Current Medicinal Chemistry - Anti-Infective Agents - Volume 3, Issue 1, 2004

The current trend of therapy requires the use of antibiotics, which combine a high level in vitro antibacterial activity with the capacity to act in concert with the immune system in a way that potentiates the host's defence mechanisms. Whilst such additional effects on the immune system by the antibiotic may be of secondary importance in patients with normal host defence mechanisms, they are of primary importance in patients with depression of the immune system, who are highly susceptible to infections, often difficult to treat, even with the current and modern antimicrobial agents. This investigation delineates our own results regarding the impact of some antimicrobial agents such as the most recent β- lactams, carbapenems, trinems, glycopeptides, quinolones, aminoglycosides and macrolides upon the primary functions of phagocytes, namely human polymorphonuclear granulocytes and macrophages. The ability of the above mentioned drugs to penetrate human phagocytes and their consequences upon subsequent phagocytic ingestion and killing of ingested bacteria, both Gram-positive and Gram-negative, are here reported. Moreover the influence exerted by some of these antibiotics either on phagocytic functions or on the release of cytokines is illustrated. The beneficial properties of some b-lactams, which result in “restoring” the depressed phagocyte-dependent response in patients on chronic hemodialysis or in renal transplant recipients, are also focused.

The current pandemic of sexually transmitted HIV / AIDS has created an urgent need for a new type of microbicide, one that is both a spermicide and a virucide. WHI-07 is a novel 5-bromo 6-methoxy aryl phosphoramidate derivative of 3'-azido-3'-deoxythymidine (zidovudine, ZDV / AZT) with potent anti-HIV and spermicidal activities. WHI-07 was rationally designed to bypass the thymidine kinase dependency of ZDV activation in genital tract secretions. WHI-07 was formulated via a nontoxic gel-microemulsion for intravaginal use as a potential candidate anti-HIV spermicide. The in vivo efficacy as well as safety studies of WHI-07 included: (i) vaginal as well as rectal microbicide efficacy studies in the feline immunodeficiency virus (FIV) / domestic cat model for AIDS; (ii) in vivo retention of anti-HIV activity in the nonhuman primate; (iii) vaginal contraceptive efficacy studies in rabbits; (iv) single- and/ or multiple-dose toxicity studies in mice, rabbits, cats as well as monkeys; (v) mucosal, reproductive, and developmental toxicity studies in mice and rabbits; (vi) cytotoxicity, mutagenicity, and genotoxicy tests using human and yeast cells; and (vii) long-term carcinogenicity studies in mice. WHI-07 which exhibited nanomolar in vitro anti-HIV IC50 and low micromolar spermicidal EC50 values was significantly less active against genital epithelial cells and did not induce primary DNA damage in human and yeast cells. WHI-07 retained full activity in TK-deficient cells, the main carriers of HIV in semen. Both vaginal as well as rectal instillation of WHI-07 gel-microemulsion, either alone or in combination with a vanadocene dithiocarbamate, effectively protected domestic cats from a subsequent vaginal or rectal exposure to feline T cells chronically infected with a mucosally transmissible FIV strain. WHI-07 gel-microemulsion was a potent vaginal contraceptive in the rabbit model. Both short-term (up to 90 days) and long-term (2-yr) repetitive intravaginal administrations of WHI-07 at concentrations as high as 5.7 ´ 106 times its in vitro anti-HIV IC50 and 5700-times its spermicidal EC50 were not associated with mucosal, systemic, reproductive or developmental toxicity in mice and rabbits and did not produce increased carcinogenicity in mice. WHI-07 has clinical potential as a safe prophylactic contraceptive anti-HIV microbicide for sexually active women.

Data from the first phase III HIV vaccine trial does not indicate efficacy regarding the production of neutralizing antibodies and prevention of HIV infection. The induction of a potent HIV-specific cellular response through therapeutic vaccination is now thought to be a more attainable goal through HIV DNA vaccines. This review will summarize the immunologic rationale behind the development of vaccines that elicit cellular immune responses, and will then illustrate examples of DNA-based preventive and therapeutic vaccine strategies, which have recently been evaluated in pre-clinical animal studies as well as some human clinical trials; they include: (i) cytokine-augmented DNA vaccines; (ii) CpG enriched plasmid DNAs; (iii) viral vectors and prime-boost strategies; (iv) lipopeptide vaccines; (v) ex vivo dendritic cell-based, and (vii) dendritic cell-targeted vaccines. This set of data will be carefully reviewed in order to understand how this know-how has been or can be used to design meaningful “next-generation” therapeutic vaccines.

