Abstract:
The present invention relates to peptides that are parathyroid hormone (PTH) analogs, useful for the treatment of hypoparathyroidism and diseases characterized by bone mass reduction, such as osteoporosis, and for stimulating bone repair or favoring the engraftment of a bone implant; to the pharmaceutical compositions comprising these PTH-like peptides and use thereof.

Description:
The present application claims priority benefit of Italian Patent Application MI2004A001440, filed Jul. 19, 2004. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of parathyroid hormone (PTH) analogs, in particular to novel PTH-like peptides hereinafter reported, useful for the treatment of hypoparathyroidism and diseases characterized by bone mass reduction, such as osteoporosis, and for stimulating bone repair or favoring the engraftment of a bone implant. 
     STATE OF THE ART 
     Parathyroid hormone (PTH) is an 84 amino acids polypeptide that acts as the most important regulator of calcium homeostasis in the human body through its direct action on bone and kidneys. The powerful anabolic effect on bone mass makes this hormone particularly interesting as potential therapeutic agent in the therapy of osteoporosis. 
     Unfortunately, due to the elevated molecular weight of PTH, its therapeutic applications have important limitations since its synthesis is technically difficult, and therefore expensive, and the only possible administration mode is the injection route. Moreover, PTH is easily susceptible to protease attack and must be stored at low temperature due to its low stability. In addition to these technical limitations, the toxicological data, and in particular the unfavorable results of cancerogenesis studies, induce a cautious use of PTH (Vahle J. L.,  Toxicol. Pathos.  2004 July–August, 32(4): 426–38; Whitfiel J. F.,  Medscape Womens Health  2001 Oct, 6(5):7; Kuijpers G.,  BMJ  2002 Feb. 23, 324 (7335): 435–6). 
     Therefore, during the last years, investigation has focused on development of PTH-derived low molecular weight peptides which have analogous biological activity but can be administered by the oral route, are protease resistant, have structural constraints that improve the interaction with the receptor, can be easily synthesized and exhibit a greater therapeutic index. 
     Recently, it was found that a peptide composed of the first 34 amino acids of PTH is capable of inducing receptor activation and is effective in the treatment of osteoporosis in women in menopause (Neer R. M. et al, N. Eng. J. Med. 2001, 34:1434–1441). 
     However, the molecular weight of this peptide is still too high for oral administration. On the other hand, lower molecular weight peptides, for instance those consisting of the first 14 or 11 amino acids of PTH (PTH(1–14) and PTH(1–11)), proved to be inactive or exhibited very low biological activity. 
     Recently, it was found that the activity of low molecular weight peptides can be increased by introducing particular substitutions at specific amino acid positions. For example, PTH (1–11) analogs endowed with biological activity that were described in the prior art are: [Ala 3 , Gln 10 , Arg 11 ]-PTH(1–11), [Ala 3 , Gln 10 , Harg 11 ]-PTH(1–11), and [Aib 1,3 ; Gln 10 ; Harg 11 ]-PTH(1–11). 
     All studies carried out to find low molecular weight peptides with PTH-like activity showed that the substitution of valine at position 2 with both natural or non natural amino acids, such as Aib, leads to a reduction of biological activity ( Mol. and Cell. End.,  2000, 160 pp. 135–147;  J. Biol. Chem.  2000, 275, pp. 21836–21843;  Endocrinology,  2001, 142, pp. 3068–3074;  J. Biol. Chem.,  2001, 52, pp. 49003–49012; WO 03/009804). 
     Therefore, these studies have generated a prejudice in the art that position 2 of PTH is essential for receptor recognition and therefore cannot be substituted when developing PTH derived low molecular weight peptides endowed with biological activity. 
     SUMMARY OF THE INVENTION 
     Now the Applicant surprisingly found that, in contrast with the prior art teachings, substitution of valine at position 2 of PTH-(1–11) does not always lead to a decrease of biological activity. In fact, the substitution of amino acid at position 2 of PTH (1–11) with α-methyl-valine or α-methyl-leucine, combined with specific substitutions of other amino acids, results in peptides which have high biological activity and stability, and are suitable for oral administration. 
     In one aspect, the present invention is therefore directed to a peptide with PTH-like activity, comprising an amino acid sequence selected from the group consisting of: 
                                                                                                               (SEQ ID NO: 1)                    Ala-X 2 -Aib-Glu-Ile-Gln-Leu-Nle-His-Asn-Arg;                            (SEQ ID NO: 2)                    Aib-X 2 -Ser-Glu-Ile-Gln-Leu-Nle-His-Asn-Arg;                            (SEQ ID NO: 3)                    Ala-X 2 -Ser-Aib-Ile-Gln-Leu-Nle-His-Asn-Arg;               and                        (SEQ ID NO: 4)                    Aib-X 2 -Aib-Glu-Ile-Gln-Leu-Nle-His-Asn-Arg,                
wherein X 2  is selected from the group consisting of α-methyl-valine and α-methyl-leucine, and C- or N- derivatives thereof, and pharmaceutically acceptable salts thereof.
