Cationic liposomes as efficient nanocarriers for the drug delivery of an anticancer cholesterol-based ruthenium complex

Aiming for novel tools for anticancer therapies, a ruthenium complex, covalently linked to a cholesterol-containing nucleolipid and stabilized by co-aggregation with a biocompatible lipid, is here presented. The amphiphilic ruthenium complex, named ToThyCholRu, is intrinsically negatively charged and has been inserted into liposomes formed by the cationic 1,2-dioleyl-3-trimethylammoniumpropane chloride (DOTAP) to hinder the degradation kinetics typically observed for known ruthenium-based antineoplastic agents. The here described nanovectors contain up to 30% in moles of the ruthenium complex and are stable for several weeks. This drug delivery system has been characterized using dynamic light scattering (DLS), small angle neutron scattering (SANS), neutron reflectivity (NR) and electron paramagnetic resonance (EPR) techniques. Fluorescence microscopy, following the incorporation of rhodamine-B within the ruthenium-loaded liposomes, showed fast cellular uptake in human carcinoma cells, with a strong fluorescence accumulation within the cells. The in vitro bioactivity profile revealed an important antiproliferative activity and, most remarkably, the highest ability in ruthenium vectorization measured so far. Cellular morphological changes and DNA fragmentation provided evidence of an apoptosis-inducing activity, in line with several in vitro studies supporting apoptotic events as the main cause for the anticancer properties of ruthenium derivatives. Overall, these data highlighted the crucial role played by the cellular uptake properties in determining the anticancer efficacy of ruthenium-based drugs, showing DOTAP as a very efficient nanocarrier for their stabilization in aqueous media and transport in cells. In vitro bioscreens have shown the high antiproliferative activity of ToThyCholRu–DOTAP liposomes against specific human adenocarcinoma cell types. Furthermore, these formulations have proved to be over 20-fold more effective against MCF-7 and WiDr adenocarcinoma cells with respect to the nude ruthenium complex AziRu we have previously described.