Enhancement of the antitumor activity of N6-(delta 2-isopentenyl)adenosine against cultured L-1210 leukemia cells by pentostatin using a polymeric delivery system

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

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

Cytotoxic effects of Eleutherococcus senticosus aqueous extracts in combination with N6-(delta 2-isopentenyl)-adenosine and 1-beta-D-arabinofuranosylcytosine against L1210 leukemia cells

The use of the aqueous extracts of Eleutherococcus senticosus in combination with either cytarabine or N6-(delta 2-isopentenyl)-adenosine gave additive antiproliferative effects against L1210 murine leukemia. The ED50 for E. senticosus root extracts against L1210 cells was approximately 75 micrograms/mL. E. senticosus appears to be potentially useful for reducing the concentration of conventional antimetabolites used for their antiproliferative effects on tumor cells.

Increased cytotoxicity of N6-(delta 2-isopentenyl)adenosine in combination with pentostatin against L-1210 leukemia cells

Pentostatin (I), a tight-binding inhibitor of adenosine deaminase, was evaluated in combination with the partially effective antitumor nucleoside N6-(delta 2-isopentenyl)adenosine (II) for cytotoxic activity against cultured L-1210 lymphocytic mouse leukemia cells. Although I alone (less than or equal to 10 micrograms/ml) was ineffective, it significantly potentiated and prolonged the cytotoxic and cytostatic activities of II. The combination of I (2-10 micrograms/ml) with II (25 micrograms/ml) resulted in inhibition of cellular proliferation (80-96%) within 24 hr with maintenance at that level for an extended period of time due to the continued ability of I to prevent the facile deamination of the allylic side chain of II. This type of adjuvant chemoprotection has potential use for other labile oncologic agents.