A rapid and simple screening method for HIV-1 protease inhibitors using recombinant Escherichia coli

Recombinant Microorganisms as Tools for High Throughput Screening for Nonantibiotic Compounds

Microorganisms were among the first tools used for the discovery of biologically active compounds. Their utility reached a zenith during the era of antibiotic development in the 1950s and 1960s, then declined. Subsequently, a substantial role for microorganisms in the pharmaceutical industry developed with the realization that microbial fermentations were intriguing sources of nonantibiotic natural products. From recombinant DNA technology emerged another important role for microorganisms in pharmaceutical research: the expression of heterologous proteins for therapeutic products or for in vitro high throughput screens (HTSs). Recent developments in cloning, genetics, and expression systems have opened up new applications for recombinant microorganisms in screening for nonantibiotic compounds in HTSs. These screens employ microorganisms that depend upon the function of a heterologous protein for survival under defined nutritional conditions. Compounds that specifically target the heterologous protein can be identified by measuring viability of the microorganism under different nutrient selection. Advantages of this approach include a built-in selection for target selectivity, an easily measured end point that can be used for a multitude of different targets, and compatibility with automation required for HTSs. Mechanism-based HTSs using recombinant microorganisms can also address drug targets that are not readily approachable in other HTS formats, including certain enzymes; ion channels and transporters; and protein::protein, protein::DNA, and protein::RNA interactions.

A practical total synthesis of the microbial alkaline proteinase inhibitor (MAPI)

Diverse serine and cysteine proteases as well as alkaline proteinases and elastases play a crucial role in numerous biological processes. Natural peptide aldehydes such as the "microbial alkaline proteinase inhibitor" (MAPI, 1) are valuable tools to characterize novel enzymes and to study their function in nature. Within a drug discovery program we wanted to design and explore non-natural MAPI congeners with novel biological profiles. To that end we devised a simple, practical, and scalable synthesis of MAPI 1 from readily available amino acid building blocks. The modular nature of our approach allows convenient structural modification of the MAPI backbone.

A rapid and sensitive bacterial assay to determine the inhibitory effect of 'interface' peptides on HIV-1 protease co-expressed in Escherichia coli

The HIV-1 protease is essential for maturation of virus particles and is, therefore, an attractive target for antiviral drugs. The function of this protease depends on the dimerization of two identical subunits. Commonly used protease inhibitors are directed mainly against the active site of the enzyme which often leads to viral resistance. To determine the inhibitory effect of peptides interfering with the dimerization site of the HIV-1 protease, a recombinant bacterial screening assay was established. Escherichia coli was co-transformed with two different plasmids, expressing the 'interface' peptide and an active HIV-1 protease toxic for the bacteria. Co-expression of inhibitory peptides overcomes the incomplete membrane transmission of supplemented inhibitors and leads to a direct interaction of the inhibitory peptide and the HIV-1 protease. The inhibitory effect of co-expressed peptides was measured by an increased growth of co-transformed bacteria, compared with a slowly growing E. coli control culture only expressing the HIV-1 protease. Using this assay several penta- and hexa-peptides were screened for their ability to inhibit HIV-1 protease activity. One of these peptides showed a significant inhibitory effect on co-expressed recombinant HIV-1 protease.

Screening of inhibitors of HIV-1 protease using an Escherichia coli cell assay

To evaluate the available peptidic and pseudopeptidic inhibitors of HIV protease for their possible in vivo activity, a screening test using Escherichia coli was established. E. coli cells carrying the plasmid pET9c-PR containing the gene for HIV-1 protease under the control of a T7-promotor are grown in the absence and in the presence of inhibitors. The action of the toxic protease produced by the cells is counteracted by the inhibitors. Provided sufficient membrane permeability of the inhibitors exists, this results in accelerated cell growth. From the peptides known to be active in an in-vitro enzyme test, most compounds inhibit HIV protease only to a limited degree in this test. However, two short peptides (Ac-Ser-Tyr-Glu-Leu and Lys-Ile-Ser-Tyr-Asp-Tyr) protect cell growth to an considerabe extent, thus indicating that they reach the E. coli cytosol and there block HIV protease. Two pseudopeptides known to be very potent in the enzyme test (SDZ PRI 053 and CIBA 61755) also inhibit HIV-1 protease strongly in this cell growth test.

Prospects for rational approaches to anthelmintic discovery

Rational approaches to anthelmintic discovery include the design of screens for compounds directed at specific proteins in helminths that are pharmacologically distinguishable from their vertebrate homologues. The existence of several anthelmintics that selectively target the neuromusculature of helminths (e.g. levamisole, ivermectin, praziquantel, metrifonate), together with recent basic research in helminth physiology, have contributed to the recognition that neurobiology distinguishes these organisms from their vertebrate hosts. In this survey, we focus on mechanism-based screening and its application to anthelmintic discovery, with particular emphasis on targets in the neuromusculature of helminths. Few of these proteins have been exploited in chemotherapy. However, recent studies in comparative pharmacology and molecular biology, including the C. elegans genome project, have provided insights on potential new targets and, in some cases, molecular probes useful for their incorporation in mechanism-based screens.