Role of the host tissue in the anti-invasive activity of the alkyllysophospholipid, ET-18-OCH3,in vitro

Abstract

The alkyllysophospholipid, racemic-l-O-octadecyl-2-O-methylglycero-3- phosphocholine (ET-18-OCH3) was previously shown to inhibit invasion of malignant cells into precultured heart fragments (PHF) in vitro. In particular, pretreatment of PHF with 10 micrograms ET-18-OCH3 for 48 h was sufficient to induce in the host tissue resistance towards invasion by mouse MO4 cells. Resistance was obvious when MO4 cells were confronted either immediately (the pretreatment experiment) or after withdrawal of the drug 7 days prior to confrontation (the reversibility experiment). In the present study, the survival of PHF cells in the pretreatment and reversibility experiments was similar to that of untreated PHF cells as determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) test and by the PHF explantation test. The effective anti-invasive concentration was 6 micrograms/ml in the pretreatment experiment while 3 micrograms/ml was sufficient to inhibit invasion in the reversibility experiment. Induction of resistance towards invasion in pretreated PHF was shown to occur not only with MO4 cells but also with mouse LLC-H61 Lewis lung carcinoma and mouse BW-O-Li1 T-lymphoma cells. The increase in molecular weight of N-linked cell surface glycosylpeptides (N-GP) of PHF was apparent in the pretreatment experiment and was enhanced in the reversibility experiment. This effect was completely abolished in cells obtained from pretreated PHF which were converted into a cell suspension and further cultured as a monolayer on tissue culture plastic without drug for 7 days. The results reported here provide additional evidence for the causal involvement of N-GP of the PHF host tissue in the anti-invasive activity of ET-18-OCH3 in vitro.

Alkyl-lysophospholipid 1-O-octadecyl-2-O-methyl- glycerophosphocholine induces invasion through episialin-mediated neutralization of E-cadherin in human mammary MCF-7 cellsin vitro

“…2 Antithetic effects on invasion have also been reported: ET-18-OMe inhibited invasion of constitutively invasive cells, [3][4][5][6] whereas it induced invasion of otherwise noninvasive cells. 7,8 Inhibition of invasion in the presence of ET-18-OMe was explained by induction of host tissue resistance, 9 but the antithetic effects on cell-cell adhesion and the invasion-promoting effect of ET-18-OMe have not been explained.…”

An anti-invasive concentration of the alkyl-lysophospholipid ET-18-OCH3 enhances the motility of embryonal chick heart cells cultured on solid substrate

“…Indeed, assays for cytotoxicity and cell survival, performed by one of us (E.A.B.) with the same stock solution of ET-18-OCH3 in experiments parallel to the observations reported in the present paper, showed no significant differences between pretreated and untreated PHFs in the estimated number of cells that had migrated from the explant [6]; also, the survival of PHF cells after treatment of PHFs with ET-18-OCH3 for 48 h was similar to that of untreated PHF cells as determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) test [6].…”

“…It is conceivable that trypsinization, possibly in conjunction with increased cell division occurring after plating, in some proportion of the cells, may have accelerated the cell surface N-GP turnover. This may have contributed to a partial reversion of the hypersialylation [6], sufficient, in at least part of the cells, to limit the increase in motility possibly induced by hypersialylation (see below). Additionally or alternatively, ET-18-OCH3 might affect cells present in PHF-derived cultures differentially, inducing a more pronounced increase in motility in a subset of cells.…”

“…Also, a high level of sialylation of cell adhesion proteins [22][23][24] and a high content of sialic acid containing gangliosides [25,26] in the plasma membrane are positively correlated with increased cell migration during embryogenesis or neovascularization of the cornea, while an increment in plasma membrane sialic acid containing gangliosides enhances cell migration in vitro [25,27]. Bolscher et al [4] and Schallier et al [6], referring to the differential adhesion hypothesis formulated by Steinberg [27], considered that diminished cell-cell adhesion in host tissue due to increased sialylation of cell surface glycoproteins might underlie resistance to invasion through abolishing the existing difference in adhesion to each other of host cells and malignant cells. One might argue, however, that diminished intercellular adhesion between host cells would in itself tend to facilitate invasion, and that only a decrease in heterotypic adhesion between malignant cells and host cells could explain inhibition of invasion.…”

“…Induction of resistance occurred as well in conditions of (a) permanent treatment, when 10/tg ET-18-OCH3 per ml was present in the culture medium during the confron-tation assay [2,3]; (b) pretreatment of PHF with 10/lg ET-18-OCH3 per ml during 48 h followed by extensive washing and immediate confrontation with malignant cells in the absence of the drug [4]; (c) pretreatment followed by culture in absence of the drug for 4-7 days prior to confrontation with malignant cells (reversibility experiments) [5]. Induction by ET-18-OCH3 of resistance to invasion is associated with increased sialylation of N-linked cell surface glycosylpeptides (N-GP) [4,6], and this increased sialylation was observed both in pretreated PHFs and in PHF-derived cells cultured in monolayer [4].…”