The farnesyltransferase inhibitor manumycin A is a novel trypanocide with a complex mode of action including major effects on mitochondria

Identification of Antimicrobial Compounds in Two Streptomyces sp. Strains Isolated From Beehives

The World Health Organization warns that the alarming increase in antibiotic resistant bacteria will lead to 2.7 million deaths annually due to the lack of effective antibiotic therapies. Clearly, there is an urgent need for short-term alternatives that help to alleviate these alarming figures. In this respect, the scientific community is exploring neglected ecological niches from which the prototypical antibiotic-producing bacteria Streptomycetes are expected to be present. Recent studies have reported that honeybees and their products carry Streptomyces species that possess strong antibacterial activity. In this study, we have investigated the antibiotic profile of two Streptomycetes strains that were isolated from beehives. One of the isolates is the strain Streptomyces albus AN1, which derives from pollen, and shows potent antimicrobial activity against Candida albicans. The other isolate is the strain Streptomyces griseoaurantiacus AD2, which was isolated from honey, and displays a broad range of antimicrobial activity against different Gram-positive bacteria, including pathogens such as Staphylococcus aureus and Enterococus faecalis. Cultures of S. griseoaurantiacus AD2 have the capacity to produce the antibacterial compounds undecylprodigiosin and manumycin, while those of S. albus AN1 accumulate antifungal compounds such as candicidins and antimycins. Furthermore, genome and dereplication analyses suggest that the number of putative bioactive metabolites produced by AD2 and AN1 is considerably high, including compounds with anti-microbial and anti-cancer properties. Our results postulate that beehives are a promising source for the discovery of novel bioactive compounds that might be of interest to the agri-food sector and healthcare pharmaceuticals.

Activation of a Cryptic Manumycin-Type Biosynthetic Gene Cluster of Saccharothrix espanaensis DSM44229 by Series of Genetic Manipulations

(1) Background: Manumycins are small actinomycete polyketides with prominent cancerostatic and immunosuppressive activities via inhibition of various eukaryotic enzymes. Their overall activity towards human cells depends on the structural variability of both their polyketide chains, mainly the upper one. In our genetic screening project to find novel producers of anti-inflammatory manumycins, the strain Saccharothrix espanaensis DSM44229 was identified as containing a novel manumycin-type biosynthetic gene cluster (BGC). (2) Methods: The biosynthetic genes appeared to be silent under all assayed laboratory conditions. Several techniques were used to activate the BGC, including: (i) heterologous expression in various hosts, (ii) overexpression of putative pathway-specific regulatory genes, and (iii) overexpression of a bottleneck cyclizing aminolevulinate synthase gene in both natural and heterologous producers. (3) Results: Multiple novel manumycin-type compounds were produced at various levels by genetically-modified strains, sharing a tetraene lower chain structure with a colabomycin subgroup of manumycins, but possessing much shorter and saturated upper chains. (4) Conclusions: A cryptic manumycin-type BGC was successfully activated by genetic means to gain production of novel manumycin-type compounds for future comparative activity assays. Heterologously produced compounds were identical to those found after final activation of the BGC in the original strain, proving the intactness of the cloned BGC.

A dual-targeting approach to inhibit Brucella abortus replication in human cells

Brucella abortus is an intracellular bacterial pathogen and an etiological agent of the zoonotic disease known as brucellosis. Brucellosis can be challenging to treat with conventional antibiotic therapies and, in some cases, may develop into a debilitating and life-threatening chronic illness. We used multiple independent assays of in vitro metabolism and intracellular replication to screen a library of 480 known bioactive compounds for novel B. abortus anti-infectives. Eighteen non-cytotoxic compounds specifically inhibited B. abortus replication in the intracellular niche, which suggests these molecules function by targeting host cell processes. Twenty-six compounds inhibited B. abortus metabolism in axenic culture, thirteen of which are non-cytotoxic to human host cells and attenuate B. abortus replication in the intracellular niche. The most potent non-cytotoxic inhibitors of intracellular replication reduce B. abortus metabolism in axenic culture and perturb features of mammalian cellular biology including mitochondrial function and receptor tyrosine kinase signaling. The efficacy of these molecules as inhibitors of B. abortus replication in the intracellular niche suggests “dual-target” compounds that coordinately perturb host and pathogen are promising candidates for development of improved therapeutics for intracellular infections.

