Effect of verapamil on daunorubicin accumulation in Ehrlich ascites tumor cells

Abstract

Previous studies have demonstrated that verapamil may overcome resistance to anthracyclines. In vitro and in vivo experiments were performed on wild-type and resistant Ehrlich ascites tumor cells. Verapamil in concentrations of 25-50 microM enhances the accumulation of daunorubicin (DNR) in resistant cells to the same level as in wild-type cells. No significant effect of verapamil on influx or nuclear binding could be demonstrated, indicating that verapamil enhances DNR uptake by blocking active drug extrusion. Exposure of cells to a high concentration of Ca2+ did not influence the effect of verapamil on DNR accumulation, suggesting a different mode of verapamil action apart from the Ca2+-blocking effect. Attempts to circumvent acquired resistance to DNR in vivo with verapamil showed that the combination of the two drugs was more toxic than DNR given alone. The LD10 of DNR was determined as 3 mg/kg and the LD10 of the combination, as 2.5 mg/kg. The therapeutic effect of verapamil at a dose of 50 mg/kg and DNR of 2.5 mg/kg increased the life span of the mice by 50%. No difference was seen in the wild-type tumor in vivo. These data lead us to conclude that verapamil can reverse DNR resistance completely, but that verapamil at non-toxic dosage only reduces DNR resistance by 50% in vivo.

Inhibition of vincristine binding to plasma membrane vesicles from daunorubicin-resistant Ehrlich ascites cells by multidrug resistance modulators

“…This is in spite of that VER at 25 ILM has been shown to increase intracellular DNR in EHR2/ DNR + to levels approaching those found in sensitive EHR2 cells (Friche et al, 1987), and also that Tween 80 at 0.001% v/v significantly enhanced DNR accumulation in EHR2/ DNR + (T. Skovsgaard, unpublished results). This is in agreement with our previous results (Sehested et al, 1989) which failed to demonstrate any specific DNR binding site on the EHR2/DNR + plasma membrane.…”

Effect of anthracycline analogs on photolabelling of p-glycoprotein by [125I]iodomycin and [3H]azidopine: relation to lipophilicity and inhibition of daunorubicin transport in multidrug resistant cells

“…Resistance to DNR was developed and maintained in vivo in mice as previously described in detail (Dan0, 1971). In vivo the subline is at least 16-fold resistant to DNR (Friche et al, 1987) and in vitro in a clonogenic assay about 80-fold resistant (Friche et al, 1990b). No (Merck, Germany) with the solvent system ethyl acetate/diethyl ether (2:1, v/v, Rf 0.12), and extracted from the silica by ethanol (2 x 1 ml).…”

Interactions between Calcium Channel Blockers and Non‐Cardiovascular Drugs: Interactions with Anticancer Drugs

“…Moreover, neither the calcium ionophore A23187, the calcium chelator EGTA, nor the inorganic inhibitor of calcium influx lanthanum modify perhexilineincreases of daunorubicin cytotoxicity (Ramu et al 1984a) and EGTA has been shown not to increase daunorubicinaccumulation or cytotoxicity in P388/ADR cells (Ramu er al. 1984a;Friche et al 1987). Thus CCBs do not appear to enhance anthracycline cytotoxicity through a modification of cellular calcium fluxes.…”

“…Moreover, verapamil enhances adriamycin and daunorubicin activity against Ehrlich ascites carcinoma cells resistant to them in a dose-dependent way, significantly increasing the life span of the experimental animals bearing these cells. However, verapamil does not increase the cytotoxicity of these anthracyclines in Ehrlich ascites cells sensitive to them (Slater et al 1982;Friche et al 1987).…”

“…Surprisingly, a high extracellular concentration of calcium does not antagonize perhexiline-induced enhancement of daunorubicin toxicity in P388/ADR cells or verapamilinduced increase of daunorubicin activity against Ehrlich ascites daunorubicin-resistant cells (Ramu et al 1984a;Friche et a/. 1987).…”