[Characterization and cytotoxicity of mixed PEG-DSG modified liposomes]

Influence of PEG coating on the biodistribution and tumor accumulation of pH-sensitive liposomes

Liposomes are lipid vesicles widely used as nanocarriers in targeted drug delivery systems for therapeutic and/or diagnostic purposes. A strategy to prolong the blood circulation time of the liposomes includes the addition of a hydrophilic polymer polyethylene glycol (PEG) moiety onto the surface of the vesicle. Several studies claim that liposome PEGylation by a single chain length or a combination of PEG with different chain lengths may alter the liposomes' pharmacokinetic properties. Therefore, the purpose of this study was to evaluate the influence of PEG on the biodistribution of pH-sensitive liposomes in a tumor-bearing animal model. Three liposomal formulations (PEGylated or not) were prepared and validated to have a similar mean diameter, monodisperse distribution, and neutral zeta potential. The pharmacokinetic properties of each liposome were evaluated in healthy animals, while the biodistribution and scintigraphic images were evaluated in tumor-bearing mice. High tumor-to-muscle ratios were not statistically different between the PEGylated and non-PEGylated liposomes. While PEGylation is a well-established strategy for increasing the blood circulation of nanostructures, in our study, the use of polymer coating did not result in a better in vivo profile. Further studies must be carried out to confirm the feasibility of the non-PEGylated pH-sensitive liposomes for tumor treatment.

Pathogenesis of Hand-Foot Syndrome induced by PEG-modified liposomal Doxorubicin

PEGL-DOX is an excellent treatment for recurrent ovarian cancer that rarely causes side-effects like cardiotoxicity or hair loss, but frequently results in Hand-Foot Syndrome (HFS). In severe cases, it can become necessary to reduce the PEGL-DOX concentration or the duration of the drug therapy, sometimes making it difficult to continue treatment. In this study, we prepared an animal model to compare the effects of DOX versus PEGL-DOX, and we noticed that only treatment with PEGL-DOX resulted in HFS, which led us to conclude that extravasation due to long-term circulation was one of the causes of HFS. In addition, we were able to show that the primary factor leading to the skin-specific outbreaks in the extremities was the appearance of reactive oxygen species (ROS) due to interactions between DOX and the metallic Cu(II) ions abundant in skin tissue. ROS directly disturb the surrounding tissue and simultaneously induce keratinocyte-specific apoptosis. Keratinocytes express the thermoreceptor TRPM2, which is thought to be able to detect ROS and stimulate the release of chemokines (IL-8, GRO, Fractalkine), which induce directed chemotaxis in neutrophils and other blood cells. Those cells and the keratinocytes then undergo apoptosis and simultaneously release IL-1β, IL-1α, and IL-6, which brings about an inflammatory state. In the future, we plan to develop preventative as well as therapeutic treatments by trapping the ROS.

Characterization of Novel Mixed Polyethyleneglycol Modified Liposomes

In our previous paper, mixed polyetheleneglycol (PEG) modification of liposomes by a mixture of 1-monomethoxypolyethyleneglycol-2,3-distearoylglycerol (PEG-DSG) with short polyoxyethylene chain and PEG-DSG with long one was shown to increase fixed aqueous layer thickness (FALT) around the liposomal membrane, and this was useful in vivo. In this study, we investigated the characterization of mixed PEG modification of liposomes with different anchors (PEG2000-DSG and PEG2000-cholesterol (CHO)). When the liposomes was modified by a mixture of PEG2000-DSG and PEG2000-CHO, FALT was increased compared to that of each single PEG-lipids modification and the most suitable mix modification (PEG2000-DSG:PEG2000-CHO = 3:1) showed a maximum FALT. This phenomenon was speculated to be based on the difference in the insertion state of the PEG anchor unit in the liposomal membrane. PEG-CHO-modified liposomes (single or mixed PEG-modified liposomes) were easily incorporated into the liposomal membranes compared with that of single PEG-DSG-modified liposomes. Namely, it was considered that the cholesterol anchor as a single chain was able to be easily introduced, compared with the DSG anchor as two chains, and induced some interaction with both PEG modification. In conclusion, it is expected that novel PEG-modified liposomes with PEG2000-DSG and PEG2000-CHO (3:1) had superior physicochemical properties.

Characterization and cytotoxicity of mixed polyethyleneglycol modified liposomes containing doxorubicin

Liposomes are recognized as one of the useful drug carriers, but have many problems to overcome before their clinical application. Liposomes, bonding peculiarly with serum protein (opsonization), are taken up by reticuloendothelial system (RES) cells in the liver and spleen. It is known that polyethyleneglycol (PEG) modification of the liposome surface induces the formation of a fixed aqueous layer around the liposomes due to the interaction between the PEG-polymer and water molecule, and thus prevents the attraction of opsonins. Namely, PEG-modified liposomes are able to escape trapping by the RES cells, and have a prolonged circulation time. In this study, the effects of different anchors with the same PEG molecular weight on the cell uptake and cytotoxicity of mixed PEG-modified liposomal doxorubicin (DOX) were examined. The fixed aqueous layer thickness (FALT) of liposomes covered with mixtures of PEG-molecules which differ in their chain length were increased, compared to that of the single PEG2000-modified liposome. Mixed PEG-modification of liposomes with different anchors (PEG2000-(1-monomethoxypolyethyleneglycol-2,3-distearoylglycerol (DSG): cholesterol (CHO)=1:1)-modified liposome) led to an increase in the FALT, compared to that of each single PEG-modification. The uptake of DOX into Ehrlich ascites carcinoma cells by the liposomes covered with PEG-CHO was higher than the other liposomes. Thus, liposomes covered with PEG-DSG and PEG-CHO have an enhanced cytotoxicity. In conclusion, it was confirmed that mix-modified liposomes using PEG-lipid with different anchors were superior.