Ruthenium-based nanovectors for cancer therapy

Currently the medical-scientific research is focusing on the realization of non-invasive systems for cancer therapy. Biomaterials particularly suitable for drug delivery are the amphiphilic nucleolipids which self-assemble into liposomal structures [1-2]. Among the possible compounds to be included in nanocarriers as bioactive molecules there are the antiproliferative transition metal complexes. The ruthenium complexes are promising alternatives to platinum-based drugs [3], because they show an high antitumor and antimetastatic activity associated with a lower toxicity [4-7]. In particular, NAMI-A, now in Phase II of clinical trials, is endowed with relevant anticancer activity; nevertheless it is rapidly hydrolyzed in poly-oxo-species under physiological conditions [7]. Therefore, the design of stable ruthenium-based nanoaggregates is a primary goal. In this context, we have investigated by in vitro models the biological activity and toxicity of novel cationic amphiphilic liposomes containing AziRu, a NAMI-A analog [8]. The antiproliferative activity was evaluated on a panel of human cancer cell lines by a "Cell Survival Index", combining the results of cell viability evaluation with the live/death cell ratio. The results showed IC50 values for Ru-nanovectors in the low μM range, proving to be 10−20-fold more active than AziRu used for control, as a consequence of an high cellular uptake due to the nanovectorization. In fact, fluorescence microscopy studies demonstrate that the Ru-nanovectors, added with rhodamine-B, are efficiently and rapidly incorporated in human carcinoma cells. Concurrently, the intracellular fate of the active AziRu was investigated by means of an ad hoc designed fluorescently tagged analog, which exhibited a marked tendency to accumulate within or in proximity of the nuclei. To give new insight into the molecular mechanism of action, FACS analysis, Western Blot and DNA fragmentation assay were performed. The results showed both apoptosis and autophagy pathways activation. Taken together, our findings provide convincing evidence that the Ru-nanovectors are good candidate drugs, alternative to known antiproliferative agents based on transition metals. Further studies are in progress to evaluate their in vivo activity, aiming at the definition of metabolic targets and the physiological implications of these antiproliferative agents.