Research Centered on Plasmid Vectors

Viral vectors are known to be an effective means to deliver DNA into a cell. While they are engineered to improve drug safety, in some cases viral vectors have also been shown to elicit a strong immune response by the host patient.12-13 Research has demonstrated that viral vectors have the ability to insert themselves randomly into the human genome, potentially exposing subjects to mutagenesis and cancer.


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To mitigate these risks, researchers working to develop therapies based on IL-12 considered use of a non-viral vector delivery technology. Researchers at biotechnology company, Celsion Corporation, reported success in constructing a therapeutic gene into a plasmid DNA.14

The team then delivered this plasmid into human subjects with a synthetic gene delivery system.9 The investigational therapy, known as GEN-1, has been shown to produce IL-12 in cells local to the tumor site. The resultant IL-12 mediates most anticancer actions.

The use of a plasmid vector has been shown to support production of sustained levels of IL-12 over several days or in some instances throughout the life of the activated cell.15

Plasmid DNA persists in cells for a longer duration, although the duration of persistence varies with cell type. As the plasmid content per cells is diluted by continued cell division over several days, this process is eventually reduced. Unlike viral vectors, plasmid DNA does not integrate into the human genome and therefore reduces the risk of an uncontrolled persistence of IL-12.

The use of non-viral gene delivery systems also presented some new research challenges. Compared to delivery of IL-12 using viral vectors, gene delivery with plasmid DNA and a synthetic gene delivery system has been shown to be less efficient. Many earlier gene therapy trials involving non-viral vectors were not successful due to suboptimal performance of the delivery system.

Researchers targeted development of more efficient synthetic delivery systems customized for use in distinct modalities where they showed clear potential for optimal performance. Early-stage research indicated that the combination of improved delivery systems with more targeted applications could override challenges with delivery system efficiency.

In efforts to develop a clinically viable IL-12 therapy for oncology applications, researchers also had to overcome previously established pharmacokinetic limitations with rIL-12 therapy. rIL-12 has a short half-life and is typically administered in a series of bolus injections.

This can result in high levels of IL-12 in blood circulation, increasing the risk of systemic toxicity and desensitization to continued treatment. To address this challenge, researchers targeted delivery of IL-12 to the site of administration and worked to maintain target IL-12 levels for several days following a single injection.15

Results showed that gene delivery of IL-12 typically lasted for several days after a single injection, indicating that use of a nanoparticle delivery system had the potential to reduce the risk of systemic circulation of IL-12.

Targeting Ovarian Cancer

In the effort to customize IL-12 therapy delivery mechanisms for use in distinct modalities, opportunities to target ovarian cancer showed strong promise.

Ovarian cancer metastasis is largely confined to the abdominal cavity, and locally advanced disease is the primary cause of death. Initial intraperitoneal and intravenous chemotherapy treatment, following surgical cytoreduction, is the standard of care and is proven superior to intravenous-only chemotherapy treatment in ovarian cancer.16

As a result, use of an IL-12 DNA plasmid vector encased in a nanoparticle delivery system seemed ideally positioned because it could be optimized for peritoneal delivery targeting localized ovarian cancer.

The delivery system PEG-PEI-cholesterol (PPC), which is a component of GEN-1, was shown to be most effective in promoting cellular uptake of the IL-12 plasmid.14

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In patients with cancer where the disease has spread to the peritoneal cavity, there is typically a great amount of tumor cell exposure on the peritoneum and the lining of organs within the space, but the peritoneal cavity also fills with fluid (ascites) which contains many cells and cell types. GEN-1 is being developed as intraperitoneal therapy with the use of a lipopolymer delivery system that works best by intraperitoneal route, supporting the clear potential to have therapeutic benefits in ovarian cancer.9,17-18

References

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  18. Thaker P, Brady W, Bradley W, et al. Phase I study of intraperitoneal IL-12 plasmid formulated with PEG-PEI-cholesterol lipopolymer administered in combination with pegylated liposomal doxorubicin in recurrent or persistent epithelial ovarian, fallopian tube, or primary peritoneal cancer patients: an NRG/GOG study. J Clin Oncol. 2015 (suppl; abstr 5541).