Purine Nucleoside Phosphorylase Inhibitor Research Articles

Abstract 5865: Characterization and resistance mechanisms of PNP inhibitor forodesin-resistant cell lines

Abstract Background: The enzyme purine nucleoside phosphorylase (PNP) is involved in the purine salvage pathway and is present at high levels in lymphoid tissues. Children born with PNP deficiency are known to have significantly reduced T-cell counts but relatively normal B-cell immunity, suggesting PNP as one of the most promising therapeutic targets for T-cell malignancies. Forodesine (For, BCX-1777), a novel PNP inhibitor, was approved in Japan for the treatment of relapsed/refractory PTCL. To understand the cytotoxic effect of For and its mechanism of action, we established a For-resistant (For-R) leukemia cell line and explored the mechanism of resistance. Methods: We established two For-R T-lymphoblastic leukemia cell lines (CCRF-CEM and MOLT4) through repeated escalating exposure to For and 2’-deoxyguanosined(dGuo). Gene expression analysis was performed to identify the mechanisms of resistance. Results: For-R cells showed very high resistance compared to parental cells (IC50 value, CEM/CEM-R 4.2nM/>5x105nM, MOLT4/MOLT4-R 8nM/>5x105nM). When cross-resistance was examined in these For-R cells showed mild resistance to cytarabine. The expression of hENT1, a nucleoside transporter, was examined and found to be upregulated in both CEM-R and MOLT4-R cells, while the expression level of deoxycytidine kinase (dCK) was unchanged in both cells. Next, high performance liquid chromatography was used to assess the intracellular dGTP in each parental and its For-R cells. In the parental cells, intracellular dGTP levels increased promptly 4-6 hours after fosteredin administration, whereas in resistant cells, intracellular dGTP levels were higher than before fosteredin administration, and there was little change in dGTP levels after administration. Conclusion: The established For-R cell line acquired a high resistance to For and showed high intracellular dGTP levels. Imbalance in intracellular GTP levels may be involved in the induction of cell death by For. IC50 value of each cell lines Citation Format: Naoko Hosono, Kana Oiwa, Toshiki Tasaki, Rie Nishi, Luigi Scott, Owen A. O’Connor, Takahiro Yamauchi. Characterization and resistance mechanisms of PNP inhibitor forodesin-resistant cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5865.

Abstract 297: Role of purine metabolism in CLL cell pathobiology and CLL disease progression

Abstract The treatment of Chronic lymphocytic leukemia (CLL) has been revolutionized in recent years, however CLL is still incurable, and the leukemic cells often develop drug resistance. Previous studies show that the interaction of CLL cells with the bone marrow (BM) microenvironment promotes spontaneous and drug induced survival. But the nature of this interaction is still in need of a full understanding. To pursue this we discerned RNA profiles using RNA-seq in paired CLL cells isolated from untreated blood and BM (n=6) and in untreated patients CLL cells (n=4) cultured alone or cocultured with BM stromal cells (BMSCs). CLL cells from blood/BM and CLL cells cultured alone or with BMSCs were examined by Western blot (WB), untargeted metabolomics (LCMS+GCMS) and preclinical drug sensitivity assays. We found upregulation of 232 genes in CLL cells from BM vs the paired blood and 917 genes in cocultured CLL cells compared to CLL cells cultured alone (p&lt0.05, fold change &gt1.5). Here we detected only 13 genes that overlap between BM and cocultured CLL cells. When we analyzed the expression of these 13 genes in blood CLL cells from a cohort of 162 untreated patients by RNA-seq we found a positive relationship between 4 (PNP, C16orf54, MOB3A, CDK2AP2) with CLL patient clinical outcome including overall survival (OS), progression free survival (PFS), and time to first treatment (TTFT) [multivariable Cox proportional hazards models, p&lt0.05]. Out of the 4 genes, purine nucleoside phosphorylase (PNP), an enzyme in the purine salvage pathway, showed the most significant association for patient’s OS, PFS, and TTFT. Metabolomic profiling indicated an increased level of purine salvage pathway metabolites adenosine, inosine, and hypoxanthine in cocultured CLL cells. WB analysis using blood CLL cells from untreated patients showed a variable PNP protein expression (high, low/no PNP) and induction in PNP protein levels were found in blood CLL cells expressing low/no PNP only when in contact with BM/BMSCs. But PNP inhibitor forodesine did not show any significant killing in high vs low/no PNP group. When we treated CLL cells from untreated patients with Bcl2 inhibitors venetoclax, S55746 and LP-118 (Bcl-2/Bcl-xl inhibitor, Newave), CLL cells showed increasing sensitivity to the Bcl2 inhibitors associated with their PNP expression (high&gtlow&gtno PNP). But a covalent and non-covalent BTKi LP-168 (Newave) cultured with CLL cells showed no difference in drug sensitivity associated with CLL PNP levels. In contrast CLL cells when treated with both venetoclax and LP-168, showed more drug sensitivity in the high PNP expressing CLL cells vs low/no PNP. These results indicate that active purine metabolism in CLL cells can contribute to differential novel agent drug responses of CLL patients. Future studies to understand the exact mechanism of how PNP relates to this differential drug sensitivity should be instructive in regard to alternate maneuvers to treat CLL. Citation Format: Sutapa Sinha, Weiguo Han, Zhiquan Wang, Kari G. Rabe, Susan L. Slager, Chantal E. McCabe, Daniel R. O'Brien, Sameer A. Parikh, Esteban Braggio, Yi Chen, Fenlai Tan, Stephen P. Anthony, Yu Chen, Bing Dai, Yue Shen, Neil E. Kay. Role of purine metabolism in CLL cell pathobiology and CLL disease progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 297.

