Low dose leflunomide activates PI3K/Akt signalling in erythroleukemia cells and reduces apoptosis induced by anticancer agents

Comprehensive views toward the biomolecular recognition of an anticancer drug, leflunomide with human serum albumin

Biomolecular association of an anticancer drug, leflunomide (LEF) with human serum albumin (HSA), the leading ligands carrier in human circulation was characterized using biophysical (i.e., fluorescence, absorption and voltammetric) methods and computational (i.e., molecular docking and molecular dynamics simulation) techniques. Evaluations of fluorescence, absorption and voltammetric findings endorsed the complex formation between LEF and HSA. An inverse relationship of Stern-Volmer constant-temperature and hyperchromic shift of the protein's absorption signal with addition of LEF confirmed the LEF quenched the HSA fluorescence through static process. Moderate nature of binding strength (binding constant = 2.76-4.77 × 104 M-1) was detected towards the LEF-HSA complexation, while the association process was naturally driven via hydrophobic interactions, van der Waals interactions and hydrogen bonds, as evident from changes in entropy (ΔS= + 19.91 J mol-1 K-1) and enthalpy (ΔH = - 20.09 kJ mol-1), and molecular docking assessments. Spectral analyses of synchronous and three-dimensional fluorescence validated microenvironmental fluctuations near Trp and Tyr residues upon LEF binding to the protein. LEF association with HSA significantly defended temperature-induced destabilization of the protein. Although LEF was found to attach to HSA at Sudlow's sites I and II, but exhibited greater preference toward its site I, as detected by the investigations of competitive site-marker displacement. Molecular dynamics simulation assessment revealed that the complex attained equilibrium throughout simulations, showing the LEF-HSA complex constancy.Communicated by Ramaswamy H. Sarma.

Saliva as Blood Alternative in Therapeutic Monitoring of Teriflunomide-Development and Validation of the Novel Analytical Method

Therapeutic drug monitoring (TDM) is extremely helpful in individualizing dosage regimen of drugs with narrow therapeutic ranges. It may also be beneficial in the case of drugs characterized by serious side effects and marked interpatient pharmacokinetic variability observed with leflunomide and its biologically active metabolite, teriflunomide. One of the most popular matrices used for TDM is blood. A more readily accessible body fluid is saliva, which can be collected in a much safer way comparing to blood. This makes it especially advantageous alternative to blood during life-threatening SARS-CoV-2 pandemic. However, drug’s saliva concentration is not always a good representation of its blood concentration. The aim of this study was to verify whether saliva can be used in TDM of teriflunomide. We also developed and validated the first reliable and robust LC-MS/MS method for quantification of teriflunomide in saliva. Additionally, the effect of salivary flow and swab absorptive material from the collector device on teriflunomide concentration in saliva was evaluated. Good linear correlation was obtained between the concentration of teriflunomide in plasma and resting saliva (p < 0.000016, r = 0.88), and even better between plasma and the stimulated saliva concentrations (p < 0.000001, r = 0.95) confirming the effectiveness of this non-invasive method of teriflunomide’s TDM. The analyzed validation criteria were fulfilled. No significant influence of salivary flow (p = 0.198) or type of swab in the Salivette device on saliva’s teriflunomide concentration was detected. However, to reduce variability the use of stimulated saliva and synthetic swabs is advised.

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.

Leflunomide an immunomodulator with antineoplastic and antiviral potentials but drug-induced liver injury: A comprehensive review

