Assessment of the Effect of Phosphorylated Metabolites of Anti-Human Immunodeficiency Virus and Anti-Hepatitis B Virus Pyrimidine Analogs on the Behavior of Human Deoxycytidylate Deaminase

Abstract

Deoxycytidylate deaminase, catalyzing the conversion of dCMP to dUMP, is an important enzyme in the de novo synthesis of thymidine nucleotides. It also may be involved in the action, as well as the metabolism of anticancer agents. Recently, several L-and D-configuration pyrimidine deoxynucleoside analogs were found to be potent antiviral and antitumor agents. Their interaction with dCMP deaminase as a monophosphate or a triphosphate metabolite is not clear. These include D-nucleoside analogs such as-fluorocytidine, and L-FMAU. None of the L-deoxycytidine analog monophosphates act as substrates or inhibitors. Among these pyrimidine deoxynucleoside analog monophosphates, D-FMAU monophosphate (MP) is the most potent competitive inhibitor, whereas L-FMAUMP has no inhibitory activity. Interestingly, AZTMP and D4TMP also have potent inhibitory activities on dCMP deaminase. Among the dCTP and TTP analogs examined, D-and L-FMAUTP were the most potent inhibitors and had the same extent of inhibitory effect. These results suggest that a chiral specificity for the substrate-binding site may exist, but there is no chiral specificity for the regulator-binding site. This is also supported by the observation that L-OddC and L-FSddC have inhibitory activities as triphosphates but not as monophosphates. None of the D-and L-dCTP analogs activated dCMP deaminase as dCTP. The biological activities of AZT and D4T could be partially attributable to their inhibitory activity against dCMP deaminase by their phosphorylated metabolites, whereas that of ddC and the L-deoxycytidine analogs may not involve dCMP deaminase directly.

The Mechanism of Action of β- d -2′-Deoxy-2′-Fluoro-2′- C -Methylcytidine Involves a Second Metabolic Pathway Leading to β- d -2′-Deoxy-2′-Fluoro-2′- C -Methyluridine 5′-Triphosphate, a Potent Inhibitor of the Hepatitis C Virus RNA-Dependent RNA Polymerase

“…Enzymatic studies with purified human DCTD showed that this enzyme is capable of deaminating PSI-6130-MP to RO2433-MP. This enzyme is believed to be involved in regulating the intracellular concentrations of dCTP and dTTP for DNA synthesis, as the enzyme is activated in the presence of dCTP and is inhibited by dTTP (13,17). Our enzyme kinetic study was performed in the absence of any activators or inhibitors for comparison reasons.…”

Crystal Structures of Streptococcus mutans 2′-Deoxycytidylate Deaminase and Its Complex with Substrate Analog and Allosteric Regulator dCTP·Mg2+

“…gram-negative bacteria Escherichia coli and Salmonella typhimurium, dUMP is synthesized via two steps, namely, the deamination of deoxycytidine-5′-triphosphate (dCTP) to deoxyuridine-5′-triphosphate (dUTP) by dCTP deaminase and the subsequent hydrolysis of dUTP to dUMP by dUTPase. Interestingly, dCD reduces the efficiency of anticancer and antiviral drugs via deamination at the nucleotide level 3,4 ; this indicates that dCD inhibitors have potential applications in chemotherapy.…”

Enantioselectivity of human AMP, dTMP and UMP-CMP kinases

“…Viral polymerases incorporate l -derivatives more readily than do the human ones (20–21). Nucleoside degrading enzymes, such as nucleoside deaminases and phosphorylases, tend to be strictly selective for d -nucleotides although only limited data is available (11,22). The lack of degradation of l -nucleosides has however been demonstrated in mice, where l -nucleosides were gradually excreted in the unchanged form following intraperitoneal administration (5).…”