Self-assembly lipid-based nanoparticles containing zoledronic acid: a new strategy for the treatment of cancer

Introduction: Zoledronic acid (ZOL), a third generation amino-bisphosphonate (A-BP), is actually, the most potent inhibitor of the bone resorption, largely used in clinic for the treatment of bone diseases (i.e. bone metastases, osteoporosis and Paget's disease). Numerous pre-clinical studies have demonstrated a powerful pro-apoptotic effect of ZOL in several tumor cell lines, suggesting an use of ZOL as anticancer drug. However, their short plasma half-life and the rapid accumulation of ZOL in bone, hamper the achievement of effective drug levels in tumors located outside the bone compartment. Purpose: To develop a nanosystem to use ZOL in the treatment of different extra-skeletal tumors, reducing the accumulation of drug in bone and increasing its concentration in peripheral tissues, e.g. in tumor sites. Methods: We developed pegylated self-assembly nanoparticles (NPs) composed of calcium phosphate NPs containing ZOL (NP CaPZ) coated with liposomes. Briefly, two aqueous solutions of CaCl2 and Na2HPO4, respectively, were mixed under magnetic stirring and the resulting dispersion was filtered through 0.22??????m pore filters (CaP NPs). The dispersion was then mixed with an aqueous solution of ZOL, resulting in Ca2+ / PO43- NPs containing ZOL (CaPZ NPs). In the following step, CaPZ NPs were mixed with pegylated cationic liposomes for 10 min at room temperature, obtaining the so-called PLCaPZ NPs. The NPs were characterized in terms of mean diameters and size distribution, morphology and ZOL complexation efficiency. The in vitro activity and cytotoxicity of NPs containing ZOL were evaluated in different tumor cell lines. Cellular proliferation studies in the presence of ZOL was investigated by MTT assay. Finally, the antitumor activity of PLCaPZ NP was evaluated in animal model of prostate cancer. Results: PLCaPZ NPs with a mean diameter of about 147 nm and a polydispersity index of about 0.1 were obtained. Morphological analysis, performed by cFEG SEM, showed that the PLCaPZ NPs preparation consisted in an homogeneous and spherical particle dispersion. HPLC analysis of non-complexed ZOL showed an actual loading of 65 ???g of ZOL/mg lipids, corresponding to a complexation efficiency of about 70%. In all cell lines, the NPs strengthened the growth inhibition induced by free ZOL, reaching a potentiation factor of 12 in breast carcinoma cell lines. Finally, a significant reduction in tumor growth and an increased survival following administration of PLCaPZ NP was observed in a model of prostate cancer. In addition, a complete remission of the tumor, after treatment of the animals with PLCaPZ NPs, was observed in a significant percentage of animals. In the same animal model, the administration of free ZOL was not effective in reducing significantly the growth of the tumors. Conclusions: New self-assembly NPs containing ZOL were successfully developed in our lab. The use of PLCaPZ NPs allowed to achieve a potent anti-tumor effect of ZOL, demonstrated in an animal model of prostate cancer. In the same animal model, tumor growth was unaffected when using free ZOL.