Antimycobacterial activities of oxazolidinones: a review

Population pharmacokinetic analysis of linezolid in patients with different types of shock: Effect of platelet count

Linezolid was approved by the Food and Drug Administration for the treatment of serious infections. However, patients with serious frequently develop shock, and it is currently elusive whether shock affects the pharmacokinetics of linezolid. The aim of the present study was to explore whether the pharmacokinetics of linezolid are different among patients with various types of shock or patients without shock and whether potential confounders are involved in their outcomes. A population pharmacokinetic analysis using a non-linear mixed-effects model was performed to examine the pharmacokinetics of patients with different types of shock or patients without shock. The pharmacokinetics of linezolid in patients with different types of shock or patients without shock was described by a one-compartment model. In our results, the patients with different types of shock or patients without shock demonstrated no differences in pharmacokinetics, whereas the platelet count was identified as a significant influencing factor. The results demonstrated that the pharmacokinetics of linezolid exhibited no significant differences among patients with different types of shock or patients without shock, whereas the platelet count significantly affected the clearance rate of linezolid.

Identification of New Molecular Entities (NMEs) as Potential Leads against Tuberculosis from Open Source Compound Repository

The purpose of this study was to provide a number of diverse and promising early-lead compounds that will feed into the drug discovery pipeline for developing new antitubercular agents. The results from the phenotypic screening of the open-source compound library against Mycobacterium smegmatis and Mycobacterium bovis (BCG) with hit validation against M. tuberculosis (H37Rv) have identified novel potent hit compounds. To determine their druglikeness, a systematic analysis of physicochemical properties of the hit compounds has been performed using cheminformatics tools. The hit molecules were analysed by clustering based on their chemical finger prints and structural similarity determining their chemical diversity. The hit compound library is also filtered for druglikeness based on the physicochemical descriptors following Lipinski filters. The robust filtration of hits followed by secondary screening against BCG, H37Rv and cytotoxicity evaluation has identified 12 compounds with potential against H37Rv (MIC range 0.4 to 12.5 μM). Furthermore in cytotoxicity assays, 12 compounds displayed low cytotoxicity against liver and lung cells providing high therapeutic index > 50. To avoid any variations in activity due to the route of chemical synthesis, the hit compounds were re synthesized independently and confirmed for their potential against H37Rv. Taken together, the hits reported here provides copious potential starting points for generation of new leads eventually adds to drug discovery pipeline against tuberculosis.

Linezolid in the treatment of extensively drug-resistant tuberculosis

PURPOSE

To investigate the linezolid (LZD) treatment outcome and correlation between in vitro susceptibility to LZD and clinical outcome.

METHODS

We retrospectively reviewed records of tuberculosis (TB) patients who received treatment with linezolid between March 2012 and February 2013.

RESULTS

A total of 43 extensively drug-resistant (XDR) TB patients identified by drug susceptibility testing were enrolled in this study, including 15 (34.9 %) received LZD as part of individualized treatment regimens. Among the 43 XDR TB patients, 15 patients (34.9 %) obtained favorable clinical outcome, including 9 (60.0 %) from LZD group and 6 (21.4 %) from control group without LZD. Statistical analysis revealed that the percentage of favorable outcomes of LZD group was significantly higher than that of control group (P = 0.011). Furthermore, we analyzed the LZD minimum inhibitory concentrations of Mycobacterium tuberculosis (MTB) isolates from patients in LZD group and identified 4 (26.7 %) resistant to LZD. All of the patients with LZD resistance harbored adverse clinical outcome, while most of the patients infected with LZD sensitive MTB harbored favorable clinical outcome (81.8 %, 9/11). Statistical analysis revealed that the percentage of favorable outcome among the patients with LZD resistance was statistically lower than that among the LZD susceptible group (P = 0.011).

