An organoid platform to study alveolar stem cells in lung generation and cancer

Abstract

Lung adenocarcinoma (LADC) remains the most common and lethal cancer type worldwide. Although recent breakthroughs using a new class of immune-modulatory therapeutics have improved patient survival in the clinic, the majority still invariably succumb to this disease, highlighting the importance of improving treatment strategies. A wide variety of models have been developed to study LADC. Cell line- and transplant-based models offer rapid and flexible platforms for discovering and testing novel therapeutics using patient-derived specimens. On the other hand, genetically engineered mouse models (GEMMs) recapitulate key aspects of human LADC including initiation from normal pulmonary epithelial cells and progression into a malignant state. The development of organoid technology has revolutionized the way we model cancer and a vast number of other biological phenomena.

Organoids are cultured miniature organs derived from normal adult stem cells that display self-renewal, differentiation capacity and remarkable genetic stability. These features have facilitated the creation of next generation cancer models that combine the best features of their predecessors. The alveolar type 2 (AT2) cell represents the most prominent cell-of-origin of LADC. These cells serve as stem cells in the adult lung to support tissue turnover during homeostasis and regeneration after injury. They accomplish this by self-renewing and differentiating into alveolar type 1 (AT1) cells. Using organoid technology, we have developed an improved system to cultivate alveolar organoids from normal murine lungs. We demonstrated that these organoids are positive for AT2 and AT1 markers and completely lack expression of basal and club cell makers. Critically, we observed long-term proliferative potential in these organoids.

Using this improved culture system, we generated organoid models of LADC, representing three distinct molecular subclasses of this disease. We found that Kras-, Braf-, and Alk-mutant organoids with Trp53 deficiency displayed mitogen independent growth in vitro. Most strikingly, Krasmutant Trp53-inactivated organoids orthotopically transplanted into immunocompetent recipient mice formed tumors that displayed histopathological characteristics of human LADC. Taken together, the work presented here demonstrates the power of organoid technology for building clinically relevant and experimentally flexible cancer models.