Leflunomide (LF) represents the prototype member of dihydroorotate dehydrogenase (DHODH) enzyme inhibitors. DHODH is a mitochondrial inner membrane enzyme responsible for catalytic conversion of dihydroorotate into orotate, a rate-limiting step in the de novo synthesis of the pyrimidine nucleotides. LF produces cellular depletion of pyrimidine nucleotides required for cell growth and proliferation. Based on the affected cells the outcome can be attainable as immunosuppression, antiproliferative, and/or the recently gained attention of the antiviral potentials of LF and its new congeners. Also, protein tyrosine kinase inhibition is an additional mechanistic benefit of LF, which inhibits immunological events such as cellular expansion and immunoglobulin production with an enhanced release of immunosuppressant cytokines. LF is approved for the treatment of autoimmune arthritis of rheumatoid and psoriatic pathogenesis. Also, LF has been used off-label for the treatment of relapsing-remitting multiple sclerosis. However, LF antiviral activity is repurposed and under investigation with related compounds under a phase-I trial as a SARS CoV-2 antiviral in cases with COVID-19. Despite success in improving patients' mobility and reducing joint destruction, reported events of LF-induced liver injury necessitated regulatory precautions. LF should not be used in patients with hepatic impairment or in combination with drugs elaborating a burden on the liver without regular monitoring of liver enzymes and serum bilirubin as safety biomarkers. This study aims to review the pharmacological and safety profile of LF with a focus on the LF-induced hepatic injury from the perspective of pathophysiology and possible protective agents.

Nose-to-brain delivery of teriflunomide-loaded lipid-based carbopol-gellan gum nanogel for glioma: Pharmacological and in vitro cytotoxicity studies

The research work was intended to formulate teriflunomide (TFM) loaded nano lipid-based (TNLC) carbopol-gellan gum in situ gel (TNLCGHG) and to investigate its therapeutic efficacy against glioma, a brain and spine tumor. Nanoformulation was developed using gellan gum and carbopol 974P as gelling and mucoadhesive agents, respectively, Glyceryl di-behenate and Glyceryl mono-linoleate blend as lipids, and Gelucire 44/14: water blend as surfactant system. Globule size, PDI, zeta potential, encapsulation efficiency, mucoadhesive strength, and nasal permeation were found to be 117.80 nm, 0.56, -21.86 mV, 81.16%, 4.80 g, and 904 μg/cm², respectively. Anticancer efficacy of TFM-loaded nano lipid-based carbopol-gellan gum in situ gel (TNLCGHG) was determined in human U-87MG glioma cell line. IC₅₀ was found 7.0 μg/mL for TNLCGHG, 4.8 μg/mL for pure TFM, and 78.5 μg/mL for TNLC, which approve the superiority of surfactant along with gellan gum as permeation enhancer. Brain C_max for technetium (^99mTC) labeled intranasal (i.n.) ^99mTC-TNLCGHG was found 2-folds higher than ^99mTC-TNLC (i.n.) and ^99mTC-TNLC intravenous (i.v.) because the TNLCGHG formulation contains surfactant with natural gelling polymers, which promisingly improved drug permeability. Finally, this research revealed encouraging outcomes and successfully developed intranasal TNLCGHG nanoformulation as a novel tool for safe delivery of TFM in glioma patients.

Drug Screen Identifies Leflunomide for Treatment of Inflammatory Bowel Disease Caused by TTC7A Deficiency

BACKGROUND & AIMS

Mutations in the tetratricopeptide repeat domain 7A gene (TTC7A) cause intestinal epithelial and immune defects. Patients can become immune deficient and develop apoptotic enterocolitis, multiple intestinal atresia, and recurrent intestinal stenosis. The intestinal disease in patients with TTC7A deficiency is severe and untreatable, and it recurs despite resection or allogeneic hematopoietic stem cell transplant. We screened drugs for those that prevent apoptosis of in cells with TTC7A deficiency and tested their effects in an animal model of the disease.

METHODS

We developed a high-throughput screen to identify compounds approved by the US Food and Drug Administration that reduce activity of caspases 3 and 7 in TTC7A-knockout (TTC7A-KO) HAP1 (human haploid) cells and reduce the susceptibility to apoptosis. We validated the effects of identified agents in HeLa cells that stably express TTC7A with point mutations found in patients. Signaling pathways in cells were analyzed by immunoblots. We tested the effects of identified agents in zebrafish with disruption of ttc7a, which develop intestinal defects, and colonoids derived from biopsy samples of patients with and without mutations in TTC7A. We performed real-time imaging of intestinal peristalsis in zebrafish and histologic analyses of intestinal tissues from patients and zebrafish. Colonoids were analyzed by immunofluorescence and for ion transport.

