Re-engaging antimicrobial killing by macrophages to combat antimicrobial resistance

Serious bacterial infections arise because of defects in the ways that our body's immune system protects against these infections. We have established that effective clearance of bacteria in body tissues requires a type of immune cell called the macrophage to eat bacteria and when the macrophages ability to kill bacteria becomes exhausted to commit a form of cell suicide called apoptosis. This cell death helps clear the remaining viable bacteria and importantly does so by a process that is less dependent on inflammation and therefore is less likely to result in damage to organs in the body. We have defined the key molecules that regulate this process in macrophages and shown that this mechanism of bacterial killing is not working properly in several groups of patients who are at risk of serious bacterial infection. We wish to use these findings to develop a totally new approach to treating bacterial infection.

Our approach will take several types of medicine that are used by doctors to treat other types of human disease and test their ability to enhance macrophage cell death and bacterial killing. We have selected these medicines because they re-engage some of the processes that cause macrophage cell death and which may not be working properly in patients at risk of serious bacterial infection. We will modify some of these medicines to enhance their uptake by macrophages so that the treatment will be specific for macrophages and less likely to have effects on other cells in the body. We will then screen these medicines for their ability to increase macrophage cell death and to increase bacterial killing in these macrophages, using cells we have genetically engineered to be more susceptible to bacterial infection. We will explore in more depth how the most promising medicines achieve macrophage cell suicide and kill bacteria. We will do this to confirm they are acting on the specific process we believe are important. We will also test their ability to kill antibiotic resistant bacteria. We will then test whether the most promising medicines we have identified from this initial screen also enhance macrophage cell suicide in mice and whether this increases bacterial clearance, reduces inflammation or reduces death when these mice have bacterial infection in the lungs.

Our overall goal is to develop a new treatment for bacterial infection that relies on modulating the body's own response to infection. This approach will reduce our reliance on antibiotics, decreasing the development of antibiotic resistance and develop a new treatment that will act on bacteria that have become resistant to the antibiotics we currently use.

Innate immune responses are highly effective at preventing bacterial infection in most individuals. Re-engaging these host responses in patients with bacterial diseases would provide an alternative therapeutic approach to our reliance on antimicrobials. We have identified that macrophages use apoptosis-associated bacterial killing to clear bacteria and minimize neutrophilic inflammation or tissue injury. Several patient groups with enhanced susceptibility to bacterial infection have enhanced expression of the anti-apoptotic protein Mcl-1, which prevents macrophage apoptosis associated killing. Moreover we have established a unique transgenic mouse in which macrophage specific over-expression of Mcl-1 results in enhanced susceptibility to bacterial infection and reduced macrophage apoptosis-associated killing. Our aim is to test whether we can enhance macrophage apoptosis-associated killing as a therapeutic strategy to combat antimicrobial resistance.

We have identified that fluoroquinolones, bisphosphonates and BH3 mimetics act on the pathway regulating macrophage apoptosis-associated killing. We will establish a small library of these compounds, including modified forms to enhance macrophage uptake. We will use these to;
i) Identify compounds that enhance macrophage apoptosis-associated bacterial killing.
ii) Determine the mechanism by which the most promising compounds re-engage macrophage apoptosis-associated killing and establish if they enhance killing of antimicrobial resistant strains of Streptococcus pneumoniae and Staphylococcus aureus.
iii) Test whether lead compounds re-engage macrophage apoptosis-associated bacterial killing or modify inflammatory outcomes or survival in murine models of pulmonary infection, utilizing our macrophage specific Mcl-1 transgenic mice.

This proposal will provide proof-of-concept for a host-based therapeutic strategy that could be used against antimicrobial resistant bacteria and limit reliance on antimicrobials.

Clinicians. The project will lead to the development of novel therapies that kill bacteria by modulating the innate immune response. As some of the therapies are already in clinical use these impacts would be observed in the medium term (5 years) while the impact of compounds that are developed from these such as formulations to maximise macrophage delivery will be longer term (5-10 years). The fact that the parent compounds are already licensed medications should speed up some of the translation to humans. The concept that host-based therapy is a tractable approach to manage antimicrobial resistance would have short-term (2-4 year) impact and would help add enthusiasm for this approach as a strategy to combat antimicrobial resistance

Patients with infectious disease. The project would be of interest to patients and will raise awareness of antimicrobial resistance and strategies to combat this. This information can be disseminated via the University of Sheffield press office,, infection-related charities and professional societies and relevant patient groups.

Public Sector: Ultimately this research could lead to new guidelines for the prevention and management of infectious disease once the initial findings are confirmed and clinical trials have defined their indications (long term 10 years).

Industry: The development of new therapies or even of new tests to determine susceptibility of infection has the potential to generate new avenues for the pharmaceutical industry working with healthcare partners. (short to medium term 2-10 years).

General Public: Communicating information regarding the factors associated with anti-microbial resistance in general coupled with the results from this project will raise awareness in people about these issues and also enable further general preventive health advice, (immediate to mid-term impact (0-3 years).
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