Involvement of Akt/NF-κB pathway in N6-isopentenyladenosine-induced apoptosis in human breast cancer cells.

N(6)-isopentenyladenosine (i6A) inhibits the tumor cell growth by inducing cell apoptosis in various cancer cell lines. However, little is known regarding the mechanisms by which the drug induces cell apoptosis. In this study, we further explored the molecular mechanisms of i6A as an anticancer agent on a human breast cancer cell line MDA MB 231. Treatment with i6A decreased the cell proliferation of MDA MB 231 cells in a dose-dependent manner by arresting the cells at G(0)/G(1) phase. This effect was strongly associated with concomitant decrease in the level of cyclin D1, cyclin E, cdk2, and increase of p21waf1 and p27kip. In addition i6A also induced apoptotic cell death by increasing the expression of Bax, and decreasing the levels of Bcl-2 and Bcl-xL, and subsequently triggered mitochondria apoptotic pathway (release of cytochrome c and activation of caspase-3). We observed that i6A suppressed the nuclear factor kappaB (NF-κB) pathway and inhibited the Akt activation. The results of this study indicate that i6A decreases cell proliferation and induces apoptotic cell death in human breast cancer cells, possibly by decreasing signal transduction through the Akt/NF-κB cell survival pathway.

Synthesis and evaluation of in vitro anticancer activity of some novel isopentenyladenosine derivatives.

The present study describes the synthesis, the characterization and the evaluation of some derivatives of N(6)-isopentenyladenosine on T24 human bladder carcinoma cells. In particular we have modified the hydroxyl groups in the ribose moiety, the position of the isopentenyl chain in the purine ring and the base moiety. The structures of the compounds were confirmed by standard studies of NMR, MS and elemental analysis. We here show that only two derivatives, 1-(3-methyl-2-butenylamino)-9-(3'-deoxy-beta-d-ribofuranosyl)-purine hydrobromide and 2-amino-6-(3-methyl-2- butenylamino)-9-(beta-d-ribofuranosyl)-purine, inhibit the growth of T24 cells, although to a lower extent than N(6)-isopentenyladenosine. We conclude that the integrity of ribosidic and purine moiety and the N(6) position of the chain are essential for maintaining the antiproliferative activity.

N6-isopentenyladenosine: a potential therapeutic agent for a variety of epithelial cancers.

Isopentenyladenosine (i(6)A) is a product of isopentenyltransferases and, in mammals, occurs either bound to tRNA or as a free nucleoside. Sporadic reports have suggested an anticancer effect of i(6)A, mostly on leukemia cells. The present analysis of 9 human epithelial cancer cell lines derived from different types of malignant tissue revealed complete suppression of clonogenic activity in 8 of the lines after exposure to i(6)A at a concentration of 10 muM. Mechanistic studies showed that i(6)A tumor suppressor activity is associated with inhibition of cell proliferation, a block in DNA synthesis and morphological changes. These results point to i(6)A and to its possible derivatives as a new potential class of wide-spectrum anticancer agents.

Natural occurrence of an inhibitor of mammalian cell growth in human and mouse cells of normal and tumor origin.

N6-(delta2-isopentenyl)adenosine was found both as a component of tRNA and as the cytoplasmic mononucleotide in human leukemic lymphoblasts and myeloblasts from peripheral blood and bone marrow samples. This hypermodified nucleotide was also found in the tRNA and as a mononucleotide in human (MRC-5 and KB) and mouse (A9, FLV, LM, and RAG) cell lines. The relative amounts of this hypermodified nucleotide in the tRNA of the cell lines and the human leukemias were similar (the mean value being 0.06 +/- 0.03 mole % of the total tRNA nucleotide content); whereas the amounts occurring as the free cytoplasmic mononucleotide were more varied but still comparable (the mean value being 0.53 +/- .09 mole % of all cytoplasmic nucleotides) for all cells investigated with the notable exception of all normal, diploid cell lines under study (0.04 mole%). A possible relationship of the free cytoplasmic mononucleotide with the nucleotide in the tRNA for control of mammalian cell protein synthesis in vivo was investigated by addition of N6-(delta2-isopentenyl)adenosine to the culture medium. The exogenously added nucleoside caused inhibition of cell growth within 3 h and cell death within 36 h at concentrations as low as 0.4 muM. No comparable effects were seen when adenosine, adenine, or N6-(delta2-isopentenyl)-adenine were added to the cultures. The simultaneous presence of adenosine in cultures containing N6-(delta2-isopentenyl)adenosine did not alter the detrimental effects of the hypermodified nucleoside on cell growth even when the concentration of adenosine was 50-fold that of N6-(delta2-isopentenyl)adenosine. Addition of N6-(delta2-isopentenyl)adenosine to cell cultures caused within the first 6 h a significant reduction in the rates of RNA and protein synthesis; whereas DNA synthesis continued at a rate comparable to control and adenosine-treated cells for 18 h before decreasing.