Letters in Drug Design & Discovery - Volume 2, Issue 2, 2005

We demonstrated that the uracil-DNA glycosylase inhibitor, when delivered to human melanoma cells using protein transduction technology, resulted in a dose and time dependent inhibition of uracil-DNA glycosylase (UNG) and this inhibited cell proliferation. These results suggest that a novel class of inhibitors specifically targeting UNG can be developed as potential anti-cancer agents.

The most common feature of human cancer cells is aneuploidy and a defective mitotic checkpoint is thought to be responsible. Since a group of anticancer drugs target the mitotic checkpoint, this review will discuss the association of mitotic checkpoint with chemotherapeutic drug sensitivity and suggest a novel therapeutic tool to achieve chemosensitization in human cancer cells.

Animal and human studies have shown angiotensin converting enzyme (ACE) inhibitors to be protective agents against myocardial injury, especially ischemia/reperfusion injury. In this review of the application of ACE inhibitors in heart surgery, I examine the problems involved and discuss their solutions.

New inhibitors of the ß-site amyloid precursor protein cleaving enzyme (BACE-1) are described. The hydroxyethyl transition state isostere of GT1017 has been replaced by the hydroxyethylamine (HEA), the hydroxyethylsulfide or the hydroxyethylurea groups. Biological evaluation has shown that the HEA analogue, obtained as epimeric mixture, inhibited BACE-1 with an IC50=0.12μM. Stereoselective synthesis showed surprisingly that the most active stereoisomer was the (R)-HEA transition state analogue with an IC50=0.014μM.

The analysis of the S3 binding region of the Hepatitis C Virus NS3 serine protease allowed replacing the P3 amino acid of a-ketoacid tripeptide inhibitors with an amphiphilic capping group. The binding mode of α-ketoacid (8) (IC50 = 1 μM) and the role of the amphiphilic group in non-covalent phenethylamide inhibitor (15) (IC50 = 21 μM) will be discussed.

We describe herein tetrapeptidyl α-ketoamide 4A based systematic P1 modifications alone or/and in combination with further P1; variations. These SAR efforts led to the discovery of a number of potent and selective HCV NS3 protease inhibitors such as 4B, 9, and 12 endowed with impressive cellular activity as measured in the replicon assay and very good therapeutic indexes. On the basis of its overall profile, compound 4B (VX-950) has been selected for human clinical trials.

Chicken avidin is used in a wide variety of applications in the life sciences, due to its extraordinarily strong affinity for biotin. Avidin-biotin strategy has also recently established a role in medical targeting approaches for cancer treatments. An interesting new exploitation for avidin-biotin techniques is the utilization of this strong affinity in gene therapy, to target and enhance gene delivery to the appropriate target cells and tissues. In this communication, we review novel avidin fusion proteins that have been developed for enhanced gene delivery and drug targeting purposes. The principles of this approach are highlighted by the avidin fusion proteins Scavidin (fusion with the macrophage scavenger receptor class A), Lodavin (fusion with the endocytotic LDL receptor) and avidin-displaying baculovirus (Baavi). Scavidin and Lodavin are cell membrane proteins in which avidin is expressed as an extracellular portion, thereby enhancing the targeted drug and gene delivery with biotinylated drug molecules and vectors. Baavi, on the other hand, displays avidin moieties on its surface, and opens up possibilities for flexible modification of its targeting properties and other characteristics by using different biotin-conjugated molecules. Potential applications of avidin fusion proteins and future trends of targeted drug and gene delivery based on these strategies will be discussed.

Cordycepin (3;-deoxyadenosine) is a potent anti-leukemic, anti-fungal, and anti-parasitic nucleoside antibiotic. Unfortunately, the biological activity of cordycepin is attenuated by its rapid conversion to 3;-deoxyinosine by adenosine deaminase (ADA). We have synthesized a series of ADA-resistant N-aminal and N-thioaminal cordycepin derivatives, which are protected from inactivation by deamination and yet retain biological activity. These compounds are hydrolyzed at various rates to efficiently release the parent drug cordycepin, and likely serve as simple hydrolytically activated prodrugs.

A competitive dialysis method has been developed to screen compounds for their DNA binding properties, and it is based on directly comparing the binding of polyamide molecules to a series of distinctively varied, short, synthetic deoxyribonucleotides. Relative binding ratios for each polyamideoligonucleotide pairing were calculated from the concentrations of free polyamide and total polyamide in order to quantitatively compare binding to different DNA sequences. This approach works well as a preliminary screen to determine the viability of novel small molecules, prior to investing significant resources in further characterization and development of possible sequence specific DNA targeted therapeutic agents. The trends in binding affinities of the four triamide molecules (f-ImPyIm, distamycin A, f-PyPyPy and f-ImImPy; where Im is imidazole and Py is pyrrole) correlated well with data obtained from surface plasmon resonance (SPR) studies. Results from circular dichroism studies confirmed the minor groove side-by-side stacked binding motif of the triamides, and thermal stability experiments corroborated the improved DNA stability of promising polyamide-DNA complexes. The affinity of distamycin A for its cognate DNA sequence (A3T3) was unambiguously selected over the other DNA sequences tested. Alternatively, as expected from SPR, circular dichroism and thermal melting experiments, f-ImImPy showed very poor affinity for DNA sequences tested, including its cognate DNA, TCGA. Thus, the very good (distamycin A) and very poor (f-ImImPy) DNA binders were effectively screened.

