Vascular disrupting action of electroporation and electrochemotherapy with bleomycin in murine sarcoma

Abstract

Electrochemotherapy has a direct cytotoxic effect on tumour cells, and presumably, a vascular disrupting effect. In this study, on the basis of the prediction of the mathematical model, histological evaluation and physiological measurements of the tumours were carried out to confirm that electroporation and electrochemotherapy of tumours have a vascular disrupting action. In the study, SA-1 solid subcutaneous sarcoma tumours in A/J mice were treated by bleomycin (BLM) given intravenously (1 mg kg À1 ), application of electric pulses (8 pulses, 1040 V, 100 ms, 1 Hz) or a combination of both -electrochemotherapy. The vascular effect was determined by laser Doppler flowmetry, power Doppler ultrasonographic imaging and Patent blue staining. The extent of tumour hypoxia was determined immunohistochemically by hypoxia marker pimonidazole and partial pressure of oxygen (pO 2 ) in tumours by electron paramagnetic resonance oximetry. Electrochemotherapy with BLM induced good antitumour effect with 22 days, tumour growth delay and 38% tumour cures. The application of electric pulses to the tumours induced instant but transient tumour blood flow reduction (for 70%) that was recovered in 24 h. During this tumour blood flow reduction, we determined an increase in hypoxic tumour area for up to 30%, which was also reflected in reduced tumour oxygenation (for 70%). According to the described mathematical model, endothelial cells lining in tumour blood vessels are exposed to a B40% higher electric field than the surrounding tumour cells, and therefore easily electroporated, allowing access of high BLM concentration to the cytosol. Consequently, electrochemotherapy has, besides the immediate vascular disrupting action, also a delayed one (after 24 h), as a consequence of endothelial cell swelling and apoptosis demonstrated by extensive tumour necrosis, tumour hypoxia, prolonged reduction of tumour blood flow and significant tumour growth delay, and tumour cures. Our results demonstrate that in addition to the well-established direct cytotoxic effect on tumour cells, electrochemotherapy also has an indirect vascular disrupting action resulting altogether in extensive tumour cell necrosis leading to complete regression of tumours.

Selective Electroporation of Liver Tumor Nodules by Means of Hypersaline Infusion: A Feasibility Study

“…Actually, it would imply to infuse the hypersaline solution through the hepatic artery rather than through the portal vein. Briefly: the difference in conductivity between blood and endothelia causes an electric field concentration in the vessel walls [8]. As a consequence, thin vessels are likely to be disrupted during any tissue electroporation treatment.…”

Comparison between hypoxic markers pimonidazole and glucose transporter 1 (Glut-1) in murine fibrosarcoma tumours after electrochemotherapy

“…11 In the present study we compared two hypoxia markers and two consecutive sec tions from each tumour were therefore analysed. Glut-1 expression and pimonidazole binding were visualised by immunohistochemistry.…”

Potentiation of the Antitumour Effect of Cisplatin by Administering Local Electrical Pulses to Metastatic Lesions of Hamster Oral Fibrosarcoma

“…The application of electrical pulses has been reported to injure the vascular endothelial cells of the tissues surrounding tumours, thus decreasing the flow of blood to them 41 . Even in the present study, tumour growth was inhibited and survival prolonged to almost the same extent in the electroporation-only group as in the cisplatin treatment only group.…”