Bioorg Med Chem. 2012 Oct 15;20(20):6011-8.

How to blast osteoblasts? Novel dicarba analogues of amylin-(1-8) to treat osteoporosis.

 

Kowalczyk R, Brimble MA, Callon KE, Watson M, Cornish J.

The School of Chemical Sciences, University of Auckland, 23 Symonds St, Auckland 1010, New Zealand.

 

Abstract

When administered in vivo, amylin (1-8) stimulates osteoblast proliferation increasing bone volume and bone strength. The native cyclic octapeptide amylin (1-8) is unstable, however, it provides an attractive framework for the creation of more stable, orally active synthetic analogues using various peptidomimetic techniques. On-resin ring closing metathesis (RCM) on the olefinic side chains of allylglycine residues and lysine moieties functionalized with an allyloxycarbonyl (Alloc) group, was used to prepare novel carba-bridged surrogates of the disulfide bridge between Cys/2 and Cys/7 in amylin-(1-8). Commercially available N(α)-Fmoc N(ε)-Alloc protected lysine was used as a convenient substrate for Grubbs’ ring closing metathesis. Analogues of amylin-(1-8) prepared by cyclization of allylglycine residues that also contained proline residues at either position 4 or 6, or both, were also prepared to investigate the effect of proline as a ‘kink-inducing’ residue on the efficiency of the RCM reaction. Of the nine novel alkene-bridged analogues prepared, five showed promising biological activity in a proliferation study in primary foetal rat osteoblasts at physiological concentrations. Two of these analogues were chosen for further in vivo evaluation. Copyright © 2012 Elsevier Ltd. All rights reserved.

PMID: 22998786

 

Supplementary text:

Most of the current therapies to treat osteoporosis are antiresorptive and inhibit further bone loss by reducing osteoclast activity.1 The only therapy currently used that increases the action of bone forming cells (osteoblasts), is recombinant parathyroid hormone (PTH). However, PTH therapy is limited due to high cost and safety concerns.1,2 A new class of anabolic drug for the treatment of osteoporosis is therefore in great demand.

We have identified an N-terminal octapeptide derived from amylin-(1-37), namely amylin-(1-8), as a promising candidate for pharmaceutical development due to its short sequence, lack of effect on fuel metabolism and its retained anabolic effects on osteoblasts.3 This might be used as a model for the creation of orally active analogues with a potential for the treatment of osteoporosis.

Amylin-(1-8) contains a disulfide bond (Cys/2 and Cys/7) that may be an essential structural feature for osteoblast proliferation. Since disulfide bridges are labile under certain chemical and enzymatic conditions, we investigated whether a disulfide bond replacement by stable carba-bridges using Grubbs’ ring closing metathesis (RCM),4,5 would afford analogues with improved stability and/or activity compared to native amylin-(1-8).

On-resin RCM on the olefinic side chains of allylglycine residues and lysine moieties functionalized with an allyloxycarbonyl (Alloc) group, was used to prepare novel carba-bridged surrogates of the disulfide bridge in amylin‑(1‑8). Commercially available Nα-Fmoc Nε-Alloc protected lysine was used as a convenient substrate for Grubbs’ ring closing metathesis. Analogues of amylin-(1-8) prepared by cyclization of allylglycine residues that also contained proline residues at either position 2 or 4, or both, were also prepared to investigate the effect of proline as a “kink-inducing” residue on the efficiency of the RCM reaction. Of the nine novel alkene-bridged analogues prepared, five showed promising biological activity in a proliferation study in primary fetal rat osteoblasts at physiological concentrations. Two of these analogues were chosen for further in vivo evaluation. It is envisaged that these compounds will have commercial potential for the much needed oral treatment of osteoporosis.

 

Renata Kowalczyk

 

 

References:

[1].          Kraenzlin, M. E.; Meier, C. Nat. Rev. Endocrinol. 2011, 7, 647.

[2].          Bilezikian, J. P.; Matsumoto, T.; Bellido, T.; Khosla, S.; Martin, J.; Recker, R. R.; Heaney, R.; Seeman, E.; Papapoulos, S.; Goldring, S. R. Journal of Bone and Mineral Research 2009, 24, 373.

[3].          Cornish, J.; Callon, K. E.; Gasser, J. A.; Bava, U.; Gardiner, E. M.; Coy, D. H.; Cooper, G. J. S.; Reid, I. R. Am. J. Physiol. Endocrinol. Metab. 2000, 279, E730.

[4].          Miller, S. J.; Grubbs, R. H. J Am Chem Soc 1995, 117, 5855.

[5].          Miller, S. J.; Blackwell, H. E.; Grubbs, R. H. J Am Chem Soc 1996, 118, 9606.

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