State-of-the-art and trends in fibroblast growth factor receptor-directed therapies in gastro-intestinal malignancies

PURPOSE OF REVIEW

This review is timely and relevant due to the increasing recognition of the significance of the fibroblast growth factor receptor (FGFR) family in cancer biology. Understanding the role of FGFRs and their dysregulation in various cancers is crucial for developing targeted therapies and improving patient outcomes.

RECENT FINDINGS

The review highlights the importance of the FGFR family in cellular processes such as growth, proliferation, and survival. It discusses how abnormalities in FGFR2, including overexpression, gene amplification, and other genetic alterations, contribute to cancer progression, particularly in gastro-intestinal cancers. The paper also emphasizes the promising results of FGFR-targeted therapies, especially tyrosine kinase inhibitors, in certain cancers such as cholangiocarcinoma and oesophagogastric cancers.

SUMMARY

The findings underscore the potential of FGFR-targeted therapies in treating cancers with FGFR dysregulation. However, the review also addresses the challenges associated with these therapies, including toxicities and mechanisms of resistance. Understanding these complexities is essential for optimizing the efficacy of FGFR-targeted treatments and improving patient outcomes in clinical practice and research efforts.

Design, synthesis and antitumor activity of a novel FGFR2-selective degrader to overcome resistance of the FGFR2V564F gatekeeper mutation based on a pan-FGFR inhibitor

Aberrant activation of fibroblast growth factor receptors (FGFRs) contributes to the development and progression of multiple types of cancer. Although many FGFR inhibitors have been approved by the FDA, their long-term therapeutic efficacy is hampered by acquired resistance to gatekeeper mutations and low subtype selectivity. FGFR2 has been found to be frequently amplified or mutated in many tumors. In this study, we designed several PROTACs with different E3 ligands based on LY2874455. By screening the length of the linker and the binding site in various degraders, we obtained a novel and highly efficient FGFR2-selective degrader 28e (DC50 = 0.645 nM, DCmax = 86 %). Compound 28e selectively degraded FGFR2 and essentially avoided degradation of FGFR1,3,4 isoforms (DC50 > 300 nM). Compound 28e significantly inhibited the proliferation of FGFR2-overexpressing cell lines, including KATOIII, SNU16, and AN3CA (IC50 = 0.794 nM/0.207 nM/4.626 nM), comparable to parental inhibitors. At the same time, the preferred compound showed superiority over the parental inhibitor in kinase inhibitory activity against the gatekeeper mutant isoform FGFR2V564F (IC50 = 0.121 nM). In summary, we identified 28e as a novel selective degrader of FGFR2 with high potency and high potential to overcome resistance to gatekeeper mutation. The discovery of 28e provides new evidence for the strategy of pan-inhibitor-based development of selective degrading agents.

Targeting FGFR for cancer therapy

The FGFR signaling pathway is integral to cellular activities, including proliferation, differentiation, and survival. Dysregulation of this pathway is implicated in numerous human cancers, positioning FGFR as a prominent therapeutic target. Here, we conduct a comprehensive review of the function, signaling pathways and abnormal alterations of FGFR, as well as its role in tumorigenesis and development. Additionally, we provide an in-depth analysis of pivotal phase 2 and 3 clinical trials evaluating the performance and safety of FGFR inhibitors in oncology, thereby shedding light on the current state of clinical research in this field. Then, we highlight four drugs that have been approved for marketing by the FDA, offering insights into their molecular mechanisms and clinical achievements. Our discussion encompasses the intricate landscape of FGFR-driven tumorigenesis, current techniques for pinpointing FGFR anomalies, and clinical experiences with FGFR inhibitor regimens. Furthermore, we discuss the inherent challenges of targeting the FGFR pathway, encompassing resistance mechanisms such as activation by gatekeeper mutations, alternative pathways, and potential adverse reactions. By synthesizing the current evidence, we underscore the potential of FGFR-centric therapies to enhance patient prognosis, while emphasizing the imperative need for continued research to surmount resistance and optimize treatment modalities.

Design, synthesis, and biological evaluation of selective covalent inhibitors of FGFR4

Aberrant signaling via fibroblast growth factor 19 (FGF19)/fibroblast growth factor receptor 4 (FGFR4) has been identified as a driver of tumorigenesis and the development of many solid tumors, making FGFR4 is a promising target for anticancer therapy. Herein, we designed and synthesized a series of bis-acrylamide covalent FGFR4 inhibitors and evaluated their inhibitory activity against FGFRs, FGFR4 mutants, and their antitumor activity. CXF-007, verified by mass spectrometry and crystal structures to form covalent bonds with Cys552 of FGFR4 and Cys488 of FGFR1, exhibited stronger selectivity and potent inhibitory activity for FGFR4 and FGFR4 cysteine mutants. Moreover, CXF-007 exhibited significant antitumor activity in hepatocellular carcinoma cell lines and breast cancer cell lines through sustained inhibition of the FGFR4 signaling pathway. In summary, our study highlights a novel covalent FGFR4 inhibitor, CXF-007, which has the potential to overcome drug-induced FGFR4 mutations and might provide a new strategy for future anticancer drug discovery.

Cholangiocarcinoma Insights: Established Foundations and Cutting-Edge Innovations from Dr. James Cleary's Pioneering Research

