scholarly journals Investigating the mode of action of tuberculosis drugs using hypersensitive mutants of Mycobacterium smegmatis

2021 ◽  
Author(s):  
◽  
Richard Laurence Campen
Keyword(s):  
High Throughput ◽  
Mode Of Action ◽  
Drug Hypersensitivity ◽  
Resistance Mechanisms ◽  
New Drugs ◽  
Drug Resistant ◽  
Primary Target ◽  
Modes Of Action ◽  
Increased Sensitivity ◽  
High Throughput Assay

<p>Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), is the leading cause of death and disease by a bacterial pathogen worldwide. The growing incidence of drug resistant TB, especially multi-drug resistant TB highlights the need for new drugs with novel modes of action. Current treatment of TB involves a multi-drug regimen of four drugs including isoniazid and rifampicin, both of which were discovered over 40 years ago. Bedaquiline is one of the first novel TB drugs to enter clinical trials since the discovery of rifampicin, and has shown excellent activity against drug resistant TB. Although isoniazid and rifampicin are well established anti-TB drugs, significant gaps in knowledge regarding their modes of action exist. Furthermore, little information on the mode of action of the novel drug bedaquiline is known beyond its primary target. Characterisation of drug mode of action facilitates rational modifications of drugs to improve the treatment of TB.  The aim of this study was to identify novel aspects of the modes of action of isoniazid, rifampicin, and bedaquiline by characterising drug hypersensitive mutants of M. smegmatis mc²155. A sub-saturated M. smegmatis mc²155 transposon mutant collection with 1.1-fold genome coverage (7680 mutants) was constructed, with this collection estimated to contain mutations in 73.2% of all genes capable of maintaining a transposon insertion (non-essential genes). A high-throughput assay was developed for screening the collection, and mutants related to known drug mode of action were identified for isoniazid (ahpC and eccCa₁) and bedaquiline (atpB). Additionally, known mechanisms of drug inactivation were identified for isoniazid (nudC), rifampicin (arr and lspA), and bedaquiline (mmpL5). The finding that transposon mutants of nudC are hypersensitive to isoniazid independently validated the recent discovery of the role of NudC in basal isoniazid resistance by Wang et al. (2011). The remaining genes identified in this thesis represent potentially novel aspects of the modes of action or resistance mechanisms of these drugs.  Cross-sensitivity to other drugs indicated that the mechanism of sensitivity was drug specific for the mutants examined. Differential-sensitivity testing against drug analogues revealed that Arr is involved in resistance to the rifampicin analogue rifapentine as well, indicating that Arr can detoxify rifapentine similar to rifampicin. The nudC mutant showed increased sensitivity to a range of isoniazid analogues, indicating that it can detoxify these analogues similar to the parent compound. Interestingly six analogues were found to be less active against the nudC mutant than expected. A number of overexpression strains were tested against these six analogues; a nudC overexpression strain, and a strain overexpressing inhA, the primary target for isoniazid. Overexpression of nudC as well inhA increased the resistance of WT to isoniazid, but failed to increase resistance to three of the analogues, NSC27607, NSC33759, and NSC40350. Isoniazid is a prodrug and is activated by the peroxidase/catalase enzyme KatG. Overexpression of katG resulted in increased isoniazid sensitivity, as well as increased sensitivity to NSC27607, NSC33759, and NSC40350. Together these results suggest that NSC27607, NSC33759, and NSC40350 are activated by KatG, but that InhA is not the primary target. Additionally the inability of NudC overexpression to confer resistance suggests these analogues are not acting via a NAD adduct, the mechanism by which isoniazid inhibits InhA. These results suggest that there are other toxic metabolites being produced by KatG activation of these three analogues.  In conclusion, characterisation of mutants identified in a high-throughput assay for drug hypersensitivity identified genes involved in the modes of action or resistance mechanisms for isoniazid, rifampicin, and bedaquiline. Additionally, a number of novel genes were identified that have no known connections to the known modes of action or resistance mechanisms for these drugs. Further testing of a nudC mutant revealed three isoniazid analogues that appear to inhibit growth of M. smegmatis mc²155 independent of InhA, the primary target of isoniazid. This study has successfully demonstrated that screening for drug hypersensitivity can generate novel information on drug mode of action and resistance mechanisms. This information can ultimately be used to help drive the development of new drugs, and improve treatment of TB.</p>

scholarly journals Investigating the mode of action of tuberculosis drugs using hypersensitive mutants of Mycobacterium smegmatis

2021 ◽  
Author(s):  
◽  
Richard Laurence Campen
Keyword(s):  
High Throughput ◽  
Mode Of Action ◽  
Drug Hypersensitivity ◽  
Resistance Mechanisms ◽  
New Drugs ◽  
Drug Resistant ◽  
Primary Target ◽  
Modes Of Action ◽  
Increased Sensitivity ◽  
High Throughput Assay