Effect of starter unit availability on the spectrum of manumycin-type metabolites produced by Streptomyces nodosus ssp. asukaensis

AIMS

Production of minor asukamycin congeners and its new derivatives by combination of targeted genetic manipulations with specific precursor feeding in the producer of asukamycin, Streptomyces nodosus ssp. asukaensis.

METHODS AND RESULTS

Structural variations of manumycins lie only in the diverse initiation of the 'upper' polyketide chain. Inactivation of the gene involved in the biosynthesis of cyclohexanecarboxylic acid (CHC) turned off the production of asukamycin in the mutant strain and allowed an increased production of other manumycins with the branched end of the upper chain. The ratio of produced metabolites was further affected by specific precursor feeding. Precursor-directed biosynthesis of a new asukamycin analogue (asukamycin I, 28%) with linear initiation of the upper chain was achieved by feeding norleucine to the mutant strain. Another asukamycin analogue with the unbranched upper chain (asukamycin H, 14%) was formed by the CHC-deficient strain expressing a heterologous gene putatively involved in the formation of the n-butyryl-CoA starter unit of manumycin A.

CONCLUSIONS

Combination of the described techniques proved to be an efficient tool for the biosynthesis of minor or novel manumycins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Production of two novel asukamycin derivatives, asukamycins H and I, was achieved. Variations appeared in the upper polyketide chain, the major determinant of enzyme-inhibitory features of manumycins, affecting their cancerostatic or anti-inflammatory features.

The prenylation inhibitor manumycin A reduces the viability of Anaplasma phagocytophilum

Anaplasma phagocytophilum is an obligately intracellular bacterium and is the causative agent of human granulocytic anaplasmosis (HGA), an emerging and major tick-borne disease in the USA and other parts of the world. This study showed that the prenylation inhibitor manumycin A effectively blocked A. phagocytophilum infection in host cells (HL-60 or RF/6A cells). A. phagocytophilum infection activated extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase in host cells, and manumycin A treatment reduced ERK activation in A. phagocytophilum-infected host cells. As ERK activation is required for A. phagocytophilum infection, we examined whether manumycin A inhibited the bacteria directly or through host ERK signalling. Treatment of A. phagocytophilum alone with manumycin A significantly reduced the bacterial infectivity of host cells and bacterial viability in the absence of host cells, whereas pre-treatment of host cells did not inhibit bacterial infection in host cells. The inhibitory effect of manumycin A on A. phagocytophilum infection in host cells was achieved even at a concentration 100 times lower than that required for effective inhibition of mammalian cell signalling. These results suggested that manumycin A directly inactivates the bacterium, resulting in reduced infection and ERK1/2 activation. Thus, the manumycin group of drugs may have a therapeutic potential for HGA.

The essential neutral sphingomyelinase is involved in the trafficking of the variant surface glycoprotein in the bloodstream form of Trypanosoma brucei

Sphingomyelin is the main sphingolipid in Trypanosoma brucei, the causative agent of African sleeping sickness. In vitro and in vivo characterization of the T. brucei neutral sphingomyelinase demonstrates that it is directly involved in sphingomyelin catabolism. Gene knockout studies in the bloodstream form of the parasite indicate that the neutral sphingomyelinase is essential for growth and survival, thus highlighting that the de novo biosynthesis of ceramide is unable to compensate for the loss of sphingomyelin catabolism. The phenotype of the conditional knockout has given new insights into the highly active endocytic and exocytic pathways in the bloodstream form of T. brucei. Hence, the formation of ceramide in the endoplasmic reticulum affects post-Golgi sorting and rate of deposition of newly synthesized GPI-anchored variant surface glycoprotein on the cell surface. This directly influences the corresponding rate of endocytosis, via the recycling endosomes, of pre-existing cell surface variant surface glycoprotein. The trypanosomes use this coupled endocytic and exocytic mechanism to maintain the cell density of its crucial variant surface glycoprotein protective coat. TbnSMase is therefore genetically validated as a drug target against African trypanosomes, and suggests that interfering with the endocytic transport of variant surface glycoprotein is a highly desirable strategy for drug development against African trypanosomasis.