This paper provides insights into the conventional understanding of biliary tract malignancies, with a specific focus on cholangiocarcinoma (CCA). We then delve into the groundbreaking ideas presented by Dr. James Cleary. CCA, originating from biliary tree cells, manifests diverse subtypes contingent upon anatomical localization and differentiation status. These variants exhibit discrete genetic aberrations, yielding disparate clinical phenotypes and therapeutic modalities. Intrahepatic, perihilar, and distal CCAs intricately involve distinct segments of the biliary tree, further categorized as well-differentiated, moderately differentiated, or poorly differentiated adenocarcinomas based on their histological differentiation. Understanding the etiological factors contributing to CCA development assumes paramount importance. Stratifying these factors into two groups, those unrelated to fluke infestations (e.g., viral hepatitis and fatty liver conditions) and those associated with fluke infestations (e.g., chronic liver inflammation), facilitates predictive modeling. The epidemiology of CCA exhibits global variability, with Southeast Asia notably displaying higher incidences attributed primarily to liver fluke infestations. Jaundice resulting from bile duct obstruction constitutes a prevalent clinical manifestation of CCA, alongside symptoms like malaise, weight loss, and abdominal pain. Diagnostic challenges arise due to the symptomatic overlap with other biliary disorders. Employing comprehensive liver function tests and imaging modalities such as computed tomography assumes a pivotal role in ensuring accurate diagnosis and staging. However, the definitive confirmation of CCA necessitates a biopsy. Treatment modalities, predominantly encompassing surgical resection and radiation therapy, hold curative potential, although a considerable subset of patients is deemed unresectable upon exploration. Challenges intensify, particularly in cases classified as cancer of unknown origin, underscoring the imperative for early intervention. Advancements in genomic sequencing have revolutionized precision medicine in CCA. Distinct genomic markers, including fibroblast growth factor receptor 2 (FGFR2) alterations and isocitrate dehydrogenase 1 (IDH1) mutations, have emerged as promising therapeutic targets. FGFR2 alterations, encompassing mutations and rearrangements, play pivotal roles in oncogenesis, with FGFR inhibitors demonstrating promise despite identified resistance mechanisms. Similarly, IDH1 inhibitors face challenges with resistance, despite encouraging early clinical trial results, prompting exploration of novel irreversible inhibitors. Dr. James Cleary's illuminating discourse underscores the significance of diverse FGFR2 alterations and the potential of IDH1 inhibition in reshaping the treatment landscape for CCA. These findings unveil critical avenues for targeted therapeutic interventions, emphasizing the critical need for ongoing research to optimize outcomes in this challenging cancer subtype, incorporating innovative insights from Dr. Cleary.

Resistance mechanism to fibroblast growth factor receptor (FGFR) inhibitors in cholangiocarcinoma

Precision medicine is a major achievement that has impacted on management of patients diagnosed with advanced cholangiocarcinoma (CCA) over the last decade. Molecular profiling of CCA has identified targetable alterations, such as fibroblast growth factor receptor-2 (FGFR-2) fusions, and has thus led to the development of a wide spectrum of compounds. Despite favourable response rates, especially with the latest generation FGFRi, there are still a proportion of patients who will not achieve a radiological response to treatment, or who will have disease progression as the best response. In addition, for patients who do respond to treatment, secondary resistance frequently develops and mechanisms of such resistance are not fully understood. This review will summarise the current state of development of FGFR inhibitors in CCA, their mechanism of action, activity, and the hypothesised mechanisms of resistance.

Targeting FGFR Pathways in Gastrointestinal Cancers: New Frontiers of Treatment

In carcinogenesis of the gastrointestinal (GI) tract, the deregulation of fibroblast growth factor receptor (FGFR) signaling plays a critical role. The aberrant activity of this pathway is described in approximately 10% of gastric cancers and its frequency increases in intrahepatic cholangiocarcinomas (iCCAs), with an estimated frequency of 10-16%. Several selective FGFR inhibitors have been developed in the last few years with promising results. For example, targeting the FGFR pathway is now a fundamental part of clinical practice when treating iCCA and many clinical trials are ongoing to test the safety and efficacy of anti-FGFR agents in gastric, colon and pancreatic cancer, with variable results. However, the response rates of anti-FGFR drugs are modest and resistances emerge rapidly, limiting their efficacy and causing disease progression. In this review, we aim to explore the landscape of anti-FGFR inhibitors in relation to GI cancer, with particular focus on selective FGFR inhibitors and drug combinations that may lead to overcoming resistance mechanisms and drug-induced toxicities.

Design, synthesis and biological evaluation of indazole derivatives as selective covalent inhibitors of FGFR4 in wild-type and gatekeeper mutants

Fibroblast growth factor receptor 4 (FGFR4) has been proved to be an effective target for cancer therapy. Aberration in FGF19/FGFR4 signaling is oncogenic driving force in human hepatocellular carcinoma (HCC). FGFR4 gatekeeper mutations induced acquired resistance remains an unmet clinical challenge for HCC treatment. In this study, a series of 1H-indazole derivatives were designed and synthesized as new irreversible inhibitors of wild-type and gatekeeper mutant FGFR4. These new derivatives showed significant FGFR4 inhibitory and antitumor activities, among which compound 27i was demonstrated to be the most potent compound (FGFR4 IC₅₀ = 2.4 nM). Remarkably, compound 27i exhibited no activity against a panel of 381 kinases at 1 μM. Additionally, compound 27i displayed nanomolar IC₅₀s against huh7 (IC₅₀ = 21 nM) and two mutant cell lines, BaF3/ETV6-FGFR4-V550L and BaF3/ETV6-FGFR4-N535K (IC₅₀ = 2.5/171 nM). Meanwhile, compound 27i exhibited potent antitumor potency (TGI: 83.0%, 40 mg/kg, BID) in Huh7 xenograft mouse models with no obvious toxicity observed. Overall, compound 27i was identified as a promising preclinical candidate for overcoming FGFR4 gatekeeper mutations for HCC treatment.

Advances in protein kinase drug discovery through targeting gatekeeper mutations

INTRODUCTION

Acquired resistance caused by gatekeeper mutations has become a major challenge for approved kinase inhibitors used in the clinic. Consequently, the development of new-generation inhibitors or degraders to overcome clinical resistance has become an important research focus for the field.

AREAS COVERED

This review summarizes the common gatekeeper mutations in druggable kinases and the constantly evolving inhibitors or degraders designed to overcome single or double mutations of gatekeeper residues. Furthermore, the authors provide their perspectives on the medicinal chemistry strategies for addressing clinical resistance with gatekeeper mutations.

EXPERT OPINION

The authors suggest optimizing kinase inhibitors to interact effectively with gatekeeper residues, altering the binding mode or binding pocket to avoid steric clashes, improving binding affinity with the target, utilizing protein degraders, and developing combination therapy. These approaches have the potential to be effective in overcoming resistance due to gatekeeper residues.

