Metal complexes bearing EGFR-inhibiting ligands as promising anticancer agents.

Overexpression of the epidermal growth factor receptor (EGFR, erbB1) has been observed in a wide range of solid tumors and has frequently been associated with poor prognosis. As a result, EGFR inhibition has become an attractive anticancer drug design strategy, and a large number of small molecular inhibitors have been developed. Despite the widespread clinical use of EGFR tyrosine kinase inhibitors (TKIs), their drug resistance, inadequate accumulation in tumors, and severe side effects have spurred the search for better antitumor drugs. Metal complexes have attracted much attention because of their different mechanisms compared with EGFR-TKIs. Therefore, the combination of metals and inhibitors is a promising anticancer strategy. For example, Ru and Pt centers are introduced to design complexes with double or multiple targets, while Au complexes are combined with inhibitors to overcome drug resistance. Co complexes are designed as prodrugs with weak side effects and enhanced targeting by the hypoxia activation strategy, and other metals such as Rh and Fe enhance the anticancer effect of the complexes. In addition, the introduction of Ga center is beneficial to the development of nuclear imaging tracers. In this paper, metal EGFR-TKI complexes in the last 15 years are reviewed, their mechanisms are briefly introduced, and their advantages are summarized.

Induction of immunogenic cell death by novel platinum-based anticancer agents.

Traditional platinum-based anticancer drugs, led by cisplatin, play an important role in chemotherapy. However, the development of platinum compounds is limited due to serious toxicity and side effects. In recent years, studies have showed that immunogenic cell death (ICD) may be one of the potential action mechanisms of classical platinum drugs, such as oxaliplatin. This strategy combining chemotherapy and immunotherapy can effectively utilize the body's immune system to help platinum compounds to fight against tumors, and the dose can be appropriately reduced to limit toxic side effects. The induction of ICD by platinum compounds has become a research hotspot and one of the future development directions of metal drugs. Here, the progress of platinum compounds were collected and comprehensively summarized, their capacity of ICD induction and mechanism of action are exposed, providing reference for the design and synthesis of new anticancer platinum ICD inducers.

SERD-NHC-Au(I) complexes for dual targeting ER and TrxR to induce ICD in breast cancer.

The development of selective estrogen receptor degraders (SERDs) has brought new ideas for the clinical treatment of ER-positive advanced breast cancer. The successful application of combinational therapy inspired the exploration of other targets to prevent breast cancer progression. Thioredoxin reductase (TrxR) is an important enzyme that can regulate redox balance in cells and it was considered as a potential target for anticancer treatment. In this study, we firstly combine a clinical SERD candidate--G1T48 (NCT03455270), with a TrxR inhibitor--N-heterocyclic carbene gold(I) [NHC-Au(I)] to form dual targeting complexes that can regulate both signaling pathways. The most efficacious complex 23 exhibited significant antiproliferative profile through degrading ER and inhibiting TrxR activity. Interestingly, it can induce immunogenic cell death (ICD) caused by ROS. This is the first evidence to elucidate the role of ER/TrxR-ROS-ICD axis in ER positive breast cancer and this research may inspire new drug development with novel mechanisms. The in vivo xenograft study demonstrated that complex 23 had excellent antiproliferative activity toward MCF-7 cells in mice model.

Recent development of gold(I) and gold(III) complexes as therapeutic agents for cancer diseases.

Metal complexes have demonstrated significant antitumor activities and platinum complexes are well established in the clinical application of cancer chemotherapy. However, the platinum-based treatment of different types of cancers is massively hampered by severe side effects and resistance development. Consequently, the development of novel metal-based drugs with different mechanism of action and pharmaceutical profile attracts modern medicinal chemists to design and synthesize novel metal-based agents. Among non-platinum anticancer drugs, gold complexes have gained considerable attention due to their significant antiproliferative potency and efficacy. In most situations, the gold complexes exhibit anticancer activities by targeting thioredoxin reductase (TrxR) or other thiol-rich proteins and enzymes and trigger cell death via reactive oxygen species (ROS). Interestingly, gold complexes were recently reported to elicit biochemical hallmarks of immunogenic cell death (ICD) as an ICD inducer. In this review, the recent progress of gold(I) and gold(III) complexes is comprehensively summarized, and their activities and mechanism of action are documented.

