Synthesis and Significant Cytostatic Activity of 7-Hetaryl-7-deazaadenosines

Abstract

A series of 7-aryl- and 7-hetaryl-7-deazaadenosines was prepared by the cross-coupling reactions of unprotected or protected 7-iodo-7-deazaadenosines with (het)arylboronic acids, stannanes, or zinc halides. Nucleosides bearing 5-membered heterocycles at the position 7 exerted potent in vitro antiproliferative effects against a broad panel of hematological and solid tumor cell lines. Cell cycle analysis indicated profound inhibition of RNA synthesis and induction of apoptosis in treated cells. Intracellular conversion to triphosphates has been detected with active compounds. The triphosphate metabolites showed only a weak inhibitory effect on human RNA polymerase II, suggesting potentially other mechanisms for the inhibition of RNA synthesis and quick onset of apoptosis. Initial in vivo evaluation demonstrated an effect of 7-(2-thienyl)-7-deazaadenine ribonucleoside on the survival rate in syngeneic P388D1 mouse leukemia model.

7-(2-Thienyl)-7-Deazaadenosine (AB61), a New Potent Nucleoside Cytostatic with a Complex Mode of Action

“…As (i) AB61-TP is not a substrate for human polymerase a(13) or polymerase b, (ii) incorporation of AB61 analogue into cell nuclei was not decreased upon inhibition of replicative but not reparative DNA polymerases by aphidicolin, (iii) gene expression study revealed activation of DNA damage pathway, and (iv) formation of unusually large 53BP1 and/or phospho-gH2AX DNA damage foci in treated tumor cells was observed, we hypothesize that AB61 is incorporated into DNA by polymerases involved in the repair mechanisms, thus further aggravating the local DNA damage in a positive back-loop manner and thereby inducing stronger signal for 53BP1 and/or phospho-gH2AX to accumulate. We had previously reported poor inhibition of RNA polymerase II by AB61-TP (11). Having the evidence that AB61 is incorporated into RNA of exposed cells, the RNA polymerase II is not inhibited, but the RNA synthesis is down regulated, we focused on the possible consequences of AB61 incorporation into mRNA.…”

“…Efficient phosphorylation of AB61 was previously shown in a Du145 prostate cancer cell line (11). Intracellular levels of AB61, its nucleoside monophosphate (AB61-MP), diphosphate (AB61-DP), and triphosphate (AB61-TP) were determined by HPLC analysis after 1-and 3-hour treatment with AB61 (1 mmol/L or 10 mmol/L) in colon cancer cell line (HCT116) and in normal foreskin BJ fibroblasts (Table 2).…”

“…To obtain analytical standards of AB61-derived metabolites, the nucleotides dAB61-MP and AB61-DP were prepared under standard conditions for Suzuki cross-coupling reaction (11,29,30) of the corresponding nucleotide or by phosphorylation of the nucleoside, respectively. [ 3 H]-Labeled AB61 ([ 3 H]AB61) was synthesized by Suzuki cross-coupling reaction of 5-iodotubercidin with 5-chlorothiophene-2-boronic acid followed by tritiation (Fig.…”

“…The most promising derivative among the 7-hetaryl-7-adenosines is a 2-thienyl derivative AB61 (Fig. 1), which is not only highly cytotoxic against leukemic and solid tumor-derived cell lines but also noncytotoxic to normal human fibroblasts (11). In vivo antitumor activity of AB61 was demonstrated in a mouse leukemia survival model.…”

“…The preliminary studies of its mechanism of action in CCRF-CEM lymphoblasts showed fast onset of the RNA synthesis inhibition and also inhibition of DNA synthesis at higher concentrations. AB61 is efficiently phosphorylated to its 5 0 -O-triphosphate (AB61-TP) but only very mild inhibition of RNA polymerase II by AB61-TP was observed (11). More recently, AB61 and its related derivatives were found (17) to be weak inhibitors of human adenosine kinase and AB61 itself was found to be a weak substrate for this enzyme (2%) as compared with adenosine.…”