The FGF/FGFR signalling mediated anti-cancer drug resistance and therapeutic intervention

ABSTRACT Fibroblast Growth Factor (FGF) ligands and their receptors are crucial factors driving chemoresistance in several malignancies, challenging the efficacy of currently available anti-cancer drugs. The Fibroblast growth factor/receptor (FGF/FGFR) signalling malfunctions in tumor cells, resulting in a range of molecular pathways that may impact its drug effectiveness. Deregulation of cell signalling is critical since it can enhance tumor growth and metastasis. Overexpression and mutation of FGF/FGFR induce regulatory changes in the signalling pathways. Chromosomal translocation facilitating FGFR fusion production aggravates drug resistance. Apoptosis is inhibited by FGFR-activated signalling pathways, reducing multiple anti-cancer medications' destructive impacts. Angiogenesis and epithelial-mesenchymal transition (EMT) are facilitated by FGFRs-dependent signalling, which correlates with drug resistance and enhances metastasis. Further, lysosome-mediated drug sequestration is another prominent method of resistance. Inhibition of FGF/FGFR by following a plethora of therapeutic approaches such as covalent and multitarget inhibitors, ligand traps, monoclonal antibodies, recombinant FGFs, combination therapy, and targeting lysosomes and micro RNAs would be helpful. As a result, FGF/FGFR suppression treatment options are evolving nowadays. To increase positive impacts, the processes underpinning the FGF/FGFR axis' role in developing drug resistance need to be clarified, emphasizing the need for more studies to develop novel therapeutic options to address this significant problem. Communicated by Ramaswamy H. Sarma.

Discovery of 2-Amino-7-sulfonyl-7H-pyrrolo[2,3-d]pyrimidine Derivatives as Potent Reversible FGFR Inhibitors with Gatekeeper Mutation Tolerance: Design, Synthesis, and Biological Evaluation

Fibroblast growth factor receptors (FGFRs) play key roles in promoting cancer cell proliferation, differentiation, and migration. However, acquired resistance to FGFR inhibitors has become an emerging challenge in long-term cancer therapies, especially for hepatocellular carcinoma (HCC). Gatekeeper (GK) mutations are the main mechanism of resistance. Herein, we describe the discovery of a series of reversible FGFR inhibitors, particularly for GK mutations with the 2-amino-7-sulfonyl-7H-pyrrolo[2,3-d]pyrimidine scaffold. Rational design, optimization, and pharmacokinetic screening provided representative compound 19 with potent FGFR inhibition in vitro, high bioavailability, and an acceptable half-life. GK mutation tolerance was supported by assays against FGFR4^V550L and Ba/F3-TEL-FGFR4^V550L cells. Moreover, compound 19 exhibited potent antitumor potency in HUH7 xenograft mouse models with no obvious toxicity observed. Compound 19 was identified as a potential candidate for overcoming GK mutations for HCC treatment.

Targeting Gatekeeper Mutations for Kinase Drug Discovery

Clinically acquired resistance is a major challenge in cancer therapies with small-molecule kinase inhibitors (SMKIs). Gatekeeper mutations in the ATP-binding pocket of kinases are the most common mutations leading to acquired resistance. To date, seven new-generation kinase inhibitors targeting gatekeeper mutations have been approved by the FDA; however, the clinical need is still unmet. Here, we systematically summarize the types of gatekeeper mutations across the kinase family, the structural basis for acquired resistance, and newly developed SMKIs targeting gatekeeper mutations as well as highlight the opportunities and challenges of kinase drug discovery for targeting gatekeeper mutations.

Targeting FGFRs for tumor therapy: current status and novel strategies

The FGF receptors (FGFRs) belong to a family of receptor tyrosine kinases. Abundant evidence shows that FGFRs are closely related to tumor cell invasion and angiogenesis. Hence, targeted modulation of FGFRs has become an effective strategy for cancer treatment. Recently, the development of small-molecule inhibitors targeting FGFRs has been extensively studied, and three inhibitors have been approved for marketing. Based on the clinical problems with the current inhibitors, there is a need to develop novel inhibitors and technologies to address the pitfalls. This review summarizes recent advances in small-molecule inhibitors targeting FGFRs, focusing on structure-activity relationships. Moreover, recent progress of novel technologies are summarized to provide a reference for promoting the application of drugs targeting FGFRs in tumor therapy.

Design, Synthesis, and Biological Evaluation of 5-Formyl-pyrrolo[3,2-b]pyridine-3-carboxamides as New Selective, Potent, and Reversible-Covalent FGFR4 Inhibitors

The FGF19-FGFR4 signaling pathway has been extensively studied as a promising target for the treatment of hepatocellular carcinoma (HCC). Several FGFR4-selective inhibitors have been developed, but none of them receives approval. Additionally, acquired resistance caused by FGFR4 gatekeeper mutations is emerging as a serious limitation for these targeted therapies. Herein, we report a novel series of 5-formyl-pyrrolo[3,2-b]pyridine derivatives as new reversible-covalent inhibitors targeting wild-type and gatekeeper mutant variants of FGFR4 kinase. The representative compound 10z exhibited single-digit nanomolar activity against wild-type FGFR4 and the FGFR4V550L/M mutant variants in biochemical and Ba/F3 cellular assays, while sparing FGFR1/2/3. Furthermore, 10z showed significant antiproliferative activity against Hep3B, JHH-7, and HuH-7 HCC cells with IC50 values of 37, 32, and 94 nM, respectively. MALDI-TOF-MS and X-ray protein crystallography studies were consistent with 10z acting as a reversible-covalent inhibitor of FGFR4, serving as a promising lead compound for further anticancer drug development.

Protein tyrosine kinase inhibitor resistance in malignant tumors: molecular mechanisms and future perspective

Protein tyrosine kinases (PTKs) are a class of proteins with tyrosine kinase activity that phosphorylate tyrosine residues of critical molecules in signaling pathways. Their basal function is essential for maintaining normal cell growth and differentiation. However, aberrant activation of PTKs caused by various factors can deviate cell function from the expected trajectory to an abnormal growth state, leading to carcinogenesis. Inhibiting the aberrant PTK function could inhibit tumor growth. Therefore, tyrosine kinase inhibitors (TKIs), target-specific inhibitors of PTKs, have been used in treating malignant tumors and play a significant role in targeted therapy of cancer. Currently, drug resistance is the main reason for limiting TKIs efficacy of cancer. The increasing studies indicated that tumor microenvironment, cell death resistance, tumor metabolism, epigenetic modification and abnormal metabolism of TKIs were deeply involved in tumor development and TKI resistance, besides the abnormal activation of PTK-related signaling pathways involved in gene mutations. Accordingly, it is of great significance to study the underlying mechanisms of TKIs resistance and find solutions to reverse TKIs resistance for improving TKIs efficacy of cancer. Herein, we reviewed the drug resistance mechanisms of TKIs and the potential approaches to overcome TKI resistance, aiming to provide a theoretical basis for improving the efficacy of TKIs.