Minocycline, the 7-dimethylamino- 6-dimethyl-desoxytetracycline hydrochloride, is a caspase-1 inhibitor and may serve as anti-apoptotic agent, thereby acting neuroprotective. It directly inhibits both caspase-independent and -dependent mitochondrial cell death pathways, and decreases inducible nitric oxide synthetase activity. Minocycline delays disease progression in the transgenic mouse model of Huntington;s disease (HD), extending survival by 14%. HD is a late onset relentlessly progressive, neurodegenerative disorder with currently no cures or even effective therapies, death occurring 15 years after onset. In this review, recent clinical and preclinical data on minocycline in HD and neuroprotective alternatives discussed.

Human cytomegalovirus (HCMV) retinitis treated with frequent intraocular injections of ganciclovir is associated with complications such as endophthalmitis, retinal detachment and vitreous haemorrhage. Several formulations of biodegradable injectable PLGA microspheres with ganciclovir have been previously investigated as a possible alternative for treatment of HCMV retinitis. This report describes two new formulations of PLGA microspheres with ganciclovir that also include alpha tocopherol (vitamin E) or glyceryl tricaprylate/caprate (miglyol) as additives, modulating the release rate of ganciclovir. While additive free microspheres in vitro released about 90% of its ganciclovir within 20 days, the microspheres with the additives released only 20% of the drug during this period, and continued releasing the drug at the same rate for a total of 42 days.

Chronic hepatitis C is a ubiquitous disease, affecting approximately 170 million globally. The hepatitis C virus (HCV) is spread by parenteral transmission of body fluids, primarily blood or blood products. The hepatitis C viral genome is a positive-sense, single-stranded RNA molecule approximately 9.4kb in length, which encodes a polyprotein of about 3100 amino acids. There are 6 main genotypes of HCV, with each further stratified by subtype. Hepatitis C virus exists as a heterogeneous mixture of closely related viruses called quasispecies. The continuous evolution of new variant glycoproteins is a major mechanism of viral evasion of the immune system. The quasispecies diversity collapses to oligoclonality or homogeneity prior to clearance. Substantial evidence indicates that HCV genotype is clinically important with respect to efficacy of anti-viral therapy. The dual drug regime currently used to treat HCV infection consists of pegylated-interferon (peg-IFN) and the guanosine nucleoside analog ribavirin. Mutations in the viral genome are likely to contribute in large measure to the emergence of “resistance” during interferon-based therapy. The HCV genome codes for 10 proteins. The structural proteins of core, E1, E2 and P7 are positioned immediately downstream of the 5;UTR. These proteins are cleaved from the polyprotein by host-encoded proteases. The remaining proteins are released from the polyprotein by a process of autocatalytic cleavage or by the protease activity of NS3. The RNA dependent RNA polymerase (NS5B) is position immediately downstream of the 3;UTR. The current cytokine based treatment modality is based on a shotgun approach of up regulation of cellular anti-viral pathways. The net effect of IFN signalling is the down regulation of protein translation. The cellular signalling pathways induced by IFN engagement of the cognate receptor are not specific for the elimination of HCV. HCV has evolved mechanisms that hinder IFN signalling and the induction of nuclease activity that would otherwise destroy the viral genome. The net benefit to the virus is that it potentiates the establishment of persistence. The activity of the host encoded proteases necessary for the cleavage of Core-P7, the proteolytic activity of NS3, the helicase activity of NS3 and the polymerase activity of NS5B are all potential targets for the development of adjunct options for the treatment of hepatitis C virus infections. The development of novel antivirals suitable for use against HCV has learnt a great deal from the research and development of drugs used to treat HIV disease. Like HIV, HCV has the propensity to produce greater than 1010 virions per day. Each genome will have a fitness potential to survive each unique selection pressure (endogenous and/or exogenous) and it is to be expected that again like HIV, HCV will have the potential to evolve drug resistant mutants. The goal of highly active antiretroviral therapy in HIV disease is viral suppression. However, it would appear that elimination, rather than suppression of viral replication, in HCV disease is achievable at least in a proportion of patients. The phenomenon of quasispecies is likely responsible for the ineffectiveness of isolate-specific vaccines and will challenge the development of pangenotype antiviral therapies. New strategies based on antisense and ribozyme technologies may hold future promise as therapeutic adjuncts in the treatment of HCV infection.

Amidine-containing derivatives of the diphenylurea antimalarial lead compound WR268961, a putative plasmepsin inhibitor, were prepared and tested against erythrocyte-stage P. falciparum. Diamidine 8 was the most active compound, displaying IC50 values of 54 nM and 41 nM versus chloroquine sensitive (D6) and chloroquine resistant (W2) parasites, respectively.

To determine whether topically applied biologically active drugs can be used to protect the human immune system from sunlight, we studied the effect of tamarind xyloglucan polysaccharide, a natural and common fruit constituent, on solar-simulated, ultraviolet radiation-induced local immunosuppression and erythema in humans. Immunosuppression was studied in humans using a nickel contact hypersensitivity recall model. Ultraviolet dose responses were generated to determine the extent to which tamarind affected the immune response in a group of 15 volunteers. The subsequent nickel-induced erythema was quantitated using a reflectance spectrometer. 0.1 μgml-1 of topical tamarind polysaccharide reduced ultraviolet radiation-induced immunosuppression. Frozen sections of biopsies taken were analysed by immunohistochemistry. Tamarind inhibited ultraviolet radiation-induced CD11c+ dendritic cell loss from the epidermis. The ultraviolet doses used in this study did not alter the number of Mac387+ macrophages or NP57+ neutrophils infiltrating the skin. Low dose xyloglucan polysaccharide from tamarind protected from immunosuppression in humans, possibly by reducing ultraviolet radiation-induced loss of dendritic cells, demonstrating that these types of drugs may be useful adjuncts to sunscreens for protection from skin cancer.