A Gold(I) Complex Containing an Oleanolic Acid Derivative as a Potential Anti-Ovarian-Cancer Agent by Inhibiting TrxR and Activating ROS-Mediated ERS.

Many cancer cells critically rely on antioxidant systems for cell survival and are vulnerable to further oxidative impairment triggered by agents generating reactive oxygen species (ROS). Therefore, the classical design and development of inhibitors that target antioxidant defense enzymes such as thioredoxin reductase (TrxR) can be a promising anticancer strategy. Herein, it is shown that a gold(I) complex containing an oleanolic acid derivative (4 b) induces apoptosis of ovarian cancer A2780 cells by activating endoplasmic reticulum stress (ERS). It can inhibit TrxR enzyme activity to elevate ROS, mediate ERS and mitochondrial dysfunction, and finally leads to cell cycle arrest and apoptosis of A2780 cells. Notably, this complex inhibits A2780 xenograft tumor growth accompanied by increased ERS level and decreased TrxR activity in tumor tissues.

Discovery of a Potent GLUT Inhibitor from a Library of Rapafucins by Using 3D Microarrays.

Glucose transporters play an essential role in cancer cell proliferation and survival and have been pursued as promising cancer drug targets. Using microarrays of a library of new macrocycles known as rapafucins, which were inspired by the natural product rapamycin, we screened for new inhibitors of GLUT1. We identified multiple hits from the rapafucin 3D microarray and confirmed one hit as a bona fide GLUT1 ligand, which we named rapaglutin A (RgA). We demonstrate that RgA is a potent inhibitor of GLUT1 as well as GLUT3 and GLUT4, with an IC50 value of low nanomolar for GLUT1. RgA was found to inhibit glucose uptake, leading to a decrease in cellular ATP synthesis, activation of AMP-dependent kinase, inhibition of mTOR signaling, and induction of cell-cycle arrest and apoptosis in cancer cells. Moreover, RgA was capable of inhibiting tumor xenografts in vivo without obvious side effects. RgA could thus be a new chemical tool to study GLUT function and a promising lead for developing anticancer drugs.

Design, synthesis and preliminary structure-activity relationship investigation of nitrogen-containing chalcone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors: a further study based on Flavokawain B Mannich base derivatives.

In order to study the structure-activity relationship of Flavokawain B Mannich-based derivatives as acetylcholinesterase (AChE) inhibitors in our recent investigation, 20 new nitrogen-containing chalcone derivatives (4 a-8d) were designed, synthesized, and evaluated for AChE inhibitory activity in vitro. The results suggested that amino alkyl side chain of chalcone dramatically influenced the inhibitory activity against AChE. Among them, compound 6c revealed the strongest AChE inhibitory activity (IC50 value: 0.85 µmol/L) and the highest selectivity against AChE over BuChE (ratio: 35.79). Enzyme kinetic study showed that the inhibition mechanism of compound 6c against AChE was a mixed-type inhibition. The molecular docking assay showed that this compound can both bind with the catalytic site and the peripheral site of AChE.

Synthesis and acetylcholinesterase inhibitory activity of Mannich base derivatives flavokawain B.

A novel series of flavokawain B derivatives, chalcone Mannich bases (4-10) were designed, synthesized, characterized, and evaluated for the inhibition activity against acetylcholinesterase (AChE). Biological results revealed that four compounds displayed potent activities against AChE with IC50 values below 20µM. Moreover, the most promising compound 8 was 2-fold more active than rivastigmine, a well-known AChE inhibitor. The logP values of 4-10 were around 2 which indicated that they were sufficiently lipophilic to pass blood brain barriers in vivo. Enzyme kinetic study suggested that the inhibition mechanism of compound 8 was a mixed-type inhibition. Meanwhile, the molecular docking showed that this compound can both bind with the catalytic site and the periphery of AChE.

