Current Pharmaceutical Design

ISSN: 1381-6128

Current Pharmaceutical Design
Volume 13, Number 2, 2007

Contents


New Approaches to HIV-1 Inhibitor and Vaccine Design
Executive Editor: Lai-Xi Wang


Editorial Pp. 127-128


Design of Second Generation HIV-1 Integrase Inhibitors Pp. 129-141
J. Deng, R. Dayam, L.Q. Al-Mawsawi and N. Neamati
[Abstract]


HIV Entry Inhibitors Targeting gp41: From Polypeptides to Small-Molecule Compounds Pp. 143-162
S. Liu, S. Wu and S. Jiang
[Abstract]


Chemokines and Defensins as HIV Suppressive Factors: An Evolving Story Pp. 163-172
A. Garzino-Demo
[Abstract]


Carbohydrate Microarrays as Tools in HIV Glycobiology Pp. 173-183
D.M. Ratner and P.H. Seeberger
[Abstract]


Defining Carbohydrate Antigens as HIV Vaccine Candidates Pp. 185-201
A. Pashov, M. Perry, M. Dyar, M. Chow and T. Kieber-Emmons
[Abstract]


Novel Approaches for Identification of Broadly Cross-Reactive HIV-1 Neutralizing Human Monoclonal Antibodies and Improvement of Their Potency Pp. 203-212
M.-Y. Zhang and D.S. Dimitrov
[Abstract]


Rational Modifications of HIV-1 Envelope Glycoproteins for Immunogen Design Pp. 213-227
S. Phogat and R. Wyatt
[Abstract]


General Articles


Atenolol: Differences in Mode of Action Compared with other Antihypertensives. An Opportunity to Identify Features that Influence Outcome? Pp. 229-239
A. Karagiannis, D.P. Mikhailidis, A.I. Kakafika, K. Tziomalos and V.G. Athyros
[Abstract]


Pharmacogenetics and Drug Therapy in Psychiatry - The Role of the CYP2D6 Polymorphism Pp. 241-250
P. Vandel, J.M. Talon, E. Haffen and D. Sechter
[Abstract]




Abstracts
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Editorial: New Approaches to HIV-1 Inhibitor and Vaccine Design

AIDS is caused by the infection of the human immunodeficiency virus (HIV). There are two fronts in combating the worldwide epidemic of HIV/AIDS. On the one hand, the emergence of drug-resistant viruses urges the development of new anti-viral drugs that work on a mechanism of action different from those of currently available drugs; on the other hand, the control of the expanding epidemic will eventually rely on an effective preventive HIV vaccine.

This special issue consists of seven excellent review articles that focus on new approaches toward HIV inhibitor and vaccine design. The first three articles discuss some most exciting advances in HIV inhibitors that may be further developed as anti-HIV therapeutics. Dr. Nouri Neamati and co-workers [1] from University of Southern California provides an outstanding review on inhibitors targeting HIV integrase (IN), an essential enzyme for HIV replication. The authors highlight the preclinical and clinical studies of the first generation beta-diketo compounds as IN inhibitors and put a special emphasis on advances in the design of the second generation IN inhibitors with improved pharmacokinetic and metabolic properties. Dr. Shibo Jiang and co-workers [2] from the New York Blood Center focuses on another type of HIV inhibitor that targets HIV entry. A beautiful story is given on how a class of polypeptide inhibitors that block gp41-mediated membrane fusion was first discovered, which eventually led to the development of the new anti-HIV drug enfuvirtide (Fuzeon or T-20). The review is then focused on the efforts in searching for small-molecule compounds to interfere the gp41-mediated fusion processes, which may overcome the problems such as the lack of oral bioavailability associated with T-20 and other polypeptide inhibitors. Recent progress in the screening and discovery of such small-molecule inhibitors targeting gp41 is reviewed. In another excellent review, Dr. Alfredo Garzino-Demo [3] from the University of Maryland’s Institute of Human Virology describes the discovery and impact of chemokines and beta-defensins as natural HIV-suppressing factors that are produced by host cells. The importance of these host-derived natural factors in battling HIV infection is well discussed.

Heavy glycosylation is a strong defense mechanism that HIV has evolved to evade immune attacks. However, compelling experimental data suggest that the carbohydrate antigens on HIV envelope glycoproteins are also valuable targets for antiviral agents and vaccines. Two reviews in this special issue have focused on HIV carbohydrates. Dr. Daniel Ratner (Boston University) and Dr. Peter Seeberger (ETH) [4] provides a timely review on the development of carbohydrate microarrays as tools in searching for HIV-1 gp120-binding proteins specific for the viral carbohydrate antigens. The potential of the developed carbohydrate microarrays in HIV glycobiology is nicely demonstrated by effectively detecting those gp120-binding proteins including DC-SIGN, CD4, 2G12, cyanovirion, and scytovirin. In another timely review, Dr. Thomas Kieber-Emmons and co-workers [5] from University of Arkansas Medical Sciences discuss the issues of defining HIV carbohydrate antigens for vaccine design. In particular, the authors provide an excellent highlight of their own work on molecular design of peptide carbohydrate mimotopes capable of eliciting neutralizing antibodies to recognize HIV carbohydrate antigens. The peptide mimotope approach has a great potential to overcome the weak immunogenicity of HIV carbohydrate antigens.