Recent advances in therapeutic strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the most malignant subtype of breast cancer (BC) with a poor prognosis. Current treatment options are limited to surgery, adjuvant chemotherapy and radiotherapy; however, a proportion of patients have missed the surgical window at the time of diagnosis. TNBC is a highly heterogeneous cancer with specific mutations and aberrant activation of signaling pathways. Hence, targeted therapies, such as those targeting DNA repair pathways, androgen receptor signaling pathways, and kinases, represent promising treatment options against TNBC. In addition, immunotherapy has also been demonstrated to improve overall survival and response in TNBC. In this review, we summarize recent key advances in therapeutic strategies based on molecular subtypes in TNBC.

Characterization of the cholangiocarcinoma drug pemigatinib against FGFR gatekeeper mutants

Fibroblast growth factor receptor (FGFR) dysregulation is involved in a variety of tumorigenesis and development. Cholangiocarcinoma is closely related with FGFR aberrations, and pemigatinib is the first drug approved to target FGFR for the treatment of cholangiocarcinoma. Herein, we undertake biochemical and structural analysis on pemigatinib against FGFRs as well as gatekeeper mutations. The results show that pemigatinib is a potent and selective FGFR1-3 inhibitor. The extensive network of hydrogen bonds and van der Waals contacts found in the FGFR1-pemigatinib binding mode accounts for the high potency. Pemigatinib also has excellent potency against the Val-to-Ile gatekeeper mutation but less potency against the Val-to-Met/Phe gatekeeper mutation in FGFR. Taken together, the inhibitory and structural profiles exemplified by pemigatinib may help to thwart Val-to-Ile gatekeeper mutation-based resistance at earlier administration and to advance the further design and improvement for inhibitors toward FGFRs with gatekeeper mutations.

LY2874455 and Abemaciclib Reverse FGF3/4/19/CCND1 Amplification Mediated Gefitinib Resistance in NSCLC

Non-small cell lung carcinoma (NSCLC) patients who initially received tyrosine kinase inhibitor (TKI) therapy often acquired resistance via multiple complex mechanisms. The amplification of FGF3/4/19/CCND1 on chromosome 11q13 was found in many cancers with TKI resistance. However, the role of these amplifications in TKI-resistant NSCLC remains uncovered. Here, we generated the FGF3/4/19/CCND1 amplification model in the NSCLC cell lines PC-9 and HCC827. Upregulation of FGF3/4/19/CCND1 strongly promoted cell proliferation and gefitinib resistance in NSCLC cells. To find out the potential therapeutic strategies, we screened the combination of inhibitors against the FGF/FGFR signaling pathway and the CCND1/CDK4 complex and revealed that gefitinib combined with LY2874455 and abemaciclib exhibited the most effective inhibition of resistance in vitro and in vivo. Mechanistically, FGFs/CCND1 activated the MAPK pathway, which was abolished by the combination drugs. Our study provides a rationale for clinical testing of dual targeting FGFR and CCND1 with LY2874455 and abemaciclib in NSCLC patients who harbored FGF3/4/19/CCND1 amplification.

The novel FGFR inhibitor F1-7 induces DNA damage and cell death in colon cells

BACKGROUND

Fibroblast growth factor receptor (FGFR) signaling influenced tumour occurrence and development. Overexpression of FGFR had been observed in many types of cancers, including colon cancer. FGFR inhibitor is considered to be effective in treating colon cancer patients.

METHODS

First, the kinase inhibition rate was determined. MTT, western blotting, colony formation, EdU and comet assays were performed to evaluate the anti-tumour effects of F1-7 in vitro. RNA-seq and bioinformatics analysis were used for further verification. Additionally, a xenograft model was generated to investigate the anti-tumour effect of F1-7.

RESULTS

F1-7 can inhibit the proliferation of colon cancer cells in vitro. It could significantly inhibit FGFR phosphorylation and its downstream signaling pathway. Whole-genome RNA-seq analysis found that the changed genes were not only functionally focused on MAPK signaling pathway but also related to cell apoptosis and ferroptosis. Experimental evidence demonstrated that F1-7 can directly increase the level of cellular DNA damage. The occurrence of DNA damage led to cell cycle arrest and inhibition of cell metastasis and cell apoptosis. Mouse model experiments also confirmed that F1-7 could inhibit tumour growth by inhibiting the FGFR pathway.

CONCLUSIONS

F1-7 exhibits anti-tumour activity by inhibiting the FGFR pathway. It could be a novel therapeutic agent for targeting colon cancer cells.

Radiosensitization by the Selective Pan-FGFR Inhibitor LY2874455

Ionizing radiation activates cytoprotective pathways in cancer cells. Fibroblast growth factor receptor (FGFR) is a key player in these pathways. Thus, FGFR signaling is a potential target to induce radiosensitization. LY2874455 is an orally administrable selective pan-FGFR inhibitor. However, the radiosensitizing effects of LY2874455 remain unclear. In this study, we addressed this issue by using radioresistant human cancer cell lines H1703 (FGFR1 mutant), A549 (FGFR1–4 wild-type), and H1299 (FGFR1–4 wild-type). At an X-ray dose corresponding to 50%-clonogenic survival as the endpoint, 100 nM LY2874455 increased the sensitivity of H1703, A549, and H1299 cells by 31%, 62%, and 53%, respectively. The combination of X-rays and LY2874455 led to a marked induction of mitotic catastrophe, a hallmark of radiation-induced cell death. Furthermore, combination treatment suppressed the growth of A549 xenografts to a significantly greater extent than either X-rays or the drug alone without noticeable toxicity. This is the first report to show the radiosensitizing effect of a selective pan-FGFR inhibitor. These data suggest the potential efficacy of LY2874455 as a radiosensitizer, warranting clinical validation.

Fibroblast Growth Factor Receptor 1-4 Genetic Aberrations as Clinically Relevant Biomarkers in Squamous Cell Lung Cancer

Fibroblast growth factor receptor (FGFR) inhibitors (FGFRis) are a potential therapeutic option for squamous non-small cell lung cancer (Sq-NSCLC). Because appropriate patient selection is needed for targeted therapy, molecular profiling is key to discovering candidate biomarker(s). Multiple FGFR aberrations are present in Sq-NSCLC tumors-alterations (mutations and fusions), amplification and mRNA/protein overexpression-but their predictive potential is unclear. Although FGFR1 amplification reliability was unsatisfactory, FGFR mRNA overexpression, mutations, and fusions are promising. However, currently their discriminatory power is insufficient, and the available clinical data are from small groups of Sq-NSCLC patients. Here, we focus on FGFR aberrations as predictive biomarkers for FGFR-targeting agents in Sq-NSCLC. Known and suggested molecular determinants of FGFRi resistance are also discussed.