Purine nucleoside phosphorylase inhibition is an effective approach for the treatment of chemical hemorrhagic cystitis.

Hemorrhagic cystitis may be induced by infection, radiation therapy, or medications or may be idiopathic. Along with hemorrhagic features, symptoms include urinary urgency and frequency, dysuria (painful urination), and visceral pain. Cystitis-induced visceral pain is one of the most challenging types of pain to treat, and an effective treatment would address a major unmet medical need. We assessed the efficacy of a purine nucleoside phosphorylase inhibitor, 8-aminoguanine (8-AG), for the treatment of hemorrhagic/ulcerative cystitis. Lower urinary tract (LUT) function and structure were assessed in adult Sprague-Dawley rats, treated chronically with cyclophosphamide (CYP; sacrificed day 8) and randomized to daily oral treatment with 8-AG (begun 14 days prior to CYP induction) or its vehicle. CYP-treated rats exhibited multiple abnormalities, including increased urinary frequency and neural mechanosensitivity, reduced bladder levels of inosine, urothelial inflammation/damage, and activation of spinal cord microglia, which is associated with pain hypersensitivity. 8-AG treatment of CYP-treated rats normalized all observed histological, structural, biochemical, and physiological abnormalities. In cystitis 8-AG improved function and reduced both pain and inflammation likely by increasing inosine, a tissue-protective purine metabolite. These findings demonstrate that 8-AG has translational potential for reducing pain and preventing bladder damage in cystitis-associated LUT dysfunctions.

Forodesine Enhances Immune Responses through Guanosine-Mediated TLR7 Activation while Preventing Graft-versus-Host Disease.

Recent evidence indicates that specific types of nuclear acids, including guanosine and its derivatives, act as natural ligands for TLR7. This led us to hypothesize that purine nucleoside phosphorylase inhibitors not only can induce apoptosis of T cells but also can lead to TLR7 activation by accumulation of guanine nucleosides, in particular under systemic inflammation, where damaged tissues release a large amount of nucleotides. We demonstrate in the present study that a purine nucleoside phosphorylase inhibitor, forodesine, can reduce the disease severity and prolong the survival in a xenogeneic mouse model of graft-versus-host disease (GVHD). Guanine nucleosides were undetectable in mice during GVHD but increased significantly following forodesine treatment. Our invitro experiments showed that forodesine enhanced guanosine-mediated cytokine production from APCs, including alveolar macrophages and plasmacytoid dendritic cells, through TLR7 signaling. Forodesine also enhanced Ag-presenting capacity, as demonstrated by increased CD8+ T cell proliferation and higher secretion of IFN-γ and IL-12p40 in an MLR with plasmacytoid dendritic cells. Furthermore, forodesine stimulated IFN-γ production from activated T cells in the presence of a low concentration of guanosine while inhibiting their proliferation and inducing apoptotic cell death. Although forodesine ameliorated GVHD severity, mice treated with forodesine showed significantly higher levels of multiple proinflammatory cytokines and chemokines in plasma, suggesting invivo upregulation of TLR7 signaling. Our study suggests that forodesine may activate a wide range of immune cells, including T cells, through TLR7 stimulation while inhibiting GVHD by inducing apoptosis of T cells, after allogeneic hematopoietic stem cell transplant.

