Pharmacokinetic-Pharmacodynamic Evidence from a Phase 3 Trial to Support Flat-Dosing of Rifampicin for Tuberculosis

BACKGROUND

The optimal dosing strategy for rifampicin in treating drug-susceptible tuberculosis (TB) is still highly debated. In the Phase 3 clinical trial Study 31/ACTG 5349 (NCT02410772), all participants in the control regimen arm received 600 mg rifampicin daily as a flat dose. Here, we evaluated relationships between rifampicin exposure and efficacy and safety outcomes.

METHODS

We analyzed rifampicin concentration time profiles using population nonlinear mixed-effects models. We compared simulated rifampicin exposure from flat- and weight-banded dosing. We evaluated the effect of rifampicin exposure on stable culture conversion at 6 months, TB-related unfavorable outcomes at 9, 12, and 18 months using Cox proportional hazard models, and all trial-defined safety outcomes using logistic regression.

RESULTS

Our model derived rifampicin exposure ranged from 4.57 mg·h/L to 140.0 mg·h/L with a median of 41.8 mg·h/L. Pharmacokinetic simulations demonstrated that flat-dosed rifampicin provided exposure coverage similar to weight-banded dose. Exposure-efficacy analysis (N=680) showed that participants with rifampicin exposure below the median experienced similar hazards of stable culture conversion and TB-related unfavorable outcomes compared to those with exposure above the median. Exposure-safety analysis (N=722) showed that increased rifampicin exposure was not associated with increased grade 3 or higher adverse events, or serious adverse events.

CONCLUSIONS

Flat-dosing of rifampicin at 600 mg daily may be a reasonable alternative to the incumbent weight-banded dosing strategy for the standard of care 6-month regimen. Future research should assess the optimal dosing strategy for rifampicin, at doses higher than the current recommendation.

Inhibition of Pseudomonas aeruginosa Alginate Synthesis by Ebselen Oxide and Its Analogues

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that is frequently found in the airways of cystic fibrosis (CF) patients due to the dehydrated mucus that collapses the underlying cilia and prevents mucociliary clearance. During this life-long chronic infection, P. aeruginosa cell accumulates mutations that lead to inactivation of the mucA gene that results in the constitutive expression of algD-algA operon and the production of alginate exopolysaccharide. The viscous alginate polysaccharide further occludes the airways of CF patients and serves as a protective matrix to shield P. aeruginosa from host immune cells and antibiotic therapy. Development of inhibitors of alginate production by P. aeruginosa would reduce the negative impact from this viscous polysaccharide. In addition to transcriptional regulation, alginate biosynthesis requires allosteric activation by bis (3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) binding to an Alg44 protein. Previously, we found that ebselen (Eb) and ebselen oxide (EbO) inhibited diguanylate cyclase from synthesizing c-di-GMP. In this study, we show that EbO, Eb, ebsulfur (EbS), and their analogues inhibit alginate production. Eb and EbS can covalently modify the cysteine 98 (C98) residue of Alg44 and prevent its ability to bind c-di-GMP. However, P. aeruginosa with Alg44 C98 substituted with alanine or serine was still inhibited for alginate production by Eb and EbS. Our results indicate that EbO, Eb, and EbS are lead compounds for reducing alginate production by P. aeruginosa. Future development of these inhibitors could provide a potential treatment for CF patients infected with mucoid P. aeruginosa.

The Effects of Prodrug Size and a Carbonyl Linker on l-Type Amino Acid Transporter 1-Targeted Cellular and Brain Uptake

The l-type amino acid transporter 1 (LAT1, SLC7A5) imports dietary amino acids and amino acid drugs (e. g., l-DOPA) into the brain, and plays a role in cancer metabolism. Though there have been numerous reports of LAT1-targeted amino acid-drug conjugates (prodrugs), identifying the structural determinants to enhance substrate activity has been challenging. In this work, we investigated the position and orientation of a carbonyl group in linking hydrophobic moieties including the anti-inflammatory drug ketoprofen to l-tyrosine and l-phenylalanine. We found that esters of meta-carboxyl l-phenylalanine had better LAT1 transport rates than the corresponding acylated l-tyrosine analogues. However, as the size of the hydrophobic moiety increased, we observed a decrease in LAT1 transport rate with a concomitant increase in potency of inhibition. Our results have important implications for designing amino acid prodrugs that target LAT1 at the blood-brain barrier or on cancer cells.

