Discovery of 2,6-Naphthyridine Analogues as Selective FGFR4 Inhibitors for Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the most common type of liver cancer and is responsible for 90% of cases. Approximately 30% of patients diagnosed with HCC are identified as displaying an aberrant expression of fibroblast growth factor 19 (FGF19)-fibroblast growth factor receptor 4 (FGFR4) as an oncogenic-driver pathway. Therefore, the control of the FGF19-FGFR4 signaling pathway with selective FGFR4 inhibitors can be a promising therapy for the treatment of HCC. We herein disclose the design and synthesis of novel FGFR4 inhibitors containing a 2,6-naphthyridine scaffold. Compound 11 displayed a nanomolar potency against Huh7 cell lines and high selectivity over FGFR1-3 that were comparable to that of fisogatinib (8) as a reference standard. Additionally, compound 11 demonstrated remarkable antitumor efficacy in the Huh7 and Hep3B HCC xenograft mouse model. Moreover, bioluminescence imaging experiments with the orthotopic mouse model support that compound 11 can be considered a promising candidate for treating HCC.

Discovery of N-(4-((6-(3,5- Dimethoxyphenyl)-9H-purine derivatives as irreversible covalent FGFR inhibitors.

Fibroblast growth factor receptor (FGFR) is an attractive target for cancer therapy, but existing FGFR inhibitors appear to hardly meet the demand for clinical application. Herein, a number of irreversible covalent FGFR inhibitors were designed and synthesized by selecting several five- and six-membered azaheterocycles as parent scaffold with different substituents to take over the hydrophobic region in the active pocket of FGFR proteins. Among the resulting target compounds, III-30 showed the most potent effect on enzyme activity inhibition and anti-proliferative activity against the tested cancer cell lines. Significantly, III-30 could inhibit the enzyme activity by achieving irreversible covalent binding with FGFR1 and FGFR4 proteins. It could also regulate FGFR-mediated signaling pathway and mitochondrial apoptotic pathway to promote cancer cell apoptosis and inhibit cancer cell invasion and metastasis. Moreover, III-30 had a good metabolic stability and showed relatively potent anti-tumor activity in the MDA-MB-231 xenograft tumor mice model.

Discovery of novel FGFR4 inhibitors through a build-up fragment strategy.

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death. FGFR4 has been implicated in HCC progression, making it a promising therapeutic target. We introduce an approach for identifying novel FGFR4 inhibitors by sequentially adding fragments to a common warhead unit. This strategy resulted in the discovery of a potent inhibitor, 4c, with an IC50 of 33 nM and high selectivity among members of the FGFR family. Although further optimisation is required, our approach demonstrated the potential for discovering potent FGFR4 inhibitors for HCC treatment, and provides a useful method for obtaining hit compounds from small fragments.

Development of Highly Potent and Selective Covalent FGFR4 Inhibitors Based on SNAr Electrophiles.

Fibroblast growth factor receptor 4 (FGFR4) is thought to be a driver in several cancer types, most notably in hepatocellular carcinoma. One way to achieve high potency and isoform selectivity for FGFR4 is covalently targeting a rare cysteine (C552) in the hinge region of its kinase domain that is not present in other FGFR family members (FGFR1-3). Typically, this cysteine is addressed via classical acrylamide electrophiles. We demonstrate that noncanonical covalent "warheads" based on nucleophilic aromatic substitution (SNAr) chemistry can be employed in a rational manner to generate highly potent and (isoform-)selective FGFR4 inhibitors with a low intrinsic reactivity. Key compounds showed low to subnanomolar potency, efficient covalent inactivation kinetics, and excellent selectivity against the other FGFRs, the kinases with an equivalent cysteine, and a representative subset of the kinome. Moreover, these compounds achieved nanomolar potencies in cellular assays and demonstrated good microsomal stability, highlighting the potential of SNAr-based approaches in covalent inhibitor design.

FGFR4 and EZH2 inhibitors synergistically induce hepatocellular carcinoma apoptosis via repressing YAP signaling.

