Encapsulation, controlled release, and antitumor efficacy of cisplatin delivered in liposomes composed of sterol-modified phospholipids.

We employed a recently introduced class of sterol-modified lipids (SML) to produce m-PEG-DSPE containing liposome compositions with a range of cis-platinum content release rates. SML have a cholesterol succinate attached to the phosphatidylglycerol head group and a fatty acid at the 2 position. These compositions were compared to the well-studied liposome phospholipid compositions: mPEG-DSPE/Hydrogenated Soy PC/cholesterol or mPEG-DSPE/POPC/cholesterol to determine the effect of the cis-platinum release extent on C26 tumor proliferation in the BALB/c colon carcinoma mouse model. The release rates of cis-platinum from liposomes composed of SML are a function of the acyl chain length. SML-liposomes with shorter acyl chain lengths C-8 provided more rapid cisplatin release, lower in vitro IC50, and were easier to formulate compared to liposomes using traditional phospholipid compositions. Similar to other liposome cis-platinum formulations, the half-life of m-PEG-DSPE SML liposome cisplatin is substantially longer than the free drug. This resulted in a higher tumor cisplatin concentration at 48h post-dosing compared to the free drug and higher Pt-DNA adducts in the tumor. Moreover, the maximum tolerated dose of the liposome formulations where up to four fold greater than the free drug. Using X-ray fluorescence spectroscopy on tumor sections, we compared the location of platinum, to the location of a fluorescence lipid incorporated in the liposomes. The liposome platinum co-localized with the fluorescent lipid and both were non-uniformly distributed in the tumor. Non-encapsulated Cis-platinum, albeit at a low concentration, was more uniformly distributed thorough the tumor. Three liposome formulations, including the well-studied hydrogenated HSPC composition, had better antitumor activity in the murine colon 26 carcinoma model as compared to the free drug at the same dose but the SML liposome platinum formulations did not perform better than the HSPC formulation.

A robust and quantitative method for tracking liposome contents after intravenous administration.

We introduce a method for tracking the rate and extent of delivery of liposome contents in vivo based on encapsulation of 4-methylumbelliferyl phosphate (MU-P), a profluorophore of 4-methylumbelliferone (MU). MU-P is rapidly dephosphorylated by endogenous phosphatases in vivo to form MU after leakage from the liposome. The change in fluorescence spectra when MU-P is converted to MU allows for quantification of entrapped (MU-P) and released (MU) liposome contents by fluorescence or by a sensitive high performance liquid chromatography assay. We define the "cellular availability" of an agent encapsulated in a liposome as the ratio of the amount of released agent in the tissue to the total amount of agent in the tissue; this parameter quantifies the fraction of drug available for therapy. The advantage of this method over existing technologies is the ability to decouple the signals of entrapped and released liposome contents. We validate this method by tracking the circulation and tissue distribution of MU-P loaded liposomes after intravenous administration. We use this assay to compare the cellular availability of liposomes composed of engineered phosphocholine lipids with covalently attached cholesterol, sterol-modified lipids (SML), to liposomes composed of conventional phospholipids and cholesterol. The SML liposomes have similar pharmacokinetic and biodistribution patterns as conventional phospholipid-cholesterol liposomes but a slower rate of contents delivery into the tissue. Thus, MU-P enables the tracking of the rate and extent of liposome contents release in tissues and should facilitate a better understanding of the pharmacodynamics of liposome-encapsulated drugs in animals.

Clinical developments of chemotherapeutic nanomedicines: polymers and liposomes for delivery of camptothecins and platinum (II) drugs.

For the past 40 years, liposomal and polymeric delivery vehicles have been studied as systems capable of modulating the cytotoxicity of small molecule chemotherapeutics, increasing tumor bearing animal survival times, and improving drug targeting. Although a number of macromolecular-drug conjugates have progressed to clinical trials, tuning drug release to maintain efficacy in conjunction with controlling drug toxicity has prevented the clinical adoption of many vehicles. In this article, we review the motivations for and approaches to polymer and liposomal delivery with regard to camptothecin and cisplatin delivery.