Deorphaning a solute carrier 22 family member, SLC22A15, through functional genomic studies

The human solute carrier 22A (SLC22A) family consists of 23 members, representing one of the largest families in the human SLC superfamily. Despite their pharmacological and physiological importance in the absorption and disposition of a range of solutes, eight SLC22A family members remain classified as orphans. In this study, we used a multifaceted approach to identify ligands of orphan SLC22A15. Ligands of SLC22A15 were proposed based on phylogenetic analysis and comparative modeling. The putative ligands were then confirmed by metabolomic screening and uptake assays in SLC22A15 transfected HEK293 cells. Metabolomic studies and transporter assays revealed that SLC22A15 prefers zwitterionic compounds over cations and anions. We identified eight zwitterions, including ergothioneine, carnitine, carnosine, gabapentin, as well as four cations, including MPP⁺ , thiamine, and cimetidine, as substrates of SLC22A15. Carnosine was a specific substrate of SLC22A15 among the transporters in the SLC22A family. SLC22A15 transport of several substrates was sodium-dependent and exhibited a higher Km for ergothioneine, carnitine, and carnosine compared to previously identified transporters for these ligands. This is the first study to characterize the function of SLC22A15. Our studies demonstrate that SLC22A15 may play an important role in determining the systemic and tissue levels of ergothioneine, carnosine, and other zwitterions.

Drug Metabolites Potently Inhibit Renal Organic Anion Transporters, OAT1 and OAT3

Human OAT1 and OAT3 play major roles in renal drug elimination and drug-drug interactions. However, there is little information on the interactions of drug metabolites with transporters. The goal of this study was to characterize the interactions of drug metabolites with OAT1 and OAT3 and compare their potencies of inhibition with those of their corresponding parent drugs. Using HEK293 cells stably transfected with OAT1 and OAT3, 25 drug metabolites and their corresponding parent drugs were screened for inhibitory effects on OAT1-and OAT3-mediated 6-carboxyfluorescein uptake at a screening concentration of 200 μM for all but 3 compounds. 20 and 24 drug metabolites were identified as inhibitors (inhibition > 50%) of OAT1 and OAT3, respectively. Seven drug metabolites were potent inhibitors of either or both OAT1 and OAT3 with K_i values less than 1 μM. 22 metabolites were more potent inhibitors of OAT3 than OAT1. Importantly, one drug and four metabolites were predicted to inhibit OAT3 at unbound plasma concentrations achieved clinically (C_max,u/K_i values ≥ 0.1). In conclusion, our study highlights the potential interactions of drug metabolites with OAT1 and OAT3 at clinically relevant concentrations, suggesting that drug metabolites may modulate therapeutic and adverse drug response by inhibiting renal drug transporters.

Structure-Guided Optimization of Inhibitors of Acetyltransferase Eis from Mycobacterium tuberculosis

The enhanced intracellular survival (Eis) protein of Mycobacterium tuberculosis (Mtb) is a versatile acetyltransferase that multiacetylates aminoglycoside antibiotics abolishing their binding to the bacterial ribosome. When overexpressed as a result of promoter mutations, Eis causes drug resistance. In an attempt to overcome the Eis-mediated kanamycin resistance of Mtb, we designed and optimized structurally unique thieno[2,3-d]pyrimidine Eis inhibitors toward effective kanamycin adjuvant combination therapy. We obtained 12 crystal structures of enzyme-inhibitor complexes, which guided our rational structure-based design of 72 thieno[2,3-d]pyrimidine analogues divided into three families. We evaluated the potency of these inhibitors in vitro as well as their ability to restore the activity of kanamycin in a resistant strain of Mtb, in which Eis was upregulated. Furthermore, we evaluated the metabolic stability of 11 compounds in vitro. This study showcases how structural information can guide Eis inhibitor design.

Interactions of Oral Molecular Excipients with Breast Cancer Resistance Protein, BCRP

Mechanistic-understanding-based selection of excipients may improve formulation development strategies for generic drug products and potentially accelerate their approval. Our study aimed at investigating the effects of molecular excipients present in orally administered FDA-approved drug products on the intestinal efflux transporter, BCRP (ABCG2), which plays a critical role in drug absorption with potential implications on drug safety and efficacy. We determined the interactions of 136 oral molecular excipients with BCRP in isolated membrane vesicles and identified 26 excipients as BCRP inhibitors with IC₅₀ values less than 5 μM using ³H-cholecystokinin octapeptide (³H-CCK8). These BCRP inhibitors belonged to three functional categories of excipients: dyes, surfactants, and flavoring agents. Compared with noninhibitors, BCRP inhibitors had significantly higher molecular weights and SLogP values. The inhibitory effects of excipients identified in membrane vesicles were also evaluated in BCRP-overexpressing HEK293 cells at similar concentrations. Only 1 of the 26 inhibitors of BCRP identified in vesicles inhibited BCRP-mediated ³H-oxypurinol uptake by more than 50%, consistent with the notion that BCRP inhibition depends on transmembrane or intracellular availability of the inhibitors. Collectively, the results of this study provide new information on excipient selection during the development of drug products with active pharmaceutical ingredients that are BCRP substrates.