BACKGROUND: Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide, but current treatment options remain limited and cause serious life-threatening side effects. Aberrant FGFR4 signaling has been validated as an oncogenic driver of HCC, and EZH2, the catalytic subunit of the PRC2 complex, is a potential factor that contributes to acquired drug resistance in many tumors, including HCC. However, the functional relationship between these two carcinogenic factors, especially their significance for HCC treatment, remains unclear. In this study, we systematically evaluated the feasibility of a combination therapy targeting FGFR4 and EZH2 for HCC. METHODS: RNA sequencing data of patients with Liver hepatocellular carcinoma (LIHC) from The Cancer Genome Atlas (TCGA) were analyzed to determine FGFR4 and EZH2 expression and their interaction with prognosis. Moreover, the HCC cell lines, zebrafish/mouse HCC xenografts and zebrafish HCC primary tumors were treated with FGFR4 inhibitor (Roblitinib) and/or EZH2 inhibitor (CPI-169) and then subjected to cell proliferation, viability, apoptosis, and tumor growth analyses to evaluate the feasibility of combination therapy for HCC both in vitro and in vivo. Furthermore, RNA-Seq was performed in combination with ChIP-Seq data analysis to investigate the critical mechanism underlying the combination treatment with Roblitinib and CPI-169. RESULTS: EZH2 accumulated through the non-canonical NF-kB signaling in response to FGFR4 inhibitor treatment, and the elevated EZH2 levels led to the antagonism of HCC against Roblitinib (FGFR4 inhibitor). Notably, knockdown of EZH2 sensitized HCC cells to Roblitinib, while the combination treatment of Roblitinib and CPI-169 (EZH2 inhibitor) synergistically induced the HCC cell apoptosis in vitro and suppressed the zebrafish/mouse HCC xenografts and zebrafish HCC primary tumors development in vivo. Moreover, Roblitinib and CPI-169 synergistically inhibited HCC development via repressing YAP signaling. CONCLUSIONS: Collectively, our study highlighted the potential of the therapeutic combination of FGFR4 and EZH2 inhibitors, which would provide new references for the further development of clinical treatment strategies for HCC.

Design, Synthesis, and Biological Evaluation of 2-Formyl Tetrahydronaphthyridine Urea Derivatives as New Selective Covalently Reversible FGFR4 Inhibitors.

Aberrant FGF19/FGFR4 signaling is an oncogenic driver force for the development of human hepatocellular carcinoma (HCC). A series of 2-formyl tetrahydronaphthyridine urea derivatives were designed and synthesized as new covalently reversible inhibitors of FGFR4. The representative compound 9ka exhibited an IC50 value of 5.4 nM against FGFR4 and demonstrated extraordinary kinome selectivity. Compound 9ka also exhibited good oral pharmacokinetic properties with an AUC(0-t) value of 38 950.06 h·ng/mL, a T1/2 value of 3.06 h, and an oral bioavailability of 50.97%, at an oral dose of 25 mg/kg in Sprague-Dawley (SD) rats. Furthermore, compound 9ka induced significant tumor regressions in a xenograft mouse model of Hep3B2.1-7 HCC cell line without an obvious sign of toxicity upon 30 mg/kg oral administration. Compound 9ka may serve as a promising lead compound for further anticancer drug development.

BLU-554, A selective inhibitor of FGFR4, exhibits anti-tumour activity against gastric cancer in vitro.

