G3139 is an 18-mer phosphorothioate oligodeoxynucleotide (ODN) which has been targeted on the initiation codon region of the bcl-2 gene. Currently, clinical trials on G3139 for diverse tumors are underway in phase II and phase III. However, basic investigations of bcl-2 antisense ODN (G3139) and reverse ODN (G3622) have not been fully examined. In this report, we investigate cell death caused by G3139 and G3622 and the impact of antisense ODN in melanoma cell lines. We confirmed that G3139 reduced the level of bcl-2 protein and both G3139 and G3622 inhibited cell proliferation and induced apoptosis. G3139 was noted to produce a more intense effect than G3622. Although the general caspase inhibitor, Z-VAD-fmk, prevented apoptosis incompletely, the inhibition ratio of both ODNs was approximately equivalent. Our results suggested that inhibition of cell proliferation by ODNs is produced by apoptosis, but that the apoptotic pathway is not fully induced by the caspase-dependent pathway. Upon examination of the intracellular apoptotic protein dynamics, AIF localized within the mitochondria was translocated to the cytosol within 24 h, and subsequently to the nuclei after 48 h of treatment with G3139. Our results imply the following: the transfection of ODNs can induce apoptosis, the anti-tumor effect of G3139 is better than G3622, and the difference in the anti-tumor effect is specifically based upon the reduction of expression of the target DNA in malignant tumors. We consider that antisense ODNs may be an important tool for anti-tumor chemotherapy and the targeting of specific DNA is important in enhancing the anti-proliferative effect against tumors.

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