Growth arrest vs direct cytotoxicity and the importance of molecular structure for the in vitro anti-tumour activity of ether lipids

Abstract

Summary A panel of 25 different lipid agents was evaluated for in vitro activity against HT29 human colon carcinoma and HL60 promyelocytic leukaemia cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The structure-activity relationships seen with this series, including those for four sets of positional or stereoisomers, indicate that specific receptor proteins are unlikely as targets for anti-tumour lipid (ATL) action. Additional data confirm the lack of involvement of the platelet-activating factor receptor in particular and suggest that metabolic stability is a most important determinant of ATL activity. More detailed studies, with 1-O-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine (ET18-OCH3) and (±)-2-{Hydroxy[tetrahydro-2-(octadecyloxy)methylfuran-2-yl]methoxylphosphinyloxy)-N,N,N,-trimethylethaniminium hydroxide (SRI 62-834), suggest three different modes of activity, depending on drug concentration and exposure time. Low doses of up to 5 jiM in standard serum-containing medium cause population growth arrest after prolonged exposure. Growth arrest was associated with a leaky G2/M block as determined by flow cytometry. These effects are reversible. Intermediate concentrations (5-40 M) were cytotoxic, causing a net reduction in cell numbers after 2-3 days. At even higher concentrations, all lipids caused rapid, direct membrane lysis. When the clonogenic assay was used to assess the effects of ATLs, most agents reduced colony formation at concentrations above 5 jIM. However, some compounds proved stimulatory at nanomolar concentrations, suggesting that they might possess mitogenic properties. These results, particularly those concerning the concentration and time dependence, may be relevant to current clinical trials with ether lipids.

Increased cell-surface receptor expression on U-937 cells induced by 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine

“…There is evidence that inhibition of cell growth caused by ET-18-OCH 3 at sublytic concentrations (below 5±10 lM) results from cell-cycle arrest and apoptosis [4,10,11,21,22,25]. Flow cytometry analysis of dierent cell sub-populations indicated that a subpopulation that had characteristics of apoptotic cells (smaller size/higher cell density; forward compared to side scattering on¯ow cytometry plots) had low levels of CD11b and CD71 expression, suggesting that up-regulation of these markers is not directly associated with cell death.…”

“…We have shown previously that ET-18-OCH 3 and ELL-12 induce DNA fragmentation, as a marker of apoptosis, in L1210 cells [25] and in U-937 cells (data not shown), indicating the inhibition of cell growth is at least partly due to apoptosis. However, it has also been shown that incubation of cells with ET-18-OCH 3 can result in cell-cycle arrest [4,11,21]. Thus, growth inhibition by ET-18-OCH 3 may result from more than one mechanism.…”

ET-18-OCH3 (Edelfosine): A Selective Antitumour Lipid Targeting Apoptosis Through Intracellular Activation of Fas / CD95 Death Receptor

“…In addition to the apoptotic effect, ET-18-OCH 3 has been reported to inhibit cell division without concurrent inhibition of nuclear division, leading to accumulation of cells in G 2 /M, multinucleate cell formation, and subsequent cell death through apoptosis [124][125][126][127][128][129][130][131] (Mollinedo, F., del Canto-Jañez, E., Verhaegen, S. and Gajate, C., unpublished data). Inhibition of cell growth by ET-18-OCH 3 resulted from inhibition of cytokinesis [131,132] (Mollinedo, F., del Canto-Jañez, E., Verhaegen, S. and Gajate, C., unpublished data) by an unknown mechanism.…”

Rational Design of a Liposomal Drug Delivery System Based on Biophysical Studies of Phospholipase A 2 Activity on Model Lipid Membranes

“…In particular, this principle for targeted drug delivery is independent of the size of the diseased region and does not require a preceding localization of the diseased tissue. Furthermore, by designing the carrier liposome to include special lipids whose degradation products, after exposure to sPLA 2 , are converted into permeability enhancers, enzymatic activators, or certain drugs such as anticancer lysoetherlipids [55], a possible realization of Dr Erlich's 'magic bullet' can be imagined. …”