TcRho1 of Trypanosoma cruzi: role in metacyclogenesis and cellular localization

Here we have investigated the function of TcRho1, a Rho family orthologue from the parasite Trypanosoma cruzi. We have selected parasites overexpressing wild-type TcRho1 and a truncated form of TcRho1 (TcRho1-DeltaCaaX) which is unable to undergo farnesylation and supposed to interfere with recruitment of Rho effectors to membranes. TcRho1 protein was localized at the anterior region of wild-type and TcRho1 overexpressing epimastigotes, suggesting association with the Golgi apparatus. Accordingly, parasites overexpressing TcRho1-DeltaCaaX presented cytoplasmic fluorescence. To address the function of TcRho1 during differentiation, from epimastigotes to trypomastigotes, we submitted parasites overexpressing the above-cited lineages to metacyclogenesis assays. Parasites overexpressing TcRho1-DeltaCaaX generated a discrete number of metacyclic trypomastigotes when compared with other lineages. Strikingly, TcRho1-DeltaCaaX cells died synchronously during the process of metacyclogenesis.

New approaches to the microscopic imaging of Trypanosoma brucei

Protozoan parasites are fearsome pathogens responsible for a substantial proportion of human mortality, morbidity, and economic hardship. The principal disease agents are members of the orders Apicomplexa (Plasmodium, Toxoplasma, Eimeria) and Kinetoplastida (Trypanosomes, Leishmania). The majority of humans are at risk from infection from one or more of these organisms, with profound effects on the economy, social structure and quality of life in endemic areas; Plasmodium itself accounts for over one million deaths per annum, and an estimated 4 x 10(7) disability-adjusted life years (DALYs), whereas the Kinetoplastida are responsible for over 100,000 deaths per annum and 4 x 10(6) DALYs. Current control strategies are failing due to drug resistance and inadequate implementation of existing public health strategies. Trypanosoma brucei, the African Trypanosome, has emerged as a favored model system for the study of basic cell biology in Kinetoplastida, because of several recent technical advances (transfection, inducible expression systems, and RNA interference), and these advantages, together with genome sequencing efforts are widely anticipated to provide new strategies of therapeutic intervention. Here we describe a suite of methods that have been developed for the microscopic analysis of T. brucei at the light and ultrastructural levels, an essential component of analysis of gene function and hence identification of therapeutic targets.

Regulation of endothelial cell differentiation and transformation by H-Ras

Angiogenesis is regulated by growth factors which activate tyrosine kinase receptors leading to the activation of a number of intracellular signaling pathways. The specific function of H-Ras during FGF-2 stimulated endothelial cell differentiation, defined as invasive growth and formation of branching networks in fibrin gels, was investigated by using conditionally immortalized endothelial cell lines induced to express H-Ras mutants. Expression of inhibitory N17Ras did not impair differentiation in response to FGF-2 and TNF-alpha. The farnesyltransferase inhibitor FTI-277 inhibited farnesylation of Ras but did not inhibit differentiation of human microvascular endothelial cells or mouse brain endothelial cells. In contrast, activated V12Ras inhibited endothelial cell differentiation and cells displayed a transformed phenotype with an increased rate of proliferation and loss of contact inhibited growth. Furthermore, V12Ras expressing endothelial cells grew as solid tumors when injected subcutaneously into mice. Our data suggest that, in endothelial cells, H-Ras activity is not required for differentiation. However, this activity must be tightly regulated as aberrant activity can disturb the ability of endothelial cells to undergo differentiation.

The trypanosomiases

The trypanosomiases consist of a group of important animal and human diseases caused by parasitic protozoa of the genus Trypanosoma. In sub-Saharan Africa, the final decade of the 20th century witnessed an alarming resurgence in sleeping sickness (human African trypanosomiasis). In South and Central America, Chagas' disease (American trypanosomiasis) remains one of the most prevalent infectious diseases. Arthropod vectors transmit African and American trypanosomiases, and disease containment through insect control programmes is an achievable goal. Chemotherapy is available for both diseases, but existing drugs are far from ideal. The trypanosomes are some of the earliest diverging members of the Eukaryotae and share several biochemical peculiarities that have stimulated research into new drug targets. However, differences in the ways in which trypanosome species interact with their hosts have frustrated efforts to design drugs effective against both species. Growth in recognition of these neglected diseases might result in progress towards control through increased funding for drug development and vector elimination.

