Development of Promitil®, a lipidic prodrug of mitomycin c in PEGylated liposomes: From bench to bedside.

Several liposome products have been approved for the treatment of cancer. In all of them, the active agents are encapsulated in the liposome water phase passively or by transmembrane ion gradients. An alternative approach in liposomal drug delivery consists of chemically modifying drugs to form lipophilic prodrugs with strong association to the liposomal bilayer.

Therapeutic efficacy of a lipid-based prodrug of mitomycin C in pegylated liposomes: studies with human gastro-entero-pancreatic ectopic tumor models.

Background: A mitomycin-C lipid-based prodrug (MLP) formulated in pegylated liposomes (PL-MLP) was previously reported to have significant antitumor activity and reduced toxicity in mouse tumor models (Clin Cancer Res 12:1913-20, 2006). MLP is activated by thiolysis releasing mitomycin-C (MMC) which rapidly dissociates from liposomes. The purpose of this study was to examine the plasma stability, pharmacokinetics, and antitumor activity of PL-MLP in mouse models of human gastroentero-pancreatic tumors.

Heterobifunctional PEGs: efficient synthetic strategies and useful conjugation methodologies.

The desire to develop nanoparticle and liposomal formulations as drug carriers capitalizing on active transport mechanisms requires constant development of novel heterobifunctional polyethyleneglycol (PEG) constructs. Such constructs should be capable of sequentially reacting with extracellular binding ligands and structural components of nanoparticles and/or liposomes. This paper describes two syntheses of heterobifunctional PEGs useful for tethering small molecule ligands to synthetic lysine-bearing polymers.

PEGylated iminodiacetic acid zinc complex stabilizes cationic RNA-bearing nanoparticles.

Self-assembling nanoparticles comprising cationic polymers are of interest for the delivery of oligonucleotide-based therapeutics. Unfortunately, exposure of the nanoparticle cationic surface to plasma and plasma proteins compromises particle stability and circulating half-life. Herein, we report that improved nanoparticle stability can be achieved through temporary grafting of PEG to the nanoparticle surface.

Improved therapeutic activity of folate-targeted liposomal doxorubicin in folate receptor-expressing tumor models.

Purpose: The folate receptor (FR) is overexpressed in a broad spectrum of malignant tumors and represents an attractive target for selective delivery of anti-cancer agents to FR-expressing tumors. Targeting liposomes to the FR has been proposed as a way to enhance the effects of liposome-based chemotherapy.

Methods: Folate-polyethylene glycol-distearoyl-phosphatidyl-ethanolamine conjugate was inserted into pegylated liposomal doxorubicin (PLD).

Thiolytically cleavable dithiobenzyl urethane-linked polymer-protein conjugates as macromolecular prodrugs: reversible PEGylation of proteins.

New thiolytically cleavable dithiobenzyl (DTB) urethane-linked conjugates of methoxypoly(ethylene glycol) (mPEG) and a model protein, lysozyme, were prepared and thoroughly characterized. In contrast to our earlier communication [Zalipsky, et al. (1999) Bioconjugate Chem.

Targeted binding of PLA microparticles with lipid-PEG-tethered ligands.

Solid core polymeric particles are an attractive delivery vehicle as they can efficiently encapsulate drugs of different physical and chemical characteristics. However, the effective targeting of such particles for therapeutic purposes has been somewhat elusive. Here, we report novel polymeric particles comprised of poly(lactic acid) (PLA) with incorporated poly(ethylene glycol)-lipids (PEG-lipids).

Antitumor activity of new liposomal prodrug of mitomycin C in multidrug resistant solid tumor: insights of the mechanism of action.

The antitumor activity of a novel thiolytically cleavable lipid-based prodrug of mitomycin C (MMC) delivered by STEALTH liposomes (SL) was studied in drug resistant human ovarian carcinoma A2780/AD model and compared with free MMC and both free and SL forms of an established anticancer drug--doxorubicin (DOX). It was found that SL-prodrug (SL-pMMC) possessed enhanced antitumor activity when compared with the parent MMC, free DOX, and SL-DOX. An observance of the high antitumor efficiency of SL-pMMC was a result of its preferential accumulation in the tumor by the enhanced permeability and retention (EPR) effect, suppression of multidrug resistance (MDR) associated with P-glycoprotein and MRP drug efflux pumps, activation of caspase-dependent apoptosis signaling pathways and suppression of antiapoptotic cellular defense by increasing the BAX/BCL2 ratio.

Pros and cons of the liposome platform in cancer drug targeting.

Coating of liposomes with polyethylene-glycol (PEG) by incorporation in the liposome bilayer of PEG-derivatized lipids results in inhibition of liposome uptake by the reticulo-endothelial system and significant prolongation of liposome residence time in the blood stream. Parallel developments in drug loading technology have improved the efficiency and stability of drug entrapment in liposomes, particularly with regard to cationic amphiphiles such as anthracyclines. An example of this new generation of liposomes is a formulation of pegylated liposomal doxorubicin known as Doxil or Caelyx, whose clinical pharmacokinetic profile is characterized by slow plasma clearance and small volume of distribution.