N,N'-diaryl-bishydrazones in a biphenyl platform: Broad spectrum antifungal agents

N,N'-Diaryl-bishydrazones of [1,1'-biphenyl]-3,4'-dicarboxaldehyde, [1,1'-biphenyl]-4,4'-dicarboxaldehyde, and 4,4'-bisacetyl-1,1-biphenyl exhibited excellent antifungal activity against a broad spectrum of filamentous and non-filamentous fungi. These N,N'-diaryl-bishydrazones displayed no antibacterial activity in contrast to previously reported N,N'-diamidino-bishydrazones and N-amidino-N'-aryl-bishydrazones. The leading candidate, 4,4'-bis((E)-1-(2-(4-fluorophenyl)hydrazono)ethyl)-1,1'-biphenyl, displayed less hemolysis of murine red blood cells at concentrations at or below that of a control antifungal agent (voriconazole), was fungistatic in a time-kill study, and possessed no mammalian cytotoxicity and no toxicity with respect to hERG inhibition.

Interfering With DNA Decondensation as a Strategy Against Mycobacteria

Tuberculosis is once again a major global threat, leading to more than 1 million deaths each year. Treatment options for tuberculosis patients are limited, expensive and characterized by severe side effects, especially in the case of multidrug-resistant forms. Uncovering novel vulnerabilities of the pathogen is crucial to generate new therapeutic strategies. Using high resolution microscopy techniques, we discovered one such vulnerability of Mycobacterium tuberculosis. We demonstrate that the DNA of M. tuberculosis can condense under stressful conditions such as starvation and antibiotic treatment. The DNA condensation is reversible and specific for viable bacteria. Based on these observations, we hypothesized that blocking the recovery from the condensed state could weaken the bacteria. We showed that after inducing DNA condensation, and subsequent blocking of acetylation of DNA binding proteins, the DNA localization in the bacteria is altered. Importantly under these conditions, Mycobacterium smegmatis did not replicate and its survival was significantly reduced. Our work demonstrates that agents that block recovery from the condensed state of the nucleoid can be exploited as antibiotic. The combination of fusidic acid and inhibition of acetylation of DNA binding proteins, via the Eis enzyme, potentiate the efficacy of fusidic acid by 10 and the Eis inhibitor to 1,000-fold. Hence, we propose that successive treatment with antibiotics and drugs interfering with recovery from DNA condensation constitutes a novel approach for treatment of tuberculosis and related bacterial infections.

Potent 1,2,4-Triazino[5,6 b]indole-3-thioether Inhibitors of the Kanamycin Resistance Enzyme Eis from Mycobacterium tuberculosis

A common cause of resistance to kanamycin (KAN) in tuberculosis is overexpression of the enhanced intracellular survival (Eis) protein. Eis is an acetyltransferase that multiacetylates KAN and other aminoglycosides, rendering them unable to bind the bacterial ribosome. By high-throughput screening, a series of substituted 1,2,4-triazino[5,6 b]indole-3-thioether molecules were identified as effective Eis inhibitors. Herein, we purchased 17 and synthesized 22 new compounds, evaluated their potency, and characterized their steady-state kinetics. Four inhibitors were found not only to inhibit Eis in vitro, but also to act as adjuvants of KAN and partially restore KAN sensitivity in a Mycobacterium tuberculosis KAN-resistant strain in which Eis is upregulated. A crystal structure of Eis in complex with a potent inhibitor and CoA shows that the inhibitors bind in the aminoglycoside binding site snugly inserted into a hydrophobic cavity. These inhibitors will undergo preclinical development as novel KAN adjuvant therapies to treat KAN-resistant tuberculosis.