Human monoclonal antibodies capable of neutralizing a broad range of HIV-1 isolates are of great therapeutic potential and also provide an ideal template for HIV vaccine design. However, broadly neutralizing antibodies are rare in infected individuals and are difficult to elicit by active immunization. Dr. Mei-Yun Zhang and Dr. Dimiter Dimitrov [6] from the National Cancer Institute provide an excellent overview on recent advances in identifying neutralizing antibodies targeting HIV envelope glycoproteins gp120/gp41. The review focuses on several new approaches, including sequential antigen panning and competitive antigen panning methods, in identifying neutralizing antibodies. Valuable discussions on the mechanism of the exceptional neutralizing activities of an array of identified neutralizing antibodies are given. Finally, In connection with effective immunogen design, Dr. Richard Wyatt and Dr. Sanjay Phogat [7] from the National Institutes of Health’s Vaccine Research Center provide an outstanding review on our current understanding of the structure and function of HIV envelope glycoproteins. The review focuses on the structural features of the envelope glycoproteins and discusses current approaches of rational modifications of the envelope glycoproteins to augment their immunogenicity for eliciting broadly neutralizing antibodies.

I am greatly indebted to all the authors for their outstanding contributions to this special issue. Without their kind commitment of time and efforts, this special issue would have been impossible.

References

[1] Deng J, Dayam R, Al-Mawsawi LQ, Neamati N. Design of second generation HIV-1 integrase inhibitors. Curr Pharm Des 2007; 13(2): 129-141.

[2] Liu S, Wu S, Jiang S. HIV entry inhibitors targeting gp41: From polypeptides to small-molecule compounds. Curr Pharm Des 2007; 13(2): 143-162.

[3] Garzino-Demo A. Chemokines and defensins as HIV suppressive factors: An evolving story. Curr Pharm Des 2007; 13(2): 163-172.

[4] Ratner DM, Seeberger PH. Carbohydrate microarrays as tools in HIV glycobiology. Curr Pharm Des 2007; 13(2): 173-183.

[5] Pashov A, Perry M, Dyar M, Chow M, Kieber-Emmons T. Defining carbohydrate antigens as HIV vaccine candidates. Curr Pharm Des 2007; 13(2): 185-201.

[6] Zhang M-Y, Dimitrov DS. Novel approaches for identification of broadly cross-reactive HIV-1 neutralizing human monoclonal antibodies and improvement of their potency. Curr Pharm Des 2007; 13(2): 203-213.

[7] Phogat S, Wyatt R. Rational modifications of HIV-1 envelope glycoproteins for immunogen design. Curr Pharm Des 2007; 13(2): 213-227.


Lai-Xi Wang, Ph. D.
Associate Professor
Institute of Human Virology
University of Maryland Biotechnology Institute
Baltimore, MD 21201, USA
E-mail: wangx@umbi.umd.edu


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Design of Second Generation HIV-1 Integrase Inhibitors
J. Deng, R. Dayam, L.Q. Al-Mawsawi and N. Neamati

The prospect of HIV-1 integrase (IN) as a therapeutically viable retroviral drug target is on the verge of realization. The observed preclinical and clinical performance of β-diketo containing and naphthyridine carboxamide compounds provides direct proof for the clinical application of IN inhibition. These validated lead compounds are useful in the design and development of second generation IN inhibitors. The results from preclinical and clinical studies on the first generation IN inhibitors reiterate a demand for novel second generation inhibitors with improved pharmacokinetic and metabolic properties. Pharmacophore-based drug design techniques facilitate the discovery of novel compounds on the basis of validated lead compounds specific for a drug target. In this article we have comprehensively reviewed the application of pharmacophore-based drug design methods in the field of IN inhibitor discovery.