Allopurinol and oxypurinol differ in their strength and mechanisms of inhibition of xanthine oxidoreductase

Xanthine oxidoreductase (XOR) is a metalloenzyme that catalyzes the final steps in purine metabolism by converting hypoxanthine to xanthine and then uric acid. Allopurinol, an analog of hypoxanthine, is widely used as an anti-gout drug, as XOR-mediated metabolism of allopurinol to oxypurinol leads to oxypurinol rotation in the enzyme active site and reduction of the molybdenum Mo(VI) active center to Mo(IV), inhibiting subsequent urate production. However, when oxypurinol is administered directly to a mouse model of hyperuricemia, it yields a weaker urate-lowering effect than allopurinol. To better understand its mechanism of inhibition and inform patient dosing strategies, here we performed kinetic and structural analyses of the inhibitory activity of oxypurinol. Our results demonstrated that oxypurinol was less effective than allopurinol both in vivo and in vitro. We show that upon reoxidation to Mo(VI), oxypurinol binding is greatly weakened, and reduction by xanthine, hypoxanthine, or allopurinol is required for reformation of the inhibitor-enzyme complex. In addition, we show oxypurinol only weakly inhibits the conversion of hypoxanthine to xanthine and is therefore unlikely to effect feedback inhibition of de novo purine synthesis. Furthermore, we observed weak allosteric inhibition of purine nucleoside phosphorylase by oxypurinol, which has potentially adverse effects for patients. Considering these results, we propose the single-dose method currently used to treat hyperuricemia can result in unnecessarily high levels of allopurinol. While the short half-life of allopurinol in blood suggests that oxypurinol is responsible for enzyme inhibition, we anticipate multiple, smaller doses of allopurinol would reduce the total allopurinol patient load.

Investigating the Vital Role of the Identified Abietic Acid from Helianthus annuus L. Calathide Extract against Hyperuricemia via Human Embryonic Kidney 293T Cell Model.

To explore the anti-hyperuricemia components in sunflower (Helianthus annuus L.) calathide extract (SCE), we identified abietic acid (AA) via liquid chromatography-mass spectrometry and found an excellent inhibitor of xanthine oxidase (IC50 = 10.60 µM, Ki = 193.65 nM) without cytotoxicity. Based on the transcriptomics analysis of the human embryonic kidney 293T cell model established using 1 mM uric acid, we evaluated that AA showed opposite modulation of purine metabolism to the UA group and markedly suppressed the intensity of purine nucleoside phosphorylase, ribose phosphate pyrophosphokinase 2, and ribose 5-phosphate isomerase A. Molecular docking also reveals the inhibition of purine nucleoside phosphorylase and ribose phosphate pyrophosphokinase 1. The SCE exhibits similar regulation of these genes, so we conclude that AA was a promising component in SCE against hyperuricemia. This present study provided a novel cell model for screening anti-hyperuricemia natural drugs in vitro and illustrated that AA, a natural diterpenoid, is a potential inhibitor of purine biosynthesis or metabolism.

Design, Synthesis, Biological Evaluation, and Crystallographic Study of Novel Purine Nucleoside Phosphorylase Inhibitors.

Purine nucleoside phosphorylase (PNP) is a well-known molecular target with potential therapeutic applications in the treatment of T-cell malignancies and/or bacterial/parasitic infections. Here, we report the design, development of synthetic methodology, and biological evaluation of a series of 30 novel PNP inhibitors based on acyclic nucleoside phosphonates bearing a 9-deazahypoxanthine nucleobase. The strongest inhibitors exhibited IC50 values as low as 19 nM (human PNP) and 4 nM (Mycobacterium tuberculosis (Mt) PNP) and highly selective cytotoxicity toward various T-lymphoblastic cell lines with CC50 values as low as 9 nM. No cytotoxic effect was observed on other cancer cell lines (HeLa S3, HL60, HepG2) or primary PBMCs for up to 10 μM. We report the first example of the PNP inhibitor exhibiting over 60-fold selectivity for the pathogenic enzyme (MtPNP) over hPNP. The results are supported by a crystallographic study of eight enzyme-inhibitor complexes and by ADMET profiling in vitro and in vivo.

Computational, in vitro and radiation-based in vivo studies on acetamide quinazolinone derivatives as new proposed purine nucleoside phosphorylase inhibitors for breast cancer

The present work describes a quinazolinone-based lead optimization for the development of novel purine nucleoside phosphorylase (PNP) inhibitors with quinazolinone scaffold. Nineteen compounds were proposed and docked against PNP, the best 14 compounds with highest docking and affinity scores and low RMSD values were synthesized. Synthesis of new quinazolinone derivatives with variable acetamide substituents on two positions on quinazoline ring was performed. The structures assigned to the products were concordant with the microanalytical and spectral data. In vitro cytotoxicity on human breast cancer cell line (MCF7) was performed and identified compound 6g as the most potent with IC50 (0.99 ± 0.11 μM) which was further tested against five different breast cancer cell lines in addition to normal breast cell to determine the selectivity. Compound 6g was subjected to molecular dynamic simulation study, radiolabelling and biodistribution study to investigate its stability and selectivity toward breast cancers. The in vitro PNP inhibition results were aligned with the in silico, cytotoxicity, and biodistribution results where 6g showed the most potent PNP inhibitory activity with IC50 (0.159 ± 0.007 μM) when compared to Peldesine (BCX-34) IC50 (0.041 ± 0.002 μM).

