The use of Tris-lipidation to modify drug cytotoxicity in multidrug resistant cells expressing P-glycoprotein or MRP1

The search for new amphiphiles: synthesis of a modular, high-throughput library

Amphiphilic compounds are used in a variety of applications due to their lyotropic liquid-crystalline phase formation, however only a limited number of compounds, in a potentially limitless field, are currently in use. A library of organic amphiphilic compounds was synthesised consisting of glucose, galactose, lactose, xylose and mannose head groups and double and triple-chain hydrophobic tails. A modular, high-throughput approach was developed, whereby head and tail components were conjugated using the copper-catalysed azide-alkyne cycloaddition (CuAAC) reaction. The tails were synthesised from two core alkyne-tethered intermediates, which were subsequently functionalised with hydrocarbon chains varying in length and degree of unsaturation and branching, while the five sugar head groups were selected with ranging substitution patterns and anomeric linkages. A library of 80 amphiphiles was subsequently produced, using a 24-vial array, with the majority formed in very good to excellent yields. A preliminary assessment of the liquid-crystalline phase behaviour is also presented.

Synthesis and Self-Assembly of a Peptide - Amphiphile as a Drug Delivery Vehicle

The formation of functional liposomes by the self assembly of a peptide–amphiphile that comprises the neuroprotective tripeptide motif glycyl-prolyl-glutamic acid linked to a hydrophobic moiety is reported. The self-assembled peptide–lipid conjugate displays long range order and can be dispersed as nanometre sized particles.

Crystallization and phase behavior of 1,3-propanediol esters

Polymorphic influences on the phase behavior of two types of binary mixtures of saturated monoacid 1,3-propanediol esters (PADEs), dipalmitate/distearate (PP/SS) and dimyristate/distearate (MM/SS) were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and by solid fat content (SFC), hardness and microscopy measurements. Three stacking modes have been found in the PP/SS binary system. Mixed SS-PP bilayers were detected in all mixtures, SS-SS bilayers in x(PP)=0.0-0.4 mixtures and PP-PP bilayers in x(PP)=0.6-0.1 mixtures. Two different but close beta polymorphs and one beta' polymorph were detected for this system. beta' was only detected in x(PP)=0.5-0.9 mixtures for the mixed bilayers. For the MM/SS binary system, only MM-MM and SS-SS bilayers were detected and both solid phases crystallized in two different beta forms. XRD data evidenced clearly that the MM and SS components were completely immiscible in the solid state. The phase diagrams constructed using DSC data, exhibited a typical eutectic-type phase boundary. The presence of eutectics, the shape of the solidus lines as well as the analysis of the individual enthalpies of melting indicated typical phase separation for both systems. A thermodynamic study based on the Hildebrand equation and using the Bragg-Williams approximation for non-ideality of mixing confirmed the phase separation in the solid phase and suggested that the PP and SS were miscible in the liquid phase and that SS formed an ideal mixing with MM. Avrami analysis of SFC vs. time curves indicated heterogeneous nucleation and spherulitic crystal development from sporadic nuclei, and suggested that the nucleation rate was higher for the mixture at the eutectic composition. The relative hardness was correlated with the enthalpies, the final SFC and the microscopy measurements.

Crystallization and phase behavior of fatty acid esters of 1,3-propanediol

Six pure fatty acid esters of 1,3-propanediol (PADE) molecules were investigated. A careful analysis of XRD, DSC as well as SFC results has allowed the determination of their structure and phase behavior. Two beta polymorphs were observed for C10-C18 and three beta polymorphs for C8. The same first polymorph (beta1) was observed for all the samples. The second polymorph (beta2) observed for C12-C18 was different from the second beta-form observed for C8 and C10. For all properties, the short chain length C8 and C10 samples were distinguished from the C12 to C18 samples and this explained much of the observed trends in behavior. Their lamellar packing was similar and has been explained by a simple addition of multiples of the length of a carbon bond to a primitive structure. The estimated long-range order highlighted a geometric effect that enabled the small chain molecules to better order than the longest molecules. The XRD results have been confirmed by DSC. The difference in property between the short and long chain molecules has also been clearly verified by the evolution of the energy of activation for nucleation as well as the enthalpy of melting and confirmed by microscopy measurements. For all the samples, the hardness which increased with increasing chain length is correlated with final %SFC. Avrami analysis of SFC versus time indicated heterogeneous nucleation and spherulitic crystal development from sporadic nuclei, and suggested that the rate of nucleation was higher for longer chain molecules.