Developing antineoplastic agents that target peroxisomal enzymes: cytisine-linked isoflavonoids as inhibitors of hydroxysteroid 17-beta-dehydrogenase-4 (HSD17B4)

Cytisine-linked isoflavonoids (CLIFs) inhibited PC-3 prostate and LS174T colon cancer cell proliferation by inhibiting a peroxisomal bifunctional enzyme. A pull-down assay using a biologically active, biotin-modified CLIF identified the target of these agents as the bifunctional peroxisomal enzyme, hydroxysteroid 17β-dehydrogenase-4 (HSD17B4). Additional studies with truncated versions of HSD17B4 established that CLIFs specifically bind the C-terminus of HSD17B4 and selectively inhibited the enoyl CoA hydratase but not the d-3-hydroxyacyl CoA dehydrogenase activity. HSD17B4 was overexpressed in prostate and colon cancer tissues, knocking down HSD17B4 inhibited cancer cell proliferation, suggesting that HSD17B4 is a potential biomarker and drug target and that CLIFs are potential probes or therapeutic agents for these cancers.

What are the drugs of the future?

Are small molecules or biologics the drugs of the future? Small-molecule drugs have historically been the pillars of traditional medicine. However, recently, we seem to be amidst a scientific revolution with the rise of many FDA-approved biologic drugs. This opinion article looks at the current state of small molecules and biologics and assesses what the future holds for these two broad classes of drugs.

Alkylated Piperazines and Piperazine-Azole Hybrids as Antifungal Agents

The extensive use of fluconazole (FLC) and other azole drugs has caused the emergence and rise of azole-resistant fungi. The fungistatic nature of FLC in combination with toxicity concerns have resulted in an increased demand for new azole antifungal agents. Herein, we report the synthesis and antifungal activity of novel alkylated piperazines and alkylated piperazine-azole hybrids, their time-kill studies, their hemolytic activity against murine erythrocytes, as well as their cytotoxicity against mammalian cells. Many of these molecules exhibited broad-spectrum activity against all tested fungal strains, with excellent minimum inhibitory concentration (MIC) values against non-albicans Candida and Aspergillus strains. The most promising compounds were found to be less hemolytic than the FDA-approved antifungal agent voriconazole (VOR). Finally, we demonstrate that the synthetic alkylated piperazine-azole hybrids do not function by fungal membrane disruption, but instead by disruption of the ergosterol biosynthetic pathway via inhibition of the 14α-demethylase enzyme present in fungal cells.

Novel fluconazole derivatives with promising antifungal activity

The fungistatic nature and toxicity concern associated with the azole drugs currently on the market have resulted in an increased demand for new azole antifungal agents for which these problematic characteristics do not exist. The extensive use of azoles has resulted in fungal strains capable of resisting the action of these drugs. Herein, we report the synthesis and antifungal activity of novel fluconazole (FLC) analogues with alkyl-, aryl-, cycloalkyl-, and dialkyl-amino substituents. We evaluated their antifungal activity by MIC determination and time-kill assay as well as their safety profile by hemolytic activity against murine erythrocytes as well as cytotoxicity against mammalian cells. The best compounds from our study exhibited broad-spectrum activity against most of the fungal strains tested, with excellent MIC values against a number of clinical isolates. The most promising compounds were found to be less hemolytic than the least hemolytic FDA-approved azole antifungal agent voriconazole (VOR). Finally, we demonstrated that the synthetic alkyl-amino FLC analogues displayed chain-dependent fungal membrane disruption as well as inhibition of ergosterol biosynthesis as possible mechanisms of action.

Flipping the Switch "On" for Aminoglycoside-Resistance Enzymes: The Mechanism Is Finally Revealed!

In a recent issue of Structure, Caldwell et al. (2016) determined crystal structures of APH(2″)-Ia in complex with various combinations of aminoglycosides and nucleosides, which compellingly revealed that the catalytic activity of this resistance enzyme is regulated by a conformational change of the triphosphate of GTP, a mechanism previously unknown for antibiotic kinases.

Combating Enhanced Intracellular Survival (Eis)-Mediated Kanamycin Resistance of Mycobacterium tuberculosis by Novel Pyrrolo[1,5-a]pyrazine-Based Eis Inhibitors

Tuberculosis (TB) remains one of the leading causes of mortality worldwide. Hence, the identification of highly effective antitubercular drugs with novel modes of action is crucial. In this paper, we report the discovery and development of pyrrolo[1,5-a]pyrazine-based analogues as highly potent inhibitors of the Mycobacterium tuberculosis (Mtb) acetyltransferase enhanced intracellular survival (Eis), whose up-regulation causes clinically observed resistance to the aminoglycoside (AG) antibiotic kanamycin A (KAN). We performed a structure-activity relationship (SAR) study to optimize these compounds as potent Eis inhibitors both against purified enzyme and in mycobacterial cells. A crystal structure of Eis in complex with one of the most potent inhibitors reveals that the compound is bound to Eis in the AG binding pocket, serving as the structural basis for the SAR. These Eis inhibitors have no observed cytotoxicity to mammalian cells and are promising leads for the development of innovative AG adjuvant therapies against drug-resistant TB.

