Facile synthesis and cytotoxicity of substituted uracil-1'(N)-acetic acid and 4-pyridone-1'(N)-acetic acid esters of 20(S)-camptothecins.

A series of novel substituted uracil-1'(N)-acetic acid esters (5-9) and 4-pyridone-1'(N)-acetic acid esters (10-11) of 20(S)-camptothecins (CPTs) have been synthesized by the acylation method. All of these new esters were assayed for in vitro cytotoxicity against five human cancer cell lines A549, Bel7402, BGC-823, HCT-8 and A2780. The in vitro bioassay results showed that all the synthesized compounds 5-11 had cytotoxities that were higher than TPT and comparable to CPT on these five tumor cell lines, some of them even showed comparable or superior cytotoxic activity to CPT. The in vitro data exhibited the cytotoxicity of the ester depended on that of its parent compound. The ester 5, 6, 8, 10, 11 even possessed the cytotoxity activity comparable to or even a little better than CPT on A549, HCT-8 and A2780. The compound 11 had the same level of cytoxity on Bel7402 as that of CPT. Here the synthesis and the in vitro antitumor evaluation of a series of novel 20-O-linked substituted uracil-1'(N)-acetic acid and 4-pyridone-1'(N)-acetic acid esters derivatives of CPTs are reported.

BODIPY-fused uracil: synthesis, photophysical properties, and applications.

Fluorescent nucleobase and nucleic acid analogs are important tools in chemical and molecular biology as fluorescent labelling of nucleobases has applications in cellular imaging and anti-tumor activity. Boron-dipyrromethene (BODIPY) dyes exhibiting high brightness and good photostability are extensively used as fluorescent labelling agents and as type II photosensitizers for photodynamic therapy. Thus, the combination of nucleobases and BODIPY to obtain new compounds with both anti-tumor activity and fluorescent imaging functions is the focus of our research. We synthesized two new nucleobase analogs 1 and 2 by fusing the BODIPY core directly with uracil which resulted in favorable photophysical properties and high emission quantum efficiencies particularly in organic solvents. Further, we explored the newly synthesized derivatives, which possessed good singlet oxygen generation efficiencies and bio-compatibility, as potential PDT agents and our results show that they exhibit in vitro anti-tumor activities.

Uracil hydrazones: design, synthesis, antimicrobial activities, and putative mode of action.

BACKGROUND: Crop diseases caused by plant pathogenic fungi and bacteria have led to substantial losses in global food production. Chemical pesticides have been widely used as a primary means to mitigate these issues. Nevertheless, the persistent and excessive use of pesticides has resulted in the emergence of microbial resistance. Moreover, the improper application and excessive utilization of pesticides can contribute to environmental pollution and the persistence of pesticide residues. Consequently, the development of novel and highly effective bactericides and fungicides to combat plant pathogens holds immense practical importance. RESULTS: A series of uracil hydrazones IV-B was deliberately designed and evaluated for their antimicrobial efficacy. The results of bioassays indicated that most IV-B exhibited >80% inhibition against the fungal species Monilia fructigena and Sclerotium rolfsii, as well as the bacterial species Clavibacter michiganensis subsp. michiganensis, Xanthomonas oryzae pv. oryzae, and Ralstonia solanacearum, at 50 µg/mL in vitro. In vivo, IV-B20 showed 89.9% of curative and 71.8% of protective activities against C. michiganensis subsp. michiganensis at 100 µg/mL superior to thiodiazole copper and copper hydroxide. IV-B20 also showed excellent protective activity against M. fructigena (96.3% at 200 µg/mL) and S. rolfsii (80.4% at 1000 µg/mL), which were greater than chlorothalonil and equivalent to thifluzamide. Mechanistic studies revealed that IV-B20 induced oxidative damage in pathogenic bacteria and promoted the leakage of cellular contents. CONCLUSION: This study suggests that IV-B20 with uracil hydrazone skeleton has great potential as an antimicrobial candidate. These findings lay a foundation for practical application in agriculture. © 2023 Society of Chemical Industry.

