Identification of short-form RON as a novel intrinsic resistance mechanism for anti-MET therapy in MET-positive gastric cancer

MAGOH promotes gastric cancer progression via hnRNPA1 expression inhibition-mediated RONΔ160/PI3K/AKT signaling pathway activation

BACKGROUND

Gastric cancer (GC) is associated with high mortality and heterogeneity and poses a great threat to humans. Gene therapies for the receptor tyrosine kinase RON and its spliceosomes are attracting increasing amounts of attention due to their unique characteristics. However, little is known about the mechanism involved in the formation of the RON mRNA alternative spliceosome RONΔ160.

METHODS

Fourteen human GC tissue samples and six normal gastric tissue samples were subjected to label-free relative quantitative proteomics analysis, and MAGOH was identified as a candidate protein for subsequent studies. The expression of MAGOH in clinical specimens was verified by quantitative real-time PCR and western blotting. We then determined the biological function of MAGOH in GC through in vitro and in vivo experiments. RNA pulldown, RNA sequencing and RNA immunoprecipitation (RIP) were subsequently conducted to uncover the underlying mechanism by which MAGOH regulated the formation of RONΔ160.

RESULTS

Proteomic analysis revealed that MAGOH, which is located at key nodes and participates in RNA processing and mRNA splicing, was upregulated in GC tissue and GC cell lines and was associated with poor prognosis. Functional analysis showed that MAGOH promoted the proliferation, migration and invasion of GC cells in vitro and in vivo. Mechanistically, MAGOH inhibited the expression of hnRNPA1 and reduced the binding of hnRNPA1 to RON mRNA, thereby promoting the formation of RONΔ160 to activate the PI3K/AKT signaling pathway and consequently facilitating GC progression.

CONCLUSIONS

Our study revealed that MAGOH could promote the formation of RONΔ160 and activate the PI3K/AKT signaling pathway through the inhibition of hnRNPA1 expression. We elucidate a novel mechanism and potential therapeutic targets for the growth and metastasis of GC based on the MAGOH-RONΔ160 axis, and these findings have important guiding significance and clinical value for the future development of effective therapeutic strategies for GC.

An Introduction and Overview of RON Receptor Tyrosine Kinase Signaling

RON is a receptor tyrosine kinase (RTK) of the MET receptor family that is canonically involved in mediating growth and inflammatory signaling. RON is expressed at low levels in a variety of tissues, but its overexpression and activation have been associated with malignancies in multiple tissue types and worse patient outcomes. RON and its ligand HGFL demonstrate cross-talk with other growth receptors and, consequentially, positions RON at the intersection of numerous tumorigenic signaling programs. For this reason, RON is an attractive therapeutic target in cancer research. A better understanding of homeostatic and oncogenic RON activity serves to enhance clinical insights in treating RON-expressing cancers.

Blocking Short-Form Ron Eliminates Breast Cancer Metastases through Accumulation of Stem-Like CD4+ T Cells That Subvert Immunosuppression

Immunotherapy has potential to prevent and treat metastatic breast cancer, but strategies to enhance immune-mediated killing of metastatic tumors are urgently needed. We report that a ligand-independent isoform of Ron kinase (SF-Ron) is a key target to enhance immune infiltration and eradicate metastatic tumors. Host-specific deletion of SF-Ron caused recruitment of lymphocytes to micrometastases, augmented tumor-specific T-cell responses, and nearly eliminated breast cancer metastasis in mice. Lack of host SF-Ron caused stem-like TCF1+ CD4+ T cells with type I differentiation potential to accumulate in metastases and prevent metastatic outgrowth. There was a corresponding increase in tumor-specific CD8+ T cells, which were also required to eliminate lung metastases. Treatment of mice with a Ron kinase inhibitor increased tumor-specific CD8+ T cells and protected from metastatic outgrowth. These data provide a strong preclinical rationale to pursue small-molecule Ron kinase inhibitors for the prevention and treatment of metastatic breast cancer.

