala-Glu-Arg (SEQ ID NO.:5); 
               
               
                 APP 319-335 
                 means the polypeptide Ala-Lys- 
               
               
                   
                 Glu-Arg-Leu-Glu-Ala-Lys-His-Arg- 
               
               
                   
                 Glu-Arg-Met-Ser-Gln-Val-Met 
               
               
                   
                 (AKERLEAKHRERMSQVM) 
               
               
                   
                 (SEQ ID No:6); 
               
               
                 RER 
                 means the tripeptide Arg-Glu-Arg 
               
               
                   
                 (SEQ ID No:9); 
               
               
                 APP 328-330 
                 means the same as RER (SEQ ID NO.:9); 
               
               
                 Ac-RER 
                 means RER (SEQ ID NO.:9) in which one of 
               
               
                   
                 the hydrogen atoms of the —NH 2  group 
               
               
                   
                 at the N-terminus has been 
               
               
                   
                 replaced by an acetyl group; the 
               
               
                   
                 structural formula of Ac-RER is 
               
               
                   
                 given hereinbelow; 
               
               
                 RERM 
                 means the tetrapeptide Arg-Glu- 
               
               
                   
                 Arg-Met (SEQ ID No: 10); 
               
               
                 APP 328-331 
                 means the same as RERM (SEQ ID NO.:10); 
               
               
                 MRER 
                 means the tetrapeptide Met-Arg- 
               
               
                   
                 Glu-Arg (SEQ ID No: 11); 
               
               
                 APP 331-328 
                 means the same as MRER (SEQ ID NO.:11); 
               
               
                 amino acid 
                 as used herein is meant to 
               
               
                   
                 include both natural and 
               
               
                   
                 synthetic amino acids, and both D 
               
               
                   
                 and L amino acids; 
               
               
                 standard amino acid 
                 means any of the twenty standard 
               
               
                   
                 L-amino acids commonly found in 
               
               
                   
                 naturally occurring peptides; 
               
               
                 nonstandard amino acid 
                 means any amino acid, other than 
               
               
                   
                 the standard amino acids, 
               
               
                   
                 regardless of whether it is 
               
               
                   
                 prepared synthetically or derived 
               
               
                   
                 from a natural source; as used 
               
               
                   
                 herein, “synthetic amino acid” 
               
               
                   
                 also encompasses chemically 
               
               
                   
                 modified amino acids, including 
               
               
                   
                 but not limited to salts, amino 
               
               
                   
                 acid derivatives (such as 
               
               
                   
                 amides), and substitutions. 
               
               
                   
                 Amino acids contained within the 
               
               
                   
                 peptides of the present 
               
               
                   
                 invention, and particularly at 
               
               
                   
                 the carboxy- or amino-terminus, 
               
               
                   
                 can be modified by methylation, 
               
               
                   
                 amidation, acetylation or 
               
               
                   
                 substitution with other chemical 
               
               
                   
                 groups which can change the 
               
               
                   
                 peptide&#39;s circulating half life 
               
               
                   
                 without adversely affecting their 
               
               
                   
                 activity; additionally, a 
               
               
                   
                 disulfide linkage may be present 
               
               
                   
                 or absent in the peptides of the 
               
               
                   
                 invention; 
               
               
                 derivative 
                 includes any purposefully 
               
               
                   
                 generated peptide which in its 
               
               
                   
                 entirety, or in part, has a 
               
               
                   
                 substantially similar amino acid 
               
               
                   
                 sequence to the present 
               
               
                   
                 compounds; derivatives of the 
               
               
                   
                 present compounds may be 
               
               
                   
                 characterized by single or 
               
               
                   
                 multiple amino acid 
               
               
                   
                 substitutions, deletions, 
               
               
                   
                 additions, or replacements; these 
               
               
                   
                 derivatives may include (a) 
               
               
                   
                 derivatives in which one or more 
               
               
                   
                 amino acid residues of the 
               
               
                   
                 present compounds are substituted 
               
               
                   
                 with conservative or non- 
               
               
                   
                 conservative amino acids; (b) 
               
               
                   
                 derivatives in which one or more 
               
               
                   
                 amino acids are added to the 
               
               
                   
                 present compounds; (c) 
               
               
                   
                 derivatives in which one or more 
               
               
                   
                 of the amino acids of the present 
               
               
                   
                 compounds include a substituent 
               
               
                   
                 group; (d) derivatives in which 
               
               
                   
                 the present compounds or a 
               
               
                   
                 portion thereof is fused to 
               
               
                   
                 another peptide (e.g., serum 
               
               
                   
                 albumin or protein transduction 
               
               
                   
                 domain); (e) derivatives in which 
               
               
                   
                 one or more nonstandard amino 
               
               
                   
                 acid residues (i.e., those other 
               
               
                   
                 than the 20 standard L-amino 
               
               
                   
                 acids found in naturally 
               
               
                   
                 occurring proteins) are 
               
               
                   
                 incorporated or substituted into 
               
               
                   
                 the present compounds sequence; 
               
               
                   
                 and (f) derivatives in which one 
               
               
                   
                 or more nonamino acid linking 
               
               
                   
                 groups are incorporated into or 
               
               
                   
                 replace a portion of the present 
               
               
                   
                 compounds; 
               
               
                 APP 296-335, APP 317- 
                 have the meanings given in tables 
               
               
                 332, APP 321-335, APP 
                 1 and 2 hereinafter. 
               
               
                 319-332, APP 321-332, 
               
               
                 APP 321-331, APP 325- 
               
               
                 335, APP 321-330, APP 
               
               
                 327-332 and APP 316-337 
               
               
                   
               
             
          
         
       
     
     Throughout this specification and its claims amino acid sequences are written using the standard one-letter or three-letter abbreviations. All sequences are written from left to right in the direction from the N-terminus to the C-terminus. 
     The following term is defined as follows: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 reverse order sequence 
                 as used herein, the reverse order 
               
               
                   
                 sequence of a given sequence is a 
               
               
                   
                 sequence in which the order of 
               
               
                   
                 amino acid residues is reversed 
               
               
                   
                 compared with the given sequence 
               
               
                   
                 when reading in the direction from 
               
               
                   
                 the N-terminus to the C-terminus 
               
               
                   
                 and vice versa; thus, for example, 
               
               
                   
                 SMRER (SEQ ID NO.:4) is the reverse order 
               
               
                   
                 sequence of RERMS (SEQ ID NO.:3), each 
               
               
                   
                 being read as stated above from left to right 
               
               
                   
                 in the N-terminal to C-terminal 
               
               
                   
                 direction; further, 
               
               
                   
                 MVQSMRERHKAELREKA (SEQ ID No: 7) 
               
               
                   
                 (also referred to herein as APP 
               
               
                   
                 335-319) is the reverse order 
               
               
                   
                 sequence of APP 319-335 defined 
               
               
                   
                 above. 
               
