Dihydroorotate dehydrogenase inhibitor A771726 (leflunomide) induces apoptosis and diminishes proliferation of multiple myeloma cells

Targeting vulnerability in tumor therapy: Dihydroorotate dehydrogenase

Dihydroorotate dehydrogenase (DHODH) is a key enzyme in the de novo pyrimidine biosynthetic pathway and a recognized therapeutic target in various diseases. In oncology research, DHODH has gained increasing importance and become a hot target for various tumor therapy studies. This review highlights three key points: (1) DHODH enables its diverse biological functions through its unique structural features and dominates the regulation of tumor metabolism and cell fate; (2) DHODH activates oncogenic signals, drives metastatic adaptation, and remodels drug resistance networks in tumors, making it a metabolic-signaling dual hub; and (3) DHODH inhibitors have shown significant efficacy in preclinical models of various tumors but face multiple challenges in clinical trials, including drug-related limitations and external constraints. Given these challenges, future research should explore DHODH inhibitors as a foundation for overcoming technological and translational barriers while establishing a systematic framework for the clinical application of DHODH-targeted tumor therapies.

Combination Therapies in Drug Repurposing: Personalized Approaches to Combatting Leukaemia and Multiple Myeloma

Despite advances in cancer research, treating malignancies remains challenging due to issues like drug resistance, disease heterogeneity, and the limited efficacy of current therapies, particularly in relapsed or refractory cases. In recent years, several drugs originally approved for non-cancer indications have shown potential in cancer treatment, demonstrating anti-proliferative, anti-metastatic, and immunomodulatory effects. Drug repurposing has shown immense promise due to well-established safety profiles and mechanisms of action of the compounds. However, the implementation is fraught with clinical, logistical, regulatory, and ethical challenges, especially in diseases such as leukaemia and multiple myeloma. This chapter examines the treatment challenges in leukaemia and multiple myeloma, focusing on the role of drug repurposing in addressing therapeutic resistance and disease variability. It highlights the potential of personalized, tailored combination therapies, using repurposed drug components, to offer more effective, targeted, and cost-efficient treatment strategies, overcoming resistance and improving patient outcomes.

Transcriptomic analysis of the anti-tumor effects of leflunomide in prolactinoma

Leflunomide's anti-tumor effects have been investigated in various types of tumors; however, its impact on pituitary adenoma, particularly prolactinoma, is unclear. Hence, the current study evaluates the effects of leflunomide on prolactinoma cells in vitro and in vivo and elucidates the potential underlying mechanism(s). Cell Counting Kit-8 results revealed that leflunomide inhibits the proliferation of rat pituitary tumor cell lines (GH3 and MMQ) in a concentration-dependent manner in vitro. However, combination therapy of cabergoline and leflunomide exerted stronger inhibitory effects than cabergoline in MMQ cells in vitro and in vivo. Transcriptomics and gene ontology (GO) analyses identified genes significantly enriched in apoptotic processes and programmed cell death. Protein-Protein Interaction (PPI) networks defined the roles of hub genes (Mdm2, Cdkn1a, Plk2, and Ccng1) in leflunomide-induced cell death. GO and pathway enrichment analyses showed that the combination drug-specific differentially expressed genes were associated with inhibiting protein translation, but were active in gene expression processes. Hence, the anti-proliferative effects of leflunomide on prolactinoma cell lines may be mediated through programmed cell death pathways. Importantly, combining cabergoline with leflunomide effectively enhances the toxic effect of cabergoline, suggesting a potential therapeutic role for leflunomide in drug-resistant prolactinoma.

Multiple sclerosis and cancer: Navigating a dual diagnosis

Healthcare breakthroughs are extending the lives of multiple sclerosis (MS) patients and cancer survivors, creating a growing cohort of individuals navigating a dual diagnosis. Determining the relationship between MS and cancer risk remains challenging, with inconclusive findings confounded by age, risk exposures, comorbidities, genetics and the ongoing introduction of new MS disease-modifying therapies (DMTs) across study periods.This research places significant emphasis on cancer survival, with less attention given to the impact on MS outcomes. Our review explores the existing literature on MS, cancer risk and the intersection of DMTs and cancer treatments. We aim to navigate the complexities of managing MS in cancer survivors to optimise outcomes for both conditions. Continuous research and the formulation of treatment guidelines are essential for guiding future care. Collaboration between neuro-immunology and oncology is crucial, with a need to establish databases for retrospective and ultimately prospective analysis of outcomes in these rapidly evolving fields.

Mechanisms of S-phase arrest and mitochondrial dysfunction in complex III by DHODH inhibitors in tumorigenic TNBC cells

Dihydroorotate dehydrogenase (DHODH) inhibitors have recently gained increasing research interest owing to their potential for treating breast cancers. We explored their effects in different breast cancer subtypes, focusing on mitochondrial dysfunction. The sensitivity of different subtypes to the inhibitors was investigated with respect to DHODH expression, tumorigenic, and receptor status. Analysis of respiratory complexes, cell cycle, reactive oxygen species (ROS), and cell differentiation were performed. Four cell lines with different receptor status were included, namely MCF-7, MDAMB-231, SKBR-3, and MCF-10A. We showed that MCF-7 and MDAMB-231 cells of the subtypes (ER+/PR+/HER2-) and (ER-/PR-/HER2-), respectively, were responsive to brequinar. Brequinar (BQR) caused cell cycle arrest in the S-phase in sensitive subtypes of breast cells but induced cell differentiation only in poorly differentiated breast cells. All cell subtypes showed increased generation of ROS, both intracellular and mitochondrial ROS with a greater increase seen in mitochondrial ROS in response to DHODH inhibitor, subsequently contributing to mitochondrial dysfunction. BQR also disrupts the function of complex III in ER+/PR+ and triple negative breast cancer (TNBC) subtypes. Collectively, we have found that MDAMB-231 TNBC cell was the most affected by DHODH inhibition in terms of sensitivity, cell cycle arrest, induction of cell differentiation, production of ROS, and mitochondrial complexes disruption. In conclusion, these findings suggest that DHODH inhibitors can potentially become a valuable targeted therapy for TNBC subtype and further consolidates its therapeutic potential as part of the combinatorial therapy against this resilient breast cancer subtype.

Signaling effect, combinations, and clinical applications of triciribine

Triciribine (TCN) is a tricyclic nucleoside. Its synthesis was first described in 1971. Subsequent studies have indicated that TCN plays a role in inhibiting DNA synthesis and was revealed to possess a higher selectivity for Akt. Although a single dose of TCN demonstrated limited activity in solid tumors at the clinical level, combinations of TCN with various agents, such as specific inhibitors, tyrosine kinase inhibitor dasatinib, ErbB inhibitor tipifarnib, IGF1-R inhibitor NVP-AEW541, mTORC1 inhibitor RAD-001, TNF-related apoptosis-inducing ligand, PPARγ agonist, 1,25(OH)2D3, gemcitabine, and paclitaxel, have been reported to be efficient against various malignancies such as pancreatic, breast, prostate cancer, insulinoma, gut neuroendocrine tumor, and hepatocellular carcinoma at the preclinical level. Other than malignancies, through Akt inhibition activity, TCN has also been demonstrated potential for treating lung injuries, including those encountered in COVID-19 infections.

