Induction of drug resistance to gold sodium thiomalate in a monocyte cell line, THP-1

Abstract

The expression of metallothionein, an intracellular heavy-metal-binding protein, and p-glycoprotein, an energy-dependent drug efflux pump, was examined to study the mechanism of cell resistance to gold sodium thiomalate (GST). THP-1, one of the monocyte-derived cell lines, was cultured for 6 months and resistance to 25 microg/ml of GST (GST-resistant cells) was thus induced. The GST-resistant cells were then cultured with bucillamine to examine the presence of cross-resistance. The intracellular GST concentration was examined by flameless atomic absorption spectroscopy. The cell viability was determined by the uptake of 3-4,5 dimethylthiazole-2,5 diphenyl tetrazolium bromide (MTT). The expression of p-glycoprotein was detected by Western blotting using monoclonal anti-p-glycoprotein antibody. The expression of metallothionein was detected using the indirect immunofluorescence technique. GST-resistant cells did not show any cross-resistance to bucillamine. The rate of cytoplasmic GST accumulation decreased in the GST-resistant cells, while the rate of GST efflux also decreased. The expression of p-glycoprotein in the GST-resistant cells was not significantly different from that in the cells not treated with GST. On the other hand, the GST-resistant cells showed a higher expression of metallothionein than cells not treated with GST. These findings suggest that the induced resistance to GST might partly be due to an induction of metallothionein.

Modulation of the Cellular Accumulation and Intracellular Activity of Daptomycin towards Phagocytized Staphylococcus aureus by the P-Glycoprotein (MDR1) Efflux Transporter in Human THP-1 Macrophages and Madin-Darby Canine Kidney Cells

“…P-gp has been described in THP-1 macrophages (17), and our observation that the bulk of the protein is located at the cell surface is consistent with a detoxification function. We, however, are facing two difficulties in the context of our study, namely, (i) how daptomycin could be effluxed by P-gp, based on what we know about preferences of this transporter for truly amphiphilic compounds, and (ii) how this efflux could modulate its intracellular activity towards bacteria that sojourn and thrive not in the cytosol but within phagolysosomes.…”

“…Specifically, we show here that the activity of P-gp in THP-1 human macrophages decreases the relative potency of daptomycin towards phagocytized S. aureus by reducing its cellular concentration. This conclusion, and its specificity with respect to P-gp versus other eukaryotic efflux transporters, stems from five converging pieces of evidence gained from independent approaches, namely (i) the use of two well-known inhibitors of P-gp activity, verapamil (42) and elacridar (GF 120918) (17), in comparison with gemfibrozil, a preferential inhibitor of MRP efflux transporters, which are also present in macrophages (34); (ii) the comparison of the behavior of THP-1 macrophages with that of MDCK (wildtype) and of MDCK-MDR1 (overexpressing P-gp) cell lines; (iii) the direct measurement of the cell content in daptomycin and in DiOC 2 , a well-known substrate of P-gp (55), in the presence of molecules known to impair or to increase P-gp activity (viz. the inhibitors mentioned above and ouabain, an inducer of mdr1 expression) (7); and (iv) the silencing of mdr1 (the gene encoding P-gp in humans) expression by specific siRNA.…”

Drug resistance in rheumatology: An area in search of investigators

“…The correlation between MT induction and auranofin resistance has been confirmed [8]; MT is an inducible metal-binding cell component that is present in most animal and plant cells, and has important biologic functions that are still not completely known. It can be shown that nitric oxide releases intracellular zinc from MT [9]. A Japanese group induced resistance to sodium aurothiomalate, and found that the resistant cells overexpress MT [10]; however, this finding has not been confirmed.…”

“…It could be a defense mechanism in an activated tissue, but it was shown that P-glycoprotein expression was not related to sodium aurothiomalate resistance in vitro [9]. Maillefert et al [22] looked at P-glycoprotein expression in peripheral blood lymphocytes and found them not different from controls.…”