               
                   
               
             
          
         
       
     
     WO-A-94/09808 (The Regents of The University of California, inventor T Saito) and T Saito and various co-authors in J. Neuroscience 14 5461-5470 (1994), J. Neuobiol. 25, 585-594 (1994) and J. Cell Biol. 121, 879-886 (1993) disclose certain polypeptides corresponding to parts of human APP. These polypeptides consist of the following: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 no. of 
                   
                   
                   
                   
               
               
                 amino 
                 corresponding 
               
               
                 acid 
                 part of 
                   
                 SEQ ID 
               
               
                 residues 
                 human APP 
                 sequence 
                 NO. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 40 
                 APP 296-335 
                 TPDAVDKYLETPGDENEHAHF 
                 22 
                   
               
               
                   
                   
                 QKAKERLEAKHRERMSQVM 
               
               
                   
                   
                 [Thr-Pro-Asp-Ala-Val- 
               
               
                   
                   
                 Asp-Lys-Tyr-Leu-Glu- 
               
               
                   
                   
                 Thr-Pro-Gly-Asp-Glu- 
               
               
                   
                   
                 Asn-Glu-His-Ala-His- 
               
               
                   
                   
                 Phe-Gln-Lys-Ala-Lys- 
               
               
                   
                   
                 Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg- 
               
               
                   
                   
                 Met-Ser-Gln-Val-Met] 
               
               
                   
               
               
                 17 
                 APP 319-335 
                 AKERLEAKHRERMSQVM 
                 6 
               
               
                   
                   
                 [Ala-Lys-Glu-Arg-Leu- 
               
               
                   
                   
                 Glu-Ala-Lys-His-Arg- 
               
               
                   
                   
                 Glu-Arg-Met-Ser-Gln- 
               
               
                   
                   
                 Val-Met] 
               
               
                   
               
               
                 16 
                 APP 317-332 
                 QKAKERLEAKHRERMS 
                 12 
               
               
                   
                   
                 [Gln-Lys-Ala-Lys-Glu- 
               
               
                   
                   
                 Arg-Leu-Glu-Ala-Lys- 
               
               
                   
                   
                 His-Arg-Glu-Arg-Met- 
               
               
                   
                   
                 Ser] 
               
               
                   
               
               
                 15 
                 APP 321-335 
                 ERLEAKHRERMSQVM 
                 13 
               
               
                   
                   
                 [Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg- 
               
               
                   
                   
                 Met-Ser-Gln-Val-Met] 
               
               
                   
               
               
                 14 
                 APP 319-332 
                 AKERLEAKHRERMS 
                 14 
               
               
                   
                   
                 [Ala-Lys-Glu-Arg-Leu- 
               
               
                   
                   
                 Glu-Ala-Lys-His-Arg- 
               
               
                   
                   
                 Glu-Arg-Met-Ser] 
               
               
                   
               
               
                 12 
                 APP 321-332 
                 ERLEAKHRERMS 
                 15 
               
               
                   
                   
                 [Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg- 
               
               
                   
                   
                 Met-Ser] 
               
               
                   
               
               
                 11 
                 APP 321-331 
                 ERLEAKHRERM 
                 16 
               
               
                   
                   
                 [Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg- 
               
               
                   
                   
                 Met] 
               
               
                   
               
               
                 11 
                 APP 325-335 
                 AKHRERMSQVM 
                 17 
               
               
                   
                   
                 [Ala-Lys-His-Arg-Glu- 
               
               
                   
                   
                 Arg-Met-Ser-Gln-Val- 
               
               
                   
                   
                 Met] 
               
               
                   
               
               
                 10 
                 APP 321-330 
                 ERLEAKHRER 
                 18 
               
               
                   
                   
                 [Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg] 
               
               
                   
               
               
                 6 
                 APP 327-332 
                 HRERMS 
                 19 
               
               
                   
                   
                 [His-Arg-Glu-Arg-Met- 
               
               
                   
                   
                 Ser] 
               
               
                   
               
               
                 5 
                 APP 328-332 
                 RERMS 
                 3 
               
               
                   
                   
                 [Arg-Glu-Arg-Met-Ser] 
               
               
                   
               
               
                 4 
                 APP 328-331 
                 RERM 
                 10 
               
               
                   
                   
                 [Arg-Glu-Arg-Met] 
               
               
                   
               
               
                 3 
                 APP 328-330 
                 RER 
                 9 
               
               
                   
                   
                 [Arg-Glu-Arg] 
               
               
                   
               
             
          
         
       
     
     The same publications also refer to a 17-mer polypeptide which is the reverse-order sequence of APP 319-335 (as defined above). The reverse order sequence is also identified herein as APP 335-319. 
     G Multhorp et al is J. Mol Recognition 8, 247-257 (1995) disclose the following polypeptide which also corresponds to part of human APP: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 No. of 
                   
                   
                   
                   
               
               
                 amino 
                 corresponding 
               
               
                 acid 
                 part of 
                   
                 SEQ ID 
               
               
                 residues 
                 human APP 
                 Sequence 
                 NO. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 22 
                 APP 316-337 
                 FQKAKERLEAKHRERM 
                 20 
                   
               
               
                   
                   
                 SQVMRE 
               
               
                   
                   
                 [Phe-Gln-Lys-Ala-Lys- 
               
               
                   
                   
                 Glu-Arg-Leu-Glu-Ala- 
               
               
                   
                   
                 Lys-His-Arg-Glu-Arg- 
               
               
                   
                   
                 Met-Ser-Gln-Val-Met- 
               
               
                   
                   
                 Arg-Glu] 
               
               
                   
               
             
          
         
       
     
     SUMMARY OF THE INVENTION 
     The present invention provides a derivative of a polypeptide having the formula:
 
X 1 -Arg-Xaa-Arg-X 2   (I)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof and Xaa represents a natural or synthetic amino acid residue or a derivative thereof, at least one functional group of at least one said amino acid residue or derivative thereof being protected by a protective group.
 
     Preferably, the protected functional group(s) comprise one or more amino groups. 
     Advantageously, the amino group(s) comprise an N-terminal amino group. 
     Conveniently, at least one protected amino group is protected by replacement of only one of its hydrogen atoms by a protective group. 
     In other polypeptide derivatives, the protected functional group(s) comprise one or more carboxyl groups. 
     Advantageously, the carboxyl group(s) comprise a C-terminal carboxyl group. 
     Advantageously, the or each protective group is an acyl group represented by the formula 
                                
wherein R represents a straight- or branched-chain alkyl group, for example a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, pentyl or hexyl group, a substituted or unsubstituted cycloalkyl group, for example a methylcyclohexyl or cyclohexyl group, a substituted or unsubstituted straight- or branched-chain aralkyl group, for example a benzyl group, or a substituted or unsubstituted aryl group, for example a phenyl or tolyl group. Examples of substituents in the substituted groups mentioned above are the alkyl groups also mentioned above.
 
     Straight- or branched-chain alkyl groups are most preferred for R, methyl groups being particularly preferred. 
     In formula (I), amino acid derivatives include, for example, substituted amino acids. 
     In formula (I), X 1  and X 2  are each preferably independently from zero to 20, more preferably from zero to 10. 
     When X 1  and X 2  are both zero in formula (I), formula (I) is that of a tripeptide derivative which is preferably Ac-RER when Xaa is glutamic acid. 
     Preferably, compounds according to the invention are compounds in which X 1  and X 2  are such that formula (I) represents an amino acid sequence which is identical or closely homologous to amino acid residues 328 to 332 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom, or to a sequence which is closely homologous thereto or in which the amino acids thereof are replaced by nonstandard amino acids. 
     It is also preferred that formula (I) is one in which X 1  and X 2  are such that the formula represents a reverse-order amino acid sequence which is identical or closely homologous to amino acid residues 330 to 328 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom, or to a sequence which is closely homologous thereto or in which the amino acids thereof are replaced by nonstandard amino acids. 
     As used herein, a peptide or a portion of a peptide which is “closely homologous” means the peptide, or the portion thereof, has an amino acid homology of greater than about 80% with respect to a reference peptide, preferably greater than about 90% and, more preferably, greater than about 95%. 
     Amino acid sequence homology may be computed by using the BLASTP and TBLASTN programs which employ the BLAST (basic local alignment search tool) 2.0.14 algorithm; BLASTP and TBLASTN settings to be used in such computations are indicated in table 3 below. Amino acid sequence identity (complete homology) is reported under “Identities” by the BLASTP and TBLASTN programs. Amino acid sequence similarity (degree of homology) is reported under “Positives” by the BLASTP and TBLASTN programs. Techniques for computing amino acid sequence homology are well known to those skilled in the art, and the use of the BLAST algorithm is described in Altschul et al. (1990),  J. Mol. Biol.  215: 403-10 and Altschul et al. (1997),  Nucleic Acids Res.  25:3389-3402, the disclosures of which are herein incorporated by reference in their entirety. BLASTP and TBLASTN programs utilizing the BLAST 2.0.14 algorithm and may be accessed on the World Wide Web at the National Center for Biotechnology Information website under the National Institutes for Health domain. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Settings to be used for the computation of amino 
               
