Non-viral immune electrogene therapy induces potent antitumour responses and has a curative effect in murine colon adenocarcinoma and melanoma cancer models

Acute Effects of Intratumor DNA Electrotransfer

Intratumor therapeutic DNA electroporation or electrotransfer is in clinical trials in the United States and is under development in many other countries. Acute changes in endogenous gene expression in response to DNA or to pulse application may significantly modulate the therapeutic efficacy of the expressed proteins. Oligonucleotide arrays were used in this study to quantify changes in mRNA expression in B16-F10 mouse melanoma tumors four hours after DNA electrotransfer. The data were subjected to the DAVID v6.8 web server for functional annotation to reveal regulated genes and genetic pathways. Gene ontology analysis revealed several molecular functions related to cytoskeletal remodeling and inflammatory signaling. In B16-F10 cells, F-actin remodeling was confirmed by phalloidin staining in cells that received pulse application alone or in the presence of DNA. Chemokine secretion was confirmed in cells receiving DNA electrotransfer. These results indicate that pulse application alone or in the presence of DNA may modulate the therapeutic efficacy of therapeutic DNA electrotransfer.

Gene Electrotransfer of Plasmid-Encoding IL-12 Recruits the M1 Macrophages and Antigen-Presenting Cells Inducing the Eradication of Aggressive B16F10 Murine Melanoma

Cancer immunotherapy is currently one of the leading approaches in cancer treatment. Gene electrotransfer of plasmids encoding interleukin 12 (IL-12) into the cells leads to the production of IL-12, which drives immune cell polarization to an antitumoral response. One of the cell types that shows great promise in targeting tumor cells under the influence of IL-12 cytokine milieu is that of macrophages. Therefore, the aim of this study was to evaluate gene electrotransfer of antibiotic resistance-free plasmid DNA-encoding murine IL-12 (mIL-12) in mice bearing aggressive B16F10 murine melanoma. IL-12 electrotransfer resulted in the complete long-term eradication of the tumors. Serum mIL-12 and murine interferon γ (mIFNγ) were increased after IL-12 gene electrotransfer. Further on, hematoxylin and eosin (HE) staining showed increased infiltration of immune cells that lasted from day 4 until day 14. Immunohistochemistry (IHC) staining of F4/80, MHCII, and CD11c showed higher positive staining in the IL-12 gene electrotransfer group than in the control groups. Immune cell infiltration into the tumors and the high density of MHCII- and CD11c-positive cells suggest an antitumor polarization of macrophages and the presence of antigen-presenting cells that contributes to the important antitumor effectiveness of IL-12.

Asymmetric Waveforms Decrease Lethal Thresholds in High Frequency Irreversible Electroporation Therapies

Irreversible electroporation (IRE) is a promising non-thermal treatment for inoperable tumors which uses short (50-100 μs) high voltage monopolar pulses to disrupt the membranes of cells within a well-defined volume. Challenges with IRE include complex treatment planning and the induction of intense muscle contractions. High frequency IRE (H-FIRE) uses bursts of ultrashort (0.25-5 μs) alternating polarity pulses to produce more predictable ablations and alleviate muscle contractions associated with IRE. However, H-FIRE generally ablates smaller volumes of tissue than IRE. This study shows that asymmetric H-FIRE waveforms can be used to create ablation volumes equivalent to standard IRE treatments. Lethal thresholds (LT) of 505 V/cm and 1316 V/cm were found for brain cancer cells when 100 μs IRE and 2 μs symmetric H-FIRE waveforms were used. In contrast, LT as low as 536 V/cm were found for 2 μs asymmetric H-FIRE waveforms. Reversible electroporation thresholds were 54% lower than LTs for symmetric waveforms and 33% lower for asymmetric waveforms indicating that waveform symmetry can be used to tune the relative sizes of reversible and irreversible ablation zones. Numerical simulations predicted that asymmetric H-FIRE waveforms are capable of producing ablation volumes which were 5.8-6.3x larger than symmetric H-FIRE waveforms indicating that in vivo investigation of asymmetric waveforms is warranted.

Cytosolic DNA Sensor Upregulation Accompanies DNA Electrotransfer in B16.F10 Melanoma Cells

In several preclinical tumor models, antitumor effects occur after intratumoral electroporation, also known as electrotransfer, of plasmid DNA devoid of a therapeutic gene. In mouse melanomas, these effects are preceded by significant elevation of several proinflammatory cytokines. These observations implicate the binding and activation of intracellular DNA-specific pattern recognition receptors or DNA sensors in response to DNA electrotransfer. In tumors, IFNβ mRNA and protein levels significantly increased. The mRNAs of several DNA sensors were detected, and DAI, DDX60, and p204 tended to be upregulated. These effects were accompanied with reduced tumor growth and increased tumor necrosis. In B16.F10 cells in culture, IFNβ mRNA and protein levels were significantly upregulated. The mRNAs for several DNA sensors were present in these cells; DNA-dependent activator of interferon regulatory factor (DAI), DEAD (Asp-Glu-Ala-Asp) box polypeptide 60 (DDX60), and p204 were significantly upregulated while DDX60 protein levels were coordinately upregulated. Upregulation of DNA sensors in tumors could be masked by the lower transfection efficiency compared to in vitro or to dilution by other tumor cell types. Mirroring the observation of tumor necrosis, cells underwent a significant DNA concentration-dependent decrease in proliferation and survival. Taken together, these results indicate that DNA electrotransfer may cause the upregulation of several intracellular DNA sensors in B16.F10 cells, inducing effects in vitro and potentially in vivo.