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.