Protein Corona Attenuates the Targeting of Antitumor Sialyl Lewis X-Decorated Liposomes to Vascular Endothelial Cells under Flow Conditions.

Previously, we showed in the human umbilical vein endothelial cells (HUVECs) model that a liposome formulation of melphalan lipophilic prodrug (MlphDG) decorated with selectin ligand tetrasaccharide Sialyl Lewis X (SiaLeX) undergoes specific uptake by activated cells and in an in vivo tumor model causes a severe antivascular effect. Here, we cultured HUVECs in a microfluidic chip and then applied the liposome formulations to study their interactions with the cells in situ under hydrodynamic conditions close to capillary blood flow using confocal fluorescent microscopy. The incorporation of 5 to 10% SiaLeX conjugate in the bilayer of MlphDG liposomes increased their consumption exclusively by activated endotheliocytes. The increase of serum concentration from 20 to 100% in the flow resulted in lower liposome uptake by the cells. To elucidate the possible roles of plasma proteins in the liposome-cell interactions, liposome protein coronas were isolated and analyzed by shotgun proteomics and immunoblotting of selected proteins. Proteomic analysis showed that a gradual increase in SiaLeX content correlated with the overall enrichment of the liposome-associated proteins with several apolipoproteins, including the most positively charged one, ApoC1, and serum amyloid A4, associated with inflammation, on the one hand, and a decrease in the content of bound immunoglobulins, on the other. The article discusses the potential interference of the proteins in the binding of liposomes to selectins of endothelial cells.

Liposomal Formulation of a PLA2-Sensitive Phospholipid-Allocolchicinoid Conjugate: Stability and Activity Studies In Vitro.

To assess the stability and efficiency of liposomes carrying a phospholipase A2-sensitive phospholipid-allocolchicinoid conjugate (aC-PC) in the bilayer, egg phosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylglycerol-based formulations were tested in plasma protein binding, tubulin polymerization inhibition, and cytotoxicity assays. Liposomes L-aC-PC10 containing 10 mol. % aC-PC in the bilayer bound less plasma proteins and were more stable in 50% plasma within 4 h incubation, according to calcein release and FRET-based assays. Liposomes with 25 mol. % of the prodrug (L-aC-PC25) were characterized by higher storage stability judged by their hydrodynamic radius evolution yet enhanced deposition of blood plasma opsonins on their surface according to SDS-PAGE and immunoblotting. Notably, inhibition of tubulin polymerization was found to require that the prodrug should be hydrolyzed to the parent allocolchicinoid. The L-aC-PC10 and L-aC-PC25 formulations demonstrated similar tubulin polymerization inhibition and cytotoxic activities. The L-aC-PC10 formulation should be beneficial for applications requiring liposome accumulation at tumor or inflammation sites.

Cyclopentane rings in hydrophobic chains of a phospholipid enhance the bilayer stability to electric breakdown.

Archaeal lipids ensure unprecedented stability of archaea membranes in extreme environments. Here, we incorporate a characteristic structural feature of an archaeal lipid, the cyclopentane ring, into hydrocarbon chains of a short-chain (C12) phosphatidylcholine to explore whether the insertion would allow such a lipid (1,2-di-(3-(3-hexylcyclopentyl)-propanoate)-sn-glycero-3-phosphatidylcholine, diC12cp-PC) to form stable bilayers at room temperature. According to fluorescence-based assays, in water diC12cp-PC formed liquid-crystalline bilayers at room temperature. Liposomes produced from diC12cp-PC retained calcein for over a week when stored at +4 °C. diC12cp-PC could also form model bilayer lipid membranes that were by an order of magnitude more stable to electrical breakdown than egg PC membranes. Molecular dynamics simulation showed that the cyclopentane fragment fixes five carbon atoms (or four C-C bonds), which is compensated by the higher mobility of the rest of the chain. This was found to be the reason for the remarkable stability of the diC12cp-PC bilayer: restricted conformational mobility of a chain segment increases the membrane bending modulus (compared to a normal hydrocarbon chain of the same length). Here, higher stiffness practically does not affect the line tension of a membrane pore edge. Rather it makes it more difficult for diC12cp-PC to rearrange in order to line the edge of a hydrophilic pore; therefore, fewer pores are formed.

Phospholipidic Colchicinoids as Promising Prodrugs Incorporated into Enzyme-Responsive Liposomes: Chemical, Biophysical, and Enzymological Aspects.

Enzyme-responsive liposomes release their cargo in response to pathologically increased levels of enzymes at the target site. We report herein an assembly of phospholipase A2-responsive liposomes based on colchicinoid lipid prodrugs incorporated into lipid bilayer of the nanosized vesicles. The liposomes were constructed to addresses two important issues: (i) the lipid prodrugs were designed to fit the structure of the enzyme binding site; and (ii) the concept of lateral pressure profile was used to design lipid prodrugs that introduce almost no distortions into the lipid bilayer packing, thus ensuring that corresponding liposomes are stable. The colchicinoid agents exhibit antiproliferative activity in subnanomolar range of concentrations.

Liposomal formulation of a methotrexate lipophilic prodrug: assessment in tumor cells and mouse T-cell leukemic lymphoma.

In a previous study, a formulation of methotrexate (MTX) incorporated in the lipid bilayer of 100-nm liposomes in the form of diglyceride ester (MTX-DG, lipophilic prodrug) was developed. In this study, first, the interactions of MTX-DG liposomes with various human and mouse tumor cell lines were studied using fluorescence techniques. The liposomes composed of egg phosphatidylcholine (PC)/yeast phosphatidylinositol/MTX-DG, 8:1:1 by mol, were labeled with fluorescent analogs of PC and MTX-DG. Carcinoma cells accumulated 5 times more MTX-DG liposomes than the empty liposomes. Studies on inhibitors of liposome uptake and processing by cells demonstrated that the formulation used multiple mechanisms to deliver the prodrug inside the cell. According to the data from the present study, undamaged liposomes fuse with the cell membrane only 1.5-2 hours after binding to the cell surface, and then, the components of liposomal bilayer enter the cell separately. The study on the time course of plasma concentration in mice showed that the area under the curve of MTX generated upon intravenous injection of MTX-DG liposomes exceeded that of intact MTX 2.5-fold. These data suggested the advantage of using liposomal formulation to treat systemic manifestation of hematological malignancies. Indeed, the administration of MTX-DG liposomes to recipient mice bearing T-cell leukemic lymphoma using a dose-sparing regimen resulted in lower toxicity and retarded lymphoma growth rate as compared with MTX.