For over 50 years, patients with drug-sensitive and drug-resistant tuberculosis have undergone long, arduous, and complex treatment processes with several antimicrobials. With the prevalence of drug-resistant strains on the rise and new therapies for tuberculosis urgently required, we assessed whether manipulating iron levels in macrophages infected with mycobacteria offered some insight into improving current antimicrobials that are used to treat drug-resistant tuberculosis. We investigated if the iron chelator, desferrioxamine, can support the function of human macrophages treated with an array of second-line antimicrobials, including moxifloxacin, bedaquiline, amikacin, clofazimine, linezolid and cycloserine. Primary human monocyte-derived macrophages were infected with Bacillus Calmette-Guérin (BCG), which is pyrazinamide-resistant, and concomitantly treated for 5 days with desferrioxamine in combination with each one of the second-line tuberculosis antimicrobials. Our data indicate that desferrioxamine used as an adjunctive treatment to bedaquiline significantly reduced the bacterial load in human macrophages infected with BCG. Our findings also reveal a link between enhanced bactericidal activity and increases in specific cytokines, as the addition of desferrioxamine increased levels of IFN-γ, IL-6, and IL-1β in BCG-infected human monocyte-derived macrophages (hMDMs) treated with bedaquiline. These results provide insight, and an in vitro proof-of-concept, that iron chelators may prove an effective adjunctive therapy in combination with current tuberculosis antimicrobials.

Almost 140 years after its discovery, tuberculosis remains the leading infectious cause of death globally. For half a century, patients with drug-sensitive and drugresistant tuberculosis have undergone long, arduous, and complex treatment processes with several antimicrobials that primarily function through direct bactericidal activity. Long-term utilization of these antimicrobials has been well-characterized and associated with numerous toxic side-effects. With the prevalence of drug-resistant strains on the rise and new therapies for tuberculosis urgently required, a more thorough understanding of these antimicrobials is a necessity. In order to progress from the "one size fits all" treatment approach, understanding how these antimicrobials affect mitochondrial function and bioenergetics may provide further insight into how these drugs affect the overall functions of host immune cells during tuberculosis infection. Such insights may help to inform future studies, instigate discussion, and help toward establishing personalized approaches to using such antimicrobials which could help to pave the way for more tailored treatment regimens. While recent research has highlighted the important role mitochondria and bioenergetics play in infected host cells, only a small number of studies have examined how these antimicrobials affect mitochondrial function and immunometabolic processes within these immune cells. This short review highlights how these antimicrobials affect key elements of mitochondrial function, leading to further discussion on how they affect bioenergetic processes, such as glycolysis and oxidative phosphorylation, and how antimicrobial-induced alterations in these processes can be linked to downstream changes in inflammation, autophagy, and altered bactericidal activity.

Tuberculosis (TB) remains a global health challenge. Patients with drug-sensitive and drug-resistant TB undergo long, arduous, and complex treatment regimens, often involving multiple antimicrobials. While these drugs were initially implemented based on their bactericidal effects, some studies show that TB antimicrobials can also directly affect cells of the immune system, altering their immune function. As use of these antimicrobials has been the mainstay of TB therapy for over fifty years now, it is more important than ever to understand how these antimicrobials affect key pathways of the immune system. One such central pathway, which underpins the immune response to a variety of infections, is immunometabolism, namely glycolysis and oxidative phosphorylation (OXPHOS). We hypothesise that in addition to their direct bactericidal effect on Mycobacterium tuberculosis (Mtb), current TB antimicrobials can modulate immunometabolic profiles and alter mitochondrial function in primary human macrophages. Human monocyte-derived macrophages (hMDMs) were differentiated from PBMCs isolated from healthy blood donors, and treated with four first-line and six second-line TB antimicrobials three hours post stimulation with either iH37Rv-Mtb or lipopolysaccharide (LPS). 24 h post stimulation, baseline metabolism and mitochondrial function were determined using the Seahorse Extracellular Flux Analyser. The effect of these antimicrobials on cytokine and chemokine production was also assayed using Meso Scale Discovery Multi-Array technology. We show that some of the TB antimicrobials tested can significantly alter OXPHOS and glycolysis in uninfected, iH37Rv-Mtb, and LPS-stimulated hMDMs. We also demonstrate how these antimicrobial-induced immunometabolic effects are linked with alterations in mitochondrial function. Our results show that TB antimicrobials, specifically clofazimine, can modify host immunometabolism and mitochondrial function. Moreover, clofazimine significantly increased the production of IL-6 in human macrophages that were stimulated with iH37Rv-Mtb. This provides further insight into the use of some of these TB antimicrobials as potential host-directed therapies in patients with early and active disease, which could help to inform TB treatment strategies in the future.

Background: The current standard of care for locally advanced esophageal adenocarcinoma (EAC) involves neo-adjuvant chemoradiation therapy (neo-CRT) followed by surgery. However, response to neo-CRT is poor and resistance remains a significant barrier to effective treatment. There are currently no clinical biomarkers to predict treatment response in EAC. Evidence supports a role for microRNA-34a (miR-34a) as a tumor suppressor in cancer, however, the role of miR-34a in the tumor response to therapy in EAC is largely unknown. Methods: Irradiation of EAC cell lines was performed using an Xstrahl RS225 X-ray irradiator at a clinically-relevant dose of 2 Gy. Radiosensitivity of EAC cell lines (OE33 P, OE33 R, OE33, OE19, Flo-1Par and Flo-1LM) was assessed by the gold standard clonogenic assay. miR-34a expression was assessed by qPCR. EAC tumor biopsies were obtained from consenting patients undergoing diagnostic endoscopy. Pathological response of the resected tumor was assigned by a pathologist using the Mandard Tumor Regression scale. miRTarBase and KEGG pathway analysis were used to identify predicted target genes and pathways of miR-34a. Results: miR-34a was demonstrated to be expressed in a panel of EAC cell lines (OE33 P, OE33 R, OE19, Flo-1Par and Flo-1LM cells). Interestingly, miR-34a expression was significantly decreased in EAC cell line models of both acquired radioresistance (OE33 R) and inherent radioresistance (OE19). miR-34a was also significantly decreased in a model of radioresistant metastatic EAC (Flo-1LM). Supporting in vitro data, in pre-treatment tumor biopsies from EAC patients (n=18), miR-34a was significantly decreased in patients having a subsequent poor pathological response to neo-CRT, when compared to patients having a good pathological response to neo-CRT. Target and pathway analysis demonstrated miR-34a-mediated regulation of genes and pathways associated with treatment resistance, including the complement system, cellular metabolism and p53 signaling, among others. Conclusion: Decreased miR-34a expression is associated with radioresistance across a panel of in vitro EAC models and in pre-treatment tumor biopsies from EAC patients having a poor pathological response to neo-CRT. This highlights a potential role for miR-34a as a novel biomarker predicting response to neo-CRT in EAC. Analysis of validated and predicted gene targets of miR-34a identified a number of pathways associated with treatment resistance. We are currently investigating the functional role of miR-34a in modulating tumor response to radiation in vitro to determine its potential as a novel therapeutic target to boost treatment response in EAC. Citation Format: Christina Cahill, Stephen G. Maher, Rebecca O'Brien, Wei-Lin Winnie Wang, John V. Reynolds, Jacintha O'Sullivan, Niamh Lynam-Lennon. Investigating the role of miRNA-34a in the resistance of esophageal adenocarcinoma to neoadjuvant chemoradiation therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3806.