Medicinal chemistry aspects of uracil containing dUTPase inhibitors targeting colorectal cancer.

Deoxyuridine-5'-triphosphate nucleotidohydrolase (dUTPase), a vital enzyme in pyrimidine metabolism, is a prime target for treating colorectal cancer. Uracil shares structural traits with DNA/RNA bases, prompting exploration by medicinal chemists for pharmacological modifications. Some existing drugs, including thymidylate synthase (TS) and dUTPase inhibitors, incorporate uracil moieties. These derivatives hinder crucial cell proliferation pathways encompassing TS, dUTPases, dihydropyrimidine dehydrogenase, and uracil-DNA glycosylase. This review compiles uracil derivatives that have served as dUTPase inhibitors across various organisms, forming a library for targeting human dUTPase. Insights into their structural requisites for human applications and comparative analyses of binding pockets are provided for analyzing the compounds against human dUTPase.

The biochemically defined super relaxed state of myosin-A paradox.

The biochemical SRX (super-relaxed) state of myosin has been defined as a low ATPase activity state. This state can conserve energy when the myosin is not recruited for muscle contraction. The SRX state has been correlated with a structurally defined ordered (versus disordered) state of muscle thick filaments. The two states may be linked via a common interacting head motif (IHM) where the two heads of heavy meromyosin (HMM), or myosin, fold back onto each other and form additional contacts with S2 and the thick filament. Experimental observations of the SRX, IHM, and the ordered form of thick filaments, however, do not always agree, and result in a series of unresolved paradoxes. To address these paradoxes, we have reexamined the biochemical measurements of the SRX state for porcine cardiac HMM. In our hands, the commonly employed mantATP displacement assay was unable to quantify the population of the SRX state with all data fitting very well by a single exponential. We further show that mavacamten inhibits the basal ATPases of both porcine ventricle HMM and S1 (Ki, 0.32 and 1.76 µM respectively) while dATP activates HMM cooperatively without any evidence of an SRX state. A combination of our experimental observations and theories suggests that the displacement of mantATP in purified proteins is not a reliable assay to quantify the SRX population. This means that while the structurally defined IHM and ordered thick filaments clearly exist, great care must be employed when using the mantATP displacement assay.

Dextran sulfate sodium and uracil induce inflammatory effects and disrupt the chitinous peritrophic matrix in the midgut of Tribolium castaneum.

Dextran sulfate sodium is used in inflammatory bowel disease (IBD) mice models to trigger chronic intestinal inflammation. In this study, we have analyzed DSS effects in the genetic model and pest beetle, Tribolium castaneum, which can be easily and cost-effectively cultivated and examined in very large quantities compensating for individual variations. We fed the larvae with DSS and uracil, which is known to induce the production of reactive oxygen species by activating DUOX, a member of the NADPH oxidase family. Both chemicals induced IBD-like phenotypes, including impaired growth and development, midgut thickening, epithelial swelling, and a loss of epithelial barrier function. RNAi mediated knockdown of DUOX expression enhanced the effects of DSS and uracil on mortality. Finally, we showed that both treatments result in an altered activity of the intestinal microbiome, similar as observed in IBD patients. Our findings suggest that both chemicals impair the epithelial barrier by increasing the permeability of the peritrophic matrix. The loss of the barrier function may facilitate the entry of midgut bacteria triggering innate immune responses that also affect the intestinal microbiome. As the observed effects resemble those induced by DSS treatment in mice, T. castaneum might be suitable high-throughput invertebrate model for IBD research and preclinical studies.

Effects of six pyrimidine analogs on the growth of Tetrahymena thermophila and their implications in pyrimidine metabolism.

