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Drug resistance in cultured rat liver epithelial cells spontaneously and chemically transformed
1Department of Medicine, Montreal General Hospital Research Institute, Quebec, Canada.
Abstract:
Cultured rat liver epithelial cells (RLE) transformed with repeated treatments of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) demonstrate many features of the common biochemical phenotype of multidrug resistance (MDR) seen in vivo in 'resistant hepatocytes'. The cells have increased glutathione-S-transferase placental subunit (GST-Yp), gamma-glutamyltranspeptidase (GGT), glutathione (GSH) and glutathione peroxidase and are resistant to MNNG. Phenotypically identical RLE cells spontaneously transformed by selective culture conditions showed low levels of GGT and GST and were not resistant to MNNG. Both chemical and spontaneous transformants are cross resistant to doxorubicin although resistance is consistently greater in chemical transformants. No direct correlation was found between the degree of resistance to doxorubicin and MDR gene expression in either of the chemically or spontaneously transformed RLE cells. These observations suggest that in chemical carcinogenesis, other mechanisms of drug detoxification are involved and that MDR expression is not a consistent feature.
Insights
Chemical treatments induce multidrug resistance (MDR) in rat liver cells, increasing detoxification enzymes. However, MDR gene expression did not correlate with doxorubicin resistance, suggesting alternative mechanisms in chemical carcinogenesis.
Area of Science:
- Hepatocellular Carcinogenesis
- Drug Resistance Mechanisms
- Biochemical Phenotyping
Background:
- Multidrug resistance (MDR) is a common phenotype in resistant hepatocytes observed in vivo.
- Rat liver epithelial cells (RLE) provide a model for studying cellular transformation and resistance.
- N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a chemical carcinogen used to induce cellular changes.
Purpose of the Study:
- To investigate the biochemical phenotype of RLE cells transformed by MNNG.
- To compare MDR features in chemically vs. spontaneously transformed RLE cells.
- To explore the relationship between drug resistance and MDR gene expression.
Main Methods:
- Cultured RLE cells were repeatedly treated with MNNG.
- Spontaneous transformation of RLE cells was induced via selective culture.
- Assays for glutathione-S-transferase placental subunit (GST-Yp), gamma-glutamyltranspeptidase (GGT), glutathione (GSH), and glutathione peroxidase were performed.
- Doxorubicin resistance and MDR gene expression were evaluated.
Main Results:
- MNNG-transformed RLE cells exhibited increased GST-Yp, GGT, GSH, and glutathione peroxidase, conferring resistance to MNNG.
- Both chemical and spontaneous transformants showed cross-resistance to doxorubicin, with higher resistance in chemical transformants.
- No direct correlation was found between doxorubicin resistance levels and MDR gene expression.
Conclusions:
- Chemical carcinogenesis via MNNG induces MDR-like phenotypes in RLE cells with elevated detoxification enzymes.
- Spontaneously transformed cells show a different biochemical profile and lower doxorubicin resistance compared to chemical transformants.
- MDR gene expression is not consistently linked to doxorubicin resistance, indicating other drug detoxification mechanisms are involved in chemical carcinogenesis.