Irreversible inhibition of human cytomegalovirus replication by topoisomerase II inhibitor, etoposide: a new strategy for the treatment of human cytomegalovirus infection

Topoisomerase II β Gene Specific siRNA Delivery by Nanoparticles Prepared with c-ter Apotransferrin and its Effect on HIV-1 Replication

Topoisomerase II beta (Topo IIβ) is one of the two isoforms of type II topoisomerases present in higher eukaryotes. This 180 kDa nuclear protein involves in different cellular processes like transcription, recombination, etc., apart from its normal topological functions. Previously, we have reported the association of this isoform along with the other isoform topoisomerase II alpha (Topo IIα) with HIV-1 reverse transcription complex and the downregulation of Topo IIβ expression resulted in incomplete reverse transcription. In this study, we have tested the Topo IIβ specific siRNA delivery using protein nanoparticles prepared with c-terminal domine of transferrin (c-ter) for the first time. Results show that, c-ter nanoparticles resemble apotransferrin nanoparticles in drug holding capability and drug delivery but with small in size. Topo IIβ specific siRNA delivered in the form of c-ter nanoformulation resulted in knockdown of Topo IIβ expression for the prolonged periods and which intern resulted in decreased viral replication of HIV-1.

Development of a high-content screen for the identification of inhibitors directed against the early steps of the cytomegalovirus infectious cycle

Human cytomegalovirus (CMV) is a latent and persistent virus whose proliferation increases morbidity and mortality of immune-compromised individuals. The current anti-CMV therapeutics targeting the viral DNA polymerase or the major immediate-early (MIE) gene locus are somewhat effective at limiting CMV-associated disease. However, due to low bioavailability, severe toxicity, and the development of drug resistant CMV strains following prolonged treatment, current anti-CMV therapeutics are insufficient. To help address this shortfall, we established a high-content assay to identify inhibitors targeting CMV entry and the early steps of infection. The infection of primary human fibroblasts with a variant of the CMV laboratory strain AD169 expressing a chimeric IE2-yellow fluorescence protein (YFP) (AD169IE2-YFP) provided the basis for the high-content assay. The localization of IE2-YFP to the nucleus shortly following an AD169IE2-YFP infection induced a robust fluorescent signal that was quantified using confocal microscopy. The assay was optimized to achieve outstanding assay fitness and high Z' scores. We then screened a bioactive chemical library consisting of 2080 compounds and identified hit compounds based on the decrease of fluorescence signal from IE2-YFP nuclear expression. The hit compounds likely target various cellular processes involved in the early steps of infection including capsid transport, chromatin remodeling, and viral gene expression. Extensive secondary assays confirmed the ability of a hit compound, convallatoxin, to inhibit infection of both laboratory and clinical CMV strains and limit virus proliferation. Collectively, the data demonstrate that we have established a robust high-content screen to identify compounds that limit the early steps of the CMV life cycle, and that novel inhibitors of early infection events may serve as viable CMV therapeutics.

Involvement of human topoisomerase II isoforms in HIV-1 reverse transcription

HIV-1 reverse transcription (RTn) involves synthesis of double strand DNA (dsDNA) from viral genomic RNA. Topoisomerase II (Topo II) alpha and beta maintains topological reorganization of dsDNA regions and catalytic inhibition of these isoforms repressed viral replicative cycle. Present study is aimed to understand the role of Topo II isoforms in HIV-1 early replication. Topo IIα and β showed differential expression in SupT1 cells and PBMCs during early hours of HIV-1 infection where Topo IIα expression increased after 4h, while Topo IIβ showed relatively higher expression at 1 and 4h. In Topo IIα and/or β down regulated cells, transcription of viral genes gag, pol and env as well as proviral DNA synthesis was abolished. In Topo IIα and/or β down regulated cells, strong stop DNA synthesis was unaffected while other downstream events of reverse transcription such as first strand transfer, full length minus strand synthesis, and second strand transfer were completely inhibited, which affects HIV-1 replication. Further, co-localization of Topo II isoforms with HIV-1 reverse transcriptase was observed in SupT1 cells and PBMCs by immunofluorescence. These results collectively suggest a role of Topo II isoforms during HIV-1 RTn probably by promoting the alignment of viral RNA-DNA hybrids.

The multi-targeted kinase inhibitor sorafenib inhibits human cytomegalovirus replication

Human cytomegalovirus (HCMV) is a major pathogen in immunocompromised individuals. Here, non-toxic concentrations of the anti-cancer kinase inhibitor sorafenib were shown to inhibit replication of different HCMV strains (including a ganciclovir-resistant strain) in different cell types. In contrast to established anti-HCMV drugs, sorafenib inhibited HCMV major immediate early promoter activity and HCMV immediate early antigen (IEA) expression. Sorafenib is known to inhibit Raf. Comparison of sorafenib with the MEK inhibitor U0126 suggested that sorafenib inhibits HCMV IEA expression through inhibition of Raf but independently of signaling through the Raf downstream kinase MEK 1/2. In concordance, siRNA-mediated depletion of Raf but not of MEK-reduced IEA expression. In conclusion, sorafenib diminished HCMV replication in clinically relevant concentrations and inhibited HCMV IEA expression, a pathophysiologically relevant event that is not affected by established anti-HCMV drugs. Moreover, we demonstrated for the first time that Raf activation is involved in HCMV IEA expression.

