Investigation of the relationship between altered intracellular pH and multidrug resistance in mammalian cells

Abstract

SummaryThe intracellular pH of a number of multidrug resistant cell lines was compared with that of their parental lines using the fluorescent probe bis-carboxyethylcarboxyfluorescein. In four different cases, cells having 5-fold resistance or more exhibited an intracellular pH which was 0.10-0.17 units higher than that of the parental cell line. A CHO cell line, AB,, and its 180-fold resistant counterpart, CHRC5, were further investigated with regard to the role of Na+/H+ antiport. The Na+/H+ antiport activity was greater at any intracellular pH for the CHRC5 cells than the AB, cells. To investigate the possible role of higher intracellular pH in multidrug resistance, the effect of several agents which are either known to reverse multidrug resistance or inhibit Na+/H+ antiport activity were examined. Verapamil was found to reverse multidrug resistance but had no effect on intracellular pH while amiloride, which acidifies the cytoxol by blocking Na+/H+ antiport activity, did not cause reversal of drug resistance. In contrast to verapamil, treatment of CHRC5 cells with cyclosporin A had a parallel effect on reversal of their drug resistant phenotype and a lowering of their intracellular pH to that of the sensitive cell level. However, cyclosporin was ineffective in either lowering the intracellular pH or reversing drug resistance in DC3F/ADX cells. Therefore, except for the effect of cyclosporin A on the CHRC5 line, the effects of other agents on reversal of multidrug resistance and intracellular pH did not correlate with each other.

Na+/H+ exchanger activity is increased in doxorubicin‐resistant human colon cancer cells and its modulation modifies the sensitivity of the cells to doxorubicin

“…The results of this work are partly in agreement with previous observations, showing that MDR cells exhibit a higher NHE activity. 28,29 Differently from Boscoboinik and colleagues, 28 who did not observe a reversal of MDR with amiloride, in our experiments EIPA (at the concentration able to inhibit NHE activity in the same cells) did cause an increase of the chemotherapeutic accumulation. This discrepancy could be accounted for by the different cells and inhibitor used: indeed, amiloride is a less potent and less specific inhibitor of NHE than EIPA.…”

Reversal of intrinsic multidrug resistance in Chinese hamster ovary cells by amiloride analogs

“…It has been suggested that sensitisers increase drug accumulation by competing with cytotoxic drugs for sites on the P-glycoprotein efflux pump (Horio et al, 1988). However, one sensitiser, cyclosporin A, has been shown to reverse acquired MDR in some cell lines but not in DC3F/ADX cells, despite the fact that these cells overexpress P-glycoprotein (Boscoboinik et al, 1990). The mechanism of intrinsic MDR is even less well understood.…”

“…In this context, our observation that the intrinsic and acquired MDR phenotypes differ with regard to their reversal by amiloride analogs points to some subtle differences in the resistance mechanism. It should however, be mentioned that acquired MDR cell lines which overexpress P-glycoprotein are also known to differ in their reversal characteristics by cyclosporin A (Boscoboinik et al, 1990). The different reversing agents may provide a valuable probe for examining the heterogeneity of the MDR phenotype and for investigating the underlying mechanism(s).…”

“…In this work, for the first time, we show that several analogs of amiloride can reverse intrinsic MDR without greatly affecting the acquired MDR. Amiloride is an inhibitor of Na+/H+ antiport. The activity of this ion transporter is elevated in drug resistant cell lines (Boscoboinik et al, 1990). Analogs of amiloride vary greatly in the potency and specificity by which they inhibit this antiporter (Kleyman & Cragoe, 1988 (Keizer & Joenje, 1989;Boscoboinik et al, 1990), it seemed possible that acidification of pH,, through inhibition of the Na+/H+ antiporter, could contribute to the sensitisation of drug resistant cell lines.…”

PH Regulation by Breast Cancer Cells In Vitro and In Vivo

“…Hence, the phenomenon is known as multidrug resistance (MDR). The most well-studied mechanism of multidrug resistance involves the MDR-1 gene product, P-glycoprotein (P-gp), a drug pump which also transports protons (Thiebaut et al, 1990;Boscoboinik et al, 1990). However, P-gp accounts for only 50% of the observed MDR phenotypes (Gottesman and Pastan, 1993).…”