Discovering Potential in Non-Cancer Medications: A Promising Breakthrough for Multiple Myeloma Patients

MM is a common type of cancer that unfortunately leads to a significant number of deaths each year. The majority of the reported MM cases are detected in the advanced stages, posing significant challenges for treatment. Additionally, all MM patients eventually develop resistance or experience relapse; therefore, advances in treatment are needed. However, developing new anti-cancer drugs, especially for MM, requires significant financial investment and a lengthy development process. The study of drug repurposing involves exploring the potential of existing drugs for new therapeutic uses. This can significantly reduce both time and costs, which are typically a major concern for MM patients. The utilization of pre-existing non-cancer drugs for various myeloma treatments presents a highly efficient and cost-effective strategy, considering their prior preclinical and clinical development. The drugs have shown promising potential in targeting key pathways associated with MM progression and resistance. Thalidomide exemplifies the success that can be achieved through this strategy. This review delves into the current trends, the challenges faced by conventional therapies for MM, and the importance of repurposing drugs for MM. This review highlights a noncomprehensive list of conventional therapies that have potentially significant anti-myeloma properties and anti-neoplastic effects. Additionally, we offer valuable insights into the resources that can help streamline and accelerate drug repurposing efforts in the field of MM.

Targeting cancer-specific metabolic pathways for developing novel cancer therapeutics

Cancer is a heterogeneous disease characterized by various genetic and phenotypic aberrations. Cancer cells undergo genetic modifications that promote their proliferation, survival, and dissemination as the disease progresses. The unabated proliferation of cancer cells incurs an enormous energy demand that is supplied by metabolic reprogramming. Cancer cells undergo metabolic alterations to provide for increased energy and metabolite requirement; these alterations also help drive the tumor progression. Dysregulation in glucose uptake and increased lactate production via "aerobic glycolysis" were described more than 100 years ago, and since then, the metabolic signature of various cancers has been extensively studied. However, the extensive research in this field has failed to translate into significant therapeutic intervention, except for treating childhood-ALL with amino acid metabolism inhibitor L-asparaginase. Despite the growing understanding of novel metabolic alterations in tumors, the therapeutic targeting of these tumor-specific dysregulations has largely been ineffective in clinical trials. This chapter discusses the major pathways involved in the metabolism of glucose, amino acids, and lipids and highlights the inter-twined nature of metabolic aberrations that promote tumorigenesis in different types of cancer. Finally, we summarise the therapeutic interventions which can be used as a combinational therapy to target metabolic dysregulations that are unique or common in blood, breast, colorectal, lung, and prostate cancer.

Targeting nucleotide metabolism: a promising approach to enhance cancer immunotherapy

Targeting nucleotide metabolism can not only inhibit tumor initiation and progression but also exert serious side effects. With in-depth studies of nucleotide metabolism, our understanding of nucleotide metabolism in tumors has revealed their non-proliferative effects on immune escape, indicating the potential effectiveness of nucleotide antimetabolites for enhancing immunotherapy. A growing body of evidence now supports the concept that targeting nucleotide metabolism can increase the antitumor immune response by (1) activating host immune systems via maintaining the concentrations of several important metabolites, such as adenosine and ATP, (2) promoting immunogenicity caused by increased mutability and genomic instability by disrupting the purine and pyrimidine pool, and (3) releasing nucleoside analogs via microbes to regulate immunity. Therapeutic approaches targeting nucleotide metabolism combined with immunotherapy have achieved exciting success in preclinical animal models. Here, we review how dysregulated nucleotide metabolism can promote tumor growth and interact with the host immune system, and we provide future insights into targeting nucleotide metabolism for immunotherapeutic treatment of various malignancies.

Oral Conventional Synthetic Disease-Modifying Antirheumatic Drugs with Antineoplastic Potential: a Review

There is an increasing trend of malignancy worldwide. Disease-modifying antirheumatic drugs (DMARDs) are the cornerstones for the treatment of immune-mediated inflammatory diseases (IMIDs), but risk of malignancy is a major concern for patients receiving DMARDs. In addition, many IMIDs already carry higher background risks of neoplasms. Recently, the black box warning of malignancies has been added for Janus kinase inhibitors. Also, the use of biologic DMARDs in patients with established malignancies is usually discouraged owing to exclusion of such patients in pivotal studies and, hence, lack of evidence. In contrast, some conventional synthetic DMARDs (csDMARDs) have been reported to show antineoplastic properties and can be beneficial for patients with cancer. Among the csDMARDs, chloroquine and hydroxychloroquine have been the most extensively studied, and methotrexate is an established chemotherapeutic agent. Even cyclosporine A, a well-known drug associated with cancer risk, can potentiate the effect of some chemotherapeutic agents. We review the possible mechanisms behind and clinical evidence of the antineoplastic activities of csDMARDs, including chloroquine and hydroxychloroquine, cyclosporine, leflunomide, mycophenolate mofetil, mycophenolic acid, methotrexate, sulfasalazine, and thiopurines. This knowledge may guide physicians in the choice of csDMARDs for patients with concurrent IMIDs and malignancies.

Nitrile-containing pharmaceuticals: target, mechanism of action, and their SAR studies

The nitrile group is an important functional group widely found in both pharmaceutical agents and natural products. More than 30 nitrile-containing pharmaceuticals have been approved by the FDA for the management of a broad range of clinical conditions in the last few decades. Incorporation of a nitrile group into lead compounds has gradually become a promising strategy in rational drug design as it can bring additional benefits including enhanced binding affinity to the target, improved pharmacokinetic profile of parent drugs, and reduced drug resistance. This paper reviews the existing drugs with a nitrile moiety that have been approved or in clinical trials, involving their targets, molecular mechanism of pharmacology and SAR studies, and classifies them into different categories based on their clinical usages.

