Fibrinogen-coated lipid-based drug delivery systems: A novel approach for targeted delivery of anti-cancer taxanes to tumors

In this study, we investigated an innovative approach for site-specific delivery of taxane anti-cancer agents. Based on earlier observation that tumors exhibit markedly elevated levels of fibrin(ogen), we hypothesized that fibrinogen-coated lipid vesicles selectively accumulate within tumor tissue and as such, this approach can be utilized to target drugs to the neoplastic loci. We first prepared a fibrinogen coated emulsion formulation of docetaxel, a widely used taxane anti-cancer agent, and optimized it with respect to particle size, stability and fibrinogen biological functionality. This formulation was then rigorously tested employing clinically relevant tumor models. First, cytotoxicity of docetaxel containing formulations was assessed against human breast carcinoma MCF-7, mouse melanoma B16FI0, L1210 leukemia and rat lymphoma Nb2-11 cells in culture. For this purpose, we employed clonogenic, cell proliferation and tritiated thymidine uptake assays. Fibrinogen coated emulsions retained, and in some cases significantly enhanced, the cytotoxic activity of docetaxel. In vivo anti-tumor efficacy of fibrinogen coated docetaxel emulsions was assessed employing B16F10 melanoma bearing C57BL/6 mice. The melanoma cells were implanted via an intra-peritoneal injection. On days 2 and 9 following tumor implantation, mice were treated with docetaxel solution (currently marketed formulation-Taxotere), docetaxel emulsion or fibrinogen-coated docetaxel emulsion (docetaxel dose, 20 mg/kg in each case; control groups: saline, blank emulsions). Anti-tumor efficacy was assessed as delay in tumor growth and % increase in life span (%ILS) of animals. Fibrinogen-coated docetaxel emulsions caused a remarkable increase (>7-fold) in the survival compared to the currently used docetaxel formulation, while uncoated docetaxel emulsions caused a 4.5-fold increase in life spans. Mean life spans in saline treated group were 15.7 +/− 1.16days, in Taxotere treated group were 23 +/− 4.71 days, in uncoated docetaxel emulsions were 48.9 +/− 18.27 days and in fibrinogen coated docetaxel emulsions were 68.6 +/− 36.45 days.{09}In fact, as of this writing, 40% of the mice in the fibrinogen coated docetaxel emulsion group remain tumor free (117 days post-tumor implantation).{09}Biodistribution studies revealed that the docetaxel levels were significantly higher in tumors and lower in normal tissues of animals treated with the fibrinogen-coated emulsion. In conclusion, our study proposes an entirely new approach for tumor-specific delivery of antineoplastic agents. Our experience with docetaxel containing fibrinogen-coated emulsions indicates that this approach leads to remarkable increase in anti-tumor efficacy of the drug in animal studies.{09}Further studies to better understand the mechanism of increased anti-tumor efficacy, to optimize this formulation and dosing regimen and to extend the application to other tumor types are warranted.