Cellular transport and lipid interactions of miltefosine.

Miltefosine (hexadecylphosphocholine, HePC) is an alkyl phospholipid which was first developed as an anticancer agent for local treatment of skin metastases. It was later found to have remarkable activity against Leishmania parasites by the oral route and is marketed as Impavido(R) for this indication. The mechanism of action of HePC involves interaction with lipids and in particular membrane lipids - phospholipids and sterols. Studies of interactions between HePC and these lipids carried out in model systems suggest an affinity of HePC for cholesterol-rich lipid rafts. The uptake of HePC by cancer cells begins by insertion into the plasma membrane which may be followed by internalization. Within the plasma membrane, HePC interferes with the functioning of a number of enzymes involved in phospholipid metabolism, including protein kinase C and the phospholipases A(2), C and D, and can also induce apoptosis. Effects on lipid metabolism have also been observed in Leishmania parasites. In these organisms, a proposed mechanism of HePC uptake can be proposed: HePC inserts into the outer leaflet of the plasma membrane as monomers when its concentration is below the critical micellar concentration (CMC) and as both monomers and oligomers when it is above the CMC. Thereafter, a two-subunit aminophospholipid translocase, LdMT-LdRos3, internalizes the drug. Some evidence obtained in the Caco-2 intestinal cell model suggests that a similar process may occur during the oral absorption of HePC. Finally, the use of phospholipid vesicles (liposomes) as carrier systems for HePC, reducing its toxic side-effects, is reviewed.

Interaction of sitamaquine with membrane lipids of Leishmania donovani promastigotes.

Sitamaquine is an 8-aminoquinoline which is active by the oral route for the treatment of life-threatening visceral leishmaniasis caused by Leishmania donovani, with an IC50 of 29.2 microM against the promastigote form in vitro. At high concentration (100 microM), sitamaquine affected parasite motility, morphology and growth in a way that was only partially reversible. As a first approach to determine its mechanism of action, we describe the interaction of sitamaquine with parasite membrane components, representing the first barrier to be crossed by the drug. Analysis of the physicochemical interactions of sitamaquine with monolayers of phospholipids and sterols at the air-water interface showed that these interactions only occurred in the presence of anionic phospholipids. Thus, electrostatic interactions between positively charged sitamaquine and the negative polar headgroups are a pre-requisite for subsequent hydrophobic interactions between the sitamaquine aromatic ring and the alkyl chains of phospholipids leading to drug insertion into the monolayer.

Hexadecylphosphocholine interaction with lipid monolayers.

The phospholipid analogue miltefosine or hexadecylphosphocholine (HePC) is a drug of high interest in the treatment for fatal visceral leishmaniasis (VL) due to Leishmania donovani particularly because of its activity by oral route. In this study, the interaction of HePC with a monolayer of beta-palmitoyl-gamma-oleyl-phosphatidylcholine (POPC) as membrane model or sterol (ergosterol or cholesterol) was investigated. At a constant pressure of 25 mN/m, the adsorption kinetics of HePC into the monolayers showed that HePC molecules are inserted into the monolayer of lipids as monomers until the critical micellar concentration (CMC). At HePC concentrations superior to the CMC, the micelles of HePC are deployed at the interface as groups of monomers into the POPC or sterol monolayer. The study of mixture of HePC/(POPC or sterol), spread at the air-water interface, shows that a simple miscibility between HePC and POPC is observed, whereas a high condensation appears between HePC and sterols showing a high affinity between HePC and sterols. In addition, HePC does not act as detergent disturbing membrane integrity.

Competition of natural polyamines with dimethylsilyl analogues and monovalent cations in presence of a charged dipalmitoylphosphatidylglycerol monolayer.

The interaction at the air/water interface of dipalmitoylphosphatidylglycerol (DPPG) with natural and dimethylsilyl polyamines are investigated first in the presence of NaCl in the subphase. Next, experiments are performed to study the competition between natural polyamines and dimethylsilyl analogues. The results obtained by surface pressure and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) with NaCl, are compared with those obtained with distilled water. A decrease of the DPPG mean molecular area is observed due to the local diminution of the Na+ concentration close to the polar head group and the simultaneous onset of interactions between the amino group of natural polyamines and the polar head group of DPPG. The same effects occur with azhepsi, followed by an insertion of the hydrophobic dimethylsilyl group. Near the polar head groups DPPG, a substitution of the Na+ by the amino groups of polyamines occurs. For the competition experiments, whereas a partial substitution is possible after putrescine and spermine adsorption, it is almost complete after spermine adsorption. Since the number of amino groups of azhepsi and spermine are the same, hydrophobic interactions due to the presence of dimethylsilyl group occur between azhepsi and the alkyl chains of DPPG. This favoured insertion of azhepsi provides a basis for understanding of the action of dimethylsilyl derivatives in the case of an antitumour strategy.

Interaction of natural polyamines and dimethylsilyl analogues with a phospholipid monolayer: a study by Brewster angle microscopy and PM-IRRAS.

This work presents an analysis of the physicochemical interactions of natural and dimethylsilyl polyamines with an anionic deuterated phospholipid monolayer, d(62)DPPG (dipalmitoyl phosphatidyl glycerol), at the air-water interface. It was motivated by previous studies, which suggested an antitumour strategy based on the accumulation of derivatives such as bis(7-amino-4-azaheptyl) dimethylsilyl (azhepSi), in order to diminish the concentration of natural polyamines (spermine and putrescine) whose metabolism is strongly activated in tumour cells. Our results, obtained by the surface-pressure technique, Brewster angle microscopy (BAM) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), support the idea of an interaction between the polar head groups of d(62)DPPG and amino groups followed by an adsorption of polyamines up to the carbonyl group. Moreover, an insertion of the dimethylsilyl group up to the alkyl chains occurs with azhepSi, in agreement with the observation that the cohesion of the alkyl chain is lower in this case, as compared with the effect of natural polyamines.