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Ganciclovir uptake in human mammary carcinoma cells expressing herpes simplex virus thymidine kinase
U Haberkorn1, K Khazaie, I Morr
1Department of Oncological Diagnostics and Therapy, German Cancer Research Center, Heidelberg, Federal Republic of Germany. u.haberkorn@dkfz-heidelberg.de
Abstract:
Assessment of suicide enzyme activity would have considerable impact on the planning and the individualization of suicide gene therapy of malignant tumors. This may be done by determining the pharmacokinetics of specific substrates. We generated ganciclovir (GCV)-sensitive human mammary carcinoma cell lines after transfection with a retroviral vector bearing the herpes simplex virus thymidine kinase (HSV-tk) gene. Thereafter, uptake measurements and HPLC analyses were performed up to 48 h in an HSV-tk-expressing cell line and in a wild-type cell line using tritiated GCV. HSV-tk-expressing cells showed higher GCV uptake and phosphorylation than control cells, whereas in wild-type MCF7 cells no phosphorylated GCV was detected. In bystander experiments the total GCV uptake was related to the amount of HSV-tk-expressing cells. Furthermore, the uptake of GCV correlated closely with the growth inhibition (r = 0.92). Therefore, the accumulation of specific substrates may serve as an indicator of the HSV-tk activity and of therapy outcome. Inhibition and competition experiments demonstrated slow transport of GCV by the nucleoside carriers. The slow uptake and low affinity to HSV-tk indicate that GCV is not an ideal substrate for the nucleoside transport systems or for HSV-tk. This may be the limiting factor for therapy success, necessitating the search for better substrates of HSV-tk.
Insights
Assessing suicide enzyme activity, like herpes simplex virus thymidine kinase (HSV-tk), is crucial for cancer gene therapy. Ganciclovir (GCV) uptake correlates with tumor cell killing, but its slow transport limits therapy success.
Area of Science:
- Oncology
- Molecular Biology
- Gene Therapy
Background:
- Suicide gene therapy offers a promising approach for treating malignant tumors.
- Accurate assessment of suicide enzyme activity is essential for individualizing therapy and predicting outcomes.
Purpose of the Study:
- To evaluate the utility of measuring ganciclovir (GCV) pharmacokinetics as an indicator of herpes simplex virus thymidine kinase (HSV-tk) activity.
- To assess the correlation between GCV uptake, HSV-tk activity, and therapeutic efficacy in a preclinical cancer model.
Main Methods:
- Generation of GCV-sensitive human mammary carcinoma cell lines via retroviral transfection with the HSV-tk gene.
- Measurement of tritiated GCV uptake and phosphorylation in HSV-tk-expressing and wild-type cells using HPLC analysis.
- Conducting bystander experiments and correlating GCV uptake with cell growth inhibition.
Main Results:
- HSV-tk-expressing cells demonstrated significantly higher GCV uptake and phosphorylation compared to wild-type cells.
- A strong positive correlation (r = 0.92) was observed between GCV uptake and tumor cell growth inhibition.
- GCV exhibited slow transport via nucleoside carriers and low affinity for HSV-tk, suggesting it may not be an optimal substrate.
Conclusions:
- GCV accumulation can serve as a reliable indicator of HSV-tk activity and potential therapy outcome in suicide gene therapy.
- The limitations in GCV transport and affinity highlight the need for developing more effective substrates for HSV-tk-based cancer gene therapy.