BACKGROUND: Fibroblast growth factor receptor 4 (FGFR4) plays a key role in cancer progression, including tumour proliferation, invasion, and metastasis. Recent studies have shown that the FGFR4 selective inhibitor BLU-554 has clinical benefits on tumour regression in hepatocellular carcinoma patients. However, the effect of BLU-554 on gastric cancer remains unknown. METHODS: Changes in cell proliferation, apoptosis and cell cycle, migration, and invasion capabilities of MKN-45 cells treated with FGFR4 selective inhibitors were detected by CCK-8 assay, flow cytometry, transwell assay, and wound healing assay, respectively. Western blotting was used to detect the effect of BLU-554 on the expression of FGFR4, FRS2α, and p-ERK1/2. RESULTS: As the concentration of the inhibitor increased, the survival rate of gastric cancer cells decreased, and the trend of BLU-554 was more obvious; a high dose of BLU-554 caused significant cell apoptosis and cell cycle arrest as well as reduced cell invasion ability. The expression levels of FGFR4, FRS2α, and p-ERK1/2 were also significantly reduced when cells were treated with medium and high doses of BLU-554. CONCLUSION: BLU-554 inhibited the mitogen-activated protein kinase (RAS-RAF-MEK-ERK) pathway by inhibiting FGFR4, ultimately impeding the proliferation and invasion of gastric cancer cells and promoting cell apoptosis and cell cycle arrest.

Design, synthesis and biological evaluation of quinazoline derivatives as potent and selective FGFR4 inhibitors.

Aberrant activation of the fibroblast growth factor 19-fibroblast growth factor receptor 4 (FGF19-FGFR4) signaling pathway has been proved to promote hepatocellular carcinoma (HCC) proliferation. It is assumed that the first FGFR4 inhibitor BLU9931 did not enter clinical studies, presumably due to its rapid metabolism in liver microsomes. Here, we report the development of series of quinazoline derivatives based on FGFR4 inhibitor BLU9931 through structural modification of its solvent region pocket to minimize its potential metabolic liability. Among them, compound 35a exhibited comparable or superior kinase inhibitory activity (IC50 = 8.5 nM) and selectivity in cells. More importantly, compound 35a improved liver microsomes stability compared to BLU9931. Cellular mechanistic studies demonstrated that 35a induced apoptosis via the FGFR4 signaling pathway blockage. In addition, the computational simulation revealed the possible binding mode to FGFR4 protein, which provides a plausible explanation of high potent and metabolic stability.

Dual inhibition of FGFR4 and BCL-xL inhibits multi-resistant ovarian cancer with BCL2L1 gain.

AIM: Overexpression of BCL2L1 (BCL-xL) was associated with platinum resistance in ovarian cancer (OvCa). However, role of copy number (CN) gain of BCL2L1 in OvCa remains elusive. METHODS: In silico analyses of multiple public datasets were perform. Validation was carried out in our tissue microarray (TMA) of OvCa cases. In vitro and in vivo assays was performed to explore potential targeted compound against BCL2L1-gained OvCa. RESULTS: BCL2L1 was gained in ~60% of OvCa. BCL2L1 was differentially expressed between healthy and cancerous ovarian cases. BCL2L1 gain was not prognostic either in overall or in progression-free survival but higher BCL2L1 expression was associated with worsened survival, indicating biological distinction between CN gain and overexpression of the gene. BCL2L1 gain was associated with multi-resistance to various drug with no significant sensitivity to any single agent. Only CRISPR-mediated BCL2L1 knockout, but not shRNA could be inhibitive. Combined genetic silencing of FGFR4/NCAM and BCL2L1 with shRNA induced potent inhibition of BCL2L1-gained OvCa with durable effect. Combined inhibition of FGFR/BCL-xL was required for inhibiting BCL2L1-gained OvCa in vitro and in vivo. Only dual inhibition of FGFR/BCL-xL without platinum was tolerable in vivo. CONCLUSION: Gain of BCL2L1 is associated with resistance to multiple anti-cancer agents in OvCa. Dual inhibition of FGFR4 and BCL-xL showed potent effect and tolerable toxicity, holding promise to further translation.

Aberrant FGFR4 signaling worsens nonalcoholic steatohepatitis in FGF21KO mice.

