Current Medicinal Chemistry - Volume 12, Issue 6, 2005

Immune responses to cancer cells can be elicited in vivo by administering synthetic peptides derived from proteins uniquely or overexpressed on tumor cells (tumor associated antigens - TAAs). Peptides derived from TAAs are presented in the context of major histocompatibility complex (MHC) molecules to cytotoxic T cells (CTL), which can recognize and lyze tumor cells. In contrast to peptides derived from an exogenous source (viral or bacterial), tumor peptides bind weakly to MHC class I molecules. The low binding affinity of these peptides makes them poor candidates for vaccination due to the poor immunogenic response produced. In order to enhance antigen recognition and hence immunogenicity, peptide binding affinity for MHC can be initially improved by modifying the 'anchor' residues. However, the task at hand is highly unpredictable and minor changes in peptide sequence can alter/abolish the T cell response. Furthermore, despite the wealth of information obtained over the last decade from high resolution X-ray structures of MHC class I in complex with peptides (pMHC) as well as pMHC in complex with T cell receptor (TcR), prediction remains difficult. Nonetheless, peptides represent convenient chemical entities that can be rapidly synthesized in clinical grade for therapeutic applications. Herein, the rationale behind modifying TAAs will be discussed including the synthesis/use of proteolytically tolerant peptides (and peptide mimetics) which incorporate non-natural amino acids, retro-inversion and cyclization to improve bioavailability.

The photoaffinity labeling technique is based on UV-light induced crosslinking of proteins to photoreactive DNA. Photoreactive groups can be introduced at different points of DNA (base or phosphate) either at the ends or in inner positions of the DNA chain by combination of enzymatic and chemical synthesis. Varying the structure of photoreactive DNA one can design the intermediates of different stages of DNA replication or DNA repair and apply them to identify the proteins crosslinked to specific positions of the DNA chain in single- or double-stranded DNA, partial DNA duplexes, gapped or nicked duplexes or DNA carrying flap structures. A wide range of base-substituted dNTP analogs containing photoreactive groups of different photoreactivity and spacers of various lengths has been synthesized and characterized. Photoreactive dNTP analogs have been shown to be effective substrates of viral, bacterial and eukaryotic DNA polymerases. The efficiencies of crosslinking of DNA bearing various photoreactive dNMP to protein and DNA targets were estimated. New approaches for enzymatic introduction of photoreactive groups onto the 5;-end of oligonucleotides and into the inner positions of DNA chain have been elaborated. Photoreactive DNAs have been successfully used to study enzymes and protein factors of DNA replication and repair in reconstituted systems and cellular/nuclear extracts. Photoaffinity labeling technique was shown to be a prominent tool of proteomics to elucidate structural and functional aspects of protein-DNA interactions. It can be also applied for identification of proteins including unknown ones, which interact with specific DNA intermediates in cellular/nuclear extracts.

Betulinic acid is a naturally occurring pentacyclic triterpenoid and has been shown to exhibit a variety of biological activities including inhibition of human immunodeficiency virus (HIV), antibacterial, antimalarial, antiinflammatory, anthelmintic and antioxidant properties. This article reports a survey of the literature dealing with betulinic acid related biological properties that has appeared from the 1990's to the beginning of 2003. A broad range of medical and pharmaceutical disciplines are covered, including a brief introduction about discovery, phytochemical aspects, organic synthesis, anti-HIV and cytotoxic mechanisms of action. Various structural modifications carried out and their biological and pharmacokinetic profiles are also incorporated.

