Identification of novel and potent PROTACs targeting FAK for non-small cell lung cancer: Design, synthesis, and biological study

Targeting focal adhesion kinase (FAK) for cancer therapy: FAK inhibitors, FAK-based dual-target inhibitors and PROTAC degraders

Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, plays an essential role in regulating cell proliferation, migration and invasion through both kinase-dependent enzymatic function and kinase-independent scaffolding function. The overexpression and activation of FAK is commonly observed in various cancers and some drug-resistant settings. Therefore, targeted disruption of FAK has been identified as an attractive strategy for cancer treatment. To date, numerous structurally diverse inhibitors targeting distinct domains of FAK have been developed, encompassing kinase domain inhibitors, FERM domain inhibitors, and FAT domain inhibitors, with several FAK inhibitors advanced to clinical trials. Moreover, given the critical role of FAK scaffolding function in signal transduction, FAK-targeted PROTACs have also been developed. Although no current FAK-targeted therapeutics have been approved for the market, the combination of FAK inhibitors with other anticancer drugs has shown considerable promise in the clinic. This review provides an overview of current drug discovery strategies targeting FAK, including the development of FAK inhibitors, FAK-based dual-target inhibitors and proteolysis-targeting chimeras (PROTACs) in both literature and patent applications. Accordingly, their design and optimization process, mechanisms of action and biological activities are discussed to offer insights into future directions of FAK-targeting drug discovery in cancer therapy.

Annual review of PROTAC degraders as anticancer agents in 2022

Following nearly two decades of development, significant advancements have been achieved in PROTAC technology. As of the end of 2022, more than 20 drugs have entered clinical trials, with ARV-471 targeting estrogen receptor (ER) showing remarkable progress by entering phase III clinical studies. In 2022, significant progress has been made on multiple targets. The first reversible covalent degrader designed to target the KRASG12C mutant protein, based on cyclopropionamide, has been reported. Additionally, the activity HDCA1 degrader surpassed submicromolar levels during the same year. A novel FEM1B covalent ligand called EN106 was also discovered, expanding the range of available ligands. Furthermore, the first PROTAC drug targeting SOS1 was reported. Additionally, the first-in-class degraders that specifically target BRD4 isoforms (BRD4 L and BRD4 S) have recently been reported, providing a valuable tool for further investigating the biological functions of these isoforms. Lastly, a breakthrough was also achieved with the first degrader targeting both CDK9 and Cyclin T1. In this review, we aimed to update the PROTAC degraders as potential anticancer agents covering articles published in 2022. The design strategies, degradation effects, and anticancer activities were highlighted, which might provide an updated sight to develop novel PROTAC degraders with great potential as anticancer agents as well as favorable drug-like properties.

Roles and inhibitors of FAK in cancer: current advances and future directions

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that exhibits high expression in various tumors and is associated with a poor prognosis. FAK activation promotes tumor growth, invasion, metastasis, and angiogenesis via both kinase-dependent and kinase-independent pathways. Moreover, FAK is crucial for sustaining the tumor microenvironment. The inhibition of FAK impedes tumorigenesis, metastasis, and drug resistance in cancer. Therefore, developing targeted inhibitors against FAK presents a promising therapeutic strategy. To date, numerous FAK inhibitors, including IN10018, defactinib, GSK2256098, conteltinib, and APG-2449, have been developed, which have demonstrated positive anti-tumor effects in preclinical studies and are undergoing clinical trials for several types of tumors. Moreover, many novel FAK inhibitors are currently in preclinical studies to advance targeted therapy for tumors with aberrantly activated FAK. The benefits of FAK degraders, especially in terms of their scaffold function, are increasingly evident, holding promising potential for future clinical exploration and breakthroughs. This review aims to clarify FAK's role in cancer, offering a comprehensive overview of the current status and future prospects of FAK-targeted therapy and combination approaches. The goal is to provide valuable insights for advancing anti-cancer treatment strategies.

The application of PROTAC in HDAC

Inducing protein degradation by proteolysis targeting chimera (PROTAC) has provided great opportunities for scientific research and industrial applications. Histone deacetylase (HDAC)-PROTAC has been widely developed since the first report of its ability to induce the degradation of SIRT2 in 2017. To date, ten of the eighteen HDACs (HDACs 1-8, HDAC10, and SIRT2) have been successfully targeted and degraded by HDAC-PROTACs. HDAC-PROTACs surpass traditional HDAC inhibitors in many aspects, such as higher selectivity, more potent antiproliferative activity, and the ability to disrupt the enzyme-independent functions of a multifunctional protein and overcome drug resistance. Rationally designing HDAC-PROTACs is a main challenge in development because slight variations in chemical structure can lead to drastic effects on the efficiency and selectivity of the degradation. In the future, HDAC-PROTACs can potentially be involved in clinical research with the support of the increased amount of in vivo data, pharmacokinetic evaluation, and pharmacological studies.

PROTAC therapy as a new targeted therapy for lung cancer

Despite recent advances in molecular therapeutics, lung cancer is still a leading cause of cancer deaths. Currently, limited targeted therapy options and acquired drug resistance present significant barriers in the treatment of patients with lung cancer. New strategies in drug development, including those that take advantage of the intracellular ubiquitin-proteasome system to induce targeted protein degradation, have the potential to advance the field of personalized medicine for patients with lung cancer. Specifically, small molecule proteolysis targeting chimeras (PROTACs), consisting of two ligands connected by a linker that bind to a target protein and an E3 ubiquitin ligase, have been developed against many cancer targets, providing promising opportunities for advanced lung cancer. In this review, we focus on the rationale for PROTAC therapy as a new targeted therapy and the current status of PROTAC development in lung cancer.

