Discovery of quinone-directed antitumor agents selectively bioactivated by NQO1 over CPR with improved safety profile

Synthesis of 2,3-Dialkyl-5-hydroxybenzofurans via a One-pot, Three-step Reaction Sequence of 2-Monosubstituted 1,3-Diketones and 1,4-Benzoquinones

An economical one-pot, three-step reaction sequence of readily available 2-monosubstituted 1,3-diketones and 1,4-benzoquinones has been explored for the facile access of 2,3-dialkyl-5-hydroxybenzofurans. By using cheap K2CO3 and conc. HCl as the reaction promoters, the reaction occurs smoothly via sequential Michael addition, aromatization, retro-Claisen, deacylation, hemiketalization, and dehydration processes under mild conditions in a practical manner. Additionally, an interesting phenomenon was observed during the derivatization studies, where the dihydroquinoline was converted into tetrahydroquinoline and quinoline products, respectively, via a disproportionation process.

Novel NQO1 substrates bearing two nitrogen redox centers: Design, synthesis, molecular dynamics simulations, and antitumor evaluation

By analyzing the crystal structure of NQO1, an additional binding region for the ligand was discovered. In this study, a series of derivatives with a novel skeleton bearing two nitrogen redox centers were designed by introducing amines or hydrazines to fit with the novel binding region of NQO1. Compound 24 with a (4-fluorophenyl)hydrazine substituent was identified as the most efficient substrate for NQO1 with the reduction rate and catalytic efficiency of 1972 ± 82 μmol NADPH/min/μmol NQO1 and 6.4 ± 0.4 × 10⁶ M^-1s^-1, respectively. Molecular dynamics (MD) simulation revealed that the distances between the nitrogen atom of the redox centers and the key Tyr128 and Tyr126 residues were 3.5 Å (N₁-Tyr128) and 3.4 Å (N₂-Tyr126), respectively. Compound 24 (IC₅₀/A549 = 0.69 ± 0.09 μM) showed potent antitumor activity against A549 cells both in vitro and in vivo through ROS generation via NQO1-mediated redox cycling, leading to a promising NQO1-targeting antitumor candidate.

Highly Accessible Computational Prediction and In Vivo/In Vitro Experimental Validation: Novel Synthetic Phenyl Ketone Derivatives as Promising Agents against NAFLD via Modulating Oxidoreductase Activity

Nonalcoholic fatty liver disease (NAFLD) has reached epidemic proportions with no pharmacological treatment approved. Several highly accessible computational tools were employed to predict the activities of twelve novel compounds prior to actual chemical synthesis. We began our work by designing two or three hydroxyl groups appended to the phenyl ketone core, followed by prediction of drug-likeness and targets. Most predicted targets for each compound overlapped with NAFLD targets (≥80%). Enrichment analysis showed that these compounds might regulate oxidoreductase activity. Then, these compounds were synthesized and confirmed by IR, MS, ¹H, and ¹³C NMR. Their cell viability demonstrated that twelve compounds exhibited appreciable potencies against NAFLD (EC₅₀ values ≤ 13.5 μM). Furthermore, the most potent compound 5f effectively prevented NAFLD progression as evidenced by the change in histological features. 5f significantly reduced total cholesterol and triglyceride levels in vitro/in vivo, and the effects of 5f were significantly stronger than those of the control drug. The proteomic data showed that oxidoreductase activity was the most significantly enriched, and this finding was consistent with docking results. In summary, this validated presynthesis prediction approach was cost-saving and worthy of popularization. The novel synthetic phenyl ketone derivative 5f holds great therapeutic potential by modulating oxidoreductase activity to counter NAFLD.

