Smoking Kills Human Lung Small Airway on a Chip Video
Channel: Ali Hassan Memon
Date: 22/12/2017

Highlights
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Organ-on-a-chip technology recapitulates human cancer growth and invasion patterns

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Physiological breathing motions suppress cancer cell growth and invasion

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Tumor cells become resistant to drug therapy without breathing motions

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This model permits analysis of cancer persister cells in vitro


Summary
Here, we show that microfluidic organ-on-a-chip (organ chip) cell culture technology can be used to create in vitro human orthotopic models of non-small-cell lung cancer (NSCLC) that recapitulate organ microenvironment-specific cancer growth, tumor dormancy, and responses to tyrosine kinase inhibitor (TKI) therapy observed in human patients in vivo. Use of the mechanical actuation functionalities of this technology revealed a previously unknown sensitivity of lung cancer cell growth, invasion, and TKI therapeutic responses to physical cues associated with breathing motions, which appear to be mediated by changes in signaling through epidermal growth factor receptor (EGFR) and MET protein kinase. These findings might help to explain the high level of resistance to therapy in cancer patients with minimal residual disease in regions of the lung that remain functionally aerated and mobile, in addition to providing an experimental model to study cancer persister cells and mechanisms of tumor dormancy in vitro.

Introduction
Development of improved cancer therapeutics requires better experimental models (Hackam and Redelmeier, 2006). To meet this challenge, animal researchers have moved away from conventional subcutaneous implants because they do not mimic organ-specific differences in cancer growth or responses to therapy observed in patients (Fidler et al., 1994). Instead, human tumor xenografts are often implanted in mice at the “orthotopic” organ site from which the tumors were derived (Killion et al., 1999; Gould et al., 2015). These in vivo orthotopic cancer models better mimic tumor growth and metastasis; however, when using these models, it still remains extremely difficult to identify contributions of the microenvironment to tumor growth or visualize cancer cell behaviors over time, and the organ-specific microenvironment is still not human. Thus, there has been a search for in vitro models of human cancer that might provide an alternative approach.

A key challenge in developing in vitro cancer models is that static 2D cultures primarily promote high rates of cancer cell proliferation, whereas tumors can exhibit varying levels of growth and differentiation when growing in human organs in vivo, and growth properties and drug responses can significantly differ based on the organ-specific microenvironment. As a result, most drug development programs result in discovery of therapeutics that inhibit proliferation, whereas it is extremely difficult to test for drugs that kill persister cells within dormant cancers, or tumors in different growth or differentiation states. While more complex in vitro human cancer models have been developed that permit study of various tumor responses (e.g., growth, migration, invasion, angiogenesis, extravasation, and drug effects) (Choi et al., 2015; Skardal et al., 2015; Portillo-Lara and Annabi, 2016), none of these recapitulate complex organ-level patterns of cancer growth or therapeutic responses seen in patients. We therefore set out to develop human-based in vitro orthotopic cancer models utilizing organ-on-a-chip (organ chip) technology. Organ chips are microfluidic cell culture devices created with microchip manufacturing methods that contain continuously perfused hollow microchannels inhabited by living cells arranged to simulate organ-level pathophysiology. By recapitulating the multicellular architectures, tissue-tissue interfaces, chemical gradients, mechanical cues, and vascular perfusion of the body, these devices produce levels of tissue and organ functionality not possible with conventional 2D or 3D culture systems (Bhatia and Ingber, 2014). We previously described a human lung alveolus chip containing two microfluidic channels separated by a porous extracellular matrix (ECM)-coated membrane lined on one side by human alveolar epithelial cells and pulmonary microvascular endothelium on the other, which mimics multiple normal lung functions (infection-induced recruitment of immune cells, breathing-induced absorption of nano-particulates and associated inflammation, interleukin-2 (IL-2)-induced pulmonary edema, inflammation-induced pulmonary thrombosis, etc.) as well as response to drug therapies observed in vivo (Huh et al., 2010, 2012; Jain et al., 2017). We also developed a similar 2-channel lung small airway chip lined by human bronchiolar epithelial cells interfaced with lung endothelium that recapitulates small airway structure and functions, including normal mucociliary clearance, cytokine production in response to infection, and changes in transcriptome when exposed to cigarette smoke (Benam et al., 2016a, 2016b).