The potential use of weapons of mass destruction (nuclear, biological or chemical) by terrorist organizations represents a major threat to world peace and safety. Only a limited number of vaccines are available to protect the general population from the medical consequences of these weapons. In addition there are major health concerns associated with a pre-exposure mass vaccination of the general population. To reduce or eliminate the impact of these terrible threats, new drugs must be developed to safely treat individuals exposed to these agents. A review of all therapeutic agents under development for the treatment of the illnesses and injuries that result from exposure to nuclear, biological or chemical warfare agents is beyond the scope of any single article. The intent here is to provide a focused review for medicinal and organic chemists of three widely discussed and easily deployed biological warfare agents, botulinum neurotoxin and ricin toxins and the bacteria Bacillus anthracis. Anthrax will be addressed because of its similarity in both structure and mechanism of catalytic activity with botulinum toxin. The common feature of these three agents is that they exhibit their biological activity via toxin enzymatic hydrolysis of a specific bond in their respective substrate molecules. A brief introduction to the history of each of the biological warfare agents is presented followed by a discussion on the mechanisms of action of each at the molecular level, and a review of current potential inhibitors under investigation.

Many drugs, both approved and in development, exert their effects through transcription factors. The complexity of the biology of transcriptional regulation, however, presents challenges to the effective design of therapies that directly target transcription factors. This review focuses on the different approaches that are currently pursued in therapeutics and drug discovery aimed at targeting transcription factors and signaling molecules, and their areas of effect in transcription factor biology. A relatively recent approach termed “transcription therapy” has been applied for a number of drugs in development, which may potentially provide a new avenue for targeting transcription factors for therapeutic purposes.

Medicinal compounds from plants represent one of the largest and most diverse groups of plant secondary metabolites. The advent of advanced bioinformatics tools and modern genetic technology allowed for manipulation of biosynthetic pathways with the potential of generating novel chemical entities. First, public databases of secondary metabolite related enzymes were interrogated to identify relevant plant genes from vinca rosea (Catharanthus roseus) and other species. Genes of interest were tested after cloning by transfection into tobacco cell cultures using DNA viral vectors. The biosynthetic enzymes coded by these genes were over-expressed in the host. Automated solvent extraction procedure was employed to extract secondary metabolites from plant leaf tissues and transfected tobacco cell culture samples. The composition of the extracts was analyzed by state of the art bioanalytical methods such as high performance liquid chromatography and capillary electrophoresis to monitor changes in secondary metabolite patterns.

Within the flavonoid class of natural products the prenylated sub-class is quite rich in structural variety and pharmacological activity. In the last twenty years a huge number of new structures has been reported, mostly from Leguminosae and Moraceae, with few coming from other genera. The presence, in different forms, of the isoprenoid chain can lead to impressive changes in biological activity, mostly attributed to an increased affinity for biological membranes and to an improved interaction with proteins. Molecules, such as xanthohumol and sophoraflavanone G, while being very structurally simple, show numerous pharmacological applications and are ideal candidates for SAR aimed to the discovery of new drugs. Only recently the biogenesis of these compounds has been more extensively studied and much attention has been focused on the enzymes involved in the modification and transfer of the prenyl unit.

The HIV-1 regulatory proteins Tat and Rev and the accessory proteins Vpr, Vpu and Vif are essential for efficient viral replication, and their cytoplasmic production suggests that they should be processed for recognition by cytotoxic T lymphocytes. However, only limited data is available, evaluating the role of immune responses directed against these proteins in natural HIV-1 infection. Recent advances in the methods used for the characterization of HIV-1-specific cellular immune responses, including quantification of antigen-specific IFN-γ production by ELISpot assay and flow-cytometry-based intracellular cytokine quantification, have allowed for a much more comprehensive assessment of virus-specific immune responses. Emerging data show that the regulatory and accessory proteins serve as important targets for HIV-1-specific T cell responses, and multiple CTL epitopes have been identified in functionally important regions of these proteins. Moreover, the use of autologous peptides have allowed for the detection of significantly stronger HIV-1-specific T cell responses in the more variable regulatory and accessory HIV-1 proteins Tat and Vpr. These data indicate that despite the small size of these proteins, regulatory and accessory proteins are targeted by cellular immune responses in natural HIV-1 infection and contribute importantly to the total HIV-1-specific CD8+ T cell response. A multi-component vaccine, with the inclusion of these proteins plus structural proteins remains the most promising choice for an effective AIDS vaccine.