<p>Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), is the leading cause of death and disease by a bacterial pathogen worldwide. The growing incidence of drug resistant TB, especially multi-drug resistant TB highlights the need for new drugs with novel modes of action. Current treatment of TB involves a multi-drug regimen of four drugs including isoniazid and rifampicin, both of which were discovered over 40 years ago. Bedaquiline is one of the first novel TB drugs to enter clinical trials since the discovery of rifampicin, and has shown excellent activity against drug resistant TB. Although isoniazid and rifampicin are well established anti-TB drugs, significant gaps in knowledge regarding their modes of action exist. Furthermore, little information on the mode of action of the novel drug bedaquiline is known beyond its primary target. Characterisation of drug mode of action facilitates rational modifications of drugs to improve the treatment of TB.  The aim of this study was to identify novel aspects of the modes of action of isoniazid, rifampicin, and bedaquiline by characterising drug hypersensitive mutants of M. smegmatis mc²155. A sub-saturated M. smegmatis mc²155 transposon mutant collection with 1.1-fold genome coverage (7680 mutants) was constructed, with this collection estimated to contain mutations in 73.2% of all genes capable of maintaining a transposon insertion (non-essential genes). A high-throughput assay was developed for screening the collection, and mutants related to known drug mode of action were identified for isoniazid (ahpC and eccCa₁) and bedaquiline (atpB). Additionally, known mechanisms of drug inactivation were identified for isoniazid (nudC), rifampicin (arr and lspA), and bedaquiline (mmpL5). The finding that transposon mutants of nudC are hypersensitive to isoniazid independently validated the recent discovery of the role of NudC in basal isoniazid resistance by Wang et al. (2011). The remaining genes identified in this thesis represent potentially novel aspects of the modes of action or resistance mechanisms of these drugs.  Cross-sensitivity to other drugs indicated that the mechanism of sensitivity was drug specific for the mutants examined. Differential-sensitivity testing against drug analogues revealed that Arr is involved in resistance to the rifampicin analogue rifapentine as well, indicating that Arr can detoxify rifapentine similar to rifampicin. The nudC mutant showed increased sensitivity to a range of isoniazid analogues, indicating that it can detoxify these analogues similar to the parent compound. Interestingly six analogues were found to be less active against the nudC mutant than expected. A number of overexpression strains were tested against these six analogues; a nudC overexpression strain, and a strain overexpressing inhA, the primary target for isoniazid. Overexpression of nudC as well inhA increased the resistance of WT to isoniazid, but failed to increase resistance to three of the analogues, NSC27607, NSC33759, and NSC40350. Isoniazid is a prodrug and is activated by the peroxidase/catalase enzyme KatG. Overexpression of katG resulted in increased isoniazid sensitivity, as well as increased sensitivity to NSC27607, NSC33759, and NSC40350. Together these results suggest that NSC27607, NSC33759, and NSC40350 are activated by KatG, but that InhA is not the primary target. Additionally the inability of NudC overexpression to confer resistance suggests these analogues are not acting via a NAD adduct, the mechanism by which isoniazid inhibits InhA. These results suggest that there are other toxic metabolites being produced by KatG activation of these three analogues.  In conclusion, characterisation of mutants identified in a high-throughput assay for drug hypersensitivity identified genes involved in the modes of action or resistance mechanisms for isoniazid, rifampicin, and bedaquiline. Additionally, a number of novel genes were identified that have no known connections to the known modes of action or resistance mechanisms for these drugs. Further testing of a nudC mutant revealed three isoniazid analogues that appear to inhibit growth of M. smegmatis mc²155 independent of InhA, the primary target of isoniazid. This study has successfully demonstrated that screening for drug hypersensitivity can generate novel information on drug mode of action and resistance mechanisms. This information can ultimately be used to help drive the development of new drugs, and improve treatment of TB.</p>

scholarly journals High-Throughput Screening of Psychotropic Compounds: Impacts on Swimming Behaviours in Artemia franciscana

Toxics ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 64
Author(s):  
Shanelle A. Kohler ◽  
Matthew O. Parker ◽  
Alex T. Ford
Keyword(s):  
High Throughput ◽  
Swimming Speed ◽  
High Throughput Screening ◽  
Artemia Franciscana ◽  
Animal Behaviour ◽  
Crustacean Species ◽  
Significant Difference ◽  
Increased Sensitivity ◽  
Light Side ◽  
High Throughput Assay

