Enhanced Delivery and Antitumor Effect of Doxorubicin Encapsulated in Long-Circulating Liposomes

Clinical developments in nanotechnology for cancer therapy

Nanoparticle approaches to drug delivery for cancer offer exciting and potentially "game-changing" ways to improve patient care and quality of life in numerous ways, such as reducing off-target toxicities by more selectively directing drug molecules to intracellular targets of cancer cells. Here, we focus on technologies being investigated clinically and discuss numerous types of therapeutic molecules that have been incorporated within nanostructured entities such as nanoparticles. The impacts of nanostructured therapeutics on efficacy and safety, including parameters like pharmacokinetics and biodistribution, are described for several drug molecules. Additionally, we discuss recent advances in the understanding of ligand-based targeting of nanoparticles, such as on receptor avidity and selectivity.

Pharmacokinetics, safety, and efficacy of a liposome encapsulated thymidylate synthase inhibitor, OSI-7904L [(S)-2-[5-[(1,2-dihydro-3-methyl-1-oxobenzo[f]quinazolin-9-yl)methyl]amino-1-oxo-2-isoindolynl]-glutaric acid] in mice

OSI-7904L [(S)-2-[5-[(1,2-dihydro-3-methyl-1-oxobenzo[f]quinazolin-9-yl)methyl]amino-1-oxo-2-isoindolynl]-glutaric acid] is a liposomal formulation of the highly specific, noncompetitive, thymidylate synthase inhibitor OSI-7904 (also known as GW1843, 1843U89, and GS7904). The liposome formulation was developed to enhance the therapeutic index and dose schedule convenience of this potent antifolate compound. The studies presented here were conducted to determine the antitumor efficacy, distribution, pharmacokinetics, and safety of OSI-7904L in mice. In a human colon adenocarcinoma xenograft model in mice, OSI-7904L demonstrated superior antitumor efficacy compared with OSI-7904 or 5-fluorouracil. Furthermore, OSI-7904L could be administered less frequently than OSI-7904 although still generating greater tumor growth inhibition. Distribution studies confirmed that OSI-7904L-treated animals had much greater plasma, tissue, and tumor exposure than did OSI-7904-treated animals. Tumor exposures, based on area under the curve, in OSI-7904L-treated mice were increased over 100-fold compared with tumor exposures in OSI-7904-treated mice. Plasma exposures following OSI-7904L administration were greater than dose proportional consistent with saturation of plasma clearance mechanisms. OSI-7904L was much more toxic than OSI-7904 in the mouse with primary toxicities to the intestines, bone marrow, and thymus. Minimal toxicity to the lungs and liver was noted. These data clearly demonstrated that in mice, OSI-7904L has an increased plasma residence time as well as increased tissue and tumor exposure compared with OSI-7904, thus resulting in increased potency and toxicity. Potential benefits of OSI-7904L include improved efficacy and a more convenient schedule of administration.

Optimization study of doxorubicin liposomal preparations coated with laminin fragments

Immunoliposomes, coated with two peptide sequences and loaded with doxorubicin, were prepared. The influence of different parameters in the sequential steps of liposomal preparations was studied as, for instance, lipid composition, size reduction methods, elimination of non-entrapped drug, and peptide coating sequence. Results were evaluated, such as entrapment efficiency, phospholipid/drug and phospholipid/peptide relationship, and size of final preparations. Effective size reduction was only achieved through probe sonication and the presence of peptides on the surface of liposomes, which does not modify, significantly, the final phospholipid/drug relationship, related to the initial values; however, they promoted a slight increase in the size of final preparations. Dialysis was the most suitable method to wash liposomes from reactants, drug and peptides, as well as being the cleanest process to avoid microbial contamination without significant dilution. Peptide coating yields were similar for liposomal compositions presenting free carboxyl groups on the surface. As determined by other authors, the presence of polyethylene glycol monomethoxy chains on the surface reduces the reactivity of NPGE carboxylic groups.

Biodistribution of NX211, liposomal lurtotecan, in tumor-bearing mice

Prolonging tumor exposure to topoisomerase I inhibitors has been correlated to enhance the efficacy of those agents. Lurtotecan, a water-soluble camptothecin analog, was formulated as a liposomal drug, NX211, to enhance the delivery of drug to tumors. Tumor-bearing mice were treated with either [14C]NX211 containing [14C]lurtotecan, [3H]NX211 containing [3H]phosphatidylcholine or [14C]lurtotecan, euthanized at selected times post-injection, and tissues, plasma, urine and feces were collected. These studies demonstrated that KB tumors of [14C]NX211-treated mice had approximately 70-fold greater concentrations of [14C]lurtotecan at 24 h, respectively, compared to concentrations of [14C]lurtotecan of the KB tumors of [14C]lurtotecan-treated mice. The area under curve (AUC) from 0 to 48 h of [14C]lurtotecan for the KB tumors of [14C]NX211-treated animals was over 17-fold greater than the AUC of [14C]lurtotecan for the tumors of [14C]lurtotecan-treated animals. Treatment with [3H]NX211 demonstrated that the lipid component continually accumulated over 24 h in the tissues. HPLC analysis of extracted material from tumors of [14C]NX211-treated mice showed that more than 95% of the radioactive material was intact [14C]lurtotecan. These findings are one of the keys justifying the development of a liposomal formulation of lurtotecan, which has the intent to increase tumor exposure and increase antitumor efficacy.

In vitro cytotoxic effect of N-(phosphonacetyl)-L-aspartic acid in liposome against C-26 murine colon carcinoma

We have investigated the in vitro cytotoxic effect of liposome-encapsulated N-(phosphonacetyl)-L-aspartic acid (PALA) against C-26 murine colon cancer cells, and have compared it in this regard to free PALA. Three different PALA-containing liposomal formulations using distearoylphosphatidylcholine (DSPC), distearoylphosphatidylglycerol (DSPG), and polyethyleneglycol-derivatized distearoylphosphatidylethanolamine (PEG-DSPE) were made and their cytotoxicity was measured. In 72 hr continuous exposure experiment with C-26 cells, the 50% growth inhibitory concentration (IC50) of DSPG-PALA liposome formulation was 0.09 microM, which showed about 65-fold more potent than unencapsulated free PALA (5.1 microM). Similar degree of increase in cytotoxicity was also observed in 1 hr exposure experiment. However, the IC50 of PEG-DSPE-PALA liposome and DSPC-PALA liposome were 10.7 microM and 11.8 microM, respectively, which showed slightly less potent than unencapsulated free PALA. Physical characteristics of PALA-liposomes, such as the size and drug:lipid ratio were also determined. In conclusion, negatively-charged DSPG-PALA liposome showed the highest cytotoxic effect among tested on the C-26 cells in vitro.