Improving antibiotic therapy for Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is a slow-growing bacterium that causes tuberculosis (TB), which is a leading cause of death from an infectious disease worldwide. The emergence of drug-resistant strains has made TB increasingly difficult to treat, especially in individuals with weakened immune systems, such as those with HIV/AIDS, who experience severe lung damage, persistent symptoms, and high mortality rates. Current treatment outcomes for drug-resistant TB are poor due to the need for prolonged and complex regimens, which often result in significant side effects, low patient adherence, and high rates of treatment failure. These challenges highlight the urgent need to understand the mechanisms behind antibiotic treatment failure and to develop new and improved therapeutic strategies. The aim of my thesis is to address these issues by exploring strategies to improve drug delivery and optimise antibiotic interactions within treatment regimens to maximize Mtb killing. In my research chapters 3-5, my work aims to contribute to the development of more effective therapeutic approaches against Mtb. In my first chapter, I developed linezolid prodrugs to deliver linezolid to the site of Mtb infection, with the aim of increasing efficacy and minimizing off-target effects. I identified two methods of incorporating linezolid into a prodrug system and then explored two prodrug systems: a cephalosporin-linezolid conjugate and an antibody-linezolid conjugate (AAC). I tested the proof of concept of these prodrugs by assessing their selective release of linezolid, stability and cytotoxicity. These findings suggest that targeted drug delivery strategies could improve the efficacy of linezolid and potentially other antibiotics against Mtb. In my second chapter, I developed a high-throughput liquid chromatography-mass spectrometry (LC/MS) method to quantify antibiotic accumulation and metabolism within Mtb. This method allowed me to accurately measure antibiotic concentrations retained within Mtb, accounting for cell wall and plastic binding effects, and provided a new tool for assessing drug permeability, retention, and metabolism within Mtb. The application of this method to different TB antibiotics revealed significant variations in their intracellular accumulation, providing insights into the factors influencing drug efficacy. In my third chapter, I utilised the LC/MS method I developed to evaluate how pairwise combinations of 21 clinically relevant antibiotics affect retention, metabolism, and Mtb killing. This analysis identified antibiotic combinations with synergistic effects on retention and metabolism, which could explain their enhanced Mtb killing. Conversely, I identified combinations showing antagonism in retention and metabolism that could be correlated to their reduced Mtb killing. My findings highlighted the potential of specific combinations, such as beta-lactams with aminoglycosides or clofazimine, to enhance Mtb killing, while also identifying combinations that may reduce treatment efficacy due to antagonistic effects. I also analysed the metabolism of antibiotics within Mtb and examined how combinations of antibiotics influence their metabolic activation and degradation, potentially impacting their therapeutic efficacy. These findings provide valuable insights that could guide the development of optimized combination therapies to enhance patient outcomes. Collectively, my findings provide new understanding into antibiotic delivery, retention, metabolism, and their interactions within Mtb. This work offers potential avenues for improving the design of TB treatments, particularly for overcoming challenges associated with drug resistance and enhancing the efficacy of existing antibiotics.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Crawshay-Williams, Felicity

Advisor dc:contributor.advisor

• Floto, Andres

• Antibiotic conjugates
• Drug–drug interactions
• Mycobacterium tuberculosis
• Targeted drug delivery

Licence

• https://www.repository.cam.ac.uk/bitstreams/d75744f9-3a01-4663-9111-6b20fcbcac4f/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0009-0007-6150-5968

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/390757