Abstract
N6-substituted adenine and adenosine derivatives called cytokinins have been documented in plants. N6-Isopentenyladenosine (i(6)A), a product of isopentenyltransferases, binds to tRNA and to adenosine receptors. Sporadic reports have suggested an anticancer effect of i(6)A, due to inhibition of cell proliferation, block in DNA synthesis and morphological changes, and have proposed i(6)A and their derivatives as a new potential anticancer agents. AIM of this study was to determine the effect of i(6)A on cell proliferation and survival of thyroid cells.
Methods: the immortalized human thyroid cell line TAD-2 was used as a model of proliferating cells. The cells were treated with i(6)A and cell cycle and survival were analyzed by flow cytometry, DNA ladder analysis and Western blot for caspases and related substrates.
Results: after 12 h of treatment with i(6)A, the cells showed a rouded shaped morphology. i(6)A demonstrated a dose-dependent citotoxic effect with a 100% cell death by 24 h. DNA analysis demonstrated the 200 bp fragmentation characteristic of apoptosis, as also caspase 3 and PARP cleavage. Adenosine demonstrated a potent inhibitory effect on i(6)A citotoxic effect. Co-treatment with adenosine completely prevented the morphology change and apoptosis induced by i(6)A, suggesting that the drammatic effects of i(6)A on cell viability were mediated by adenosine receptors. The citotoxic effect of i(6)A was not observed in cells induced to quiescence by serum withdrawal.
Conclusions: The metabolic effects or direct biological activities of N6-Isopentenyladenosine affected cytoskeleton, proliferation and apoptosis of proliferating thyroid cells. These observations seem to indicate a possible use of N6-Isopentenyladenosine as anticancer drug.