Carrier-mediated delivery of antiviral agents

Improved Delivery through Biological Membranes. Synthesis, Characterization and Antiviral Activity of a Series of Ribavirin Chemical Delivery Systems: 5 and Carboxamide Derivatives

A number of 1-methyl-1,4-dihydrotrigonellinate derivatives of ribavirin and various ribavirin esters were prepared as potential brain-targeting delivery forms. Systemic administration of a model system (1-[5′-(1-methyl-3-carbonyl-1,4-dihydropyridine)-2′,3′-bis-O-isobutyrate-β-D-ribofuranosyl]1,2,4-triazol-3-carboxamide) resulted in a significant brain concentration of the corresponding pyridinium salt. Antiviral testing accomplished with the aid of a mouse model, in which a Phlebovirus (Punta Toro virus) was intracranially inoculated, showed that while ribavirin itself was without effect, several ribavirin chemical delivery systems (CDS) exerted significant activity. These responses included increased number of survivors and increased mean survival time. It is suggested that the CDS approach may improve the efficacy of ribavirin towards various RNA viral encephalitis diseases.

Targeting drugs to the brain by redox chemical delivery systems

Chemical delivery systems (CDSs) based on the redox conversion of a lipophilic dihydropyridine to an ionic, lipid-insoluble pyridinium salt have been developed to improve the access of therapeutic agents to the central nervous system. A dihydropyridinium-type CDS or a redox analog of the drug is sufficiently lipophilic to enter the brain by passive transport, then undergoes an enzymatic oxidation to an ionic pyridinium compound, which promotes retention in the CNS. At the same time, peripheral elimination of the entity is accelerated due to facile conversion of the CDS in the body. This review discusses chemical, physicochemical, biochemical, and biological aspects in relation to the principles and practical implementation of the redox brain-targeting approach to various classes of drugs. Representative examples to the brain-enhanced delivery of neurotransmitters, steroids, anticonvulsants, antibiotics, antiviral, anticancer and antidementia agents, and neuropeptides and their analogs are presented in detail. In vivo and in vitro studies and preliminary clinical data of several novel derivatives have been promising, which could lead to a practical use of the redox CDSs after proper pharmaceutical development. The investigations accentuate the need for considering physicochemical, metabolic, and pharmacokinetic properties in designing of carrier systems that are able to target drugs into the central nervous system.

Recent advances in the brain targeting of neuropharmaceuticals by chemical delivery systems

Brain-targeted chemical delivery systems represent a general and systematic method that can provide localized and sustained release for a variety of therapeutic agents including neuropeptides. By using a sequential metabolism approach, they exploit the specific trafficking properties of the blood-brain barrier and provide site-specific or site-enhanced delivery. After a brief description of the design principles, the present article reviews a number of specific delivery examples (zidovudine, ganciclovir, lomustine benzylpenicillin, estradiol, enkephalin, TRH, kyotorphin), together with representative synthetic routes, physicochemical properties, metabolic pathways, and pharmacological data. A reevaluated correlation for more than 60 drugs between previously published in vivo cerebrovascular permeability data and octanol/water partition coefficients is also included since it may be useful in characterizing the properties of the blood-brain barrier, including active transport by P-glycoprotein.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Antiviral activity and pharmacokinetics of HOE 602, an acyclic nucleoside, in animal models

The acyclic nucleoside derivative HOE 602 (2-amino-9-[1,3-bis(isopropoxy)-2-propoxymethyl]purine) was evaluated for its antiviral activity in cell culture and for its therapeutic efficacy in mice infected with herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) or with murine cytomegalovirus (MCMV). HOE 602 was inactive in vitro against a variety of DNA- and RNA-viruses. However it prevented symptoms and mortality in mice systemically infected with HSV-1, HSV-2 or MCMV when administered intraperitoneally or orally at a dosage of 100 mumol/kg twice per day. Pharmacokinetic studies in mice and macaques revealed that HOE 602 was converted via three metabolic steps to ganciclovir, which seemed to be the antivirally active compound. The bioavailability of ganciclovir after oral administration of HOE 602 or ganciclovir was similar in mice, while in rhesus monkeys much higher serum levels of ganciclovir were reached with HOE 602. After intraperitoneal or intravenous administration higher drug levels were obtained with ganciclovir. The excellent therapeutic efficacy in animal models, the high enteral absorption in monkeys, and the favourable physical properties will hopefully lead to an orally active drug against cytomegalovirus and severe herpes infections in man.

Noninvasive drug delivery to the brain

Although brain-targeted delivery of pharmaceuticals can be achieved by direct introduction of the drug into the CNS, the techniques available for accomplishing this are associated with various medical risks which are unacceptably high. Methods for noninvasive delivery of pharmacologically active agents to the brain are discussed with emphasis placed on chemical delivery systems.