Design, Synthesis and Biological Evaluation of 1,2,3-triazole derivatives as potential antichagasic agents

Chagas disease constitutes a relevant public health issue in several regions of the world, and in recent years it has been reported that a global concern is also developing due to migrations. This pathology is caused by the infection with the parasite Trypanosoma cruzi (T. cruzi), for which only two drugs have been approved for clinical use: benznidazole and nifurtimox, both of them developed almost 40 years ago. Unfortunately, these two drugs suffer from frequent and severe side-effects, which in turn limit their use in prolonged treatments. In this context, the design and development of new anti Chagas compounds exhibiting both a high efficacy and safety constitute an urgent need.

As part of the advances in the knowledge related to the infection with T. cruzi, including its molecular biology details, several druggable targets have been identified for the development of therapeutic compounds. In particular, the group of enzymes named cysteine proteases constitute very attractive targets, since they are expressed throughout the lifecycle of the parasite. Specifically, cruzipain (CZP) has been actively studied towards its inhibition by means of diverse type of organic molecules, including both reversible and irreversible inhibitors. The latter ones have gained significant interest in the last years due to the extensive explorations of the structure-activity relationships related to this type of compounds, further supporting the rational design of new efficient inhibitors.

Structurally, CZP is an homodimer formed by a two polypeptide chains composed of 215 amino acid residues, organized in two well defined domains forming an interface at which the enzyme catalytic site is located. As said before, CZP belongs to the family of cysteine proteases, thus it contains a catalytically active cysteine (CYS25) residue that is indispensable for its proteolytic activity. At least three subdomains (S1, S2 and S3) have been described within the catalytic site, conferring the selectively and efficiency of binding to both substrates and inhibitors. Several crystallographic structures of CZP have been previously reported in the literature, opening the possibility to apply computer-aided drug design (CADD) techniques to aid in the design and synthesis of efficient and selective inhibitors. It is worth mentioning that CZP exhibits a high structural homology with cathepsins, a family of enzymes that are required for normal cell functionality. Consequently, potentially irreversible CZP inhibitors are required to exhibit a high selectivity in order to consider a plausible clinical use.

In this context, the rational design of CZP inhibitors is particularly focused towards the preparation of molecules able to potently and selectively bind to this catalytic site, further eliciting a blockade (either reversible or irreversible) on the CYS25 residue. From the structural point of view, irreversible inhibitors bear two main molecular regions: a) a scaffold conferring a stable binding and efficient positioning of the ligand within the catalytic site (typically stabilized by non-covalent forces), and b) a reactive group capable of forming a covalent bond (and irreversible inhibition) with the catalytically active CYS25 residue (i.e. a warhead structure). Several reports have dealt with the structure-activity relationship exploration of both substructures, and although important knowledge has been gained, there is still further need to explore the corresponding structure-activity relationship related to the binding of inhibitors within the S1, S2 and S3 regions of the catalytic site. As early examples of CZP inhibitors, compounds K777 and K02 can be mentioned, as representative structures of a plethora of peptidomimetic compounds designed as anti Chagas agents. As expected, this type of compounds present suboptimal biopharmaceutical properties (such as low bioavailability and extensive first-pass metabolism), limiting their clinical use.

In line with the efforts to optimize these biopharmaceutical properties, the development of non-peptidic inhibitors is being actively explored, including the use of bioisosteric replacements on the peptidic bond. Among them, 1,2,3-triazoles constitutes a very promising scaffold for the required bioisosteric replacement, with multiple reports presenting detailed explorations of the specific structural requirements needed by a molecule to efficiently comply with the S1, S2 and S3 substructures topologies.

Since bibliographic reports have demonstrated the possibility of efficiently optimizing both the potency and selectivity of 1,2,3-triazole based CZP inhibitors, and taking into account that there is still plenty of knowledge to be gained in respect to their interaction with S1, S2 and S3 subsites, in the present research proposal we aim to exhaustively study the possibilities of designing efficient CZP inhibitors by further decorating the 1,2,3-triazole nucleus. Specifically, we aim to exhaustively apply CADD techniques for the construction of massive triazole derivatives libraries, which will be further subjected to in silico receptor-based screening in the search of promising anti Chagas compounds. This multidisciplinary study further extends to synthetic and biological activity measurements efforts.