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NC3Rs: National Centre for the Replacement Refinement & Reduction of Animals in Research
CRACK IT Challenge

Differentiating alveolar macrophage responses to inhaled medicines

Inhalation Translation

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  • Replacement


The Inhalation Translation CRACK IT Challenge project team has created a website to share the 3Rs protocols for improved toxicity assessment of inhaled therapies developed through the project. Find out more on the King's College website.

Chronic inflammatory diseases of the airways, such as asthma and chronic obstructive pulmonary disease (COPD), remain areas of considerable unmet medical need. Few new drugs have made it to the clinic during the past 50 years, with many that perform well in preclinical animal studies failing in humans owing to lack of safety and/or efficacy. The failure to translate promising drug candidates from animal studies and other preclinical assays to humans has led to questions about the utility and relevance of current preclinical models and demand for more predictive tools. Animals (mainly rodents) are pre-dosed with candidate drugs and then exposed to a pro-inflammatory challenge (e.g. lipopolysaccharides (LPS)). Lung biopsies or lavage are then examined at defined time points to assess both anti-inflammatory efficacy and toxicity of the compound. This process has a number of limitations and uses a significant number of animals.

One of the difficulties in assessing inhaled drugs in toxicity studies is the alveolar macrophage response and its relevance to safe dosing in the clinic. One characteristic of inhaled dry powder toxicity studies is the appearance of foamy macrophages (FM), but it is unclear if this is due to general particulate overload or a pharmacologically-driven adverse event. This is further complicated when subtle changes in macrophage numbers, appearance and activation are observed, as they may represent an adaptive response to the dosed material, or the initial stages of an adverse health effect. The inability to discriminate between such responses triggers additional in vivo assessments to determine whether there are secondary consequences of FM appearance, such as inflammation, to make go/no-go decisions on candidate drugs. To improve inhaled drug development, a better understanding is required of FM biology, the influence of different macrophage phenotypes on other lung cells and species differences. This knowledge base would reduce costly and repetitive toxicological studies in animals required to optimise safe doses.

The team, led by Prof Ben Forbes of KCL are focused in the development of novel technologies for assessing alveolar macrophage modulation and inflammatory responses during regulatory safety testing of new inhaled medicines. Outcomes will include important new insights into macrophage responses (including species differences) based on in vitro and enhanced, in vivo evaluations which require fewer animals. ‘Foamy’ macrophage (FM) responses are commonly observed during nonclinical development, but are difficult to interpret. They have shown that the FM presentation can be modelled in vitro, differentiated using an FM toolkit which was developed in pilot studies, and characterised based on functional and phenotypic responses (temporal and dose-related) to different materials. Based on these high-throughput methods, they will develop predictive algorithms to prevent unsuitable compounds entering nonclinical testing. Biomarkers and further insights into macrophage responses will be sought using (i) state-of-the-art (and beyond) mass spectroscopy imaging of single cells and tissue slices, (ii) targeted transcriptomics/toxicological pathway analysis, (iii) parallel evaluation of two non-invasive monitoring techniques for longitudinal studies: exhaled breath analysis and CT imaging. These approaches have been selectively combined by an expert multi-disciplinary consortium which, with the advice and in-kind contributions of industry sponsors, will deliver a high-value solution to the Inhalation Translation Challenge. Commercialisation of the technologies will ensure their widespread availability to reduce animal use whilst improving the amount and in vivo usefulness of data from mandatory testing. Vigorous stakeholder engagement will ensure the Challenge solutions have industry and regulatory acceptance and are disseminated effectively.

Full details about this CRACK IT Challenge can be found on the CRACK IT website.


Forbes, B (2018). Research activities following a Drugns in the Lungs Network workshop on induced alveolar macrophage responses. Inhalation Magazine

Hoffman E et al. (2017). Morphometric Characterization of Rat and Human Alveolar Macrophage Cell Models and their Response to Amiodarone using High Content Image Analysis. Pharm. Res. 34 (12): 2466-2476, DOI 10.1007/s11095-017-2176-5.

Hoffman E et al. (2015). In Vitro Multiparameter Assay Development Strategy toward Differentiating Macrophage Responses to Inhaled Medicines. Mol. Pharmaceutics 12 (8), pp 2675–2687, DOI: 10.1021/acs.molpharmaceut.5b00048.