Pharmaceutical NanotechnologyVascular targeting of doxorubicin using cationic liposomes
Introduction
Physiological barriers have been shown to hinder effective delivery of drugs to tumors (Jain, 1998, Pluen et al., 2001). In order to reach cancer cells, a therapeutic agent must first cross the vasculature and then travel through the interstitium. Vascular targeting avoids these barriers by attacking the blood supply instead of cancer cells, either suppressing vessel formation (antiangiogenic therapy) or abolishing established vascular networks (antivascular therapy) (Denekamp, 1982, Thurston et al., 1998). Subsequently, tumor cells undergo apoptosis as a consequence of impaired nutrient and oxygen supply. Due to their high rate of proliferation, tumor endothelial cells have increased susceptibility to cytotoxic drugs (Denekamp, 1999). Furthermore, these cells are more genetically stable and are thus less prone to drug resistance compared to tumor cells. Selective delivery of cytotoxic drugs to tumor endothelium is, therefore, a promising therapeutic strategy.
Liposomes have been evaluated as a carrier of anticancer chemotherapeutic agents, such as doxorubicin (Mayer et al., 1989). Neutral liposomes exhibit preferential localization in solid tumors based on enhance permeation and retention (EPR) effect (Papahadjopoulos et al., 1991, Huang et al., 1992, Yuan et al., 1994), which relies on gradual passive accumulation of liposomes in the tumor (Huang et al., 1992, Yuan et al., 1994, Wu et al., 1993). In contrast, cationic liposomes are rapidly cleared from circulation by liver, spleen, and lung, and primarily have been used in gene delivery (McLean et al., 1997, Mahato et al., 1995, Litzinger et al., 1996). The unique properties of cationic liposomes for targeting tumor endothelium suggest that they may have utility as drug carriers. Strieth et al. (2004) and Schmitt-Sody et al. (2003) reported that paclitaxel encapsulated in cationic liposomes exhibited improved antitumor efficacy of, which was associated with impaired function of tumor microvasculature. The study of Thurston et al. (1998) showed that uptake of cationic liposomes by endothelial cells in angiogenic blood vessels was considerably greater than that of extravasation from these vessels. Furthermore, this uptake was selective to cationic liposomes and that anionic, neutral, or sterically stabilized neutral liposomes were not taken up by these cells.
The aim of our study was to evaluate in vitro cytotoxicity, in vivo biodistribution, pharmacokinetics and efficacy of doxorubicin delivered in cationic liposomes.
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Materials
Egg phosphatidylcholine (EPC), cholesterol (CHOL), and methoxy-polyethylene glycol (M.W. 2000) distearoyl phosphatidylethanolamine (mPEG-DSPE) were purchased from Avanti Polar Lipids, Inc. (Alabaster, AL, USA). 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT), doxorubicin (DOX), and dimethyl dioctadecyl ammonium bromide (DDAB) were purchased from Sigma Chemical Co. (St. Louis, MO, USA). All other chemicals were analytical or HPLC grade.
Cell culture
KB, a human oral carcinoma cell line,
Properties of cationic L-DOX
Cationic liposomes containing 20% DDAB and control liposomes were prepared by repeated extrusion through polycarbonate membranes with a pore size of 100 nm and DOX were incorporated by remote loading. Properties of the liposomes are summarized in Table 1, including particle size, DOX loading efficiency and zeta potential.
We found that increasing the mol% of cationic lipid resulted in increased accumulation in the lung and reduced plasma half-life of the liposomal formulation. Percentage (20%) of
Discussion
The vascular network is a highly accessible target for tumor therapy. Cationic liposomes have been shown to accumulate selectively in angiogenic tumor endothelial cells. Therefore, they are promising as a drug carrier for delivery to the tumor endothelium.
This study reports the characterization of cationic liposomal formulations of DOX. Enhancement in both cellular uptake and in vitro cytotoxicity was demonstrated. This might be due to the ability of cationic liposomes to interact with cells
Conclusion
A cationic liposomal DOX formulation was synthesized and evaluated. The formulation was efficiently taken up by and showed enhanced cytotoxicity in KB and L1210 cells. Pharmacokinetic and biodistribution studies indicated that cationic L-DOX showed rapid clearance from the blood, rapid accumulation in the tumor, and increased therapeutic efficacy. Further studies will focus on understanding of mechanisms of the observed antitumor activity by drugs delivered via cationic liposomes.
Acknowledgement
This work was supported in part by NSF grant EEC-0425626.
References (22)
- et al.
Transmembrane ammonium sulfate gradients in liposomes produce efficient and stable entrapment of amphipathic weak bases
Biochim. Biophys. Acta
(1993) - et al.
Folate-mediated tumor cell targeting of liposome-entrapped doxorubincin in vitro
Biochim. Biophys. Acta
(1995) - et al.
Fate of cationic liposomes and their complex with oligonucleotide in vivo
Biochim. Biophys. Acta
(1996) - et al.
Physicochemical and pharmacokinetic characteristics of plasmid DNA/cationic liposome complexes
J. Pharm. Sci.
(1995) - et al.
Strategy for the treatment of acute myelogenous leukemia based on folate receptor β-targeted liposomal doxorubicin combined with receptor induction using all-trans retinoic acid
Blood
(2002) - et al.
Cationic charge determines the distribution of liposomes between the vascular and extravascular compartments of tumors
Cancer Res.
(2002) Endothelial cell proliferation as a novel approach to targeting tumor therapy
Br. J. Cancer
(1982)The tumor microcirculation as a target in cancer therapy: a clearer perspective
Eur. J. Clin. Invest.
(1999)- et al.
Pharmacokinetics and therapeutics of sterically stabilized liposomes in mice bearing C-26 colon carcinoma
Cancer Res.
(1992) The next frontier of molecular medicine: delivery of therapeutics
Nat. Med.
(1998)