Development and structure-activity relationships of tanshinones as selective 11β-hydroxysteroid dehydrogenase 1 inhibitors

11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1) represents a promising drug target for metabolic syndrome, including obesity and type 2 diabetes. Our initial screen of a collection of natural products from Danshen led to the identification of tanshinones as the potent and selective 11β-HSD1 inhibitors. To improve the druggability and explore the structure-activity relationships (SARs), more than 40 derivatives have been designed and synthesized using tanshinone IIA and cryptotanshinone as the starting materials. More than 10 derivatives exhibited potent in vitro 11β-HSD1 inhibitory activity and good selectivity over 11β-HSD2 across human and mouse species. Based on the biological results, SARs were further discussed, which was also partially rationalized by a molecular docking model of 1 bound to the 11β-HSD1. Remarkably, compounds 1, 17 and 30 significantly inhibited 11β-HSD1 in 3T3-L1 adipocyte and in livers of ob/ob mice, which merits further investigations as anti-diabetic agents. This study not only provides a series of novel selective 11β-HSD1 inhibitors with promising therapeutic potentials in metabolic syndromes, but also expands the boundaries of the chemical and biological spaces of tanshinones.

Design, synthesis, and evaluation of proliferation inhibitory activity of novel L-shaped ortho-quinone analogs as anticancer agents

In this study, we present the design and synthesis of novel fully synthetic L-shaped ortho-quinone analogs with tanshinone IIA as the lead compoud, which is a molecule with numerous pharmacological benefits and potential to treat life-threatening diseases, such as cancer and viral infections. 24 L-shaped ortho-quinone analogs were designed and synthesized via click chemistry and introduced 1,2,3-triazole at the C-2 terminal of the furan ring. The cytotoxicity of these analogs toward different cancer cell lines was investigated in vitro. The new TD compounds showed potent inhibitory activities toward prostate cancer (PC3), leukemia (K562), breast cancer (MDA-231), lung cancer (A549), and cervical cancer (Hela) cell lines. Among them, TD1, TD11, and TD17 showed excellent broad-spectrum cytotoxic effects on five cancer cell lines by inducing apoptosis and arresting the cell cycle phase. Besides, TD1, TD11, and TD17 could target-bind with NQO1 protein in the prostate cancer cells PC3 leukemia cells K562. The results showed that removing the methyl group at C-3 and introducing 1,2,3-triazoles at the C-2 terminal of the furan ring were effective strategies for improving the broad-spectrum anticancer activity of L-shaped ortho-quinone analogs.

Design, synthesis and biological evaluation of tanshinone IIA-based analogues: Potent inhibitors of microtubule formation and angiogenesis

We report the structural optimization of tanshinone IIA, a natural product which possesses anti-tumor properties but low water-solubility, weak antiproliferative activity and poor PK properties. A new series of ring A/C/D modified tanshinone analogues were synthesized and studied for their antiproliferative capacities against six human cancer cell lines. SAR study revealed that ring A cleavage of tanshinone IIA led to improved anti-cancer activity. Introduction of a methoxy group to the phenyl ring could enhance the anti-cancer activity even further. Compound 2f with methoxy group at C-8 position was selected as an early lead with IC₅₀ values of 0.28-3.16 μM against six tested cell lines. 2f could bind to tubulin colchicine site, inhibit tubulin assembly and disrupt the normal formation of microtubule networks. Cellular mechanistic studies revealed that 2f induced apoptotic cell death of A549 cells in a dose-dependent manner. In vitro investigations showed that 2f impeded the tubule-formation of HUVECs and potently inhibited the proliferation, migration and invasion of A549 cells as well as HUVECs. Furthermore, the in vivo anti-angiogenic effect of 2f was confirmed via a zebrafish model test. The satisfactory physicochemical property and metabolic stability of 2f, as well as improved water-solubility, further suggested that 2f could serve as a promising tubulin inhibitor and anti-angiogenic agent.

Rational designed highly sensitive NQO1-activated near-infrared fluorescent probe combined with NQO1 substrates in vivo: An innovative strategy for NQO1-overexpressing cancer theranostics

Since NQO1 is overexpressed in many cancer cells, it can be used as a biomarker for cancer diagnosis and targeted therapy. NQO1 substrates show potent anticancer activity through the redox cycle mediated by NQO1, while the NQO1 probes can monitor NQO1 levels in cancers. High sensitivity of probes is needed for diagnostic imaging in clinic. In this study, based on the analysis of NQO1 catalytic pocket, the naphthoquinone trigger group 13 rationally designed by expanding the aromatic plane of the benzoquinone trigger group 10 shows significantly increased sensitivity to NQO1. The sensitivity of the naphthoquinone trigger group-based probe A was eight times higher than that of benzoquinone trigger group-based probe B in vivo. Probe A was selectively and efficiently sensitive to NQO1 with good safety profile and plasma stability, enabling its combination with NQO1 substrates in vivo for NQO1-overexpressing cancer theranostics for the first time.