Fibroblast growth factor receptor (FGFR) inhibitors as anticancer agents: 3D-QSAR, molecular docking and dynamics simulation studies of 1, 6-naphthyridines and pyridopyrimidines

Fibroblast growth factor receptor (FGFR) plays a vital role in tissue regeneration, angiogenesis, and embryogenesis. 3D-QSAR and molecular modeling methods are widely used for designing novel compounds for the determination of inhibitory activity against the biological target. In the present study, 3D-QSAR (CoMFA and CoMSIA) analysis was performed on 1, 6-naphthyridines, and pyridopyrimidines as potential FGFR inhibitors as anticancer agents. The best CoMFA and CoMSIA models were generated from test and training set derivatives with leave-one-out correlation coefficients (q²) 0.591 and 0.667, cross-validated correlation coefficients (r²_cv) 0.584 and 0.652, conventional coefficients (r²_ncv) 0.978 and 0.975 respectively. The developed models were validated by a test set of 12 compounds providing acceptable predictive correlation coefficient (r²_pred) 0.61 and 0.68 for both models. The generated CoMFA and CoMSIA contour maps could be used to design novel 1, 6-naphthyridine analogs. Molecular docking studies indicated that compound 75 occupied the active site of the FGFR kinase interacting with Glu520 in the catalytic region, Asp630 in the DFG motif, and Met524 in the hinge region which compared with standard drug Ponatinib. The molecular dynamics simulation analysis revealed that the inhibitor 75 displayed binding stability in the active site of the FGFR4 by making two hydrogen bonds and one π-cation interaction. Collectively the outcome of the study suggested that the applications of ligand-based and structure-based approaches could be applied for the design of new FGFR4 inhibitors as anticancer agents.Communicated by Ramaswamy H. Sarma.

Structure-based design of a dual-warhead covalent inhibitor of FGFR4

The fibroblast growth factor 19 (FGF19)/fibroblast growth factor receptor 4 (FGFR4) signaling pathways play critical roles in a variety of cancers, such as hepatocellular carcinoma (HCC). FGFR4 is recognized as a promising target to treat HCC. Currently, all FGFR covalent inhibitors target one of the two cysteines (Cys477 and Cys552). Here, we designed and synthesized a dual-warhead covalent FGFR4 inhibitor, CXF-009, targeting Cys477 and Cys552 of FGFR4. We report the cocrystal structure of FGFR4 with CXF-009, which exhibits a dual-warhead covalent binding mode. CXF-009 exhibited stronger selectivity for FGFR4 than FGFR1-3 and other kinases. CXF-009 can also potently inhibit the single cystine mutants, FGFR4(C477A) and FGFR4(C552A), of FGFR4. In summary, our study provides a dual-warhead covalent FGFR4 inhibitor that can covalently target two cysteines of FGFR4. CXF-009, to our knowledge, is the first reported inhibitor that forms dual-warhead covalent bonds with two cysteine residues in FGFR4. CXF-009 also has the potential to overcome drug induced resistant FGFR4 mutations and might serve as a lead compound for future anticancer drug discovery.

Design, Synthesis, and Biological Evaluation of Aminoindazole Derivatives as Highly Selective Covalent Inhibitors of Wild-Type and Gatekeeper Mutant FGFR4

Aberrant FGF19/FGFR4 signaling has been shown to be an oncogenic driver of growth and survival in human hepatocellular carcinoma (HCC) with several pan-FGFR inhibitors and FGFR4-selective inhibitors currently being evaluated in the clinic. However, FGFR4 gatekeeper mutation induced acquired resistance remains an unmet clinical challenge for HCC treatment. Thus, a series of aminoindazole derivatives were designed and synthesized as new irreversible inhibitors of wild-type and gatekeeper mutant FGFR4. One representative compound (7v) exhibited excellent potency against FGFR4, FGFR4^V550L, and FGFR4^V550M with nanomolar activity in both the biochemical and cellular assays while sparing FGFR1/2/3. While compound 7v demonstrated modest in vivo antitumor efficacy in nude mice bearing the Huh-7 xenograft model consistent with its unfavorable pharmacokinetic properties, it provides a promising new starting point for future drug discovery combating FGFR4 gatekeeper mediated resistance in HCC patients.

Structural study of ponatinib in inhibiting SRC kinase

Ponatinib is a multi-target tyrosine kinase inhibitor that targets ABL, SRC, FGFR, and so on. It was designed to overcome the resistance of BCR-ABL mutation to imatinib, especially the gatekeeper mutation ABL^T315I. The molecular mechanism by which ponatinib overcomes mutations of BCR-ABL and some other targets has been explained, but little information is known about the characteristics of ponatinib binding to SRC. Here, we showed that ponatinib inhibited wild type SRC kinase but failed to inhibit SRC gatekeeper mutants in both biochemical and cellular assays. We determined the crystal structure of ponatinib in complex with the SRC kinase domain. In addition, by structural analysis, we provided a possible explanation for why ponatinib showed different effects on SRC and other kinases with gatekeeper mutations. The resistance mechanism of SRC gatekeeper mutations to ponatinib may provide meaningful information for designing inhibitors against SRC family kinases in the future.

Structural insights into the potency and selectivity of covalent pan-FGFR inhibitors

FIIN-2, TAS-120 (Futibatinib) and PRN1371 are highly potent pan-FGFR covalent inhibitors targeting the p-loop cysteine of FGFR proteins, of which TAS-120 and PRN1371 are currently in clinical trials. It is critical to analyze their target selectivity and their abilities to overcome gatekeeper mutations. In this study, we demonstrate that FIIN-2 and TAS-120 form covalent adducts with SRC, while PRN1371 does not. FIIN-2 and TAS-120 inhibit SRC and YES activities, while PRN1371 does not. Moreover, FIIN-2, TAS-120 and PRN1371 exhibit different potencies against different FGFR gatekeeper mutants. In addition, the co-crystal structures of SRC/FIIN-2, SRC/TAS-120 and FGFR4/PRN1371 complexes reveal structural basis for kinase targeting and gatekeeper mutations. Taken together, our study not only provides insight into the potency and selectivity of covalent pan-FGFR inhibitors, but also sheds light on the development of next-generation FGFR covalent inhibitors with high potency, high selectivity, and stronger ability to overcome gatekeeper mutations.