               
                 acid sequence similarity or identity with BLASTP and 
               
               
                 TBLASTN programs utilizing the BLAST 2.0.14 algorithm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Expect Value 
                 10 
               
               
                   
                 Filter 
                 Low complexity filtering 
               
               
                   
                   
                 using SEG program* 
               
               
                   
                 Substitution Matrix 
                 BLOSUM62 
               
               
                   
                 Gap existence cost 
                 11 
               
               
                   
                 Per residue gap cost 
                  1 
               
               
                   
                 Lambda ratio 
                  0.85 
               
               
                   
                 Word size 
                  3 
               
               
                   
                   
               
               
                   
                 *The SEG program is described by Wootton and Federhen (1993), Comput. Chem. 17: 149-163. 
               
             
          
         
       
     
     Preferably, X 1  in formula (I) represents:
 
X 3 -Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His  (SEQ ID NO.:23)
 
wherein X 3  represents from zero to 21 natural or synthetic amino acid residues or derivatives thereof, and/or X 2  represents
 
Met-Ser-Gln-Val-Met-X 4   (SEQ ID NO.:24)
 
wherein X 4  represents from zero to 25, natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably each independently from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa is glutamic acid, the amino acid residues of the formula corresponds to the sequence of amino acid residues 319 to 335 of human APP. 
     It is also preferred that X 1  in (I) represents:
 
X 3 -Met-Val-Gln-Ser-Met  (SEQ ID NO.:25)
 
wherein X 3  represents from zero to 25, natural or synthetic amino acid residues or derivatives thereof, and/or X 2  represents:
 
His-Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala-X 4   (SEQ ID NO.:26)
 
wherein X 4  represents from zero to 21, natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably independently each from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa is glutamic acid, the amino acid residues of the formula corresponds to the reverse-order sequence of amino acid residues 335 to 319 of human APP. 
     The invention also provides compounds of formula (I) in which X 2  represents:
 
Met-X 4  
 
wherein X 4  represents from zero to 29 natural or synthetic amino acid residues or derivatives thereof.
 
     In such compounds, X 2  preferably represents:
 
Met-Ser-X 4  
 
wherein X 4  represents from zero to 28 natural or synthetic amino acid residues or derivatives thereof.
 
     Further, the invention provides compounds of formula (I) in which X 1  represents:
 
X 3 -Met
 
wherein X 3  represents from zero to 29 natural or synthetic amino acid residues or derivatives thereof.
 
     In such compounds, X 1  preferably represents:
 
X 3 -Ser-Met
 
wherein X 3  represents from zero to 28 natural or synthetic amino acid residues or derivatives thereof.
 
     The invention thus provides derivatives of the stated kind of the peptides RER (SEQ ID NO.:9), RERM (SEQ ID NO.:10), MRER (SEQ ID NO.:11), RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4). 
     The most preferred of such derivatives is the compound Ac-RER which has the structural formula: 
     
       
                 
         
             
             
         
      
     
     In addition to the compounds mentioned hereinbefore, the present invention also provides the compounds (including the stated derivatives of RER (SEQ ID NO.:9), RERM (SEQ ID NO.:10), MRER (SEQ ID NO.:11), SMRER (SEQ ID NO.:4) and RERMS (SEQ ID NO.:3)) for use in medicine and their use in the preparation of medicaments for the treatment of neurodegenerative diseases, including Alzheimer&#39;s disease, and as cognitive enhancers. 
     The invention further provides pharmaceutical compositions comprising the compounds (including the stated derivatives of RER (SEQ ID NO.:9), RERM (SEQ ID NO.:10), MRER (SEQ ID NO.:11), SMRER (SEQ ID NO.:4) and RERMS (SEQ ID NO.:3)) and a pharmaceutically-acceptable carrier and also compositions in which a compound according to the invention (including the stated derivatives of RER (SEQ ID NO.:9), RERM (SEQ ID NO.:10), MRER (SEQ ID NO.:11), SMRER (SEQ ID NO.:4) and RERMS (SEQ ID NO.:3)) is chemically or physically linked to a further molecule or vehicle to form a complex for pharmaceutical delivery of the compound. 
     Further, the invention provides a method of treatment of a neurodegenerative disease in a human or non-human animal suffering or potentially suffering from the disease is administered with an amount of a composition referred to in the preceding paragraph or a compound according to the present invention effective to treat the disease. The invention also provides a method of producing a cognitive enhancement in a human or non-human animal by administering to the animal a said composition or compound in an amount effective to produce the enhancement. 
     The compounds which are most preferred in the medical uses and pharmaceutical compositions are the stated derivatives of the following:
 
Arg-Glu-Arg  (SEQ ID No: 9)
 
which corresponds to amino acid residues 328-330 of human APP,
 
Arg-Glu-Arg-Met  (SEQ ID No: 10)
 
which corresponds to amino acid residues 328-331 of human APP,
 
Met-Arg-Glu-Arg  (SEQ ID No: 11)
 
which is the reverse-order polypeptide corresponding to the above,
 
Arg-Glu-Arg-Met-Ser  (SEQ ID No: 3)
 
which corresponds to amino acid residues 328-332 of human APP,
 
Ser-Met-Arg-Glu-Arg  (SEQ ID No: 4)
 
which is the reverse-order polypeptide corresponding to the above,
 
                             Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His-   (SEQ ID No: 6)           Arg-Glu-Arg-Met-Ser-Gln-Val-Met            
which corresponds to amino acid residues 319-335 of human APP, and
 
                             Met-Val-Gln-Ser-Met-Arg-Glu-Arg-His-   (SEQ ID No: 7)           Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala            
which is the reverse-order polypeptide corresponding to the above.
 
     The present invention also provides a compound having a formula comprising:
 
X 1 -Arg-Glu-Arg-X 2   (II)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 32 natural or synthetic amino acid residues or derivatives thereof, and Xaa represents a natural or synthetic amino acid residue or a derivative thereof, it being preferred that the compound is none of the following (as hereinbefore defined): APP 296-335, APP 319-335, APP 317-332, APP 321-335, APP 319-332, APP 321-332, APP 321-331, APP 325-335, APP 321-330, APP 327-332, APP 328-332, APP 328-331, APP 328-330, APP 335-319 and APP 316-337.
 
     In formula (II), X 1  and X 2  are preferably and independently each from zero to 22, more preferably from zero to 12. Most preferably, one or both of X 1  and X 2  is zero. 
     Preferably, X 1  and X 2  are such that formula (II) represents an amino acid sequence which is identical or closely homologous to amino acid residues 328 to 330 of human APP and up to 32 successive amino acid residues of human APP extending in each direction therefrom, the formula also comprising sequences closely homologous to said sequence and sequences in which said amino acids thereof are replaced by nonstandard amino acids and/or by derivatives of acid amino acids. 
     It is also preferred that X 1  and X 2  are such that formula (II) represents a reverse-order amino acid sequence which is identical or closely homologous to amino acid residues 330 to 328 of human APP and up to 32 successive amino acid residues of human APP extending in each direction therefrom, the formula also comprising sequences closely homologous to said reverse-order sequence and sequences in which said amino acids thereof are replaced by nonstandard amino acids and/or by derivatives of acid amino acids. 
     The invention further provides a compound having a formula comprising:
 
X 1 -Arg-Xaa-Arg-X 2   (III)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 32 natural or synthetic amino acid residues or derivatives thereof and Xaa represents a natural or synthetic amino acid residue or a derivative thereof, for use in medicine.
 