The Mitochondria-Independent Cytotoxic Effect of Leflunomide on RPMI-8226 Multiple Myeloma Cell Line

Leflunomide, an anti-inflammatory agent, has been shown to be effective in multiple myeloma (MM) treatment; however, the mechanism of this phenomenon has not been fully elucidated. The aim of the study was to assess the role of mitochondria and dihydroorotate dehydrogenase (DHODH) inhibition in the cytotoxicity of leflunomide in relation to the MM cell line RPMI 8226. The cytotoxic effect of teriflunomide-an active metabolite of leflunomide-was determined using MTT assay, apoptosis detection, and cell cycle analysis. To evaluate DHODH-dependent toxicity, the cultures treated with teriflunomide were supplemented with uridine. Additionally, the level of cellular thiols as oxidative stress symptom was measured as well as mitochondrial membrane potential and protein tyrosine kinases (PTK) activity. The localization of the compound in cell compartments was examined using HPLC method. Teriflunomide cytotoxicity was not abolished in uridine presence. Observed apoptosis occurred in a mitochondria-independent manner, there was also no decrease in cellular thiols level. Teriflunomide arrested cell cycle in the G2/M phase which is not typical for DHODH deficiency. PTK activity was decreased only at the highest drug concentration. Interestingly, teriflunomide was not detected in the mitochondria. The aforementioned results indicate DHODH- and mitochondria-independent mechanism of leflunomide toxicity against RPMI 8226 cell line.

A combined Chemical, Computational and invitro approach identifies SBL 105 as novel DHODH inhibitor in Acute Myeloid Leukemia cells

Inhibition of the dihydroorotate dehydrogenase (DHODH) has been successful at the preclinical level in controlling myeloid leukemia. However, poor clinical trials warrant the search for new potent DHODH inhibitors. Herein we present a novel DHODH inhibitor SBL-105 effective against myeloid leukemia. Chemical characteristics were identified by ¹H NMR, ¹³C NMR, and mass spectroscopy. Virtual docking and molecular dynamic simulation analysis were performed using the automated protocol with AutoDock-VINA, GROMACS program. Human-recombinant (rh) DHODH was used for enzyme inhibition study. THP-1, TF-1, HL-60, and SKM-1 cell lines were used. MTT assay was used to assess cell viability. Flow cytometry was employed for cell cycle, apoptosis, and differentiation analysis. Chemical analysis identified the compound to be 3-benzylidene-6,7-benz-chroman-4-one (SBL-105). The compound showed high binding efficacy toward DHODH with a ΔG_binding score of −10.9 kcal/mol. Trajectory analysis indicated conserved interactions of SBL-105–DHODH to be stable throughout the 200-ns simulation. SBL-105 inhibited rh DHODH with an IC₅₀ value of 48.48 nM. The GI₅₀ values of SBL-105 in controlling THP-1, TF-1, HL-60, and SKM-1 cell proliferations were 60.66, 45.33, 73.98, and 86.01 nM, respectively. A dose-dependent increase in S-phase cell cycle arrest and total apoptosis was observed by SBL-105 treatment in both cell types, which were reversed in the presence of uridine. The compound also increased the differentiation marker CD11b-positive populations in both THP-1 and TF-1 cells, which were decreased under uridine influence. SBL-105, a novel DHODH inhibitor, identified using computational and in vitro analysis, was effective in controlling AML cells and needs attention for further preclinical developments.

Inhibiting pyrimidine biosynthesis impairs Peste des Petits Ruminants Virus replication through depletion of nucleoside pools and activation of cellular immunity

Replication of peste des petits ruminants virus (PPRV) strongly depends on the cellular environment and resources of host cells including nucleoside pool. Thus, enzymes involved in nucleoside biosynthesis (such as pyrimidine biosynthesis pathway) are regarded as attractive targets for antiviral drug development. Here, we demonstrate that brequinar (BQR) and leflunomide (LFM) which are two specific inhibitors of DHODH enzyme and 6-azauracil (6-AU) which is an ODase enzyme inhibitor robustly inhibit PPRV replication in HEK293T cell line as well as in peripheral blood mononuclear cells isolated from goat. We further demonstrate that these agents exert anti-PPRV activity via the depletion of purimidine nucleotide. Interestingly, these inhibitors can trigger the transcription of antiviral interferon-stimulated genes (ISGs). However, the induction of ISGs is largely independent of the classical JAK-STAT pathway. Combination of BQR with interferons (IFNs) exerts enhanced ISG induction and anti-PPRV activity. Taken together, this study reveals an unconventional novel mechanism of crosstalk between nucleotide biosynthesis pathways and cellular antiviral immunity in inhibiting PPRV replication. In conclusion, targeting pyrimidine biosynthesis represents a potential strategy for developing antiviral strategies against PPRV.

Folate metabolism: a re-emerging therapeutic target in haematological cancers

Folate-mediated one carbon (1C) metabolism supports a series of processes that are essential for the cell. Through a number of interlinked reactions happening in the cytosol and mitochondria of the cell, folate metabolism contributes to de novo purine and thymidylate synthesis, to the methionine cycle and redox defence. Targeting the folate metabolism gave rise to modern chemotherapy, through the introduction of antifolates to treat paediatric leukaemia. Since then, antifolates, such as methotrexate and pralatrexate have been used to treat a series of blood cancers in clinic. However, traditional antifolates have many deleterious side effects in normal proliferating tissue, highlighting the urgent need for novel strategies to more selectively target 1C metabolism. Notably, mitochondrial 1C enzymes have been shown to be significantly upregulated in various cancers, making them attractive targets for the development of new chemotherapeutic agents. In this article, we present a detailed overview of folate-mediated 1C metabolism, its importance on cellular level and discuss how targeting folate metabolism has been exploited in blood cancers. Additionally, we explore possible therapeutic strategies that could overcome the limitations of traditional antifolates.

DHODH inhibition synergizes with DNA-demethylating agents in the treatment of myelodysplastic syndromes

Dihydroorotate dehydrogenase (DHODH) catalyzes a rate-limiting step in de novo pyrimidine nucleotide synthesis. DHODH inhibition has recently been recognized as a potential new approach for treating acute myeloid leukemia (AML) by inducing differentiation. We investigated the efficacy of PTC299, a novel DHODH inhibitor, for myelodysplastic syndrome (MDS). PTC299 inhibited the proliferation of MDS cell lines, and this was rescued by exogenous uridine, which bypasses de novo pyrimidine synthesis. In contrast to AML cells, PTC299 was inefficient at inhibiting growth and inducing the differentiation of MDS cells, but synergized with hypomethylating agents, such as decitabine, to inhibit the growth of MDS cells. This synergistic effect was confirmed in primary MDS samples. As a single agent, PTC299 prolonged the survival of mice in xenograft models using MDS cell lines, and was more potent in combination with decitabine. Mechanistically, a treatment with PTC299 induced intra-S-phase arrest followed by apoptotic cell death. Of interest, PTC299 enhanced the incorporation of decitabine, an analog of cytidine, into DNA by inhibiting pyrimidine production, thereby enhancing the cytotoxic effects of decitabine. RNA-seq data revealed the marked downregulation of MYC target gene sets with PTC299 exposure. Transfection of MDS cell lines with MYC largely attenuated the growth inhibitory effects of PTC299, suggesting MYC as one of the major targets of PTC299. Our results indicate that the DHODH inhibitor PTC299 suppresses the growth of MDS cells and acts in a synergistic manner with decitabine. This combination therapy may be a new therapeutic option for the treatment of MDS.