Characterization of an aromatic trifluoromethyl ketone as a new warhead for covalently reversible kinase inhibitor design

An aromatic trifluoromethyl ketone moiety was characterized as a new warhead for covalently reversible kinase inhibitor design to target the non-catalytic cysteine residue. Potent and selective covalently reversible inhibitors of FGFR4 kinase were successfully designed and synthesized by utilizing this new warhead. The binding mode of a representative inhibitor was fully characterized by using multiple technologies including MALDI-TOF mass spectrometry, dialysis assay and X-ray crystallographic studies etc. This functional group was also successfully applied to discovery of a new JAK3 inhibitor, suggesting its potential application in designing other kinase inhibitors.

Molecular mechanisms of the anti-cancer drug, LY2874455, in overcoming the FGFR4 mutation-based resistance

In recent years, many strategies have been used to overcome the fibroblast growth factor receptor (FGFR) tyrosine kinase inhibitors (TKIs) resistance caused by different mutations. LY2874455 (or 6LF) is a pan-FGFR inhibitor which is identified as the most efficient TKI for all resistant mutations in FGFRs. Here, we perform a comparative dynamics study of wild type (WT) and the FGFR4 V550L mutant for better understanding of the 6LF inhibition mechanism. Our results confirm that the pan-FGFR inhibitor 6LF can bind efficiently to both WT and V550L FGFR4. Moreover, the communication network analysis indicates that in apo-WT FGFR4, αD–αE loop behaves like a switch between open and close states of the substrate-binding pocket in searching of its ligand. In contrast, V550L mutation induces the active conformation of the FGFR4 substrate-binding pocket through disruption of αD–αE loop and αG helix anti-correlation. Interestingly, 6LF binding causes the rigidity of hinge and αD helix regions, which results in overcoming V550L induced resistance. Collectively, the results of this study would be informative for designing more efficient TKIs for more effective targeting of the FGFR signaling pathway.

FGFR Inhibitors: Clinical Activity and Development in the Treatment of Cholangiocarcinoma

PURPOSE OF REVIEW

Cholangiocarcinoma is an aggressive cancer with a poor prognosis and limited treatment. Gene sequencing studies have identified genetic alterations in fibroblast growth factor receptor (FGFR) in a significant proportion of cholangiocarcinoma (CCA) patients. This review will discuss the FGFR signaling pathway's role in CCA and highlight the development of therapeutic strategies targeting this pathway.

RECENT FINDINGS

The development of highly potent and selective FGFR inhibitors has led to the approval of pemigatinib for FGFR2 fusion or rearranged CCA. Other selective FGFR inhibitors are currently under clinical investigation and show promising activity. Despite encouraging results, the emergence of resistance is inevitable. Studies using circulating tumor DNA and on-treatment tissue biopsies have elucidated underlying mechanisms of intrinsic and acquired resistance. There is a critical need to not only develop more effective compounds, but also innovative sequencing strategies and combinations to overcome resistance to selective FGFR inhibition. Therapeutic development of precision medicine for FGFR-altered CCA is a dynamic process of involving a comprehensive understanding of tumor biology, rational clinical trial design, and therapeutic optimization. Alterations in FGFR represent a valid therapeutic target in CCA and selective FGFR inhibitors are treatment options for this patient population.

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.

Targeting FGFR in intrahepatic cholangiocarcinoma [iCCA]: leading the way for precision medicine in biliary tract cancer [BTC]?

Introduction: The increasing availability of next-generation DNA sequencing (NGS) opens the opportunity to tailor therapies to potential targets. Intrahepatic cholangiocarcinoma (iCCA) has the most actionable genomic targets of the hepatobiliary malignancies, including mutations in Isocitrate Dehydrogenase (IDH) and Fibroblast Growth Factor Receptor (FGFR), particularly FGFR2. With the recent accelerated approval of pemigatinib and several trials currently underway, FGFR2 inhibition will set the mold for tailored therapies in hepatobiliary cancer.Areas covered: We review the current standard of therapy for iCCA, the genomic targets, and the role of FGFR inhibitors in developing the treatment landscape. The FGFR mechanism of actionand use of IDH1/2 inhibition and immunotherapy in iCCA are also discussed. We queried the PubMed and ClinicalTrials.gov databases, along with conference proceedings for relevant data.Expert opinion: While more mature data are needed from the trials in progress, currently published analyses show survival benefit with FGFR2 inhibitors in patients positive for FGFR2 fusion who have failed the standard of care. Infigratinib, futibatinib, pemigatinib and derazantinib have all demonstrated promising activity iCCA patients harboring FGFR2 fusion. Eventually, head-to-head trials will be needed to fully understand the benefits of each agent and the role of reversible versus irreversible FGFR2 inhibitors.

Targeting the Fibroblast Growth Factor Receptor (FGFR) in Advanced Cholangiocarcinoma: Clinical Trial Progress and Future Considerations

Landmark molecular profiling efforts have identified multiple targetable alterations in cholangiocarcinoma. Among the molecular-driven subsets of cholangiocarcinoma, targeting the fibroblast growth factor receptor (FGFR) has shown promise and represents the first targeted therapy to be approved in treatment-refractory, advanced cholangiocarcinoma. In this review, we provide an up-to-date overview of the clinical development of FGFR inhibitors in advanced cholangiocarcinoma. We review the FGFR pathway and discuss emerging issues including resistance to FGFR inhibitors. We end with a discussion on future considerations to optimize the potential of this class of therapeutics in advanced cholangiocarcinoma.

FGFR-TKI resistance in cancer: current status and perspectives

Fibroblast growth factor receptors (FGFRs) play key roles in promoting the proliferation, differentiation, and migration of cancer cell. Inactivation of FGFRs by tyrosine kinase inhibitors (TKI) has achieved great success in tumor-targeted therapy. However, resistance to FGFR-TKI has become a concern. Here, we review the mechanisms of FGFR-TKI resistance in cancer, including gatekeeper mutations, alternative signaling pathway activation, lysosome-mediated TKI sequestration, and gene fusion. In addition, we summarize strategies to overcome resistance, including developing covalent inhibitors, developing dual-target inhibitors, adopting combination therapy, and targeting lysosomes, which will facilitate the transition to precision medicine and individualized treatment.

