Antiviral and cytotoxicity evaluation of 3-nitro-3-deazauridine.

3-Nitro-3-deazauridine (3N-3DU) is a new synthetic nucleoside having activity against members of 5 RNA virus families including: paramyxoviruses (parainfluenza, PIV), picornaviruses (rhino-, RV), rhabdoviruses (vesicular stomatitis, VSV), togaviruses (Semliki Forest, SFV) and bunyaviruses (Punta Toro, PTV). In this report, we evaluate and compare its activity with the parent nucleoside, 3-deazauridine (3DU) and ribavirin as drug standards. Comparison of drug activities utilizes observations of antiviral indices, which are determined by the following formula: maximum tolerated dose (MTD)/minimum inhibitory concentration (MIC). The antiviral index (AI) of 3N-3DU (AI 15.3) was comparable to ribavirin and much higher than 3DU when evaluated against PIV. The 3N-3DU was the most active of the three when tested against RV (AI 24.1), SFV (AI 76.9) or VSV (AI 50). In contrast to the RV activity, 3N-3DU (AI 0.5) and 3DU (AI less than 0.1) were less active than ribavirin (AI 1.3) when evaluated against poliovirus, type 1 (PoV). Ribavirin (AI 10.0) was more active than 3N-3DU (AI 2.4) and 3DU (AI less than 0.1) against PTV. 3N-3DU exhibited comparable toxicity to ribavirin in KB cells, was 4-fold less toxic in WISH cells and 4-fold more toxic in LLC-MK2 cells. Overall, 3N-3DU is markedly less toxic than its parent nucleoside, 3DU. It appears from this study that the structural modification of 3DU resulting from the addition of the nitro group in the 3 position of the base reduces toxicity and enhances the antiviral activity.

3-Deazauridine (NSC 126849): an interesting modulator of biochemical response.

3-Deazauridine (NSC 126849) is a structural analog of uridine that inhibits the biosynthesis of Cytidine-5'-Triphosphate by competitive inhibition of Cytidine Triphosphate synthetase which is considered to be the primary mode of action of this nucleoside analog. Despite a paucity of clinical attention given to this drug as a single agent, it has generated much enthusiasm as a biological response modulator because of its synergistic effect with a number of antitumor agents including Cytosine Arabinoside, 5-aza-2'-deoxycytidine, 5-azacytidine, thymidine and D-galactosamine, although only the cytosine arabinoside/3-Deazauridine combination has been explored clinically. In this paper, the current status of the drug and future perspectives will be discussed.

Pleiotropic mutants of Chinese hamster cells with altered cytidine 5'-triphosphate synthetase.

Following chemical mutagenesis and multiple-step indirect selection, four clones of Chinese hamster V79 cells were isolated which exhibited auxotrophy for thymidine, deoxycytidine, or deoxyuridine but not for cytidine or uridine. All were resistant to uridine, 3-deazauridine, 5-fluorouridine, thymidine, and cytosine arabinoside at concentrations that were toxic to wild-type V79 cells. The cytidine 5'-triphosphate (CTP) and deoxycytidine 5'-triphosphate (dCTP) pools in the mutants were expanded, but the uridine 5'-triphosphate (UTP) pool either decreased or remained unchanged relative to the wild-type level. Furthermore, since the parental cells appear to be deficient in dCMP deaminase activity and CTP (or one of its metabolites) has been shown to inhibit uridine 5'-diphosphate (UDP) reduction, an elevated CTP level should lead to the observed thymidine auxotrophy. It also explains the joint resistance of mutant clones to thymidine and cytosine arabinoside. The change in the ratio of intracellular dCTP to thymidine 5'-triphosphate (dTTP) may be responsible for the elevation in the rates of spontaneous mutations in these mutants.

Cytotoxic and biochemical effects of thymidine and 3-deazauridine on human tumor cells.

Cytotoxicity and perturbations of the deoxyribonucleoside triphosphate pools caused by thymidine were studied in thymidine-sensitive and -resistant human tumor cells. Incubation with 1 mM thymidine reduced cell viability by more than 90% in the three sensitive cell lines (two melanomas and one adrenal carcinoma) and reduced the growth rate without decreasing the viability of resistant LO melanoma cells. Thymidine (1 mM) greatly increased the ratio of the deoxythymidine 5'-triphosphate to deoxycytidine 5'-triphosphate pools in the sensitive cells compared to LO cells and also caused larger relative increases in the pool sizes of deoxyguanosine 5'-triphosphate and deoxyadenosine 5'-triphosphate in the sensitive compared to the resistant cells. 3-Deazauridine, known to inhibit synthesis of deoxycytidine 5'-triphosphate and cytidine 5'-triphosphate in other cell lines, potentiated the cytotoxicity of thymidine for thymidine-sensitive BE melanoma and LO cells. In LO cells, 3-deazauridine (50 microM) decreased the intracellular pool of deoxycytidine 5'-triphosphate to the level obtained with 1 mM thymidine. Lower concentrations of deoxycytidine as compared to cytidine were required to protect BE and LO cells against the cytotoxicity of thymidine plus 3-deazauridine. Deoxycytidine also was more effective than was cytidine in preventing loss of cell viability after exposure to thymidine or to 3-deazauridine individually. In these human melanoma cells, ribonucleotide reductase may be a major site of action of thymidine, of 3-deazauridine, and of both drugs in combination. These results indicate that in human tumor cells the cytotoxic effect of thymidine correlates with greater perturbations of the pyrimidine deoxyribonucleoside 5'-triphosphate pools and that thymidine and 3-deazauridine, which independently reduce the intracellular levels of deoxycytidine 5'-triphosphate, act synergistically against human tumor cells.

Phase I study of 3-deazauridine in the treatment of adults with solid tumors.

A phase I trial of the uridine analog 3-deazauridine was undertaken in 44 adults with solid tumors. The drug was given as a 5-day continuous infusion repeated every 3-4 weeks. The dose-limiting toxic effect was granulocytopenia. Patients with prior nitrosourea therapy or extensive irradiation also had significant thrombocytopenia, and the lowest dose tested, 800 mg/m2/day, was excessive for this group. Mucositis was occasionally severe and was particularly marked in previously irradiated areas. Nausea was mild to moderate. There were isolated episodes of rash, headache, chest pain, and blurred vision. For patients without extensive prior therapy, the recommended dose is 1000 mg/m2/day. No complete or partial remissions were noted.