Cancer Cell Biology Training Program

Currently, there are few medical options for patients diagnosed with pancreatic ductal adenocarcinoma (PDAC), which itself boasts only a 5% survival rate two years after initial diagnosis.  PDAC is particularly unique in its mutational profile; nearly 100% of these tumors contain an activating K-Ras mutation necessary for tumor initiation and maintenance [1].  Consequently, there is considerable research interest in delineating the roles and mechanisms of K-Ras activation in PDAC, to help foster the goal of developing anti-K-Ras inhibitors for PDAC treatment.  A recent study from the Settleman group found that some pancreatic cancers were dependent on mutant KRASfor survival [2].  However, the mechanistic underlying of this K-Ras dependency has yet to be elucidated. 

Presently, there is support for the importance of five key effectors for Ras-mediated oncogenesis:  the Raf serine/threonine protein kinase, the class I PI3K lipid kinases, and guanine nucleotide exchange factors for Ral (RalGEF), Rac (Tiam1) and Rap (PLC epsilon) small GTPases [3].  For my studies, I will focus on determining the role of each effector pathway in K-Ras dependency. To accomplish this, I will utilize a panel of K-Ras mutant PDAC cell lines to validate and extend the K-Ras dependency described by Singh et al [2].  A number of different techniques will be employed to measure K-Ras dependency including apoptosis, cell proliferation, invasion, and anchorage-independent growth.  In order to accomplish these studies we will use two well-verified stable RNAis to deplete all PDAC cell lines of K-Ras.  Second, I will determine whether any one activated effector will phenocopy mutant K-Ras and hence, render K-Ras mutant tumor cells K-Ras independent.  Once a specific effector pathway has been validated, we will further dissect the specific components of that pathway necessary for K-Ras dependency.  Should a candidate target within the effector pathway be identified, we will investigate possible pharmacologic methods of blocking target function.  Additionally, mouse models will be used to further investigate our initial in vitro findings in a more physiological setting.  We will use mouse orthotopic xenograft tumors to assess our ability to prevent K-Ras signaling via occlusion of the designated effector pathway.  Thus my goals for the next year entail applying state-of-the art methodologies to mechanistically dissect how mutant Ras drives aberrant cancer growth.               

References:

• Bardeesy N. and DePinho R.A. (2002). Pancreatic Cancer Biology and Genetics. Nature Reviews Cancer 2:897-909.
  
  
• Singh A., Greninger P., Rhodes D., Koopman L., Violette S., Bardeesy N., Settleman J. (2009). A gene expression signature associated with "K-Ras addiction" reveals regulators of EMT and tumor cell survival. Cancer Cell 2;15:489-500.
  
  
• Yeh, J.J., and Der, C.J. (2007). Targeting signal transduction in pancreatic cancer treatment. Expert Opin. Ther. Targets 11: 673-694.

1. Figure 1. Ras effector signaling cascades.