Characterization of ibrutinib as a non-covalent inhibitor of SRC-family kinases

Ibrutinib is a BTK-targeted irreversible inhibitor. In this study, we demonstrate that ibrutinib potently inhibits SRC activity in a non-covalent manner via mass spectrometry and crystallography. The S345C mutation renders SRC to bind covalently with ibrutinib, and restores the potency of ibrutinib against the gatekeeper mutant. The co-crystal structure of ibrutinib/SRC shows Ser345 of SRC did not form covalent bond with ibrutinib, leading to a decrease of potency and loss of the ability to overcome the gatekeeper mutation of SRC. The X-ray crystallographic studies also provide structural insight into why ibrutinib behaves differently against gatekeeper mutants of different kinases.

Structural basis of tropifexor as a potent and selective agonist of farnesoid X receptor

Farnesoid X receptor (FXR) is considered as a potential target for the treatment of several liver disorders such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Tropifexor is a highly potent and non-steroidal FXR agonist that has progressed into phase II clinical trials in patients with PBC. The clinical trials demonstrate that tropifexor improved serum markers of patients with liver diseases and lower side effect such as pruritus that might be implicated with TGR5 activation. However, the molecular mechanism of the potency and selectivity of tropifexor remains unclear. In this study, the binding affinity of FXR and tropifexor is measured by isothermal titration calorimetry (ITC) assays. The crystal structure of the FXR/tropifexor complex is determined at 2.7 Å resolution to explain the molecular mechanism of tropifexor bound to FXR-LBD. Structural comparison with other FXR/agonists structures reveals the conformational change in the FXR/tropifexor structure. Moreover the structural superposition of TGR5/tropifexor indicates that the steric hindrance between tropifexor and TGR5 might be a possible explanation for the impotency arises of tropifexor to TGR5. Overall, our analyses might provide an insight into the molecular mechanism of tropifexor binding to FXR-LBD and account for the high selectivity of tropifexor for FXR versus TGR5.

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.

FGFR inhibitors in cholangiocarcinoma: what's now and what's next?

Patients with intrahepatic cholangiocarcinoma (iCCA) face a highly dismal prognosis, due to late stage diagnosis, the relative chemoresistance of the disease, and an overall limited portfolio of established therapeutic concepts. In recent years, a number of next generation sequencing studies have provided detailed information on the molecular landscape of biliary malignancies, and have laid the groundwork for the evaluation of novel, targeted therapeutic opportunities. Although nearly 40% of patients harbor genetic alterations for which targeted options exist, rapid translation into clinical trials is hampered by the overall low patient numbers. One of the most frequent genetic events in patients with iCCAs are fusions that involve the fibroblast growth factor receptor 2 (FGFR2). Impressive results from pivotal phase II studies in pre-treated patients have confirmed that FGFR-inhibitors are a promising therapeutic option for this genetic subgroup, and the rapid pace with which these inhibitors are being clinically developed is clearly justified by the imminent benefit for the patients. However, the success of these agents should not blind us to key challenges that need to be addressed to optimize FGFR-directed therapies in the future. A better understanding of mechanisms that convey primary and secondary resistance will be crucial to improve up-front patient stratification, to prolong the duration of response, and to implement reasonable co-treatment approaches. In this review, we provide background information on the pathobiology of oncogenic FGFR fusions and selected genetic testing strategies, summarize the latest clinical data, and discuss future directions of FGFR-directed therapies in patients with iCCA.

Facts and New Hopes on Selective FGFR Inhibitors in Solid Tumors

Precision oncology relies on the identification of molecular alterations, responsible for tumor initiation and growth, which are suitable targets of specific inhibitors. The development of FGFR inhibitors represents an edifying example of the rapid evolution in the field of targeted oncology, with 10 different FGFR tyrosine kinase inhibitors actually under clinical investigation. In parallel, the discovery of FGFR activating molecular alterations (mainly FGFR3 mutations and FGFR2 fusions) across many tumor types, especially urothelial carcinomas and intrahepatic cholangiocarcinomas, widens the selection of patients that might benefit from selective FGFR inhibitors. The ongoing concomitant clinical evaluation of selective FGFR inhibitors in molecularly selected solid tumors brings new hopes for patients with metastatic cancer, for tumors so far excluded from molecularly guided treatments. Matching molecularly selected tumors with selective FGFR inhibitors has indeed led to promising results in phase I and II trials, justifying their registration to be expected in a near future, such as the recent accelerated approval of erdafitinib granted by the FDA for urothelial cancer. Widening our knowledge of the activity, efficacy, and toxicities relative to the selective FGFR tyrosine kinase inhibitors under clinical investigation, according to the exact FGFR molecular alteration, will be crucial to determine the optimal therapeutic strategy for patients suffering from FGFR-driven tumors. Similarly, identifying with appropriate molecular diagnostic, every single tumor harboring targetable FGFR alterations will be of utmost importance to attain the best outcomes for patients with FGFR-driven cancer.

Structural basis of binding of homodimers of the nuclear receptor NR4A2 to selective Nur-responsive DNA elements

Proteins of nuclear receptor subfamily 4 group A (NR4A), including NR4A1/NGFI-B, NR4A2/Nurr1, and NR4A3/NOR-1, are nuclear transcription factors that play important roles in metabolism, apoptosis, and proliferation. NR4A proteins recognize DNA response elements as monomers or dimers to regulate the transcription of a variety of genes involved in multiple biological processes. In this study, we determined two crystal structures of the NR4A2 DNA-binding domain (NR4A2-DBD) bound to two Nur-responsive elements: an inverted repeat and an everted repeat at 2.6-2.8 Å resolution. The structures revealed that two NR4A2-DBD molecules bind independently to the everted repeat, whereas two other NR4A2-DBD molecules form a novel dimer interface on the inverted repeat. Moreover, substitution of the interfacial residue valine 298 to lysine as well as mutation of DNA bases involved in the interactions abolished the dimerization. Overall, our structural, biochemical, and bioinformatics analyses provide a molecular basis for the binding of the NR4A2 protein dimers to NurREs and advance our understanding of the dimerization specificity of nuclear receptors.