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HIV Entry Inhibitors Targeting gp41: From Polypeptides to Small-Molecule Compounds
S. Liu, S. Wu and S. Jiang

HIV envelope glycoprotein transmembrane subunit gp41 plays a critical role in the fusion between viral and target cell membranes. Upon gp120 binding to CD4 and a coreceptor (CCR5 or CXCR4), gp41 changes its conformation by forming N-helix trimer between N-heptad repeats (NHRs) and then six-helix bundle between the N-trimer and the C-heptad repeats (CHRs). Peptides derived from the NHR and CHR of gp41 extracellular region have demonstrated potent inhibitory activity on the HIV mediated cell fusion. One of these peptides, T-20, became the first success of a new class of anti-HIV agents, named HIV entry inhibitors. However, a relatively long peptide such as T-20 suffers from several limitations including lack of oral bioavailability and high cost of production. Great efforts have been made to develop alternative peptides and proteins with improved anti-HIV-1 activity, increased bioavailability and reduced cost of production. The most promising approach is the development of small molecule HIV entry inhibitors targeting gp41. Any molecule that blocks the process of NHR homotrimerization and the six-helix bundle formation by targeting the gp41 NHR, NHR trimer and CHR may inhibit HIV-mediated membrane fusion. The progress in development of those anti-HIV agents targeting gp41, from polypeptides to small-molecule compounds, is reviewed.


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Chemokines and Defensins as HIV Suppressive Factors: An Evolving Story
A. Garzino-Demo

When attacked by HIV, the immune system counteracts infection with elicitation of HIV-specific antibodies and cytotoxic T lymphocytes. In most cases however, these defenses are unable to resolve HIV infection, which progresses, if left untreated, ravaging the immune system and leading to AIDS and, eventually, to death. Nonetheless, there are additional components of the immune system, from both the innate and the adaptive components, that are associated with improved clinical status and, in some cases, even with protection from infection. Two distinct families of such factors have been studied in depth: chemokines and β-defensins. CCR5 chemokines, which are involved in adaptive immunity, are molecules produced by lymphocytes, and thus are likely to play a role in controlling HIV systemically. β-defensins are instead produced by epithelial cells, and thus are important in controlling infection at mucosal sites. Both of these families of molecules, therefore, are involved in crucial battlegrounds for fighting HIV infection. Here, we review the evidence that argues for their importance in AIDS pathogenesis and in preventive and therapeutic approaches to combat HIV infection.


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Carbohydrate Microarrays as Tools in HIV Glycobiology
D.M. Ratner and P.H. Seeberger

Progress in carbohydrate microarray technology has positioned the glycochip among the expanding set of biophysical tools available to researchers. Synthetically-derived glycochips unite established microarray techniques with the versatility and structural precision of synthetic carbohydrate chemistry. A comprehensive demonstration of carbohydrate microarrays is illustrated by the chip-based study of protein/carbohydrate and protein/glycoprotein interactions as they relate to HIV glycobiology. Composed of a series of high-mannose oligosaccharides, carbohydrate microarrays were prepared utilizing a covalent linking strategy to immobilize synthetically-defined glycans in a uniform orientation. In concert with a simple glycoprotein array, these microarrays were used to establish the individual and competitive binding profiles of five gp120 binding proteins – DC-SIGN, CD4, 2G12 cyanovirin-N, and scytovirin – and established the carbohydrate structural requirements for these interactions.


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Defining Carbohydrate Antigens as HIV Vaccine Candidates
A. Pashov, M. Perry, M. Dyar, M. Chow and T. Kieber-Emmons

The induction of high affinity antibodies capable of broad neutralization and protection against infection and/or disease is a major goal in the development of a vaccine for human immunodeficiency virus (HIV). Insights into the structure and function of the envelope (Env) protein of HIV-1 suggest that the virus is under strong selection pressure by the immune response leading to constant mutations in the Env protein including the N-glycosylation sites. Initially considered a shield against the immune system, the heavily glycosylated outer surface of the HIV Env protein has drawn attention lately as a legitimate target. The dense cluster of high mannose glycans and the great variety of complex glycans present epitopes that might impact on disease progression. Indeed a number of mannose binding proteins and at least one human anti-mannose antibody - 2G12, are broadly neutralizing. Due to the low immunogenicity of carbohydrates, these targets on HIV are of limited value unless new powerful immunogens are found. One approach would be the molecular design of peptide carbohydrate mimotopes that can elicit neutralizing antibodies by recruiting optimal T cell help. Here we review existing data on carbohydrate interactions and HIV immunogenicity that serves as a basis for structural concepts and approaches used for vaccine design targeting HIV associated carbohydrate antigens. In particular, the value and the limitations of chemical (peptide libraries), structural and immunological information is illustrated.


