Antivascular effects of electrochemotherapy: implications in treatment of bleeding metastases

Solid tumors of various etiologies can be treated efficiently by electrochemotherapy (ECT), a combined use of electroporation (EP) and chemotherapeutic drugs, such as bleomycin and cisplatin. EP alone and ECT in particular, induce a profound reduction in tumor blood flow, which contributes to the antitumor effect. After EP and ECT, the time course of blood flow changes and follows the same two-phase pattern. The first rapid and short-lived vasoconstriction phase is followed by the second much longer-lived phase resulting from disrupted cytoskeletal structures and a compromised barrier function of the microvascular endothelium. In the case of ECT, however, tumor vascular endothelial cells are also affected by the chemotherapeutic drug, which leads to irrecoverable damage to tumor vessels and to a further decrease in tumor blood flow within hours after application of ECT. Tumor cells surviving the direct effects of ECT are consequently exposed to lack of oxygen and nutrients and are pushed into the secondary cascade of induced cell death. Clinically, the antitumor effectiveness of ECT has been proven extensively in the treatment of melanoma metastases, with 70-80% complete responses. The antivascular effects of ECT were also exploited for palliative treatment of bleeding melanoma metastases, with immediate cessation of bleeding and very good antitumor effectiveness. The antivascular effect of ECT is of utmost importance for translation of ECT into the treatment of deep-seated tumors, especially in well vascularized organs, such as the liver, where it prevents bleeding of the treated area.