Structure and activity of specific inhibitors of thymidine phosphorylase to potentiate the function of antitumor 2′-deoxyribonucleosides

doi:10.1016/S0006-2952(00)00253-7

Biochemical Pharmacology

Volume 59, Issue 10, 15 May 2000, Pages 1227-1236

https://doi.org/10.1016/S0006-2952(00)00253-7 Get rights and content

Abstract

A new class of 5-halogenated pyrimidine analogs substituted at the 6-position was evaluated as competitive inhibitors of thymidine phosphorylase (TPase). The most potent member of the series was 5-chloro-6-(2-iminopyrrolidin-1-yl)methyl-2,4(1H,3H)-pyrimidinedione hydrochloride (TPI), which has an apparent K_i value of 1.7 × 10⁻⁸ M. TPI selectively inhibited the activity of TPase, but not that of uridine phosphorylase, thymidine kinase, orotate phosphoribosyltransferase, or dihydropyrimidine dehydrogenase. In vitro inhibition studies of TPI using a thymidine analogue, 5-trifluoromethyl-2′-deoxyuridine (F₃dThd), as the substrate demonstrated that F₃dThd phosphorolytic activity was inhibited markedly by TPI (1 × 10⁻⁶ M) in extracts from the liver, small intestine, and tumors of humans, from the liver and small intestine of cynomolgus monkeys, and from the liver of rodents, but not from the liver or small intestine of dogs or the small intestine of rodents, suggesting that the distribution of TPase differs between humans and animal species, and that TPI could contribute to the modulation of TPase in humans. When F₃dThd or 5-iodo-2′-deoxyuridine (IdUrd) was coadministered to mice with TPI at a molar ratio of 1:1, the blood levels of F₃dThd (or IdUrd) were about 2-fold higher than when F₃dThd (or IdUrd) was administered alone. In monkeys, the maximum concentration (C_max) and the area under the concentration–time curve (AUC) after oral F₃dThd alone were 0.23 μg/mL and 0.28 μg · hr/mL, respectively, but markedly increased to 15.18 μg/mL (approximately 70-fold) and 28.47 μg · hr/mL (approximately 100-fold), respectively, when combined with equimolar TPI. Combined oral administration of TPI significantly potentiated the antitumor activity of F₃dThd on AZ-521 human stomach cancer xenografts in nude mice. In conclusion, TPI may contribute not only to inhibition of TPase-mediated biological functions but also to potentiation of the biological activity of various 2′-deoxyuridine and thymidine derivatives by combining with them.

Section snippets

Chemicals and animals

The compounds with TPase inhibitory activity were synthesized at the Taiho Pharmaceutical Co., Ltd. [6-³H]dThd (603.1 GBq/mmol), [2-¹⁴C]dThd (2.0 GBq/mmol), and [5-³H]Urd (925 GBq/mmol) were obtained from New England Nuclear, Moravek Biochemicals Inc., and Amersham Life Science, respectively. [6-³H]F₃dThd (366.3 GBq/mmol) and [6-³H]5-FU (854.7 GBq/mmol) were obtained from Moravek Biochemicals Inc. F₃dThd and 5-trifluoromethyluracil were purchased from the Yuki Gosei Kogyo Co., Ltd. and PCR

Inhibitory effects of thymidine analogs substituted at the 3′- or 5′-position

To develop TPase specific inhibitors, we focused first on modifying the sugar portion (3′- or 5′-position) of deoxynucleoside analogs. As shown in Table 1, none of the 3′- and 5′-substituted 2′-deoxynucleosides tested inhibited TPase activity. About 100 pyrimidine derivatives substituted with alkyl, phenyl, and carbonyl residues instead of the deoxyribose moiety at the N-1 position also had no inhibitory activity at concentrations up to 0.1 mM (data not shown).