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Novel Approaches for Identification of Broadly Cross-Reactive HIV-1 Neutralizing Human Monoclonal Antibodies and Improvement of Their Potency
M.-Y. Zhang and D.S. Dimitrov

Human monoclonal antibodies (hmAbs) that neutralize HIV isolates from different clades at physiologically relevant concentrations (broadly cross-reactive neutralizing antibodies (bcnAbs)) are rare in infected individuals. Only small number of such antibodies have been identified and extensively characterized, but efforts to elicit them in vivo have not been successful. We have recently developed novel approaches, based on sequential (SAP) and competitive (CAP) antigen panning methodologies, and the use of antigens with increased exposure of conserved epitopes, for enhanced identification of bcnAbs to gp120-gp41. Some of the antibodies identified by using these approaches (X5, m6, m9) bind better to gp120-CD4 complexes than to gp120 alone (CD4i antibodies); they exhibit exceptional neutralizing activity and breadth of neutralization as scFvs and on average lower potency as Fabs and IgGs. Other antibodies that compete with CD4 for binding to gp120 (m14, m18) (CD4bs antibodies) are weaker neutralizers but also exhibit broad neutralizing activity although at relatively high concentrations. The anti-gp41 antibodies (m43, m44, m45, m47 and m48) appear to have broad cross-reactivity and bind to a new group of conserved conformational epitopes distinct from those of the bcnAbs 4E10, 2F5 and Z13. Recently, the crystal structures of X5, m14 and m18 have been solved and compared to those of 17b and b12; they all contain long H3s that play a major role in their mechanism of binding. The H3s of X5, m6 and m9, unlike the others known, appear to be very flexible which may be related to the mechanism of their exceptional neutralizing activity. The further characterization of the molecular interactions of the bcnAbs with gp120-gp41 will undoubtedly help in our understanding of the mechanisms of virus neutralization, and in the design of entry inhibitors and vaccines.


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Rational Modifications of HIV-1 Envelope Glycoproteins for Immunogen Design
S. Phogat and R. Wyatt

An effective vaccine against the human immunodeficiency virus type 1 (HIV-1) will likely require the elicitation of broadly neutralizing antibodies as well as cellular responses. The HIV exterior envelope glycoprotein trimers, gp120, and the transmembrane glycoprotein, gp41, mediate entry and are the sole viral targets for neutralizing antibodies. However, as subunit immunogens the envelope glycoproteins do not efficiently elicit antibodies capable of neutralizing the extremely diverse array of viruses circulating in the human population. The preponderance of data suggest that inefficient generation of broadly neutralizing antibodies is due to naturally evolved mechanisms of immune evasion inherent in the unmodified HIV envelope glycoproteins. Because the established modes of anti-viral vaccine development, live-attenuation and virus inactivation have not yet been successful for HIV, we and others have focused on subunit vaccine design. In this review, we describe current approaches of rational modification of the envelope glycoproteins based upon structure, antigenicity, biochemistry and biophysics to alter the properties of the envelope glycoproteins such that, as sub-unit immunogens, they now better elicit broadly neutralizing antibodies. The application of structure-assisted, rational subunit vaccine design may be a general paradigm for future efforts to develop vaccines against emerging human pathogens.


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Atenolol: Differences in Mode of Action Compared with other Antihypertensives. An Opportunity to Identify Features that Influence Outcome?
A. Karagiannis, D.P. Mikhailidis, A.I. Kakafika, K. Tziomalos and V.G. Athyros

The beneficial effect of antihypertensive treatment on the risk of major vascular events is well established. Several trials comparing older and newer drugs in the treatment of primary hypertension suggested that it is the blood pressure achieved, rather than choice of the drug that determines most of the primary outcomes.

Beta-blockers have been widely used to treat hypertension and are still recommended as first-line drugs in guidelines. However, recent meta-analyses of trials (either placebo-controlled or using drug comparisons) involving atenolol (a popular beta-blocker), have cast doubt on the suitability of atenolol as a first-line antihypertensive drug.

We consider the mechanisms which might be responsible for the inferiority of atenolol in preventing vascular morbidity and mortality in patients with primary hypertension. This knowledge may help design drugs that are not only more effective in achieving blood pressure targets but that also markedly decrease vascular events.


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Pharmacogenetics and Drug Therapy in Psychiatry - The Role of the CYP2D6 Polymorphism
P. Vandel, J.M. Talon, E. Haffen and D. Sechter

The importance of pharmacogenetics in medicine is growing with the identification of genetic variability by faster screening methods using automatic sequencers. A particularly interesting finding is that apart from environmental and psychological factors, drug response may be influenced by several biological factors as a result of genetic determinants leading to interindividual variability. Several mutations in genes coding for enzymes of the drug metabolizing system, as well as for neurotransmitter receptors or degrading enzymes and monoamine transport proteins, have been identified and investigated in psychiatry.

But, despite the fact that some genetic polymorphisms of enzymes (mainly cytochrome P450 2D6) are well known, the application of pharmacogenetics as a therapeutic tool for improving patient care is rare.

This review has three parts. In the first an overview is given of CYP450 characteristics and the genetic polymorphisms of interest to psychiatry. In the second the clinical implications of the CYP2D6 polymorphism are reviewed and in the third part other aspects on pharmacogenetic research in psychiatry are discussed.

The aim of our review is to promote the application of pharmacogenetics in everyday clinical practice.