Related Experiment Video
Updated: Sep 30, 2026
Genome-wide Screen for miRNA Targets Using the MISSION Target ID Library
Published on: April 6, 2012
Expression of MRP4 confers resistance to ganciclovir and compromises bystander cell killing
Masashi Adachi1, Janardhan Sampath, Lu-bin Lan
1Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Abstract:
The multidrug resistance protein MRP4, a member of the ATP-binding cassette superfamily, confers resistance to purine-based antiretroviral agents. However, the antiviral agent ganciclovir (GCV) has not been shown to be a substrate of MRP4. GCV is important not only in antiviral therapy, but also in the selective killing of tumor cells modified to express herpes simplex virus thymidine kinase (HSV-TK). We therefore tested the effect of MRP4 on the cytotoxicity of GCV, on the ability of GCV to kill cells genetically modified to express HSV-TK, and on the bystander effect in which unmodified target cells are killed by GCV. Cells overexpressing MRP4 had markedly increased resistance to the cytotoxicity of GCV. Although, expression of recombinant HSV-TK increased the intracellular concentration of GCV nucleotide, cells were rescued by the cytoprotective effect of MRP4. In cells that overexpressed MRP4, intracellular accumulation of GCV metabolites was reduced, efflux of these metabolites was increased, and resistance to bystander killing was increased. Therefore, MRP4 can strongly reduce the susceptibility of HSV-TK-expressing cells to GCV, and its overexpression in adjacent cells protects them from bystander cell death. These findings indicate that a nucleotide transporter, such as MRP4, modulates the cellular response to GCV and thus may influence not only the efficacy of antiviral therapy, but also prodrug-based gene therapy, which is critically dependent upon bystander cell killing.
Insights
The multidrug resistance protein MRP4 reduces ganciclovir (GCV) effectiveness in killing cancer cells, even those modified with herpes simplex virus thymidine kinase (HSV-TK). MRP4 also protects nearby cells from GCV-induced bystander killing.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- The multidrug resistance protein MRP4 (ATP-binding cassette superfamily) confers resistance to purine-based antiretroviral agents.
- Ganciclovir (GCV) is crucial for antiviral therapy and selective tumor cell killing via herpes simplex virus thymidine kinase (HSV-TK).
- MRP4's role with GCV, particularly in HSV-TK-mediated therapy and bystander effects, remained unclear.
Purpose of the Study:
- To investigate the impact of MRP4 on GCV cytotoxicity.
- To determine MRP4's effect on GCV's ability to eliminate HSV-TK-modified tumor cells.
- To assess MRP4's influence on the bystander effect in GCV-based therapies.
Main Methods:
- Cell lines overexpressing MRP4 were utilized.
- Cytotoxicity assays were performed to measure GCV's effect.
- Intracellular GCV metabolite concentrations and efflux were analyzed.
- Bystander killing assays were conducted.
Main Results:
- Cells overexpressing MRP4 exhibited significantly increased resistance to GCV cytotoxicity.
- MRP4 expression rescued HSV-TK-expressing cells despite increased intracellular GCV nucleotide levels.
- MRP4 overexpression reduced GCV metabolite accumulation, enhanced their efflux, and increased resistance to bystander killing.
Conclusions:
- MRP4 significantly diminishes GCV susceptibility in HSV-TK-expressing cells.
- Overexpressed MRP4 in adjacent cells confers protection against bystander cell death.
- Nucleotide transporters like MRP4 modulate cellular responses to GCV, impacting antiviral therapy and prodrug gene therapy efficacy.