Promising therapeutic targets for antileishmanial drugs

Current treatments for the parasitic disease leishmaniasis are unsatisfactory due to their route of administration, toxicity and expense. Resistance is also developing to first-line antimonial drugs. Fortunately, a handful of antileishmanial agents, such as the orally available compound miltefosine, are currently in clinical trials. In addition, several promising drug targets and lead molecules are being studied with the goal of developing new antileishmanial agents. Drug candidates have been identified through the continued investigation of parasite sterol metabolism and parasite proteases. New antileishmanial molecules have also been discovered through the study of novel targets and pathways, such as the bisphosphonate inhibitors of isoprenoid biosynthesis. This review presents a synopsis of the drug targets and lead compounds that have been investigated over the last few years against leishmaniasis, gives a perspective on the chemotherapeutic potential of each and discusses some of the obstacles to antileishmanial drug development.

A phase II trial of farnesyl protein transferase inhibitor SCH 66336, given by twice-daily oral administration, in patients with metastatic colorectal cancer refractory to 5-fluorouracil and irinotecan

BACKGROUND

ras genes encode Ras proteins that are important for signal transduction in cancer cells. Farnesyl protein transferase (FPTase) is an enzyme that is responsible for a critical post-translational modification of Ras.

PATIENTS AND METHODS

We report the results of a phase II trial of SCH 66336, an FPTase inhibitor, in patients with metastatic colorectal cancer. This is the first reported experience of an FPTase inhibitor in this disease. All patients were considered refractory to first- and second-line therapy. A total of 21 evaluable patients were treated with a starting dose of 200 mg b.i.d. given continuously.

RESULTS

The major side-effects were fatigue (grade 1 in 42%, grade 2 in 42% and grade 3 in 14%), diarrhea (grade 1 in 23% and grade 3 in 42%) and nausea (grade 2 in 16%). Elevations in serum creatinine (grade 2 or 3) were observed in 19% of patients and appeared to be related to dehydration induced by diarrhea. Significant hematological toxicity was not observed (only grade 1 thrombocytopenia in 19% and grade 2 or 3 anemia in 28%). Pharmacological studies revealed adequate mean pre-dose plasma concentrations in this group of patients on day 15 of therapy. No objective responses were observed, although stable disease was seen in three patients for several months. Administration of SCH 66336 was accompanied by gastrointestinal toxicity.

CONCLUSIONS

Future development of this compound cannot be recommended as monotherapy in this disease.

TcRho1, a farnesylated Rho family homologue from Trypanosoma cruzi: cloning, trans-splicing, and prenylation studies

Rho GTPases are members of the Ras superfamily and are involved in signal transduction pathways, including maintenance of cell morphology and motility, cell cycle progression, and transcription activation. We report the molecular identification in trypanosomatids (Trypanosoma cruzi) of the first member of the Rho family. The cloned Rho protein, TcRho1, shares approximately 40% homology with other members of the Rho family. Southern blot analysis revealed that TcRHO1 is a single copy gene per haploid genome, and Northern blot assays showed a transcript of 1200 nucleotides in length. Mapping the 5'-untranslated region of TcRHO1 transcripts revealed at least five different transcripts derived from differential trans-splicing. Three of the five transcripts contain the trans-splicing site within the coding region of the TcRHO1 gene. TcRho1 also contains the C-terminal sequence CQLF (CAAX motif), which is predicted to direct post-translation prenylation of the cysteine residue. A synthetic peptide containing this C-terminal motif, when tested against Q-Sepharose chromatography fractions from T. cruzi cytosol, was shown to be efficiently farnesylated, but not geranylgeranylated, despite the fact that the CAAX motif with X = Phe specifies geranylgeranylation by mammalian protein geranylgeranyltransferase I. Furthermore, immunoblot analyses of epimastigote protein with anti-S-farnesylcysteine methyl ester and anti-TcRho1 antisera strongly suggested that TcRho1 is farnesylated in vivo. The farnesylation of proteins such as Rho GTPases could be the basis for the selective cytotoxic action of protein farnesyltransferase inhibitors on trypanosomatids versus mammalian cells.

New drugs for the treatment of human African trypanosomiasis: research and development

Chemotherapy of human African trypanosomiasis is problematic because of the high frequency of severe adverse events, the long duration and high cost of treatment, and an increasing number of treatment-refractory cases. New cost-efficient, easy-to-use drugs are urgently needed. Whereas basic research on potential drug targets is anchored in academia, the complex, highly regulated and very expensive process of preclinical and clinical drug development is almost exclusively in the hands of pharmaceutical companies. Jennifer Keiser, August Stich and Christian Burri here review, from the angle of industrial drug research and development, the past ten years of research activities at different stages of the development of trypanocidal drugs, and assess future prospects. The absence of compounds in clinical development Phases I-III indicates no new drugs will become available in the next few years.