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.

A Novel Small-Molecule Inhibitor of MRCK Prevents Radiation-Driven Invasion in Glioblastoma

Glioblastoma (GBM) is an aggressive and incurable primary brain tumor that causes severe neurologic, cognitive, and psychologic symptoms. Symptoms are caused and exacerbated by the infiltrative properties of GBM cells, which enable them to pervade the healthy brain and disrupt normal function. Recent research has indicated that although radiotherapy (RT) remains the most effective component of multimodality therapy for patients with GBM, it can provoke a more infiltrative phenotype in GBM cells that survive treatment. Here, we demonstrate an essential role of the actin-myosin regulatory kinase myotonic dystrophy kinase-related CDC42-binding kinase (MRCK) in mediating the proinvasive effects of radiation. MRCK-mediated invasion occurred via downstream signaling to effector molecules MYPT1 and MLC2. MRCK was activated by clinically relevant doses per fraction of radiation, and this activation was concomitant with an increase in GBM cell motility and invasion. Furthermore, ablation of MRCK activity either by RNAi or by inhibition with the novel small-molecule inhibitor BDP-9066 prevented radiation-driven increases in motility both in vitro and in a clinically relevant orthotopic xenograft model of GBM. Crucially, treatment with BDP-9066 in combination with RT significantly increased survival in this model and markedly reduced infiltration of the contralateral cerebral hemisphere.Significance: An effective new strategy for the treatment of glioblastoma uses a novel, anti-invasive chemotherapeutic to prevent infiltration of the normal brain by glioblastoma cells.Cancer Res; 78(22); 6509-22. ©2018 AACR.

Abstract 1933: A novel small molecule inhibitor of MRCK shows utility in blocking radiation induced invasion of glioblastoma cells in vitro and in vivo

Myotonic dystrophy kinase-related CDC42-binding kinases MRCKα and MRCKβ regulate actin-myosin contractility and are members of the AGC family of serine/threonine kinases. MRCKs are closely related to the Rho-regulated ROCK kinases, which is reflected in their shared abilities to phosphorylate a similar set of substrates, including myosin II light chain proteins (MLC) and myosin phosphatase target subunit 1 (MYPT1). However, MRCK and ROCK may phosphorylate these substrates at different subcellular localisations leading to diverging effects on cell invasion and migration.

Glioblastoma (GBM) is an aggressive and incurable primary brain tumor. Patients are treated with surgery, radiotherapy and chemotherapy but prognosis remains poor, with a median survival of 15 months. Complete surgical resection of GBM is difficult because these tumours are frequently invasive. Recent research has indicated that, while radiotherapy extends life expectancy of patients, it can provoke a more infiltrative phenotype in those GBM cells that survive treatment.

We have developed potent and selective small molecule MRCK inhibitors exemplified by BDP-9066, which inhibits pMLC in a selective cellular assay with an EC50 28.3 nM, whilst displaying high selectivity over ROCK1 where the EC50 10.6 µM. This compound, and others in the series, have been used in numerous cellular assay systems to demonstrate that MRCK inhibition suppresses the invasion and migration of cancer cells including, breast, skin SCC and glioblastoma.

We have used BDP-9066 to demonstrate that MRCK inhibition is effective at perturbing radiation-induced migration of GBM cells in culture at concentrations that block phosphorylation of MLC. Using a clinically relevant intracranial mouse model that recapitulates key histological features of the disease, we have shown that BDP-9066 inhibits the invasion of G7 GBM cells into the contralateral hemisphere of the brain. These experiments highlight the potential utility of MRCK inhibition in the treatment of GBM in patients.

Citation Format: Heather J. McKinnon, Joanna Birch, Laura McDonald, Mairi Sime, Daniel Croft, Diane Crighton, Martin Drysdale, Lesley Gilmore, Christopher Gray, Jennifer Konczal, Duncan McArthur, Patricia McConnell, Mokdad Mezna, Alexander Schuettelkopf, Karen Strathdee, Justin Bower, Michael F. Olson, Anthony J. Chalmers. A novel small molecule inhibitor of MRCK shows utility in blocking radiation induced invasion of glioblastoma cells in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1933.

Liver X receptor agonism promotes articular inflammation in murine collagen-induced arthritis

OBJECTIVE

Liver X receptors (LXRs) have previously been implicated in the regulation of inflammation and have, in general, been ascribed an antiinflammatory role. This study was therefore undertaken to explore the biologic mechanisms of LXRs in vivo and in vitro in an experimental inflammatory arthritis model.

METHODS

Male DBA/1 mice were immunized with type II collagen and treated from an early or established stage of arthritis with 2 different concentrations of the LXR agonists T1317 and GW3965 or vehicle control. The mice were monitored for articular inflammation and cartilage degradation by scoring for clinical signs of arthritis, histologic examination of the joints, and analysis of serum cytokine and antibody levels. In vitro, primary human monocytes and T cells were cultured in the presence of GW3965 or T1317, and the concentrations of proinflammatory cytokines were measured by multiplex assay.

RESULTS

Contrary to expectations, LXR agonism with the use of 2 discrete, specific molecular entities led to substantial exacerbation of articular inflammation and cartilage destruction in this murine collagen-induced arthritis model. This was associated ex vivo with elevated cytokine expression, with enhanced Th1 and Th17 cellular responses, and with elevated collagen-specific autoantibody production. In vitro, LXR agonists, in concert with lipopolysaccharide, promoted cytokine and chemokine release from human monocytes, and similar effects were observed in a T cell-macrophage coculture model that closely recapitulates the pathways that drive synovial cytokine release.

CONCLUSION

Since LXRs are present in rheumatoid arthritis (RA) synovium, these results suggest that LXR-mediated pathways could exacerbate the chronic inflammatory response typical of RA.

Delayed Recovery of Receptor-Mediated Functional Responses to Acetylcholine in Mouse Isolated Carotid Arteries following Endothelial Denudation in vivo

The time-course of endothelial regrowth and functional recovery following polytetrafluoroethylene filament-induced endothelial denudation in vivo was studied in the left common carotid artery of the mouse. This technique does not result in any intimal hyperplasia, enabling the investigation of endothelial function without any confounding effect of intimal thickening. Endothelial coverage was assessed histologically, and functional recovery was assessed as restoration of receptor-mediated, endothelium-dependent relaxation to acetylcholine in vitro. Re-endothelialization of the carotid artery was complete within 8 days of denudation. However, relaxations to acetylcholine, which are mediated by endothelium-derived nitric oxide, were only partially restored 10 days after the procedure. At this time point, arterial responses to either phenylephrine, the receptor-independent endothelium-dependent dilator cyclopiazonic acid, or the nitric oxide donor diethylamine NONOate, were not significantly different to controls. At 25 days after denudation, acetylcholine-evoked responses remained significantly depressed compared to controls but at 90 days full recovery was observed. These data indicate that following mechanical denudation of the mouse carotid artery, although endothelial re-growth is complete within 8 days, recovery of endothelial cell function - assessed as the ability of the regenerated endothelium to mediate acetylcholine-stimulated relaxation - remains impaired for a prolonged period.