Cytotoxicity of bacterial-derived toxins to immortal lung epithelial and macrophage cells

Health risks associated with inhalation and deposition of biological materials have been a topic of great concern due to highly publicized cases of inhalation anthrax, of new regulations on the release of particulate matter, and to increased concerns on the hazards of indoor air pollution. Here, we present an evaluation of the sensitivity of two immortal cell lines (A549, human lung carcinoma epithelia) and NR8383 (rat alveolar macrophages) to a variety of bacterial-derived inhalation hazards and simulants including etoposide, gliotoxin, streptolysin O, and warfarin. The cell response is evaluated through quantification of changes in mitochondrial succinate dehydrogenase activity, release of lactate dehydrogenase, initiation of apoptosis, and through changes in morphology as determined by visible light microscopy and scanning electron microscopy. These cells display dose-response relations to each toxin, except for triton which has a step change response. The first observable responses of the epithelial cells to these compounds are changes in metabolism for one toxin (warfarin) and alterations in membrane permeability for another (gliotoxin). The other four toxins display a similar time course in response as gauged by changes in metabolism and loss of membrane integrity. Macrophages are more sensitive to most toxins; however, they display a lower level of stability. This information can be used in the design of cell-based sensors responding to these and similar hazards.

A study of the Topoisomerase II activity in HIV-1 replication using the ferrocene derivatives as probes

Human Topoisomerase II is present in two isoforms, 170KDa alpha and 180KDa beta. Both the isoforms play a crucial role in maintenance of topological changes during DNA replication and recombination. It has been shown that Topoisomerase II activity is required for HIV-1 replication and the enzyme is phosphorylated during early time points of HIV-1 replication. In the present study, we have studied the molecular action of Topoisomerase II inhibitors, azalactone ferrocene (AzaFecp), Thiomorpholide amido methyl ferrocene (ThioFecp), and Ruthenium benzene amino pyridine (Ru(ben)Apy) on cell proliferation and also on various events of HIV-1 replication cycle. The Topoisomerase II beta over-expressing neuroblastoma cell line shows a higher sensitivity to these compounds compared to the Sup-T1 cell line. All the three Topoisomerase II inhibitors show significant anti-HIV activity at nanomolar concentrations against an Indian isolate of HIV-1(93IN101) in Sup-T1 cell line. An analysis of action of these compounds on proviral DNA synthesis at 5h of post-infection shows that they inhibit proviral DNA synthesis as well as the formation of pre-integration complexes completely. Further analysis, using polymerase chain reaction and western blot, showed that both the Topoisomerase II alpha and beta isoforms are present in the pre-integration complexes, suggesting their significant role in HIV-1 replication.

Alterations of A549 lung cell gene expression in response to biochemical toxins

Health risks associated with the inhalation of potentially toxic materials have been a topic of great public concern. In vitro cellular analyses can provide mechanistic information on the molecular-level responses of lung-derived cell lines to a variety of these hazards. This understanding may be used to develop methods to reduce the damage from such toxins or to detect early stages of their effects. Here we describe an evaluation of the alterations in gene expression of an immortalized lung cell line (A549, human type II epithelia) to a variety of inhalation health hazards including etoposide, gliotoxin, streptolysin O, methyl methansesulfonate (MMS), and Triton X-100. The A549 cells display a dose-response relationship to each toxin with initial responses including alterations in metabolic activity, increases in membrane permeability, and initiation of response genes. In general, membrane-damaging agents (streptolysin O and Triton X-100) induce production of new ion channel proteins, structural proteins, and metabolic enzymes. Gliotoxin impacted the metabolic machinery, but also altered ion channels. Etoposide and MMS caused alterations in the cell cycle, induced DNA repair enzymes, and initiated apoptotic pathways, but MMS also induced immune response cascades. The mechanism of cell response to each toxin is supported by physiological analyses that indicated a fairly slow initiation of cell response to all compounds tested, except for Triton, which caused rapid decline in cell function due to solubilization of the cell membrane. However, Triton does induce production of a number of cell membrane-associated proteins and so its effects at low concentrations are likely translated throughout the cell. Together these results indicate a broader array of cellular responses to each of the test toxins than have previously been reported.

