Calu is related to the Calu-3 human lung adenocarcinoma cell line. These cells express the cystic fibrosis transmembrane conductance regulator and several acinar cell markers, form polarized monolayers with tight junctions, and have robust cAMP-stimulated anion transport, which is essential for airway fluid secretion, humidifying inspired air, and mucociliary transport [2]. They are also used to study drug-related properties like pulmonary permeability, drug-drug interactions, and aerosol deposition [3,7].

In recent research, Calu-3 cells have been used to develop 3D in vitro lung models. These cells, when assembled onto the CellFate® matrix, present angiotensin-converting enzyme-2 (ACE-2) activity, which is relevant for understanding diseases such as COVID-19 [1]. Additionally, studies on Calu-3 cells have explored the effects of various substances. For example, quercetin improves and protects Calu-3 airway epithelial barrier function, while TNF-α causes a multiphasic compromise of this barrier function [4,6]. The transport of nicotine across Calu-3 cell monolayers has also been investigated, showing that it is influenced by nicotine salts and flavor additives in e-liquids [5].

In conclusion, Calu-3 cells serve as a valuable in vitro model for studying multiple biological processes relevant to the respiratory system, including anion secretion, airway barrier function, and the pathophysiology of diseases like COVID-19. Research using these cells helps in understanding disease mechanisms and developing safer and more effective inhaled therapeutics.