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pH regulation in sensitive and multidrug resistant Ehrlich ascites tumor cells
T Litman1, S F Pedersen, B Kramhøft
1Department of Medical Physiology, Panum Institute, Copenhagen, Denmark.
Summary
Intracellular pH regulation in cancer cells was studied. P-glycoprotein (P-gp) expression did not correlate with pH regulation, but drug resistance did, suggesting other mechanisms are involved.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Intracellular pH (pHi) homeostasis is crucial for normal cell function and is often dysregulated in cancer.
- Ehrlich ascites tumor cells (EHR2) and their daunorubicin-resistant, P-glycoprotein (P-gp)-expressing variants (EHR2/1.3) were used to investigate pHi regulation.
- P-gp is a key transporter involved in multidrug resistance (MDR) in cancer cells.
Purpose of the Study:
- To investigate the role of P-glycoprotein (P-gp) in the maintenance and regulation of intracellular pH (pHi) in daunorubicin-resistant cancer cells.
- To determine if P-gp expression or activity correlates with altered pHi regulation.
- To explore alternative mechanisms contributing to drug resistance and pHi homeostasis.
Main Methods:
- Studied pHi regulation in wild-type EHR2 cells and five P-gp-expressing resistant strains.
- Measured steady-state pHi in the absence and presence of glucose.
- Assessed glucose-induced acidification and proton efflux rates.
- Evaluated the activity of the Na+/H+ exchanger.
- Investigated the effect of P-gp modulators on pHi regulation.
Main Results:
- Steady-state pHi was similar across cell lines with varying P-gp expression, irrespective of glucose presence.
- Resistant EHR2/1.3 cells showed reduced glucose-induced acidification and increased proton efflux compared to wild-type EHR2 cells.
- These pHi differences were not attributable to increased Na+/H+ exchanger activity.
- No correlation was found between P-gp levels and pHi regulation, nor were P-gp modulators effective.
- A correlation was observed between daunorubicin resistance/accumulation and acid extrusion rate.
Conclusions:
- P-glycoprotein (P-gp) expression does not directly influence intracellular pH (pHi) regulation in these Ehrlich ascites tumor cell lines.
- Mechanisms other than P-gp contribute to altered acid extrusion rates and drug resistance.
- The observed correlation between drug resistance and acid extrusion suggests a link between cellular defense mechanisms beyond P-gp.