Recepteur d'Origine Nantais known as RON is a member of the receptor tyrosine kinase (RTK) superfamily which has recently gained increasing attention as cancer target for therapeutic intervention. The aim of this work was to perform an alignment-independent three-dimensional quantitative structure-activity relationship (3D QSAR) study for a series of RON inhibitors. A 3D QSAR model based on GRid-INdependent Descriptors (GRIND) methodology was generated using a set of 19 compounds with RON inhibitory activities. The generated 3D QSAR model revealed the main structural features important in the potency of RON inhibitors. The results obtained from the presented study can be used in lead optimization projects for designing of novel compounds where inhibition of RON is needed.

Background: RON (Recepteur d′Origine Nantais) receptor tyrosine kinase is a promising target for anti‐cancer therapeutics. The aim of this study was to identify new RON inhibitors using virtual screening methods. Methods: To this end, a ligand‐based virtual screening approach was employed for screening of ZINC database on the homology model of RON receptor. All the selected hits were inspected in terms of drug‐likeness, ADME properties, and toxicity profiles. Ligand‐based similarity searches along with further filtering criteria led to the identification of two compounds, TKI1 and TKI2 that were evaluated using in vitro cell‐based RON inhibition assays. Results: The results showed that TKI1 and TKI2 could reduce phosphorylation of RON. Both compounds showed inhibitory activity of the downstream mTOR pathway with no apparent effects on other signaling mediators in a dose‐dependent manner. Conclusion: These compounds can provide a basis for developing novel anti‐RON inhibitors applicable to cancer therapy using medicinal chemistry‐oriented optimization strategies.

The cover image is based on the Research Article A potential signaling axis between RON kinase receptor and hypoxia-inducible factor-1 alpha in pancreatic cancer by Akihisa Kato et al., https://doi.org/10.1002/mc.23339.

The Cancer Genome Atlas (TCGA) of a pancreatic cancer cohort identified high MST1R (RON tyrosine kinase receptor) expression correlated with poor prognosis in human pancreatic cancer. RON expression is null/minimal in normal pancreas but elevates from pan-in lesions through invasive carcinomas. We report using multiple approaches RON directly regulates HIF-1 alpha, a critical driver of genes involved in cancer cell invasion and metastasis. RON and HIF-1 alpha are highly co-expressed in the 101 human PDAC tumors analyzed and RON expression correlated with HIF-1 alpha expression in a subset of PDAC cell lines. knockdown of RON expression in RON positive cells blocked HIF-1 alpha expression, whereas ectopic RON expression in RON null cells induced HIF-1 alpha expression suggesting the direct regulation of HIF-1 alpha by RON kinase receptor. RON regulates HIF-1 alpha through an unreported transcriptional mechanism involving PI3 kinase-mediated AKT phosphorylation and Sp1-dependent HIF-1 alpha promoter activity leading to increased HIF-1 alpha mRNA expression. RON/HIF-1 alpha modulation altered the invasive behavior of PDAC cells. A small-molecule RON kinase inhibitor decreased RON ligand, MSP-induced HIF-1 alpha expression, and invasion of PDAC cells. Immunohistochemical analysis on RON knockdown orthotopic PDAC tumor xenograft confirmed that RON inhibition significantly blocked HIF-1 alpha expression. RON/HIF-1 alpha co-expression also exists in triple-negative breast cancer cells, a tumor type that also lacks molecular therapeutic targets. This is the first report describing RON/HIF-1 alpha axis in any tumor type and is a potential novel therapeutic target.

Malignant pleural mesothelioma (MPM) is an aggressive inflammatory cancer with a poor survival rate. Treatment options are limited at best and drug resistance is common. Thus, there is an urgent need to identify novel therapeutic targets in this disease in order to improve patient outcomes and survival times. MST1R (RON) is a trans-membrane receptor tyrosine kinase (RTK), which is part of the c-MET proto-oncogene family. The only ligand recognized to bind MST1R (RON) is Macrophage Stimulating 1 (MST1), also known as Macrophage Stimulating Protein (MSP) or Hepatocyte Growth Factor-Like Protein (HGFL). In this study, we demonstrate that the MST1-MST1R (RON) signaling axis is active in MPM. Targeting this pathway with a small molecule inhibitor, LCRF-0004, resulted in decreased proliferation with a concomitant increase in apoptosis. Cell cycle progression was also affected. Recombinant MST1 treatment was unable to overcome the effect of LCRF-0004 in terms of either proliferation or apoptosis. Subsequently, the effect of an additional small molecular inhibitor, BMS-777607 (which targets MST1R (RON), MET, Tyro3, and Axl) also resulted in a decreased proliferative capacity of MPM cells. In a cohort of MPM patient samples, high positivity for total MST1R by IHC was an independent predictor of favorable prognosis. Additionally, elevated expression levels of MST1 also correlated with better survival. This study also determined the efficacy of LCRF-0004 and BMS-777607 in xenograft MPM models. Both LCRF-0004 and BMS-777607 demonstrated significant anti-tumor efficacy in vitro, however BMS-777607 was far superior to LCRF-0004. The in vivo and in vitro data generated by this study indicates that a multi-TKI, targeting the MST1R/MET/TAM signaling pathways, may provide a more effective therapeutic strategy for the treatment of MPM as opposed to targeting MST1R alone.

