**1. Introduction**

358 Breast Cancer – Focusing Tumor Microenvironment, Stem Cells and Metastasis

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Alkylphospholipids have shown promising results in several clinical studies (Mollinedo 2007) and among them Perifosine (octadecyl(1,1-di-methyl-4-piperidinium-4-yl)phosphate, OPP), and miltefosine (hexadecylphosphatidylcholine (HPC)) seems to be most promising for breast cancer therapy (Fichtner, Zeisig et al. 1994). For this type of tumor, an antitumor effect was found only for hormone receptor negative tumors *in vivo*, while no effect was found for receptor positive tumors. The reason for this difference is not yet understood and requires further studies. The exact mechanism of action of alkylphospholipids on the molecular level is still not well known in detail. It is clear that they do not target DNA, but they insert into the plasma membrane and subsequently induce a broad range of biological effects, ultimately leading to cell death.

Unfortunately, administration of free (micellar) alkylphospholipids results in unwanted side effects, reflected in gastrointestinal toxicity and hemolytic activity, which limits the application of higher doses of alkylphospholipids. To achieve better therapeutic effects of alkylphospholipids *in vivo* with less side effects, different liposomal formulations of alkylphospholipids have been tested and showed diminished hemolytic activity. On the other hand, in most cases, cytotoxic activity of liposomes was also lower as compared to free alkylphospholipids (Zeisig et al., 1998).

For efficient application of liposomes as nanocarriers in breast cancer therapy it is not only necessary to investigate the properties of the nanocarrier, which has to transport the drug to the (target) cell, but also the properties of the target cell. The main difference between Perifosine (OPP) resistent MCF7 cells and OPP sensitive MT-3 cells is in the uptake of OPP liposomes by cells and the transport of OPP across plasma membrane. At physiological temperatures the rate of transfer of OPP across plasma membrane increases to greater extent in OPP resistant MCF7 cells, while the uptake of liposomal OPP formulations is lower for

Interaction of Alkylphospholipid Formulations with Breast Cancer

Fig. 1. Structural formula of pharmaceutically tested alkylphospholipids.

Hexadecyl-2-

phosphate

(2-methoxy-3-

Table 1. Names, abbreviation, IUPAC names, formula, molecular weights and references of

Erucylphosphocholine is an alkylphospholipids derivative with a 22 carbon atom chain and a cis-13,14 double bond. Although it differs from miltefosine only in alkyl chain length and the presence of a double bond (Fig. 1), significant differences were found in pharmacological properties. This structural modification increases hydrophobicity resulting in the formation of lamellar supramolecular structures, which abolished hemolytic side effects and allows Erucylphosphocholine to be administrated intravenously (Erdlenbruch et al., 1999; Kaufmann-Kolle et al., 1996; van Blitterswijk & Verheij, 2008). It is a potent inducer of apoptosis (Jendrossek et al., 2003) that exerts more potent antineoplastic effects *in vitro* and

(trimethylazaniumyl) ethylphosphat

(1,1-dimethylpiperidin-1-ium-4-yl) octadecyl

[(Z)-docos-13-enyl] 2- (trimethylazaniumyl) ethyl phosphate

octadecyloxypropyl) 2- (trimethylazaniumyl) ethyl phosphate

 **CAS-number IUPAC-name Formula, molecular weight** 

**(g/mol), reference** 

C25H52NO4P, 461.66, (Hilgard et al., 1997)

C27H56NO4P, 489.71, (Erdlenbruch et al., 1998)

C27H58NO6P, 523.73, (Heesbeen et al., 1991)

1988)

C21H46NO4P, 407.57, (Eibl & Unger, 1990; Unger et al.,

**Name Abbreviation(s)** 

58066-85-6

57716-52-4

77286-66-9

EuPC; C22:1-PC 143317-74-2

Miltefosine HPC, HePC,

Perifosine OPP, D21266

Edelfosine ET-18-OCH3

most common alkylphospholipids

*in vivo* than Miltefosine.

Erucyl

phosphocholine

Cells in the Context of Anticancer Drug Development 363

OPP resistant MCF7 cells as compared to OPP sensitive MT3 breast cancer cells. On the other hand the properties of an efficient OPP formulation are mainly determined by cholesterol concentration, which should be below 50 mol%.