Xanthine dehydrogenase rewires metabolism and the survival of nutrient deprived lung adenocarcinoma cells by facilitating UPR and autophagic degradation.

Xanthine dehydrogenase (XDH) is the rate-limiting enzyme in purine catabolism by converting hypoxanthine to xanthine and xanthine to uric acid. The altered expression and activity of XDH are associated with the development and prognosis of multiple types of cancer, while its role in lung adenocarcinoma (LUAD) remains unknown. Herein, we demonstrated that XDH was highly expressed in LUAD and was significantly correlated with poor prognosis. Though inhibition of XDH displayed moderate effect on the viability of LUAD cells cultured in the complete medium, it significantly attenuated the survival of starved cells. Similar results were obtained in XDH-knockout cells. Nucleosides supplementation rescued the survival of starved LUAD cells upon XDH inhibition, while inhibition of purine nucleoside phosphorylase abrogated the process, indicating that nucleoside degradation is required for the XDH-mediated survival of LUAD cells. Accordingly, metabolic flux revealed that ribose derived from nucleoside fueled key carbon metabolic pathways to sustain the survival of starved LUAD cells. Mechanistically, down-regulation of XDH suppressed unfolded protein response (UPR) and autophagic flux in starved LUAD cells. Inhibition of XDH decreased the level of amino acids produced by autophagic degradation, which was accompanied with down-regulation of mTORC1 signaling. Supplementation of amino acids including glutamine or glutamate rescued the survival of starved LUAD cells upon knockout or inhibition of XDH. Finally, XDH inhibitors potentiated the anti-cancer activity of 2-deoxy-D-glucose that induced UPR and/or autophagy in vitro and in vivo. In summary, XDH plays a crucial role in the survival of starved LUAD cells and targeting XDH may improve the efficacy of drugs that induce UPR and autophagy in the therapy of LUAD.

Purine Nucleoside Phosphorylase Inhibition Attenuates the Progression of Anemia and Organ Damage in Sickle Cell Mice

Purine nucleoside phosphorylase (PNP) converts guanosine to guanine, inosine to hypoxanthine, and 2'-deoxyguanosine to guanine, and leads to the downstream formation of the pro-oxidant and vasculotoxic hypoxanthine and xanthine. Red blood cells are rich in PNP, yet PNP's role in the pathogenesis of sickle cell disease (SCD) is not known. Our group showed that patients with SCD have increased PNP release and activity, leading to accelerated guanosine/inosine metabolism and increased production of vasculotoxic hypoxanthine/xanthine (Bilan VP et al. 2018). Thus, we proposed that PNP may have a major pathogenic role in red blood cell sickling, hemolytic angioproliferation, cell aggregation and end organ damage, and that PNP inhibition may be beneficial in the treatment of SCD. The highly potent PNP inhibitor 8-aminoguanine is the product of the conversion of the endogenous guanosine metabolite and pro-drug 8-aminoguanosine (8-AG). We investigated the safety and efficacy of short-term (8 weeks) and chronic (20 weeks) treatment of Townes sickle mice (SS) and their non-sickling controls (AA) with 8-AG (60mg/kg/day administered ad libitum in the drinking water). We collected blood and urine samples at multiple intervals using metabolic cages. To determine 8-AG body disposition and PNP inhibition, urine samples were analyzed for purines by liquid chromatography - tandem mass spectrometry (LC-MS/MS). Both AA and SS mice tolerated 8-AG well with no evidence of toxicity. In both AA (n= 15) and SS (n=40) mice there was very efficient conversion of 8-AG that resulted in a 40-50-fold increase in urinary 8-aminoguanine concentrations (p<0.001). In 8-AG treated SS mice we observed reduced hypoxanthine levels, with an increased inosine/hypoxanthine ratio. Additionally, guanosine was increased, guanine was reduced, and an increased guanosine/guanine ratio was observed (p<0.05), suggesting potent PNP inhibition. In SS mice, the 8-week treatment with 8-AG significantly reduced hemoglobinuria (p<0.05) and albuminuria (p<0.05), attenuated left ventricular (LV, p<0.01) and right ventricular (RV, p<0.05) hypertrophy, limited hepatomegaly (p<0.001), and improved RV contractility (p<0.05), with a trend towards reduced lung weights and splenomegaly. In SS mice, 20-week treatment with 8-AG significantly slowed the progression of anemia as evidenced by attenuated age-related drops in hemoglobin and hematocrit levels, and it attenuated hemoglobinuria and albuminuria while significantly reducing splenomegaly (p=<0.05) and hepatomegaly (p<0.05, Figure). Semi-quantitative histopathological analysis suggested reduced iron deposition (Prussian blue stain, Figure), and reduced ischemic (H&E stain) and fibrotic (trichrome stain, Figure) injury in the spleen and liver from SS mice treated with 8-AG. Our data suggest that the PNP inhibitor 8-AG may have a pharmacological benefit in SCD and may warrant further investigation as a multi-pronged treatment approach for SCD. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Purine nucleoside phosphorylase controls nicotinamide riboside metabolism in mammalian cells

