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BACKGROUND Three metastatic human melanoma cell lines generated from patient removed lymph nodes and spleen metastasis were established in our laboratory. OBJECTIVE To investigate the mechanisms enhancing the cytotoxic effects of Bleomycin (BLM), herpes simplex virus thymidine kinase/ganciclovir Suicide Gene (SG) and human interferon-β gene (hIFNβ) lipofection in early passages of these melanoma cell lines. METHODS In these cell lines, we determined: cytotoxicity, bystander effect, lipofection efficiencies, apoptosis, necrosis, senescence, colony forming capacity and mitochondrial membrane depolarization after treatments. RESULTS The three assayed cell lines displayed sensitivity to single and combined BLM/gene treatments. BLM improved the antitumor and anti-clonogenic effects of SG and hIFNβ genes. Considering the low lipofection efficiencies (<10%), one of the main causes of the SG and hIFNβ gene effectiveness was their bystander effect. In one of these cell lines, this effect eradicated up to 60% of the cells although <1% expressed the transgene. In the three cell lines, BLM alone or combined with SG or hIFNβ gene significantly increased the percentage of cells exhibiting membrane compromise, DNA damage, and senescence. Interestingly, the strong BLM/hIFNβ gene combination was able to generate from 73% to 98% of non-viable cells. The high proportion of senescent cells induced by BLM alone or combined with genes strongly decreased the clonogenic capacity of surviving cells. CONCLUSION The presented results indicate that BLM improves the antitumor effects of SG and hIFNβ transgene expression. Altogether, these findings strongly support the clinical potential of these combined approaches.