New fused bicyclic lactam head groups as rigidified analogs of thieno[3,2-b]pyridine-based kinase inhibitor LCRF-0004 were designed and synthesized. Depending on the functionalities and the size of these bicyclic head groups, potent inhibitors of RON tyrosine kinase with various level of selectivity against c-Met tyrosine kinase were obtained.

New heteroarylcarboxamide head groups substituted with two aromatic rings analogs of thieno[3,2-b]pyridine-based kinase inhibitor LCRF-0004 were designed and synthesized. Potent inhibitors of RON tyrosine kinase with various level of selectivity for c-Met RTK were obtained.

Despite breakthroughs in the clinical development of tyrosine kinase inhibitors, challenges remain in overcoming resistance to these molecular targeted therapies. Advances in our understanding of mechanisms of resistance to targeted agents will improve patient outcome. While secondary mutations play a key role, the activation of parallel signaling pathways has been shown to alter the sensitivity to targeted inhibition. Resistance to inhibitors of the EGFR or VEGFR families may occur through the activation of Met, EphA2 and Axl receptor tyrosine kinase pathways, suggesting combined inhibition of these targets as a strategy to prevent resistance to approved EGFR- and VEGFRs -targeted therapies. We have developed a novel multitargeted receptor tyrosine kinase inhibitor, MG516, with nanomolar activities in in vitro enzymatic assays against members of the Eph receptor family, Axl, Met and VEGFR1,2,3. In carcinoma cell lines, MG516 potently inhibits phosphorylation of EphA2, Axl and Met. Inhibition of Met downstream signaling as well as the inhibition of Met-dependent biological endpoints, such as motility and wound healing is also achieved. In human umbilical vein endothelial cells (HUVECs),VEGFR2 activation and VEGF-dependent angiogenesis are blocked. Potent anti-tumor activity is demonstrated across a broad range of human xenograft models including lung, gastric, glioblastoma, colorectal and breast carcinomas. Anti-tumor activity is achieved at oral doses as low as 2.5mg/kg in the absence of overt toxicity, weight loss or myelosuppression. Immunohistochemistry analyses of xenograft tumors after treatment with MG516 reveal a decrease in the proliferation of tumor cells, a decrease in tumor vascularization, pharmacodynamic inhibition of target phosphorylation and decreases in target expression, including EphA2. Consistent with targeting multiple oncogenic pathways simultaneously, the combination of MG516 with EGFR inhibition results in improved tumor growth inhibition. Importantly, in a gastric cancer model exhibiting resistance to sunitinib following prolonged treatment with this agent, MG516 induces tumor regression. Thus, MG516 offers potential for clinical development of a novel therapeutic, by targeting a combination of oncogenic kinases involved in tumor development, progression and resistance to targeted therapies. Citation Format: Normand Beaulieu, Helene Sainte-Croix, Claire Bonfils, Michael Mannion, Stephane Raeppel, Lubo Isakovic, Stephen Claridge, Oscar Saavedra, Franck Raeppel, Arkadii Vaisburg, James Wang, Marielle Fournel, Jeffrey M. Besterman, Christiane R. Maroun. Preclinical characterization of MG516, a novel inhibitor of receptor tyrosine kinases involved in resistance to targeted therapies. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 930. doi:10.1158/1538-7445.AM2013-930

A novel series of N-(3-(6-substituted-aminopyridin-3-yloxy)phenyl)-2-oxo-3-phenylimidazolidine-1-carboxamides targeting TrkA receptor tyrosine kinase was identified. SAR study of the series allowed us to design and synthesize compounds possessing inhibitory activity of TrkA kinase enzyme in the low nanomolar range with low residual activity against c-Met and with no significant activity against VEGFR2.