RESULTS

TTC7A-KO HAP1 cells have abnormal morphology and undergo apoptosis, due to increased levels of active caspases 3 and 7. We identified drugs that increased cell viability; leflunomide (used to treat patients with inflammatory conditions) reduced caspase 3 and 7 activity in cells by 96%. TTC7A-KO cells contained cleaved caspase 3 and had reduced levels of phosphorylated AKT and X-linked inhibitor of apoptosis (XIAP); incubation of these cells with leflunomide increased levels of phosphorylated AKT and XIAP and reduced levels of cleaved caspase 3. Administration of leflunomide to ttc7a^-/- zebrafish increased gut motility, reduced intestinal tract narrowing, increased intestinal cell survival, increased sizes of intestinal luminal spaces, and restored villi and goblet cell morphology. Exposure of patient-derived colonoids to leflunomide increased cell survival, polarity, and transport function.

CONCLUSIONS

In a drug screen, we identified leflunomide as an agent that reduces apoptosis and activates AKT signaling in TTC7A-KO cells. In zebrafish with disruption of ttc7a, leflunomide restores gut motility, reduces intestinal tract narrowing, and increases intestinal cell survival. This drug might be repurposed for treatment of TTC7A deficiency.

Nanostructured lipid carriers engineered for intranasal delivery of teriflunomide in multiple sclerosis: optimization and in vivo studies

BACKGROUND

Multiple sclerosis (MS) is one of the most severe autoimmune disorder of the central nervous system (CNS).

OBJECTIVE

The present research work was aimed to formulate and investigate teriflunomide (TFM)-loaded intranasal (i.n.) nanostructured lipid carriers (NLC) for the treatment of multiple sclerosis (MS).

METHODS

The TFM-loaded NLC (TFM-NLC) nanoparticles were prepared by melt emulsification ultrasonication method using biodegradable and biocompatible polymers. The Box-Behnken statistical design was applied to optimize the formulation. The optimized NLC formulation was subjected to evaluate for particle size, entrapment efficiency (%), in vitro and ex vivo permeation. The safety and efficacy of optimized formulations were demonstrated using pharmacodynamic, subacute toxicity and hepatotoxicity data.

RESULTS

Experimental data demonstrated that optimized NLC formulation (F17) showed significant size (99.82 ± 1.36 nm), zeta potential (-22.29 ± 1.8 mV) and % entrapment efficiency (83.39 ± 1.24%). Alternatively, ex vivo permeation of TFM mucoadhesive NLC (TFM-MNLC) and TFM-NLC was observed 830 ± 7.6 and 651 ± 9.8 µg/cm², respectively. Whereas, TFM-MNLC shows around 2.0-folds more J_ss than the TFM-NLC. Finally, TFM-MNLC (i.n.) formulation produced the rapid remyelination in cuprizone-treated animals and decreases the number of entries in open compartment of EPM when compared with negative control and TFM-NLC (oral) animals. Simultaneously, the nanoformulation did not reflect any gross changes in hepatic biomarkers and subacute toxicity when compared with control.

CONCLUSIONS

Hence it can be inferred that the nose-to-brain delivery of TFM-MNLC can be considered as effective and safe delivery for brain disorders.

Drug repurposing in cancer

Cancer is a major health issue worldwide, and the global burden of cancer is expected to increase in the coming years. Whereas the limited success with current therapies has driven huge investments into drug development, the average number of FDA approvals per year has declined since the 1990s. This unmet need for more effective anti-cancer drugs has sparked a growing interest for drug repurposing, i.e. using drugs already approved for other indications to treat cancer. As such, data both from pre-clinical experiments, clinical trials and observational studies have demonstrated anti-tumor efficacy for compounds within a wide range of drug classes other than cancer. Whereas some of them induce cancer cell death or suppress various aspects of cancer cell behavior in established tumors, others may prevent cancer development. Here, we provide an overview of promising candidates for drug repurposing in cancer, as well as studies describing the biological mechanisms underlying their anti-neoplastic effects.

