Abstract B8: Targeting p21-activated kinases in human lung cancer

Abstract P21-activated kinases (PAKs) are important mediators of Rac and Cdc42 GTPase function as well as pathways required for Ras-driven tumorigenesis. PAKs have been implicated in signaling by growth factor receptors and morphogenetic processes that control cell polarity, invasion and actin cytoskeleton organization. To better understand the role of PAK1 in lung tumorigenesis, PAK1 genomic copy number and expression were determined for a panel of adenocarcinoma and squamous non-small cell lung cancers (NSCLC) and small cell lung cancers (SCLC). 64% of squamous NSCLC samples were positive for PAK1 expression and 52% of all cases showed staining of moderate (2+) or strong (3+) immunohistochemical intensity in the malignant cells. Nuclear localization of PAK1 was also evident in a significant proportion of squamous NSCLCs. Adjacent normal lung tissue did not express appreciable levels of PAK1. Selective PAK1 inhibition was associated with delayed cell cycle progression in vitro and in vivo. NSCLC cells were profiled using a library of pathway-targeted small molecule inhibitors and several synergistic combination therapies, including combination with antagonists of inhibitor of apoptosis (IAP) proteins, were revealed for PAK1. Dual inhibition of PAK1 and X chromosome-linked IAP (XIAP) efficiently increased effector caspase activation and apoptosis of NSCLC cells. Together, our results provide evidence for dysregulation of PAK1 in NSCLC and a role for PAK1 in cellular survival and proliferation in this indication.