Safety of Interleukin-12 Gene Therapy Against Cancer: A Murine Biodistribution and Toxicity Study

Abstract

As a prerequisite for a human clinical trial using interleukin (IL)-12 gene therapy, the biodistribution and safety of IL-12, administered as an intradermal naked DNA injection, was evaluated in mice. The pNGVL3-mIL12 plasmid used in this study is a nonviral vector designed to induce a high level of IL-12 protein expression during a transient transfection of the host cell. The biodistribution was evaluated by a polymerase chain reaction (PCR) assay that is capable of detecting less than 100 copies of the plasmid in the context of host DNA. Twenty-four hours after three intradermal injections of 0.5 microg or 5 microg of pNGVL3-mIL12 plasmid, the plasmid was detectable in various internal organs, the blood, and the injection site. The plasmid was detectable in the gonads of only one animal at the high-dose treatment 24 hr after the injections. In the majority of the organs the plasmid was undetectable throughout the study. Possible side effects were monitored by histology and clinical chemistry, and the level of IL-12 protein expression was assessed by enzyme-linked immunosorbent assay (ELISA). No treatment-related histologic abnormalities were detected and the blood chemistry parameters showed no toxicity. The IL-12 protein was undetectable at all times at the injection site and interferon (IFN)-gamma levels at the injection site and in the serum were at background levels. The results of this murine safety study indicate that based on the distribution pattern of the plasmid in the body and the undetectable toxicities in the tissues, the use of the pNGVL3-hIL12 plasmid in cancer gene therapy clinical trials can be considered as safe.

Intratumoral injection of IL-12 plasmid DNA – results of a phase I/IB clinical trial

“…In previous murine studies, we were also unable to demonstrate systemic levels of IL-12 at the same dose evaluated in this study. 50 Thus, the lack of detection of IL-12 in blood samples was not unexpected and is consistent with the lack of systemic toxicity we demonstrated in this study.…”

“…We chose a dose for this clinical trial that was effective with tumors of somewhat similar size in mice, and that was recommended for safety considerations, based on murine safety data and on discussions with the FDA. 50 It is possible that with a higher local dose of IL-12 we would have generated a stronger local effect and may have induced a systemic antitumor effect. We did not measure local IL-12 protein expression to confirm the presence and the amount of gene expression, although this was confirmed in vitro before this study.…”

Evaluation of Toxicity following Electrically Mediated Interleukin-12 Gene Delivery in a B16 Mouse Melanoma Model

“…A successful anticancer treatment protocol should be one that initiates an extensive, rapid immune response without inducing these toxic side effects. Delivery of IL-12 in the form of gene therapy for melanomas has shown some success without serious adverse side effects (3,4) and has reached clinical trials (5).…”

Therapeutic effect of recombinant plasmid-encoded human interleukin-12 in tumor-bearing mice

“…Imboden et al also reported that there were no abnormalities in organ histology and serum biochemical A B markers in mice administered the recombinant plasmid (pNGVL-3-mIL12) at a dose of 0.5 to 5 µg. Levels of serum IFN-γ were also normal, demonstrating that recombinant plasmids containing IL-12 are safe in vivo and could be used in gene therapy (24).…”