Design, synthesis and pharmacological evaluation of chalcone derivatives as acetylcholinesterase inhibitors.

A novel series of chalcone derivatives (4a-8d) were designed, synthesized, and evaluated for the inhibition activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The logP values of the compounds were shown to range from 1.49 to 2.19, which suggested that they were possible to pass blood brain barriers in vivo. The most promising compound 4a (IC50: 4.68 µmol/L) was 2-fold more potent than Rivastigmine against AChE (IC50: 10.54 µmol/L) and showed a high selectivity for AChE over BuChE (ratio: 4.35). Enzyme kinetic study suggested that the inhibition mechanism of compound 4a was a mixed-type inhibition. Meanwhile, the result of molecular docking showed its potent inhibition of AChE and high selectivity for AChE over BuChE.

Metal N-heterocyclic carbene complexes as potential antitumor metallodrugs.

The discovery of cisplatin's antitumor activity in 1969 prompted the search for novel metal-containing complexes as potential anticancer drugs. Among these novel complexes, metal N-heterocyclic carbene (NHC) complexes have recently gained considerable attention because they perfectly fit prerequisites for efficient drug design and fast optimization. Moreover, most of them have shown higher cytotoxicity than cisplatin. This review describes the advances that have been achieved in using transition metal (Ag, Au, Pt, Pd, Cu, Ni, and Ru) complexes containing NHC ligands as antitumor agents. Their modes of action at the cellular lever are further discussed. All these initial achievements clearly demonstrate the great potential of metal-NHC complexes as antitumor agents.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice.

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Simultaneous Activation of Immunogenic Cell Death and cGAS-STING Pathway by Liver- and Mitochondria-Targeted Gold(I) Complexes for Chemoimmunotherapy of Hepatocellular Carcinoma.

Induction of immunogenic cell death (ICD) and activation of the cyclic GMP-AMP synthase stimulator of interferon gene (cGAS-STING) pathway are two potent anticancer immunotherapeutic strategies in hepatocellular carcinoma (HCC). Herein, 12 liver- and mitochondria-targeting gold(I) complexes (9a-9l) were designed and synthesized. The superior complex 9b produced a considerable amount of reactive oxygen species (ROS) and facilitated DNA excretion, the ROS-induced ICD and DNA activated the cGAS-STING pathway, both of which evoked an intense anticancer immune response in vitro and in vivo. Importantly, 9b strongly inhibited tumor growth in a patient-derived xenograft model of HCC. Overall, we present the first case of simultaneous ICD induction and cGAS-STING pathway activation within the same gold-based small molecule, which may provide an innovative strategy for designing chemoimmunotherapies for HCC.

A terbium(III) complex-based time-resolved luminescent probe for selenocysteine as an inhibitor of selenoproteins.

A terbium(III) complex-based time-resolved luminescence probe for selenocysteine can inhibit selenoprotein activity via a selenolate-triggered cleavage reaction of sulfonamide bonds in living cells.

Discovery of novel quinoline scaffold selective estrogen receptor degraders (SERDs) for treatment of ER positive breast cancer with enhanced antiproliferative bioactivity through immunogenic cell death (ICD) effects.

Combination therapy proven to be an effective therapeutic approach for estrogen receptor (ER)-positive breast cancer. Currently, cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are combined with aromatase inhibitors (AIs) or selective estrogen receptor degraders (SERDs) as first-line therapy for advanced ER-positive breast cancer. Herein, a new family of quinoline scaffold SERDs was synthesized and evaluated in MCF-7 cells. Among them, compounds 18j and 24d exhibited remarkable MCF-7 inhibition, both alone and in combination with ribociclib (CDK4/6 inhibitor), in vitro and in vivo. Meanwhile, compounds 18j and 24d effectively degraded ER and inhibited ER downstream signaling pathways. Interestingly, compounds 18j and 24d induced endoplasmic reticulum stress (ERS) and triggered immunogenic cell death (ICD) via damage-associated molecular patterns (DAMPs) in MCF-7 cells. These findings highlight the immune-related and enhanced antiproliferative effects of oral SERDs in ER positive breast cancer treatment.