 
     In another aspect, the present invention is directed to pharmaceutical compositions comprising at least one of the above said peptides, or C- or N- derivatives thereof, or pharmaceutically acceptable salts thereof. 
     The present invention is further drawn to a method of treating hypoparathyroidism and diseases characterized by bone mass reduction and to a method of stimulating bone repair and favoring the engraftment of a bone implant comprising administering to a patient in need of such a treatment an effective amount of at least one of the above said peptides, or a C- or N- derivative thereof, or a pharmaceutically acceptable salt thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the invention, by “Aib” the α-aminoisobutyric acid is meant, and by “Nle” norleucine is meant. 
     According to a particularly preferred embodiment of the present invention, X 2  is α-methyl-valine. 
     Compared to PTH (1–11) analogs known in the art, the present peptides exhibit a higher biological activity associated with greater resistance to protease degradation. The synthesis of said peptides is preferably performed by a solid phase technique, in which a resin suitable to anchor the C-terminal amino acid of the peptide is used as the solid phase. The extension of the peptide in N-terminal direction is then obtained by reaction of the amino acid bound to the resin with the next amino acid, appropriately protected usually by a FMOC or BOC group, according to a protocol that is well known to any expert in the field (Fields G. B. et al.  Int. J. Peptide and Protein Res.  1990, 35; 161; Chone W. C. et al. “ Fmoc Solid Phase Peptide Synthesis: a practical approach”,  Oxford University Press 2000) and combines the HOBut/HBTU/Dipea activaction with the activation by means of acyl fluoride. 
     In fact, for steric reasons, formation of a peptide bond involving α-methyl amino acids requires the activation of the carboxyl group by means of acyl fluorides. The same activation is applied to all the residues that follow the α-methyl amino acid present in the sequence. 
     The peptides of the present invention have a powerful PTH-like activity and are therefore indicated for the manufacture of medicaments useful in the treatment of hypoparathyroidism and of diseases characterized by a reduction of bone mass, as for instance osteoporosis, or as adjuvants in implantology and in repair of bone fractures. 
     Moreover, the present peptides showed to be able to stimulate bone repair and favor the engraftment of bone implants, and can be therefore administered in a therapeutically effective dose to this aim. 
     Therefore the present invention refers also to pharmaceutical compositions comprising at least one of said peptides in presence of pharmaceutically acceptable excipients and/or diluents. 
     Said peptides are particularly suitable for oral administration. Therefore, according to a particularly preferred embodiment, the pharmaceutical compositions of the invention are formulated for oral administration, for instance in the form of tablets, capsules, granulates, drops or syrups. 
     The following example is given to provide a non limiting illustration of the present invention. 
     EXAMPLE 1  
     Peptide Synthesis 
     a) Preparation and Conjugation of Resin 
     The RINK AMIDE MBHA resin from NOVABIOCHEM is swollen for 30′ in NMP. It is filtered and the procedure is repeated for additional 30′. The resin is filtered again, then suspended in 20% piperidine solution in NMP for 45′. The resin is filtered and washed repeatedly with NMP. The resin is then suspended in NMP solution for 1 hour, with 4 equivalents of HOBt and HBTU, 8 equivalents of DIPEA. It is then filtered and washed with NMP. This procedure is followed for all amino acids that are not alpha-methylated. 
     b) Preparation of Acyl Fluoride 
     1 equivalent of amino acid protected by a Fmoc group is suspended in anhydrous CH 2 Cl 2  and 1 equivalent of piridine is added. The temperature is brought to 0° C. and 2 equivalents of fluorocyanide are added. The temperature is allowed to rise to room temperature. After 3 hours, the reaction is stopped by addition of ice and CH 2 Cl 2 . The two phases are separated, the organic phase is washed with cold water and dried over Na 2 SO 4 . The organic solvent is removed, thus obtaining a glassy solid of white-yellow color. 
     An analysis of the so obtained product is performed by FT-IR spectroscopy. The acyl fluoride signal is detected at 1860–1830 cm −1  (Carpino L. A.,  J. Am. Chem. Soc.  1990, 112, 9651). 
     c) Solid Phase Reaction 
     3 equivalents of acyl fluoride are reacted for 2 hours with 1 equivalent of DIPEA in DMF dried overnight on A4 molecular sieves (Wenschuh H.,  J. Org. Chem.  1994, 59, 3275).