     In formula (III), X 1  and X 2  are preferably independently each from zero to 22, more preferably from zero to 12. Most preferably, one or both of X 1  and X 2  is zero. 
     Preferably, X 1  and X 2  are such that formula (III) represents an amino acid sequence which is identical or closely homologous to amino acid residues 328 to 330 of human APP and up to 32 successive amino acid residues of human APP extending in each direction therefrom, the formula also comprising sequences closely homologous to said sequence and sequences in which said amino acids thereof are replaced by nonstandard amino acids and/or by derivatives of acid amino acids. 
     It is also preferred that X 1  and X 2  are such that formula (III) represents a reverse-order amino acid sequence which is identical or closely homologous to amino acid residues 330 to 328 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom, the formula also comprising sequences closely homologous to said reverse-order sequence and sequences in which said amino acids thereof are replaced by nonstandard amino acids and/or by derivatives of acid amino acids. 
     A particularly preferred compound is one in which X 1  and X 2  represents:
 
X 3 -Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His  (SEQ ID NO.:27)
 
wherein X 3  represents from zero to 23 natural or synthetic amino acid residues or derivatives thereof, and/or X 2  represents:
 
Met-Ser-Gln-Val-Met-X 4   (SEQ ID NO.:28)
 
wherein X 4  represents from zero to 27 natural or synthetic amino acid residues or derivatives thereof.
 
     Another preferred compound is one in which X 1  and X 2  represents:
 
X 3 -Met-Val-Gln-Ser-Met  (SEQ ID NO.:29)
 
wherein X 3  represents from zero to 27 natural or synthetic amino acid residues or derivatives thereof, and/or X 2  represents:
 
His-Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala-X 4   (SEQ ID NO.:30)
 
wherein X 4  represents from zero to 23 natural or synthetic amino acid residues or derivatives thereof.
 
     In such compounds, X 3  and X 4  are preferably independently each from zero to 20, more preferably from zero to 10. Most preferably, one or both of X 3  and X 4  is zero. 
     Xaa in formulae (I) and (III) is preferably glutamic acid. 
     The present invention also provides the use of a compound having a formula comprising:
 
X 1 -Arg-Xaa-Arg-X 2   (III)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 32 natural or synthetic amino acid residues or derivatives thereof and Xaa represents a natural or synthetic amino acid residue or a derivative thereof, in the preparation of a medicament for use in the treatment of a neurodegenerative disease or as a cognitive enhancer.
 
     In addition, the invention provides a pharmaceutical composition comprising such a compound and a pharmaceutically acceptable carrier. 
     Moreover, the invention provides a said compound which is chemically or physically linked to a further molecule or vehicle to form a complex for pharmaceutical delivery of the compound. 
     Furthermore, the invention provides methods of treating a neurodegenerative disease or of obtaining a cognitive enhancement in a human or non-human animal by administering to the animal an effective amount of a compound according to the invention, optionally in the form of a pharmaceutical composition as referred to. 
     The present invention provides a compound having a formula comprising:
 
X 1 -Arg-Xaa 1 -Arg-Xaa 2 -Xaa 3 -X 2   (IV)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof and Xaa 1 , Xaa 2  and Xaa 3 , which may be the same or different, each represents a natural or synthetic amino acid or a derivative thereof.
 
     The amino acid derivatives include, for example, substituted amino acids. 
     X 1  and X 2  are each preferably from zero to 20, more preferably from zero to 10. 
     When X 1  and X 2  are both zero, the formula is that of a pentapeptide which is RERMS (SEQ ID NO.:3) when Xaa 1  is glutamic acid, Xaa 2  is methionine and Xaa 3  is serine. 
     In a compound according to the invention, Xaa 1  is preferably glutamic acid, Xaa 2  is preferably methionine and Xaa 3  is preferably serine. 
     Preferably, the compound is one in which X 1  and X 2  are such that (IV) represents an amino acid sequence which is identical or closely homologous to amino acid residues 328 to 332 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom. 
     The degree of homology is preferably at least 80%, more preferably at least 90% and, most preferably, at least 95%. 
     The invention also provides compounds having a formula comprising:
 
X 1 -Xaa 3 -Xaa 2 -Arg-Xaa 1 -Arg-X 2   (V)
 
wherein X 1 , X 2 , Xaa 1 , Xaa 2  and Xaa 3  are as stated hereinbefore.
 
     When X 1  and X 2  are both zero, the formula is that of a pentapeptide which is SMRER (SEQ ID NO.:4) when Xaa 1  is glutamic acid, Xaa 2  is methionine and Xaa 3  is serine. 
     Such formulae represent the reverse-order sequences of the formulae mentioned hereinbefore. 
     Preferably, the compound is one in which X 1  and X 2  are such that the formula represents a reverse-order amino acid sequence which is identical or closely homologous to amino acid residues 332 to 328 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom. 
     The degree of homology is again preferably at least 80%, more preferably at least 90% and, most preferably, at least 95%. 
     Preferably, X 1  in (IV) represents:
 
X 3 -Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His  (SEQ ID NO.:31)
 
and/or X 2  represents
 
Gln-Val-Met-X 4  
 
X 3  and X 4  being the same or different and representing from zero to 30 natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably each from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa 1 , Xaa 2  and Xaa 3  are glutamic acid, methionine and serine, respectively, the formula corresponds to the sequence of amino acid residues 319 to 335 of human APP. 
     Preferably, X 1  in (V) represents:
 
X 3 -Met-Val-Gln
 
and/or X 2  represents:
 
His-Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala-X 4   (SEQ ID NO.:32)
 
wherein X 3  and X 4 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably each from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa 1 , Xaa 2  and Xaa 3  are glutamic acid, methionine and serine, respectively, the formula corresponds to the reverse-order sequence of amino acid residues 335 to 319 of human APP. 
     In addition to the compounds mentioned hereinbefore, the present invention also provides the compounds (including RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4)) for use in medicine and their use in the preparation of medicaments for the treatment of neurodegenerative diseases, including Alzheimer&#39;s disease, and as cognitive enhancers. 
     The invention further provides pharmaceutical compositions comprising the compounds (including RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4)) and a pharmaceutically-acceptable carrier and also compositions in which a compound according to the invention (including RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4)) is chemically or physically linked to a further molecule or vehicle to form a complex for pharmaceutical delivery of the compound. 
     The compounds which are most preferred in the medical uses and pharmaceutical compositions are the following:
 
Arg-Glu-Arg-Met-Ser  (SEQ ID No:3)
 
which corresponds to amino acid residues 328-332 of human APP,
 
Ser-Met-Arg-Glu-Arg  (SEQ ID No:4)
 
which is the reverse-order polypeptide of the above,
 
                             Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His-   (SEQ ID No: 6)           Arg-Glu-Arg-Met-Ser-Gln-Val-Met            
which corresponds to amino acid residues 319-335 of human APP, and
 
                             Met-Val-Gln-Ser-Met-Arg-Glu-Arg-His-   (SEQ ID No: 7)           Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala            
which is the reverse-order polypeptide of the above.
 
     The present invention provides a compound having a formula comprising:
 
X 1 -Arg-Xaa-Arg-X 2   (VI)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof and Xaa represents a natural or synthetic amino acid or a derivative thereof. Xaa is preferably glutamic acid.
 
