Radiosensitization of human pancreatic cancer by piperlongumine analogues

Design, synthesis, and biological studies of nitric oxide-donating piperlongumine derivatives triggered by lysyl oxidase as anti-triple negative breast cancer agents

Nitric oxide (NO) is an important gas messenger molecule with a wide range of biological functions. High concentration of NO exerts promising antitumor effects and is regarded as one of the hot spots in cancer research, that have limitations in their direct application due to its gaseous state, short half-life (seconds) and high reactivity. Lysyl oxidase (LOX) is a copper-dependent amine oxidase that is responsible for the covalent bonding between collagen and elastin and promotes tumor cell invasion and metastasis. The overexpression of LOX in triple-negative breast cancer (TNBC) makes it an attractive target for TNBC therapy. Herein, novel NO donor prodrug molecules were designed and synthesized based on the naturally derived piperlongumine (PL) skeleton, which can be selectively activated by LOX to release high concentrations of NO and PL derivatives, both of them play a synergistic role in TNBC therapy. Among them, the compound TM-1 selectively released NO in highly invasive TNBC cells (MDA-MB-231), and TM-1 was also confirmed as a potential TNBC cell line inhibitor with an inhibitory concentration of 2.274 μM. Molecular docking results showed that TM-1 had a strong and selective binding affinity with LOX protein.

Profiling of small-molecule necroptosis inhibitors based on the subpockets of kinase-ligand interactions

Necroptosis is a highly regulated cell death (RCD) form in various inflammatory diseases. Receptor-interacting protein kinase 1 (RIPK1) and RIPK3 are involved in the pathway. Targeting the kinase domains of RIPK1 and/or 3 is a drug design strategy for related diseases. It is generally accepted that essential reoccurring features are observed across the human kinase domains, including RIPK1 and RIPK3. They present common N- and C-terminal domains that are built up mostly by α-helices and β-sheets, respectively. The current RIPK1/3 kinase inhibitors mainly interact with the kinase catalytic cleft. This article aims to present an in-depth profiling for ligand-kinase interactions in the crucial cleft areas by carefully aligning the kinase-ligand cocrystal complexes or molecular docking models. The similarity and differential structural segments of ligands are systematically evaluated. New insights on the adaption of the conserved and selective kinase domains to the diversity of chemical scaffolds are also provided. In a word, our analysis can provide a better structural requirement for RIPK1 and RIPK3 inhibition and a guide for inhibitor discovery and optimization of their potency and selectivity.

Therapeutic Approaches in Pancreatic Cancer: Recent Updates

Cancer is a significant challenge for effective treatment due to its complex mechanism, different progressing stages, and lack of adequate procedures for screening and identification. Pancreatic cancer is typically identified in its advanced progression phase with a low survival of ~5 years. Among cancers, pancreatic cancer is also considered a high mortality-causing casualty over other accidental or disease-based mortality, and it is ranked seventh among all mortality-associated cancers globally. Henceforth, developing diagnostic procedures for its early detection, understanding pancreatic cancer-linked mechanisms, and various therapeutic strategies are crucial. This review describes the recent development in pancreatic cancer progression, mechanisms, and therapeutic approaches, including molecular techniques and biomedicines for effectively treating cancer.

Neuroprotective effect of a Keap1-Nrf2 Protein-Protein Inter-action inhibitor on cerebral Ischemia/Reperfusion injury

Oxidative stress has been confirmed to be closely related to the occurrence and development of cerebral ischemic/reperfusion (I/R). The Keap1-Nrf2 pathway is widely recognized as a defensive system to maintain cellular redox homeostasis. Targeting Keap1-Nrf2 interaction by small molecules to release Nrf2 should be a promising strategy to treat cerebral I/R injury. The piperazinyl-naphthalenesulfonamide 6 K was reported to be a Keap1-Nrf2 protein-protein interaction inhibitor, showing promising antioxidative effect. Herein, this study is to investigate whether 6 K could prevent brain from I/R injury. The related mechanism of oxidative stress was also elucidated using in vivo mice middle cerebral artery occlusion (MCAO) model and in vitro SH-SY5Y oxygen-glucose deprivation/reperfusion (OGD/R) model. The results indicated that treatment of 6 K markedly decreased infarct volume, apoptotic neurons and oxidative damage and promoted neurologic recovery in vivo. The cell model revealed that the reactive oxygen species (ROS) was decreased, and cell viability was increased. Western blots and immunofluorescence staining demonstrated that compound treatment promoted Nrf2 release and nuclear translocation. The downstream protective enzymes were significantly enhanced at both in vivo and in vitro levels. Collectively, 6 K is a promising protective agent against cerebral I/R injury through activation of Nrf2 to suppress oxidative stress.