DHODH and cancer: promising prospects to be explored

Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.

Metabolic Effects of Recurrent Genetic Aberrations in Multiple Myeloma

Oncogene activation and malignant transformation exerts energetic, biosynthetic and redox demands on cancer cells due to increased proliferation, cell growth and tumor microenvironment adaptation. As such, altered metabolism is a hallmark of cancer, which is characterized by the reprogramming of multiple metabolic pathways. Multiple myeloma (MM) is a genetically heterogeneous disease that arises from terminally differentiated B cells. MM is characterized by reciprocal chromosomal translocations that often involve the immunoglobulin loci and a restricted set of partner loci, and complex chromosomal rearrangements that are associated with disease progression. Recurrent chromosomal aberrations in MM result in the aberrant expression of MYC, cyclin D1, FGFR3/MMSET and MAF/MAFB. In recent years, the intricate mechanisms that drive cancer cell metabolism and the many metabolic functions of the aforementioned MM-associated oncogenes have been investigated. Here, we discuss the metabolic consequences of recurrent chromosomal translocations in MM and provide a framework for the identification of metabolic changes that characterize MM cells.

Dihydroorotate Dehydrogenase Inhibitors Promote Cell Cycle Arrest and Disrupt Mitochondria Bioenergetics in Ramos Cells

BACKGROUND

The re-emerging of targeting Dihydroorotate Dehydrogenase (DHODH) in cancer treatment particularly Acute Myelogenous Leukemia (AML) has corroborated the substantial role of DHODH in cancer and received the attention of many pharmaceutical industries.

OBJECTIVE

The effects of Brequinar Sodium (BQR) and 4SC-101 on lymphoblastoid cell lines were investigated.

METHODS

DHODH expression and cell proliferation inhibition of lymphoblastoid and lymphoma cell lines were analyzed using Western blot analysis and XTT assay, respectively. JC-1 probe and ATP biochemiluminescence kit were used to evaluate the mitochondrial membrane potential and ATP generation in these cell lines. Furthermore, we explored the cell cycle progression using Muse™ Cell Cycle Kit.

RESULTS

Ramos, SUDHL-1 and RPMI-1788 cells are fast-growing cells with equal expression of DHODH enzyme and sensitivity to DHODH inhibitors that showed that the inhibition of DHODH was not cancer-specific. In ATP depletion assay, the non-cancerous RPMI-1788 cells showed only a minor ATP reduction compared to Ramos and SUDHL-1 (cancer) cells. In the mechanistic impact of DHODH inhibitors on non-cancerous vs cancerous cells, the mitochondrial membrane potential assay revealed that significant depolarization and cytochrome c release occurred with DHODH inhibitors treatment in Ramos but not in the RPMI-1788 cells, indicating a different mechanism of proliferation inhibition in normal cells.

CONCLUSION

The findings of this study provide evidence that DHODH inhibitors perturb the proliferation of non-cancerous cells via a distinct mechanism compared to cancerous cells. These results may lead to strategies for overcoming the impact on non-cancerous cells during treatment with DHODH inhibitors, leading to a better therapeutic window in patients.

Inhibition of de novo pyrimidine synthesis augments Gemcitabine induced growth inhibition in an immunocompetent model of pancreatic cancer

Leflunomide (Lef) is an agent used in autoimmune disorders that interferes with DNA synthesis. De Novo pyrimidine synthesis is a mechanism of Gemcitabine (Gem) resistance in pancreatic cancer. This study aims to assess the efficacy and changes in the tumor microenvironment of Lef monotherapy and in combination with Gem, in a syngeneic mouse model of pancreatic cancer. Methods: MTS proliferation assays were conducted to assess growth inhibition by Gem (0-20 nM), Lef (0-40 uM) and Gem+Lef in KPC (KrasLSL.G12D/+;p53R172H/+; PdxCretg/+) cells in vitro. An in vivo heterotopic KPC model was used and cohorts were treated with: PBS (control), Gem (75 mg/kg/q3d), Lef (40 mg/kg/d), or Gem+Lef. At d28 post-treatment, tumor burden, proliferation index (Ki67), and vascularity (CD31) were measured. Changes in the frequency of peripheral and intratumoral immune cell subsets were evaluated via FACS. Liquid chromatography-mass spectrometry was used for metabolomics profiling. Results: Lef inhibits KPC cell growth and synergizes with Gem in vitro (P<0.05; Combination Index 0.44 (<1 indicates synergy). In vivo, Lef alone and in combination with Gem delays KPC tumor progression (P<0.001). CTLA-4+T cells are also significantly decreased in tumors treated with Lef, Gem or in combination (Gem+Lef) compared to controls (P<0.05). Combination therapy also decreased the Ki67 and vascularity (P<0.01). Leflunomide inhibits de novo pyrimidine synthesis both in vitro (p<0.0001) and in vivo (p<0.05). Conclusions: In this study, we demonstrated that Gem+Lef inhibits pancreatic cancer growth, decrease T cell exhaustion, vascularity and as proof of principle inhibits de novo pyrimidine synthesis. Further characterization of changes in adaptive immunity are necessary to characterize the mechanism of tumor growth inhibition and facilitate translation to a clinical trial.

Inhibition of the de novo pyrimidine biosynthesis pathway limits ribosomal RNA transcription causing nucleolar stress in glioblastoma cells

Glioblastoma is the most common and aggressive type of cancer in the brain; its poor prognosis is often marked by reoccurrence due to resistance to the chemotherapeutic agent temozolomide, which is triggered by an increase in the expression of DNA repair enzymes such as MGMT. The poor prognosis and limited therapeutic options led to studies targeted at understanding specific vulnerabilities of glioblastoma cells. Metabolic adaptations leading to increased synthesis of nucleotides by de novo biosynthesis pathways are emerging as key alterations driving glioblastoma growth. In this study, we show that enzymes necessary for the de novo biosynthesis of pyrimidines, DHODH and UMPS, are elevated in high grade gliomas and in glioblastoma cell lines. We demonstrate that DHODH's activity is necessary to maintain ribosomal DNA transcription (rDNA). Pharmacological inhibition of DHODH with the specific inhibitors brequinar or ML390 effectively depleted the pool of pyrimidines in glioblastoma cells grown in vitro and in vivo and impaired rDNA transcription, leading to nucleolar stress. Nucleolar stress was visualized by the aberrant redistribution of the transcription factor UBF and the nucleolar organizer nucleophosmin 1 (NPM1), as well as the stabilization of the transcription factor p53. Moreover, DHODH inhibition decreased the proliferation of glioblastoma cells, including temozolomide-resistant cells. Importantly, the addition of exogenous uridine, which reconstitutes the cellular pool of pyrimidine by the salvage pathway, to the culture media recovered the impaired rDNA transcription, nucleolar morphology, p53 levels, and proliferation of glioblastoma cells caused by the DHODH inhibitors. Our in vivo data indicate that while inhibition of DHODH caused a dramatic reduction in pyrimidines in tumor cells, it did not affect the overall pyrimidine levels in normal brain and liver tissues, suggesting that pyrimidine production by the salvage pathway may play an important role in maintaining these nucleotides in normal cells. Our study demonstrates that glioblastoma cells heavily rely on the de novo pyrimidine biosynthesis pathway to generate ribosomal RNA (rRNA) and thus, we identified an approach to inhibit ribosome production and consequently the proliferation of glioblastoma cells through the specific inhibition of the de novo pyrimidine biosynthesis pathway.

