UCLA

Lung cancer is the leading cause of cancer death in the United States and the world. The most effective therapy is surgical resection, but lung cancer recurs in approximately 50% of patients, most commonly as metastatic disease. This suggests that micrometastatic disease is often already present at the time of surgery, but below current levels of clinical detection. This is consistent with the reports of circulating tumor cells (CTCs) in patients with Stage I non-small cell lung cancer (NSCLC). Although metastatic behavior is often considered a late event, these clinical findings suggest that the metastatic process is also operative early in the pathogenesis of the disease. These clinical observations are consistent with recent laboratory-based investigations indicating that dissemination may occur during early tumor development. Furthermore, recent studies implicate the genetic program associated with epithelial-mesenchymal transition (EMT) in driving early metastatic behavior during pancreatic premalignancy. Herein we demonstrate that common NSCLC-associated mutations (p53 loss and KRAS activating mutation) and over-expression of Snail, a driver of the EMT program, results in enhanced motility in non-transformed human bronchial epithelial cells (HBECs). In analyzing motility at the single-cell level, great heterogeneity in velocity was unveiled; over an order of magnitude difference between the fastest and slowest moving cell exists. Our overarching hypothesis is that there are factors attributed to highly motile cells that extend beyond speed, particularly enhanced metastasis. We developed a novel selection technique involving migration through microporous membranes, and we successfully isolated cells with the highest and lowest migratory capacity. And while it is widely believed that cell migration is a transient and stochastic event, we show the intrinsic and heritable nature of this behavior. Concomitant with changes in migration were changes in biophysical properties such as cell volume, ability to spread, and deformability. Highly migratory and deformable cells also show increased survival in a murine model of metastasis, overcoming a crucial juncture in metastatic inefficiency first described by Leonard Weiss and observed by many others in the field. At the molecular level, highly migratory cells show increased activation of Rac1, a Rho-family GTPase involved in actin polymerization and cell motility. Pharmacological inhibition of Rac1 decreases motility in highly migratory cells. Inhibition of RhoA, a negative regulator of Rac1, enhances motility in both highly migratory and non-migratory HBECs. Highly migratory cells form fewer and smaller colonies than unselected counterparts in an anchorage-independent growth assay. However, cells within colonies formed by micropore-selected cells move rapidly, whereas cells in unselected colonies remain stationary. This corroborates a "grow or go" phenotype described by others.

Metastasis is the predominate cause of cancer death in patients, and while tumor formation is attributed to uncontrolled cell growth, metastasis is more related to aberrant cell motility and deformability. Although a tumor is made up of many cancer cells, only a small percentage of these cells are metastatic. The work included in this dissertation has important implications in determining the mechanisms behind aberrant lung epithelial cell motility in both early and late stages of the disease, and provides the foundation for future research that may lead to preventative therapeutic approaches to thwart these processes.