Nicotinamide riboside (NR) is an effective precursor of nicotinamide adenine dinucleotide (NAD) in human and animal cells. NR supplementation can increase the level of NAD in various tissues and thereby improve physiological functions that are weakened or lost in experimental models of aging or various human pathologies. However, there are also reports questioning the efficacy of NR supplementation. Indeed, the mechanisms of its utilization by cells are not fully understood. Herein, we investigated the role of purine nucleoside phosphorylase (PNP) in NR metabolism in mammalian cells. Using both PNP overexpression and genetic knockout, we show that after being imported into cells by members of the equilibrative nucleoside transporter family, NR is predominantly metabolized by PNP, resulting in nicotinamide (Nam) accumulation. Intracellular cleavage of NR to Nam is prevented by the potent PNP inhibitor Immucillin H in various types of mammalian cells. In turn, suppression of PNP activity potentiates NAD synthesis from NR. Combining pharmacological inhibition of PNP with NR supplementation in mice, we demonstrate that the cleavage of the riboside to Nam is strongly diminished, maintaining high levels of NR in blood, kidney, and liver. Moreover, we show that PNP inhibition stimulates Nam mononucleotide and NAD+ synthesis from NR invivo, in particular, in the kidney. Thus, we establish PNP as a major regulator of NR metabolism in mammals and provide evidence that the health benefits of NR supplementation could be greatly enhanced by concomitant downregulation of PNP activity.

P1312: FORODESINE AMPLIFIES HOST INNATE IMMUNE RESPONSE THROUGH TOLL-LIKE RECEPTOR 7 ACTIVATION WHILE PREVENTING EXPERIMENTAL GRAFT-VERSUS-HOST DISEASE

Background: Forodesine, a novel inhibitor of purine nucleoside phosphorylase (PNP), causes nucleotide pool imbalances by accumulating intracellular deoxyguanosine, thereby resulting in selective apoptosis of T-cells. Recent evidence indicates that specific types of nuclear acids including guanosine and its derivatives act as natural ligands for toll-like receptor 7 (TLR7). So far, it is unclear whether and how forodesine can modulate host innate immunity, including antigen-presenting cells (APCs) such as macrophages and dendritic cells (DCs), which express TLR7 abundantly. Aims: The aim of this study is to investigate the role of forodesine in host APC function as well as donor T-cell activation both in vivo graft-versus-host disease (GVHD) models and in vitro cell assays. Methods: NOG mice were subjected to 250 cGy total body irradiation followed by intravenous injection of human isolated T-cells. Mice were treated with forodesine (20 mg/kg) or vehicle daily after transplantation. Results: Despite the mice without treatment developing severe GVHD after transplantation, guanosine and deoxyguanosine were hardly detected in the plasma, suggesting that purine nucleosides released from damaged tissues were rapidly degraded by PNP. In fact, inhibition of PNP activity by forodesine markedly increased plasma guanosine levels, whereas deoxyguanosine was still undetectable. This was also the case in GVHD target organs, including liver and lungs. At the same level of guanosine in the liver, forodesine promoted TNF-a production from in vitro alveolar macrophage cultures. Preincubation with a TLR7 antagonist, ODN20958, attenuated the TNF-a production from macrophages stimulated by guanosine and forodesine. Nuclease treatment did not reduce macrophage TNF-a production, suggesting that single-strand RNA, a well-known TLR7 ligand, is not involved in this response. Similar results were observed in Flt3-ligand-induced plasmacytoid DCs. Not only TNF-a but also IL-12 production was induced by the combination of guanosine and forodesine, and was comparable to that in pDCs pulsed with R848, a potent agonist of TLR7/8. These observations suggest that a sustained high level of guanosine caused by forodesine treatment lead to continuous activation of TLR7 signaling, resulting in cytokine production from APCs. Meanwhile, as reported previously, forodesine inhibited the proliferation of human T-cells activated with CD3 and CD28 antibodies in the presence of deoxyguanosine. Of note, however, this combination did not impair but rather stimulated IFN-g production from activated T-cells cocultured with pDCs. This suggests that T-cell priming capacity mediated by the interaction with pDCs is conserved through TLR7 activation. Finally, we investigated the in vivo effects of forodesine on survival, body weight change, and disease severity of GVHD mice. Forodesine treatment significantly prolonged survival of the mice compared with control mice, with a median survival of 17.5 days vs 14 days, respectively (p = 0.029). The mean body weight loss percentage at day 9 was 11.5% vs 19.0% in the forodesine group and control, respectively (p = 0.003). Furthermore, the clinical GVHD scores were also lower in the forodesine group vs control (4.9 vs 0.6 points, p = 0.001). Image:Summary/Conclusion: This study demonstrates that forodesine amplifies host innate immune response through TLR7 signaling, while ameliorating T-cell GVH reaction. Further studies are needed to investigate whether forodesine can provide host protection against infections in a transplant setting.

