c-myc Antisense Oligodeoxynucleotides Enhance the Efficacy of Cisplatin in Melanoma Chemotherapy in Vitro and in Nude Mice

This study was designed to assess the efficacy of a new antimelanoma therapeutic strategy that relies on the use of a c-myc antisense 15-mer phosphorothioate oligodeoxynucleotide ([SJODN), in combination with cisplatin (cis-dlamminedichloroplatinwn; DDP), which is currently used in the clinical management ofmelanoma patients. Proliferation and colony formation of melanoma cells were both inhibited by the DDP/c-myc anti sense [SIODN combination to a greater extent than that observed with either agent alone. Inhibition was most effective when DDP was followed by c-myc antisense [SJODNs. Cell cycle flow cytometric analysis of cells exposed to the two agents either alone or In combination demonstrated that (a) c-myc antisense [SIODNs Induced an accumulation of cells in S phase and apoptosis in a fraction of the cells, detectable at day 5 after the beginning of treatment (b) DDP induced a block in G2-M phase detect able at day 1, which was partially recovered, and apoptosis similar in extent to that induced by c-myc antisense [SJODNs; and (c) DDP and c-myc antisense [S]ODNs together Induced arrest in G2-M phase, which was maximum at day 3, Le., delayed as compared to the block induced by DDP. The combination induced a higher percentage of apoptosis, evident at day 3 from the Start of treatment, that correlated with a marked reduction in Bcl-2 expression. Mice bearing human melanoma xenografts and treated sequentially with DDP and c-myc antisense (SIODNs showed a higher inhibition of tumor growth, reduction In the number of lung metastases,and increasem life span comparedwith those treatedwith either agent alone. Together, these data lend support to the development of anticancer therapies involving oncogene-targeted antisense ODNs and conventional antineoplastic drugs