A novel transcriptional inhibitor induces apoptosis in tumor cells and exhibits antiangiogenic activity.

Using a high-throughput cell-based assay, we identified a nucleoside analogue 4-amino-6-hydrazino-7-beta-D-ribofuranosyl-7H-pyrrolo(2,3-d)-pyrimidine-5-carboxamide (ARC), which has the properties of a general transcriptional inhibitor. Specifically, ARC inhibits the phosphorylation of RNA polymerase II by positive transcription elongation factor-b, leading to a block in transcriptional elongation. ARC was able to potently repress p53 targets p21 and hdm2 (human homologue of mdm2) protein levels, but dramatically increased p53 levels similar to other transcriptional inhibitors, including flavopiridol. This increase in p53 corresponded to the down-regulation of short-lived protein hdm2, which is a well-established negative regulator of p53. Remarkably, ARC induced potent apoptosis in human tumor and transformed, but not in normal cells, and possessed strong antiangiogenic activity in vitro. Although ARC promoted the accumulation of p53, ARC-induced apoptosis in tumor cells was p53-independent, suggesting that it may be useful for the treatment of tumors with functionally inactive p53. Furthermore, cell death induced by ARC had a strong correlation with down-regulation of the antiapoptotic gene survivin, which is often overexpressed in human tumors. Taken together, our data suggests that ARC may be an attractive candidate for anticancer drug development.