N6‐isopentenyladenosine arrests tumor cell proliferation by inhibiting farnesyl diphosphate synthase and protein prenylation

Abstract

The physiological effects of a variety of N6-substituted adenine and adenosine derivatives called cytokinins have been documented in plants, but information on their occurrence and function in other biological system is limited. Here we investigated the anti-proliferative effect of N6-isopentenyladenosine (i6A), an adenosine and isoprenoid derivative, in a thyroid cell system, FRTL-5 wild-type, and K-ras transformed KiMol cells. Addition of i6A to FRTL-5 cells caused a dose-dependent arrest of the G0-G1 cell phase transition associated with a reduction of cells in the S phase that was much more evident in KiMol cells. I6A arrested tumor cell proliferation by inhibiting farnesyl diphosphate synthase (FPPS) and protein prenylation. Indeed the addition of farnesol reversed these effects and i6A affected protein prenylation, in particular lamin B processing. I6A effect was not mediated by the adenosine receptor but was due to a direct modulation of FPPS enzyme activity as a result of its uptake inside the cells. I6A inhibited FPPS activity more efficaciously in KiMol cells than in normal FRTL-5. Moreover, the i6A anti-proliferative effect was evaluated in vivo in a nude mouse xenograft model, where KiMol cells were implanted subcutaneously. Mice treated with i6A showed a drastic reduction in tumor volume. Our findings indicate that this isoprenoid end product might be used for antineoplastic therapy, an application emulating that of the lovastatin and/or farnesyl-transferase inhibitors

Pharmacogenomics and analogues of the antitumour agent N6‐isopentenyladenosine

“…Despite abundant evidence of the in vitro antitumour activity of i 6 A, this molecule has only a slight effect, if any, on tumour growth in rodents, 12 as well as in a pilot clinical trial. 13 The reason(s) for this discrepancy may rest in a rapid catabolism 14 or short plasma half-life of i 6 A, in analogy to other nucleosides.…”

“…As a tRNA modification, i 6 A contributes to reading frame maintenance, 3 and the lack of i 6 A in selenocysteine tRNA can affect synthesis of selenoproteins. 4 We previously showed that i 6 A exerts potent in vitro antitumour activity on human epithelial cancer cell lines derived from different types of tumours.…”

“…As a tRNA modification, i 6 A contributes to reading frame maintenance, 3 and the lack of i 6 A in selenocysteine tRNA can affect synthesis of selenoproteins. 4 We previously showed that i 6 A exerts potent in vitro antitumour activity on human epithelial cancer cell lines derived from different types of tumours. 5 Several i 6 A mechanisms of action have been hypothesized, including inhibition of cell proliferation, 5 inhibition of protein prenylation, 6 induction of apoptosis, 7,8 inhibition of DNA, RNA and/or protein synthesis, 2,9 and inhibition of nucleoside transport.…”

“…4 We previously showed that i 6 A exerts potent in vitro antitumour activity on human epithelial cancer cell lines derived from different types of tumours. 5 Several i 6 A mechanisms of action have been hypothesized, including inhibition of cell proliferation, 5 inhibition of protein prenylation, 6 induction of apoptosis, 7,8 inhibition of DNA, RNA and/or protein synthesis, 2,9 and inhibition of nucleoside transport. 10,11 However, the precise mechanism of action of i 6 A in inhibiting cancer cell proliferation in vitro remains to be clarified.…”

“…13 The reason(s) for this discrepancy may rest in a rapid catabolism 14 or short plasma half-life of i 6 A, in analogy to other nucleosides. 15 Here, we performed a gene expression profile analysis of i 6 Atreated cells to clarify the mechanism of action of i 6 A. Furthermore, we analysed 6 i 6 A analogues for their activity on different human cancer cell lines, and performed an in vivo study using 1 of these analogues compared to i 6 A.…”