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A relationship between multidrug resistance and growth-state dependent cytotoxicity of the lysosomotropic detergent
P D Wilson1, D Hreniuk, J Lenard
1Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School (at Rutgers), Piscataway 08854.
Abstract:
Multidrug resistance (MDR) in cultured cells and tumors is associated with overproduction of P-glycoprotein, a plasma membrane efflux pump normally present at very low levels. The cytotoxic action of N-dodecylimidazole (C12-Im), a lysosomotropic detergent, on cultured cells was previously shown to be strongly dependent on growth state, with rapidly growing cells being most sensitive and confluent cells most resistant. We show here that this may be due to a growth dependent increase in cellular P-glycoprotein activity. Both verapamil and nifedipine, structurally unrelated P-glycoprotein inhibitors, increased markedly the sensitivity of CHO fibroblasts to killing by C12-Im; the increase was greater in confluent than in growing cells. Also, verapamil inhibitable 3H-daunomycin efflux was more efficient from confluent than from subconfluent cells. The MDR cell line CH(R)C5 differed from all cell lines previously examined in that it did not show a growth-dependent decrease in C12-Im sensitivity, and sensitivity was not increased by verapamil or nifedipine. We suggest that a growth-dependent increase in MDR activity is a general property of cultured cells, except for those specifically overexpressing P-glycoprotein.
Insights
Multidrug resistance (MDR) in cells increases with P-glycoprotein activity, especially in confluent cells. Inhibitors of P-glycoprotein enhance sensitivity to N-dodecylimidazole (C12-Im), suggesting MDR is a general property of cultured cells.
Area of Science:
- Cell Biology
- Pharmacology
- Biochemistry
Background:
- Multidrug resistance (MDR) in cells and tumors is often linked to increased P-glycoprotein, a plasma membrane efflux pump.
- The cytotoxic effects of N-dodecylimidazole (C12-Im), a lysosomotropic detergent, vary with cell growth state, with confluent cells being more resistant than rapidly growing cells.
Purpose of the Study:
- To investigate the role of P-glycoprotein activity in the growth-dependent sensitivity of cultured cells to N-dodecylimidazole (C12-Im).
- To determine if P-glycoprotein inhibitors can modulate C12-Im sensitivity in different cell growth states.
Main Methods:
- Assessing the sensitivity of CHO fibroblasts to C12-Im in the presence and absence of P-glycoprotein inhibitors (verapamil, nifedipine) across different growth phases.
- Measuring verapamil-inhibitable 3H-daunomycin efflux in cells at various growth stages.
- Comparing C12-Im sensitivity and inhibitor response in a multidrug-resistant cell line (CH(R)C5).
Main Results:
- P-glycoprotein inhibitors (verapamil, nifedipine) significantly increased C12-Im sensitivity in CHO fibroblasts, particularly in confluent cells.
- Verapamil-inhibitable 3H-daunomycin efflux was more pronounced in confluent cells compared to subconfluent cells.
- The multidrug-resistant cell line CH(R)C5 exhibited no growth-dependent change in C12-Im sensitivity and was unresponsive to P-glycoprotein inhibitors.
Conclusions:
- A growth-dependent increase in P-glycoprotein activity contributes to multidrug resistance in cultured cells.
- This phenomenon appears to be a general characteristic of cultured cells, excluding those with constitutive high P-glycoprotein expression.
