Received for publication November 30, 2005.
Revised May 4, 2006.
Accepted for publication May 4, 2006.

5'-O-tritylated nucleoside derivatives: inhibition of thymidine phosphorylase and angiogenesis

Abstract

Thymidine phosphorylase (TPase) is one of the key enzymes involved in the pyrimidine nucleoside salvage pathway. However, TPase also stimulates angiogenesis and its expression correlates well with microvessel density and metastasis in a variety of human tumors. We have recently shown that 5'-O-trityl-inosine (KIN59) allosterically inhibits TPase enzymatic activity. KIN59 also inhibits TPase-induced angiogenesis in the chick chorioallantoic membrane (CAM) assay. The trityl group was found to be instrumental to preserve both the anti-TPase and anti-angiogenic effect. We have now synthesized a variety of novel 5'-O-trityl nucleoside derivatives. Enzyme activity studies showed that the anti-TPase activity is significantly improved by replacement of the hypoxanthine base by thymine (3.5-fold, i.e. KIN6), and the introduction of chloride on the trityl group (7-fold, i.e. TP136), whereas removal of 2'-hydroxyl in the ribose did not significantly alter the anti-TPase activity. Enzyme kinetic studies also demonstrated that TP124 [1-(5'-O-trityl-beta-D-ribofuranosyl)thymine], like KIN59, inhibits TPase in a non-competitive fashion both with respect to phosphate and thymidine. Most KIN59 analogues markedly inhibited TPase-induced angiogenesis in the CAM assay. In vitro studies showed that the anti-angiogenic effect of these compounds is not attributed to endothelial cell toxicity. For several compounds, there was no stringent correlation between their anti-TPase and anti-angiogenic activity, indicating that these compounds may also act on other angiogenesis mediators. Interestingly, the anti-angiogenic 5'-O-trityl nucleoside analogues also caused degradation of pre-existing, immature vessels at the site of drug exposure. Thus, 5'-O-trityl nucleoside derivatives combine anti-angiogenic and vascular-targeting activities, which opens perspectives for their potential use as anti-cancer agents.

Key words: Enzymology, Nucleoside/Nucleotide derivatives, Angiogenesis