Specific CD4 down-modulating compounds with potent anti-HIV activity

Inhibitors of the Sec61 Complex and Novel High Throughput Screening Strategies to Target the Protein Translocation Pathway

Proteins targeted to the secretory pathway start their intracellular journey by being transported across biological membranes such as the endoplasmic reticulum (ER). A central component in this protein translocation process across the ER is the Sec61 translocon complex, which is only intracellularly expressed and does not have any enzymatic activity. In addition, Sec61 translocon complexes are difficult to purify and to reconstitute. Screening for small molecule inhibitors impairing its function has thus been notoriously difficult. However, such translocation inhibitors may not only be valuable tools for cell biology, but may also represent novel anticancer drugs, given that cancer cells heavily depend on efficient protein translocation into the ER to support their fast growth. In this review, different inhibitors of protein translocation will be discussed, and their specific mode of action will be compared. In addition, recently published screening strategies for small molecule inhibitors targeting the whole SRP-Sec61 targeting/translocation pathway will be summarized. Of note, slightly modified assays may be used in the future to screen for substances affecting SecYEG, the bacterial ortholog of the Sec61 complex, in order to identify novel antibiotic drugs.

Reduction of Progranulin-Induced Breast Cancer Stem Cell Propagation by Sortilin-Targeting Cyclotriazadisulfonamide (CADA) Compounds

Cyclotriazadisulfonamide (CADA) compounds selectively down-modulate two human proteins of potential therapeutic interest, cluster of differentiation 4 (CD4) and sortilin. Progranulin is secreted from some breast cancer cells, causing dedifferentiation of receiving cancer cells and cancer stem cell proliferation. Inhibition of progranulin binding to sortilin, its main receptor, can block progranulin-induced metastatic breast cancer using a triple-negative in vivo xenograft model. In the current study, seven CADA compounds (CADA, VGD020, VGD071, TL020, TL023, LAL014, and DJ010) were examined for reduction of cellular sortilin expression and progranulin-induced breast cancer stem cell propagation. In addition, inhibition of progranulin-induced mammosphere formation was examined and found to be most significant for TL020, TL023, VGD071, and LAL014. Full experimental details are given for the synthesis and characterization of the four new compounds (TL020, TL023, VGD071, and DJ010). Comparison of solubilities, potencies, and cytotoxicities identified VGD071 as a promising candidate for future studies using mouse breast cancer models.

Syntheses and anti-HIV and human cluster of differentiation 4 (CD4) down-modulating potencies of pyridine-fused cyclotriazadisulfonamide (CADA) compounds

CADA compounds selectively down-modulate human cell-surface CD4 protein and are of interest as HIV entry inhibitors and as drugs for asthma, rheumatoid arthritis, diabetes and some cancers. Postulating that fusing a pyridine ring bearing hydrophobic substituents into the macrocyclic scaffold of CADA compounds may lead to potent compounds with improved properties, 17 macrocycles were synthesized, 14 with 12-membered rings having an isobutylene head group, two arenesulfonyl side arms, and fused pyridine rings bearing a para substituent. The analogs display a wide range of CD4 down-modulating and anti-HIV potencies, including some with greater potency than CADA, proving that a highly basic nitrogen atom in the 12-membered ring is not required for potency and that hydrophobic substituents enhance potency of pyridine-fused CADA compounds. Cytotoxicities of the new compounds compared favorably with those of CADA, showing that incorporation of a pyridine ring into the macrocyclic scaffold can produce selective compounds for potently down-modulating proteins of medicinal interest.

A Proteomic Survey Indicates Sortilin as a Secondary Substrate of the ER Translocation Inhibitor Cyclotriazadisulfonamide (CADA)

The small molecule CADA was shown to down-modulate the expression of human CD4 in a signal peptide-dependent way through inhibition of its cotranslational translocation across the ER membrane. Previous studies characterizing general glycoprotein levels and the expression of 14 different cell surface receptors showed selectivity of CADA for human CD4. Here, a PowerBlot Western Array was used as a screen to analyze the proteome of CADA-treated SUP-T1 human CD4⁺ T lymphocytes. This high-throughput monoclonal antibody panel-based immunoblotting assay of cellular signaling proteins revealed that only a small subset of the 444 detected proteins was differentially expressed after treatment with CADA. Validation of these proteomic data with optimized immunoblot analysis confirmed the CADA-induced change in expression of the cell cycle progression regulator pRb2 and the transcription factor c-Jun. However, the up-regulation of pRb2 or down-modulation of c-Jun by CADA had no impact on cell cycle transition. Also, the reduced protein level of human CD4 did not inhibit T cell receptor signaling. Interestingly, the signal peptide-containing membrane protein sortilin was identified as a new substrate for CADA. Both cellular expression and in vitro cotranslational translocation of sortilin were significantly reduced by CADA, although to a lesser extent as compared with human CD4. Our data demonstrate that a small signal peptide-binding drug is able to down-modulate the expression of human CD4 and sortilin, apparently with low impact on the cellular proteome.

