Abstract 1873: The role of p21-activated kinase 4 (PAK4) in cancer stemness and epithelial-to-mesenchymal transition

Abstract

Abstract The p21-activated kinase 4 (PAK4) is a key downstream effector of the Rho family GTPases. PAK4 is found to be over-expressed in many oncogenic Ras-driven cancers and cell lines but not in their normal counterparts. Mesenchymal pancreatic ductal adenocarcinoma (PDAC) stem cells (CSCs) that are triple positive for stemness markers (CD133+, CD44+, and EpCam+) as well as Ras and snail transduced human mammary epithelial cells (HMLER-snail) showed enhanced expression of PAK4 along with activation of Rho, Rac1 and CDC42. PAK4 RNA interference resulted in disruption of PDAC CSC spheroids, reduction of mesenchymal markers (i.e. vimentin and snail) and suppression of CSCs potential to form subcutaneous tumors in mice. These findings point to a novel role of PAK4 in promoting oncogenic Ras-driven EMT and stemness. Using PDAC CSCs (MiaPaCa-2 and L3.6pl) and human mammary epithelial cells (HMECs) that are transduced with Ras and the EMT promoter snail (HMLE-Snail and HMLER-Snail), we investigated the impact of PAK4 allosteric modulators [PAMs (KPT-7189, KPT-7523, KPT-9274 and KPT-9307)] on the reversal of EMT and stemness. The toxicity and efficacy of PAMs were evaluated in vitro and in multiple sub-cutaneous xenograft models. PAMs show anti-proliferative activity in vitro against different PDAC CSCs and HMECs while sparing normal cells. Cell growth inhibition was concurrent with apoptosis induction, suppression of colony formation and reversal of mesenchymal morphology to epithelial (MET). PAMs not only reduced PAK4 RNA and protein steady state levels but also inhibited proliferative and anti-apoptotic signals downstream of PAK4. PAMs caused suppression of EMT markers (EpCAM, vimentin and snail) and re-expression of an epithelial promoter E-cadherin. PAM treatment inhibited RhoA, Rac1 and CDC42 activation in GLISA assays. KPT-9274 showed remarkable anti-tumor activity in sub-cutaneous xenograft models of CSCs and residual tumors showed suppression of EMT markers that was concurrent with inhibition of PAK4 signaling. These studies open a novel therapeutic opportunity against EMT and cancer stem cells through PAK4 inhibition. Citation Format: Asfar S. Azmi, Irfana Muqbil, Amro Aboukameel, William Senapedis, Erkan Baloglu, Yosef Landesman, Sharon Shacham, Michael Kauffman, Philip A. Philip, Ramzi M. Mohammad. The role of p21-activated kinase 4 (PAK4) in cancer stemness and epithelial-to-mesenchymal transition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1873.