CONCLUSION

This study demonstrates that linezolid has efficacy against XDR pulmonary TB patients, even in shorter duration of administration. The XDR TB patients infected with LZD-resistant isolates were more likely to obtain the adverse clinical outcome under the treatment of regimen containing LZD.

Mitochondrial cardiolipin is required for Nlrp3 inflammasome activation

Nlrp3 inflammasome activation occurs in response to numerous agonists but the specific mechanism by which this takes place remains unclear. All previously evaluated activators of the Nlrp3 inflammasome induce the generation of mitochondrial reactive oxygen species (ROS), suggesting a model in which ROS is a required upstream mediator of Nlrp3 inflammasome activation. Here we have identified the oxazolidinone antibiotic linezolid as a Nlrp3 agonist that activates the Nlrp3 inflammasome independently of ROS. The pathways for ROS-dependent and ROS-independent Nlrp3 activation converged upon mitochondrial dysfunction and specifically the mitochondrial lipid cardiolipin. Cardiolipin bound to Nlrp3 directly and interference with cardiolipin synthesis specifically inhibited Nlrp3 inflammasome activation. Together these data suggest that mitochondria play a critical role in the activation of the Nlrp3 inflammasome through the direct binding of Nlrp3 to cardiolipin.

Genome-wide expression profiling of the response to linezolid in Mycobacterium tuberculosis

Tuberculosis (TB) is still one of the most common causes of death in the world. The emergence of multidrug-resistant and extensively drug-resistant (XDR-TB) Mycobacterium tuberculosis (M. tuberculosis) strains has increased the importance of searching for alternative targets to develop new antimycobacterial drugs. Linezolid, the first of oxazolidinones, is active in vitro against M. tuberculosis, but the response mechanisms of M. tuberculosis to linezolid are still poorly understood. To reveal the possible mechanism of action of linezolid against M. tuberculosis, commercial oligonucleotide microarrays were used to analyze the genome-wide transcriptional changes triggered by treatment with subinhibitory concentrations of linezolid. Quantitative real-time RT-PCR was performed for selected genes to verify the microarray results. A total of 729 genes were found to be differentially regulated by linezolid. Among these, 318 genes were upregulated, and 411 genes were downregulated. A number of important genes were significantly regulated that are involved in various pathways, such as protein synthesis, sulfite metabolism, and genes involved in the cell envelope and virulence. This genome-wide transcriptomics approach produced the first insights into the response of M. tuberculosis to a linezolid challenge.

Lessons from seven decades of antituberculosis drug discovery

Despite massive global efforts tuberculosis rates continue to climb and drug-resistance rates are rising to alarming levels. Discovering new agents for treating this bacterial pathogen poses unique challenges, but these challenges have been faced throughout the entire modern history of research into anti-infectives. This review looks back at every decade since the 1940s and summarizes the most important drugs developed during each decade highlighting the lessons learned during these successful medicinal chemistry programs. Looking forward we must accelerate the integration of these past lessons with the impressive advances that have been made in the basic understanding of the biology of this disease.

Clinical Experience with Linezolid at a Large Academic Medical Center: A Case Series and Review of the Literature

Purpose

The objectives of this study were to evaluate current patterns of use, microbiologic cure rates, and hematologic toxicities, including identification of risk factors, associated with linezolid utilization at our institution.

Methods

Utilization, clinical, microbiological, and toxicity data were collected prospectively over an 8-month period (August 1, 2006 to March 31, 2007). Binary logistic and multivariate stepwise regression analyses were performed to identify potential risk factors for linezolid-associated thrombocytopenia and anemia.