Tuning Side Arm Electronics in Unsymmetrical Cyclotriazadisulfonamide (CADA) Endoplasmic Reticulum (ER) Translocation Inhibitors to Improve their Human Cluster of Differentiation 4 (CD4) Receptor Down-Modulating Potencies

Cyclotriazadisulfonamide prevents HIV entry into cells by down-modulating surface CD4 receptor expression through binding to the CD4 signal peptide. According to a two-site binding model, 28 new unsymmetrical analogues bearing a benzyl tail group and nine bearing a cyclohexylmethyl tail have been designed and synthesized. The most potent new CD4 down-modulator (40 (CK147); IC50 63 nM) has a 4-dimethylaminobenzenesulfonyl side arm. One of the two side arms was varied with substituents in different positions. This gave a range of CD4 down-modulation potencies that correlated well with anti-HIV-1 activities. The side arms of 21 of the new benzyl-tailed analogues were modeled by means of quantum mechanical calculations. For CADA analogues with arenesulfonamide side arms, the pIC50 values for CD4 down-modulation correlated with the component of the electric dipole moment in the aromatic ring, suggesting that an attractive electronic interaction is a major factor determining the stability of the complex between the molecule and its target.

Yet another ten stories on antiviral drug discovery (part D): paradigms, paradoxes, and paraductions

This review article presents the fourth part (part D) in the series of stories on antiviral drug discovery. The stories told in part D focus on: (i) the cyclotriazadisulfonamide compounds; (ii) the {5-[(4-bromophenylmethyl]-2-phenyl-5H-imidazo[4,5-c]pyridine} compounds; (iii) (1H,3H-thiazolo[3,4-a]benzimidazole) derivatives; (iv) T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) and (v) its structurally closely related analogue pyrazine 2-carboxamide (pyrazinamide); (vi) new strategies for the treatment of hemorrhagic fever virus infections, including, as the most imminent, (vii) dengue fever, (viii) the veterinary use of acyclic nucleoside phosphonates; (ix) the potential (off-label) use of cidofovir in the treatment of papillomatosis, particularly RRP (recurrent respiratory papillomatosis); and (x) finally, the prophylactic use of tenofovir to prevent HIV infections.

Human immunodeficiency virus type 1 escape from cyclotriazadisulfonamide-induced CD4-targeted entry inhibition is associated with increased neutralizing antibody susceptibility

Continuous specific downmodulation of CD4 receptor expression in T lymphocytes by the small molecule cyclotriazadisulfonamide (CADA) selected for the CADA-resistant human immunodeficiency virus type 1 (HIV-1) NL4.3 virus containing unique mutations in the C4 and V5 regions of gp120, likely stabilizing the CD4-binding conformation. The amino acid changes in Env were associated with decreased susceptibility to anti-CD4 monoclonal antibody treatment of the cells and with higher susceptibility of the virus to soluble CD4. In addition, the acquired ability of a CADA-resistant virus to infect cells with low CD4 expression was associated with an increased susceptibility of the virus to neutralizing antibodies from sera of several HIV-1-infected patients.

HIV entry inhibitors and their potential in HIV therapy

This review discusses recent progress in the development of anti-HIV agents targeting the viral entry process. The three main classes (attachment inhibitors, co-receptor binding inhibitors, and fusion inhibitors) are further broken down by specific mechanism of action and structure. Many of these inhibitors are in advanced clinical trials, including the HIV maturation inhibitor bevirimat, from the authors' laboratories. In addition, the CCR5 inhibitor maraviroc has recently been FDA-approved. Possible roles for these agents in anti-HIV therapy, including treatment of virus resistant to current drugs, are also discussed.

Post Operative Infection and Increased Survival in Osteosarcoma Patients: Are They Associated?