Discovery of CZS-241: A Potent, Selective, and Orally Available Polo-Like Kinase 4 Inhibitor for the Treatment of Chronic Myeloid Leukemia

Recent studies demonstrate that PLK4 has emerged as a therapeutic target for the treatment of multiple cancers owing to its indispensable role in cell division. Herein, starting from previously identified effective compound CZS-034, based on rational drug design strategies, tyrosine kinase receptor A (TRKA) selectivity- and metabolic stability-guided structure-activity relationship (SAR) exploration were carried out to discover a highly potent (IC₅₀ = 2.6 nM) and selective (SF = 1054.4 over TRKA) PLK4 inhibitor B43 (CZS-241) with acceptable human liver microsome stability (t_1/2 = 31.5 min). Moreover, compound B43 effectively inhibited leukemia cells in 29 tested cell lines, especially chronic myeloid leukemia (CML) cell lines K562 and KU-812. Pharmacokinetic characteristics revealed that compound B43 possessed over 4 h of half-life and 70.8% bioavailability in mice. In the K562 cells xenograft mouse model, a 20 mg/kg/day dosage treatment obviously suppressed tumor progression. As a potential and novel PLK4-targeted candidate drug for CML, compound B43 is undergoing extensive preclinical safety evaluation.

PROTACS: A technology with a gold rush-like atmosphere

Abnormally expressed or malfunctioning proteins may affect or even damage cells, leading to the onset of diseases. Proteolysis targeting chimera (PROTAC) technology has been proven to be a fresh therapeutic strategy, superior to conventional small molecule inhibitors for the treatment of diseases caused by pathogenic proteins. Unlike conventional small molecule inhibitors that are occupancy-driven, PROTACs are heterobifunctional small molecules with catalytic properties. They combine with E3 ligases and target proteins to form a ternary complex, rendering the target protein ubiquitous and subsequently degraded by the proteasome. This paper focuses first on significant events in the development of PROTAC technology from 2001 to 2022, followed by a brief overview of various PROTACs categorized by target proteins. In addition, the applications of PROTACs in the treatment of diseases and fundamental biology are also under discussion.

The dual FAK-HDAC inhibitor MY-1259 displays potent activities in gastric cancers in vitro and in vivo

Epigenetic regulation and Focal adhesion kinase (FAK) are considered to be two important targets for the development of antitumor drugs. Studies have shown that the combination of FAK and HDAC inhibitors could exhibit synergistic effects in a subset of cancer cells in vitro and in vivo. At present, there are few reports on dual target inhibitors of FAK and HDAC. Here, we first reported a new compound MY-1259 as a dual FAK and HDAC6 inhibitor, which exhibited efficient treatment effects on gastric cancers in vitro and in vivo. MY-1259 exhibited potent inhibitory activities against FAK (IC₅₀ = 132 nM) and HDAC6 (IC₅₀ = 16 nM). Notably, MY-1259 showed selective inhibitory potency on HDAC6 over HDAC1, HDAC2 and HDAC3. In addition, MY-1259 could potently inhibit the proliferative activities of MGC-803 and BGC-823 cells (IC₅₀ = 3.91 and 15.46 nM, respectively, using flow cytometry counting), induce cell apoptosis, and cellular senescence. MY-1259 could effectively down-regulate the levels of Ac-Histone H3 and Ac-α-tubulin, and also inhibit the phosphorylation of FAK at three phosphorylation sites Y397, Y576/577 and Y925, thereby inhibiting the activation of ERK and AKT/mTOR. MY-1259 exhibited more effective antitumor effect in vivo than the HDAC inhibitor SAHA and FAK inhibitor TAE-226 alone or in combination, showing the advantages of FAK/HDAC dual inhibitors in the treatment of gastric cancers. Therefore, the results in this work suggested that inhibition of FAK and HDAC by MY-1259 might represent a promising strategy for the treatment of gastric cancers.

Advancing targeted protein degradation for metabolic diseases therapy

The development and application of traditional drugs represented by small molecule chemical drugs and biological agents, especially inhibitors, have become the mainstream drug development. In recent years, targeted protein degradation (TPD) technology has become one of the most promising methods to remove specific disease-related proteins using cell self-destruction mechanisms. Many different TPD strategies are emerging based on the ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP), including but not limited to proteolysis-targeting chimeras (PROTAC), molecular glues (MG), lysosome targeting chimeras (LYTAC), chaperone-mediated autophagy (CMA)-targeting chimeras, autophagy-targeting chimera (AUTAC), autophagosome-tethering compound (ATTEC), and autophagy-targeting chimera (AUTOTAC). The advent of targeted degradation technology can change most protein targets in human cells from undruggable to druggable, greatly expanding the therapeutic prospect of refractory diseases such as metabolic syndrome. Here, we summarize the latest progress of major TPD technologies, especially in metabolic syndrome and look forward to providing new insights for drug discovery.

PROTACting the kinome with covalent warheads

The dawn of targeted degradation using proteolysis-targeting chimeras (PROTACs) against recalcitrant proteins has prompted numerous efforts to develop complementary drugs. Although many of these are specifically directed against undruggable proteins, there is increasing interest in small molecule-based PROTACs that target intracellular pathways, and some have recently entered clinical trials. Concurrently, small molecule-based PROTACs that target protumorigenic pathways in cancer cells, the tumor microenvironment (TME), and angiogenesis have been found to have potent effects that synergize with the action of antibodies. This has led to the augmentation of PROTACs with variable substitution patterns. Several combinations with small molecules targeting undruggable proteins are now under clinical investigation. In this review, we discuss the recent milestones achieved as well as challenges encountered in this area of drug development, as well as our opinion on the best path forward.