Quantitation of uridine and L-dihydroorotic acid in human plasma by LC-MS/MS using a surrogate matrix approach

Uridine and L-dihydroorotate (DHO) are important intermediates of de novo as well as salvage pathways for the biosynthesis of pyrimidines, which are the building blocks of nucleic acids - DNA and RNA. These metabolites are known to be significant biomarkers of pyrimidine synthesis during the development of DHODH inhibitor drugs for treatment of several cancers and immunological disorders. Here we are reporting a validated LC-MS/MS assay for the quantitation of uridine and DHO in K₂EDTA human plasma. Due to presence of endogenous uridine and DHO in the biological matrix, a surrogate matrix approach with bovine serum albumin (BSA) solution was used. Human plasma samples were spiked with stable isotope labeled internal standards, processed by protein precipitation, and analyzed using LC-MS/MS. Parallelism was successfully demonstrated between human plasma (the authentic matrix) and BSA (the surrogate matrix). The linear analytical ranges of the assay were set at 30.0-30,000 ng/mL for uridine and 3.00-3,000 ng/mL for DHO. This validated LC-MS/MS method demonstrated excellent accuracy and precision. The overall accuracy was between 91.9 % and 106 %, and the inter-assay precision (%CV) were less than 4.2 % for uridine in human plasma. The overall accuracy was between 92.8 % and 106 %, and the inter-assay precision (%CV) were less than 7.2 % for DHO in human plasma. Uridine and DHO were found to be stable in human plasma for at least 24 h at room temperature, 579 days when stored at -20 °C, 334 days when stored at -70 °C, and after five freeze/thaw cycles. The assay has been successfully applied to human plasma samples to support clinical studies. Novel Aspect: A surrogate matrix approach to quantify endogenous uridine and DHO concentrations in human plasma.

Leflunomide regulates c-Myc expression in myeloma cells through PIM targeting

Teriflunomide, the active metabolite of leflunomide, downregulates c-Myc expression through inhibition of PIM kinases. Leflunomide together with lenalidomide significantly extended survival in an in vivo MM model.

Leflunomide Inhibits Proliferation and Induces Apoptosis via Suppressing Autophagy and PI3K/Akt Signaling Pathway in Human Bladder Cancer Cells

INTRODUCTION

Bladder cancer is a lethal human malignancy. Currently, treatment for bladder cancer is limited. The anti-tumor effects of leflunomide have attracted much more concern in multiple human cancers.

MATERIALS AND METHODS

This study evaluated the anti-tumor effects of leflunomide on cell viability, colony formation, apoptosis, and cell cycle in two human bladder carcinoma cell lines, 5637 and T24. Meanwhile, the underlying mechanism including PI3K/Akt signaling pathway and autophagy modulation was also identified.

RESULTS

Leflunomide markedly inhibited the growth of both bladder cancer cell lines and induced apoptosis and cell cycle arrest in S phase. The phosphorylation levels of Akt and P70S6K in both cell lines were significantly down-regulated with leflunomide treatment. Furthermore, the deceased formation of autophagosomes and the accumulation of LC3II and P62 suggested the blockade of autophagy by leflunomide. Modulation of autophagy with rapamycin and chloroquine markedly attenuated and enhanced the cytostatic effects of leflunomide, respectively.

CONCLUSION

Leflunomide significantly reduced the cell viability of bladder cancer cells via inducing apoptosis and cell cycle arrest and suppressing the PI3K/Akt signaling pathway. In addition, the blockade of autophagy was observed, and autophagy inhibition enhanced leflunomide-mediating anti-tumor effects. Our data presented here offer novel ideas for comprehensive therapeutic regimes on bladder cancer.

Repurposing leflunomide for relapsed/refractory multiple myeloma: a phase 1 study

The inexpensive, well-tolerated, immunomodulatory agent leflunomide, used extensively for the treatment of rheumatoid arthritis, has been shown to produce significant activity against multiple myeloma (MM) in pre-clinical studies. We conducted a phase 1 study (clinicaltrials.gov: NCT02509052) of single agent leflunomide in patients with relapsed/refractory MM (≥3 prior therapies). At dose levels 1 and 2 (20 and 40 mg), no dose-limiting toxicities (DLTs) were observed. At dose level 3 (60 mg), one patient experienced elevated alanine aminotransferase; an additional three patients were enrolled at this dose level without further DLTs. Overall, toxicities were infrequent and manageable. Nine out of 11 patients achieved stable disease (SD), two subjects experiencing SD for nearly one year or longer. The tolerable safety profile of leflunomide, combined with a potential disease stabilization, is motivating future studies of leflunomide, in combination with other MM drugs, or as an approach to delay progression of smoldering MM.

Old drugs, new uses: Drug repurposing in hematological malignancies

Discovery and development of novel anti-cancer drugs are expensive and time consuming. Systems biology approaches have revealed that a drug being developed for a non-cancer indication can hit other targets as well, which play critical roles in cancer progression. Since drugs for non-cancer indications would have already gone through the preclinical and partial or full clinical development, repurposing such drugs for hematological malignancies would cost much less, and drastically reduce the development time, which is evident in case of thalidomide. Here, we have reviewed some of the drugs for their potential to repurpose for treating the hematological malignancies. We have also enlisted resources that can be helpful in drug repurposing.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

The pathway to pyrimidines: The essential focus on dihydroorotate dehydrogenase, the mitochondrial enzyme coupled to the respiratory chain

This paper is based on the Anne Simmonds Memorial Lecture, given by Monika Löffler at the International Symposium on Purine and Pyrimidine Metabolism in Man, Lyon 2019. It is dedicated to H. Anne Simmonds (died 2010) - a founding member of the ESSPPMM, since 2003 Purine and Pyrimidine Society - and her outstanding contributions to the identification and study of inborn errors of purine and pyrimidine metabolism. The distinctive intracellular arrangement of pyrimidine de novo synthesis in higher eukaryotes is important to cells with a high demand for nucleic acid synthesis. The proximity of the enzyme active sites and the resulting channeling in CAD and UMP synthase is of kinetic benefit. The intervening enzyme dihydroorotate dehydrogenase (DHODH) is located in the mitochondrion with access to the ubiquinone pool, thus ensuring efficient removal of redox equivalents through the constitutive activity of the respiratory chain, also a mechanism through which the input of 2 ATP for carbamylphosphate synthesis is balanced by Oxphos. The obligatory contribution of O₂ to de novo UMP synthesis means that DHODH has a pivotal role in adapting the proliferative capacity of cells to different conditions of oxygenation, such as hypoxia in growing tumors. DHODH also is a validated drug target in inflammatory diseases. This survey of selected topics of personal interest and reflection spans some 40 years of our studies from tumor cell cultures under hypoxia to in vitro assays including purification from mitochondria, localization, cloning, expression, biochemical characterization, crystallisation, kinetics and inhibition patterns of eukaryotic DHODH enzymes.