BACKGROUND

Despite neo-adjuvant chemotherapy osteosarcomas having significant mortality, recent studies have shown survival advantages following infections for some tumour types. This study investigates the effect of post-operative infection in patients treated for osteosarcoma using endoprosthetic replacement and neo-adjuvant chemotherapy.

MATERIAL AND METHODS

A consecutive series of 547 patients underwent surgery between 1981 and 2001 for osteosarcoma. Patients were excluded from the study if over 60 years old at diagnosis (n = 14) as they would not routinely receive chemotherapy. Studies showed that 70% of deep infections occur within one year from reconstruction. Therefore landmark analysis was performed; all patients infected after 12 months of reconstruction were excluded (15 patients, 2.7%) and those who died within 12 months from diagnosis due to metastases were excluded (105 patients, 19.2%), leaving 412 patients. Any survival advantage of early infection was analysed by Kaplan-Meier survival analysis from this landmark point.

RESULTS

Overall population survival was 65% at 10 years after landmarking. There were 41 patients (10%) who developed an infection within one year of implantation. These patients had significantly better survival (p = 0.017). The 10-year survival for patients with osteosarcoma with infection was 84.5% compared to 62.3% in the non-infected group after landmarking. There was no significant difference in the percentage post-chemotherapy specimen necrosis between the two groups (p = 0.36). Infection was an independent prognostic factor on cox regression analysis.

CONCLUSIONS

There was evidence for increased survival after deep post-operative infection in osteosarcoma patients, in keeping with other research. The authors feel this warrants further investigation.

Design and cellular kinetics of dansyl-labeled CADA derivatives with anti-HIV and CD4 receptor down-modulating activity

A new class of anti-retrovirals, cyclotriazadisulfonamide (CADA) and its derivatives, specifically down-regulate CD4, the main receptor of HIV, and prevent HIV infection in vitro. In this work, several CADA derivatives, chemically labeled with a fluorescent dansyl group, were evaluated for their biological features and cellular uptake kinetics. We identified a derivative KKD-016 with antiviral and CD4 down-modulating capabilities similar to those of the parental compound CADA. By using flow cytometry, we demonstrated that the dose-dependent cellular uptake of this derivative correlated with CD4 down-modulation. The uptake and activity of the dansyl-labeled compounds were not dependent on the level of expression of CD4 at the cell surface. Removal of the CADA compounds from the cell culture medium resulted in their release from the cells followed by a complete restoration of CD4 expression. The inability of several fluorescent CADA derivatives to down-modulate CD4 was not associated with their lower cellular uptake and was not reversed by facilitating their cell penetration by a surfactant. These results prove the successful integration of the dansyl fluorophore into the chemical structure of a CD4 down-modulating anti-HIV compound, and show the feasibility of tracking a receptor and its down-modulator simultaneously. These fluorescent CADA analogs with reversible CD4 down-regulating potency can now be applied in further studies on receptor modulation, and in the exploration of their potentials as preventive and therapeutic anti-HIV drugs.

Synthesis and structure-activity relationship studies of CD4 down-modulating cyclotriazadisulfonamide (CADA) analogues

HIV attachment via the CD4 receptor is an important target for developing novel approaches to HIV chemotherapy. Cyclotriazadisulfonamide (CADA) inhibits HIV at submicromolar levels by specifically down-modulating cell-surface and intracellular CD4. An effective five-step synthesis of CADA in 30% overall yield is reported. This synthesis has also been modified to produce more than 50 analogues. Many tail-group analogues have been made by removing the benzyl tail of CADA and replacing it with various alkyl, acyl, alkoxycarbonyl and aminocarbonyl substituents. A series of sidearm analogues, including two unsymmetrical compounds, have also been prepared by modifying the CADA synthesis, replacing the toluenesulfonyl sidearms with other sulfonyl groups. Testing 30 of these compounds in MT-4 cells shows a wide range of CD4 down-modulation potency, which correlates with ability to inhibit HIV-1. Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were constructed using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) approaches. The X-ray crystal structures of four compounds, including CADA, show the same major conformation of the central 12-membered ring. The solid-state structure of CADA was energy minimized and used to generate the remaining 29 structures, which were similarly minimized and aligned to produce the 3D-QSAR models. Both models indicate that steric bulk of the tail group, and, to a lesser extent, the sidearms mainly determine CD4 down-modulation potency in this series of compounds.