     The amino acid derivatives include, for example, substituted amino acids. 
     X 1  and X 2  are each preferably from zero to 20, more preferably from zero to 10. 
     When X 1  and X 2  are both zero, the formula is that of a tripeptide which is Arg-Glu-Arg (RER (SEQ ID NO.:9)) when Xaa is glutamic acid. 
     Preferably, the compound is one in which X 1  and X 2  are such that (I) represents an amino acid sequence which is identical or closely homologous to amino acid residues 328 to 330 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom. 
     It is also preferred that the compound is one in which X 1  and X 2  are such that the formula represents a reverse-order amino acid sequence which is identical or closely homologous to amino acid residues 330 to 328 of human APP and up to 30 successive amino acid residues of human APP extending in each direction therefrom. 
     In each case, the degree of homology is again preferably at least 80%, more preferably at least 90% and, most preferably, at least 95%. 
     Preferably, X 1  in (VI) represents:
 
X 3 -Ala-Lys-Glu-Arg-Leu-Glu-Ala-Lys-His  (SEQ ID NO.:31)
 
and/or X 2  represents
 
Met-Ser-Gln-Val-Met-X 4   (SEQ ID NO.:33)
 
X 3  and X 4  being the same or different and representing from zero to 30 natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably each from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa is glutamic acid, the formula corresponds to the sequence of amino acid residues 319 to 335 of human APP. 
     It is also preferred that X 1  in (VI) represents:
 
X 3 -Met-Val-Gln-Ser-Met  (SEQ ID NO.:34)
 
and/or X 2  represents:
 
His-Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala-X 4   (SEQ ID NO.:32)
 
wherein X 3  and X 4 , which may be the same or different, each represents from zero to 30 natural or synthetic amino acid residues or derivatives thereof.
 
     X 3  and X 4  are again preferably each from zero to 20, more preferably from zero to 10. 
     When X 3  and X 4  are both zero and Xaa is glutamic acid, the formula corresponds to the reverse-order sequence of amino acid residues 335 to 319 of human APP. 
     The invention also provides compounds having the formula (VI) in which Xaa is glutamic acid and either X 1  is methionine and X 2  is zero, or X 1  is zero and X 2  is methionine. These are the compounds Met-Arg-Glu-Arg (MRER) (SEQ ID No: 11) and Arg-Glu-Arg-Met (RERM) (SEQ ID No: 10), respectively. 
     The present invention also provides the compounds mentioned above (including RER (SEQ ID NO.:9)) for use in medicine and their use in the preparation of medicaments for the treatment of neurodegenerative diseases, including Alzheimer&#39;s disease, and as cognitive enhancers. 
     The invention further provides pharmaceutical compositions comprising the compounds (including RER (SEQ ID NO.:9)) and a pharmaceutically-acceptable carrier and also compositions in which a compound according to the invention (including RER (SEQ ID NO.:9)) is chemically or physically linked to a further molecule or vehicle to form a complex for pharmaceutical delivery of the compound. 
     The compound which is most preferred in the medical uses and pharmaceutical compositions is:
 
Arg-Glu-Arg  (SEQ ID No:9)
 
which corresponds to amino acid residues 328-330 of human APP.
 
     The invention further provides a compound having a formula comprising
 
X 1 -Ser-Met-Arg-Glu-Arg-X 2   (VII) (SEQ ID NO.:35)
 
wherein X 1  and X 2 , which may be the same or different, each represents from zero to 30 amino acid residues, the amino acid residues of X 1  and X 2  being such that, when X 1  and X 2  are not both zero, the formula represents a reverse-order sequence corresponding to amino acid residues 332 to 328 of human APP and from zero to 30 successive amino acid residues of human APP extending in each direction therefrom, the formula also comprising sequences closely homologous to said reverse-order sequence and sequences in which said amino acids thereof are replaced by nonstandard amino acids and/or by derivatives of said amino acids, provided always that the compound is not
 
     
       
         
               
               
               
             
           
               
                 Met-Val-Gln-Ser-Met-Arg-Glu-Arg-His- 
                 (SEQ ID No: 7) 
                   
               
               
                 Lys-Ala-Glu-Leu-Arg-Glu-Lys-Ala 
               
             
          
         
       
