Polydeoxyribonucleotides Antagonize Nucleoside Analogues in Cancer Therapy.

Background: In the past years, an increasing number of nucleic acid based drug candidates (e.g. antisense oligonucleotides, aptamers, ribozymes, RNA interference) have been identified and already tested in clinical trials. But until now, no information is available whether these treatment approaches might interfere with chemically related drugs, e.g. nucleoside analogues used in cancer or viral therapy.

Objective: In the current survey we investigated, whether randomly synthesized single-stranded polydeoxyribonucleotides of different length could interfere with the cytotoxic effects of nucleoside analogues (e.g. fludarabine, cytarabine) on lymphocytes or myeloid blasts.

Methods: For this purpose, T-lymphocytes or CD33 positive myeloid blasts (purity >95%) were labelled with [1μM] carboxyfluorescein diacetate, succinimidyl ester (5(6)-CFDA-SE) and incubated with different concentrations of fludarabine or cytarabine (200μM, 20μM und 2μM). Cellular proliferation was induced by addition of CD3/CD28 Dynabeads for the T-cells, or a cytokine cocktail containing 50ng/mL of SCF, 25ng/mL of IL-3, 100ng/mL of GM-CSF, 100ng/mL of G-CSF, 2 U/mL of EPO, 0.47g/L of transferrin, and 5×10-5mmol/L of 2-ME for the myeloid blasts. Random polydeoxribonucleotides of different length (20–80b) and concentrations were added immediately or with a delay of 24, 48 or 72 hours to the assay. After 5 days, quantitative CFDA distribution was measured by flow cytometry to assess the cellular proliferation of the T cells and the myeloid blasts. Moreover, cell viability was measured by trypan blue exclusion. Each experiment was performed at least three times.

Results: Polydeoxyribonucleotides of different length and composition could antagonize the cytotoxic effects of nucleoside analogues (fludarabine, cytarabine) in both, T-cells and myeloid blasts. Thereby, the antagonistic effects of polydeoxyribonucleotides revealed to be concentration- and time dependent. Moreover interference with a equimolar concentrations of polydeoxyribonucletides could be detected even with a delay of 48 hours. Of importance, the concentration of nucleoside analogues used in these experiments, referred to concentrations applied in standard clinical treatment protocols.

Conclusion: Treatment approaches using polydeoxyribonucleotides, might be critical in context with nucleoside analogues, like fludarabine and cytarabine and diminish the efficacy of these drugs. Further experiments are necessary to elucidate the precise mechanism of these effects.