Cobalamin potentiates vinblastine cytotoxicity through downregulation of mdr-1 gene expression in HepG2 cells

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• P-glycoprotein (Pgp), encoded by the multidrug resistance-1 (mdr-1) gene, is a key factor in cancer cells developing resistance to chemotherapy.
• Changes in mdr-1 gene promoter methylation are linked to its expression, potentially influenced by S-adenosyl-methionine levels.

Purpose of the Study:

• To investigate the role of the methionine cycle, specifically cobalamin (a cofactor for Methionine-Synthase), in regulating mdr-1 gene expression in HepG2 cells.
• To determine if cobalamin affects Pgp expression and function, and consequently, cancer cell sensitivity to chemotherapy.

Main Methods:

• Semiquantitative RT-PCR was used to measure mdr-1 gene expression.
• Cellular retention of Rhodamine 123 and vinblastine cytotoxicity assays were performed.
• Methylation-specific PCR analyzed the mdr-1 gene promoter methylation status.

Main Results:

• Cobalamin supplementation increased Methionine-Synthase activity and significantly decreased mdr-1 gene expression.
• This led to increased retention of Rhodamine 123 and enhanced vinblastine cytotoxicity, comparable to Pgp blockers.
• Cobalamin also prevented methotrexate-induced upregulation of mdr-1, without altering promoter methylation.

Conclusions:

• Cobalamin effectively downregulates mdr-1 gene expression, Pgp expression, and Pgp function.
• This results in increased cancer cell sensitivity to vinblastine, suggesting a novel approach to overcome chemotherapy resistance.
• These findings hold promise for developing improved therapeutic strategies for cancer patients facing drug resistance.