Structure-Based Design of Novel Alkynyl Thio-Benzoxazepinone Receptor-Interacting Protein Kinase-1 Inhibitors: Extending the Chemical Space from the Allosteric to ATP Binding Pockets

Systemic inflammatory response syndrome (SIRS), characterized by severe systemic inflammation, represents a major cause of health loss, potentially leading to multiple organ failure, shock, and death. Exploring potent RIPK1 inhibitors is an effective therapeutic strategy for SIRS. Recently, we described thio-benzoxazepinones as novel RIPK1 inhibitors and confirmed their anti-inflammatory activity. Herein, we further synthesized novel thio-benzoxazepinones by introducing substitutions on the benzene ring by an alkynyl bridge in order to extend the chemical space from the RIPK1 allosteric to ATP binding pockets. The in vitro cell and kinase assays found that compounds 2 and 29 showed highly potent activity against necroptosis (EC₅₀ = 3.7 and 3.2 nM) and high RIPK1 inhibitory activity (K_d = 9.7 and 70 nM). Prominently, these two analogues possessed better in vivo anti-inflammatory effects than the clinical candidate GSK'772 and effectively blocked hypothermia and deaths in a TNFα-induced SIRS model.

Profiling of the chemical space on the phenyl group of substituted benzothiazole RIPK3 inhibitors

Necroptosis is confirmed as a precisely programmed cell death that is activated in caspase-deficient conditions. Receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like pseudokinase (MLKL) are the key regulators involved in the signaling pathway. However, accumulating evidence suggests that RIPK1 also works in apoptosis and inflammation pathways independent of necroptosis. Differently, RIPK3 signals necroptosis independent of RIPK1. Thus, identification of specific RIPK3 inhibitors is of great importance for the drug development associated with necroptosis. The benzothiazole carboxamide is a privileged scaffold as RIPK3 inhibitors developed by our group recently. In this study, we work on the phenyl group in-between of benzothiazole and carboxamide to profile the chemical space. Finally, a chlorinated derivative XY-1-127 was found to specifically inhibit necroptosis rather than apoptosis with an EC₅₀ value of 676.8 nM and target RIPK3 with a K_d of 420 nM rather than RIPK1 (K_d = 4300 nM). It was also confirmed to block the formation of necrosome by inhibiting RIPK3 phosphorylation at 1 μM in necroptosis cells. This work discovers the chemical space insights on the phenyl group of the substituted benzothiazole RIPK3 inhibitors and provides a new lead compound for further development.

Engineering piperlongumine-inspired analogs as Nrf2-dependent neuroprotectors against oxidative damage by an electrophilicity-based strategy

Oxidative stress contributes significantly to the development of neurodegenerative diseases, thus developing nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent neuroprotectors is highly required for either prevention or treatment of these diseases. This work highlights an electrophilicity-based strategy that allows finding more active Nrf2-dependent neuroprotectors than natural piperlongumine (PL). Electrophilic modification was applied on both the exocylic and endocyclic Michael acceptors of PL, which includes placement of an electron-withdrawing trifluoromethyl group on its aromatic ring in the ortho, meta, or para position to the exocyclic olefin, and further introduction of an electron-withdrawing α-chlorine on its lactam ring. From a panel of PL analogs, we identified PLCl-4CF₃, characterized by the presence of p-trifluoromethyl group and α-chlorine, to be significantly superior to the parent PL in protecting PC12 cells from oxidative damage induced by 6-hydroxydopamine hydrochloride. Mechanistic studies reveal that the increased electrophilicity of PLCl-4CF₃ in its two Michael acceptors allows its ability to covalently modify Cys-151 at Keap1, facilitating inhibition against Nrf2 ubiquitination, translocation of Nrf2 into the nucleus, induction of phase 2 enzymes and final protection of PC12 cells from oxidative damage.