Abstract 5801: Xanthine oxidoreductase mediates the survival of starved lung adenocarcinoma cells by inducing UPR and autophagic degradation

Abstract Background &amp; Purpose: Lung adenocarcinoma (LUAD) is the most common and aggressive subtype of non-small cell lung cancer, and is the leading cause of cancer-associated mortality worldwide. Upregulation of purine degradation pathway is observed in LUAD. Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in purine catabolism by converting hypoxanthine to xanthine and xanthine to uric acid. The altered expression and activity of XOR in cancer tissues are usually associated with prognosis of cancer, while its role in LUAD remains unknown. Methods: XOR expression in LUAD tissues were detected by immunohistochemistry. XOR knock-out LUAD cells were generated by CRISPR-Cas9 system. Clonogenic survival of LUAD cells was determined by crystal violet staining. The expression of genes involving in unfolded protein response (UPR) and autophagy was detected by RT-qPCR and the protein level was detected by Western blotting. Autophagic flux was observed by immunofluorescent microscopy. The level of amino acids and ATP/ADP/AMP were determined by UPLC-QTOFMS. Metabolic flux was analyzed by radio-labeled metabolites measured by UPLC-QTOFMS. Results: XOR is highly expressed in LUAD and significantly associated with poor clinical prognosis. Knocking out or inhibition of XOR attenuated the survival of starved LUAD cells. Nucleoside supplementation rescued the survival of starved LUAD cells upon XOR inhibition, while inhibition of purine nucleoside phosphorylase (PNP) impended the process, indicating that ribose produced by nucleoside degradation is required for the XOR-mediated the survival of LUAD cells. Accordingly, metabolic flux revealed that ribose derived from nucleoside fueled key carbon metabolic pathways to sustain the survival of starved LUAD cells. Mechanistically, downregulation of XOR suppressed UPR and autophagic degradation in starved LUAD cells. Consistently, inhibition of XOR decreased the level of amino acids produced by autophagic degradation, which was accompanied with down-regulation of mTORC1 signaling. Supplementation of amino acids including glutamine, glutamate or aspartate rescued the survival of starved LUAD cells, indicating that autophagic degradation plays a key role in XOR-mediated LUAD cells survival under nutrient stress. Finally, XOR inhibitors potentiated the anti-proliferative activity of 2-deoxy-D-glucose that induced UPR and/or autophagy in LUAD cells. Conclusions: We found that knock-out or inhibition of XOR attenuated UPR and autophagy in starved LUAD cells, which resulted in nutrients scarcity due to blockade of the degradation of nucleosides and proteins, and finally cell death. These findings demonstrate that XOR plays a crucial role in the survival of LUAD cells, suggesting that targeting XOR is a potential strategy to improve the efficacy of drugs that are able to induce UPR and autophagy. Citation Format: Manman Chen, Wei Guo, Xiaozhen Guo, Cen Xie, Linghua Meng. Xanthine oxidoreductase mediates the survival of starved lung adenocarcinoma cells by inducing UPR and autophagic degradation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5801.

Interactions of 2,6-substituted purines with purine nucleoside phosphorylase from Helicobacter pylori in solution and in the crystal, and the effects of these compounds on cell cultures of this bacterium

Helicobacter pylori represents a global health threat with around 50% of the world population infected. Due to the increasing number of antibiotic-resistant strains, new strategies for eradication of H. pylori are needed. In this study, we suggest purine nucleoside phosphorylase (PNP) as a possible new drug target, by characterising its interactions with 2- and/or 6-substituted purines as well as the effect of these compounds on bacterial growth. Inhibition constants are in the micromolar range, the lowest being that of 6-benzylthio-2-chloropurine. This compound also inhibits H. pylori 26695 growth at the lowest concentration. X-ray structures of the complexes of PNP with the investigated compounds allowed the identification of interactions of inhibitors in the enzyme’s base-binding site and the suggestion of structures that could bind to the enzyme more tightly. Our findings prove the potential of PNP inhibitors in the design of drugs against H. pylori.

