Interactions of Alkylphosphocholines with Model Membranes—The Langmuir Monolayer Study

Anita Wnętrzak,Kazimierz Łątka,Patrycja Dynarowicz-Łątka

doi:10.1007/s00232-013-9557-4

Anita Wnętrzak, Kazimierz Łątka + Show 1 more

Open Access

https://doi.org/10.1007/s00232-013-9557-4

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Abstract

Alkylphosphocholines (APCs) belong to a class of synthetic antitumor lipids, which are new-generation anticancer agents. In contrast to traditional antitumor drugs, they do not attack the cell nucleus but, rather, the cellular membrane; however, their mechanism of action is not fully understood. This work compared the interactions of selected APCs [namely, hexadecylphosphocholine (miltefosine), octadecylphosphocholine and erucylphosphocholine] with the most important membrane lipids [cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)] and examined their influence on a model membrane of tumor and normal cells. As a simple model of membranes, Langmuir monolayers prepared by mixing cholesterol either with a saturated phosphatidylcholine (DPPC), for a normal cell membrane, or with an unsaturated one (POPC), for a tumor cell membrane, have been applied. The APC–lipid interactions, based on experimental surface pressure (π) versus mean molecular area (A) isotherms, were analyzed qualitatively (with mean molecular area values) as well as quantitatively (with the ΔG exc function). Strong attractive interactions were observed for mixtures of APCs with cholesterol, contrary to the investigated phosphatidylcholines, for which the interactions were found to be weak with a tendency to separation of film components. In ternary monolayers it has been found that the investigated model systems (cholesterol/DPPC/APC vs cholesterol/POPC/APC) differ significantly as regards the interactions between film-forming molecules. The results demonstrate stronger interactions between the components of cholesterol/POPC/APC monolayers compared to cholesterol/POPC film, mimicking tumor cell membranes. In contrast, the interactions in cholesterol/DPPC/APC films were found to be weaker than those in the cholesterol/DPPC system, serving as a model of healthy cell membranes, thus proving that the incorporation of APCs is, from a thermodynamic point of view, unfavorable for binary cholesterol/DPPC monolayers. It can be concluded that the composition of healthy cell membranes is a natural barrier preventing the incorporation of APCs into normal cells.

Highlights

To gain insight into the mechanism of physiological activity of biomolecules acting at the cellular membrane level, different methods can be applied, which are usually based on examining the interactions between a bioactive molecule and cellular membrane components
The results demonstrate stronger interactions between the components of cholesterol/POPC/APC monolayers compared to cholesterol/ POPC film, mimicking tumor cell membranes
Regarding the isotherms for pure membrane lipids, their characteristics are very well known and our results are in a good agreement with the data already published

Summary

Introduction

To gain insight into the mechanism of physiological activity (mode of action, selectivity, toxicity) of biomolecules acting at the cellular membrane level, different methods can be applied, which are usually based on examining the interactions between a bioactive molecule and cellular membrane components. Most popular are Langmuir monolayers (Peetla et al 2009), liposomes or vesicles (Kell 1981), black lipid membranes (Ottova and Tien 1997) and surfaceconfined membrane systems (Richter et al 2006) None of these models is perfect and fully universal (advantages and disadvantages of using the above-mentioned membrane models are discussed in Hac-Wydro and Dynarowicz-Łatka 2008), the Langmuir monolayer technique, the principles of which can be found elsewhere (Gaines 1966), is a potent and frequently applied method for mimicking cellular membranes (Maget-Dana 1999; Hac-Wydro and Dynarowicz-Łatka 2008; Brockman 1999) and very useful to study biomolecule–membrane interactions. These interactions can be considered crucial for understanding the mode of action of drugs acting on the membrane level (MagetDana 1999; Hac-Wydro and Dynarowicz-Łatka 2008)

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