Background: Nonalcoholic steatohepatitis (NASH) is the most severe form of non-alcoholic fatty liver disease (NAFLD) and a potential precursor of hepatocellular carcinoma (HCC). In our previous studies, we found that endocrine fibroblast growth factor 21 (FGF21) played a key role in preventing the development of NASH, however, the FGF15/19 mediated-FGFR4 signaling worsened NASH and even contributed to the NASH-HCC transition. The aim of this study is to determine whether FGF15/FGFR4 signaling could alleviate or aggravate NASH in the FGF21KO mice. Methods: NASH models were established in FGF21KO mice fed with high fat methionine-choline deficient (HFMCD) diet to investigate FGF15/FGFR4 signaling during early stage NASH and advanced stage NASH. Human hepatocytes, HepG2 and Hep3B cells, were cultured with human enterocytes Caco-2 cells to mimic gut-liver circulation to investigate the potential mechanism of NASH development. Results: Significant increase of FGF15 production was found in the liver of the NASH-FGF21KO mice, however the increased FGF15 protein was unable to alleviate hepatic lipid accumulation. In contrast, up-regulated FGF15/19/FGFR4 signaling was found in the FGF21KO mice with increased NASH severity, as evident by hepatocyte injury/repair, fibrosis and potential malignant events. In in vitro studies, blockage of FGFR4 by BLU9931 treatment attenuated the lipid accumulation, up-regulated cyclin D1, and epithelial-mesenchymal transition (EMT) in the hepatocytes. Conclusion: The increased FGF15 in NASH-FGF21KO mice could not substitute for FGF21 to compensate its lipid metabolic benefits thereby to prevent NASH development. Up-regulated FGFR4 signaling in NASH-FGF21KO mice coupled to proliferation and EMT events which were widely accepted to be associated with carcinogenic transformation.

GZD824 overcomes FGFR1-V561F/M mutant resistance in vitro and in vivo.

Abnormallyactivated FGFR1 has been validated as a therapeutic target for differentcancers. Although a variety of FGFR inhibitors have shown benefit in manyclinical patients with FGFR1 aberration, FGFR1 mutant resistance such as V561Mmutation, has been reported. To date however, no FGFR inhibitors have beenapproved to treat patients with FGFR mutant resistance. Herein, we report that GZD824, athird generation ABL inhibitor (Phase II, China), overcomes FGFR1-V561F/M mutant resistance in vitro and in vivo. GZD824potently suppresses FGFR1/2/3 with an IC50 value of 4.14 ± 0.96, 2.77 ± 0.082, and 8.10 ± 0.15 nmol/L. It effectively overcomes FGFR1-V561F/M and other mutantresistance in Ba/F3 stable cells (IC50 :8.1-55.0 nM), and effectively inhibits the growth of Ba/F3-FGFR1-V561F/M mutantxenograft tumors in vivo (TGI=73.4%, 49.8% at20mg/kg, p.o, q2d). GZD824may be considered to be an effective drug to treat patients with FGFR1 abnormalactivation or mutant resistance in clinical trials.

Exploring liver cancer biology through functional genetic screens.

As the fourth leading cause of cancer-related death in the world, liver cancer poses a major threat to human health. Although a growing number of therapies have been approved for the treatment of hepatocellular carcinoma in the past few years, most of them only provide a limited survival benefit. Therefore, an urgent need exists to identify novel targetable vulnerabilities and powerful drug combinations for the treatment of liver cancer. The advent of functional genetic screening has contributed to the advancement of liver cancer biology, uncovering many novel genes involved in tumorigenesis and cancer progression in a high-throughput manner. In addition, this unbiased screening platform also provides an efficient tool for the exploration of the mechanisms involved in therapy resistance as well as identifying potential targets for therapy. In this Review, we describe how functional screens can help to deepen our understanding of liver cancer and guide the development of new therapeutic strategies.

Fibroblast growth factor 23 (FGF23) induces ventricular arrhythmias and prolongs QTc interval in mice in an FGF receptor 4-dependent manner.