Results

A total of 116 linezolid courses (102 patients) were identified with a mean duration of therapy of 12.3 days. Appropriate infectious disease service approval and consults were found in 87.9% and 62.1% of the cases, respectively. Bloodstream, urinary tract, and respiratory tract infections accounted for 29%, 21%, and 16% of clinical indications, respectively. Vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and coagulase-negative staphylococci accounted for 43%, 24%, and 7% of clinical isolates, respectively. Overall, the microbiologic cure rate among evaluable patients was 83.8%. Development of thrombocytopenia was found in approximately 30% of linezolid-treated patients. Risk factors for linezolid-associated thrombocytopenia included female gender (OR 5.66, P = .002), serum creatinine (SCr) ≥ 2 mg/dL (OR 4.48, P = .009), intensive care unit admission (OR 3.06, P = .038), and duration of therapy ≥ 28 days (OR 3.76, P = .049).

Conclusion

Utilization patterns may suggest strategies for conserving linezolid, including improved compliance with current approval policies and clinical pathway development. Linezolid microbiological cure rates were similar to those found in the primary literature. Linezolid-associated thrombocytopenia was common and risk factors were identified. Further well-designed prospective studies are needed to confirm these findings. Hosp Pharm-2010;45(12):916-926

New drugs and regimens for treatment of TB

Tools for effective TB control have been available for years. Case finding, active medications, case management and directly observed therapy are the foundations for the management of TB. The current TB epidemic, centered in resource-limited settings is fueled by the HIV-1 epidemic. Lack of ability to diagnose and treat drug-resistant TB has led to development of more extensive patterns of resistance. Among the currently available drugs, there is reason to hope that rifamycins paired with fluoroquinolones will lead to shorter treatment regimens for drug-susceptible TB. As the result of novel public-private collaborations and investments of resources, new drugs are being developed. These include TMC207, already shown to have activity early in the treatment of multidrug-resistant TB and others that are likely to be active against persistor organisms, and have the prospect to dramatically shorten treatment courses for active and latent TB. Given that these drugs have novel mechanisms of action, combinations have the prospect to be highly active even against multidrug-resistant organisms.

Linezolid Resistance in Staphylococci

Linezolid, the first oxazolidinone to be used clinically, is effective in the treatment of infections caused by various Gram-positive pathogens, including multidrug resistant enterococci and methicillin-resistant Staphylococus aureus. It has been used successfully for the treatment of patients with endocarditis and bacteraemia, osteomyelitis, joint infections and tuberculosis and it is often used for treatment of complicated infections when other therapies have failed.

Linezolid resistance in Gram-positive cocci has been encountered clinically as well as in vitro, but it is still a rare phenomenon. The resistance to this antibiotic has been, until now, entirely associated with distinct nucleotide substitutions in domain V of the 23S rRNA genes. The number of mutated rRNA genes depends on the dose and duration of linezolid exposure and has been shown to influence the level of linezolid resistance. Mutations in associated ribosomal proteins also affect linezolid activity. A new phenicol and clindamycin resistance phenotype has recently been found to be caused by an RNA methyltransferase designated Cfr. This gene confers resistance to lincosamides, oxazolidinones, streptogramin A, phenicols and pleuromutilins, decrease the susceptibility of S. aureus to tylosin, to josamycin and spiramycin and thus differs from erm rRNA methylase genes.

Research into new oxazolidinones with improved characteristics is ongoing. Data reported in patent applications demonstrated that some oxazolidinone derivatives, also with improved characteristics with respect to linezolid, are presently under study: at least three of them are in an advanced phase of development.

The chemical biology of new drugs in the development for tuberculosis

With the worldwide emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis (Mtb), there are serious concerns about the continued ability to contain this disease. We discuss the most promising new drugs in late-stage development that might be useful in treating MDR and XDR forms of the disease. These agents have novel mechanisms of action that are not targeted by the standard drugs used presently to treat susceptible strains.