Resistance to ursolic acid-induced apoptosis through involvement of melanogenesis and COX-2/PGE2 pathways in human M4Beu melanoma cancer cells

Melanoma is one of the most aggressive forms of cancer with a continuously growing incidence worldwide and is usually resistant to chemotherapy agents, which is due in part to a strong resistance to apoptosis. Previously, we had showed that B16-F0 murine melanoma cells undergoing apoptosis are able to delay their own death induced by ursolic acid (UA), a natural pentacyclic triterpenoid compound. We had demonstrated that tyrosinase and TRP-1 up-regulation in apoptotic cells and the subsequent production of melanin were implicated in an apoptosis resistance mechanism. Several resistance mechanisms to apoptosis have been characterized in melanoma such as hyperactivation of DNA repair mechanisms, drug efflux systems, and reinforcement of survival signals (PI3K/Akt, NF-κB and Raf/MAPK pathways). Otherwise, other mechanisms of apoptosis resistance involving different proteins, such as cyclooxygenase-2 (COX-2), have been described in many cancer types. By using a strategy of specific inhibition of each ways, we suggested that there was an interaction between melanogenesis and COX-2/PGE2 pathway. This was characterized by analyzing the COX-2 expression and activity, the expression of tyrosinase and melanin production. Furthermore, we showed that anti-proliferative and proapoptotic effects of UA were mediated through modulation of multiple signaling pathways including Akt and ERK-1/2 proteins. Our study not only uncovers underlying molecular mechanisms of UA action in human melanoma cancer cells but also suggest its great potential as an adjuvant in treatment and cancer prevention.

Teriflunomide, an immunomodulatory drug, exerts anticancer activity in triple negative breast cancer cells

Triple-negative breast cancer (TNBC) is defined as a group of primary breast cancers lacking expression of estrogen, progesterone, and human epidermal growth factor receptor-2 (HER-2) receptors, characterized by higher relapse rate and lower survival compared with other subtypes. Due to lack of identified targets and molecular heterogeneity, conventional chemotherapy is the only available option for treatment of TNBC, but non-discordant positive therapeutic efficacy could not be achieved. Here, we demonstrated that these TNBC cells were sensitive to teriflunomide, which was a well-known immunomodulatory drug for treatment of relapsing multiple sclerosis (MS). Potent anti-cancer effects in TNBC in vitro, including proliferation inhibition, cell cycle delay, cell apoptosis, and suppression of cell motility and invasiveness, could be achieved with this agent. Of note, we showed that multiple signals involved in TNBC proliferation, survival, migratory, and invasive potential were under regulation by teriflunomide. Among them, we identified down-regulation of growth factor receptors to abolish growth maintenance, suppression of c-Myc, and cyclin D1 to contribute to its anti-proliferative effect, modulation of components of cell cycle to induce S-phase arrest, degradation of Bcl-xL, and up-regulation of BAX via activation of MAPK pathway to induce apoptosis, and inhibition of epithelial-mesenchymal transition (EMT) process, matrix metalloproteinase-9 (MMP9) expression, and inactivation of Src/FAK to reduce TNBC migration and invasion. The results identified teriflunomide may be of therapeutic benefit for the more aggressive and difficult-to-treat breast cancer subtype, indicating the use of teriflunomide for clinical trials for treatment of TNBC patients.

Cyclooxygenase-2 positively regulates Akt signalling and enhances survival of erythroleukemia cells exposed to anticancer agents

