The antitumor mechanism of 1-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)-cytosine: effects of its triphosphate on mammalian DNA polymerases

Synthesis of 4'-Thionucleosides as Antitumor and Antiviral Agents

Many attempts have been made to synthesize structurally novel nucleoside derivatives in order to identify effective compounds for the treatment of tumors and virus-caused disease. At our laboratories, as part of our efforts to synthesize 4'-thionucleosides, we have identified and characterized biologically active nucleosides. During the course of our synthetic study, we developed the Pummerer-type thioglycosylation reaction. As a result, we synthesized a potent antineoplastic nucleoside, 1-(2-deoxy-2-fluoro-β-D-4-thio-arabino-furanosyl)cytosine (4'-thioFAC), and several novel 4'-thionucleosides that possess antiherpes virus activities.

FF-10502, an Antimetabolite with Novel Activity on Dormant Cells, Is Superior to Gemcitabine for Targeting Pancreatic Cancer Cells

In this paper, we report that 1-(2-deoxy-2-fluoro-4-thio-β-d-arabinofuranosyl) cytosine (FF-10502), a pyrimidine nucleoside antimetabolite with a chemical structure similar to gemcitabine, shows beneficial anticancer activity via a novel mechanism of action on dormant cells. The growth inhibition of pancreatic cancer cell lines by FF-10502 (IC₅₀, 60-330 nM) was moderately weaker than that by gemcitabine in vitro. In contrast, an in vivo orthotopic implantation model in mice with established human pancreatic cancer cell line, SUIT-2, revealed no mortality with FF-10502 intravenous treatment, which was related to regression of implanted tumor and little metastasis, whereas 75% of the mice treated with gemcitabine died by day 128. Two in vivo patient-derived xenograft models with gemcitabine-resistant pancreatic cancer cells also demonstrated complete tumor growth suppression with FF-10502, but only partial inhibition with gemcitabine. We also investigated the mechanism of action of FF-10502 by using dormant cancer cells, which are reportedly involved in the development of resistance to chemotherapy. In vitro serum starvation-induced dormant SUIT-2 cells developed resistance to gemcitabine even in combination with DNA damage inducers (DDIs; H₂O₂, cisplatin, and temozolomide). Interestingly, FF-10502 in combination with DDIs significantly induced concentration-dependent cell death in accordance with enhanced DNA damage. FF-10502 was far more potent than gemcitabine in inhibiting DNA polymerase β, which may explain the difference in dormant cell injury, although further investigations for direct evidences are necessary. In conclusion, our study demonstrated the beneficial antitumor effects of FF-10502 in clinically relevant in vivo models, and suggests the importance of preventing DNA repair unlike gemcitabine.

Role of Protein Linked DNA Breaks in Cancer

Topoisomerases are a group of specialized enzymes that function to maintain DNA topology by introducing transient DNA breaks during transcription and replication. As a result of abortive topoisomerases activity, topoisomerases catalytic intermediates may be trapped on the DNA forming topoisomerase cleavage complexes (Topcc). Topoisomerases trapping on the DNA is the mode of action of several anticancer drugs, it lead to formation of protein linked DAN breaks (PDBs). PDBs are now considered as one of the most dangerous forms of endogenous DNA damage and a major threat to genomic stability. The repair of PDBs involves both the sensing and repair pathways. Unsuccessful repair of PDBs leads to different signs of genomic instabilities such as chromosomal rearrangements and cancer predisposition. In this chapter we will summarize the role of topoisomerases induced PDBs, identification and signaling, repair, role in transcription. We will also discuss the role of PDBs in cancer with a special focus on prostate cancer.

Understanding Ribonucleotide Reductase Inactivation by Gemcitabine

This paper focuses on the inhibition of ribonucleotide reductase (RNR) by gemcitabine, 2',2'-difluoro-2'-deoxycytidine (dFdC), a deoxycytidine analogue that is a very active drug against solid tumors and is currently commercialized as gemzar. RNR inactivation is reductant-dependent and occurs in a very different way from that of other known substrate analogues. In the presence of reductants monomer R1 of RNR is inhibited, whereas in the absence of reductants the radical is lost and monomer R2 is inhibited. As inside the cell reductants are available, it is likely that R1 inactivation is the most favorable mechanism responsible for drug cytotoxicity. This inhibition pathway has been unknown to date, but we have conducted a theoretical study that has led us to the first proposal of a mechanism for RNR inhibition by dFdC in the presence of reductants.

Intravesical gemcitabine therapy for superficial transitional cell carcinoma: Results of a Phase II prospective multicenter study

OBJECTIVES

To determine the tolerability and efficacy after 1 year of weekly intravesical gemcitabine therapy in patients with intermediate-risk and high-risk superficial transitional cell carcinoma.