Toward an optimized therapy for tuberculosis? Drugs in clinical trials and in preclinical development

Tuberculosis (TB) continues to be one of the greatest challenges in the global public health arena. Current therapeutic agents against TB are old and inadequate, particularly in the face of many new challenges. Multidrug-resistant TB (MDR-TB) has become prevalent in many parts of the world and extensively drug-resistant TB (XDR-TB) is rapidly emerging. There are few or essentially no effective drugs available to treat these drug-resistant forms of TB. TB and human immunodeficiency virus (HIV) coinfection has become another major problem in areas with high prevalence of HIV infection. Simultaneous treatment of TB and HIV is difficult due to the severe drug-drug interactions between the first-line rifamycin-containing TB therapy and antiretroviral agents. However, there have been some encouraging developments in TB drug research and development within the past decade. At present there are 6 compounds, including 3 novel agents, in late stages of clinical development. There are even larger numbers of compounds and projects in the TB drug pipeline at the discovery stage and in early stages of clinical development, mainly targeting treatment shortening and drug resistance. Despite these encouraging developments, the current TB drug pipeline is not sufficient to address the multitude of challenges inherent in the current standard of TB therapy. A stronger TB drug pipeline and a new paradigm for the development of novel TB drug combinations are needed.

Population pharmacokinetics of linezolid in adults with pulmonary tuberculosis

Nineteen adults with pulmonary tuberculosis received linezolid (600 mg) once or twice daily in an early bactericidal activity trial. A one-compartment population model produced median values for the absorption rate constant, volume of distribution, and elimination rate constant of 1.5 h(-1), 29.6 liters, and 0.25 h(-1) (once daily) and 2.7 h(-1), 32.1 liters, and 0.15 h(-1) (twice daily). Linezolid administered twice daily produced higher values for free drug area under the concentration-time curve (AUC)/MIC and time above MIC. Both regimens achieved free AUC/MIC ratios > 100. Median times above the MIC for free drug were 100% (twice daily) and 63% (once daily).

Managing TB in the 21st century: existing and novel drug therapies

With an estimated one-third of the world's population infected with Mycobacterium tuberculosis (MTB) and approximately 1.6 million deaths in 2006 attributed to tuberculosis (TB) world-wide, TB remains a major public health concern today. Considerable advances have been made in the effective treatment of TB, in particular with the adoption of directly observed therapy short course (DOTS), in national TB control programs, but in spite of this the currently available regimens are suboptimal. The long courses of therapy required, together with significant medication side-effects and resulting difficulties with adherence to therapy all contribute to increasing problems with emerging drug resistance. There is thus an urgent need for new antituberculous drug development, especially to enable effective shorter course therapy for drug-susceptible and resistant TB, to find effective drugs for treatment of drug-resistant TB, to shorten therapy for latent TB infection and to reduce drug interactions in combination with antiretroviral therapy, a major issue in the treatment of HIV co-infected patients. This review will attempt to summarize the current recommendations for treatment of TB and then describe the most promising new antimicrobials with activity against MTB, focusing on the ones currently undergoing clinical trials.

Early and extended early bactericidal activity of linezolid in pulmonary tuberculosis

RATIONALE

Linezolid, the first oxazolidinone approved for clinical use, has effective in vitro and promising in vivo activity against Mycobacterium tuberculosis.

OBJECTIVES

To evaluate the early and extended early bactericidal activity of linezolid in patients with pulmonary tuberculosis.

METHODS

Randomized open label trial. Thirty patients with newly diagnosed smear-positive pulmonary tuberculosis (10 per arm) were assigned to receive isoniazid (300 mg daily) and linezolid (600 mg twice daily or 600 mg once daily) for 7 days. Sputum for quantitative culture was collected for 2 days before and then daily during 7 days of study drug administration. Bactericidal activity was estimated by measuring the decline in bacilli during the first 2 days (early bactericidal activity) and the last 5 days of study drug administration (extended early bactericidal activity).

MEASUREMENTS AND MAIN RESULTS

The mean early bactericidal activity of isoniazid (0.67 log10 cfu/ml/d) was greater than that of linezolid twice and once daily (0.26 and 0.18 log10 cfu/ml/d, respectively). The extended early bactericidal activity of linezolid between Days 2 and 7 was minimal.