SIGNIFICANCE

The discovery that SF-Ron promotes antitumor immune responses has significant clinical implications. Therapeutic antibodies targeting full-length Ron may not be effective for immunotherapy; poor efficacy of such antibodies in trials may be due to their inability to block SF-Ron. Our data warrant trials with inhibitors targeting SF-Ron in combination with immunotherapy. This article is highlighted in the In This Issue feature, p. 2945.

Short-form RON (sf-RON) enhances glucose metabolism to promote cell proliferation via activating β-catenin/SIX1 signaling pathway in gastric cancer

Recepteur d'origine nantais (RON) has been implicated in cell proliferation, metastasis, and chemoresistance of various human malignancies. The short-form RON (sf-RON) encoded by RON transcripts was overexpressed in gastric cancer tissues, but its regulatory functions remain illustrated. Here, we found that sf-RON promoted gastric cancer cell proliferation by enhancing glucose metabolism. Furthermore, sf-RON was proved to induce the β-catenin expression level through the AKT1/GSK3β signaling pathway. Meanwhile, the binding sites of β-catenin were identified in the promoter region of SIX1 and it was also demonstrated that β-catenin positively regulated SIX1 expression. SIX1 enhanced the promoter activity of key proteins in glucose metabolism, such as GLUT1 and LDHA. Results indicated that sf-RON regulated the cell proliferation and glucose metabolism of gastric cancer by participating in a sf-RON/β-catenin/SIX1 signaling axis and had significant implications for choosing the therapeutic target of gastric cancer.

Combination of HGF/MET-targeting agents and other therapeutic strategies in cancer

MET receptor has emerged as a druggable target across several human cancers. Agents targeting MET and its ligand hepatocyte growth factor (HGF) including small molecules such as crizotinib, tivantinib and cabozantinib or antibodies including rilotumumab and onartuzumab have proven their values in different tumors. Recently, capmatinib was approved for treatment of metastatic lung cancer with MET exon 14 skipping. In this review, we critically examine the current evidence on how HGF/MET combination therapies may take advantage of synergistic effects, overcome primary or acquired drug resistance, target tumor microenvironment, modulate drug metabolism or tackle pharmacokinetic issues. Preclinical and clinical studies on the combination of HGF/MET-targeted agents with conventional chemotherapeutics or molecularly targeted treatments (including EGFR, VEGFR, HER2, RAF/MEK, and PI3K/Akt targeting agents) and also the value of biomarkers are examined. Our deeper understanding of molecular mechanisms underlying successful pharmacological combinations is crucial to find the best personalized treatment regimens for cancer patients.

Targeting the HGF/MET Axis in Cancer Therapy: Challenges in Resistance and Opportunities for Improvement

Among hundreds of thousands of signal receptors contributing to oncogenic activation, tumorigenesis, and metastasis, the hepatocyte growth factor (HGF) receptor - also called tyrosine kinase MET - is a promising target in cancer therapy as its axis is involved in several different cancer types. It is also associated with poor outcomes and is involved in the development of therapeutic resistance. Several HGF/MET-neutralizing antibodies and MET kinase-specific small molecule inhibitors have been developed, resulting in some context-dependent progress in multiple cancer treatments. Nevertheless, the concomitant therapeutic resistance largely inhibits the translation of such targeted drug candidates into clinical application. Until now, numerous studies have been performed to understand the molecular, cellular, and upstream mechanisms that regulate HGF/MET-targeted drug resistance, further explore novel strategies to reduce the occurrence of resistance, and improve therapeutic efficacy after resistance. Intriguingly, emerging evidence has revealed that, in addition to its conventional function as an oncogene, the HGF/MET axis stands at the crossroads of tumor autophagy, immunity, and microenvironment. Based on current progress, this review summarizes the current challenges and simultaneously proposes future opportunities for HGF/MET targeting for therapeutic cancer interventions.