Research Progress on Bioactive Metal Complexes against ER-Positive Advanced Breast Cancer.

Breast cancer is the most prevalent cancer in women and represents a serious disease that is harmful to life and health. In 1977, with the approval of tamoxifen, endocrine therapy has become the main clinical treatment for ER-positive (ER+) breast cancer. Although patients initially respond well to endocrine therapies, drug resistance often emerges and side effects can be challenging. To overcome drug resistance, the exploration for new drugs is a priority. Metal complexes have demonstrated significant antitumor activities, and platinum complexes are widely used in the clinic against various cancers, including breast cancer. In this Perspective, the first section describes the classification and mechanism of endocrine therapy drugs for ER+ breast cancer, and the second section summarizes research since 2000 into metal complexes with activity toward ER+ breast cancer. Finally, we discuss the opportunities, challenges, and future directions for metal complexes in the treatment of ER+ breast cancer.

Tumor-Targeting NHC-Au(I) Complex Induces Immunogenic Cell Death in Hepatocellular Carcinoma.

Immunogenic cell death (ICD) is a promising direction of cancer immunotherapy in hepatocellular carcinoma (HCC). A series of novel NHC-Au(I) complexes derived from 4,5-diarylimidazole, containing glycyrrhetinic acid (GA) as an efficient targeting ligand for HCC, were herein designed and synthesized. Among these, complex 4C exhibited excellent effectiveness for tumor targeting and antitumor activity, which induced the occurrence of ICD in HCC cells. Additionally, 4C can effectively inhibit TrxR enzyme activity, increase reactive oxygen species (ROS) expression, lead to redox homeostasis disorder, mediate mitochondrial dysfunction and endoplasmic reticulum stress (ERS), and cause the characteristic discharge of damage-associated molecular patterns (DAMPs) in HCC cells. More importantly, 4C showed a great ICD-inducing effect in a vaccination mouse model and activated antitumor immunity in a tumor-bearing C57BL/6 mouse model, which is consistent with the in vitro results. In conclusion, we found the potential of Au(I) complex with HCC-targeted capability for effective tumor immunotherapy.

NSAID-Au(I) Complexes Induce ROS-Driven DAMPs and Interpose Inflammation to Stimulate the Immune Response against Ovarian Cancer.

Inflammation contributes to the development of ovarian cancer, and chemoresistance is a principal obstacle in ovarian cancer treatment. Herein, we designed and synthesized a series of gold(I) complexes derived from NSAIDs or their analogues. Among them, complex B3 (Npx-Au) displayed higher antitumor activity than cisplatin and other gold(I) complexes. Npx-Au could induce oxidative stress and the damage-associated molecular patterns (DAMPs) process by the inhibition of TrxR activity. Mechanistic studies revealed that simultaneous downregulation of COX-2 and PD-L1 was observed after Npx-Au treatment. Interestingly, in vivo experiments demonstrated that Npx-Au treatment could stimulate the immune response via reducing the expression of PD-L1, inducing DC maturation and increasing the infiltration of T (CD4+ and CD8+) cells. Collectively, our studies found that the gold(I) complex Npx-Au could elicit immunogenic cell death (ICD) and provide a promising strategy for chemotherapy combined with immunotherapy in the treatment of ovarian cancer.

Design, synthesis and biological evaluation of fluorinated selective estrogen receptor degraders (FSERDs) --- A promising strategy for advanced ER positive breast cancer.

