Conformationally restricted thrombin inhibitors resistant to proteolytic digestion
Research article published in Biochemistry (1992)
Abstract
A new type of thrombin exo-site inhibitor has been designed with enhanced inhibitory potency and increased metabolic stability. With the aid of the model of the structure of the thrombin-hirudin fragment complex [Yue, S.-Y., DiMaio, J., Szewczuk, Z., Purisima, E. O., Ni, F., & Konishi, Y. (1992) Protein Eng. 5, 77-85], cyclic analogs of the hirudin fragment (hirudin55-65) were designed and synthesized. In these analogs, the side chains of appropriately substituted residues, 58 and 61, were joined in order to restrict the conformation of the inhibitor. An analog with an 18-membered lactam ring showed higher antithrombin activity (IC50 = 0.57 microM) than the corresponding analogs with 17- or 16-membered rings and was 2-fold more potent than its linear counterpart. Even 4-fold greater enhancement was obtained when a shorter fragment, hirudin 55-62, was cyclized. This cyclization not only improved the potency but, more importantly, dramatically increased the resistance to proteolytic digestion. Remarkable enhancement of stability to proteolysis was observed for peptide bonds located in the exocyclic linear peptide segments. These results are discussed using molecular modeling.
Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.
Summary
Conformationally restricted thrombin inhibitors resistant to proteolytic digestion.
Why This Matters for Hirudotherapy
This study describes the rational design of cyclic analogs derived from the hirudin fragment (residues 55–65) to create conformationally restricted thrombin exo-site inhibitors with improved potency and proteolytic stability. The most effective analog, incorporating an 18-membered lactam ring, exhibited an IC50 of 0.57 µM—twice as potent as its linear counterpart—and cyclization dramatically enhanced resistance to enzymatic degradation, even in adjacent exocyclic peptide bonds. For ASH's domain, this work is relevant as a proof-of-concept for medicinal chemistry built directly on the hirudin scaffold, demonstrating how the leech-derived thrombin inhibitor can serve as a template for next-generation antithrombotic drug design. The study is purely preclinical and biochemical, involving no live leeches and no clinical data; results reflect in vitro inhibition and stability assays, with clinical relevance remaining speculative.
Citation
Conformationally restricted thrombin inhibitors resistant to proteolytic digestion
Szewczuk Z et al. · Biochemistry, 1992
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