The Receptor Tyrosine Kinase RON and Its Isoforms as Therapeutic Targets in Ewing Sarcoma

The receptor tyrosine kinase (RTK) RON is linked to an aggressive metastatic phenotype of carcinomas. While gaining interest as a therapeutic target, RON remains unstudied in sarcomas. In Ewing sarcoma, we identified RON among RTKs conferring resistance to insulin-like growth factor-1 receptor (IGF1R) targeting. Therefore, we explored RON in pediatric sarcoma cell lines and an embryonic Tg(kdrl:mCherry) zebrafish model, using an shRNA-based approach. To examine RON–IGF1R crosstalk, we employed the clinical-grade monoclonal antibody IMC-RON8, alone and together with the IGF1R-antibody IMC-A12. RON silencing demonstrated functions in vitro and in vivo, particularly within micrometastatic cellular capacities. Signaling studies revealed a unidirectional IGF1-mediated cross-activation of RON. Yet, IMC-A12 failed to sensitize cells to IMC-RON8, suggesting additional mechanisms of RON activation. Here, RT-PCR revealed that childhood sarcomas express short-form RON, an isoform resistant to antibody-mediated targeting. Interestingly, in contrast to carcinomas, treatment with DNA methyltransferase inhibitor did not diminish but increased short-form RON expression. Thus, this first report supports a role for RON in the metastatic progression of Ewing sarcoma. While principal molecular functions appear transferrable between carcinomas, Ewing sarcoma and possibly more common sarcoma subtypes, RON highlights that specific regulations of cellular networks and isoforms require better understanding to successfully transfer targeting strategies.

Expression of the Short Form of RON/STK in Feline Mammary Carcinoma

RON is a tyrosine kinase receptor activated by the macrophage-stimulating protein (MSP) ligand that is overexpressed in human breast cancer. In humans, RON protein can be present in different isoforms, and the most studied isoform is represented by the short form of RON ( sf-RON), which is generated by an alternative promoter located in intron 10 of the RON complementary DNA (cDNA). It plays an important role in breast cancer progression. Considering the many similarities between feline mammary carcinoma (FMC) and human breast cancer, the aim of this study was to investigate the expression of both RON and MSP in FMCs and to identify the presence of the sf-RON transcript. Tissue samples of spontaneous mammary tumors were collected from 60 queens (10 benign lesions, 50 carcinomas). All of the samples were tested for RON and MSP expression by immunohistochemistry; moreover, RNA was extracted from paraffin-embedded tissue samples, and the cDNA was tested by reverse transcription-polymerase chain reaction (RT-PCR) to identify the presence of sf-RON. Immunohistochemistry detected the expression of RON and MSP in 34 of 50 (68%) and 29 of 50 (58%) FMCs, respectively. RT-PCR revealed the presence of the short-form in 18 of 47 (38%) FMCs. This form originates, as in humans, from an alternative promoter (P2), and it codes for the proper feline short form ( sf-RON). sf-RON expression was associated with poorly differentiated tumors and with a shorter disease-free ( P < .05; hazard ratio [HR], 2.2) period and a shorter survival ( P < .05; HR, 2.2). These results support FMC as a suitable model in comparative oncology and identify sf-RON expression as potential predictor of outcomes for this disease.

Efficacy prediction of targeted therapy for gastric cancer: The current status (Review)

Despite significant progress in the treatment of gastric cancer (GC), the prognosis remains poor and the mortality is high. Targeted drugs have been incorporated into routine treatment to improve treatment efficacy. However, the therapy response is still below 50%. Therefore, there is a need to identify predictive factors for patient response to a specific drug in order to improve the efficacy of drug therapy. The present article reviewed the predictive factors for target therapy in GC, including epidermal growth factor receptor, human epidermal receptor 2, vascular endothelial growth factor family, molecules in the mesenchymal‑epithelial transition pathway and the mammalian target of rapamycin. Additionally, the present review described the interactions between these molecules and signaling pathways.

