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Self Amplifying RNA IL-12 Delivery Enhanced Tumor Control In Mice: Silva-Pillipich et al. (Cell: 2022)

Alphavirus vectors utilizing self-amplifying RNA (saRNA) can generate transient yet potent transgene expression while eliciting innate immune responses, making them a promising tool for antitumor therapy. Typically, these vectors are delivered as viral particles, but they can also be administered as RNA. 

To explore this, Silva-Pillipich et al. (Cell: 2022) investigated the in vivo electroporation of Semliki Forest virus (SFV) saRNA for localized treatment of subcutaneous MC38 colorectal tumors in mice. The researchers first optimized the saRNA electroporation conditions within the tumors using an SFV vector carrying the luciferase gene. Subsequently, they assessed the therapeutic potential of this approach using SFV saRNA encoding interleukin-12 (SFV-IL-12), a potent anti-tumor cytokine.

The delivery of SFV-IL-12 saRNA through electroporation significantly enhanced tumor control and improved overall survival compared to mice treated solely with electroporation or SFV-IL-12 saRNA alone. Furthermore, the effectiveness of SFV-IL-12 saRNA electroporation was further enhanced when combined with systemic PD-1 blockade. This therapeutic strategy was validated in a hepatocellular carcinoma tumor model, underscoring its potential as a valuable approach for cancer immunotherapy. Importantly, this method could be readily translated to clinical practice, particularly for tumors accessible via percutaneous means.



Interleukin-12 (IL-12) stands out as one of the most potent anti-tumoral cytokines due to its ability to stimulate T cells, natural killer (NK) cells, and NK T cells, and exert an antiangiogenic effect. However, systemic expression of IL-12 can lead to toxicity, primarily because of the induction of high levels of interferon (IFN)-γ. To address this challenge, strategies have been developed to enable localized expression of IL-12 within tumors, often employing viral vectors encoding this cytokine. These approaches have demonstrated impressive anti-tumor efficacy while minimizing toxicity. Nonetheless, the use of replicative viruses in therapeutic strategies carries inherent risks, and regulatory constraints can hinder their translation into clinical practice.

In light of these challenges, non-viral vectors, particularly RNA vectors, have garnered considerable interest. RNA-based therapies have shown promising expression capabilities and safety profiles, extending beyond vaccines to various therapeutic strategies. The main hurdle for these technologies lies in formulating them to reach target cells at the required therapeutic levels.

This study explores the use of an innovative approach based on in vivo electroporation to introduce self-amplifying RNA (saRNA) derived from Semliki Forest virus (SFV) into tumor cells, encoding the IL-12 transgene. The SFV vector consists of a single positive-strand RNA containing a viral replicase capable of self-amplifying the viral RNA within host cells. Importantly, this vector lacks the genes encoding viral structural proteins, which are replaced by the transgene of interest. The mRNA coding for the desired protein is abundantly amplified from a viral subgenomic promoter (sgPr) present in the negative-strand RNA produced during the replication process. Consequently, this system achieves very high and transient expression of the transgene, while also inducing interferon-I (IFN-I) responses and apoptosis in the transduced cells. In this research, the focus was on optimizing the intratumoral electroporation conditions for SFV saRNA. The results highlighted effective anti-tumor immune responses in murine models of colon and liver cancer when employing the SFV-IL-12 vector delivered through this innovative approach.


Reference 

https://www.cell.com/molecular-therapy-family/nucleic-acids/fulltext/S2162-2531(22)00189-5


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