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Electrotransfer of plasmid DNA radiosensitizes B16F10 tumors through activation of immune response
Monika Savarin1, Urska Kamensek1, Maja Cemazar2
1Department of Experimental Oncology, Institute of Oncology Ljubljana, Ljubljana, Slovenia.
Background:
Tumor irradiation combined with adjuvant treatments, either vascular targeted or immunomodulatory, is under intense investigation. Gene electrotransfer of therapeutic genes is one of these approaches. The aim of this study was to determine, whether gene electrotransfer of plasmid encoding shRNA for silencing endoglin, with vascular targeted effectiveness, can radiosensitize melanoma B16F10 tumors.
Materials And Methods:
The murine melanoma B16F10 tumors, growing on the back of C57Bl/6 mice, were treated by triple gene electrotransfer and irradiation. The antitumor effect was evaluated by determination of tumor growth delay and proportion of tumor free mice. Furthermore, histological analysis of tumors (necrosis, apoptosis, proliferation, vascularization, presence of hypoxia and infiltration of immune cells,) was used to evaluate the therapeutic mechanisms.
Results:
Gene electrotransfer of plasmid silencing endoglin predominantly indicated vascular targeted effects of the therapy, since significant tumor growth delay and 44% of tumor free mice were obtained. In addition, irradiation had minor effects on radioresistant melanoma, with 11% of mice tumor free. The combined treatment resulted in excellent effectiveness with 88% of mice tumor free, with more than half resistant to secondary tumor challenge, which was observed also with the plasmid devoid of the therapeutic gene. Histological analysis of tumors in the combined treatment group, demonstrated similar mode of action of the gene electrotransfer of plasmid encoding shRNA for silencing endoglin and devoid of it, both through the induction of an immune response.
Conclusions:
The results of this study indicate that irradiation can in radioresistant melanoma tumors, by release of tumor associated antigens, serve as activator of the immune response, besides directly affecting tumor cells and vasculature. The primed antitumor immune response can be further boosted by gene electrotransfer of plasmid, regardless of presence of the therapeutic gene, which was confirmed by the high radiosensitization, resulting in prolonged tumor growth delay and 89% of tumor free mice that were up to 63% resistant to secondary challenge of tumor. In addition, gene electrotransfer of therapeutic plasmid for silencing endoglin has also a direct effect on tumor vasculature and tumors cells; however in combination with radiotherapy this effect was masked by pronounced immune response.
Insights
Gene electrotransfer combined with irradiation significantly enhances tumor eradication in radioresistant melanoma. This approach primes an immune response, leading to prolonged tumor growth delay and lasting resistance to secondary tumors.
Area of Science:
- Oncology
- Gene Therapy
- Immunology
Background:
- Adjuvant treatments combined with tumor irradiation are under investigation for enhanced cancer therapy.
- Gene electrotransfer (GE) is an emerging approach for delivering therapeutic genes.
- The study investigates GE of endoglin-silencing shRNA to radiosensitize melanoma.
Purpose of the Study:
- To evaluate if GE of endoglin-silencing shRNA can radiosensitize melanoma B16F10 tumors.
- To assess the vascular-targeted effectiveness of endoglin silencing via GE.
- To determine the combined efficacy of GE and irradiation against melanoma.
Main Methods:
- Murine melanoma B16F10 tumors were treated with GE and irradiation.
- Antitumor effects were measured by tumor growth delay and tumor-free survival.
- Histological analyses assessed tumor necrosis, apoptosis, proliferation, vascularization, hypoxia, and immune cell infiltration.
Main Results:
- GE of endoglin-silencing plasmid showed vascular-targeted effects, yielding significant tumor growth delay and 44% tumor-free mice.
- Irradiation alone had limited effects on radioresistant melanoma (11% tumor-free).
- The combined treatment achieved 88% tumor-free survival, with significant resistance to secondary tumor challenge, irrespective of the therapeutic gene's presence.
Conclusions:
- Irradiation activates the immune response in radioresistant melanoma by releasing tumor-associated antigens.
- GE boosts the primed antitumor immune response, leading to high radiosensitization and prolonged tumor growth delay.
- The combined therapy resulted in 89% tumor-free mice, with 63% resistant to secondary challenge, primarily driven by immune response.
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