On-flow magnetic particle activity assay for the screening of human purine nucleoside phosphorylase inhibitors

Human purine nucleoside phosphorylase (HsPNP) catalyzes reversible phosphorolysis of nucleosides and deoxynucleosides in the purine cascade. HsPNP has been a target on behalf of the development of new leads for the treatment of a variety of T-cell mediated disorders. Several studies on the HsPNP are focused on the identification of effective, safe, and selective inhibitors. Therefore, this study describes the development of direct, simple, reliable, and inexpensive enzymatic assays to screen HsPNP inhibitors. Initially, HsPNP was covalently immobilized on the surface of magnetic particles (MPs). Due to the versatility of the MPs as solid support for enzyme immobilization, two different methods to monitor the enzyme activity are presented. Firstly, the activity of HsPNP-MPs was assessed offline by HPLC-DAD quantifying the formed hypoxanthine. Then, HsPNP-MPs were trapped in a peek tube, furnishing a microreactor which was inserted on-flow in an HPLC-DAD system to monitor the enzyme activity by the hypoxanthine quantification. Kinetic assays provided KMapp values for the inosine substrate of 488.2 ± 49.1 and 1084 ± 111 µM for the offline and on-flow assays, respectively. For the first time, kinetic studies for Pi as substrate using the HsPNP-MPs exhibits a Michaelis-Menten kinetic, yielding KMapp values for offline and on-flow of 521.2 ± 62.9 µM and 601 ± 66.5 µM, respectively. Inhibition studies conducted with a fourth generation immucillin derivative (DI4G) were employed as proof of concept to validate the use of the HsPNP-MPs assays for screening purposes. Additionally, a small library containing 11 compounds was used to assess the selectivity of the developed assays. The results showed that both presented assays can be applied to selectively recognizing and characterizing HsPNP inhibitors. Particularly, the on-flow method exhibited a high throughput and performance because of its automation and represents an easy and practical approach to reuse the HsPNP-MPs. Besides, this novel enzyme activity assay model can be further applied to other biological targets.

A comprehensive method for determining cellular uptake of purine nucleoside phosphorylase and adenylosuccinate synthetase inhibitors by H. pylori

Due to the growing number of Helicobacter pylori strains resistant to currently available antibiotics, there is an urgent need to design new drugs utilizing different molecular mechanisms than those that have been used up to now. Enzymes of the purine salvage pathway are possible targets of such new antibiotics because H. pylori is not able to synthetize purine nucleotides de novo. The bacterium’s recovery of purines and purine nucleotides from the environment is the only source of these essential DNA and RNA building blocks. We have identified formycins and hadacidin as potent inhibitors of purine nucleoside phosphorylase (PNP) and adenylosuccinate synthetase (AdSS) from H. pylori — two key enzymes of the purine salvage pathway. However, we have found that these compounds are not effective in H. pylori cell cultures. To address this issue, we have developed a universal comprehensive method for assessing H. pylori cell penetration by drug candidates, with three alternative detection assays. These include liquid chromatography tandem mass spectrometry, UV absorption, and inhibition of the target enzyme by the tested compound. Using this approach, we have shown that cellular uptake by H. pylori of formycins and hadacidin is very poor, which reveals why their in vitro inhibition of PNP and AdSS and their effect on H. pylori cell cultures are so different. The cell penetration assessment method developed here will be extremely useful for validating the cellular uptake of other drug candidates, facilitating the design of new potent therapeutic agents against H. pylori.Key points• A method for assessing H. pylori cells penetration by drug candidates is described.• Three alternative detection assays that complement each other can be used.• The method may be adapted for other bacteria as well.

Updated Report of a Phase I/II Multicenter Study of Forodesine, a Purine Nucleoside Phosphorylase Inhibitor, in Japanese Patients with Relapsed Peripheral T-Cell Lymphoma

Updated Report of a Phase I/II Multicenter Study of Forodesine, a Purine Nucleoside Phosphorylase Inhibitor, in Japanese Patients with Relapsed Peripheral T-Cell Lymphoma

Antileukemic Activity and Pharmacodynamics of Intravenous Forodesine (BCX-1777), a Novel Purine Nucleoside Phosphorylase (PNP) Inhibitor, in Phase I/II Trials in Patients with Advanced T-Cell Malignancies.