Application of cation-π interactions in enzyme-substrate binding: Design, synthesis, biological evaluation, and molecular dynamics insights of novel hydrophilic substrates for NQO1

Cation-π interaction is a type of noncovalent interaction formed between the π-electron system and the positively charged ion or moieties. In this study, we designed a series of novel NQO1 substrates by introducing aliphatic nitrogen-containing side chains to fit with the L-shaped pocket of NQO1 by the formation of cation-π interactions. Molecular dynamics (MD) simulation indicated that the basic N atom in the side chain of NQO1 substrates, which is prone to be protonated under physiological conditions, can form cation-π interactions with the Phe232 and Phe236 residues of the NQO1 enzyme. Compound 4 with a methylpiperazinyl substituent was identified as the most efficient substrate for NQO1 with the reduction rate and catalytic efficiency of 1263 ± 61 μmol NADPH/min/μmol NQO1 and 2.8 ± 0.3 × 10⁶ M^-1s^-1, respectively. Notably, compound 4 exhibited increased water solubility (110 μg/mL) compared to that of β-lap (43 μg/mL), especially under acidic condition (pH = 3, solubility > 1000 μg/mL). Compound 4 (IC₅₀/A549 = 2.4 ± 0.6 μM) showed potent antitumor activity against NQO1-rich cancer cells through ROS generation via NQO1-mediated redox cycling. These results emphasized that the application of cation-π interactions by introducing basic aliphatic amine moiety is beneficial for both the water solubility and the NQO1-substrate binding, leading to promising NQO1-targeting antitumor candidates with improved druglike properties.

Recent Advances in the Selective Oxidative Dearomatization of Phenols to o-Quinones and o-Quinols with Hypervalent Iodine Reagents

ortho-Quinones are valuable molecular frameworks with diverse applications across biology, materials, organic synthesis, catalysis, and coordination chemistry. Despite their broad utility, their synthesis remains challenging, in particular via the direct oxidation of readily accessible phenols, due to the need to affect regioselective ortho oxidation coupled with the sensitivity of the resulting o-quinone products. The perspective looks at the emergence of I(V) hypervalent iodine reagents as an effective class of oxidants for regioselective o-quinone synthesis. The application of these reagents in regioselective phenol oxidation to both o-quinones and o-quinols will be discussed, including a recent report from our laboratory on the first method for the oxidation of electron-deficient phenols using a novel nitrogen-ligated I(V) reagent. Also included are select examples of total syntheses utilizing this methodology as well as recent advancements in chiral I(V) reagent design for asymmetric phenol dearomatization.

Synthesis of naphthodihydrofurans via an iron(iii)-catalyzed reduction radical cascade reaction

A convenient method for the synthesis of naphthodihydrofurans has been developed by iron(iii)-catalyzed cascade reaction of reducing radicals.

A comprehensive review on β-lapachone: Mechanisms, structural modifications, and therapeutic potentials

β-Lapachone (β-lap, 1), an ortho-naphthoquinone natural product isolated from the lapacho tree (Tabebuia avellanedae) in many regions of South America, has received extensive attention due to various pharmacological activities, such as antitumor, anti-Trypanosoma cruzi, anti-Mycobacterium tuberculosis, antibacterial, and antimalarial activities. Related mechanisms of β-lap have been widely investigated for a full understanding of its therapeutic potentials. Numerous derivatives of β-lap have been reported with aims to generate new chemical entities, improve the corresponding biological potency, and overcome disadvantages of its physical and chemical properties and safety profiles. This review will give insight into the pharmacological mechanisms of β-lap and provide a comprehensive understanding of its structural modifications with regard to different therapeutic potentials. The available clinical trials related to β-lap and its derivatives are also summarized.

