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Secreted human beta-glucuronidase: a novel tool for gene-directed enzyme prodrug therapy
D Weyel1, H H Sedlacek, R Müller
1Institute of Molecular Biology and Tumor Research (IMT), Philipps-University Marburg, Germany.
Abstract:
A major problem of tumor gene therapy is the low transduction efficiency of the currently available vectors. One way to circumvent this problem is the delivery of therapeutic genes encoding intracellular enzymes for the conversion of a prodrug to a cytotoxic drug which can then spread to neighboring non-transduced cells (bystander effect). One possibility to improve the bystander effect could be the extracellular conversion of a hydrophilic prodrug to a lipophilic, cell-permeable cytotoxic drug. Toward this end, we have used a secreted form of the normally lysosomal human beta-glucuronidase (s-betaGluc) to establish an extracellular cytotoxic effector system that converts an inactivated glucuronidated derivative of doxorubicin (HMR 1826) to the cytotoxic drug. We demonstrate that s-betaGluc-transduced tumor cells convert HMR 1826 to doxorubicin which is taken up by both transduced and non-transduced cells. s-betaGluc in combination with HMR 1826 efficiently induces tumor cell killing both in cell culture and in vivo. This effect is mediated through a pronounced bystander effect of the generated cytotoxic drug. Most notably, this gene therapeutic strategy is shown to be clearly superior to conventional chemotherapy with doxorubicin. Gene Therapy (2000) 7, 224-231.
Insights
This study introduces a novel gene therapy approach using secreted beta-glucuronidase to convert a prodrug into a potent cancer drug, enhancing the bystander effect for superior tumor cell killing compared to traditional chemotherapy.
Area of Science:
- Oncology
- Gene Therapy
- Biochemistry
Background:
- Low transduction efficiency of current gene therapy vectors limits efficacy.
- The bystander effect, where therapeutic genes kill neighboring cells, is a key strategy.
- Extracellular prodrug conversion offers a potential improvement for the bystander effect.
Purpose of the Study:
- To develop an extracellular cytotoxic effector system using secreted human beta-glucuronidase (s-betaGluc).
- To evaluate the conversion of a doxorubicin prodrug (HMR 1826) to a cytotoxic drug.
- To assess the efficacy of this system in vitro and in vivo, focusing on the bystander effect.
Main Methods:
- Transduction of tumor cells with a gene encoding secreted human beta-glucuronidase (s-betaGluc).
- Administration of a glucuronidated doxorubicin prodrug (HMR 1826).
- Assessment of HMR 1826 conversion to doxorubicin and subsequent cell killing in cell culture and in vivo models.
Main Results:
- s-betaGluc-transduced cells efficiently converted HMR 1826 to cytotoxic doxorubicin.
- Generated doxorubicin was taken up by both transduced and non-transduced tumor cells.
- The s-betaGluc/HMR 1826 system demonstrated potent tumor cell killing via a strong bystander effect, outperforming conventional doxorubicin chemotherapy.
Conclusions:
- Extracellular conversion of a prodrug by secreted enzymes can enhance gene therapy efficacy.
- This novel gene therapy strategy shows significant promise, offering advantages over traditional chemotherapy.
- The developed system effectively utilizes the bystander effect for improved tumor treatment.