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

Trends in covalent drug discovery: a 2020-23 patent landscape analysis focused on select covalent reacting groups (CRGs) found in FDA-approved drugs

INTRODUCTION

Covalent drugs contain electrophilic groups that can react with nucleophilic amino acids located in the active sites of proteins, particularly enzymes. Recently, there has been considerable interest in using covalent drugs to target non-catalytic amino acids in proteins to modulate difficult targets (i.e. targeted covalent inhibitors). Covalent compounds contain a wide variety of covalent reacting groups (CRGs), but only a few of these CRGs are present in FDA-approved covalent drugs.

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This review summarizes a 2020-23 patent landscape analysis that examined trends in the field of covalent drug discovery around targets and organizations. The analysis focused on patent applications that were submitted to the World International Patent Organization and selected using a combination of keywords and structural searches based on CRGs present in FDA-approved drugs.

EXPERT OPINION

A total of 707 patent applications from >300 organizations were identified, disclosing compounds that acted at 71 targets. Patent application counts for five targets accounted for ~63% of the total counts (i.e. BTK, EGFR, FGFR, KRAS, and SARS-CoV-2 Mpro). The organization with the largest number of patent counts was an academic institution (Dana-Farber Cancer Institute). For one target, KRAS G12C, the discovery of new drugs was highly competitive (>100 organizations, 186 patent applications).

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.

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.

Discovery of 6-Formylpyridyl Urea Derivatives as Potent Reversible-Covalent Fibroblast Growth Factor Receptor 4 Inhibitors with Improved Anti-Hepatocellular Carcinoma Activity

Fibroblast growth factor receptor 4 (FGFR4) has been considered as a potential anticancer target due to FGF19/FGFR4 mediated aberrant signaling in hepatocellular carcinoma (HCC). Several FGFR4 inhibitors have been reported, but none have gained approval. Herein, a series of 5-formyl-pyrrolo[3,2-b]pyridine-3-carboxamides and a series of 6-formylpyridyl ureas were characterized as selective reversible-covalent FGFR4 inhibitors. The representative 6-formylpyridyl urea 8z exhibited excellent potency against FGFR4WT, FGFR4V550L, and FGFR4V550M with IC50 values of 16.3, 12.6, and 57.3 nM, respectively. It also potently suppressed proliferation of Ba/F3 cells driven by FGFR4WT, FGFR4V550L, and FGFR4V550M, and FGFR4-dependent Hep3B and Huh7 HCC cells, with IC50 values of 1.2, 13.5, 64.5, 15.0, and 20.4 nM, respectively. Furthermore, 8z displayed desirable microsomal stability and significant in vivo efficacy in the Huh7 HCC cancer xenograft model in nude mice. The study provides a promising new lead for anticancer drug discovery directed toward overcoming FGFR4 gatekeeper mutation mediated resistance in HCC patients.

Structural basis and selectivity of sulfatinib binding to FGFR and CSF-1R

Acquired drug resistance poses a challenge for single-target FGFR inhibitors, leading to the development of dual- or multi-target FGFR inhibitors. Sulfatinib is a multi-target kinase inhibitor for treating neuroendocrine tumors, selectively targeting FGFR1/CSF-1R. To elucidate the molecular mechanisms behind its binding and kinase selectivity, we determined the crystal structures of sulfatinib with FGFR1/CSF-1R. The results reveal common structural features and distinct conformational adaptability of sulfatinib in response to FGFR1/CSF-1R binding. Further biochemical and structural analyses disclose sensitivity of sulfatinib to FGFR/CSF-1R gatekeeper mutations. The insensitivity of sulfatinib to FGFR gatekeeper mutations highlights the indispensable interactions with the hydrophobic pocket for FGFR selectivity, whereas the rotatory flexibility may enable sulfatinib to overcome CSF-1RT663I. This study not only sheds light on the structural basis governing sulfatinib's FGFR/CSF-1R inhibition, but also provides valuable insights into the rational design of dual- or multi-target FGFR inhibitors with selectivity for CSF-1R and sensitivity to gatekeeper mutations.

Past, present, and future of FGFR inhibitors in cholangiocarcinoma: from biological mechanisms to clinical applications

INTRODUCTION

Biliary tract carcinoma (BTC) is a heterogenous group of aggressive hepatic malignancies, second to hepatocellular carcinoma per prevalence. Despite clinical research advancement, the overall 5-year survival rate is just above 2%. With the identification of somatic core mutations in half of cholangiocarcinomas. In the intrahepatic subtype (iCCA), it is possible to target mutational pathways of pharmacological interest.

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Major attention has been drawn to fibroblast growth factor receptor (FGFR), especially the type 2 (FGFR2), found mutated in 10-15% of iCCAs. FGFR2 fusions became the target of novel tyrosine-kinase inhibitors investigated in clinical studies, showing promising results so as to gain regulatory approval by American and European committees in recent years. Such drugs demonstrated a better impact on the quality of life compared to standard chemotherapy; however, side effects including hyperphosphatemia, gastrointestinal, eye, and nail disorders are common although mostly manageable.

EXPERT OPINION

As FGFR inhibitors may soon become the new alternative to standard chemotherapy in FGFR-mutated cholangiocarcinoma, accurate molecular testing and monitoring of acquired resistance mechanisms will be essential. The possible application of FGFR inhibitors in first-line treatment, as well as in combination with current standard treatments, remains the next step to be taken.

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.

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.

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.

Signaling Pathway and Small-Molecule Drug Discovery of FGFR: A Comprehensive Review

Targeted therapy is a groundbreaking innovation for cancer treatment. Among the receptor tyrosine kinases, the fibroblast growth factor receptors (FGFRs) garnered substantial attention as promising therapeutic targets due to their fundamental biological functions and frequently observed abnormality in tumors. In the past 2 decades, several generations of FGFR kinase inhibitors have been developed. This review starts by introducing the biological basis of FGF/FGFR signaling. It then gives a detailed description of different types of small-molecule FGFR inhibitors according to modes of action, followed by a systematic overview of small-molecule-based therapies of different modalities. It ends with our perspectives for the development of novel FGFR inhibitors.