Resolution of enantiomers of a series of chiral alkoxy-modified phthalocyaninato nickel(II) complexes by enantioselective HPLC.

We have resolved the enantiomers of a series of chiral modified metallophthalocyaninato complexes of nickel bearing alkoxy groups at the 14 and 28 positions on what would otherwise be a normal phthalocyaninato ligand and conforming to the general formula [14,28-(RO)(2)Pc]Ni(ii), where R = Me, Et, or n-Pr. The complex for which R = n-Pr is reported here for the first time. Resolution of the enantiomers of these complexes was accomplished via HPLC utilizing an immobilized carbohydrate-based stationary phase, resulting in baseline resolution of peaks corresponding to enantiomers of the complexes, with R(s) values in excess of five. Isolation of milligram quantities of the complexes bearing methoxy and n-propoxy groups in high enantiomeric excess has been achieved via semi-preparative-scale HPLC on the same stationary phase. Resolved samples of these compounds do not appear to racemize at an appreciable rate, nor do they readily exchange alkoxy groups with alcohols while stirring in alcoholic solution. The spectroscopic details and the crystallographically-determined solid-state structure for the complex where R = n-Pr are reported, and are highly similar to those that have been observed for the previously reported analogues. It has been shown by NMR that the chirality and C(2) molecular symmetry of the complex bearing n-propoxy groups is maintained in solution.

Anti-tumor activity of liposome encapsulated fluoroorotic acid as a single agent and in combination with liposome irinotecan.

To test the hypothesis that co-delivery of synergistic drug combinations in the same liposome provides a better anti-tumor effect than the drugs administered in separate liposomes, fluoroorotic acid (FOA) alone and in combination with irinotecan (IRN) were encapsulated in liposomes and evaluated for their anti-tumor activity in the C26 colon carcinoma mouse model. A new chaotropic loading strategy was devised wherein FOA was dissolved in 7 M urea to increase its solubility. This enabled the passive loading of FOA into liposomes at a high concentration. IRN was remote loaded into liposomes that contained the ammonium salt of the multi-valent 1,2,3,4-butanetetracarboxylic acid with a greater than 90% efficiency and at a drug to lipid ratio of 0.2:1. When the two molecules were loaded into the same liposome, FOA was used to remote load IRN. Modulation of the drug/lipid ratio, temperature, and loading time allowed for consistent co-encapsulation of FOA+IRN at various molar ratios. The anti-tumor activity of L-FOA, L-IRN, L-FOA-IRN (5:1), and the L-FOA+L-IRN mixture (5:1) were examined in the C26 mouse model. The maximum tolerated dose of L-FOA was 10 mg/kg given weekly as compared to 100 mg/kg of the non-encapsulated FOA. Delivering two drugs in the same liposome provided a statistically better anti-tumor effect than delivering the drugs in separate liposomes at the same drug ratio. However, the synergistic activity of the 5:1 ratio of free drugs measured on C26 cells in vitro was not observed in the C26 tumor mouse model. These findings point out the challenges to the design of synergistic treatment protocols based upon results from in vitro cytotoxicity studies. L-FOA at 10 mg/kg as a single agent provided the best anti-tumor efficacy which supports previous suggestions that L-FOA has useful properties as a liposome dependent drug.

Design, synthesis, and biological evaluation of a robust, biodegradable dendrimer.

PEGylated dendrimers are attractive for biological applications due to their tunable pharmacokinetics and ability to carry multiple copies of bioactive molecules. The rapid and efficient synthesis of a robust and biodegradable PEGylated dendrimer based on a polyester-polyamide hybrid core is described. The architecture is designed to avoid destructive side reactions during dendrimer preparation while maintaining biodegradability. Therefore, a dendrimer functionalized with doxorubicin (Dox) was prepared from commercial starting materials in nine, high-yielding linear steps. Both the dendrimer and Doxil were evaluated in parallel using equimolar dosage in the treatment of C26 murine colon carcinoma, leading to statistically equivalent results with most mice tumor-free at the end of the 60 day experiment. The attractive features of this dendritic drug carrier are its simple synthesis, biodegradability, and versatility for application to a variety of drug payloads with high drug loadings.