Fibroblast growth factor 23 (FGF23) is a phosphate regulating protein hormone released by osteocytes. FGF23 becomes markedly elevated in chronic kidney disease (CKD), for which the leading cause of death is cardiovascular disease, particularly sudden cardiac death. Previously, we found that FGF23 increases intracellular Ca2+ in cardiomyocytes and alters contractility in mouse ventricles ex vivo via FGF receptor 4 (FGFR4). In the present study, we demonstrate that FGF23 induces cardiac arrhythmias and prolongs QTc interval in mice, and we tested whether these effects are mediated through FGFR4. In isolated Langendorff perfused hearts, FGF23 perfusion increased mechanical arrhythmias in the form of premature ventricular beats (PVBs), and induced runs of ventricular tachycardia in 6 of 11 animals, which were attenuated with pretreatment of an anti-FGFR4 blocking antibody. Ex vivo ECG analysis of isolated intact hearts showed increased ventricular arrhythmias and QTc prolongation after FGF23 infusion compared with vehicle. In vivo, injection of FGF23 into the jugular vein led to the emergence of premature ventricular contractions (PVCs) in 5 out of 11 experiments. FGF23 also produced a significant lengthening effect upon QTc interval in vivo. In vivo FGFR4 blockade ameliorated the arrhythmogenic and QTc prolonging effects of FGF23. Finally, FGF23 increased cardiomyocyte Ca2+ levels in intact left ventricular muscle which was inhibited by FGR4 blockade. We conclude that FGF23/FGFR4 signaling in the heart may contribute to ventricular arrhythmogenesis and repolarization disturbances commonly observed in patients with CKD via Ca2+ overload and may be an important therapeutic target to reduce cardiac mortality in CKD.NEW & NOTEWORTHY Here we provide direct evidence that fibroblast growth factor 23 (FGF23), a phosphaturic hormone elevated in chronic kidney disease, is proarrhythmic. FGF23 acutely triggered ventricular arrhythmias and prolonged corrected QT interval (QTc) in isolated mouse hearts and in vivo. FGF23 also increased Ca2+ levels in ventricular muscle tissue. Blockade of the FGF receptor 4 signaling pathway using a monoclonal antibody ameliorated ventricular arrhythmias, QTc prolongation, and elevated ventricular Ca2+ induced by FGF23, and may represent a potential therapeutic target in chronic kidney disease.

Pyrrolo[2,3-b]pyridine-3-one derivatives as novel fibroblast growth factor receptor 4 inhibitors for the treatment of hepatocellular carcinoma.

Aberrant signaling of the FGF/FGFR pathway occurs frequently in cancers and is an oncogenic driver in many solid tumors, especially liver cancer. With the resurgence of interest in irreversible inhibitors, efforts have been directed to the discovery of irreversible FGFR4 inhibitors. Currently, several selective irreversible inhibitors containing pyrrolo[2,3-b]pyridine-3-one and pyrrolo[2,3-d]pyrimidin-2-amine skeletons were designed and synthesized as FGFR4 inhibitors. Among the screened compounds, derivative 25 showed excellent enzymatic inhibitory activity (IC50, 51.6 nM) and antiproliferative potency of 0.1397 µM against Hep3B cell lines. Compound 25 exhibited good in vitro human liver microsomal stability with the half-life of 62.0 min, which was more stable than BLU9931 (46.7 min). But the in vivo pharmacokinetic results showed that the oral bioavailability was only 6.65%, which needs to be improved in the next work. These results showed that compound 25 might be an effective lead compound for further investigation to treat the hepatocellular carcinoma.