Although endocrine therapies involving pharmaceuticals, such as tamoxifen and aromatase inhibitors, had initially demonstrated good responses in patients with estrogen receptor-positive (ER+) breast cancer, they often led to drug resistance. ER plays a vital role in the progression of metastatic diseases. Fulvestrant, a first generation selective estrogen receptor degrader (SERD), can effectively downregulate the ER protein and inhibit its downstream signaling pathways. However, as the drug needs to be intramuscularly injected, its widespread use is limited owing to poor patient compliance. Herein, we described a novel class of orally bioavailable fluorine-substituted SERDs that exhibit improved pharmacokinetic profiles. We substituted the hydroxyl group of clinical SERD candidate 6 with a fluorine atom to diminish phase II metabolism. The subsequent structure-activity relationship (SAR) investigation identified 22h and 27b, which can effectively degrade ER in a dose-dependent manner and exhibit considerable antiproliferative potency and efficacy in vitro and in vivo. The excellent pharmacokinetic profiles of 27b render it promising candidate of clinically useful oral SERD.

Gold(I) selenium N-heterocyclic carbene complexes as potent antibacterial agents against multidrug-resistant gram-negative bacteria via inhibiting thioredoxin reductase.

Multidrug-resistant (MDR) Gram-negative bacteria have become a global threat to human life and health, and novel antibiotics are urgently needed. The thioredoxin (Trx) system can be used as an antibacterial target to combat MDR bacteria. Here, we found that two active gold(I) selenium N-heterocyclic carbene complexes H7 and H8 show more promising antibacterial effects against MDR bacteria than auranofin. Both H7 and H8 irreversibly inhibit the bacterial TrxR activity via targeting the redox-active motif, abolishing the capacity of TrxR to quench reactive oxygen species (ROS) and finally leading to oxidative stress. The increased cellular superoxide radical levels impact a variety of functions necessary for bacterial survival, such as cellular redox balance, cell membrane integrity, amino acid metabolism, and lipid peroxidation. In vivo data present much better antibacterial activity of H7 and H8 than auranofin, promoting the wound healing and prolonging the survival time of Carbapenem-resistant Acinetobacter baumannii (CRAB) induced peritonitis. Most notably in this study, we revealed the influence of gold(I) complexes on both the Trx system and the cellular metabolic states to better understand their killing mechanism and to support further antibacterial drug design.

A chromosome-level genome assembly reveals that a bipartite gene cluster formed via an inverted duplication controls monoterpenoid biosynthesis in Schizonepeta tenuifolia.

Biosynthetic gene clusters (BGCs) are regions of a genome where genes involved in a biosynthetic pathway are in proximity. The origin and evolution of plant BGCs as well as their role in specialized metabolism remain largely unclear. In this study, we have assembled a chromosome-scale genome of Japanese catnip (Schizonepeta tenuifolia) and discovered a BGC that contains multiple copies of genes involved in four adjacent steps in the biosynthesis of p-menthane monoterpenoids. This BGC has an unprecedented bipartite structure, with mirrored biosynthetic regions separated by 260 kilobases. This bipartite BGC includes identical copies of a gene encoding an old yellow enzyme, a type of flavin-dependent reductase. In vitro assays and virus-induced gene silencing revealed that this gene encodes the missing isopiperitenone reductase. This enzyme evolved from a completely different enzyme family to isopiperitenone reductase from closely related Mentha spp., indicating convergent evolution of this pathway step. Phylogenomic analysis revealed that this bipartite BGC has emerged uniquely in the S. tenuifolia lineage and through insertion of pathway genes into a region rich in monoterpene synthases. The cluster gained its bipartite structure via an inverted duplication. The discovered bipartite BGC for p-menthane biosynthesis in S. tenuifolia has similarities to the recently described duplicated p-menthane biosynthesis gene pairs in the Mentha longifolia genome, providing an example of the convergent evolution of gene order. This work expands our understanding of plant BGCs with respect to both form and evolution, and highlights the power of BGCs for gene discovery in plant biosynthetic pathways.