Mesoporous Silica Nanoparticle-Based Combination of NQO1 Inhibitor and 5-Fluorouracil for Potent Antitumor Effect Against Head and Neck Squamous Cell Carcinoma (HNSCC)

Head and neck squamous cell carcinomas (HNSCC) are one of the deadliest forms of cancer, and 90% of its origin is from squamous cells. NAD(P)H:quinone oxidoreductase 1 (NQO1), an enzyme overexpressed in squamous cell carcinoma, plays an important role in proliferation and chemoresistance. The main aims were to study the inhibitory effect of ß-lapachone (ARQ761 in clinical form) in HNSCC and to study the combinational effect of 5-FU and ß-lap in improving the therapeutic efficacy in HNSCC. Lipid bilayer-assembled mesoporous silica nanoparticles loaded with 5-FU/ß-lap were prepared and studied for its physicochemical and biological properties. ß-lap showed a concentration-dependent inhibition of NQO1 enzyme activity in Cal33 cells. Notably, significant inhibitory effect was observed at a dose of 20-50 μg/ml of ß-lap. Combination of 5-FU+ß-lap resulted in lower cell viability; most notably, 5-FU/ß-lap-loaded mesoporous silica nanoparticles (FNQ-MSN) exhibited significantly lower cell viability compared with that of any of the individual drug or physical combinations. ß-lap resulted in a decrease in the protein band of NQO1 compared with control; however, most notable decrease in the NQO1 level was observed in the FNQ-MSN-treated cell group. FNQ-MSN resulted in more than 60% of cell apoptosis (early and late apoptosis) and predominant nuclear fragmentation of cancer cells indicating the superior anticancer effect of a carrier-based combination regimen. Notable decrease in tumor volume was observed with the physical mixture of 5-FU+ß-lap; however, combined treatment of carrier-based 5-FU and ß-lap (FNQ-MSN) significantly delayed the tumor growth and prolonged the survival of tumor-bearing xenograft mice. These findings suggest the potential of NQO1 inhibitor in enhancing the chemotherapeutic potential of 5-FU in the treatment of HNSCC.

Potent Cytotoxicity of Novel L-Shaped Ortho-Quinone Analogs through Inducing Apoptosis

Twenty-seven L-shaped ortho-quinone analogs were designed and synthesized using a one pot double-radical synthetic strategy followed by removing methyl at C-3 of the furan ring and introducing a diverse side chain at C-2 of the furan ring. The synthetic derivatives were investigated for their cytotoxicity activities against human leukemia cells K562, prostate cancer cells PC3, and melanoma cells WM9. Compounds TB1, TB3, TB4, TB6, TC1, TC3, TC5, TC9, TC11, TC12, TC14, TC15, TC16, and TC17 exhibited a better broad-spectrum cytotoxicity on three cancer cells. TB7 and TC7 selectively displayed potent inhibitory activities on leukemia cells K562 and prostate cancer cells PC3, respectively. Further studies indicated that TB3, TC1, TC3, TC7, and TC17 could significantly induce the apoptosis of PC3 cells. TC1 and TC17 significantly induced apoptosis of K562 cells. TC1, TC11, and TC14 induced significant apoptosis of WM9 cells. The structure-activity relationships evaluation showed that removing methyl at C-3 of the furan ring and introducing diverse side chains at C-2 of the furan ring is an effective strategy for improving the anticancer activity of L-shaped ortho-quinone analogs.

Dearomatization of Electron-Deficient Phenols to ortho-Quinones: Bidentate Nitrogen-Ligated Iodine(V) Reagents

Despite their broad utility, the synthesis of ortho-quinones remains a significant challenge, in particular, access to electron-deficient derivatives remains an unsolved problem. Reported here is the first general method for the synthesis of electron-deficient ortho-quinones by direct oxidation of phenols. The reaction is enabled by a novel bidentate nitrogen-ligated iodine(V) reagent, a previously unexplored class of compounds which we have termed Bi(N)-HVIs. The reaction is extremely general and proceeds with excellent regioselectivity for the ortho over para isomer. Functionalization of the ortho-quinone products was examined, resulting in a facile one-pot synthesis of catechols, as well as the incorporation of a variety of heteroatom nucleophiles. This method represents the first synthetic application of Bi(N)-HVIs and demonstrates their potential as a platform for the further development of highly reactive, but also highly tunable, I(V) reagents.

