Waiting to Inhale
Safety Assessment
Clive Roper

Waiting to Inhale

New research could advance the expanding field of in vitro inhalation toxicology

For those of us who suffer from asthma or chronic obstructive pulmonary disease—and there are millions of us—the standard way we take our medicine is by inhaling it. This action directly delivers the drug to the lungs.

Inhaled drugs are localized to the target organ, which generally allows for a lower dose than is necessary with oral or injectable drugs, and thus fewer and less severe adverse effects. 

Animal models—primarily rodents—are widely-used in the development of inhalation therapies. No clinical trial can proceed without knowing how the drug performed in animals. But cell cultures and 3D models are also an indispensable tool because they can help us to predict the drug responses observed. 

The cell culture technology has been developing almost at breakneck speed in recent years. From the century-old process of culturing cells in a Petri dish and then watching the cells grow and multiply, we are now in the midst of a 3D revolution where the cells are structured together in a more physiological way. 3D models are significantly re-shaping how we study cancer, heart disease and metabolic disease.

In the research of respiratory diseases, we have 3D models of the human airway that recapitulate the typical characteristics of our own breathing environment, such as the tight juncture proteins, ciliated cells, basal cells and mucous traps that make up the airway epithelium.

It’s not a perfect analogy, but I liken it to going from the 2D version to the IMAX Digital version of Avatar or Star War; one is able to observe cells that form the front line of defense against respiratory toxins with much greater resolution, and, in our case, identify specific liabilities that indicate a high risk of airway toxicity or predict a nontoxic starting dose for in vivo studies.

Our laboratory in Edinburgh currently uses two 3D human-derived reconstructed airway tissue models (EpiAirway and MucilAir) for measuring toxicity or assessing efficacy of inhalable chemicals or drugs. Using these 3D tissue models, we have identified, tested and routinely use specific markers of toxicity associated with epithelial damage. These human tissue models have been used in support of our 3Rs program by helping us to design better animal inhalation toxicology tests or as replacement of the animal tests in occupational toxicology risk assessment.

But it gets better. We are now in the process of evaluating a novel Charles River CD rat derived in vitro airway model, in partnership with MatTek, for in vitro to in vivo extrapolation. This key new model now provides us with full translation from rat in vitro and rat in vivo to “normal” human in vitro to “diseased human in vitro to better predict what may happen to patients in the clinic.

We have selected 14 chemicals with a range of known respiratory toxicity including not toxic. MatTek have supplied human and rat EpiAirway tissues for testing. The chemicals are applied to the tissue units, incubated at physiological temperature for 3 hours, washed and left to recover incubated at physiological temperature for 21 hours. The tissues are then assessed for cytotoxicity and histology endpoints. In order to understand the reproducibility of the assay, this will be performed on three separate occasions.

This work, which is being supported by a grant from Charles River’s Innovation Fund, will bring us even closer to an apples-to-apples comparison of animal and human data, and put us in an even better position of meeting our commitment of reducing, refining and replacing research animals in our experiments.