Chemical library screen for novel inhibitors of Kaposi's sarcoma-associated herpesvirus processive DNA synthesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma and certain lymphoproliferative disorders. The role of KSHV lytic replication has been implicated in the tumor pathogenesis. A highly specific molecular complex formed by the KSHV DNA polymerase (POL8) and processivity factor (PF8) is indispensable for lytic viral DNA synthesis and may serve as an excellent molecular anti-KSHV target. The majority of conventional nucleoside-based anti-herpetic DNA synthesis inhibitors require intracellular phosphorylation/activation before they can exert inhibitory activity as competitive substrates for viral DNA polymerases. Novel and more potent inhibitors of KSHV DNA synthesis may be discovered through POL8/PF8-targeted high throughput screening (HTS) of small molecule chemical libraries. We developed a microplate-based KSHV POL8/PF8-mediated DNA synthesis inhibition assay suitable for HTS and screened the NCI Diversity Set that comprised 1992 synthetic compounds. Twenty-eight compounds exhibited greater than 50% inhibition. The inhibitory activity was confirmed for 25 of the 26 hit compounds available for further testing, with the 50% inhibitory concentrations ranging from 0.12+/-0.07 microM (mean+/-S.D.) to 10.83+/-4.19 microM. Eighteen of the confirmed active compounds efficiently blocked KSHV processive DNA synthesis in vitro. One of the hit compounds, NSC 373989, a pyrimidoquinoline analog, was shown to dose-dependently reduce the levels of KSHV virion production and KSHV DNA in lytically induced KSHV-infected BCBL-1 cells, suggesting that the compound blocked lytic KSHV DNA synthesis. HTS for KSHV POL8/PF8 inhibitors is feasible and may lead to discovery of novel non-nucleoside KSHV DNA synthesis inhibitors.

Adeno-associated virus mediated endostatin gene therapy in combination with topoisomerase inhibitor effectively controls liver tumor in mouse model

AIM: rAAV mediated endostatin gene therapy has been examined as a new method for treating cancer. However, a sustained and high protein delivery is required to achieve the desired therapeutic effects. We evaluated the impact of topoisomerase inhibitors in rAAV delivered endostatin gene therapy in a liver tumor model.

METHODS: rAAV containing endostatin expression cassettes were transduced into hepatoma cell lines. To test whether the topoisomerase inhibitor pretreatment increased the expression of endostatin, Western blotting and ELISA were performed. The biologic activity of endostatin was confirmed by endothelial cell proliferation and tube formation assays. The anti-tumor effects of the rAAV-endostatin vector combined with a topoisomerase inhibitor, etoposide, were evaluated in a mouse liver tumor model.

RESULTS: Topoisomerase inhibitors, including camptothecin and etoposide, were found to increase the endostatin expression level in vitro. The over-expressed endostatin, as a result of pretreatment with a topoisomerase inhibitor, was also biologically active. In animal experiments, the combined therapy of topoisomerase inhibitor, etoposide with the rAAV-endostatin vector had the best tumor-suppressive effect and tumor foci were barely observed in livers of the treated mice. Pretreatment with an etoposide increased the level of endostatin in the liver and serum of rAAV-endostatin treated mice. Finally, the mice treated with rAAV-endostatin in combination with etoposide showed the longest survival among the experimental models.

CONCLUSION: rAAV delivered endostatin gene therapy in combination with a topoisomerase inhibitor pretreatment is an effective modality for anticancer gene therapy.

Antitumor agents. 207. Design, synthesis, and biological testing of 4beta-anilino-2-fluoro-4'-demethylpodophyllotoxin analogues as cytotoxic and antiviral agents

2-Fluoropodophyllotoxin (11) and several 4beta-anilino-2-fluoro-4'-O-demethyl analogues were synthesized and evaluated in both antineoplastic and antiviral assays. These compounds were moderately active against some cancer cell lines, but they were less active than the corresponding nonfluorinated analogues. Compound 11 exhibited the best activity against KB carcinoma with a GI(50) of approximately 30 nM. Most compounds exhibited moderate activity against HCMV with ID(50) and ID(90) values in the range of 1 microM and 4 microM, respectively. Both 9 and 11 showed an unusual 10-fold selectivity for HSV-2 compared to HSV-1.