Discovery of Nonquinone Substrates for NAD(P)H: Quinone Oxidoreductase 1 (NQO1) as Effective Intracellular ROS Generators for the Treatment of Drug-Resistant Non-Small-Cell Lung Cancer

The elevation of oxidative stress preferentially in cancer cells by efficient NQO1 substrates, which promote ROS generation through redox cycling, has emerged as an effective strategy for cancer therapy, even for treating drug-resistant cancers. Here, we described the identification and structural optimization studies of the hit compound 1, a new chemotype of nonquinone substrate for NQO1 as an efficient ROS generator. Further structure-activity relationship studies resulted in the most active compound 20k, a tricyclic 2,3-dicyano indenopyrazinone, which selectively inhibited the proliferation of NQO1-overexpressing A549 and A549/Taxol cancer cells. Furthermore, 20k dramatically elevated the intracellular ROS levels through NQO1-catalyzed redox cycling and induced PARP-1-mediated cell apoptosis in A549/Taxol cells. In addition, 20k significantly suppressed the growth of A549/Taxol xenograft tumors in mice with no apparent toxicity observed in vivo. Together, 20k acts as an efficient NQO1 substrate and may be a new option for the treatment of NQO1-overexpresssing drug-resistant NSCLC.

An NAD(P)H:Quinone Oxidoreductase 1 Responsive and Self-Immolative Prodrug of 5-Fluorouracil for Safe and Effective Cancer Therapy

Tripartite prodrug 1, composed of an NAD(P)H:quinone oxidoreductase 1 (NQO1)-responsive trigger group, a self-immolative linker, and the active drug 5-fluorouracil (5-FU), was designed and synthesized for site-specific cancer therapy. Upon bioreductive activation by NQO1, 1 can release the parent drug 5-FU specifically in NQO1-overexpressing cancer cells. This prodrug exerts comparable antitumor activity and a more favorable safety profile compared with 5-FU both in vitro and in vivo.

Development of novel amino-quinoline-5,8-dione derivatives as NAD(P)H:quinone oxidoreductase 1 (NQO1) inhibitors with potent antiproliferative activities

Fourteen novel amino-quinoline-5,8-dione derivatives (6a-h and 7a-h) were designed and synthesized by coupling different alkyl- or aryl-amino fragments at the C6- or C7-position of quinoline-5,8-dione. All target compounds showed antiproliferative potency in the low micromolar range in both drug sensitive HeLaS3 and multidrug resistant KB-vin cell lines. Compounds 6h, 6d, 7a, and 7d exhibited more potent antiproliferative effects than the other compounds. Especially, compounds 6d and 7d displayed NQO1-dependent cytotoxicity and competitive NQO1 inhibitory effects in both drug sensitive HeLaS3 and multidrug resistant KB-vin cell lines. Furthermore, compounds 6h, 6d, 7a, and 7d induced a dose-dependent lethal mitochondrial dysfunction in both drug sensitive HeLaS3 and multidrug resistant KB-vin cells by increasing intracellular reactive oxygen species (ROS) levels. Notably, compound 7d selectively inhibited cancer cells, but not non-tumor liver cell proliferation in vitro, and significantly triggered HeLaS3 cell apoptosis by regulating apoptotic proteins of Bcl-2, Bax, and cleaved caspase-3 in a dose-dependent manner. Our findings suggest that these novel C6- or C7-substituted amino-quinoline-5,8-dione derivatives, such as 7d, could be further developed in the future as potent and selective antitumor agents to potentially circumvent multi-drug resistance (MDR).

Vinylation of a Secondary Amine Core with Calcium Carbide for Efficient Post-Modification and Access to Polymeric Materials

We developed a simple and efficient strategy to access N-vinyl secondary amines of various naturally occurring materials using readily available solid acetylene reagents (calcium carbide, KF, and KOH). Pyrrole, pyrazole, indoles, carbazoles, and diarylamines were successfully vinylated in good yields. Cross-linked and linear polymers were synthesized from N-vinyl carbazoles through free radical and cationic polymerization. Post-modification of olanzapine (an antipsychotic drug substance) was successfully performed.