FGF401 and vinorelbine synergistically mediate antitumor activity and vascular normalization in FGF19-dependent hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a lethal cancer with limited therapeutic options, and standard therapy with sorafenib provides only modest survival benefits. Fibroblast growth factor 19 (FGF19) has been proposed as a driver oncogene, and targeting its receptor, FGFR-4, may provide a better alternative to standard therapy for patients with FGF19-driven tumors. Sixty-three HCC patient-derived xenograft (PDX) models were screened for FGF19 expression. Mice bearing high and low FGF19-expressing tumors were treated with FGF401 and/or vinorelbine, and the antitumor activity of both agents was assessed individually and in combination. Tumor vasculature and intratumoral hypoxia were also examined. High FGF19 expression was detected in 14.3% (9 of 63) of the HCC models tested and may represent a good target for HCC treatment. FGF401 potently inhibited the growth of high FGF19-expressing HCC models regardless of FGF19 gene amplification. Furthermore, FGF401 inhibited the FGF19/FGFR-4 signaling pathway, cell proliferation, and hypoxia, induced apoptosis and blood vessel normalization and prolonged the overall survival (OS) of mice bearing high FGF19 tumors. FGF401 synergistically acted with the microtubule-depolymerizing drug vinorelbine to further suppress tumor growth, promote apoptosis, and prolong the OS of mice bearing high FGF19 tumors, with no evidence of increased toxicity. Our study suggests that a subset of patients with high FGF19-expressing HCC tumors could benefit from FGF401 or FGF401/vinorelbine treatment. A high level of FGF19 in a tumor may serve as a potential biomarker for patient selection.

Development of a Potent and Specific FGFR4 Inhibitor for the Treatment of Hepatocellular Carcinoma.

Abnormal activation of the fibroblast growth factor 19 (FGF19)/fibroblast growth factor receptor 4 (FGFR4) signaling pathway has been shown to drive the proliferation of a significant portion of hepatocellular carcinoma (HCC). Resistance and toxicity are serious drawbacks that have been observed upon use of the current first- and second-line treatment options for HCC, therefore warranting the investigation of alternative therapeutic approaches. We report the development and biological characterization of a covalent inhibitor that is highly potent and exquisitely specific to FGFR4. The crystal structure of this inhibitor in complex with FGFR4 was solved, confirming its covalent binding and revealing its binding mode. We also describe the first clickable probe for FGFR4 that can be used to directly measure target engagement in cells. Our compound exhibited great antitumor activity in HCC cell lines and tumor xenograft models. These results provide evidence of a promising therapeutic lead for the treatment of a subset of HCC patients.

Discovery of Roblitinib (FGF401) as a Reversible-Covalent Inhibitor of the Kinase Activity of Fibroblast Growth Factor Receptor 4.

FGF19 signaling through the FGFR4/ß-klotho receptor complex has been shown to be a key driver of growth and survival in a subset of hepatocellular carcinomas, making selective FGFR4 inhibition an attractive treatment opportunity. A kinome-wide sequence alignment highlighted a poorly conserved cysteine residue within the FGFR4 ATP-binding site at position 552, two positions beyond the gate-keeper residue. Several strategies for targeting this cysteine to identify FGFR4 selective inhibitor starting points are summarized which made use of both rational and unbiased screening approaches. The optimization of a 2-formylquinoline amide hit series is described in which the aldehyde makes a hemithioacetal reversible-covalent interaction with cysteine 552. Key challenges addressed during the optimization are improving the FGFR4 potency, metabolic stability, and solubility leading ultimately to the highly selective first-in-class clinical candidate roblitinib.

Futibatinib Is a Novel Irreversible FGFR 1-4 Inhibitor That Shows Selective Antitumor Activity against FGFR-Deregulated Tumors.