CONCLUSIONS

Linezolid has modest early bactericidal activity against rapidly dividing tubercle bacilli in patients with cavitary pulmonary tuberculosis during the first 2 days of administration, but little extended early bactericidal activity. Clinical trial registered with www.clinicaltrials.gov (NCT00396084).

Synthesis, optimization and structure-activity relationships of 3,5-disubstituted isoxazolines as new anti-tuberculosis agents

In the course of the development of a potent series of nitrofuranylamide anti-tuberculosis agents, we investigated if the exceptional activity resulted in part from the isoxazoline core and if it possessed any intrinsic anti-tuberculosis activity. This led to the discovery of an isoxazoline ester with appreciable anti-tuberculosis activity. In this study we explored the anti-tuberculosis structure-activity relationship of the isoxazoline ester compound through systematic modification of the 3,5-di-substituted isoxazoline core. Two approaches were used: (i) modification of the potentially metabolically labile ester functionality at the 3 position with acids, amines, amides, reverse amides, alcohols, hydrazides, and 1,3,4-oxadiazoles; (ii) substitution of the distal benzyl piperazine ring in the 5 position of the isoxazoline ring with piperazyl-ureas, piperazyl-carbamates, biaryl systems, piperidines and morpholine. Attempts to replace the ester group at C-3 position of isoxazoline with a variety of bioisosteric head groups led to significant loss of the tuberculosis inhibition indicating that an ester is required for anti-tuberculosis activity. Optimization of the isoxazoline C-5 position produced compounds with improved anti-tuberculosis activity, most notably the piperazyl-urea and piperazyl-carbamate analogs.

New oxazolidinones

Due to the emergence of resistance to known antibiotics to various organisms, for example, Staphylococcus, Streptococcus, Enterococci, and Pseudomonas there is a renewed interest in the discovery of new antibacterials. Oxazolidinones, totally synthetic class of novel antibacterials, possess activity against drug-resistant Gram-positive pathogens, especially MRSA. Linezolid, the first approved drug from this class, has shown a great promise in saving lives of many patients by acting against drug-resistant Gram-positive organisms. However, its use is somewhat limited because of its myelotoxicity when used long term (>21 days). Various research groups are active in this area either to improve myelotoxicity profile of linezolid or to expand the spectrum of activity of linezolid. In spite of active research in this area, the discovery of an oxazolidinone possessing improved myelotoxicity compared to linezolid, linezolid-like efficacy, and PK remains challenging.

Synthesis and antibacterial activity of potent heterocyclic oxazolidinones and the identification of RBx 8700

Several potent oxazolidinone antibacterial agents were obtained by systematic modification of the linker between the five-membered heterocycle and the piperazinyl ring of RBx 7644 (Ranbezolid, 1) and its thienyl analogue 2, leading to the identification of an expanded spectrum compound RBx 8700 (6b).

Discovery of novel isoxazolines as anti-tuberculosis agents

Nitrofuranyl isoxazolines with increased proteolytic stability over nitrofuranyl amides were designed and synthesized leading to discovery of several compounds with potent in vitro anti-tuberculosis activity. However, their in vivo activity was limited by high protein binding and poor distribution. Consequently, a series of non-nitrofuran containing isoxazolines were prepared to determine if the core had residual anti-tuberculosis activity. This led to the discovery of novel isoxazoline 12 as anti-tuberculosis agent with a MIC(90) value of 1.56microg/mL.

Synthesis and antibacterial activity of novel oxazolidinones with methylene oxygen- and methylene sulfur-linked substituents at C5-position

Novel oxazolidinone derivatives of the lead compound RBx 8700, containing methylene oxygen- and methylene sulfur-linked substituents at the C5-position, were synthesized. Antibacterial screening of these compounds against a panel of resistant and susceptible Gram-positive and fastidious Gram-negative bacteria gave compounds 2 and 4 as new antibacterial agents.