7-(2-Thienyl)-7-deazaadenosine (AB61) showed nanomolar cytotoxic activities against various cancer cell lines but only mild (micromolar) activities against normal fibroblasts. The selectivity of AB61 was found to be due to inefficient phosphorylation of AB61 in normal fibroblasts. The phosphorylation of AB61 in the leukemic CCRF-CEM cell line proceeds well and it was shown that AB61 is incorporated into both DNA and RNA, preferentially as a ribonucleotide. It was further confirmed that a triphosphate of AB61 is a substrate for both RNA and DNA polymerases in enzymatic assays. Gene expression analysis suggests that AB61 affects DNA damage pathways and protein translation/folding machinery. Indeed, formation of large 53BP1 foci was observed in nuclei of AB61-treated U2OS-GFP-53BP1 cells indicating DNA damage. Random incorporation of AB61 into RNA blocked its translation in an in vitro assay and reduction of reporter protein expression was also observed in mice after 4-hour treatment with AB61. AB61 also significantly reduced tumor volume in mice bearing SK-OV-3, BT-549, and HT-29 xenografts. The results indicate that AB61 is a promising compound with unique mechanism of action and deserves further development as an anticancer agent.
DNA interstrand cross-linking (ICL) agents are an important group of cytotoxic drugs with the capability of binding covalently between two strands of DNA, thereby preventing vital processes such as replication or transcription in dividing cells. In anticancer therapy however, their potential is limited due to the resistance by various mechanisms. In order to develop highly effective antitumor drugs it is necessary to study both effective ICL formations and their subsequent repair mechanisms. This review presents an overview of development over the past decade and the use of both well-known and new DNA interstrand cross-linking agents. Their potential in applications especially as anticancer chemotherapeutics in the framework of current knowledge of repair mechanisms and development of combined chemotherapy is discussed.
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