Advanced approaches of developing targeted covalent drugs

In recent years, the development of targeted covalent inhibitors has gained popularity around the world. Specific groups (electrophilic warheads) form irreversible bonds with the side chain of nucleophilic amino acid residues, thus changing the function of biological targets such as proteins. Since the first targeted covalent inhibitor was disclosed in the 1990s, great efforts have been made to develop covalent ligands from known reversible leads or drugs by addition of tolerated electrophilic warheads. However, high reactivity and "off-target" toxicity remain challenging issues. This review covers the concept of targeted covalent inhibition to diseases, discusses traditional and interdisciplinary strategies of cysteine-focused covalent drug discovery, and exhibits newly disclosed electrophilic warheads majorly targeting the cysteine residue. Successful applications to address the challenges of designing effective covalent drugs are also introduced.

Role of Necroptosis in Central Nervous System Diseases

Necroptosis is a type of precisely regulated necrotic cell death activated in caspase-deficient conditions. Multiple factors initiate the necroptotic signaling pathway, including toll-like receptor 3/4, tumor necrosis factor (TNF), dsRNA viruses, and T cell receptors. Presently, TNF-induced necroptosis via the phosphorylation of three key proteins, receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, and mixed lineage kinase domain-like protein, is the best-characterized process. Necroptosis induced by Z-DNA-binding protein 1 (ZBP-1) and toll/interleukin-1 receptor (TIR)-domain-containing adapter-inducing interferon (TRIF) plays a significant role in infectious diseases, such as influenza A virus, Zika virus, and herpesvirus infection. An increasing number of studies have demonstrated the close association of necroptosis with multiple diseases, and disrupting necroptosis has been confirmed to be effective for treating (or managing) these diseases. The central nervous system (CNS) exhibits unique physiological structures and immune characteristics. Necroptosis may occur without the sequential activation of signal proteins, and the necroptosis of supporting cells has more important implications in disease development. Additionally, necroptotic signals can be activated in the absence of necroptosis. Here, we summarize the role of necroptosis and its signal proteins in CNS diseases and characterize typical necroptosis regulators to provide a basis for the further development of therapeutic strategies for treating such diseases. In the present review, relevant information has been consolidated from recent studies (from 2010 until the present), excluding the patents in this field.

Application of a fluorine strategy in the lead optimization of betulinic acid to the discovery of potent CD73 inhibitors

The ecto-5'-nucleotidase (CD73) is an important enzyme in the adenosine pathway and catalyzes the extracellular hydrolysis of adenosine monophosphate (AMP) yielding adenosine which is involved in the inflammation and immunosuppression. Inhibitors of CD73 have potential as novel immunotherapy agents for the treatment of cancer and infection. In this study, we discovered a series of fluorinated betulinic acid derivatives as potent CD73 inhibitors by a fluorine scanning strategy. Among these, three compounds ZM522, ZM553 and ZM557 exhibited inhibitory activity with IC₅₀ values of 0.56 uM, 0.74 uM and 0.47 uM, respectively. In addition, these compounds showed a 7-fold, 5-fold and 8-fold increase in activity compared to the positive control drug α, β-methylene adenosine diphosphate (APCP) against the human CD73 enzyme. Two of these (ZM522 and ZM553) also exhibited effective interferon gamma (INF-γ) elevation and indicated the regulation of rescued T cell activation. Therefore, our study provides both a lead optimization strategy and potential compounds for further development of small molecule CD73 inhibitors.

Recent Advances in Natural Product-Based Hybrids as Anti-Cancer Agents

Cancer is one of the top leading causes of death worldwide. It is a heterogenous disease characterized by unregulated cell proliferation and invasiveness of abnormal cells. For the treatment of cancer, natural products have been widely used as a source of therapeutic ingredients since ancient times. Although natural compounds and their derivatives have demonstrated strong antitumor activity in many types of cancer, their poor pharmacokinetic properties, low cell selectivity, limited bioavailability and restricted efficacy against drug-resistant cancer cells hinder their wide clinical application. Conjugation of natural products with other bioactive molecules has given rise to a new field in drug discovery resulting to the development of novel, bifunctional and more potent drugs for cancer therapy to overcome the current drawbacks. This review discusses multiple categories of such bifunctional conjugates and highlights recent trends and advances in the development of natural product hybrids. Among them, ADCs, PDCs, ApDCs, PROTACs and AUTOTACs represent emerging therapeutic agents against cancer.

