Apoptosis of L1210 Leukemia Cells Induced By 3-Deazaadenosine Analogs - Differential Expression of C-Myc, Nf-Kappa B and Molecular Events

A new class of potent apogens (apoptosis-inducing agents) has been identified, consisting of 3-deazaadenosine (DZA), 3-deaza-(+/-)aristeromycin (DZAri) and 1-beta-D-arabinofuranosyl-1H-imidazo[4,5-(c) under bar]pyridine (ara-3-deazaadenine; DZAra-A). They are inhibitors of S-adenosylhomocysteine hydrolase and indirect inhibitors of methylation. Furthermore, they have also been found to form 3-deaza-nucleotide analogs. The DZA analogs, DZA, DZAri, and DZAra-A, induced DNA fragmentation in a dose-and time-dependent manner, reaching a maximum at 250 mu M after 72 h. Cycloheximide at 0.5 mu g/ml completely blocked the DNA fragmentation induced by 250 mu M of each of the analogs. Interestingly, exogenous 100 mu M L-homocysteine thiolactone abrogated the DNA fragmentation caused by DZAri and DZAra-A? but not by DZA. Flow cytometric analysis showed that DZA arrested the cells in the G(2)/M phase, whereas the S phase was arrested by DZAri. Correlated with the effect of DZA was a rapid decrease in the expression of c-myc, whereas nur77 and GAPDH were unaffected. In comparison, there was an elevated expression of IFN-gamma mRNA without apparent change in bax, p53 or GAPDH mRNA after 24 h. After treatment with DZA, there was an elevated expression of NF-kappa B DNA binding activity, which became more pronounced at 24 h. Simultaneously, there was an apparent disappearance of AP-1 activity. Thus, DZA most likely inhibited the RNA synthesis of c-myc, a reduction of which could trigger a cascade of gene transcription leading to apoptosis in L1210 cells. [References: 42]

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