     
     Subject to the above proviso, formula (VII) thus includes within its scope polypeptides which consist of a core sequence of the five amino acid residues 332 to 328 of human APP in reverse order relative to human APP and, extending therefrom in the N-terminal direction, up to 30 of amino acid residues 333 to 362 of human APP and, in the C-terminal direction, up to 30 of amino acid residues 327 to 328 of human APP, the whole forming a reverse-order sequence relative to human APP. 
     In formula (VII), X 1  is preferably from zero to 20 and/or X 2  is from zero to 20. More preferably, X 1  is from zero to 10 and/or X 2  is from zero to 10. Still more preferably, X 1  and/or X 2  is zero. 
     In other preferred compounds of formula (VII), X 1  is 2 or less and X 2  is 8 or less. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings of this specification consist of the following: 
         FIG. 1  which shows the amino acid sequence of human APP (SEQ ID NO.:1) and chick APP (SEQ ID NO.:2), as referred to hereinbefore; 
         FIG. 2  shows the effect of β-amyloid 12-28 polypeptide on memory formation; 
         FIG. 3  shows the effect of RERMS (SEQ ID NO.:3) on β-amyloid 12-28 induced amnesia; 
         FIG. 4  shows the effect of RERMS (SEQ ID NO.:3) on anti-APP induced amnesia; 
         FIG. 5  shows the effect of RERMS (SEQ ID NO.:3), SMRER (SEQ ID NO.:4) and RSAER (SEQ ID NO.:5) on APP-antisense induced amnesia; 
         FIG. 6  shows the effect of APP 319-335 on APP-antisense induced amnesia; 
         FIG. 7  shows the effect of RERMS (SEQ ID NO.:3) on weak training; 
         FIG. 8  shows the effect of APP 319-335 on weak training; 
         FIG. 9  shows the effect of RER (SEQ ID NO.:9) on weak training; 
         FIG. 10  shows the effects of RER (SEQ ID NO.:9) and Ac-RER on β-amyloid 12-28 induced amnesia; 
         FIG. 11  shows the effect of Ac-RER on weak training; 
         FIG. 12  shows the effects of differing doses of RER (SEQ ID NO.:9) and Ac-RER; and 
         FIG. 13  shows the effect of Ac-RER on β-amyloid 12-28 induced amnesia. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described further by way of example with reference to the following experimental procedures and results. 
     Materials and Methods 
     Animals and Training 
     Commercially obtained Ross Chunky eggs were incubated and hatched in brooders and held until 16±6 hours old. Chicks were placed in pairs in small aluminium pens. Following an equilibration period of an hour, the chicks were pretrained and trained essentially as described by Lossner and Rose (J. Neurochem. 41, 1357-1363 (1983), the contents of which are incorporated herein by reference). Pretraining involved three 10 s presentations of a small (2 mm diameter) white bead, at approximately 5 minute intervals. Chicks, which failed to peck the bead at least twice in three presentations (less than 5%), were not used subsequently, but remained in their pens for the duration of the experiment. Two training techniques were used: “strong” and “weak” training. In both, 5 to 10 minutes after the last pre-training trial, chicks were trained by a 10 s presentation of a 4 mm diameter chrome bead, which had been dipped in the bitter-tasting methylanthranilate. Control chicks pecked at a water-coated or dry bead. In the “strong” version of the task, 100% methylanthranilate was used. In the “weak” version, 10% methylanthranilate was used. Chicks spontaneously pecked at the training or control beads within 20 s. Chicks that peck at the bitter bead evinced a disgust reaction and would not normally peck at a similar, but dry bead for some hours subsequently. At various times following training chicks were tested, by offering them a dry 4 mm diameter chrome bead, followed 10 minutes later by a small (2 mm diameter) white bead, each for 20 to 30 s. Animals were tested by an experimenter blind as to which treatment each chick had received. Chicks are considered to remember the task if they avoid the chrome bead at test but peck at the white bead (discriminate), and to have forgotten it if they peck at both beads. Recall is calculated as a percent avoidance score (percentage of chicks which avoid the chrome bead) and as a discrimination score (percentage of chicks which avoid the chrome but peck at the white bead). The use of the discrimination score ensures that chicks can indeed see and peck accurately at the bead; and hence that the avoidance of the chrome bead is not due to non-specific factors such as lack of visuo-motor coordination, motivation, attention, arousal, etc. but is a positive act, demonstrating memory for the distasteful stimulus. Each chick was trained and tested only once and differences between groups tested for statistical significance by g-test described by Sokal and Rohlf (Biometry: the Principles and Practice of Statistics in Biological Research (2nd edition), W H Freeman, New York (1981)), the contents of which are incorporated herein by reference. The validity of this particular training task used to assess memory formation is extensively discussed by Andrew (Neural and Behavioural Plasticity: the Use of the Domestic Chick as a Model, Oxford University Press, Oxford, UK (1991), the contents of which are incorporated herein by reference. 
     Chicks trained on the strong version of the task were found to recall the avoidance for at least 48 hours, and more than 80% were found normally to avoid and discriminate on test at 24 hours. Therefore if agents that are amnesic—that is, cause the chick not to remember—are administered, chicks will demonstrate forgetting by pecking rather than avoiding the chrome bead on test. By contrast, chicks were found normally to remember the “weak” version of the task for only a few hours—some 6 to 8 hours in all; retention at 24 hours was normally reduced to some 20 to 30%. Thus the learning experience is not committed to long-term memory. Agents that are memory enhancers can thus be tested. A memory enhancing agent, administered to a chick trained on the weak learning task, produces an increase in retention—increased avoidance of the chrome bead—at 24 hours. That is, such memory enhancers help convert weak to strong learning by enabling the transition from shorter to longer-term memory. 
     Peptide Injections 
     Bilateral intracranial injections (2 μg/hemisphere) of either saline, or solutions in saline of different peptides (0.5 to 5 μg/hemisphere) homologous to different regions of the external domain of human APP were injected intracerebrally into a specific brain region, known to be required for memory formation (the intermediate hyperstriatum ventrale) at different time-points pre- or post-training using a 5 μg Hamilton syringe fitted with a plastic sleeve to allow a penetration of 3 mm. After completion of the injection, the needle was kept in place for 5 s. Correct placement was ensured by using a specially designed headholder described by Davis et al (Physiol. Behav. 22, 177-184 (1979), the contents of which are incorporated herein by reference) and was routinely visually monitored postmortem. Peptides or other substances were administered at various times either before or after the training protocol. Chicks were tested at different time points post-training as described above. The general behaviour of the chicks following injections was observed to detect any potential non-specific or adverse reactions to the injections. 
     Peptide Materials 
     The polypeptides administered were synthesised using a conventional peptide synthesiser in a manner which is well-known to those skilled in the art. The synthesised polypeptides were purified by use of RP-HPLC and purity further checked by mass spectrometry (MALDI-TOF), both techniques being well known to those skilled in the art. The polypeptides after synthesis were kept under argon in a lyophilised state, the argon preventing oxidation of cysteine, methionine and tryptophan in particular. 
     Polypeptide synthesis as just mentioned is carried out by MWG-Biotech UK Limited of Milton Keynes, UK. 
     RERMS (SEQ ID NO.:3) is also available from Bachem Limited of St. Helens, Merseyside, UK. 
     Ac-RER can be synthesised by techniques well-known to those skilled in the art. It was obtained from Cambridge Research Biochemicals Limited of Billingham, Cleveland, UK. 
     For further details regarding synthetic methods for the preparation of peptides and peptide derivatives, reference is made to “Principles of Peptide Synthesis” by M. Bodanszky, 2nd Edition (Springer Laboratory, 1993), the entire contents of which are incorporated herein by reference. 
     EXPERIMENTAL RESULTS 
     It is well known in many animal model systems for the study of memory that injection of β-amyloid and β-amyloid peptides, such as β-amyloid 12-28, results in a failure of animals to retain recently acquired memories.  FIG. 2  shows this result for a chick; injection of β-amyloid 12-28 into the brain 30 minutes prior to training chicks on the passive avoidance task results in amnesia in animals tested 30 minutes subsequently. 
       FIG. 2  shows in the left-hand half the percent avoidance measured in terms of total avoidance and discrimination for a saline control and in the right-hand half the percent avoidance measured when β-amyloid 12-28 is injected as described above 30 minutes pretraining and memory is tested 30 minutes posttraining. 
     However, if amnesia is induced by injection of β-amyloid 12-28 30 minutes pretraining, and RERMS (SEQ ID NO.:3) is injected 20 minutes pretraining, memory retention is restored.  FIG. 3  shows that in this case memory is normal at 24 hours post-training. 
       FIG. 3  shows on the left the percent avoidance measured in terms of total avoidance and discrimination for a saline control, in the centre the corresponding results when β-amyloid 12-28 is injected 30 minutes pretraining and memory tested 24 hours posttraining, and on the right the results when the pretraining injection of β-amyloid 12-28 is followed 10 minutes later by RERMS (SEQ ID NO.:3) and memory is again tested 24 hours posttraining. 
     It is thus shown that RERMS (SEQ ID NO.:3) can prevent the memory loss produced by β-amyloid 12-28, a component of the amyloid plaques characteristic of Alzheimer&#39;s disease. 
     It is known that disrupting the normal function of APP by blocking its external domain with a specific monoclonal antibody (mb22C11) around the time of training, whilst without effect on the ability of chicks to learn the passive avoidance response, prevents the transition to long term memory. The monoclonal antibody mb22C11, available from Boehringer-Mannheim, specifically recognises an epitope consisting of part of the external domain of APP. 
       FIG. 4  shows on the left the percent avoidance measured for chicks injected with a saline control, in the centre the percent avoidance measured when mb22C11 is injected (1-5 μg in 2 μl) intracerebrally as described hereinbefore for peptide injections 30 minutes pretraining and, on the right, the percent avoidance measured when RERMS (SEQ ID NO.:3) is also injected 25 minutes after mb22C11 (5 minutes pretraining). In all cases, memory was tested 24 hours posttraining. 
     The results shown in  FIG. 4  demonstrate that RERMS (SEQ ID NO.:3) injected 5 minutes before training will prevent antibody induced memory loss and that the peptide RERMS (SEQ ID NO.:3) can prevent anti-APP induced memory loss. Thus, RERMS (SEQ ID NO.:3) can prevent the memory loss resulting from disrupting the normal function of APP. 
       FIGS. 5 and 6  show the effect of inducing memory loss by injection of a 16-mer end-protected phosphodiester oligodeoxynucleotide designed to correspond to the transcription start sites 146 and AUG1786 of the APP mRNA, immediately upstream of a ribozyme binding site. The oligodeoxynucleotide, 5′-CCC GAG GAC TGA GCC A-3′ (SEQ ID No: 21) was further modified on the 2nd and 13th nucleotides to prevent internal looping and is available from King&#39;s College Molecular Medicine Unit, London, UK. The oligodeoxynucleotide was used in scrambled (SC) and antisense (AS) forms and administered as described hereinbefore for peptide administration in an amount of 0.6 to 1.0 μg in 2 μl. 
     In a first experiment, chicks were injected with saline, RERMS (SEQ ID NO.:3), SMRER (SEQ ID NO.:4) and RSAER (SEQ ID NO.:5) in various combinations in the amounts stated hereinbefore. 
     The results are shown in  FIG. 5  which shows the percent avoidances measured on the “strong” learning task described hereinbefore.  FIG. 5   a  shows the effect compared with a saline control of administration separately of SC oligodeoxynucleotide 12 hours pretraining and AS oligodeoxynucleotide 12 hours pretraining, together with the effect of administration of RERMS (SEQ ID NO.:3) following the AS oligodeoxynucleotide 30 minutes pretraining. 
       FIG. 5   a  shows that the SC oligodeoxynucleotide had no effect on memory but the AS compound had a significant effect of memory loss which was avoided to a substantial extent when RERMS (SEQ ID NO.:3) was administered. 
       FIG. 5   b  shows that similar results were obtained with the reverse-order pentapeptide SMRER (SEQ ID NO.:4). 