Tetrahymena are ciliated protists that have been used to study the effects of toxic chemicals, including anticancer drugs. In this study, we tested the inhibitory effects of six pyrimidine analogs (5-fluorouracil, floxuridine, 5'-deoxy-5-fluorouridine, 5-fluorouridine, gemcitabine, and cytarabine) on wild-type CU428 and conditional mutant NP1 Tetrahymena thermophila at room temperature and the restrictive temperature (37°C) where NP1 does not form the oral apparatus. We found that phagocytosis was not required for pyrimidine analog entry and that all tested pyrimidine analogs inhibited growth except for cytarabine. IC50 values did not significantly differ between CU428 and NP1 for the same analog at either room temperature or 37°C. To investigate the mechanism of inhibition, we used two pyrimidine bases (uracil and thymine) and three nucleosides (uridine, thymidine, and 5-methyluridine) to determine whether the inhibitory effects from the pyrimidine analogs were reversible. We found that the inhibitory effects from 5-fluorouracil could be reversed by uracil and thymine, from floxuridine could be reversed by thymidine, and from 5'-deoxy-5-fluorouridine could be reversed by uracil. None of the tested nucleobases or nucleosides could reverse the inhibitory effects of gemcitabine or 5-fluorouridine. Our results suggest that the five pyrimidine analogs act on different sites to inhibit T. thermophila growth and that nucleobases and nucleosides are metabolized differently in Tetrahymena.

Synthesis, Base Pairing Properties, and Biological Activity Studies of Platinum(II) Complexes Based on Uracil Nucleosides.

The synthesis and base pairing properties of platinum complexes based on uridine and deoxyuridine nucleosides and preliminary studies of their antiproliferative activity are described. Platinum(II) uridine and deoxyuridine complexes were synthesized by C-I oxidative addition to Pt(0)(PPh3)4. First, the synthesis was performed with protected nucleosides to generate complexes 1 and 2, which were deprotected under basic conditions, affording complexes 3 and 4 in good yields. The synthesis with the unprotected nucleosides was also performed and provided complexes 3 and 4 effectively. Base pairing interactions were measured for complex 1, either for self-base pairing or for the Watson-Crick base pair. Complex 1 undergoes self-base pairing in CDCl3, and this aggregation was found not to be dependent on metalation. Contrastingly, for the Watson-Crick base pair with adenine, base pairing was also observed, but metalation was found to affect hydrogen bonding considerably. Complexes 3 and 4 and the corresponding ligand precursors were evaluated for their antiproliferative activity against human glioblastoma cell line U-251. The compounds showed IC50 values of 3.30 (3) and 1.84 (4) µM but are also toxic for nontumorous cell lines.

Real-world evidence of trifluridine/tipiracil plus bevacizumab in metastatic colorectal cancer using an administrative claims database in Japan.

BACKGROUND: Trifluridine/tipiracil (FTD/TPI) and regorafenib (REG) are standard therapies for refractory metastatic colorectal cancer (mCRC). No results of large real-world data directly comparing FTD/TPI + bevacizumab (BEV) with FTD/TPI or REG monotherapy have been reported. We evaluated the efficacy and safety of FTD/TPI + BEV in a real-world setting. MATERIALS AND METHODS: This retrospective study used a Japanese claims database provided by Medical Data Vision Co., Ltd. (Tokyo, Japan). Eligible patients were aged 20 years and over with a diagnosis of mCRC, and received their first dose of FTD/TPI or REG from 2014 to 2021. The primary endpoint was overall survival (OS) in a propensity score matching (PSM) population in which PSM was carried out by matching using a 1 : 1 ratio for the FTD/TPI + BEV group and the control group (FTD/TPI or REG) by propensity score. To enhance robustness, sensitivity analyses of OS were carried out using the inverse probability treatment weighted (IPTW) approach and the analysis in the all eligible population. Secondary endpoints included time to treatment discontinuation (TTD), incidence of adverse events, and post-treatment. RESULTS: Eligible population was 2369 for the FTD/TPI + BEV group and 9318 for the control group. The PSM population was 1787 for each group. Median OS (mOS) was longer in the FTD/TPI + BEV group compared to the control group [17.0 versus 11.6 months, hazard ratio (HR) = 0.70, P < 0.001] in the PSM population. Similarly, mOS was longer for the FTD/TPI + BEV group compared to that for the control group in IPTW analyses and in the all eligible population (both HRs = 0.68). Median TTD was 3.3 months for the FTD/TPI + BEV group and 1.8 months for the control group in the PSM population (P < 0.001). CONCLUSIONS: Real-world data showed that FTD/TPI + BEV was significantly associated with OS and TTD compared to FTD/TPI or REG. In clinical practice, FTD/TPI + BEV can be a favorable regimen for refractory mCRC.

