Pancreatic cancer is the most deadly cancer type, with just an 8% 5-year survival. The most common subtype, pancreatic ductal adenocarcinoma (PDAC), is typified by the nearly universal KRAS mutational activation (~95%), followed by loss of the tumor suppressor CDKN2A (~95%), which encodes INK4A, an endogenous inhibitor of the CDK4/6 cell-cycle regulatory proteins. Loss of CDKN2A activity is a major step in KRAS- mediated PDAC tumorigenesis. KRAS and INK4A cooperate to accelerate PDAC metastatic development, in part, by converging to block RB tumor suppressor activity. While no anti-KRAS targeted therapies have reached the clinic, inhibitors of CDK4/6 are clinically approved. With the loss of CDKN2A being critical to allow KRAS-driven PDAC progression, restoration of CDKN2A function via pharmacologic inhibition of CDK4/6 should be an effective anti-KRAS therapeutic strategy. My preliminary results suggest that CDK4/6 inhibitors may benefit patient outcome in PDAC, especially in combination with ERK inhibitors, which block the most critical KRAS effector signaling pathway. Therefore, I propose to pre-clinically validate CDK4/6 inhibitors for anti-cancer activity, to discover synergistic combinations with other pharmacologic agents, and to identify potential resistance mechanisms which may limit their clinical effectiveness.
In Specific Aim 1, I will validate CDK4/6 inhibitors alone and with ERK inhibitors for PDAC therapy by determining the short and long-term cellular consequences of inhibition in two-dimensional culture, three-dimensional organoid culture, and in vivo mouse models. To identify novel and clinically actionable small molecule inhibitors which sensitize resistant cell lines to CDK4/6 inhibitors, I will use high-throughput combinatorial compound screens in Aim 2 to identify compounds that synergistically enhance CDK4/6 inhibitor activity, and I will establish the mechanistic basis of synergy. Finally, in Aim 3, I will apply the Cancer Toolkit gain-of-function and a CRISPR/Cas9 loss-of-function genetic functional screens to identify novel mechanisms of resistance to CDK4/6 inhibition and will fully validate promising hits using pharmacologic and molecular biology techniques. These genetic screens will suggest small molecule combination therapy to overcome de novo or acquired CDK4/6 inhibitor resistance. In summary, my studies will make novel findings on CDK4/6 as cancer drivers and as therapeutic targets. To complete these studies, I will apply state-of-the-art methods that will provide me with training that will establish my expertise in all facets of anti-cancer drug discovery. Finally, my findings may be rapidly transitioned to clinical evaluation and will hopefully accelerate the development of new therapies for this deadly cancer.
Pancreatic cancer is typified by a nearly universal activation of the KRAS oncogene, and experimental studies show that if the aberrant functions of KRAS can be stopped, pancreatic cancer growth will be abruptly halted. Unfortunately, despite more than three decades of effort, no effective anti-KRAS therapies have reached the patient. In this proposal, I will validate a new approach: that inhibitors of the CDK4 and CDK6 proteins, which are activated by KRAS signaling, are an effective pancreatic cancer therapy, and I will use small molecule and genetic screens to identify novel combination strategies and potential clinical resistance mechanisms to CDK4/6 inhibition.