Homobivalent, Trivalent, and Covalent PROTACs: Emerging Strategies for Protein Degradation

Proteolysis-targeting chimeras (PROTACs) is a fast-growing technology providing many strengths over inhibition of protein activity directly and is attracting increasing interest in new drug discovery and development. However, efficiently identifying potent and drug-like degraders is still challenging in the development of PROTACs. Complementary to traditional PROTACs, several emerging types of PROTACs, such as homobivalent PROTACs based on two E3 ligases (e.g., CRBN, VHL, MDM2, TRIM24), chemical- or biological-based trivalent/multitargeted PROTACs, and covalent PROTACs, are rising for targeted protein degradation. These new types of PROTACs have several advantages over the traditional PROTACs including high selectivity, low toxicity, better therapeutic effects, and so on. In this perspective, we will summarize the latest development of representative PROTACs focusing on research mainly in past 10 years and discuss their advantages and disadvantages. Moreover, the outlook and perspectives on the associated challenges and future directions will be provided.

Crystallography-Guided Optimizations of the Keap1-Nrf2 Inhibitors on the Solvent Exposed Region: From Symmetric to Asymmetric Naphthalenesulfonamides

Directly inhibiting the Keap1-Nrf2 protein-protein interaction has been investigated as a promising strategy to activate Nrf2 for anti-inflammation. We previously reported a naphthalensulfonamide Keap1-Nrf2 inhibitor NXPZ-2, but have not determined the exact binding mode with Keap1. This symmetric naphthalenesulfonamide compound has relatively low solubility. Herein, we first determined a crystal complex (resolution: 2.3 Å) of human Keap1 Kelch domain with NXPZ-2. Further optimizations on the solvent exposed region obtained asymmetric naphthalenesulfonamides and three crystal structures of Keap1 in complex with designed compounds. Among them, the asymmetric piperazinyl-naphthalenesulfonamide 6k with better aqueous solubility showed the best K_D2 value of 0.21 μM to block the interaction. The productions of ROS and NO and the expression of TNF-α were inhibited by 6k in the in vitro model. This compound could relieve inflammations by significantly increasing the Nrf2 nuclear translocation in the LPS-induced ALI model with promising pharmacokinetic properties.

Nanotechnology Driven Cancer Chemoradiation: Exploiting the Full Potential of Radiotherapy with a Unique Combination of Gold Nanoparticles and Bleomycin

One of the major issues in current radiotherapy (RT) is the associated normal tissue toxicity. Enhancement of the RT effect with novel radiosensitizers can address this need. In this study, gold nanoparticles (GNPs) and bleomycin (BLM) were used as a unique combination of radiosensitizers. GNPs offer a two-fold promise as a delivery vehicle for BLM and as a radiosensitizing agent. In this study, GNPs were functionalized and complexed with BLM using a gold-thiol bond (denoted GNP-BLM). Our results show that there was a 40% and 10% decrease in cell growth with GNP-BLM vs. free BLM for the MIA PaCa-2 and PC-3 cell lines, respectively. Testing the GNP-BLM platform with RT showed an 84% and 13% reduction in cell growth in MIA PaCa-2 cells treated with GNP-BLM and GNPs, respectively. Similar results were seen with PC-3 cells. The efficacy of this approach was verified by mapping DNA double-strand breaks (DSBs) as well. Therefore, this proposed incorporation of nanomedicine with RT is promising in achieving a significantly higher therapeutic ratio which is necessary to make a paradigm change to the current clinical approach.