Crystal structures of non-uracil ring fragments in complex with Mycobacterium tuberculosis uracil DNA glycosylase (MtUng) as a starting point for novel inhibitor design: A case study with the barbituric acid fragment.

Uracil DNA glycosylase (UDG or Ung) is a key enzyme involved in uracil excision from the DNA as a repair mechanism. Designing Ung inhibitors is thus a promising strategy to treat different cancers and infectious diseases. The uracil ring and its derivatives have been shown to inhibit Mycobacterium tuberculosis Ung (MtUng), resulting from specific and strong binding with the uracil-binding pocket (UBP). To design novel MtUng inhibitors, we screened several non-uracil ring fragments hypothesised to occupy MtUng UBP due to their high similarity to the uracil structural motif. These efforts have resulted in the discovery of novel MtUng ring inhibitors. Here we report the co-crystallised poses of these fragments, confirming their binding within the UBP, thus providing a robust structural framework for the design of novel lead compounds. We selected the barbituric acid (BA) ring as a case study for further derivatisation and SAR analysis. The modelling studies predicted the BA ring of the designed analogues to interact with the MtUng UBP much like the uracil ring. The synthesised compounds were screened in vitro using radioactivity and a fluorescence-based assay. These studies led to a novel BA-based MtUng inhibitor 18a (IC50 = 300 µM) displaying ∼24-fold potency over the uracil ring.

Electro-organic synthesis of C-5 sulfenylated amino uracils: Optimization and exploring topoisomerase-I based anti-cancer profile.

Cancer is spreading worldwide and is one of the leading causes of death. The use of existing chemotherapeutic agents is frequently limited due to side effects. As a result, it is critical to investigate new agents for cancer treatment. In this context, we developed an electrochemical method for the synthesis of a series of thiol-linked pyrimidine derivatives (3a-3p) and explored their anti-cancer potential. The biological profile of the synthesized compounds was evaluated against breast (MDAMB-231 and MCF-7) and colorectal (HCT-116) cancer cell lines. 3b and 3d emerged to be the most potent agents, with IC50 values ranging between 0.98 to 2.45 µM. Target delineation studies followed by secondary anticancer parameters were evaluated for most potent compounds, 3b and 3d. The analysis revealed compounds possess DNA intercalation potential and selective inhibition towards human topoisomerase (hTopo1). The analysis was further corroborated by DNA binding studies and in silico-based molecular modeling studies that validated the intercalating binding mode between the compounds and the DNA.

Synthesis of 1-[ω-(Bromophenoxy)alkyl]-3-naphthalenylmethyl Derivatives of Uracil and Their Analogues As Probable Inhibitors of Human Cytomegalovirus Replication.

The synthesis of a new series of 1-[ω-(bromophenoxy)alkyl]-uracil derivatives containing in position 3 naphthalen-1-yl-, naphthalen-2-yl-, 1-bromonaphthalen-2-ylmethyl, benzyl, and anthracene 9-methyl fragment was carried out. The antiviral properties of the synthesized compounds were studied against human cytomegalovirus. It was found that the compound that contained a bridge of five methylene groups has a high anti-cytomegalovirus activity in vitro.

Prodrug Strategies for the Development of ß-l-5-((E)-2-Bromovinyl)-1-((2S,4S)-2-(hydroxymethyl)-1,3-(dioxolane-4-yl))uracil (l-BHDU) against Varicella Zoster Virus (VZV).

