Thiazomycins, thiazolyl peptide antibiotics from Amycolatopsis fastidiosa.

Thiazolyl peptides are a class of highly rigid trimacrocyclic compounds consisting of varying but large numbers of thiazole rings. The need for new antibacterial agents to treat infections caused by resistant bacteria prompted a reinvestigation of this class, leading to the previous isolation of thiazolyl peptides, namely, thiazomycin (5) and thiazomycin A (6), congeners of nocathiacins (1-4). Continued chemical screening led to the isolation of six new thiazolyl peptide congeners (8-13), of which three had truncated structures lacking an indole residue. From these, compound 8 showed activity similar to thiazomycin. Two compounds (9 and 10) showed intermediate activities, and the three truncated compounds (11-13) were essentially inactive. The discovery of the truncated compounds revealed the minimal structural requirements for activity and suggested probable biosynthetic pathways for more advanced compounds. The isolation, structure elucidation, antibacterial activity, and proposed biogenesis of thiazomycins are herein described.

Isolation, structure, and antibacterial activity of philipimycin, a thiazolyl peptide discovered from Actinoplanes philippinensis MA7347.

Bacterial resistance to antibiotics, particularly to multiple drug resistant antibiotics, is becoming cause for significant concern. The only really viable course of action is to discover new antibiotics with novel mode of actions. Thiazolyl peptides are a class of natural products that are architecturally complex potent antibiotics but generally suffer from poor solubility and pharmaceutical properties. To discover new thiazolyl peptides potentially with better desired properties, we designed a highly specific assay with a pair of thiazomycin sensitive and resistant strains of Staphylococcus aureus, which led to the discovery of philipimycin, a new thiazolyl peptide glycoside. It was isolated along with an acid-catalyzed degradation product by bioassay-guided fractionation. Structure of both compounds was elucidated by extensive application of 2D NMR, 1D TOCSY, and HRESIFT-MS/MS. Both compounds showed strong antibacterial activities against gram-positive bacteria including MRSA and exhibited MIC values ranging from 0.015 to 1 microg/mL. Philipimycin was significantly more potent than the degradation product. Both compounds showed selective inhibition of protein synthesis, indicating that they targeted the ribosome. Philipimycin was effective in vivo in a mouse model of S. aureus infection exhibiting an ED50 value of 8.4 mg/kg. The docking studies of philipimycin suggested that a part of the molecule interacts with the ribosome and another part with Pro23, Pro22, and Pro26 of L11 protein, which helped in explaining the differential of activities between the sensitive and resistant strains. The design and execution of the bioassay, the isolation, structure, in vitro and in vivo antibacterial activity, and docking studies of philipimycin and its degradation product are described.

Isolation, structure, and antibacterial activity of thiazomycin A, a potent thiazolyl peptide antibiotic from Amycolatopsis fastidiosa.

Thiazolyl peptides are a class of thiazole-rich macrocyclic potent antibacterial agents. Recently, we described thiazomycin, a new member of thiazolyl peptides, discovered by a thiazolyl peptide specific chemical screening. This method also allowed for the discovery of a new thiazolyl peptide, thiazomycin A, which carries modification in the oxazolidine ring of the amino sugar moiety. Thiazomycin A is a specific inhibitor of protein synthesis (IC(50) 0.7 microg/mL) and a potent Gram-positive antibacterial agent with minimum inhibitory concentration (MIC) ranging 0.002-0.25 microg/mL. The isolation and structure elucidation and biological activities of thiazomycin A are described.

Control and prevention of MRSA infections.

Methicillin-resistant Staphylococcus aureus (MRSA) has posed an immense problem for clinicians in the hospital setting for years, emerging as the most frequent nosocomial infection. To deal with this problem pathogen and others, infectious disease specialists have developed a variety of procedures for their control and prevention, involving options from preventative measures such as decolonization and isolation of MRSA-confirmed patients, to the more simple procedures of hand washing, expanding glove use, and reducing time in the hospital. With the realization that MRSA is now a community problem, there are expanded efforts toward more direct intervention, such as the use of anti-MRSA antibacterials and vaccines, in an attempt to reduce the overall burden of MRSA.

Antibacterial evaluations of thiazomycin- a potent thiazolyl peptide antibiotic from Amycolatopsis fastidiosa.

Thiazomycin is a novel thiazolyl peptide closely related to nocathiacin I. It was isolated from Amycolatopsis fastidiosa by chemical and biological screening. Thiazomycin showed highly potent bactericidal activity against Gram-positive pathogens (MIC range 0.002 approximately 0.064 microg/ml) and did not show cross-resistance to clinically relevant antibiotic classes such as beta-lactams, vancomycin, oxazolidinone and quinolones. It was highly efficacious against Staphylococcus aureus infection in mice exhibiting an ED(99) value of 0.15 mg/kg by subcutaneous administration. It inhibited bacterial growth by selective inhibition of protein synthesis and it was thought to interact with L11 protein and 23S rRNA of the 50S ribosome. Structurally, it possesses an oxazolidine ring in the amino-sugar residue that provides further opportunities for selective chemical modifications that are not feasible with other thiazolyl peptides. More importantly such a modification can potentially lead to semi-synthetic compounds that overcome problems that have hampered clinical development of this class of compounds. Despite its positive attributes, emergence of an unacceptable frequency of resistance poses significant challenges for further development of thiazomycin and this class of molecules for therapeutic use.

