Research Overview of Project 3

Combination Inhibition of ERK for Pancreatic Cancer Treatment

The KRAS oncogene is mutated in ~95% of pancreatic ductal adenocarcinoma (PDAC). There is considerable experimental evidence that continued expression of mutant KRAS is essential for PDAC maintenance. It is generally accepted that an effective anti-KRas therapy will have a significant impact on pancreatic cancer, with inhibition of KRAS effector signaling considered the most promising direction for advancement to the clinic. In particular, considerable effort and interest is now focused on inhibitors of the Raf-MEK-ERK mitogen-activated protein kinase (MAPK) cascade.

Project 3
Project 3: Inhibitors of the Raf-MEK-ERK protein kinase cascade. A, Inhibitors of the Raf-MEK-ERK protein kinase cascade. Shown are inhibitors of each step of the cascade that are currently under clinical evaluation as compiled from Representative ERK substrates that will be used as biomarkers to monitor the effect of BVD-523 on ERK signaling are shown. B, Raf inhibitors cause the paradoxical activation of ERK in RAS-mutant cancer cells. C, Mechanisms that drive de novo or acquired resistance to MEK inhibitors. Multiple resistance mechanisms (*) can cause reactivation of ERK downstream from the inhibitor block point have been identified. ERK-independent mechanisms (e.g., the activation of phosphoinositide 3-kinase/AKT serine/threonine kinase/mammalian target of rapamycin signaling) can also overcome the dependency of cancer cells on ERK. D, BVD-523 structure. BVD-523 is a highly potent (ERK1 Ki, <300 pM; ERK2 Ki = 40 pM) and selective (> 1,000-fold vs. CDK1, CDK2, CDK5, CDK6, GSK3B; >10,000-fold vs. 70 other kinases) ATP-competitive protein kinase inhibitor.

However, Raf and MEK inhibitors have shown limited-to-no efficacy in RAS-mutant cancers, due primarily to cancer cell adaptation and ERK reactivation to overcome the inhibitor action. These findings have prompted the development of ERK inhibitors, with four inhibitors recently entering clinical evaluation. Among them, BVD-523, a small molecule that targets ERK1 and ERK2 in the sub-nanomolar range, is the leading compound entering oncology clinical trials (NCT01781429). The innovation of our studies is our focus on a first-in-class direct inhibitor of ERK and applying unbiased genetic and chemical library screens to identify combination therapies to overcome limitations for its use for PDAC.

Project 3 includes four aims to advance the clinical development of BVD-523 for PDAC treatment:

Aim 1: Clinically evaluate BVD-523 anti-tumor activity and biomarkers of response in patients with PDAC

Aim 2: Identify molecular mechanisms for acquired resistance to BVD-523 in KRAS-mutant PDAC

Aim 3: Identify combination inhibitor approaches that overcome de novo resistance and render BVD-523 treatment cytotoxic

Aim 4: Assess combination inhibitor strategies with BVD-523 for anti-tumor activity in state-of-the-art organoid culture and mouse models of pancreatic cancer

Project 3’s goal is to identify combinations that overcome de novo and acquired resistance, as well as cytostatic and transient responses and normal tissue toxicity, for future clinical evaluation. When completed, our study will have identified predictive biomarkers for ERK treatment response, allowing us to identify the most effective ERK combinations to be tested in clinical studies.