Brucellosis is a highly contagious bacterial zoonosis that affects millions of people worldwide. The infection induces debilitating and incapacitating severe diseases, with mild to serious complications. The intracellular localization of Brucella spp. makes treatment difficult, since most antibiotics, although effective in vitro, do not actively pass through cellular membranes. Therefore, complete eradication of the microorganisms is difficult to achieve, and the incidence of relapses is rather high. Hence, drug delivery systems such as liposomes and biodegradable microspheres should be most useful for targeting these intracellular sites where the organisms are located. Many examples and promising results of the use of drug delivery systems for the treatment of intracellular infectious diseases already contribute to the literature and demonstrate the great potential of these technologies. In the present manuscript, we review our work on the development of new approaches to an effective pharmaceutical dosage form for the treatment of brucellosis. For this purpose, we prepared and evaluated a number of liposomal and microparticulate formulations for the efficient encapsulation of gentamicin and a competent therapeutic activity towards infected models in vitro and in vivo. Liposomes loaded with gentamicin sulphate eliminated completely intracellular Brucella in infected cultured monocytes-macrophages. In vivo, gentamicin-loaded cationic liposomes produced a protective effect in mice challenged with a lethal dose of B. abortus. Further, gentamicin sulphate microencapsulated into poly(lactide) (PLA) and its copolymers with glycolide (PLGA) provided controlled release of the drug, typically with biphasic profiles, what may represent an advantage over the use of liposomes. In vitro, this biodegradable particulate delivery system was efficiently phagocytosed, induced cell activation and reduced intracellular Brucella infection in cultured monocyte-macrophages. In conclusion, liposomes and biodegradable microspheres loaded with antibiotics appear useful for targeting monocytes and reducing intracellular Brucella infection; these delivery systems should represent a promising alternative approach for the treatment of brucellosis.

Infectious diseases are one of the leading causes of death in the world. This major medical concern is due to the continual emergence of new infectious diseases and reemergence of old pathogens, together with an increasing number of pathogens resistant to antimicrobial drugs. The generation of new anti-infective agents for resolving these medical problems has emerged as an urgent issue in modern medicine. The availability of genome sequences, and the development of various high-throughput techniques and computational tools offer holistic and integrative strategies for dissecting the interplay between microbial pathogens and their hosts (infectomics). Both microbial and host signatures of infectomes, which mirror the interplay between pathogens and their hosts, provide invaluable fountains in the search for novel antimicrobial therapies. There are several major issues in the discovery and development of new drugs, from target discovery and validation to animal models and clinical trials. However, infectomic approaches integrating genomics, proteomics and glycomics will become increasingly important. Essential Therapeutics Inc. has successfully used functional genomic methods to identify several hundred antimicrobial targets in representative bacterial, fungal and viral pathogens. Recent advances in chemical genomics and proteomics have revolutionized drug discovery research by allowing the parallel processing of multiple genomic targets against large numbers of diverse compounds. The identification of small-molecule modulators of biological functions that are usually executed by large molecules (DNAs, RNAs, proteins and polysaccharides), and the process of transforming these into high-content lead series, are key activities in modern drug discovery. This review focuses on infectomics and its applications to antimicrobial drug discovery.

The vast majority of the world population is infected with herpesviruses. Herpes simplex virus (HSV) infections are the cause of herpes labialis (cold sores) and herpes genitalis (genital herpes). In some cases HSV infections can progress into sight-impairing (herpetic keratitis) or life-threatening disease such as herpes encephalitis or disseminated disease especially in neonates and the immunocompromized patient population. While severe disease is associated with significant morbidity and mortality, the majority of HSV infections in the immunocompetent patient population is often benign and self-limiting from the medical standpoint, but they have an enormous impact on personal relationships and interfere with social contacts and everyday activities. Chemotherapy with acyclovir (Zovirax) and penciclovir (Vectavir, Denavir) and their respective prodrugs valacyclovir (Valtrex) and famciclovir (Famvir) is safe, but only effective if treatment is initiated early during the disease course. Furthermore, these drugs can abrogate disease symptoms but do neither cure nor reduce frequency of recurrent disease. To date no vaccination against herpes simplex disease is available. Broad-spectrum potency, efficacy (especially if treatment is delayed), growing resistance in the immunocompromized patient population, safety including poly-pharmacy and the unmet medical need to cure or reduce frequency of recurrent disease were the key criteria in the search for the next generation of drugs directed at novel antiviral targets. Recently, novel helicase-primase inhibitors superior to marketed drugs regarding all parameters of the preclinical profile have been published. This review summarizes the discovery and current medicinal chemistry of the novel compound classes and provides an up-to-date interpretation of the significant challenge to establish novel therapies for herpes disease.