METHODS

A total of 116 patients with intermediate-risk and high-risk bladder cancer who had undergone transurethral resection were treated with one cycle (once a week for 6 weeks) of gemcitabine 2000 mg. Local and systemic tolerability and efficacy were evaluated.

RESULTS

In terms of the tolerability of gemcitabine, 14 patients (12.0%) reported urgency, 6 (5.1%) dizziness and slight fever (less than 38 degrees C), 1 (0.8%) severe abdominal pain, with ulcerative lesions of the bladder mucosa at cystoscopy, and 1 (0.8%) parosmia. The remaining 94 patients (81.3%) did not report any local side effects during the treatment period. In terms of efficacy, recurrence developed in 29 patients (25.4%) a mean of 7 months after transurethral resection; 85 patients (74.6%) were disease free after 12 months. The univariate analysis showed a greater level of efficacy in patients with a first occurrence (P = 0.0408), patients who had had no previous treatment (P = 0.0368), and patients with Stage pTa superficial transitional cell carcinoma (P = 0.0018). The multivariate analysis did not reveal any significant data. No significant differences were found between the intermediate-risk and high-risk patients in tolerability or efficacy. No recurrence developed in 18 (75%) of 24 intermediate-risk bacille Calmette-Guérin-refractory or 7 (43.7%) of 16 high-risk bacille Calmette-Guérin-refractory patients.

CONCLUSIONS

The results of our study have confirmed the good tolerability and 1 year efficacy of intravesical gemcitabine. The treatment schedule proposed resulted in high patient compliance, and the results can be compared with the results of studies using other intravesical treatments.

Anti-tumor efficacy of the nucleoside analog 1-(2-deoxy-2-fluoro-4-thio-?-D-arabinofuranosyl) cytosine (4?-thio-FAC) in human pancreatic and ovarian tumor xenograft models

1-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl) cytosine (4'-thio-FAC) is a deoxycytidine analog that has been shown previously to have impressive anti-proliferative and cytotoxic effects in vitro and in vivo toward colorectal and gastric tumors. In our present studies, the pharmacokinetic behavior in nude mice and the effectiveness of 4'-thio-FAC against human pancreatic and ovarian tumor growth were assessed in comparison with standard chemotherapeutic agents. Potent in vitro anti-proliferative effects were observed against pancreatic (Capan-1, MIA-PaCa-2, BxPC-3) and ovarian (SK-OV-3, OVCAR-3, ES-2) cancer cell lines with IC(50) of 0.01-0.2 microM. In vivo anti-tumor activity was evaluated in nude mice bearing subcutaneously (s.c.) implanted human pancreatic tumor xenografts or intraperitoneally (i.p.) disseminated human ovarian xenografted tumors. Oral daily administration of 4'-thio-FAC for 8-10 days significantly inhibited the growth of gemcitabine-resistant BxPC-3 pancreatic tumors and induced regression of gemcitabine-refractory Capan-1 tumors. 4'-Thio-FAC was also a highly effective inhibitor of ovarian peritoneal carcinomatosis. In the SK-OV-3 and ES-2 ovarian cancer models, 4'-thio-FAC prolonged survival to a greater extent than that observed with gemcitabine. Furthermore, the superiority of 4'-thio-FAC to carboplatin and paclitaxel was demonstrated in the ES-2 clear cell ovarian carcinoma model. Studies provide evidence that 4'-thio-FAC is a promising new alternative to gemcitabine and other chemotherapeutic drugs in the treatment of a variety of tumor indications, including pancreatic and ovarian carcinoma.

Inhibitory Effects of 9-(4-Thio-.BETA.-D-ribo-pentofuranosyl)guanine on Tumor Growth and Angiogenesis

BACKGROUND

To find a nucleoside with anti-angiogenic activity, we tried to screen an active compound from our nucleoside library.

MATERIALS AND METHODS

The compound inhibiting the growth of human umbilical vein endothelial cell (HUVEC) induced by the conditioned medium of lung carcinoma cell line PC-9 was screened. The antitumor activity of the compound was evaluated against murine sarcoma S-180 implanted onto chick embryo chorioallantoic membrane (CAM).

RESULTS

9-(4-Thio-beta-D-ribo-pentofuranosyl)guanine (4'-thioguanosine) was found to be a potent inhibitor of the growth of HUVEC. The growth of S-180 implanted onto CAM was also inhibited by 4'-thioguanosine whereas the in vitro growth of S-180 was not inhibited. The administration of 4'-thioguanosine in mice caused unexpected side effect which suggested neurotoxicity.

CONCLUSIONS

Antitumor effect of 4'-thioguanosine on S-180 was suggested to be due to inhibition of tumor angiogenesis. Because of toxicity of 4'-thioguanosine in mice, further development of the derivatives which have lower toxicity is required.