Isolation and structure elucidation of thiazomycin- a potent thiazolyl peptide antibiotic from Amycolatopsis fastidiosa.

Thiazolyl peptides are a class of rigid macrocyclic compounds richly populated with thiazole rings. They are highly potent antibiotics but none have been advanced to clinic due to poor aqueous solubility. Recent progress in this field prompted a reinvestigation leading to the isolation of a new thiazolyl peptide, thiazomycin, a congener of nocathiacins. Thiazomycin possesses an oxazolidine ring as part of the amino-sugar moiety in contrast to the dimethyl amino group present in nocathiacin I. The presence of the oxazolidine ring provides additional opportunities for chemical modifications that are not possible with other nocathiacins. Thiazomycin is extremely potent against Gram-positive bacteria both in vitro and in vivo. The titer of thiazomycin in the fermentation broth was very low compared to the nocathiacins I and III. The lower titer together with its sandwiched order of elution presented significant challenges in large scale purification of thiazomycin. This problem was resolved by the development of an innovative preferential protonation based one- and/or two-step chromatographic method, which was used for pilot plant scale purifications of thiazomycin. The isolation and structure elucidation of thiazomycin is herein described.

Can biotech deliver new antibiotics?

The evolution of support for the discovery and development of antibacterial (or antibiotic) agents from the larger pharmaceutical companies to the entrepreneur-like small biotechnology companies has been an experiment in the making for the past 15 years. The word 'experiment' is precisely chosen as the outcome is not certain. Many of the antibiotic biotech organizations that were most likely to undertake the task of picking up where large pharmaceutical companies left off have failed to survive, despite their use of outstanding science and their novel approaches to the development of discovery platforms. So this leaves one with the question of 'can biotech deliver the new antibiotics?'.

Empirical antibacterial drug discovery--foundation in natural products.

Natural products have been a rich source in providing leads for the development of drugs for the treatment of bacterial infections. However, beyond the discovery of the natural product, thienamycin and the synthetic lead, oxazolidinone in the 1970s, there has been a dearth of new compounds. This commentary provides an overview of current antibiotic leads and their mechanism of action, and highlights tools that can be applied to the discovery of new antibiotics.

Antibacterial drug discovery--then, now and the genomics future.

Drug discovery research in the area of infectious diseases, in particular that dealing with antibacterial/antibiotic susceptibility and resistance, is in a process of continuing evolution. Steeped in the history of the highly successful intervention with chemotherapeutic agents to treat human infections, the emergence of drug-resistant pathogens worldwide presents a serious unmet medical need, if not a pending catastrophe. Research in both academia and industry over the past 30 years using molecular biology, genetics and more recently--bacterial genomics--has assembled key enabling technologies to increase productivity and success rates in the discovery and development of novel antibacterial agents. However genomics is not limited only to antibacterial target selection but provides the opportunity to further understand key interactions in the use of antibacterial compounds as therapeutic agents (such as resistance emergence, susceptibility, efflux, interactions between compound and pathogen, etc.). Genomics also offers the potential for insights into: bacterial niche adaptation, host susceptibility, treatment regimens, antibiotic resistance, pharmacokinetics (e.g., host metabolism differences), safety and the microbial genesis of chronic diseases (e.g., gastric ulceration).

Antibiotics: where did we go wrong?

In the late 1960s, the medical need for new antibiotics began to be questioned, and the pharmaceutical industry shifted its emphasis of antibacterials from that of a therapeutic leader to a low-priority research area. Although infectious diseases, in particular those caused by bacterial infections, are still among the top causes of mortality in the world, industrial support continues to wane. The shift from this important area of antimicrobial research has been attributed to a combination of science, medical, marketing and business reasons. This decline in antibacterial drug discovery, coupled with increasing risk as a result of infections caused by drug-resistant bacterial pathogens, represents a clear public health threat.

Recent developments in glycopeptide antibacterials.

The glycopeptide class of antibiotics, namely vancomycin and teicoplanin, are intravenously administered in the hospital setting for the treatment of the most severe of Gram-positive infections. Although a mainstay of the hospital formulary for over four decades, the rise of increasingly frequent high-level vancomycin resistance in enterococci and low-level resistance in staphylococci (as well as a few high-level vancomycin resistance cases) has highlighted the need for the identification of naturally occurring and semi-synthetically modified glycopeptide derivatives that have antibacterial activity against these resistant strains. Among the leading development candidates are dalbavancin, oritavancin, telavancin and ramoplanin, each of which provides a unique microbiological and pharmacological profile to fill an important unmet medical need.

