Antitumor drug delivery in multicellular spheroids by electropermeabilization

Electrochemotherapy (ECT) is a physical technique that allows cytotoxic molecules to be efficiently released in tumor cells by inducing transient cell plasma membrane permeabilization. The main antitumoral drugs used in ECT are nonpermeant bleomycin and low permeant cisplatin. The method is nowadays applied in clinics as a palliative treatment. In order to improve it, we took advantage of a human 3D multicellular tumor spheroid as a model of tumor to visually and molecularly assess the effect of ECT. We used bleomycin and cisplatin to confirm its relevance and doxorubicin to show its potential to screen new antitumor drug candidates for ECT. Confocal microscopy was used to visualize the topological distribution of permeabilized cells in 3D spheroids subjected to electric pulses. Our results revealed that all cells were efficiently permeabilized, whatever their localization in the spheroid, even those in the core. The combination of antitumor drugs and electric pulses (ECT) led to changes in spheroid macroscopic morphology and cell cohesion, to tumor spheroid growth arrest and finally to its complete apoptosis-mediated dislocation, mimicking previously observed in vivo situations. Taken together, these results indicate that the spheroid model is relevant for the study and optimization of electromediated drug delivery protocols.