Inhibitory activity of 6-substituted 5-chlorouracil derivatives

Since Niedzwicki et al.[19] had

Discussion

Inhibitors of pyrimidine nucleoside phosphorylases may serve as useful modulators by inhibiting the catabolism of pyrimidine nucleoside analogs such as FdUrd, F₃dThd, and IdUrd that possess chemotherapeutic activity. Pyrimidine phosphorylase inhibitors have been reported by several investigators. Baker and Kelley [36] reported finding that 5-benzyluracil inhibits the activity of uridine phosphorylase from Walker 256 cells with an ic₅₀ value of 1.4 × 10⁻⁶ M. Niedzwicki et al.[15] also reported

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Citation Excerpt :
In addition, it significantly reduced the growth rate of KB/TP cell transplantation in nude mice at a dose of 50 mg/kg/d. In the next year, Fukushima and coworkers prepared the same type of pyrimidine analogs (5 and 6) and tested their inhibitory activity on human TP (hTP) (Fig. 3) (Fukushima et al., 2000). The study also found compound 5a (IC50 = 0.035 μM) presented better potency against TP in the series 5.
Thymidine phosphorylase (TP) is an important enzyme for the synthesis and decomposition of pyrimidine, which can specifically catalyze the reversible phosphorolysis of thymidine to thymine and 2-deoxy-α-D-ribose-1-phosphate in the body. TP is highly expressed in many solid tumor tissues and can induce angiogenesis and anti-apoptotic effect, as well as tumor growth and metastasis. Therefore, TP inhibitors play a major role in the treatment. In recent years, a large number of synthetic TP inhibitors have been widely reported. In this article, the research progress of synthetic TP inhibitors was reviewed, including inhibitory activity, cytotoxicity, structure-activity relationship (SAR), inhibitory kinetics, mechanism of interaction and molecular docking. In our reviewed inhibitors, pyrimidine derivatives account for about a half, but it is a lack for research on other biological activities of pyrimidine derivatives and further exploration of the inhibitory mechanism of excellent inhibitors. Meanwhile, application of radiolabeled inhibitors to assess TP expression in tumors and prognosis of cancer chemotherapy in vivo is rarely reported. In addition, the study on the synergistic anticancer activity of TP inhibitors in combination with other anticancer drugs is less. Therefore, it is valuable to look forward to developing more and more potent TP inhibitors and applying them in the clinical treatment of cancer in the future.
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Thymidine phosphorylase (TP) catalyzes the reversible phosphorolysis of thymidine, maintaining nucleoside homeostasis for DNA repair and replication. In many cancers TP is expressed at high levels and promotes thymidine catabolism, ultimately generating 2-deoxyribose (2dDR) that can support multiple procancer processes, including glycation of proteins, alternative metabolism, extracellular matrix remodeling, and angiogenesis. Therefore, inhibition of TP is an attractive anticancer strategy; however, an alternative approach that exploits the catalytic activity of TP to activate 5-fluorouracil (5-FU) prodrugs has been clinically successful. Here, we review the structure, function, and regulation of TP, its multiple supporting roles in cancer growth and survival. We summarize TP inhibitor and prodrug development and propose TP-targeting strategies that could potentiate the action of current therapies.

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Structure and activity of specific inhibitors of thymidine phosphorylase to potentiate the function of antitumor 2′-deoxyribonucleosides

Abstract

Section snippets

Chemicals and animals

Inhibitory effects of thymidine analogs substituted at the 3′- or 5′-position

Inhibitory activity of 6-substituted 5-chlorouracil derivatives

Discussion

J Biol Chem

J Biol Chem

Biochim Biophys Acta

Biochim Biophys Acta

Biochim Biophys Acta

J Biol Chem

J Biol Chem

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Biochem Biophys Res Commun

Prog Growth Factor Res

Eur J Cancer

Biochim Biophys Acta

Studies of fluorinated pyrimidines. XVIII. The degradation of 5-fluoro-2′-deoxyuridine and related compounds by nucleoside phosphorylase

Biochemistry

Thymidine phosphorylaseSubstrate specificity for 5-substituted 2′-deoxyuridines

J Med Chem

Pyrimidine nucleoside phosphorylase in rodents and humans

Jpn J Cancer Chemother