Abstract 292: Interleukin-12 gene therapy combined with local ablative technique electrochemotherapy for treatment of canine mastocytoma

Electrochemotherapy is now well established ablative local tumor treatment for veterinary as well as human cancer. Electrochemotherapy combines the use of permeabilizing electric pulses applied directly at the tumor site with the injection of chemotherapeutic drugs, cisplatin or bleomycin. Increased membrane permeability enables enhanced entry of chemotherapeutic drug into the cells and resulted in higher tumor cell kill. Up to 80% complete responses are obtained after single electrochemotherapy treatment of cutaneous tumors of different histology (Yarmush et al. Annu Rev Biomed Eng. 2014; 16:295-320). To add a systemic component to this very effective local treatment, in preclinical studies it was combined with several different immune therapies, including gene therapy with plasmid DNA encoding interleukin-12 (IL-12) (Radiol Oncol. 2012;46:302-11). In our on-going clinical research, the effect of IL-12 gene therapy combined with electrochemotherapy was evaluated in 18 client- owned dogs with mastocytomas. Written consent for participation was obtained from the owners and the study was approved by the competent authorities (Veterinary administration and Administration for biotechnology of the Ministry of agriculture and environment; Republic Ethical Committee for the experiments involving animals). Electrochemotherapy using intratumoral injection of bleomycin and application of electric pulses was preformed prior to gene therapy. Plasmid encoding IL-12 was injected peritumorally into the skin and immediately thereafter electric pulses were applied. Local response of tumors was evaluated by measurements of tumors’ size. Systemic response was assessed by determination of IL-12 and IFN-γ in patients’ sera. Safety of gene therapy was evaluated by qRT-PCR measurement for the presence of plasmid DNA at the site of application and possible horizontal gene transfer by in vitro transformation of plasmid DNA encoding IL-12 into the bacteria isolated from the dog's (patient’s) skin. One month after the therapy, 11 dogs (61%) had a complete response, 4 (22%) partial response, and 3 (16%) stable disease. At the end of observation period (median 25 months) 16 dogs (89%) had complete response and 2 had to be euthanized due to the progression of disease. In all dogs, except two, serum IFN-γ or IL-12 levels were detected, without systemic toxicity. At the site of DNA plasmid application, except for one patient, the plasmid was not detected at 1 week post-treatment. No horizontal gene transfer was detected; plasmid was not detected in any of the residential bacteria and in vitro transformation of plasmid into isolated strains was negative. Collectively, the results of our on-going clinical trial demonstrate that IL-12 gene therapy combined with electrochemotherapy is safe, feasible and effective treatment for canine mastocytoma. Citation Format: Maja Cemazar, Jerneja Ambrozic Avgustin, Gregor Sersa, Darja Pavlin, Ana Krhac Levacic, Natasa Tesic, Mitja Rak, Ursa Lampreht, Natasa Tozon. Interleukin-12 gene therapy combined with local ablative technique electrochemotherapy for treatment of canine mastocytoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 292. doi:10.1158/1538-7445.AM2015-292