Anti-HIV agents targeting the interaction of gp120 with the cellular CD4 receptor

Perhaps one of the most effective approaches to prevent and inhibit viral infections is to block host cell receptors that are used by viruses to gain cell entry. Major advances have been made over the past decade in the understanding of the molecular mechanism of HIV entry into target cells. A crucial step in this entry process is the interaction of the external HIV envelope glycoprotein, gp120, with the cellular CD4 receptor molecule. This binding step represents a potential target for new antiviral agents, and current efforts to develop safe and effective HIV entry inhibitors are focused on natural ligands and/or monoclonal antibodies that interfere with gp120/CD4 interaction. Also, small synthetic compounds obtained either by high-throughput screening of large compound libraries or by structure-guided rational design have recently entered the antiretroviral arena. In this review, the anti-HIV activity of novel entry inhibitors targeting gp120/CD4 interaction is outlined, and special attention is given to the cyclotriazadisulfonamide compounds, which are the most specific CD4-targeted antiviral drugs described so far.

Cyclotriazadisulfonamides: promising new CD4-targeted anti-HIV drugs

It is imperative to continue efforts to identify novel effective therapies that can assist in containing the spread of HIV. Recently acquired knowledge about the HIV entry process points to new strategies to block viral entry. For most HIV strains, the successful infection of their target cells is mainly dependent on the presence of the CD4 surface molecule, which serves as the primary virus receptor. The attachment of the viral envelope to this cellular CD4 receptor can be considered as an ideal target with multiple windows of opportunity for therapeutic intervention. Therefore, drugs that interfere with the CD4 receptor, and thus inhibit viral entry, may be promising agents for the treatment of AIDS. The CD4-targeted HIV entry inhibitors cyclotriazadisulfonamides represent a novel class of small molecule antiviral agents with a unique mode of action. The lead compound, CADA, specifically interacts with the cellular CD4 receptor and is active against a wide variety of HIV strains at submicromolar levels when evaluated in different cell-types such as T cells, monocytes and dendritic cells. Moreover, a strict correlation has been demonstrated between anti-HIV activity and CD4 interaction of about 20 different CADA analogues. In addition, CADA acted synergistically in combination with all other FDA-approved anti-HIV drugs as well as with compounds that target the main HIV co-receptors. In this article, the characteristics of cyclotriazadisulfonamide compounds are presented and the possible application of CADA as a microbicide is also discussed.

Fever therapy revisited

The phenomenon of spontaneous regression and remission from cancer has been observed by many physicians and was described in hundreds of publications. However, suggestive clues on cause or trigger are sparse and not substantiated by much experimental evidence. In this review, literature is surveyed and summarised and possible causes are discussed. At least in a larger fraction of cases a hefty feverish infection is linked with spontaneous regression in time and is investigated as putative trigger. Epidemiological and immunological evidence is put into perspective. An online forum to discuss the possible application of fever therapy in the future can be accessed at http://bioinfo.tg.fh-giessen.d e/fever-and-cancer.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

Emerging drug targets for antiretroviral therapy

Current targets for antiretroviral therapy (ART) include the viral enzymes reverse transcriptase and protease. The use of a combination of inhibitors targeting these enzymes can reduce viral load for a prolonged period and delay disease progression. However, complications of ART, including the emergence of viruses resistant to current drugs, are driving the development of new antiretroviral agents targeting not only the reverse transcriptase and protease enzymes but novel targets as well. Indeed, enfuvirtide, an inhibitor targeting the viral envelope protein (Env) was recently approved for use in combination therapy in individuals not responding to current antiretroviral regimens. Emerging drug targets for ART include: (i) inhibitors that directly or indirectly target Env; (ii) the HIV enzyme integrase; and (iii) inhibitors of maturation that target the substrate of the protease enzyme. Env mediates entry of HIV into target cells via a multistep process that presents three distinct targets for inhibition by viral and cellular-specific agents. First, attachment of virions to the cell surface via nonspecific interactions and CD4 binding can be blocked by inhibitors that include cyanovirin-N, cyclotriazadisulfonamide analogues, PRO 2000, TNX 355 and PRO 542. In addition, BMS 806 can block CD4-induced conformational changes. Secondly, Env interactions with the co-receptor molecules can be targeted by CCR5 antagonists including SCH-D, maraviroc (UK 427857) and aplaviroc (GW 873140), and the CXCR4 antagonist AMD 070. Thirdly, fusion of viral and cellular membranes can be inhibited by peptides such as enfuvirtide and tifuvirtide (T 1249). The development of entry inhibitors has been rapid, with an increasing number entering clinical trials. Moreover, some entry inhibitors are also being evaluated as candidate microbicides to prevent mucosal transmission of HIV. The integrase enzyme facilitates the integration of viral DNA into the host cell genome. The uniqueness and specificity of this reaction makes integrase an attractive drug target. However, integrase inhibitors have been slow to reach clinical development, although recent contenders, including L 870810, show promise. Inhibitors that target viral maturation via a unique mode of action, such as PA 457, also have potential. In addition, recent advances in our understanding of cellular pathways involved in the life cycle of HIV have also identified novel targets that may have potential for future antiretroviral intervention, including interactions between the cellular proteins APOBEC3G and TSG101, and the viral proteins Vif and p6, respectively. In summary, a number of antiretroviral agents in development make HIV entry, integration and maturation emerging drug targets. A multifaceted approach to ART, using combinations of inhibitors that target different steps of the viral life cycle, has the best potential for long-term control of HIV infection. Furthermore, the development of microbicides targeting HIV holds promise for reducing HIV transmission events.