Stimulation of Myc transactivation by the TATA binding protein in promoter-reporter assays.

BACKGROUND: The c-Myc oncogenic transcription factor heterodimerizes with Max, binds specific DNA sites and regulates transcription. The role of Myc in transcriptional activation involves its binding to TRRAP and histone acetylases; however, Myc's ability to activate transcription in transient transfection assays is remarkably weak (2 to 5 fold) when compared to other transcription factors. Since a deletion Myc mutant D106-143 and a substitution mutant W135E that weakly binds TRRAP are still fully active in transient transfection reporter assays and the TATA binding protein (TBP) has been reported to directly bind Myc, we sought to determine the effect of TBP on Myc transactivation. RESULTS: We report here a potent stimulation of Myc transactivation by TBP, allowing up to 35-fold transactivation of reporter constructs. Although promoters with an initiator (InR) element briskly responded to Myc transactivation, the presence of an InR significantly diminished the response to increasing amounts of TBP. We surmise from these findings that promoters containing both TATA and InR elements may control Myc responsive genes that require brisk increased expression within a narrow window of Myc levels, independent of TBP. In contrast, promoters driven by the TATA element only, may also respond to modulation of TBP activity or levels. CONCLUSION: Our observations not only demonstrate that TBP is limiting for Myc transactivation in transient transfection experiments, but they also suggest that the inclusion of TBP in Myc transactivation assays may further improve the characterization of c-Myc target genes.

Antibacterials: are the new entries enough to deal with the emerging resistance problems?

Fifty years of making analogs based on less than ten antibacterial scaffolds has resulted in the development and marketing of over 100 antibacterial agents but, with the exception of the oxazolidinone core, no new scaffolds have emerged in the past 30 years to address emerging resistance problems. As the support for antibacterial research shifts away from large pharmaceutical companies, a wave of biotechnology companies have pursued a diverse choice of targets resulting in several novel classes of agent in late-stage development. Although critical for certain resistance niche needs, these agents are unlikely to provide the solution to the requirement for a major novel scaffold class of antibacterials.

Microbial genomics and novel antibiotic discovery: new technology to search for new drugs.

The process of prokaryotic drug discovery has been a model of success for over fifty years, yet the number of exploited bacterial targets is a mere fraction, less than 0.1% of the potential targets (based on total number of bacterial genes identified by gene sequence projects). To better understand the potential for drug intervention, multiple paradigms have been established in the pharmaceutical industry, all with some semblance of commonality and uniqueness to provide proprietary positioning, yet no company has been successful to date in taking a genomics approach to the finish line of having a genomics-based drug on the market. Within this overview, we provide a strategic overview of a sample process for the identification, validation and exploitation of novel antibacterial targets ascertained through a bioinformatics-based genomics drug discovery program.

Antibiotics and pharmacogenomics.

The widespread use of antibiotics impacts both the bacterial ecology and the host at multiple levels, both advantageously and deleteriously. Since serious bacterial infection can lead to death in the absence of antibiotic therapy, antibiotics remain a necessary weapon in the clinician's arsenal for maintaining good health. It is thus critical that the placement and usage of these crucial antibiotics be constantly improved, and that emerging antibiotic resistance is vigorously assessed. To realize both these ends, it may be valuable to turn to the discipline of pharmacogenomics and develop it for use in a fairly novel way, that is, as the means by which to determine and analyze the impact of antibiotic therapy on both the pathogen and host.

Antibacterial drug discovery & development summit.

Over 100 senior researchers and managers from academic and industrial research organisations attended this 2-day annual international discovery summit on antibacterial R&D. A number of firms, particularly biotechnology firms, presented compounds that are advancing through clinical development. In addition, areas for basic research and development included metallo-beta-lactamases, ribosomal structural studies and phage-selected targets were described.

What are we looking for in new antibacterials and how do we design it?

The need for new antibacterial agents is a pressing, unmet medical need, but success has been limited, resulting in decreased business interest. Part of the problem is the lack of clarity regarding what would make a new-generation 'blockbuster' antibacterial and how this agent could be designed. To this end, the authors outline a few ideas regarding the changes in approach in order to accomplish these needs, including a fundamental change in the drug discovery process.

Pharmacoeconomics of treatment with the newer anti-Gram-positive agents.

The unmet medical need of emerging resistance among Gram-positive pathogens, such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and penicillin-resistant Streptococcus pneumoniae, has driven industry towards the identification and development of novel anti-Gram-positive agents. Among the newer agents are improved quinolones, a lipopeptide, an oxazolidinone and novel glycopeptides. Scientific distinctions between these drugs, which impact on the placement, usage and, ultimately, the pharmacoeconomics of several of these new agents, may lead to further consideration despite poor initial observations of minimal improvement. Key differences in the characteristics of these drugs (i.e., spectrum, activity, resistance emergence, efficacy, target, safety) provide a basis for an emerging pharmacoeconomic-based distinction between these newer anti-Gram-positive agents.