CONNECT · From Supramolecular to Covalent Boron Clusters Membrane Carriers

From Supramolecular to Covalent Boron Clusters Membrane Carriers

Overview of the Research Project The transport of small biomolecules and molecular drugs such as proteins, nucleic acids, and synthetic nanomaterials within living cells has remained a significant challenge in life sciences. At the same time, due to its capacity to enable targeting of molecules to specific locations or organelles within the cell, research on intracellular transport for imaging and drug delivery is receiving special attention. However, direct delivery of exogenous cargo into the cytosol requires overcoming the plasma membrane, which serves as a protective barrier separating the cell's internal environment from the outside. To transport molecules across membranes, synthetic carriers have been designed and, to date, they have all been based on the amphiphilic dogma. As a consequence of their amphiphilicity, current synthetic transporters tend to aggregate, alone or with other (bio)molecules, limiting their aqueous solubility and stability. Thus, this project abandoned the typical amphiphilic model of membrane transport and proposed the use of superchaotropic boron clusters for the transport of a broad range of hydrophilic chemical substances across lipid membranes and inside cells. This transport is enabled by the superchaotropic properties of the boron cluster, which disrupt the hydrogen bonding network of water more effectively than standard chaotropic ions in the Hofmeister series. These carriers offer distinct advantages over their amphiphilic counterparts, including high water solubility, preventing aggregation, and great stability. Currently, these carriers operate through weak supramolecular interactions, which facilitate the release of the cargo within the cell. However, the exact mechanism and specificity of this transport, as well as the cargo capacity and potential for co-transport of other substances, remain unclear. To address this knowledge gap, the project aimed to covalently attach a cargo molecule to the dodecaborate cluster, ensuring exclusive transport of the desired cargo. Therefore, the primary goal of the project was to explore, for the first time, the covalent modification of model biomolecules (e.g., peptides, fluorophores) with boron superchaotropic clusters to develop a new range of self-transported molecules. One of the potential synthetic routes that was explored was the formation of a triazole group using Copper(I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction to link the cargo and the dodecaborate cluster. To achieve this, we developed a synthetic route to functionalize the dodecaborate cluster starting with the B–H functionalization of the commercial compound salt to obtain B–OH (hydroxylated cluster). Then, we proceed to halogenate (Br) the dodecaborate cluster, which involves the exchange of B-H bonds to yield B–Br, as the brominated cluster has previously demonstrated a good balance between carrier activity and toxicity. Finally, we introduce an alkyne moiety through a nucleophilic substitution reaction to yield the final alkyne compound, which will enable the covalent bonding of the cargo via a CuAAC reaction. This study demonstrates the viability of functionalizing boron clusters with bioactive cargos such as 5-Carboxytetramethylrhodamine azide. The development of these revolutionary molecules as membrane transporters will give rise to a new type of penetration molecule. The creation of a new technology for membrane transport using the covalent introduction of superchaotropic substituents into prototype peptide sequences or other biomolecules, such as fluorophores, will potentially impact the market of pharmaceutical formulation and potentially increase the competitiveness of European institutions and companies. Nevertheless, the introduction of clusters with amino acids is still in progress; we are confident (preliminary studies) that the new application of chaotropic clusters will impact the field of membrane transport by using more controllable, non-aggregating, and less toxic vehicles.

Data: CORDIS, © European Union