Cell death was induced by electroporation in HL60 cells, a human promyeloid leukaemia strain, in order to determine by both morphological and biochemical criteria whether necrotic or apoptotic processes occurred. Cells sampled at several times after electroporation were analyzed for the assessment of the following end-points: (i) chromosomal DNA fragmentation; (ii) cell viability; (iii) mono- and oligonucleosomes in the cytoplasmic fraction; (iv) apoptotic index; and (v) morphology of treated cells. The results indicate that about 50% of the cells killed by electroporation die through necrosis, while the remaining 50% of the cells undergo apoptosis. Chromosome damage was also studied by cytogenetic analysis at metaphase. The possibility of killing tumour cells by electroporation, as a variant of electrotherapy, constitutes, in our opinion, a promising procedure in cancer therapy, avoiding the undesirable side effects normally derived from treatment with cytotoxic drugs.

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Since topoisomerase poisons allow the enzyme to cut and covalently bind to DNA but abort the subsequent rejoining of the molecule after relieving the torsional stress. To study their action we have made use of a supercoiled form of the pRYG plasmid that bears a specific topoisomerase recognition and binding region. The conversion of the supercoiled circular double-stranded DNA to the linear and open circle forms in the presence of a topoisomerase II poison and a denaturation step by proteinase K-SDS is indicative of the efficiency of our test agents to stabilize the cleavable complex. Using this system, three glucosylated isoflavones (6'-methoxy-pseudobaptigenin-7-O-beta-glucoside, genistin, and daidzin) isolated from cytotoxic chloroform and ethyl acetate extracts of Retama sphaerocarpa Boissier, were found to have the ability to stabilize the cleavage complex human DNA topoisomerase II.

The effect of DNA ligase from T4 phage on the modulation of the damage induced by bleomycin was studied. CH06 cells were electroporated with either bleomycin alone or bleomycin plus T4 DNA ligase, and both cytogenetic and clonogenic assays were carried out in parallel. Our results show that T4 DNA ligase is able to decrease the frequency of chromosome aberrations in bleomycin-treated cells while increasing cell survival.

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