Animal behaviour is becoming increasingly popular as an endpoint in ecotoxicology due to its increased sensitivity and speed compared to traditional endpoints. However, the widespread use of animal behaviours in environmental risk assessment is currently hindered by a lack of optimisation and standardisation of behavioural assays for model species. In this study, assays to assess swimming speed were developed for a model crustacean species, the brine shrimp Artemia franciscana. Preliminary works were performed to determine optimal arena size for this species, and weather lux used in the experiments had an impact on the animals phototactic response. Swimming speed was significantly lower in the smallest arena, whilst no difference was observed between the two larger arenas, suggesting that the small arena was limiting swimming ability. No significant difference was observed in attraction to light between high and low light intensities. Arena size had a significant impact on phototaxis behaviours. Large arenas resulted in animals spending more time in the light side of the arena compared to medium and small, irrespective of light intensity. The swimming speed assay was then used to expose specimens to a range of psychotropic compounds with varying modes of action. Results indicate that swimming speed provides a valid measure of the impacts of behaviour modulating compounds on A. franciscana. The psychotropic compounds tested varied in their impacts on animal behaviour. Fluoxetine resulted in increased swimming speed as has been found in other crustacean species, whilst oxazepam, venlafaxine and amitriptyline had no significant impacts on the behaviours measured. The results from this study suggest a simple, fast, high throughput assay for A. franciscana and gains insight on the impacts of a range of psychotropic compounds on the swimming behaviours of a model crustacean species used in ecotoxicology studies.

scholarly journals High-throughput decoding of drug targets and drug resistance mechanisms in African trypanosomes

Parasitology ◽  
2013 ◽  
Vol 141 (1) ◽  
pp. 77-82 ◽  
Author(s):  
DAVID HORN
Keyword(s):  
Drug Resistance ◽  
High Throughput ◽  
Drug Targets ◽  
Sequence Data ◽  
Resistance Mechanisms ◽  
New Drugs ◽  
Drug Uptake ◽  
Microbial Pathogens ◽  
African Trypanosomes ◽  
Genome Scale

SUMMARYThe availability of genome sequence data has facilitated the development of high-throughput genetic screening approaches in microbial pathogens. In the African trypanosome, Trypanosoma brucei, genome-scale RNA interference screens have proven particularly effective in this regard. These genetic screens allow for identification of the genes that contribute to a particular pathway or mechanisms of interest. The approach has been used to assess loss-of-fitness, revealing the genes and proteins required for parasite viability and growth. The outputs from these screens predict essential and dispensable genes and facilitate drug target prioritization efforts. The approach has also been used to assess resistance to anti-trypanosomal drugs, revealing the genes and proteins that facilitate drug uptake and action. These outputs also highlight likely mechanisms underlying clinically relevant drug resistance. I first review these findings in the context of what we know about current drugs. I then describe potential contributions that these high-throughput approaches could make to the development and implementation of new drugs.

scholarly journals Exploring Phytochemicals for Combating Antibiotic Resistance in Microbial Pathogens

2021 ◽  
Vol 12 ◽  
Author(s):  
Tushar Khare ◽  
Uttpal Anand ◽  
Abhijit Dey ◽  
Yehuda G. Assaraf ◽  
Zhe-Sheng Chen ◽  
...  
Keyword(s):  
Drug Resistance ◽  
Antibiotic Resistance ◽  
Current Knowledge ◽  
Plant Secondary Metabolites ◽  
Agricultural Practices ◽  
Resistance Mechanisms ◽  
New Drugs ◽  
Microbial Pathogens ◽  
Drug Resistant ◽  
Microbial Drug Resistance

Antibiotic resistance or microbial drug resistance is emerging as a serious threat to human healthcare globally, and the multidrug-resistant (MDR) strains are imposing major hurdles to the progression of drug discovery programs. Newer antibiotic-resistance mechanisms in microbes contribute to the inefficacy of the existing drugs along with the prolonged illness and escalating expenditures. The injudicious usage of the conventional and commonly available antibiotics in human health, hygiene, veterinary and agricultural practices is proving to be a major driver for evolution, persistence and spread of antibiotic-resistance at a frightening rate. The drying pipeline of new and potent antibiotics is adding to the severity. Therefore, novel and effective new drugs and innovative therapies to treat MDR infections are urgently needed. Apart from the different natural and synthetic drugs being tested, plant secondary metabolites or phytochemicals are proving efficient in combating the drug-resistant strains. Various phytochemicals from classes including alkaloids, phenols, coumarins, terpenes have been successfully demonstrated their inhibitory potential against the drug-resistant pathogens. Several phytochemicals have proved effective against the molecular determinants responsible for attaining the drug resistance in pathogens like membrane proteins, biofilms, efflux pumps and bacterial cell communications. However, translational success rate needs to be improved, but the trends are encouraging. This review highlights current knowledge and developments associated challenges and future prospects for the successful application of phytochemicals in combating antibiotic resistance and the resistant microbial pathogens.

