Survival of cancer patients has greatly improved in recent years. However, in many cases, current treatments are still not adequate. Thus, new innovative approaches in cancer treatment are needed. With the advent of molecular techniques, targeted therapies are being developed to increase the specificity of therapeutic molecules to tumor cells, and to decrease the side effects of the treatment, resulting in a good therapeutic index. Another way of increasing therapeutic index is targeted delivery of drugs and rational combination of therapeutic approaches. Our pursuit to improve the therapeutic index comprises of i) development and validation of new, targeted delivery methods ii) targeting tumors with novel therapeutic molecules and iii) validating efficacy of different therapy combinations, with an added emphasis on iv) translating our work into clinics.
We have been extensively involved in the development of biomedical applications of electroporation. The technology utilizes application of electric pulses as a drug delivery system, and it can be applied for delivery of drugs or DNA to tumors and other tissues. Electrochemotherapy is aimed at delivery of chemotherapeutic drugs, such as bleomycin or cisplatin to tumors, and has reached wide clinical acceptance. Gene electrotransfer, on the other hand, is still in development but holds a great potential for clinical application, especially for gene therapy of cancer and DNA vaccination. It has already been tested in first clinical trials, utilizing plasmid encoding immunomodulatory cytokine interleukin12 (IL12), and in the second one, a plasmid encoding antiangiogenic AMEP, where safety and feasibility of the gene electrotransfer were proven.
Recently we have started using cold plasma as a new nonviral gene delivery systems, where the research in gene therapy is only in its beginnings. However, already in this early stages, this technique holds great promise, especially for gene transfer to the skin. Plasma is an ionized gas, which interacts with target tissue and generates reactive species involved in biological processes. Similar to electroporation, plasma creates an electric field at the treatment site sufficient to permeabilize the cell membrane, what makes plasma treatment as a potential non-viral gene delivery method.
Vascular targeted therapies already proved to be effective for cancer treatment, also in combination with radiotherapy, however, due to high toxicity and eventual development of tumor resistance to currently used vascular targeted therapeutics, new targets are being sought. One of such potential new target is endoglin, a co-receptor of TGFβ. We have shown that silencing of endoglin leads to prevention of new vessel growth and the disruption of existing tumor blood vessels.
Another approach to increase the specificity of gene therapy is the use of tissue-specific promoters, which have an added benefit of providing a better safety profile of the therapy. Among the promoters that we are developing are promoters of endothelin, smooth muscle gamma actin, and collagen, which are specifically targeting vasculature, muscle, and skin.
Many biological therapies are already in the clinics as an adjuvant therapy to radiotherapy. Among these, bevacizumab is an example of the successful antiangiogenic approach using antibodies. An alternative to antibodies as an adjuvant therapy is the use of gene electrotransfer to specifically target angiogenesis or to modulate the immune response. This was already demonstrated by our group using plasmid encoding IL12 (Fig 4). Currently, we are exploring the efficacy of our vascular targeting and immune modulating gene therapies as adjuvant therapies for radiotherapy.
Based on our experience with preparing and executing clinical trials in veterinary (in collaboration with Veterinary Faculty, University of Ljubljana) and human oncology, we anticipate translating our knowledge gained in preclinical studies into clinical trials.
Having access to veterinary patients gives us an invaluable platform that represents a stepping stone between pre-clinical research on cells and mice and clinical trials on patients. Thus, we are able to test novel therapies, such as gene electrotransfer, which is still in early stages of clinical testing, on spontaneous tumors in animals that closely resemble human tumors encountered in clinics. In this way, we were already able to show that gene electrotransfer can be an efficient adjuvant therapy to several standard therapies (Fig 5).
We are also furthering the use of electrochemotherapy by running clinical trials for treating deep-seated tumors such as liver metastasis and using ECT in previously not yet treated tumor localities (Fig 6).