Researchers at Harvard University are using Organs-on-Chips technology to develop human orthotopic lung cancer models.

Scientists at the Wyss Institute for Biologically Inspired Engineering led by Founding Director and Wyss Core Faculty member Donald Ingber have applied their human Organs-on-Chips technology to gain insight into the behavior of lung tumors and their response to different drugs. 

The researchers have taken their microchip models of the air-conducting small airway (Lung Airway Chips) and the oxygen and carbon dioxide-exchanging alveoli at the tips of the small airways (Alveolus Chip) in the lungs to develop human orthotopic lung cancer models. Specifically, they looked at adenocarcinoma, a form of non-small cell lung cancer (NSCLC) (~85% of all lung cancers are diagnosed as NSCLCs) that accounts for 40% of all NSCLCs. In humans, NSCLC adenocarcinoma cells initially appear at the interface between the lung’s small airways and alveoli, but the tumor then primarily grows within the alveolar structures.

The two chips have been combined to model the basic tissue architecture and functionalities of these two lung regions. Different types of lung cells are located in one of two microchannels that run parallel through the chip. The two channels are separated by a thin porous membrane from a microvessel. In the second channel, this membrane is lined with human lung endothelium cells. As a result, the small airway epithelium is thicker, stiffer and covered with moving cilia, while the thinner alveolar epithelium is more permeable to enable efficient gas exchange. The latter is exposed to cyclic mechanical deformations to mimic breathing motions in the chip, and cell culture medium is continuously passed through the vascular channel to mimic blood flow.

When NSCLC adenocarcinoma cells were grown in the two chips, the cells grew rapidly in the microengineered alveolar microenvironment but remained quiescent in the Airway Chip, which is similar to the behavior of these tumor cells in the human lung. Co-plating and injection strategies were developed to allow stable integration of a small number of NSCLC cells into the two lung chips.

“This approach allows us to recreate key hallmarks of this cancer, including its growth and invasion patterns, and to determine how they are influenced by cues from surrounding normal cells. In the Airway Cancer Chips, cancer cells remained dormant for up to 12 days before they started to grow, while in Alveolar Cancer Chips they commence their growth much more rapidly, and once they reach a critical mass, they separate themselves and invade the endothelium as part of their metastatic process,” said first author Bryan Hassell, Ph.D., who as a Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) Graduate Student on Ingber’s team developed the lung cancer-on-a-chip platform.

Added Ingber, who is also the Judah Folkman Professor of Vascular Biology at HMS and the Vascular Biology Program at Boston Children’s Hospital, as well as Professor of Bioengineering at SEAS: “Our lung cancer-on-chip platforms can model central aspects of orthotopic NSCLC in real time and high-resolution, and much more closely than other in vivo and in vitro approaches. They offer a literal window on the biological tumor complexities.” said Ingber.

For instance, the researchers found that application of cyclic mechanical forces to the lung epithelial channel to mimic breathing motions led to inhibition of cancer cell growth and invasion. The scientists believe that growth of lung cancer cells in lung alveoli reduces their natural motion, which then allows faster growth and more invasive behavior.

The researchers also looked at the impact of cyclical mechanical motion on the sensitivity of NSCLC cells to a tyrosine kinase inhibitor (TKI) anti-cancer drug that targets frequently mutated enzymes, including epidermal growth factor receptor (EGFR). Current TKIs often lose their potency because cancer cells can produce EGFR variants that are not affected by them.

In the Alveolar Cancer Chip, the growth and spread of NSCLC cells resistant to a first-generation TKI was halted using a third-generation TKI when breathing motions were absent, such as would be the case if large tumors that fill the alveoli. They did, however, continue to grow slowly when breathing motions were present. However, in breathing mode, they become impervious to the drug and continue to survive and grow slowly, essentially creating cancer ‘persister’ cells that are known to be the nemesis of cancer therapy.

“The effects of breathing motions on cancer cell behavior in our models could explain how tumor cells, which remain from a shrinking tumor after therapy, could become persister cells, able to defy drug therapy, linger and eventually cause the cancer to relapse. Our orthotopic in vitro platform thus could be well-suited for dissecting how these persister cells arise, and they may be a useful tool in future drug development efforts that aim to eradicate them,” said Ingber.