Varicella zoster virus (VZV) establishes lifelong infection after primary disease and can reactivate. Several drugs are approved to treat VZV diseases, but new antivirals with greater potency are needed. Previously, we identified ß-l-5-((E)-2-bromovinyl)-1-((2S,4S)-2-(hydroxymethyl)-1,3-(dioxolane-4-yl))uracil (l-BHDU, 1), which had significant anti-VZV activity. In this communication, we report the synthesis and evaluation of numerous l-BHDU prodrugs: amino acid esters (14-26), phosphoramidates (33-34), long-chain lipids (ODE-l-BHDU-MP, 38, and HDP-l-BHDU-MP, 39), and phosphate ester prodrugs (POM-l-BHDU-MP, 41, and POC-l-BHDU-MP, 47). The amino acid ester l-BHDU prodrugs (l-phenylalanine, 16, and l-valine, 17) had a potent antiviral activity with EC50 values of 0.028 and 0.030 µM, respectively. The phosphate ester prodrugs POM-l-BHDU-MP and POC-l-BHDU-MP had a significant anti-VZV activity with EC50 values of 0.035 and 0.034 µM, respectively, and no cellular toxicity (CC50 > 100 µM) was detected. Out of these prodrugs, ODE-l-BHDU-MP (38) and POM-l-BHDU-MP (41) were selected for further evaluation in future studies.

Design and synthesis of uracil/thiouracil based quinoline scaffolds as topoisomerases I/II inhibitors for chemotherapy: A new hybrid navigator with DFT calculation.

In this work, a novel promising hybrid mode of uracil/thiouracil based quinoline pharmacophore i.e. 5a-f was rationalized and synthesized based on rigidification and lipophilic principles, and following the reported pharmacophoric features of camptothecin & doxorubicin. Concurrently, a non-rigid mode pharmacophore i.e. 7a-f was also designed and synthesized. The anti-proliferative activity of the compounds was assessed against three different cancer cell lines, namely A549 lung cancer, MCF-7 breast adenocarcinoma, and HepG-2 hepatic carcinoma. Further, promising candidates were evaluated against A549, and MCF-7 and for their ability to inhibit topoisomerases I &II. Compound 5f was observed to be the most active congener, displaying the highest cell inhibition of 84.4% for topoisomerase I and 92%, for topoisomerase II at a concentration of 100 µM. When its cytotoxicity was evaluated against A549 cells, 5f arrested the cell cycle at the S phase and increased the apoptosis ratio by 46.31%. DFT calculation of 5f showed higher dipole moment and greater negative energy values (-247531.510 kcal/mol) with positive & negative poles, and better stability reflection. Furthermore, molecular docking of 5f to both enzymes showed good agreement with the biological assessment. This study has given insight for further consideration of the highly promising hybrid 5f.

Design, synthesis and antitumor activity of novel pyran-functionalized uracil derivatives: docking studies.

Aim: Synthesis of novel pyran-based uracils that may have potent antitumor activity against hepatocellular carcinoma HepG2 and ovarian cancer SKOV3 cell lines. Materials & methods: Novel pyran-based uracils were synthesized and their anticancer activity was assessed using methyl thiazolyl tetrazolium and wound-healing assays to detect their cytotoxicity and their antiproliferative and antimigratory activities. Results: Compounds 3, 5, 6, 7, 8, 9, 10, 11 and 13 significantly inhibited cell proliferation of the HepG2 cell line. Compounds 7, 8, 9 and 13 significantly inhibited the proliferation of SKOV3 cells, which was also proven through docking studies with topoisomerase I. Conclusion: The molecular docking analysis revealed that 7 and 9 are two major compounds found to possess higher degrees of interaction with DNA gyrase.

Synthesis and Biological Evaluation of Novel Uracil Derivatives as Thymidylate Synthase Inhibitors.