FGFR signaling is deregulated in many human cancers, and FGFR is considered a valid target in FGFR-deregulated tumors. Here, we examine the preclinical profile of futibatinib (TAS-120; 1-[(3S)-[4-amino-3-[(3,5-dimethoxyphenyl)ethynyl]-1H-pyrazolo[3, 4-d] pyrimidin-1-yl]-1-pyrrolidinyl]-2-propen-1-one), a structurally novel, irreversible FGFR1-4 inhibitor. Among a panel of 296 human kinases, futibatinib selectively inhibited FGFR1-4 with IC50 values of 1.4 to 3.7 nmol/L. Futibatinib covalently bound the FGFR kinase domain, inhibiting FGFR phosphorylation and, in turn, downstream signaling in FGFR-deregulated tumor cell lines. Futibatinib exhibited potent, selective growth inhibition of several tumor cell lines (gastric, lung, multiple myeloma, bladder, endometrial, and breast) harboring various FGFR genomic aberrations. Oral administration of futibatinib led to significant dose-dependent tumor reduction in various FGFR-driven human tumor xenograft models, and tumor reduction was associated with sustained FGFR inhibition, which was proportional to the administered dose. The frequency of appearance of drug-resistant clones was lower with futibatinib than a reversible ATP-competitive FGFR inhibitor, and futibatinib inhibited several drug-resistant FGFR2 mutants, including the FGFR2 V565I/L gatekeeper mutants, with greater potency than any reversible FGFR inhibitors tested (IC50, 1.3-50.6 nmol/L). These results indicate that futibatinib is a novel orally available, potent, selective, and irreversible inhibitor of FGFR1-4 with a broad spectrum of antitumor activity in cell lines and xenograft models. These findings provide a strong rationale for testing futibatinib in patients with tumors oncogenically driven by FGFR genomic aberrations, with phase I to III trials ongoing. SIGNIFICANCE: Preclinical characterization of futibatinib, an irreversible FGFR1-4 inhibitor, demonstrates selective and potent antitumor activity against FGFR-deregulated cancer cell lines and xenograft models, supporting clinical evaluation in patients with FGFR-driven tumors. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/22/4986/F1.large.jpg.

FGFR4: A promising therapeutic target for breast cancer and other solid tumors.

The fibroblast growth factor receptor (FGFR) signaling pathway has long been known to cancer researchers because of its role in cell survival, proliferation, migration, and angiogenesis. Dysregulation of FGFR signaling is frequently reported in cancer studies, but most of these studies focus on FGFR1-3. However, there is growing evidence implicating an important and unique role of FGFR4 in oncogenesis, tumor progression, and resistance to anti-tumor therapy in multiple types of cancer. Importantly, there are several novel FGFR4-specific inhibitors in clinical trials, making FGFR4 an attractive target for further research. In this review, we focus on assessing the role of FGFR4 in cancer, with an emphasis on breast cancer. First, the structure, physiological functions and downstream signaling pathways of FGFR4 are introduced. Next, different mechanisms reported to cause aberrant FGFR4 activation and their functions in cancer are discussed, including FGFR4 overexpression, FGF ligand overexpression, FGFR4 somatic hotspot mutations, and the FGFR4 G388R single nucleotide polymorphism. Finally, ongoing and recently completed clinical trials targeting FGFRs in cancer are reviewed, highlighting the therapeutic potential of FGFR4 inhibition for the treatment of breast cancer.

PD173074 blocks G1/S transition via CUL3-mediated ubiquitin protease in HepG2 and Hep3B cells.

Fibroblast growth factor receptors (FGFRs) are frequently altered in a variety of human cancer cells and are overexpressed in hepatocellular carcinoma (HCC). Several literatures have proven that they are efficacious for HCC therapy, however, the underlying mechanism remains unclear. Here, we found FGFR4 was overexpressed in HCC cell lines HepG2 and Hep3B and we used PD173074, an FGFR4 inhibitor, to explore the role of FGFR4 and its underlying mechanism in these cell lines. The results showed that PD173074 significantly arrested HepG2 and Hep3B cells in G1 phase and inhibited cell proliferation. Furthermore, Western blot analysis revealed that PD173074 decreased the levels of P-FRS2α, P-ERK, CDK2, cyclin E and NF-κB (p65) in the nucleus while it increased the levels of ubiquitin and CUL3, an E3 ubiquitin ligase which involves in cyclin E degradation. Meanwhile, the data from RT-qPCR showed that PD173074 also decreased miR-141 level. In conclusion, these results suggest that FGFR4 is involved in HCC by ERK/CUL3/cyclin E signaling pathway, and the finding may provide a potential theoretical basis for treatment by targeting FGFR4 in HCC.