Combating Enhanced Intracellular Survival (Eis)-Mediated Kanamycin Resistance of Mycobacterium tuberculosis by Novel Pyrrolo[1,5-a]pyrazine-Based Eis Inhibitors

Tuberculosis (TB) remains one of the leading causes of mortality worldwide. Hence, the identification of highly effective antitubercular drugs with novel modes of action is crucial. In this paper, we report the discovery and development of pyrrolo[1,5-a]pyrazine-based analogues as highly potent inhibitors of the Mycobacterium tuberculosis (Mtb) acetyltransferase enhanced intracellular survival (Eis), whose up-regulation causes clinically observed resistance to the aminoglycoside (AG) antibiotic kanamycin A (KAN). We performed a structure-activity relationship (SAR) study to optimize these compounds as potent Eis inhibitors both against purified enzyme and in mycobacterial cells. A crystal structure of Eis in complex with one of the most potent inhibitors reveals that the compound is bound to Eis in the AG binding pocket, serving as the structural basis for the SAR. These Eis inhibitors have no observed cytotoxicity to mammalian cells and are promising leads for the development of innovative AG adjuvant therapies against drug-resistant TB.

Development of ebsulfur analogues as potent antibacterials against methicillin-resistant Staphylococcus aureus

Antibiotic resistance is a worldwide problem that needs to be addressed. Staphylococcus aureus is one of the dangerous "ESKAPE" pathogens that rapidly evolve and evade many current FDA-approved antibiotics. Thus, there is an urgent need for new anti-MRSA compounds. Ebselen (also known as 2-phenyl-1,2-benzisoselenazol-3(2H)-one) has shown promising activity in clinical trials for cerebral ischemia, bipolar disorder, and noise-induced hearing loss. Recently, there has been a renewed interest in exploring the antibacterial properties of ebselen. In this study, we synthesized an ebselen-inspired library of 33 compounds where the selenium atom has been replaced by sulfur (ebsulfur derivatives) and evaluated them against a panel of drug-sensitive and drug-resistant S. aureus and non-S. aureus strains. Within our library, we identified three outstanding analogues with potent activity against all S. aureus strains tested (MIC values mostly ⩽2μg/mL), and numerous additional ones with overall very good to good antibacterial activity (1-7.8μg/mL). We also characterized the time-kill analysis, anti-biofilm ability, hemolytic activity, mammalian cytotoxicity, membrane-disruption ability, and reactive oxygen species (ROS) production of some of these analogues.

A complex game of hide and seek: the search for new antifungals

Fungal infections directly affect millions of people each year. In addition to the invasive fungal infections of humans, the plants and animals that comprise our primary food source are also susceptible to diseases caused by these eukaryotic microbes. The need for antifungals, not only for our medical needs, but also for use in agriculture and livestock causes a high demand for novel antimycotics. Herein, we provide an overview of the most commonly used antifungals in medicine and agriculture. We also present a summary of the recent progress (from 2010-2016) in the discovery/development of new agents against fungal strains of medical/agricultural relevance, as well as information related to their biological activity, their mode(s) of action, and their mechanism(s) of resistance.

Identification of Ebsulfur Analogues with Broad-Spectrum Antifungal Activity

Invasive fungal infections are on the rise due to an increased population of critically ill patients as a result of HIV infections, chemotherapies, and organ transplantations. Current antifungal drugs are helpful, but are insufficient in addressing the problem of drug-resistant fungal infections. Thus, there is a growing need for novel antimycotics that are safe and effective. The ebselen scaffold has been evaluated in clinical trials and has been shown to be safe in humans. This makes ebselen an attractive scaffold for facile translation from bench to bedside. We recently reported a library of ebselen-inspired ebsulfur analogues with antibacterial properties, but their antifungal activity has not been characterized. In this study, we repurposed ebselen, ebsulfur, and 32 additional ebsulfur analogues as antifungal agents by evaluating their antifungal activity against a panel of 13 clinically relevant fungal strains. The effect of induction of reactive oxygen species (ROS) by three of these compounds was evaluated. Their hemolytic and cytotoxicity activities were also determined using mouse erythrocytes and mammalian cells. The MIC values of these compounds were found to be in the range of 0.02-12.5 μg mL(-1) against the fungal strains tested. Notably, yeast cells treated with our compounds showed an accumulation of ROS, which may further contribute to the growth-inhibitory effect against fungi. This study provides new lead compounds for the development of antimycotic agents.