Nucleosides and Nucleotides. 158. 1-(3-C-Ethynyl-β-d-ribo-pentofuranosyl)- cytosine, 1-(3-C-Ethynyl-β-d-ribo-pentofuranosyl)uracil, and Their Nucleobase Analogues as New Potential Multifunctional Antitumor Nucleosides with a Broad Spectrum of Activity

Abstract

We previously designed 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)uracil (EUrd) as a potential multifunctional antitumor nucleoside antimetabolite. It showed a potent and broad spectrum of antitumor activity against various human tumor cells in vitro and in vivo. To determine the structure-activity relationship, various nucleobase analogues of EUrd, such as 5-fluorouracil, thymine, cytosine, 5-fluorocytosine, adenine, and guanine derivatives, were synthesized by condensation of 1-O-acetyl-2,3,5-tri-O-benzoyl-3-C-ethynyl-alpha,beta-D-ribo-pentofur anose (6) and the corresponding pertrimethylsilylated nucleobases in the presence of SnCl4 or TMSOTf as a Lewis acid in CH3CN followed by debenzoylation. The in vitro tumor cell growth inhibitory activity of these 3'-C-ethynyl nucleosides against mouse leukemia L1210 and human nasopharyngeal KB cells showed that 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd) and EUrd were the most potent inhibitors in the series, with IC50 values for L1210 cells of 0.016 and 0.13 microM and for KB cells of 0.028 and 0.029 microM, respectively. 5-Fluorocytosine, 5-fluorouracil, and adenine nucleosides showed much lower activity, with IC50 values of 0.4-2.5 microM, while thymine and guanine nucleosides did not exhibit any activity up to 300 microM. We next evaluated the tumor cell growth inhibitory activity of ECyd and EUrd against 36 human tumor cell lines in vitro and found that they were highly effective against these cell lines with IC50 values in the nanomolar to micromolar range. These nucleosides have a similar inhibitory spectrum. The in vivo antitumor activities of ECyd and EUrd were compared to that of 5-fluorouracil against 11 human tumor xenografts including three stomach, three colon, two pancreas, one renal, one breast, and one bile duct cancers. ECyd and EUrd showed a potent tumor inhibition ratio (73-92% inhibition relative to the control) in 9 of 11 and 8 of 11 human tumors, respectively, when administered intravenously for 10 consecutive days at doses of 0.25 and 2.0 mg/kg, respectively, while 5-fluorouracil showed potent inhibitory activity against only one tumor. Such excellent antitumor activity suggests that ECyd and EUrd are worth evaluating further for use in the treatment of human cancers.

Inhibition of HIF-1α by the anticancer drug TAS106 enhances X-ray-induced apoptosis in vitro and in vivo

“…1-(3-C-ethynyl-b-D-ribo-pentofuranosyl)cytosine (TAS106) was synthesised as described elsewhere (Hattori et al, 1996). Ultrapure nitrogen gas (99.999%) was obtained from Air Water Technical Supply (Ishikari, Japan).…”

“…On the basis of its inhibitory effect on RNA polymerase, TAS106 is known to regulate the expression of its target proteins at the transcriptional level (Maehara et al, 1982;Hattori et al, 1996;Matsuda and Sasaki, 2004). In this study, we examined the effect of TAS106 on the mRNA expression of HIF-1a using semiquantitative RT -PCR.…”

“…The ribonucleoside anticancer drug 1-(3-C-ethynyl-b-D-ribopentofuranosyl)cytosine (TAS106, ECyd) shown in Figure 1A was first synthesised in 1995 and has been developed as a novel anticancer drug (Hattori et al, 1996). When TAS106 (ECyd) is ingested into tumour cells, it is rapidly phosphorylated to ECyd 5 0 -triphosphate, which has the potential to inhibit RNA synthesis because of its inhibition of RNA polymerase, leading to cell death (Shimamoto et al, 2002;Matsuda and Sasaki, 2004).…”

Cellular and Biochemical Mechanisms of the Resistance of Human Cancer Cells to a New Anticancer Ribo‐nucleoside, TAS‐106

“…1) is a new cytidine analogue showing significant cytotoxicity and antitumor activity in preclinical therapeutic models. [1][2][3] The results of several studies show that TAS-106 acts by interfering with RNA metabolism.2, 4-7) Further in vitro studies on RNA polymerase II, an enzyme expressed in the nuclear extracts from HeLa cells, revealed that the triphosphate of TAS-106, ECTP, inhibited in a concentration-dependent manner the activity of that enzyme.4) The action of TAS-106 on RNA polymerase-specific transcription was demonstrated to be without specificity for RNA polymerase I, II or III in K562 human leukemia cells.5) Moreover, in preliminary experiments, RNA polymerase was inhibited competitively by ECTP with a K i value of 21 nM (apparent K m value of CTP, 8.0 µM) in isolated nuclei of FM3A mouse mammary tumor cells.6, 7) ECTP was found to accumulate as the major intracellular metabolite following the exposure of the cells to TAS-106 for 4 h and was then very slowly eliminated from the cells.5, 6) Therefore, intracellular accumulation and retention of the active metabolite ECTP may contribute to the potent cytotoxicity of TAS-106. This profile, considered to reflect a unique mechanism of antitumor activity and cellular metabolism, makes TAS-106 different from other antitumor nucleosides and TAS-106 is a promising candidate as a therapeutic agent for cancer patients.…”

“…1) is a new cytidine analogue showing significant cytotoxicity and antitumor activity in preclinical therapeutic models. [1][2][3] The results of several studies show that TAS-106 acts by interfering with RNA metabolism.…”