Cyclooxygenase-2 (COX-2) has been found to be highly expressed in many types of cancers and to contribute to tumorigenesis via the inhibition of apoptosis, increased angiogenesis and invasiveness. In hematological malignancies, COX-2 expression was found to correlate with poor patient prognosis. However, the exact role of COX-2 expression in these malignancies, and particularly in erythroleukemias, remains unclear. The aim of this work was to describe and understand the relationships between COX-2 expression and apoptosis rate in erythroleukemia cells after apoptosis induction by several anticancer agents. We used three different erythroleukemia cell lines in which COX-2 expression was modulated by transfection with either COX-2 siRNA or COX-2 cDNA. These cellular models were then treated with apoptosis inducers and apoptosis onset and intensity was followed. Cell signalling was evaluated in unstimulated transfected cells or after apoptosis induction. We found that COX-2 inhibition rendered erythroleukemia cells more sensitive to apoptosis induction and that in cells overexpressing COX-2 apoptosis induction was reduced. We demonstrated that COX-2 inhibition decreased the pro-survival Akt signalling and activated the negative regulator of Akt signalling, phosphatase and tensin homologue deleted on chromosome 10 (PTEN). Conversely, in COX-2 overexpressing cells, Akt signalling was activated and PTEN was inhibited. In these last cells, inhibition of casein kinase 2 or Akt signalling restored sensitivity to apoptotic agents. Our findings highlighted that COX-2 can positively regulate Akt signalling mostly through PTEN inhibition, partly via casein kinase 2 activation, and enhances survival of erythroleukemia cells exposed to anticancer agents.

Leflunomide inhibits the apoptosis of human embryonic lung fibroblasts infected by human cytomegalovirus

BACKGROUND

The immunomodulatory drug leflunomide (LEF) is frequently used for treating human cytomegalovirus (HCMV), but its antiviral mechanism is still unclear. In this study,we therefore investigated the effects of the active LEF metabolite A771726 on the HCMV lifecycle in human embryonic lung fibroblasts. We clarified the mechanism of LEF antiviral infection, and provide a new way to treat immune dysfunction patients with HCMV infection.

METHODS

The experiment was divided into four groups: the control group, the HCMV group, the ganciclovir+HCMV group as well as the LEF+HCMV group. MTT was used for assessment of the cell inhibitory rate. Apoptosis was measured by staining with fluorescein isothiocyanate Annexin V and propidium iodide. Statistical significance was determined by paired t-test using SPSS software.

RESULTS

The results of the study showed that cell proliferation was significantly inhibited by HCMV at 24 hours and 48 hours. With increasing HCMV concentration, the value-added inhibition of the cells was significantly decreased compared with the control group, and was statistically significant (P<0.01). Ganciclovir can increase proliferation of cells infected with HCMV; compared with the control group it was statistically significant (P<0.05). Meanwhile, with LEF treatment cell proliferation was significantly improved at 24 hours and 48 hours, with statistical significance (P<0.05). The apoptosis rate of human embryonic lung fibroblasts infected with HCMV increased significantly at 24 hours, 48 hours and 72 hours, and as time goes on the apoptosis rate increases statistically significantly (P<0.01) compared with the control group The apoptosis rate of the HCMV infection group decreased by adding LEF,and was statistically significant (P<0.05).

CONCLUSIONS

In this study we show that LEF is an exciting new drug for cytomegalovirus infection. LEF significantly inhibited HCMV infection-induced apoptosis and proliferation, playing an important role in the treatment of patients infected by HCMV. In this study we explored the potential usefulness of LEF for cytomegalovirus infection and found it to be a cost-effective new treatment for cytomegalovirus infection that deserves further study.

Cyclopamine and jervine induce COX-2 overexpression in human erythroleukemia cells but only cyclopamine has a pro-apoptotic effect

Erythroleukemia is generally associated with a very poor response and survival to current available therapeutic agents. Cyclooxygenase-2 (COX-2) has been described to play a crucial role in the proliferation and differentiation of leukemia cells, this enzyme seems to play an important role in chemoresistance in different cancer types. Previously, we demonstrated that diosgenin, a plant steroid, induced apoptosis in HEL cells with concomitant COX-2 overexpression. In this study, we investigated the antiproliferative and apoptotic effects of cyclopamine and jervine, two steroidal alkaloids with similar structures, on HEL and TF1a human erythroleukemia cell lines and, for the first time, their effect on COX-2 expression. Cyclopamine, but not jervine, inhibited cell proliferation and induced apoptosis in these cells. Both compounds induced COX-2 overexpression which was responsible for apoptosis resistance. In jervine-treated cells, COX-2 overexpression was NF-κB dependent. Inhibition of NF-κB reduced COX-2 overexpression and induced apoptosis. In addition, cyclopamine induced apoptosis and COX-2 overexpression via PKC activation. Inhibition of the PKC pathway reduced both apoptosis and COX-2 overexpression in both cell lines. Furthermore, we demonstrated that the p38/COX-2 pathway was involved in resistance to cyclopamine-induced apoptosis since p38 inhibition reduced COX-2 overexpression and increased apoptosis in both cell lines.