Multiple Sclerosis and Cancer: The Ying-Yang Effect of Disease Modifying Therapies

Over the past two decades, the field of multiple sclerosis (MS) has been transformed by the rapidly expanding arsenal of new disease modifying therapies (DMTs). Current DMTs for MS aim to modulate innate and adaptive immune responses toward a less inflammatory phenotype. Since the immune system is also critical for identifying and eliminating malignant cells, immunosuppression from DMTs may predictably increase the risk of cancer development in MS patients. Compared with healthy controls, patients with autoimmune conditions, such as MS, may already have a higher risk of developing certain malignancies and this risk may further be magnified by DMT treatments. For those patients who develop both MS and cancer, these comorbid presentations create a challenge for clinicians on how to therapeutically address management of cancer in the context of MS autoimmunity. As there are currently no accepted guidelines for managing MS patients with prior history of or newly developed malignancy, we undertook this review to evaluate the molecular mechanisms of current DMTs and their potential for instigating and treating cancer in patients living with MS.

Combined small molecule and loss-of-function screen uncovers estrogen receptor alpha and CAD as host factors for HDV infection and antiviral targets

OBJECTIVE

Hepatitis D virus (HDV) is a circular RNA virus coinfecting hepatocytes with hepatitis B virus. Chronic hepatitis D results in severe liver disease and an increased risk of liver cancer. Efficient therapeutic approaches against HDV are absent.

DESIGN

Here, we combined an RNAi loss-of-function and small molecule screen to uncover host-dependency factors for HDV infection.

RESULTS

Functional screening unravelled the hypoxia-inducible factor (HIF)-signalling and insulin-resistance pathways, RNA polymerase II, glycosaminoglycan biosynthesis and the pyrimidine metabolism as virus-hepatocyte dependency networks. Validation studies in primary human hepatocytes identified the carbamoyl-phosphatesynthetase 2, aspartate transcarbamylase and dihydroorotase (CAD) enzyme and estrogen receptor alpha (encoded by ESR1) as key host factors for HDV life cycle. Mechanistic studies revealed that the two host factors are required for viral replication. Inhibition studies using N-(phosphonoacetyl)-L-aspartic acid and fulvestrant, specific CAD and ESR1 inhibitors, respectively, uncovered their impact as antiviral targets.

CONCLUSION

The discovery of HDV host-dependency factors elucidates the pathogenesis of viral disease biology and opens therapeutic strategies for HDV cure.

Dysregulation of de novo nucleotide biosynthetic pathway enzymes in cancer and targeting opportunities

Cancer is a disease of uncontrolled cell growth and a major cause of death worldwide. Many molecular events characterize tumor initiation and progression. Global gene expression analyses using next-generation sequencing, proteomics and metabolomics show genomic, epigenetic, and metabolite concentration changes in various tumors. Molecular alterations identified include multiple cancer-driving mutations, gene fusions, amplifications, deletions, and post-translational modifications. Data integration from many high-throughput platforms unraveled dysregulation in many metabolic pathways in cancer. Since cancer cells are fast-growing, their metabolic needs are enhanced, hence the requirement for de novo synthesis of essential metabolites. One critical requirement of fast-growing cells and a historically important pathway in cancer is the nucleotide biosynthetic pathway and its enzymes are valuable targets for small molecule inhibition. Purines and pyrimidines are building blocks of DNA synthesis and due to their excessive growth, cancer cells extensively utilize de novo pathways for nucleotide biosynthesis. Methotrexate, one of the early chemotherapeutic agents, targets dihydrofolate reductase of the folate metabolic pathway that is involved in nucleotide biosynthesis. In this review, we discuss the nucleotide biosynthetic pathways in cancer and targeting opportunities.

Leflunomide Synergizes with Gemcitabine in Growth Inhibition of PC Cells and Impairs c-Myc Signaling through PIM Kinase Targeting

The immunosuppressive agent leflunomide has been used in the treatment of over 300,000 patients with rheumatoid arthritis. Its active metabolite, teriflunomide (Ter), directly inhibits dihydroorotate dehydrogenase (DHODH), an enzyme involved in nucleoside synthesis. We report that Ter not only shows in vitro anti-proliferative activity in pancreatic cancer (PC) cells as a single agent but also synergizes with the chemotherapeutic gemcitabine (Gem) in growth inhibition of PC cells. The growth-inhibitory effects of Ter are not solely caused by inhibition of DHODH. Through a kinase screening approach, we identified the PIM-3 serine-threonine kinase as a novel direct target. Subsequent dose-response kinase assays showed that Ter directly inhibited all three PIM family members, with the highest activities against PIM-3 and -1. The PIM-3 kinase was the PIM family member most often associated with PC oncogenesis and was also the kinase inhibited the most by Ter among more than 600 kinases investigated. Ter in PC cells induced changes in phosphorylation and expression of PIM downstream targets, consistent with the effects achieved by overexpression or downregulation of PIM-3. Finally, pharmacological inhibition of PIM proteins not only diminished PC cell proliferation, but also small-molecule pan-PIM and PIM-3 inhibitors synergized with Gem in growth inhibition of PC cells.

Cross-Cancer Pleiotropic Associations with Lung Cancer Risk in African Americans

BACKGROUND

Identifying genetic variants with pleiotropic associations across multiple cancers can reveal shared biologic pathways. Prior pleiotropic studies have primarily focused on European-descent individuals. Yet population-specific genetic variation can occur, and potential pleiotropic associations among diverse racial/ethnic populations could be missed. We examined cross-cancer pleiotropic associations with lung cancer risk in African Americans.

METHODS

We conducted a pleiotropic analysis among 1,410 African American lung cancer cases and 2,843 controls. We examined 36,958 variants previously associated (or in linkage disequilibrium) with cancer in prior genome-wide association studies. Logistic regression analyses were conducted, adjusting for age, sex, global ancestry, study site, and smoking status.