Natural Indole Alkaloids from Marine Fungi: Chemical Diversity and Biological Activities

The indole scaffold is one of the most important heterocyclic ring systems for pharmaceutical development, and serves as an active moiety in several clinical drugs. Fungi derived from marine origin are more liable to produce novel indole-containing natural products due to their extreme living environments. The indole alkaloids from marine fungi have drawn considerable attention for their unique chemical structures and significant biological activities. This review attempts to provide a summary of the structural diversity of marine fungal indole alkaloids including prenylated indoles, diketopiperazine indoles, bisindoles or trisindoles, quinazoline-containing indoles, indole-diterpenoids, and other indoles, as well as their known biological activities, mainly focusing on cytotoxic, kinase inhibitory, antiinflammatory, antimicrobial, anti-insecticidal, and brine shrimp lethal effects. A total of 306 indole alkaloids from marine fungi have been summarized, covering the references published from 1995 to early 2021, expecting to be beneficial for drug discovery in the future.

Brachytherapy Approach Using 177Lu Conjugated Gold Nanostars and Evaluation of Biodistribution, Tumor Retention, Dosimetry and Therapeutic Efficacy in Head and Neck Tumor Model

Brachytherapy can provide sufficient doses to head and neck squamous cell carcinoma (HNSCC) with minimal damage to nearby normal tissues. In this study, the β^--emitter ¹⁷⁷Lu was conjugated to DTPA-polyethylene glycol (PEG) decorated gold nanostars (¹⁷⁷Lu-DTPA-pAuNS) used in surface-enhanced Raman scattering and photothermal therapy (PTT). The accumulation and therapeutic efficacy of ¹⁷⁷Lu-DTPA-pAuNS were compared with those of ¹⁷⁷Lu-DTPA on an orthotopic HNSCC tumor model. The SPECT/CT imaging and biodistribution studies showed that ¹⁷⁷Lu-DTPA-pAuNS can be accumulated in the tumor up to 15 days, but ¹⁷⁷Lu-DTPA could not be detected at 24 h after injection. The tumor viability and growth were suppressed by injected ¹⁷⁷Lu-DTPA-pAuNS but not nonconjugated ¹⁷⁷Lu-DTPA, as evaluated by bioluminescent imaging. The radiation-absorbed dose of the normal organ was the highest in the liver (0.33 mSv/MBq) estimated in a 73 kg adult, but that of tumorsphere (0.5 g) was 3.55 mGy/MBq, while intravenous injection of ¹⁷⁷Lu-DTPA-pAuNS resulted in 1.97 mSv/MBq and 0.13 mGy/MBq for liver and tumorsphere, respectively. We also observed further enhancement of tumor-suppressive effects by a combination of ¹⁷⁷Lu-DTPA-pAuNS and PTT compared to ¹⁷⁷Lu-DTPA-pAuNS alone. In conclusion, ¹⁷⁷Lu-DTPA-pAuNS may be considered as a potential radiopharmaceutical agent for HNSCC brachytherapy.

Ligand-based substituent-anchoring design of selective receptor-interacting protein kinase 1 necroptosis inhibitors for ulcerative colitis therapy

Receptor-interacting protein (RIP) kinase 1 is involved in immune-mediated inflammatory diseases including ulcerative colitis (UC) by regulating necroptosis and inflammation. Our group previously identified TAK-632 (5) as an effective necroptosis inhibitor by dual-targeting RIP1 and RIP3. In this study, using ligand-based substituent-anchoring design strategy, we focused on the benzothiazole ring to obtain a series of TAK-632 analogues showing significantly improving on the anti-necroptosis activity and RIP1 selectivity over RIP3. Among them, a conformational constrained fluorine-substituted derivative (25) exhibited 333-fold selectivity for RIP1 (K_d = 15 nmol/L) than RIP3 (K_d > 5000 nmol/L). This compound showed highly potent activity against cell necroptosis (EC₅₀ = 8 nmol/L) and systemic inflammatory response syndrome (SIRS) induced by TNF-α in vivo. Especially, it was able to exhibit remarkable anti-inflammatory treatment efficacy in a DSS-induced mouse model of UC. Taken together, the highly potent, selective, orally active anti-necroptosis inhibitor represents promising candidate for clinical treatment of UC.

