This effect was also found even in nonphagocytic cells, although, for these cells, free CLO was more efficient. In vivo, dogs with spontaneous

malignant histiocytosis and treated with CLO-containing liposomes elicited significant tumor regression in two of five treated animals. The authors also reported an antitumor activity following i.v. administration of CLO-containing liposomes in several different nonhistiocytic mouse tumor models, thus suggesting the antitumor activity may have been mediated by a combination Inhibitors,research,lifescience,medical of both direct and indirect tumor effects [38]. Liposomes have been used to deliver BPs directly to cancer cells (Table 1). Neridronate (NER) encapsulated into liposomes increased the inhibition activity on cell growth on human breast cancer cells (MDA-MB-231) by 50 times, compared to the free drug [39]. Table 1 Summary of the most meaningful Protein Tyrosine Kinase inhibitor studies published on nanotechnology to deliver BPs in cancer. Moreover, even at a lower concentration, liposomal Inhibitors,research,lifescience,medical NER showed a suppressive effect on tumor cell mobility in vitro, whereas free NER showed almost no effect. Reasonably, liposomes should mediate the enhanced bisphosphonate uptake into the cells, although this hypothesis Inhibitors,research,lifescience,medical was demonstrated only by indirect evidence by

co-encapsulation of fluorescent dye together with the drug. In order to directly deliver BP in tumor cells, accumulation in MPS should be avoided. Thus, nanocarriers with stealth properties able to avoid opsonization should be preferred. In the light

of this consideration, stealth liposomes encapsulating ZOL (lipoZOL) designed for tumor targeting Inhibitors,research,lifescience,medical were developed [40, 42]. ZOL was encapsulated into liposomes by different strategies, and the reverse-phase evaporation technique was selected to achieve the highest encapsulation efficiency (unpublished data). With this technique, the use of an alkaline buffer improved the ZOL solubility into the aqueous phase of liposomes, thus increased the drug encapsulation efficiency up to about 5% [40]. Liposomes were able to significantly prolong Inhibitors,research,lifescience,medical ZOL circulation time. Free ZOL was quickly cleared too from blood, with 0.1-0.2% of the injected dose still present 1h after injection. ZOL encapsulation into liposomes, especially PEGylated liposomes, significantly increased ZOL circulation time, with more than 10% of the injected dose still present into the blood 24h following the injection [42]. Concerning the in vitro activity of lipoZOL, contrasting results have been found. In particular, our group demonstrated that the use of lipoZOL, compared with free ZOL, increased the cytotoxic effect until a potentiation factor of about 20 [40]. The effect was confirmed in cell lines of different cancer, namely, prostate, breast, head/neck, lung and pancreas, and multiple myeloma, with an IC50 ranging from 4 to about 200μM.