Nitrogen monoxide (NO)-mediated iron release from cells is linked to NO-induced glutathione efflux via multidrug resistance-associated protein 1

Nitrogen monoxide (NO) plays a role in the cytotoxic mechanisms of activated macrophages against tumor cells by inducing iron (Fe) release. We have shown that NO-mediated Fe efflux from cells required glutathione (GSH), and we have hypothesized that a GS-Fe-NO complex was released. Hence, we studied the role of the GSH-conjugate transporter multidrug resistance-associated protein 1 (MRP1) in NO-mediated Fe efflux. MCF7-VP cells overexpressing MRP1 exhibited a 3- to 4-fold increase in NO-mediated 59Fe and GSH efflux compared with WT cells (MCF7-WT) over 4 h. Similar results were found for other MRP1-overexpressing cell types but not those expressing another drug efflux pump, P-glycoprotein. NO-mediated 59Fe and GSH efflux were temperature- and energy-dependent and were significantly decreased by the GSH-depleting agent and MRP1 transport inhibitor L-buthionine-[S,R]-sulfoximine. Other MRP1 inhibitors, MK571, probenecid, and difloxacin, significantly inhibited NO-mediated 59Fe release. EPR spectroscopy demonstrated the dinitrosyl-dithiol-Fe complex (DNIC) peak in NO-treated cells was increased by MRP1 inhibitors, indicating inhibited DNIC transport from cells. The extent of DNIC accumulation correlated with the ability of MRP1 inhibitors to prevent NO-mediated 59Fe efflux. MCF7-VP cells were more sensitive than MCF7-WT cells to growth inhibition by effects of NO, which was potentiated by L-buthionine-[S,R]-sulfoximine. These data indicate the importance of GSH in NO-mediated inhibition of proliferation. Collectively, NO stimulates Fe and GSH efflux from cells via MRP1. Active transport of NO by MRP1 overcomes diffusion that is inefficient and nontargeted, which has broad ramifications for understanding NO biology.

Hydrophobic Transmembrane-Peptide Lipid Conjugations Enhance Membrane Binding and Functional Activity in T-Cells

Application of different delivery methods for therapeutic peptides has gained much attention in recent years. In this paper we conjugated a transmembrane hydrophobic peptide (core peptide; CP) derived from the T-cell antigen receptor alpha-chain sequence with either one (LP1), two (LP2), or three (LP3) palmitic acids through a Tris linkage. The effect of these lipopeptides (LPs) were compared to CP's activity both in vitro and in model membrane binding experiments using surface plasmon resonance. The influence of charged amino acids, arginine and lysine, within the CP sequence was examined by synthesizing analogues where arginine and lysine were replaced by the neutral amino acid alanine and these analogues were subsequently Tris-lipid conjugated with either one (XP1), two (XP2), or three (XP3) palmitic acids through a Tris linkage. The results indicated that the amount of irreversible binding for LPs were all greater than that of the underivatized CP in model membranes. None of the LPs could be dissociated from the liposome membranes, even after prolonged washing. Binding results for the neutral conjugates showed that only the XP1 bound to model membranes. This binding was 20% as efficient compared to LP1. In biological assays it was found that LP1 and XP1 were toxic to cells. LP3 inhibited IL-2 production more effectively than CP. Control lipopeptides (XP2, XP3) did not inhibit IL-2 production. These results demonstrate that the number of lipids conjugated to peptide, and the charged amino acids of CP, are both essential factors for peptide function and activity that can be enhanced by lipidation.