RESULTS

We identified three novel genomic regions significantly associated (FDR-corrected P <0.10) with lung cancer risk (rs336958 on 5q14.3, rs7186207 on 16q22.2, and rs11658063 on 17q12). On chromosome16q22.2, rs7186207 was significantly associated with reduced risk [OR = 0.43; 95% confidence interval (CI), 0.73-0.89], and functional annotation using GTEx showed rs7186207 modifies DHODH gene expression. The minor allele at rs336958 on 5q14.3 was associated with increased lung cancer risk (OR = 1.47; 95% CI, 1.22-1.78), whereas the minor allele at rs11658063 on 17q12 was associated with reduced risk (OR = 0.80; 95% CI, 0.72-0.90).

CONCLUSIONS

We identified novel associations on chromosomes 5q14.3, 16q22.2, and 17q12, which contain HNF1B, DHODH, and HAPLN1 genes, respectively. SNPs within these regions have been previously associated with multiple cancers. This is the first study to examine cross-cancer pleiotropic associations for lung cancer in African Americans.

IMPACT

Our findings demonstrate novel cross-cancer pleiotropic associations with lung cancer risk in African Americans.

Targeting of Hematologic Malignancies with PTC299, A Novel Potent Inhibitor of Dihydroorotate Dehydrogenase with Favorable Pharmaceutical Properties

PTC299 was identified as an inhibitor of VEGFA mRNA translation in a phenotypic screen and evaluated in the clinic for treatment of solid tumors. To guide precision cancer treatment, we performed extensive biological characterization of the activity of PTC299 and demonstrated that inhibition of VEGF production and cell proliferation by PTC299 is linked to a decrease in uridine nucleotides by targeting dihydroorotate dehydrogenase (DHODH), a rate-limiting enzyme for de novo pyrimidine nucleotide synthesis. Unlike previously reported DHODH inhibitors that were identified using in vitro enzyme assays, PTC299 is a more potent inhibitor of DHODH in isolated mitochondria suggesting that mitochondrial membrane lipid engagement in the DHODH conformation in situ is required for its optimal activity. PTC299 has broad and potent activity against hematologic cancer cells in preclinical models, reflecting a reduced pyrimidine nucleotide salvage pathway in leukemia cells. Archived serum samples from patients treated with PTC299 demonstrated increased levels of dihydroorotate, the substrate of DHODH, indicating target engagement in patients. PTC299 has advantages over previously reported DHODH inhibitors, including greater potency, good oral bioavailability, and lack of off-target kinase inhibition and myelosuppression, and thus may be useful for the targeted treatment of hematologic malignancies.

Revisiting the role of dihydroorotate dehydrogenase as a therapeutic target for cancer

Identified as a hallmark of cancer, metabolic reprogramming allows cancer cells to rapidly proliferate, resist chemotherapies, invade, metastasize, and survive a nutrient-deprived microenvironment. Rapidly growing cells depend on sufficient concentrations of nucleotides to sustain proliferation. One enzyme essential for the de novo biosynthesis of pyrimidine-based nucleotides is dihydroorotate dehydrogenase (DHODH), a known therapeutic target for multiple diseases. Brequinar, leflunomide, and teriflunomide, all of which are potent DHODH inhibitors, have been clinically evaluated but failed to receive FDA approval for the treatment of cancer. Inhibition of DHODH depletes intracellular pyrimidine nucleotide pools and results in cell cycle arrest in S-phase, sensitization to current chemotherapies, and differentiation in neural crest cells and acute myeloid leukemia (AML). Furthermore, DHODH is a synthetic lethal susceptibility in several oncogenic backgrounds. Therefore, DHODH-targeted therapy has potential value as part of a combination therapy for the treatment of cancer. In this review, we focus on the de novo pyrimidine biosynthesis pathway as a target for cancer therapy, and in particular, DHODH. In the first part, we provide a comprehensive overview of this pathway and its regulation in cancer. We further describe the relevance of DHODH as a target for cancer therapy using bioinformatic analyses. We then explore the preclinical and clinical results of pharmacological strategies to target the de novo pyrimidine biosynthesis pathway, with an emphasis on DHODH. Finally, we discuss potential strategies to harness DHODH as a target for the treatment of cancer.

Leflunomide counter akt s cardiac hypertrophy

Cardiac hypertrophy (CH) is a major independent risk factor for heart failure and mortality. However, therapeutic interventions that target hypertrophy signaling in a load-independent way are unavailable. In a recent issue of Clinical Science (vol. 132, issue 6, 685-699), Ma et al. describe that the anti-inflammatory drug leflunomide markedly antagonized CH, dysfunction, and fibrosis induced by aortic banding or angiotensin-II in mice or by agonists in cultured cells. Unexpectedly, this occurred not via anti-inflammatory mechanisms but rather via inhibtion of Akt (protein kinase B, PKB) signaling. We further discuss the mechanisms underlying Akt activation and its effects on CH and review possible mechanisms of leflunomide effects. Despite some caveats, the availability of such a newly repurposed compound to treat CH can be a relevant advance.

A77 1726 (leflunomide) blocks and reverses cardiac hypertrophy and fibrosis in mice

T-cell infiltration and the subsequent increased intracardial chronic inflammation play crucial roles in the development of cardiac hypertrophy and heart failure (HF). A77 1726, the active metabolite of leflunomide, has been reported to have powerful anti-inflammatory and T cell-inhibiting properties. However, the effect of A77 1726 on cardiac hypertrophy remains completely unknown. Herein, we found that A77 1726 treatment attenuated pressure overload or angiotensin II (Ang II)-induced cardiac hypertrophy in vivo, as well as agonist-induced hypertrophic response of cardiomyocytes in vitro In addition, we showed that A77 1726 administration prevented induction of cardiac fibrosis by inhibiting cardiac fibroblast (CF) transformation into myofibroblast. Surprisingly, we found that the protective effect of A77 1726 was not dependent on its T lymphocyte-inhibiting property. A77 1726 suppressed the activation of protein kinase B (AKT) signaling pathway, and overexpression of constitutively active AKT completely abolished A77 1726-mediated cardioprotective effects in vivo and in vitro Pretreatment with siRNA targetting Fyn (si Fyn) blunted the protective effect elicited by A77 1726 in vitro More importantly, A77 1726 was capable of blocking pre-established cardiac hypertrophy in mice. In conclusion, A77 1726 attenuated cardiac hypertrophy and cardiac fibrosis via inhibiting FYN/AKT signaling pathway.