Acquired On-Target Clinical Resistance Validates FGFR4 as a Driver of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality worldwide with no clinically confirmed oncogenic driver. Although preclinical studies implicate the FGF19 receptor FGFR4 in hepatocarcinogenesis, the dependence of human cancer on FGFR4 has not been demonstrated. Fisogatinib (BLU-554) is a potent and selective inhibitor of FGFR4 and demonstrates clinical benefit and tumor regression in patients with HCC with aberrant FGF19 expression. Mutations were identified in the gatekeeper and hinge-1 residues in the kinase domain of FGFR4 upon disease progression in 2 patients treated with fisogatinib, which were confirmed to mediate resistance in vitro and in vivo. A gatekeeper-agnostic, pan-FGFR inhibitor decreased HCC xenograft growth in the presence of these mutations, demonstrating continued FGF19-FGFR4 pathway dependence. These results validate FGFR4 as an oncogenic driver and warrant further therapeutic targeting of this kinase in the clinic. SIGNIFICANCE: Our study is the first to demonstrate on-target FGFR4 kinase domain mutations as a mechanism of acquired clinical resistance to targeted therapy. This further establishes FGF19-FGFR4 pathway activation as an oncogenic driver. These findings support further investigation of fisogatinib in HCC and inform the profile of potential next-generation inhibitors.See related commentary by Subbiah and Pal, p. 1646.This article is highlighted in the In This Issue feature, p. 1631.

Reciprocal regulatory mechanism between miR-214-3p and FGFR1 in FGFR1-amplified lung cancer

MicroRNA (miRNA) and fibroblast growth factor receptor 1 (FGFR1) dysregulation are considered to play an important role in tumor proliferation, invasion, and metastasis. However, the regulatory mechanism between miRNAs and FGFR1 in lung cancer remains unclear and extremely critical. miR-214-3p was sharply decreased and showed a significantly negative correlation with FGFR1 in lung cancer patients (n = 30). Luciferase reporter assay confirmed that miR-214-3p could downregulate FGFR1 by directly targeting 3′-untranslated region (UTR). miR-214-3p inhibited the processes of epithelial–mesenchymal transition and Wnt/MAPK/AKT (Wnt/mitogen-activated protein kinase/AKT) signaling pathway by targeting FGFR1. Moreover, miR-214-3p not only established a negative feedback regulation loop with FGFR1 through ERK (extracellular signal-regulated kinase) but also developed a synergism with FGFR1 inhibitor AZD4547. In conclusion, our study demonstrated the regulatory mechanism between miR-214-3p and FGFR1 in lung cancer. miR-214-3p acts as a vital target in FGFR1-amplified lung cancer by forming a miR-214-3p-FGFR1-Wnt/MAPK/AKT signaling pathway network. Co-targeting miR-214-3p and FGFR1 could provide greater benefits to patients with FGFR1-amplified lung cancer.

FGFR4 overexpression and hotspot mutations in metastatic ER+ breast cancer are enriched in the lobular subtype

Invasive lobular carcinoma (ILC) is an understudied subtype of breast cancer that requires novel therapies in the advanced setting. To study acquired resistance to endocrine therapy in ILC, we have recently performed RNA-Sequencing on long-term estrogen deprived cell lines and identified FGFR4 overexpression as a top druggable target. Here, we show that FGFR4 expression also increases dramatically in endocrine-treated distant metastases, with an average fold change of 4.8 relative to the paired primary breast tumor for ILC, and 2.4-fold for invasive ductal carcinoma (IDC). In addition, we now report that FGFR4 hotspot mutations are enriched in metastatic breast cancer, with an additional enrichment for ILC, suggesting a multimodal selection of FGFR4 activation. These data collectively support the notion that FGFR4 is an important mediator of endocrine resistance in ILC, warranting future mechanistic studies on downstream signaling of overexpressed wild-type and mutant FGFR4.

Fibroblast Growth Factor Receptors (FGFRs): Structures and Small Molecule Inhibitors

Fibroblast growth factor receptors (FGFRs) are a family of receptor tyrosine kinases expressed on the cell membrane that play crucial roles in both developmental and adult cells. Dysregulation of FGFRs has been implicated in a wide variety of cancers, such as urothelial carcinoma, hepatocellular carcinoma, ovarian cancer and lung adenocarcinoma. Due to their functional importance, FGFRs have been considered as promising drug targets for the therapy of various cancers. Multiple small molecule inhibitors targeting this family of kinases have been developed, and some of them are in clinical trials. Furthermore, the pan-FGFR inhibitor erdafitinib (JNJ-42756493) has recently been approved by the U.S. Food and Drug Administration (FDA) for the treatment of metastatic or unresectable urothelial carcinoma (mUC). This review summarizes the structure of FGFR, especially its kinase domain, and the development of small molecule FGFR inhibitors.

Characterization of FGF401 as a reversible covalent inhibitor of fibroblast growth factor receptor 4

Biochemical and structural studies provide information on the mode of action of FGF401 as a selective, reversible covalent inhibitor of FGFR4.

Association of PD-L1 gene rs4143815 C>G polymorphism and human cancer susceptibility: A systematic review and meta-analysis

Programmed death ligand 1(PD-L1) mediated immune escape play important roles in the development of cancer. The gene polymorphism of PD-L1, in particular rs4143815 C > G, has been associated with the cancer risks, but with conflicting results. Therefore, this meta-analysis was aimed to assess the association between rs4143815 C > G and cancer susceptibility. A systematic literature search was performed to select the studies and the pooled odds ratio (OR) with 95% confidence interval (CI) was used to evaluate the strength of association. Eleven eligible studies containing 3711 cases and 3704 controls were enrolled in the meta-analysis. The results suggested that there is a strong association between rs4143815 C > G and the cancer risks (G vs. C: OR = 1.386, 95% CI: 1.132-1.696, p = 0.002; GG vs. CG + CC: OR = 1.843 95% CI: 1.300-2.613, p = 0.002; GG + CG vs. CC: OR = 1.280, 95% CI: 1.040-1.576, p = 0.020). Subgroup analysis based on cancer type suggested that PD-L1 rs4143815 C > G might increase the susceptibility to gastric cancer (G vs. C: OR = 1.842, 95% CI: 1.403-2.418, p < 0.001) and bladder cancer (G vs. C: OR = 2.015, 95% CI: 1.556-2.608, p < 0.001), and genotype GG carriers of PD-L1 rs4143815 C > G might have higher risks of HCC (GG vs. CG + CC: OR = 2.226 95% CI: 1.562-3.172, p < 0.001). PD-L1 rs4143815 C > G might confer an increased cancer risk, indicating this SNP may contribute to the pathogenesis of cancer and might be used as a potential biomarker to predict the susceptibility to cancer.