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Cyclic-AMP induction of gap junctional intercellular communication increases bystander effect in suicide gene therapy
G D Carystinos1, M M Katabi, D W Laird
1McGill Centre for Translational Research in Cancer, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec, Canada.
Abstract:
The phenomenon of the "bystander effect" (BE) observed in suicide gene therapy studies leads to the intriguing possibility that cytotoxicity can be achieved even in tumor cells that have not themselves been targeted with novel genetic material. There is considerable data suggesting the role of gap junction-mediated intercellular communication (GJIC) in the BE. Transfer of connexin (Cx)-encoding genes, the building blocks of GJIC, has been shown both in vitro and in vivo to increase the BE. Since the loss of GJIC is a common feature of cancer cells, we examined the consequence of GJIC up-regulation on the BE in suicide gene therapy. We used 8-bromo-cyclic-AMP to induce Cx43 and GJIC. In mixing assays, using various proportions of cells containing viral thymidine kinase delivered by an adenoviral delivery system or stably transduced by a retrovirus vector, 8-bromo-cyclic-AMP enhanced the BE of cell killing using ganciclovir. The induction in cell killing was more significant when a low percentage of the cell population was infected, which is the relevant clinical situation. We have demonstrated that this is not due to an effect on infectivity or suicide gene expression. Since decreased GJIC is part of the transformed phenotype, induction of Cxs provides an element of selectivity to suicide gene therapy. Our study adds strength to the rationale to develop clinically tolerable GJ inducers to potentiate the effect of suicide gene therapy via the BE.
Insights
The bystander effect (BE) in suicide gene therapy can be enhanced by increasing gap junction-mediated intercellular communication (GJIC). Upregulating GJIC boosts cancer cell killing, even when few cells are targeted.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapy
Background:
- The bystander effect (BE) in suicide gene therapy allows killing of non-targeted tumor cells.
- Gap junction-mediated intercellular communication (GJIC) plays a role in the BE.
- Loss of GJIC is common in cancer cells.
Purpose of the Study:
- To investigate the effect of up-regulating GJIC on the BE in suicide gene therapy.
- To determine if GJIC induction can enhance cancer cell killing in a clinically relevant scenario.
Main Methods:
- Utilized 8-bromo-cyclic-AMP to induce connexin 43 (Cx43) and GJIC.
- Performed mixing assays with varying proportions of cells treated with viral thymidine kinase (via adenoviral or retroviral vectors).
- Administered ganciclovir to induce cell killing.
Main Results:
- 8-bromo-cyclic-AMP significantly enhanced the BE and ganciclovir-induced cell killing.
- The enhancement was more pronounced when a low percentage of cells were infected, mimicking clinical conditions.
- The effect was independent of infectivity or suicide gene expression.
Conclusions:
- Inducing GJIC potentiates the bystander effect in suicide gene therapy.
- Connexin induction offers selectivity to suicide gene therapy due to decreased GJIC in cancer cells.
- Development of clinically tolerable GJ inducers is warranted to enhance suicide gene therapy efficacy.