Aryl hydrocarbon receptor agonist, leflunomide, protects the ischemic-reperfused kidney: role of Tregs and stem cells

The aryl hydrocarbon receptor (AHR) has emerged as a major modulator of inflammatory processes. We tested the hypothesis that AHR activation protects the ischemic-reperfused kidney in association with the suppression of the inflammatory response. Accordingly, male mice were treated with the nondioxin AHR agonist, leflunomide (40 mg/kg ip); vehicle-treated animals served as controls. Thereafter, the right kidney was subjected to an ischemia (45 min)-reperfusion (4 h) insult, while the left kidney served as a sham control. Renal cells prepared from ischemic-reperfused kidneys of leflunomide-treated mice displayed preservation of mitochondrial membrane potential (Ψ(m)) and decreased apoptosis and necrosis compared with vehicle-treated ischemic-reperfused kidneys. Leflunomide treatment increased regulatory T cells (Tregs; forkhead box P3+) and IL-10-positive cells but reduced IL-17- and IL-23-expressing cells in both the peripheral blood and kidney cells, indicative of down-regulation of inflammatory responses. Leflunomide treatment also increased mobilization of stems cells subsets (i.e., mesenchymal and hematopoietic stem cells and endothelial progenitor cells) in the peripheral blood and promoted their recruitment into the ischemic-reperfused kidney. Collectively, the results indicate that AHR stimulation may represent a novel renoprotective mechanism likely involving mobilization and recruitment of Tregs and stem cells into the damaged kidney.

Raf/MEK/ERK signaling inhibition enhances the ability of dequalinium to induce apoptosis in the human leukemic cell line K562

Delocalized lipophilic cations, such as dequalinium (DQA), selectively accumulate in mitochondria and display anticancer activity in cells from different malignancies. Previous studies in K562 human leukemic cells indicate that DQA causes cell damage as a consequence of an early disturbance in the mitochondrial function, inducing oxidative stress. These cells turned out to be resistant to apoptosis and died by necrosis when treated with high DQA concentrations (20 μmol/L) for long time periods (48 h). Resistance of K562 cells to DQA-induced apoptosis could be eliminated by inhibition of the kinase activity of the Bcr-Abl protein with imatinib. In this paper, we have studied the effect of DQA on the Raf/MEK/ERK1/2 and PI3K/Akt signal transduction pathways in K562 cells. Our data suggest a DQA downregulatory activity on both ERK1/2 and PI3K protein kinase activity supporting an interaction between both proteins. Moreover, inhibition of ERK1/2 with U0126 enhanced the ability of DQA to potentiate imatinib-induced apoptosis, suggesting a role of the Raf/MEK/ERK pathway and the Bcr-Abl tyrosine kinase in the K562 cell survival. This study contributes to a better understanding of the action mechanism of DQA on K562 cells and encourages the study of DQA in combination with other agents for improving the efficacy of targeted therapies and overcoming resistance to chemotherapeutic agents.