Inhibition of canonical WNT/β-catenin signaling is involved in leflunomide (LEF)-mediated cytotoxic effects on renal carcinoma cells

Leflunomide (LEF), an inhibitor of dihydroorotate dehydrogenase (DHODH) in pyrimidine biosynthetic pathway, is an immunomodulatory agent approved for the treatment of rheumatoid arthritis. In this study, we show that LEF significantly reduced cell proliferation of renal carcinoma cells in a concentration-dependent manner. LEF at 50 μM induced S-phase arrest and autophagy. Higher doses of LEF (>50 μM) effectively induced cell apoptosis. Modulating the concentration of LEF resulted in distinct effects on the expression of regulatory proteins associated with cell cycle, apoptosis, and autophagy. In particular, high concentrations of LEF inhibited canonical WNT signaling by promoting nucleo-cytoplasmic shuttling and proteasome-dependent degradation of β-catenin. Mechanistic studies showed that the repression of AKT activation partly accounted for LEF-mediated WNT inhibition. Gene expression microarray revealed that LEF treatment greatly inhibited the expression of FZD10 gene, a receptor mediating WNT/β-catenin activation. In vivo xenograft study in NOD/SCID mice further validated the inhibitory effects of LEF on tumor growth and Wnt/β-catenin signaling. However, LEF treatment also triggered cell autophagy and elevated the expression of WNT3a, which ameliorated its cytotoxic effects. The combination of LEF with a WNT inhibitor IWP-2 or autophagy inhibitor HCQ could yield an enhanced anti-tumor outcome. Taken together, these results identify the potential utility and pharmacological feature of LEF in the chemotherapy of renal cell carcinoma (RCC).

Leflunomide: A promising drug with good antitumor potential

Leflunomide, an inhibitor of dihydroorotase dehydrogenase and thereby pyrimidine synthesis, was approved for treatment of rheumatoid arthritis in 1998. During the following years, leflunomide was used in various preclinical studies as a potential cancer treatment; at the same time, more mechanisms underlying the anticancer effect of leflunomide were identified. Thus, leflunomide has been identified as a potent anticancer drug. This article summarizes the mechanisms as well as results of leflunomide in the evolving field of cancer therapy.

The anti-rheumatic drug, leflunomide, synergizes with MEK inhibition to suppress melanoma growth

Cutaneous melanoma, which develops from the pigment producing cells called melanocytes, is the most deadly form of skin cancer. Unlike the majority of other cancers, the incidence rates of melanoma are still on the rise and the treatment options currently available are being hindered by resistance, limited response rates and adverse toxicity. We have previously shown that an FDA approved drug leflunomide, used for rheumatoid arthritis (RA), also holds potential therapeutic value in treating melanoma especially if used in combination with the mutant BRAF inhibitor, vemurafenib. We have further characterized the function of leflunomide and show that the drug reduces the number of viable cells in both wild-type and BRAF^V600E mutant melanoma cell lines. Further experiments have revealed leflunomide reduces cell proliferation and causes cells to arrest in G1 of the cell cycle. Cell death assays show leflunomide causes apoptosis at treatment concentrations of 25 and 50 µM. To determine if leflunomide could be used combinatorialy with other anti-melanoma drugs, it was tested in combination with the MEK inhibitor, selumetinib. This combination showed a synergistic effect in the cell lines tested. This drug combination led to an enhanced decrease in tumor size when tested in vivo compared to either drug alone, demonstrating its potential as a novel combinatorial therapy for melanoma.

HsDHODH Microdomain-Membrane Interactions Influenced by the Lipid Composition

Human dihydroorotate dehydrogenase (HsDHODH) enzyme has been studied as selective target for inhibitors to block the enzyme activity, intending to prevent proliferative diseases. The N-terminal microdomain seems to play an important role in the enzyme function. However, the molecular mechanism of action and dynamics of this region are not totally understood yet. This study analyzes the interaction and conformation in model membranes of HsDHODH microdomain using peptide analogues containing the paramagnetic amino acid TOAC at strategic positions. In buffer solution, the analogues presented a disordered conformation, but acquired a high content of α-helical structure in membrane mimetics, which was found to be lipid dependent. The microdomain peptide structure in micelles showed a very different peptide conformation when compared to the reported crystal structure, displaying a conformational flexibility of its helices, promoted by the connecting loop, which might be functionally relevant. Electron spin resonance in membrane compositions containing POPC, POPE, and cardiolipin showed that interaction of the analogues was enhanced by the presence of cardiolipin, indicating that the microdomain preferentially interacts with cardiolipin-containing membranes. Therefore, the great flexibility of the microdomain and the cardiolipin affinity should be considered in further studies aimed at finding new inhibitory compounds to fight proliferative diseases.

Checkpoint kinase 1 inhibition sensitises transformed cells to dihydroorotate dehydrogenase inhibition

Reduction in nucleotide pools through the inhibition of mitochondrial enzyme dihydroorotate dehydrogenase (DHODH) has been demonstrated to effectively reduce cancer cell proliferation and tumour growth. The current study sought to investigate whether this antiproliferative effect could be enhanced by combining Chk1 kinase inhibition. The pharmacological activity of DHODH inhibitor teriflunomide was more selective towards transformed mouse embryonic fibroblasts than their primary or immortalised counterparts, and this effect was amplified when cells were subsequently exposed to PF477736 Chk1 inhibitor. Flow cytometry analyses revealed substantial accumulations of cells in S and G2/M phases, followed by increased cytotoxicity which was characterised by caspase 3-dependent induction of cell death. Associating PF477736 with teriflunomide also significantly sensitised SUM159 and HCC1937 human triple negative breast cancer cell lines to dihydroorotate dehydrogenase inhibition. The main characteristic of this effect was the sustained accumulation of teriflunomide-induced DNA damage as cells displayed increased phospho serine 139 H2AX (γH2AX) levels and concentration-dependent phosphorylation of Chk1 on serine 345 upon exposure to the combination as compared with either inhibitor alone. Importantly a similar significant increase in cell death was observed upon dual siRNA mediated depletion of Chk1 and DHODH in both murine and human cancer cell models. Altogether these results suggest that combining DHODH and Chk1 inhibitions may be a strategy worth considering as a potential alternative to conventional chemotherapies.

Leflunomide inhibits proliferation and tumorigenesis of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most prevalent pathological cancer occurring in the head and neck area. Progress has previously been made regarding treatment strategies of OSCC, however the 5‑year survival rate of these patients is only 50%. The present study examined if leflunomide (LEF), a drug primarily used for the treatment of rheumatoid arthritis, exhibited antitumor effects in OSCC. The results demonstrated that LEF inhibited cell proliferation and blocked the cell cycle at the S phase in OSCC cells, with upregulation of cyclin A protein expression. LEF reduced the expression of dihydroorotate dehydrogenase, which is an essential enzyme in the de novo pyrimidine biosynthetic pathway. LEF additionally inhibited colony formation in soft agar and reduced tumor growth in a xenograft model. The results suggested that LEF may act as a potential therapeutic agent in the treatment of OSCC in the future.