MNK Inhibition Sensitizes KRAS-Mutant Colorectal Cancer to mTORC1 Inhibition by Reducing eIF4E Phosphorylation and c-MYC Expression

KRAS-mutant colorectal cancers are resistant to therapeutics, presenting a significant problem for ∼40% of cases. Rapalogs, which inhibit mTORC1 and thus protein synthesis, are significantly less potent in KRAS-mutant colorectal cancer. Using Kras-mutant mouse models and mouse- and patient-derived organoids, we demonstrate that KRAS with G12D mutation fundamentally rewires translation to increase both bulk and mRNA-specific translation initiation. This occurs via the MNK/eIF4E pathway culminating in sustained expression of c-MYC. By genetic and small-molecule targeting of this pathway, we acutely sensitize KRASG12D models to rapamycin via suppression of c-MYC. We show that 45% of colorectal cancers have high signaling through mTORC1 and the MNKs, with this signature correlating with a 3.5-year shorter cancer-specific survival in a subset of patients. This work provides a c-MYC-dependent cotargeting strategy with remarkable potency in multiple Kras-mutant mouse models and metastatic human organoids and identifies a patient population that may benefit from its clinical application. SIGNIFICANCE: KRAS mutation and elevated c-MYC are widespread in many tumors but remain predominantly untargetable. We find that mutant KRAS modulates translation, culminating in increased expression of c-MYC. We describe an effective strategy targeting mTORC1 and MNK in KRAS-mutant mouse and human models, pathways that are also commonly co-upregulated in colorectal cancer.This article is highlighted in the In This Issue feature, p. 995.

Abstract LB-B32: Modulation of the Hedgehog signaling pathway in models of basal cell carcinoma by ATP-competitive PKCi inhibitors

We will describe for the first time the optimization and pharmacological characterisation of azaquinazoline based ATP-competitive inhibitors of the aPKC isoforms. The serine/threonine kinase protein kinase C iota (PKCι) and protein kinase C zeta (PKCζ) together define the atypical sub-class of the protein kinase C superfamily (aPKC). Both isoforms have emerged as master regulators of cellular polarity with PKCι implicated in the maintenance of aberrant Hedgehog (HH) pathway activity in basal cell carcinoma (BCC). Common activating mutations in the HH signalling pathway drive BCC growth through the transcription factor GLI. Inhibitors of membrane protein smoothened (SMO) are clinically effective suppressors of HH signalling in BCC. However, acquired and de novo resistance to SMO inhibitors poses severe limitations to the clinical use of these agents. PKCι has been shown to directly activate GLI1 in BCC and has been linked to SMO inhibitor resistance making a strong case for the development of a selective PKCι inhibitor. Insights from structural biology identified critical amino acid residues in the PKCι binding pocket that could be exploited through structure-based drug design to optimise inhibitor potency and selectivity over structurally related kinase targets. The phosphorylation status of the known PKCι proximal substrate LLGL2 was used as a cellular pharmacodynamic biomarker and to demonstrate in vivo PKCι inhibition. To investigate the effects of PKCι inhibitors on the HH pathway a panel of compounds covering a diversity of chemotypes were profiled using a Hedgehog pathway GLI1 reporter assay in an engineered NIH3T3 cell line. Murine and human BCC cells, dependent on HH signalling for survival, were sensitive to PKCι inhibitor treatment with concomitant dose and time dependent effects on the expression of the HH pathway activity biomarker GLI1. Taken together, these results have therapeutic implications making a strong case for further evaluation of PKCι inhibitors in the setting of SMO-inhibitor-resistant BCC cancers.

Citation Format: Jon Roffey, Christian Dillon, Anthony E. Oro, Amar N. Mirza, Kavita Y. Sarin, Sumaira Z. Aasi, Peter J. Parker, Philippe Riou, Caroline Barton, Bhavisha Patel, Caroline Barton, Andrew Turnbull, Emma Stanway, Katherine Fowler, Gregory Ott, Mark Ator. Modulation of the Hedgehog signaling pathway in models of basal cell carcinoma by ATP-competitive PKCi inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B32.

Abstract LB-99: Identification and characterization of small molecule thieno[3,2-d]pyrimidine inhibitors of Protein Kinase C iota (PKCι)

We describe a novel series of small molecule ATP-competitive inhibitors of the atypical class of Protein Kinase C (PKC). The PKC family of serine/threonine kinases are divided into four structurally and functionally distinct sub-types: classic (PKCα, PKCβ, PKCγ); novel (PKCδ, PKCε, PKCη, PKCθ); atypical (PKCι,PKCζ); and PKNs (PKN1, PKN2, PKN3). The PKCs have been defined as key regulators in a multitude of signal transduction pathways that impinge on diverse cellular processes such as proliferation, differentiation, and survival. The regulation and functions of the atypical PKCs are distinct from the classic and novel PKCs.Both atypical isoforms have been implicated in various models of cancer, and PKCι in particular has been described as a potential oncogene. Its abundance is frequently increased, primarily through PKCι gene amplification, in many epithelial tumours including: subsets of squamous non-small cell lung carcinoma, serous ovarian carcinoma, and squamous esophageal carcinoma. It has been widely demonstrated that deregulation of PKCι signalling leads to unconstrained cell growth, increased migratory and invasive behaviour, and aberrant cellular polarity, which is a hallmark of aggressive cancers. Together, these data make a strong case for the inhibition of PKCι as a novel therapeutic strategy. We have discovered a series of ATP-competitive thieno[3,2-d]pyrimidine- based PKCι inhibitors from a high throughput screen. Using structure-based design we have optimized the series and demonstrated potent and selective inhibition of PKCι in biochemical and cellular models. The biochemical, structural, and cellular characterization of these compounds will be described herein.

Citation Format: Christelle Soudy, Emma Stanway, Bhavisha Patel, Caroline Barton, Michelle Barnard, Leon Pang, Paul Owen, Andrew Turnbull, Bruce A. Ruggeri, Bruce D. Dorsey, Mark A. Ator, Greg R. Ott, Mark Linch, Philippe Riou, Peter J. Parker, Sven Kjaer, Christian Dillon, Neil Q. McDonald, Jon Roffey. Identification and characterization of small molecule thieno[3,2-d]pyrimidine inhibitors of Protein Kinase C iota (PKCι). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-99. doi:10.1158/1538-7445.AM2014-LB-99