The inhibitors of nucleotide biosynthesis leflunomide, FK778, and mycophenolic acid activate hepatitis B virus replication in vitro

The inhibitors of pyrimidine synthesis, leflunomide and FK778, have been reported to exert broad antiviral effects, in addition to their immunosuppressive activities. Their possible therapeutic benefit for transplantation medicine is currently discussed, because they also block the replication of human cytomegalovirus and human polyomavirus BK, which both cause important complications in transplant recipients. Here, we show that leflunomide and FK778 strongly enhance hepatitis B virus (HBV) replication in vitro. This activity is shared by mycophenolic acid (MPA), an inhibitor of purine biosynthesis. Stimulation of HBV replication by these agents was linked to their inhibitory effects on de novo nucleotide biosynthesis because it could be efficiently counteracted by external nucleoside supply. Mechanistically, we found that mitogen-activated protein kinase p38 played a key role for the enhancement of HBV replication by leflunomide, FK778, and MPA. All three HBV-activating compounds increased p38 phosphorylation, in contrast to the HBV inhibitors, telbivudine and cyclosporine A. Moreover, silencing of p38 expression through RNA interference efficiently counteracted the stimulatory effect of leflunomide, FK778, and MPA on HBV replication.

CONCLUSION

Our data indicate that, in contrast to their reported inhibitory effects on other viruses, both leflunomide and FK778 can augment HBV replication. Treatment with leflunomide, FK778, or MPA may bear the risk to enhance HBV replication in infected patients.

HT-29 colorectal cancer cells undergoing apoptosis overexpress COX-2 to delay ursolic acid-induced cell death

Colorectal cancer is one of the most common cancer types and the third leading cause of cancer-related death in the western world. Generally, colorectal cancers are resistant to anticancer drugs. Several lines of evidence support a critical role for cyclooxygenase-2 (COX-2) during colorectal tumorigenesis and its role in chemoresistance. In this study, we focused our interest on the role played by COX-2 in apoptosis induced in HT-29 human colorectal cancer cells by ursolic acid (UA), a triterpenoid found in a large variety of plants. We showed that UA-induced apoptosis and that COX-2 was overexpressed only in apoptotic cells. We demonstrated that this overexpression was mediated by the p38 MAP kinase pathway as inhibiting its activation using a p38-specific inhibitor, SB 203580, abrogated COX-2 expression. Inhibiting COX-2 expression either by using a p38-specific inhibitor or COX-2-specific siRNA increased apoptosis. These results demonstrated that COX-2 was involved in a resistance mechanism to UA-induced apoptosis in HT-29 cells. Cells undergoing apoptosis were able to trigger a resistance mechanism by overexpressing a protein such as COX-2 to delay their death. Furthermore, we demonstrated that this resistance mechanism was independent of PGE(2) production as the addition of the specific COX-2 activity inhibitor, NS-398, did not affect apoptosis in UA-treated cells.

The active metabolite of leflunomide, A77 1726, protects rat hepatocytes against bile acid-induced apoptosis

BACKGROUND/AIMS

Leflunomide is used in the treatment of autoimmune diseases as an anti-inflammatory agent. Leflunomide and its active metabolite A77 1726 modulate mitogen-activated protein kinases (MAPK), Src kinases, the phosphoinositide-3 kinase (PI3K)/Akt-pathway and nuclear factor (NF)-kappaB activation. Both cell protective and cytotoxic effects of leflunomide have been described. Since leflunomide affects pathways involved in hepatocyte cell survival, we examined the effects of A77 1726 on hepatocyte cell death.

METHODS

Primary rat hepatocytes were exposed to the bile acid glycochenodeoxycholic acid (GCDCA), the superoxide anion donor menadione, or tumor necrosis factor (TNF) alpha in combination with actinomycin D. Activation of MAP-kinases was determined by Western blot analysis. Apoptosis and necrosis were analyzed by acridine orange staining and caspase activity and Sytox Green staining, respectively.

RESULTS

A77 1726 dose-dependently reduces GCDCA-induced apoptosis and necrosis, but not menadione- or TNFalpha/ActD-induced apoptosis. The hepatoprotective effect of A77 1726 does not involve ERK1/2, p38 or PI3K/Akt activation. A77 1726 does not inhibit NF-kappaB activation in hepatocytes.

CONCLUSIONS

Since A77 1726 inhibits bile acid-induced apoptosis and does not sensitize hepatocytes to TNFalpha, our results suggest that A77 1726 could be considered for the treatment of chronic liver diseases accompanied by elevated bile acid levels and inflammation.