Protocadherin-8 promotes invasion and metastasis via laminin subunit γ2 in gastric cancer

Growing evidence suggests that protocadherins (PCDH) play crucial roles in pathogenesis and progression of cancers, including gastric cancer (GC). Protocadherin‐8 (PCDH8) was previously reported to be involved in metastasis of GC, but functional studies yielded inconsistent results and the molecular mechanism remained unknown. The present study aimed to explore the clinical relevance, function and molecular mechanism of PCDH8 in GC. Data from the GEPIA and Kaplan–Meier plotter databases showed that high expression of PCDH8 was significantly correlated with poorer prognosis in GC. Ectopic expression of PCDH8 in GC cells promoted invasion and migration in vitro and metastasis in vivo, and knockdown of PCDH8 inhibited invasion and migration in vitro. RNA sequencing followed by gene set enrichment analysis found a remarkable enrichment in the extracellular matrix receptor interaction pathway, with the expression of laminin subunit γ2 (LAMC2) being significantly increased in the PCDH8‐overexpressing group. High expression of LAMC2 was significantly correlated to poor prognosis in GC in GEPIA database. Upregulation of LAMC2 following PCDH8 overexpression was further confirmed by immunohistochemistry in liver metastatic lesions of nude mice. To our knowledge, this is the first report of the metastasis‐enhancing property and molecular mechanism through upregulation of LAMC2 of PCDH8 in cancer. High expression of PCDH8 could be used as a biomarker for poor prognosis in clinical practice.

Depression accelerates the development of gastric cancer through reactive oxygen species‑activated ABL1 (Review)

Depression is a common symptom among gastric cancer (GC) patients and serves as a potential indication of poor prognosis and advanced cancer clinical stage. However, the molecular mechanism of depression‑associated poor prognoses of GC patients remains unclear. Recent studies have revealed that GC patients with depression are under high levels of oxidative stress (OS) status that is accompanied by the dysfunction of numerous proto‑oncogenes, including the ABL proto‑oncogene 1 (ABL1), which is a non‑receptor tyrosine kinase. Recent evidence indicates that ABL1 was dysregulated in both major depressive disorder (MDD) and cancer patients with depression, and high levels of reactive oxygen species (ROS) can lead to the activation of ABL1 in response to OS and that activated ABL1 subsequently contributes to development of GC via interactions with the downstream targets and corresponding signaling pathways. In this review, we examine the evidence to illuminate the molecular mechanism of ABL1 in the progression of GC patients with depression and identify out new and effective methods for the initial and long‑term treatment of GC.

Overexpression of suppressor of IKBKE 1 is associated with vincristine resistance in colon cancer cells

In a previous study, the suppressor of IKBKE 1 expression level was confirmed to be higher in vincristine (VCR)-resistant HCT-8 (HCT-8/V) colon cancer cells than in non-VCR-resistant HCT-8 cells. In the current study, IKBKE 1 expression in VCR-resistant colon cancer cells was investigated further. HCT-8 and HCT-8/V human colon cancer cells were used, and polymerase chain reaction (PCR) primers were designed to amplify the IKBKE 1 gene. Fluorescence reverse transcription-quantitative PCR (RT-qPCR) was performed to detect differences in IKBKE 1 expression between sensitive and drug-resistant colon cancer cell lines. Western blotting was performed to further observe IKBKE 1 expression. Based on the RT-qPCR and western blot results, IKBKE 1 expression was observed to be markedly higher in the HCT-8/V cells, and this difference was significant (P<0.05). Thus, IKBKE 1 expression was identified to be associated with the resistance of colon cancer cells to VCR.

Strategies of targeting the extracellular domain of RON tyrosine kinase receptor for cancer therapy and drug delivery

PURPOSE

Cancer is one of the most important life-threatening diseases in the world. The current efforts to combat cancer are being focused on molecular-targeted therapies. The main purpose of such approaches is based on targeting cancer cell-specific molecules to minimize toxicity for the normal cells. RON (Recepteur d'Origine Nantais) tyrosine kinase receptor is one of the promising targets in cancer-targeted therapy and drug delivery.

METHODS

In this review, we will summarize the available agents against extracellular domain of RON with potential antitumor activities.

RESULTS

The presented antibodies and antibody drug conjugates against RON in this review showed wide spectrum of in vitro and in vivo antitumor activities promising the hope for them entering the clinical trials.

CONCLUSION

Due to critical role of extracellular domain of RON in receptor activation, the development of therapeutic agents against this region could lead to fruitful outcome in cancer therapy.