Anti-neoplastic action of peritoneal macrophages following oral administration of ether analogues of lysophospholipids

Mechanisms of action of lysophospholipid analogues against trypanosomatid parasites

Lysophospholipid analogues (LPAs) comprise a class of metabolically stable compounds that have been developed as anticancer agents for over two decades, but which have also potent and selective antiparasitic activity, particularly against trypanosomatid parasites such as Leishmania and Trypanosoma cruzi, both in vitro and in vivo. The in vivo activities of LPAs result from direct effects on their target cells and are not dependent on a functional immune system. Because of their chemical nature, LPAs have a potential for interaction with a variety of subcellular structures and biochemical pathways. However, in mammalian cells LPA-induced growth inhibition and programmed cell death is usually associated with a blockade of phosphatidylcholine (PC) biosynthesis at the level of CTP: phosphocholine citidyltransferase, probably through an increase of cellular ceramide levels due to depressed sphingomyelin synthesis. Although in trypanosomatid parasites much less information is available, inhibition of PC biosynthesis by LPA has also been documented but at the level of phosphatidylethanolamine N-methyl-transferase, as well as LPA-induced classical apoptotic phenomena. The higher activity of LPAs as inhibitors of PC biosynthesis in parasites than in mammalian cells, probably due to different biochemical pathways involved in the two types of cells, could explain their selective antiparasitic action in vivo.

The ether lipid inositol-C2-PAF is a potent inhibitor of cell proliferation in HaCaT cells

The search for specific anticancer drugs that do not interfere with DNA synthesis or influence the cytoskeleton has led to the development of modified phospholipids with antiproliferative properties. These compounds cause remodeling of the structure and function of plasma membranes. Recently, we described novel compounds, the glycosidated phospholipids, that surprisingly inhibit cell proliferation. These compounds contain alpha-D-glucose in the sn-2 position of the glycerol backbone of phosphatidylcholine (PC) and platelet-activating factor (PAF), which gives rise to 2-glucophosphatidylcholine (Glc-PC) and 1-O-octadecyl-2-O-alpha-d-glucopyranosyl-sn-2-glycero-3-phosphatidylcholine (Glc-PAF), respectively. Glc-PC and Glc-PAF inhibit the growth of HaCaT cells at nontoxic concentrations. Here we report the introduction of myo-inositol, in place of alpha-D-glucose, in the sn-2 position of the glycerol backbone; this leads to two diastereomeric 1-O-octadecyl-2-O-(2-(myo-inositolyl)-ethyl)-sn-glycero-3-(R/S)-phosphatidylcholines (Ino-C2-PAF). The inositol-containing PAF enhances the antiproliferative capacity (IC(50)=1.8 microM) and reduces the cytotoxicity relative to Glc-PAF (LC(50)=15 microM). Through biological assays, we showed that, in HaCaT cells, Ino-C2-PAF causes upregulation of the keratinocyte-specific differentiation marker involucrin, increases the activity of the differentiation marker transglutaminase, and induces apoptosis at nontoxic concentrations. Ino-C2-PAF therefore seems to be a promising candidate for development as an antiproliferative drug for the treatment of hyperproliferative diseases of the skin.

Analogs of alkyllysophospholipids: chemistry, effects on the molecular level and their consequences for normal and malignant cells

In the search for new approaches to cancer therapy, the first alkyllysophospholipid (ALP) analogs were designed and studied about two decades ago, either as potential immunomodulators or as antimetabolites of phospholipid metabolism. In the meantime, it has been demonstrated that they really act in this way. However, their special importance is based on the fact that, in addition, they interfere with key events of signal transduction, such as hormone (or cytokine)-receptor binding or processing, protein kinase C or phospholipase C function and phosphatidylinositol and calcium metabolism. There are no strict structural requirements for their activity. Differences in the cellular uptake or the state of cellular differentiation seem to be mainly responsible for higher or lower sensitivities of cells towards ALP analogs. Consequences of the molecular effects mentioned on the cellular level are cytostasis, induction of differentiation (while in contrast the effects of known inducers of differentiation such as 12-O-tetradecanoylphorbol-13-acetate are inhibited, probably as a consequence of protein kinase C inhibition) and loss of invasive properties. Already in sublytic concentrations, alterations in the membrane structure were observed, and lysis may begin at concentrations not much higher than those causing the other effects described. Few ALP analogs have already entered clinical studies or are in clinical use. ALP analogs are the only antineoplastic agents that do not act directly on the formation and function of the cellular replication machinery. Therefore, their effects are independent of the proliferative state of the target cells. Because of their interference with cellular regulatory events, including those failing in cancer cells, ALP analogs, beyond their clinical importance, are interesting model compounds for the development of new, more selective drugs for cancer therapy.

Inhibition of induced angiogenesis in a human microvascular endothelial cell line by ET-18-OCH3

Alkyl-lysophospholipids are a group of anti-cancer compounds that have previously been shown to have the unique feature of being selectively toxic to neoplastic tissues. One of these compounds, ET-18-OCH3, has been used for purging bone marrow of cancer cells in phase I clinical trials. Tumor-induced angiogenesis has been directly correlated with tumor growth and metastasis. In this study, we examined the effect ET-18-OCH3 has on a human microvascular endothelial cell line (HMEC-1), including the following functions: angiogenesis, cell-adhesion molecule expression, and cell-junction integrity. We found that ET-18-OCH3 (in vitro) reversibly inhibited induced angiogenesis at levels that did not affect viability. At lower concentrations, ET-18-OCH3 down-regulated the expression of cell-adhesion molecules and affected the integrity of cell-to-cell junctions. This observation demonstrates this versatile family of compounds to have additional targets of action.

Antineoplastic activity of alkylphosphocholines (APC) in human breast carcinomas in vivo and in vitro; use of liposomes

This study examines the in vitro and in vivo activity of alkylphosphocholines (APC) in experimental human breast carcinomas. Three analogs, hexadecylphosphocholine (HPC), octadecylphosphocholine (OPC) and eicosanylphosphocholine (EPC) were investigated. Three hormone receptor negative cell lines were sensitive to all three APCs in vitro whereas the receptor positive MCF-7 line was more resistant. Sensitivity was seen in 4/6 hormone receptor negative tumors in vivo, with HPC being the most active analog. There were no antitumor effects in the four receptor positive models. The reasons for these differences in response between hormone receptor negative and -positive lines are not yet understood and require further study. Gastrointestinal toxicity and hemolysis, the major side effects of the APCs, were reduced by the use of liposomal preparations.