       FIG. 5   c  shows that the effect obtained with RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4) is absent with the pentapeptide RSAER (SEQ ID NO.:5). 
     In a second experiment, SC and AS oligodeoxynucleotides were administered 12 hours pretraining. A polypeptide (APP 319-335) corresponding to amino acid residues 319 to 335 of human APP was injected 30 minutes pretraining. Chicks were tested for memory according to the “strong” version of the test described hereinbefore 30 minutes posttraining. 
       FIG. 6  shows successively from the left: the percent avoidance measured for a saline control; the percent avoidance measured when SC oligodeoxynucleotide was administered; the percent avoidance measured when AS oligodeoxynucleotide was administered; and the percent avoidance measured when APP 319-335 was administered 30 minutes pretraining following administration of AS oligodeoxynucleotide 12 hours pretraining. Each result is shown both in terms of total avoidance (left-hand column) and discrimination (right-hand column). 
     The results shown in  FIG. 6  demonstrate that APP319-335 can prevent antisense induced memory loss. 
       FIGS. 7 and 8  show the effects of RERMS (SEQ ID NO.:3) and APP 319-335 on memory in chicks trained on the “weak” memory test described hereinbefore. 
     As stated hereinbefore, weakly trained chicks (trained on 10% methylanthranilate) retain memory for the avoidance for only some 6 hours, and thereafter forget.  FIG. 7  shows, on the left, the percent avoidance results (in terms of total avoidance and discrimination) for chicks trained on the “strong” version of the training, in the centre the corresponding results for “weak” training and, on the right, the effect of administration of RERMS (SEQ ID NO.:3) following “weak” training. The chicks were tested for memory 24 hours posttraining; RERMS (SEQ ID NO.:3) was administered in accordance with the procedure described hereinbefore 30 minutes pretraining. 
       FIG. 8  shows the corresponding results obtained when the APP 319-335 polypeptide was used instead of RERMS (SEQ ID NO.:3). 
       FIGS. 7 and 8  show that RERMS (SEQ ID NO.:3) and APP 319-335 if injected prior to training chicks on the weak task, enhance memory at 24 hours. They thus function as cognitive enhancers (nootropic agents). Thus, RERMS (SEQ ID NO.:3) and APP 319-335 both enhance normal memory in weakly trained animals. 
       FIG. 9  shows the effect of RER (SEQ ID NO.:9) on memory in chicks trained on the “weak” memory test described hereinbefore. 
     As stated hereinbefore, weakly trained chicks (trained on 10% methylanthranilate) retain memory for the avoidance for only some 6 hours, and thereafter forget. 
       FIG. 9  shows, in the three columns on the left, on the left the percent avoidance results (in terms of total avoidance) for chicks trained on the “strong” version of the training, in the centre the corresponding results for “weak” training and, on the right, the effect of administration of RER (SEQ ID NO.:9) following “weak” training. The chicks were tested for memory 24 hours posttraining; RER (SEQ ID NO.:9) was administered in accordance with the procedure described hereinbefore 30 minutes pretraining. 
       FIG. 9  shows, on the right, the corresponding data in terms of discrimination. 
       FIG. 9  shows that RER (SEQ ID NO.:9), if injected prior to training chicks on the weak task, enhances memory at 24 hours. It thus functions as a cognitive enhancer (nootropic agent). Thus, RER (SEQ ID NO.:9) enhances normal memory in weakly trained animals. 
       FIG. 10  shows the effect of RER (SEQ ID NO.:9) and Ac-RER on β-amyloid 12-28 induced amnesia in chicks trained on the “strong” memory test described hereinbefore. 
       FIG. 10  shows from left to right the percent avoidance measured in terms of total avoidance and discrimination for
         chicks trained on the “strong” version of the training;   the amnesic effect of β-amyloid 12-28 administered at 2 μg/hemisphere 30 mins prior to training;   the effect of RER (SEQ ID NO.:9) administered at 2 μg/hemisphere 20 mins prior to training after administration of β-amyloid 12-28 30 mins prior to training; and   the effect of Ac-RER administered at 2 μg/hemisphere 20 mins prior to training after administration of β-amyloid 12-28 30 mins prior to training.       
     The results in  FIG. 10  show that both RER (SEQ ID NO.:9) and AC-RER have the effect of restoring memory measured 20 mins after administration of RER (SEQ ID NO.:9) or AC-RER, following amnesia induced by administration of β-amyloid 12-28. 
     The results also show that the memory-restorative effect of Ac-RER is less than that of RER (SEQ ID NO.:9) but indicate that Ac-RER is more stable after administration and therefore more suitable for peripheral administration. 
       FIG. 11  shows the effect of Ac-RER on memory in chicks trained on the “weak” memory test described hereinbefore. 
       FIG. 11  shows from left to right the percent avoidance measured in terms of total avoidance and discrimination for
         chicks trained on the “strong” version of the training:   chicks trained on the “weak” version of the training;   chicks trained on the “weak” version of the training after having had Ac-RER administered at 2 μg/hemisphere 30 mins beforehand; and   chicks trained on the “weak” version of the training after having had Ac-RER administered at 2 μg/hemisphere 60 mins beforehand.       
     The results in  FIG. 11  show that Ac-RER has the effect of improving the memory of weakly trained chicks when administered 30 or 60 minutes beforehand. The results also show that the effect 60 minutes after administration is still significant, although less than 30 minutes after administration. 
     The results therefore show that Ac-RER has the effect of a cognitive enhancer and that the effect is apparent over a significant time period. 
       FIG. 12  shows the effect of different doses of RER (SEQ ID NO.:9) and AC-RER on memory in chicks trained on the “weak” memory test described hereinbefore. 
       FIG. 12  shows from left to right the percent avoidance measured in terms of total avoidance and discrimination for
         chicks trained on the “strong” version of the training;   chicks trained on the “weak” version of the training;   chicks trained on the “weak” version of the training after having had RER (SEQ ID NO.:9) administered 30 mins beforehand at 0.2 μg/hemisphere;   chicks trained on the “weak” version of the training after having had RER (SEQ ID NO.:9) administered 30 mins beforehand at 1.0 μg/hemisphere;   chicks trained on the “weak” version of the training after having had RER (SEQ ID NO.:9) administered 30 mins beforehand at 2.0 μg/hemisphere;   chicks trained on the “weak” version of the training after having had Ac-RER administered 30 mins beforehand at 4.0 μg/hemisphere; and   chicks trained on the “weak” version of the training after having had Ac-RER administered 30 mins beforehand at 6.0 μg/hemisphere.       
     The results in  FIG. 12  show that both RER (SEQ ID NO.:9) and Ac-RER have the effect of improving the memory of weakly-trained chicks when administered 30 minutes beforehand and that higher doses of Ac-RER than of RER (SEQ ID NO.:9) are required to obtain a comparable effect. 
     The results therefore show that increased amounts of Ac-RER, in comparison to RER (SEQ ID NO.:9), are required to be used as a cognitive enhancer. This again indicates that Ac-RER is more stable after administration than RER (SEQ ID NO.:9) and therefore more suitable for peripheral administration. 
       FIG. 13  shows the effect of Ac-RER administered at different times on β-amyloid 12-28 induced amnesia in chicks trained on the “strong” memory test described hereinbefore. 
       FIG. 13  shows from left to right the percent avoidance measured in terms of total avoidance and discrimination for
         chicks trained on the “strong” version of the training;   the amnesic effect of β-amyloid 12-28 administered at 2 μg/hemisphere 30 mins prior to training;   the memory-restorative effect of Ac-RER administered at 4 μg/hemisphere 60 mins prior to training and 30 mins prior to administration of β-amyloid 12-28 at 2 μg/hemisphere;   the memory-restorative effect of Ac-RER administered at 4 μg/hemisphere 20 mins prior to training and 10 mins after administration of β-amyloid 12-28 at 2 μg/hemisphere; and   the memory-restorative effect of Ac-RER administered at 4 μg/hemisphere together with β-amyloid 12-28 at 2 μg/hemisphere 30 mins prior to training.       
     The results of  FIG. 13  show that Ac-RER has the effect of restoring memory when amnesia has been induced by β-amyloid 12-28. The effect is manifested regardless of whether Ac-RER is administered before, after or simultaneously with the amnesia-inducing β-amyloid 12-28. 
     The role of APP in memory formation has been attributed to its involvement in cell-to-substrate adhesion processes. The data reported suggests that the APP involvement in memory formation most probably involves change in signal transduction events. The post-training time within which the antibody and antisense-induced amnesia, and within which RER (SEQ ID NO.:9), Ac-RER, RERMS (SEQ ID NO.:3) and SMRER (SEQ ID NO.:4) prevents amnesia, corresponds to that during which memory formation is vulnerable to disruption of the putative signal-transduction functions of APP. 
     The chick system is a good one for exploring these issues, because the learning task is precise and sharply timed, and permits one also to be sure that any observed effect of an injected substance is specific to retention and not either to acquisition or to concomitant processes such as visual acuity, arousal or motor activity. Further, the role of other cell adhesion molecules in the cascade leading to synaptic modulation has been well mapped, so that the effects of either blocking or attempting to rescue functional APP activity can be set into an established context: see Rose, Learn. Memory 7, 1-17 (2000) the contents of which are fully incorporated herein by reference. 
     It is therefore indicated by the experimental results reported above that compounds of the present invention are effective for the treatment and/or prevention of neurological diseases and disorders and as cognitive enhancers (nootropic agents) in other animals, including human and non-human mammals. The compounds are therefore effective in the treatment and/or prevention of Alzheimer&#39;s disease in humans and other neurodegenerative diseases and disorders in animals generally, including humans. Such animals include transgenic and other animal models for Alzheimer&#39;s disease. 
     As used herein, except where the context indicates otherwise, the terms “treatment”, “treat” and analogous expressions used in relation to neurodegenerative diseases include within their scope not only treatment when symptoms are apparent but also the partial or total prevention of such diseases and delay in their onset in patients or animals who are subjected to treatment before onset of the disease or its symptoms become apparent. 
     The compounds of the present invention may be administered intracerebally as described above, or may be administered peripherally, for example intramuscularly, intravenously, transdermally or orally, preferably after complexation as described above. Instead or in addition, the compounds may be protected against alteration between administration and effectiveness, for example by addition of protective groups. 
     The experimental results of  FIGS. 10 to 13  show that the polypeptide derivatives of the present invention, particularly Ac-RER, are effective for longer time periods after administration than their analogues lacking protective groups and are therefore particularly suitable for peripheral administration. 
     The compounds of the present invention may also be formulated as pharmaceutical compositions as referred to hereinbefore, particularly such compositions as are capable of crossing the blood-brain barrier and thereby be suitable for peripheral administration. 
     In all events a suitable dose of peptide compounds according to the invention is from 10 to 100 μg/kg body weight of the animal being treated. 
     As used herein, the term “effective to treat” in the context of a neurodegenerative disease means that amount of the compound(s) used in the treatment which causes a reduction or stabilisation or, as the case may be, prevents or delays the appearance of such symptoms as measured by standard medical or psychological criteria, for example as disclosed in Handbook of Memory Disorders (eds: A D Baddeley, B A Wilson and F N Watts), Wiley (1995), the disclosure of which is herein incorporated by reference. 
     As used herein, the term “effective to treat” in relation to a cognitive enhancement means an amount of the compound(s) used in the treatment which causes an improvement in cognitive power as measured by psychological criteria, for example as disclosed in Handbook of Memory Disorders (eds: A D Baddeley, B A Wilson and F N Watts), Wiley (1995), the disclosure of which is herein incorporated by reference. 
     