Cell division is driven by nucleic acid metabolism, and thymidylate synthase (TYMS) catalyzes a rate-limiting step in nucleotide synthesis. As a result, thymidylate synthase has emerged as a critical target in chemotherapy. 5-Fluorouracil (5-FU) is currently being used to treat a wide range of cancers, including breast, pancreatic, head and neck, colorectal, ovarian, and gastric cancers The objective of this study was to establish a new methodology for the low-cost, one-pot synthesis of uracil derivatives (UD-1 to UD-5) and to evaluate their therapeutic potential in BC cells. One-pot organic synthesis processes using a single solvent were used for the synthesis of drug analogues of Uracil. Integrated bioinformatics using GEPIA2, UALCAN, and KM plotter were utilized to study the expression pattern and prognostic significance of TYMS, the key target gene of 5-fluorouracil in breast cancer patients. Cell viability, cell proliferation, and colony formation assays were used as in vitro methods to validate the in silico lead obtained. BC patients showed high levels of thymidylate synthase, and high expression of thymidylate synthase was found associated with poor prognosis. In silico studies indicated that synthesized uracil derivatives have a high affinity for thymidylate synthase. Notably, the uracil derivatives dramatically inhibited the proliferation and colonization potential of BC cells in vitro. In conclusion, our study identified novel uracil derivatives as promising therapeutic options for breast cancer patients expressing the augmented levels of thymidylate synthase.

A Pharmacokinetic-Pharmacodynamic Model Predicts Uracil-tegafur Effect on Tumor Shrinkage and Myelosuppression in a Colorectal Cancer Rat Model.

BACKGROUND/AIM: Oral 5-fluorouracil (5-FU)-based prodrugs, used in cancer chemotherapeutic regimens, exhibit large inter- and intra-patient variability in plasma 5-FU concentrations, contributing to treatment failure. Although dosage determination criteria according to plasma drug concentrations are required, the relationship between pharmacokinetics and drug response after multiple oral 5-FU derivative administrations remain unknown. MATERIALS AND METHODS: We evaluated the pharmacokinetics and pharmacodynamics/toxicodynamics of uracil-tegafur (UFT) after multiple administrations in colorectal cancer (CRC) model rats, and applied a pharmacometric approach to describe the time-course alterations of plasma 5-FU concentrations and tumor shrinkage. CRC was induced in rats using 1,2-dimethylhydrazine and dextran sulfate sodium. UFT (30 mg/kg as tegafur) was administered to CRC rats for 14 days. RESULTS: Plasma 5-FU exposure levels increased with the dosing time, and large variations were observed in tumor 5-FU concentrations (32.0-125.8% with coefficient of variation). Although severe hematological toxicities were not observed, a weak correlation was observed between blood platelet count and the plasma 5-FU concentration (r=0.439, p=0.176). A simple pharmacokinetic-pharmacodynamic model was developed comprising of a small number of parameters and successfully describing plasma 5-FU levels and tumor shrinkage after multiple UFT administrations. CONCLUSION: A pharmacometric model approach can help establish the dose-determination criteria based on plasma 5-FU concentration of UFT-based regimens, and contribute to improvement of clinical outcomes.

5-(Perylen-3-ylethynyl)uracil as an antiviral scaffold: Potent suppression of enveloped virus reproduction by 3-methyl derivatives in vitro.