1,3-Dihydroxyacridone derivatives as inhibitors of herpes virus replication

The nuclear enzyme DNA topoisomerase II is a candidate pharmacological target for treating herpes virus infections and the novel catalytic inhibitors, 7-chloro-1,3-dihydroxyacridone (compound 1), and 1,3,7-trihydroxyacridone (2) are potential lead compounds [Bastow, K.F., Itoigawa, M., Furukawa, H., Kashiwada, Y., Bori, I.D., Ballas, L.M., Lee, K.-H., 1994. Antiproliferative actions of 7-substituted 1,3-dihydroxyacridones; possible involvement of DNA topoisomerase II and protein kinase C as biochemical targets. Bioorg. Med. Chem. 2, 1403-1411; Vance, J.R., Bastow, K.F., 1999. Inhibition of DNA topoisomerase II catalytic activity by the antiviral agents 7-chloro,1,3-dihydroxyacridone and 1,3,7-trihydroxyacridone. Biochem. Pharmacol. 58, 703-708]. In this report, four new 1,3-dihydroxyacridone analogs with functional groups at either the 5-, 6- or 8-positions (compounds 3-6) were synthesized. Target compounds, three other analogs including compounds 1 and 2 and three anticancer drugs that inhibit DNA topoisomerase II (etoposide, amsacrine and aclarubicin) were then evaluated as selective inhibitors of herpes simplex virus (HSV) replication in cell culture and as enzyme inhibitors in vitro. Etoposide and amsacrine inhibited HSV but acted non-selectively. In general, the activities of 1,3-dihydroxyacridone derivatives as selective anti-HSV agents and as enzyme inhibitors varied inversely suggesting that DNA topoisomerase II probably is not the critical antiviral target. The 5-Cl congener (compound 3) was the most selective agent (about 26-fold under a stringent assay condition) but was not an enzyme inhibitor. Results of exploratory mechanistic studies with compounds 1 and 3 show that HSV replication was blocked at a stage after DNA and late protein synthesis. The acridone derivatives were also tested against human cytomegalovirus (HCMV) replication but none of them were active.

Etoposide as a virocidal anticytomegalovirus therapy: intravitreal toxicology and pharmacology in rabbits

BACKGROUND

Although Cytomegalovirus (CMV) retinitis is now a common intraocular infection, current therapy is only virostatic so ongoing treatment is required. Etoposide was found to be virocidal for CMV in laboratory experiments and it might prove to be beneficial clinically. We investigated the toxicity and intraocular concentration of etoposide (VP16) and its new analogue etoposide-phosphate (VP16P) following intravitreal injections in rabbit eyes.

METHODS

First a sequential dose-response was assessed with flash electroretinogram for both eyes of light- and dark-adapted rabbits (n = 7; one rabbit for each dose) over a range of light intensities before and after intravitreal injection of VP16 or VP16P to one eye; the other eye was injected with normal saline as a control. A multidose study was then performed on four rabbits. A non-toxic dose of VP16P (50 or 75 g) was injected into the vitreous of one eye on four occasions 1 week apart. A photopic electroretinogram was performed before the first injection and 6 weeks after the last injection. All the eyes from the electroretinogram studies were fixed in formalin, placed in paraffin, then stained with haematoxylin and eosin and examined under a light microscope. To determine the time-course of the intraocular concentrations of VP16P a sequential pharmacokinetic study was performed using a further 12 rabbits. Each rabbit was injected with 50 g VP16P to one eye and 75 g VP16P to the other eye. Three of these rabbits were killed at 1, 3, 6 and 9 h after injection. Samples of vitreous were assayed for both VP16 and VP16P using HPLC. An in vitro dose response assay was performed using third-passage bovine retinal pigment epithelial (RPE) cells cultured in Dulbecco's modified Eagles medium with fetal calf serum. The effect of a log-dose increment of VP16P on the RPE cell proliferation was assessed using tritiated thymidine incorporation.

RESULTS

The electroretinogram studies suggested that VP16 was toxic even with the 10 g dose. For VP16P a toxic effect was noted following injection of a single dose greater than 100 g. Multiple injections of 50 or 75 g VP16P did not produce a toxic response. Histological examination demonstrated significant abnormality only with the 500 g dose of VP16 or VP16P. VP16P was rapidly metabolized to VP16 in the eye, producing concentrations of 2.0 g/mL or more for up to 9 h following a 75-microg dose. This suggests that the electroretinogram findings following VP16 injections were confounded by a toxic effect of the ethanol solvent (which is absent from the VP16P preparation). VP16P was quite potent, the ID50 was about 0.1 g/mL for bovine RPE cells in the in vitro assay.

DISCUSSION

These results indicate that multiple 75-gVP16P intravitreal injections were not toxic to the rabbit eye and provide a therapeutic intraocular concentration for up to 9 h after the injection.

Cellular topoisomerase I activity associated with HIV-1

Topoisomerase I activity was detected in detergent-disrupted human immunodeficiency virus type 1 (HIV-1) particles. The enzyme did not require ATP for its conversion of SC DNA to an RC form, had divalent cation requirements similar to those of eukaryotic topoisomerase I, and was significantly inhibited by the specific topoisomerase I inhibitor camptothecin. However, camptothecin failed to inhibit replication of HIV in infected cells at nontoxic concentrations, and an active site motif for topoisomerase I could not be detected on the HIV genome. These results suggests that HIV does not encode a novel topoisomerase I, but rather packages the cellular enzyme.