       
         
               
             
               
               
             
               
               
             
           
               
                   
               
               
                 SEQUENCE LISTING FREE TEXT 
               
             
          
           
               
                 SEQ ID 
                   
               
               
                 NO. 
                 Free Text &lt;223&gt; 
               
               
                   
               
             
          
           
               
                 3 
                 Description of Artificial Sequence: 5-mer 
               
               
                   
                 polypeptide 
               
               
                 4 
                 Description of Artificial Sequence: 5-mer 
               
               
                   
                 polypeptide 
               
               
                 5 
                 Description of Artificial Sequence: 5-mer 
               
               
                   
                 polypeptide 
               
               
                 6 
                 Description of Artificial Sequence: 17-mer 
               
               
                   
                 polypeptide 
               
               
                 7 
                 Description of Artificial Sequence: 17-mer 
               
               
                   
                 polypeptide 
               
               
                 8 
                 Description of Artificial Sequence: 17-mer 
               
               
                   
                 polypeptide 
               
               
                 9 
                 Description of Artificial Sequence: 3-mer 
               
               
                   
                 polypeptide 
               
               
                 10 
                 Description of Artificial Sequence: 4-mer 
               
               
                   
                 polypeptide 
               
               
                 11 
                 Description of Artificial Sequence: 4-mer 
               
               
                   
                 polypeptide 
               
               
                 12 
                 Description of Artificial Sequence: 16-mer 
               
               
                   
                 polypeptide 
               
               
                 13 
                 Description of Artificial Sequence: 15-mer 
               
               
                   
                 polypeptide 
               
               
                 14 
                 Description of Artificial Sequence: 14-mer 
               
               
                   
                 polypeptide 
               
               
                 15 
                 Description of Artificial Sequence: 12-mer 
               
               
                   
                 polypeptide 
               
               
                 16 
                 Description of Artificial Sequence: 11-mer 
               
               
                   
                 polypeptide 
               
               
                 17 
                 Description of Artificial Sequence: 11-mer 
               
               
                   
                 polypeptide 
               
               
                 18 
                 Description of Artificial Sequence: 10-mer 
               
               
                   
                 polypeptide 
               
               
                 19 
                 Description of Artificial Sequence: 6-mer 
               
               
                   
                 polypeptide 
               
               
                 20 
                 Description of Artificial Sequence: 22-mer 
               
               
                   
                 polypeptide 
               
               
                 21 
                 Description of Artificial Sequence: end-protected 
               
               
                   
                 16-mer oligonucleotide modified at positions 2 &amp; 
               
               
                   
                 13 to prevent internal looping 
               
               
                 22 
                 Description of Artificial Sequence: 40-mer 
               
               
                   
                 polypeptide