Integrated Systems and Technologies Preclinical Validation of Electrochemotherapy as an Effective Treatment for Brain Tumors Birgit Agerholm-Larsen 1,3,5 , Helle K. Iversen 3,5,6 , Per Ibsen 4 , Jakob M. Moller 2 , Faisal Mahmood 1,3 , Kurt Svarre Jensen 1,3,5 , and Julie Gehl 1,3 Abstract Electrochemotherapy represents a strategy to enhance chemotherapeutic drug uptake by delivering electrical pulses which exceed the dielectric strength of the cell membrane, causing transient formation of structures that enhance permeabilization. Here we show that brain tumors in a rat model can be eliminated by electro- chemotherapy with a novel electrode device developed for use in the brain. By using this method, the cytotoxicity of bleomycin can be augmented more than 300-fold because of increased permeabilization and more direct passage of drug to the cytosol, enabling highly efficient local tumor treatment. Bleomycin was injected intracranially into male rats inoculated with rat glia-derived tumor cells 2 weeks before the application of the electrical field (32 pulses, 100 V, 0.1 ms, and 1 Hz). In this model, where presence of tumor was confirmed by magnetic resonance imaging (MRI) before treatment, we found that 9 of 13 rats (69%) receiving electro- chemotherapy displayed a complete elimination of tumor, in contrast to control rats treated with bleomycin only, pulses only, or untreated where tumor progression occurred in each case. Necrosis induced by electro- chemotherapy was restricted to the treated area, which MRI and histology showed to contain a fluid-filled cavity. In a long-range survival study, treatment side effects seemed to be minimal, with normal rat behavior observed after electrochemotherapy. Our findings suggest that electrochemotherapy may offer a safe and effective new tool to treat primary brain tumors and brain metastases. Cancer Res; 71(11); 3753–62. Ó2011 AACR. Introduction Primary and secondary malignant tumors of the brain constitute a significant challenge in cancer treatment. Surgery, radiotherapy, and medical treatment are advancing, but the prognosis is still grim and morbidity considerable (1, 2). Electroporation-based treatments may be a new contribu- tor in inhibiting tumor recurrence, while giving rise to limited side effects (3–7). Electroporation—permeabilization of mem- branes by electrical pulses—has become an expanding research field, both within nonthermal irreversible electro- poration from which cell membranes do not recover and cell death ensues (3, 4, 7–9), and within reversible electroporation where cell membranes do reseal and only transiently allow drugs (10, 11) or genes (12–20) to enter the otherwise intact cell. Electrochemotherapy designates the use of electroporation to enhance local uptake of chemotherapeutic agents (21–24), enabling an increase in cytotoxicity of a staggering 300-fold in the case of bleomycin. What is well known is that electro- chemotherapy with its high efficiency may be used as a once- only treatment, and that no treated cancer histology has yet been unresponsive to the treatment (25). Both these factors are an advantage for tumors in internal organs, including intra- cranial tumors. Electroporation-based treatments in internal organs are ongoing (www.clinicaltrials.gov; refs. 26, 27). Bleomycin is well known in oncology and is used in standard treatment regimens; for example, its use in testicular cancer (28) and intracerebral use are well described (29). The choice of bleomycin as the cytotoxic agent for electrochemotherapy has been previously described (5, 6, 22, 25, 30–32) and has a solid scientific base; thus, bleomycin acts as an enzyme creating 10 to 15 DNA strand breaks per molecule (33), which is a far more efficient rate than any other chemotherapeutic agent. Bleomy- cin is large, charged, and hydrophilic, and the cell membrane will under normal circumstances keep it from the actual target of the drug, namely DNA. Electroporation offers direct access over the cell membrane in the area encompassed by the electrodes, allowing bleomycin to exert its cytotoxic potential much more efficiently. Bleomycin as a single drug has been tried in the treatment of brain tumors before, with acceptable toxicity but limited efficacy (29). Only one previous study, by Salford and colleagues (34), investigated the use of reversible electroporation in a rat brain tumor model facilitating the Authors' Affiliations: Departments of 1 Oncology and 2 Radiology, and 3 Center for Experimental Drug and Gene Electrotransfer (C*EDGE), Copenhagen University Hospital Herlev, Herlev; 4 Department of Pathol- ogy, Copenhagen University Hospital Herlev and Hvidovre; and 5 Glostrup Research Institute and 6 Department of Neurology, Copenhagen University Hospital Glostrup, Glostrup, Denmark Corresponding Author: Julie Gehl, Department of Oncology, 54B1, Copenhagen University Hospital Herlev, 54B1, Herlev Ringvej 75, DK- 2730 Herlev, Denmark. Phone: 45-44884488; Fax: 45-44883010. E-mail: juge@heh.regionh.dk doi: 10.1158/0008-5472.CAN-11-0451 Ó2011 American Association for Cancer Research. Cancer Research www.aacrjournals.org 3753 Downloaded from http://aacrjournals.org/cancerres/article-pdf/71/11/3753/2869809/3753.pdf by guest on 12 April 2023