Amphipathic nucleoside and non-nucleoside derivatives of pentacyclic aromatic hydrocarbon perylene are known as potent non-cytotoxic broad-spectrum antivirals. Here we report 3-methyl-5-(perylen-3-ylethynyl)-uracil-1-acetic acid and its amides, a new series of compounds based on a 5-(perylen-3-ylethynyl)-uracil scaffold. The compounds demonstrate pronounced in vitro activity against arthropod-borne viruses, namely tick-borne encephalitis virus (TBEV) and yellow fever virus (YFV), in plaque reduction assays with EC50 values below 1.9 and 1.3 nM, respectively, and Chikungunya virus (CHIKV) in cytopathic effect inhibition test with EC50 values below 3.2 µM. The compounds are active against respiratory viruses as well: severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in cytopathic effect inhibition test and influenza A virus (IAV) in virus titer reduction experiments are inhibited - EC50 values below 51 nM and 2.2 µM, respectively. The activity stems from the presence of a hydrophobic perylene core, and all of the synthesized compounds exhibit comparable 1O2 generation rates. Nonetheless, activity can vary by orders of magnitude depending on the hydrophilic part of the molecule, suggesting a complex mode of action. A time-of-addition experiment and fluorescent imaging indicate that the compounds inhibit viral fusion in a dose-dependent manner. The localization of the compound in the lipid bilayers and visible damage to the viral envelope suggest the membrane as the primary target. Dramatic reduction of antiviral activity with limited irradiation or under treatment with antioxidants further cements the idea of photoinduced ROS-mediated viral envelope damage being the mode of antiviral action.

Novel slow-binding reversible acetylcholinesterase inhibitors based on uracil moieties for possible treatment of myasthenia gravis and protection from organophosphate poisoning.

A series of new compounds in which uracil and 3,6-dimethyluracil moieties are bridged with different spacers were prepared and evaluated in vitro for the acetyl- and butyrylcholinesterase (AChE and BChE) inhibitory activities. These bisuracils are shown to be very effective inhibitors of AChE, inhibiting the enzyme at nano- and lower molar concentrations with extremely high selectivity for AChE vs. BChE. Kinetic analysis showed that the lead compound 2h acts as a slow-binding inhibitor of AChE and possess a long drug-target residence time (τ = 1/koff = 18.6 ± 7.5 min). Moreover, compound 2h ameliorated muscle weakness in myasthenia gravis rat model with a lower effective dose and longer lasting effect than pyridostigmine bromide. Besides, it was shown that compound 2h has an effect of increasing efficiency of antidotal therapy as a pretreatment for poisoning by organophosphates.

Pyrimidine salvage in Toxoplasma gondii as a target for new treatment.

Toxoplasmosis is a common protozoan infection that can have severe outcomes in the immunocompromised and during pregnancy, but treatment options are limited. Recently, nucleotide metabolism has received much attention as a target for new antiprotozoal agents and here we focus on pyrimidine salvage by Toxoplasma gondii as a drug target. Whereas uptake of [3H]-cytidine and particularly [3H]-thymidine was at most marginal, [3H]-uracil and [3H]-uridine were readily taken up. Kinetic analysis of uridine uptake was consistent with a single transporter with a Km of 3.3 ± 0.8 µM, which was inhibited by uracil with high affinity (Ki = 1.15 ± 0.07 µM) but not by thymidine or 5-methyluridine, showing that the 5-Me group is incompatible with uptake by T. gondii. Conversely, [3H]-uracil transport displayed a Km of 2.05 ± 0.40 µM, not significantly different from the uracil Ki on uridine transport, and was inhibited by uridine with a Ki of 2.44 ± 0.59 µM, also not significantly different from the experimental uridine Km. The reciprocal, complete inhibition, displaying Hill slopes of approximately -1, strongly suggest that uridine and uracil share a single transporter with similarly high affinity for both, and we designate it uridine/uracil transporter 1 (TgUUT1). While TgUUT1 excludes 5-methyl substitutions, the smaller 5F substitution was tolerated, as 5F-uracil inhibited uptake of [3H]-uracil with a Ki of 6.80 ± 2.12 µM (P > 0.05 compared to uracil Km). Indeed, we found that 5F-Uridine, 5F-uracil and 5F,2'-deoxyuridine were all potent antimetabolites against T. gondii with EC50 values well below that of the current first line treatment, sulfadiazine. In vivo evaluation also showed that 5F-uracil and 5F,2'-deoxyuridine were similarly effective as sulfadiazine against acute toxoplasmosis. Our preliminary conclusion is that TgUUT1 mediates potential new anti-toxoplasmosis drugs with activity superior to the current treatment.