scholarly journals Azetidines kill Mycobacterium tuberculosis without detectable resistance by blocking mycolate assembly

2020 ◽  
Author(s):  
Alice Lanne ◽  
Yixin Cui ◽  
Edward Browne ◽  
Philip G. E. Craven ◽  
Nicholas J. Cundy ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Mode Of Action ◽  
Drug Targets ◽  
Cell Envelope ◽  
Mycolic Acid ◽  
New Drugs ◽  
Drug Resistant ◽  
Target Deconvolution ◽  
Mdr Tb ◽  
Mycobacterial Cell Wall

AbstractTuberculosis (TB) is the leading cause of global morbidity and mortality resulting from infectious disease, with over 10 million new cases and 1.5 million deaths in 2019. This global emergency is exacerbated by the emergence of multi-drug-resistant MDR-TB and extensively-drug-resistant XDR-TB, therefore new drugs and new drug targets are urgently required. From a whole-cell phenotypic screen a series of azetidines derivatives termed BGAz, that elicit potent bactericidal activity with MIC99 values <10 μM against drug-sensitive Mycobacterium tuberculosis and MDR-TB were identified. These compounds demonstrate no detectable drug resistance. Mode of action and target deconvolution studies suggest that these compounds inhibit mycobacterial growth by interfering with cell envelope biogenesis, specifically late-stage mycolic acid biosynthesis. Transcriptomic analysis demonstrates that the BGAz compounds tested display a mode of action distinct from existing mycobacterial cell-wall inhibitors. In addition, the compounds tested exhibit toxicological and PK/PD profiles that pave the way for their development as anti-tubercular chemotherapies.

scholarly journals Behavioral fingerprints predict insecticide and anthelmintic mode of action

2021 ◽  
Author(s):  
Adam McDermott-Rouse ◽  
Eleni Minga ◽  
Ida Barlow ◽  
Luigi Feriani ◽  
Philippa H Harlow ◽  
...  
Keyword(s):  
High Throughput ◽  
Mode Of Action ◽  
Behavioral Responses ◽  
Physiological Data ◽  
Discovery Process ◽  
Crucial Step ◽  
C Elegans ◽  
Modes Of Action ◽  
Automated Phenotyping ◽  
High Throughput Imaging

AbstractNovel invertebrate-killing compounds are required in agriculture and medicine to overcome resistance to existing treatments. Because insecticides and anthelmintics are discovered in phenotypic screens, a crucial step in the discovery process is determining the mode of action of hits. Visible whole-organism symptoms are combined with molecular and physiological data to determine mode of action. However, manual symptomology is laborious and requires symptoms that are strong enough to see by eye. Here we use high-throughput imaging and quantitative phenotyping to measure C. elegans behavioral responses to compounds and train a classifier that predicts mode of action with an accuracy of 88% for a set of ten common modes of action. We also classify compounds within each mode of action to discover pharmacological relationships that are not captured in broad mode of action labels. High-throughput imaging and automated phenotyping could therefore accelerate mode of action discovery in invertebrate-targeting compound development and help to refine mode of action categories.

Ribosome-Targeting Antibiotics: Modes of Action, Mechanisms of Resistance, and Implications for Drug Design

2018 ◽  
Vol 87 (1) ◽  
pp. 451-478 ◽  
Author(s):  
Jinzhong Lin ◽  
Dejian Zhou ◽  
Thomas A. Steitz ◽  
Yury S. Polikanov ◽  
Matthieu G. Gagnon
Keyword(s):  
Protein Synthesis ◽  
Bacterial Infections ◽  
Pathogenic Bacteria ◽  
Resistance Mechanisms ◽  
Public Health Care ◽  
Drug Resistant ◽  
Protein Synthesis Inhibitors ◽  
Antimicrobial Drugs ◽  
Modes Of Action ◽  
Action Mechanisms

Genetic information is translated into proteins by the ribosome. Structural studies of the ribosome and of its complexes with factors and inhibitors have provided invaluable information on the mechanism of protein synthesis. Ribosome inhibitors are among the most successful antimicrobial drugs and constitute more than half of all medicines used to treat infections. However, bacterial infections are becoming increasingly difficult to treat because the microbes have developed resistance to the most effective antibiotics, creating a major public health care threat. This has spurred a renewed interest in structure-function studies of protein synthesis inhibitors, and in few cases, compounds have been developed into potent therapeutic agents against drug-resistant pathogens. In this review, we describe the modes of action of many ribosome-targeting antibiotics, highlight the major resistance mechanisms developed by pathogenic bacteria, and discuss recent advances in structure-assisted design of new molecules.

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