In vitro drug discovery models for Mycobacterium tuberculosis relevant for host infection

ABSTRACT

Introduction: Tuberculosis is the leading cause of death from infectious disease. Current drug therapy requires a combination of antibiotics taken over >6 months. An urgent need for new agents that can shorten therapy is required. In order to develop new drugs, simple in vitro assays are required that can identify efficacious compounds rapidly and predict in vivo activity in the human.

Areas covered: This review focusses on the most relevant in vitro assays that can be utilized in a drug discovery program and which mimic different aspects of infection or disease. The focus is largely on assays used to test >1000s of compounds reliably and robustly. However, some assays used for 10s to 100s of compounds are included where the utility outweighs the low capacity. Literature searches for high throughput screening, models and in vitro assays were undertaken.

Expert opinion: Drug discovery and development in tuberculosis is extremely challenging due to the requirement for predicting drug efficacy in a disease with complex pathology in which bacteria exist in heterogeneous states in inaccesible locations. A combination of assays can be used to determine profiles against replicating, non-replicating, intracellular and tolerant bacteria.

KEYWORDS:

• Tuberculosis
• Anti-bacterial
• Anti-tubercular
• High throughput screening
• Infection models

Article Highlights

• From a drug discovery perspective, tuberculosis is a particularly challenging disease. The majority of drug discovery and development has been directed towards the treatment of active, pulmonary TB.

• The hallmark of tuberculosis, the granuloma, poses particular problems for developing new drugs both in terms of limiting compound penetration to the site of infection, but also in terms of providing several microenvironments in which bacteria reside.

• A number of reliable in vitro assays were developed which can used to support a drug discovery program for tuberculosis. These may address replicating or non-replicating bacteria, as well as intracellular bacteria.

• Simple assays to determine compound efficacy against replicating bacteria incorporating different carbon sources reflective of the infection setting are described.

• Non-replicating organisms can be generated by a range of conditions, including low pH, low oxygen and nutrient starvation, as well as combinations of these conditions and specialized strains.

• Several infection models using murine or human cells have been developed to allow testing against intracellular bacteria; in some cases, these can measure eukaryotic cytotoxicity simultaneously.

• Lesion-centric models are available to look at compound potency in caseum or in multicellular models in which in vitro granulomas are used.

This box summarizes key points contained in the article.

Declaration of interest

T Parish is the Senior Vice President of TB Discovery Research, of the Infectious Disease Research Institute. She has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer Disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This manuscript has not been funded.