Reduced toxicity and superior therapeutic activity of a mitomycin C lipid-based prodrug incorporated in pegylated liposomes.

Purpose: A lipid-based prodrug of mitomycin C [MMC; 2,3-(distearoyloxy)propane-1-dithio-4'-benzyloxycarbonyl-MMC] was designed for liposome formulation. The purpose of this study was to examine the in vitro cytotoxicity, pharmacokinetics, in vivo toxicity, and in vivo antitumor activity of this new lipid-based prodrug formulated in polyethylene glycol-coated (pegylated) liposomes.

Experimental Design: MMC was released from the MMC lipid-based prodrug (MLP) by thiolytic-induced cleavage with a variety of thiol-containing reducing agents.

Electrostatics of PEGylated micelles and liposomes containing charged and neutral lipopolymers.

The electrostatics of large unilamellar vesicles (LUVs) of various lipid compositions were determined and correlated with steric stabilization. The compositional variables studied include (a) degree of saturation, comparing the unsaturated egg phosphatidylcholine (EPC) and the fully hydrogenated soy phosphatidylcholine (HSPC) as liposome-forming lipids; (b) the effect of 40 mol % cholesterol; (c) the effect of mole % of three methyl poly(ethylene glycol) (mPEG)-lipids (the negatively charged mPEG-distearoyl phosphoethanolamine (DSPE) and two uncharged lipopolymers, mPEG-distearoyl glycerol (DSG) and mPEG-oxycarbonyl-3-amino-1,2-propanediol distearoyl ester (DS)); and (d) the negatively charged phosphatidyl glycerol (PG). The lipid phases were as follows: liquid disordered (LD) for the EPC-containing LUV, solid ordered (SO) for the HSPC-containing LUV, and liquid ordered (LO) for either of those LUV with the addition of 40 mol % cholesterol.

Tumor cell targeting of liposome-entrapped drugs with phospholipid-anchored folic acid-PEG conjugates.

Targeting of liposomes with phospholipid-anchored folate conjugates is an attractive approach to deliver chemotherapeutic agents to folate receptor (FR) expressing tumors. The use of polyethylene glycol (PEG)-coated liposomes with folate attached to the outer end of a small fraction of phospholipid-anchored PEG molecules appears to be the most appropriate way to combine long-circulating properties critical for liposome deposition in tumors and binding of liposomes to FR on tumor cells. Although a number of important formulation parameters remain to be optimized, there are indications, at least in one ascitic tumor model, that folate targeting shifts intra-tumor distribution of liposomes to the cellular compartment.

In vivo fate of folate-targeted polyethylene-glycol liposomes in tumor-bearing mice.

Purpose: To compare the in vivo tissue distribution of folate-targeted liposomes (FTLs) injected i.v. in mice bearing folate receptor (FR)-overexpressing tumors (mouse M109 and human KB carcinomas, and mouse J6456 lymphoma) to that of nontargeted liposomes (NTLs) of similar composition.

Pharmaco attributes of dioleoylphosphatidylethanolamine/cholesterylhemisuccinate liposomes containing different types of cleavable lipopolymers.

Various amounts of one of three different types of cleavable methoxy polyethylene glycol (mPEG)-phospholipids or of a non-cleavable counterpart (mPEG-DSPE) were included into pH-sensitive liposome formulations containing dioleoylphosphatidylethanolamine (DOPE) and cholesterylhemisuccinate (CHEMS) at a 6:4 molar ratio, and the effect on plasma clearance and contents release rates was determined. The cleavable lipopolymers were all based on a distearoylphosphatidyl lipid anchor, which was linked to mPEG via dithiodipropionateaminoethanol (mPEG-DTP-DSPE), dithio-3-hexanol (mPEG-DTH-DSPA), or Gly-Phe-Leu-Gly-aminoethanol (mPEG-GFLG-DSPE) linkers. In contrast to the first-generation thiolytically cleavable lipopolymer, mPEG-DTP-DSPE, the second generation conjugates contained a hindered disulfide or enzymatically cleavable tetrapeptide, respectively, as the points of scission.

Interaction of differently designed immunoliposomes with colon cancer cells and Kupffer cells. An in vitro comparison.

Purpose: Evaluate the effectiveness of distal-end coupling of a tumor-specific antibody to liposomal polyethylene glycol (PEG) chains to improve target binding and reduce interference by macrophage uptake.

Methods: Monoclonal antibody CC52, specific for CC531 rat colon carcinoma, was coupled to the bilayer of PEG-liposomes (type I) or to the distal end of bilayer-anchored PEG-chains (type II). Uptake of both (radiolabeled)liposome types by CC531 cells and rat liver macrophages was determined.