PNP represents an attractive target for drug development based on the profound, selective impairment of T-cell function seen in individuals with an inherited deficiency of PNP. Forodesine, a potent, specific transition-state analog inhibitor of PNP, is currently being investigated for safety and efficacy in T-cell and other malignancies. In a phase I/II single-center, intrapatient dose-escalation study, forodesine (starting dose: 40 mg/m2) was given to 5 patients with relapsed/refractory, aggressive T-cell leukemia/ lymphoma via a 30-min IV infusion, followed 24 hrs later by doses administered every 12 hrs for a total of 9 doses; courses could be repeated every 3–4 weeks, as required. Two patients with refractory T-cell prolymphocytic leukemia (T-PLL) and two patients with T-cell acute lymphoblastic leukemia (T-ALL) showed a decrease in leukemic or prolymphocytic counts in peripheral blood and/or bone marrow. All responders had increases in plasma 2′-deoxyguanosine (dGuo) (Cmax: 2.9 to 34 μM; baseline concentration: <.004 μM) and 4/5 responders showed elevated intracellular dGTP levels (10- to 60-fold). Forodesine was generally safe and well tolerated at all dose levels with no dose-limiting toxicities and only two adverse events (ie, acute renal failure and neutropenic infection) that were possibly drug-related. These promising results led to a phase II multi-center, open-label, repeat-dose trial in patients with advanced T-cell malignancies, in which forodesine (40 mg/m2) is infused for 30 mins for 5 days followed by at least 2 non-treatment days for up to 5 additional cycles. Out of 3 patients enrolled to-date, 2 T-ALL patients completed 6 courses of therapy with a dramatic reduction in WBC count (Fig 1A and 1B); 1 splenic T-cell lymphoma patient discontinued due to disease progression. Forodesine resulted in striking elevations in plasma dGuo. Peripheral blast cells in Patient 01 were undetectable at the start of the second course and remained undetectable after 6 courses (Fig 1A), and the bone marrow blast cells were reduced from >90% to near-normal levels. However, the contribution of a single dose of dexamethasone (40 mg IV given on Day 3) to the reduction in WBC count and blast cells is unknown. This patient's peripheral blood hematologic profile (WBC, absolute neutrophil, platelet counts and hemoglobin level) returned to near-normal, indicating a specificity of forodesine for leukemic cell populations and supporting that forodesine is an important breakthrough in the development of less toxic ALL therapy. Additional phase II results will be presented. [Display omitted]

Symmetric Nucleosides as Potent Purine Nucleoside Phosphorylase Inhibitors.

Nucleic acids are one of the most enigmatic biomolecules crucial to several biological processes. Nucleic acid-protein interactions are vital for the coordinated and controlled functioning of a cell, leading to the design of several nucleoside/nucleotide analogues capable of mimicking these interactions and hold paramount importance in the field of drug discovery. Purine nucleoside phosphorylase is a well-established drug target due to its association with numerous immunodeficiency diseases. Here, we study the binding of human purine nucleoside phosphorylase (PNP) to some bidirectional symmetric nucleosides, a class of nucleoside analogues that are more flexible due to the absence of sugar pucker restraints. We compared the binding energies of PNP-symmetric nucleosides to the binding energies of PNP-inosine/Imm-H (a transition-state analogue), by means of 200 ns long all-atom explicit-solvent Gaussian accelerated molecular dynamics simulations followed by energetics estimation using the MM-PBSA methodology. Quite interestingly, we observed that a few symmetric nucleosides, namely, ν3 and ν4, showed strong binding with PNP (-14.1 and -12.6 kcal/mol, respectively), higher than inosine (-6.3 kcal/mol) and Imm-H (-9.6 kcal/mol). This is rationalized by an enhanced hydrogen-bond network for symmetric nucleosides compared to inosine and Imm-H while maintaining similar van der Waals contacts. We note that the chemical structures of both ν3 and ν4, due to an additional unsaturation in them, resemble enzymatic transition states and fall in the category of transition-state analogues (TSAs), which are quite popular.

Discovery of a Novel Inhibitor of Human Purine Nucleoside Phosphorylase by a Simple Hydrophilic Interaction Liquid Chromatography Enzymatic Assay.

Human purine nucleoside phosphorylase (HsPNP) belongs to the purine salvage pathway of nucleic acids. Genetic deficiency of this enzyme triggers apoptosis of activated T-cells due to the accumulation of deoxyguanosine triphosphate (dGTP). Therefore, potential chemotherapeutic applications of human PNP inhibitors include the treatment of T-cell leukemia, autoimmune diseases and transplant tissue rejection. In this report, we present the discovery of novel HsPNP inhibitors by coupling experimental and computational tools. A simple, inexpensive, direct and non-radioactive enzymatic assay coupled to hydrophilic interaction liquid chromatography and UV detection (LC-UV using HILIC as elution mode) was developed for screening HsPNP inhibitors. Enzymatic activity was assessed by monitoring the phosphorolysis of inosine (Ino) to hypoxanthine (Hpx) by LC-UV. A small library of 6- and 8-substituted nucleosides was synthesized and screened. The inhibition potency of the most promising compound, 8-aminoinosine (4), was quantified through Ki and IC50 determinations. The effect of HsPNP inhibition was also evaluated in vitro through the study of cytotoxicity on human T-cell leukemia cells (CCRF-CEM). Docking studies were also carried out for the most potent compound, allowing further insights into the inhibitor interaction at the HsPNP active site. This study provides both new tools and a new lead for developing novel HsPNP inhibitors.