Improving Druggability of Novel Diarylpyrimidine NNRTIs by a Fragment-Based Replacement Strategy: From Biphenyl-DAPYs to Heteroaromatic-Biphenyl-DAPYs

A series of novel heteroaromatic-difluoro-biphenyl-diarylpyrimidines were designed as non-nucleoside anti-HIV inhibitors targeting reverse transcriptase by a fragment-based replacement strategy with the purpose of improving the druggability. Hopping five- or six-membered heterocycle groups on the biphenyl moiety as bioisosterism for intrinsically cyanophenyl gave 23 derivatives. All of these compounds possessed excellent HIV-1 inhibitory activity in the nanomolar range. Among them, 12g with a 4-pyridine group displayed excellent inhibitory activity toward WT and mutant HIV virus possessing significant selectivity. Moreover, this compound exhibited a decent improvement in druggability than etravirine and rilpivirine: (1) The hydrochloric acid salt of 12g exhibited significantly improved water solubility in different pH conditions. (2) 12g did not show apparent CYP enzymatic inhibitory activity or acute toxicity. (3) Excellent oral bioavailability was also revealed (F = 126%, rats) in 12g. Collectively, these novel heteroaromatic-biphenyl-DAPYs represent promising drug candidates for HIV clinical therapy.

Structure-based molecular hybridization design of Keap1-Nrf2 inhibitors as novel protective agents of acute lung injury

Blocking the Kelch-like epichlorohydrin-related protein 1 (Keap1)-nuclear factor-erythroid 2 related factor 2 (Nrf2) pathway represents as a promising strategy to reduce oxidative stress and related-inflammation, including acute lung injury (ALI). NXPZ-2, a naphthalensulfonamide derivative, was previously reported to effectively inhibit the Keap1-Nrf2 protein-protein interaction (PPI) by our group. In the present work, a series of novel isothiocyanate-containing naphthalensulfonamides with the thioether, sulfoxide and sulfone moieties were designed by a structure-based molecular hybridization strategy using NXPZ-2 and the Nrf2 activator sulforaphane. They possessed good Keap1-Nrf2 PPI inhibitory activity and low cytotoxicity. The molecular docking study was performed to further explain the different activity of the thioether-, sulfoxide- and sulfone-containing naphthalensulfonamides. Among these new derivatives, 2-((N-(4-((N-(2-amino-2-oxoethyl)-4-((3-isothiocyanatopropyl)sulfinyl)phenyl)sulfonamido) naphthalen-1-yl)-4-methoxyphenyl)sulfonamido)acetamide (SCN-16) showed a good K_D2 value of 0.455 μM to disrupt the PPI. In an LPS-induced peritoneal macrophage cell model, this compound could cause a significant increase in the nuclear Nrf2 protein, decrease in the cytosolic Nrf2 protein, and further elevate the downstream protective enzymes HO-1 and NQO-1, which were better than the lead compound NXPZ-2 and sulforaphane. What's more, the production of ROS and NO and the expression of pro-inflammatory cytokine TNF-α were also suppressed. In the LPS-induced ALI model, SCN-16 could significantly reduce LPS-induced inflammations and alleviate lung injuries by triggering Nrf2 nuclear translocation. Collectively, our results suggested that SCN-16 could be a novel lead compound targeting Keap1-Nrf2 protective pathway for clinical treatment of ALI.

Hydrophobic Pocket Occupation Design of Difluoro-Biphenyl-Diarylpyrimidines as Non-Nucleoside HIV-1 Reverse Transcriptase Inhibitors: from N-Alkylation to Methyl Hopping on the Pyrimidine Ring

Considering the nonideal metabolic stability of the difluoro-biphenyl-diarylpyrimidine lead compound 4, a series of novel alkylated difluoro-biphenyl-diarylpyrimidines were designed and synthesized based on their structure. Introducing alkyl or substituted alkyl groups on the linker region to block the potential metabolic sensitive sites generated 22 derivatives. Among them, compound 12a with an N-methyl group displayed excellent anti-HIV-1 activity and selectivity. The methyl group was hopped to the central pyrimidine to occupy the small linker region and maintain the water-mediated hydrogen bond observed in the binding of compound 4 with RT. The resulting compound 16y exhibited an improved anti-HIV-1 activity, much lower cytotoxicity, and nanomolar activity toward multiple mutants. In addition, 16y has a better stability in human liver microsomes than 4. Moreover, no apparent in vivo acute toxicity was observed in 16y-treated female, especially pregnant mice. This series of alkylated compounds with highly potency and safety represent a promising lead template for future discovery.