CADA, a novel CD4-targeted HIV inhibitor, is synergistic with various anti-HIV drugs in vitro

OBJECTIVE

To evaluate the anti-HIV-1 activity of the cyclotriazadisulfonamide CADA against primary isolates in vitro and the combination of CADA with approved anti-HIV drugs for potential synergy.

METHODS

Peripheral blood mononuclear cells (PBMC) were treated with CADA and infected with 16 different clinical isolates. After 8 days of infection, the median inhibitory concentration (IC50) was calculated from the p24 viral antigen content in the supernatant. MT-4 cells were infected with HIV-1NL4.3 and then cultured with CADA or other antiretroviral drugs (i.e., several reverse transcriptase, protease and entry inhibitors), alone and in combination. After 4 days, IC50 was determined for the various drugs in replicate assays. Analysis of combined effects was performed using the median effect principle (CalcuSyn; Biosoft).

RESULTS

The entry inhibitor CADA exerted a potent and consistent anti-HIV-1 activity against a wide range of R5, R5/X4 and X4 primary isolates in PBMC. From the two-drug studies, combination indices showed synergy between CADA and reverse transcriptase inhibitors (zidovudine, stavudine, lamivudine, zalcitabine, didanosine, abacavir, tenofovir, nevirapine, delavirdine and efavirenz), and protease inhibitors (lopinavir, saquinavir, indinavir, nelfinavir, amprenavir and ritonavir). In addition, the combination of CADA with the gp41 fusion inhibitor T-20 (enfuvirtide), the CXCR4 antagonist AMD3100 and the gp120-specific interacting plant lectins from Galanthus nivalis (GNA) and Hippeastrum hybrid (HHA) also resulted in a synergistic inhibition.

CONCLUSIONS

Compounds that can specifically downmodulate the CD4 receptor in PBMC have broad-spectrum anti-HIV activity against primary isolates and act synergistically when used in conjunction with currently available antiretroviral drugs. They deserve further study as potential candidate anti-HIV drugs.

HIV and cells of macrophage/dendritic lineage and other non-T cell reservoirs: new answers yield new questions

Defining how human immunodeficiency virus (HIV) interacts with macrophages, dendritic cells (DC), and other non-T cell reservoirs remains a critical area of research despite widespread use in the developed world of highly active antiretroviral therapy. In fact, as highlighted at the Fifth International Workshop on HIV and Cells of Macrophage/Dendritic Lineage and Other Reservoirs, as viral suppression in T cells becomes increasingly effective, these alternative reservoirs may take on even greater relative importance as sites for viral persistence and as a target for purging. These cells may be especially important reservoirs in several critical settings of clinical relevance, and there are major differences in the molecular mechanisms that regulate HIV replication in these cells compared with T cells. Dysfunction of these cells may also play a major role in particular aspects of pathogenesis. Three broad themes emerged from the workshop regarding areas of recent progress, which also serve to identify current research challenges of (i). determining the role played by macrophages, DC, and other non-T cell viral targets in transmission and dissemination and as viral reservoirs at various stages of disease and in different compartments in vivo; (ii). identifying the molecular mechanisms by which virus-cell interactions affect the inflammatory, immune, and other functions of these cells; and (iii). defining the unique pathways that regulate infection and replication in these cellular compartments. This issue of JLB contains several reviews and original reports resulting from the workshop that address recent progress and highlight the current research questions regarding these cell types.