Triethylated chromones with substituted naphthalenes as tubulin inhibitors

Lead/Drug Discovery from Natural Resources

Natural products and their derivatives have been shown to be effective drug candidates against various diseases for many years. Over a long period of time, nature has produced an abundant and prosperous source pool for novel therapeutic agents with distinctive structures. Major natural-product-based drugs approved for clinical use include anti-infectives and anticancer agents. This paper will review some natural-product-related potent anticancer, anti-HIV, antibacterial and antimalarial drugs or lead compounds mainly discovered from 2016 to 2022. Structurally typical marine bioactive products are also included. Molecular modeling, machine learning, bioinformatics and other computer-assisted techniques that are very important in narrowing down bioactive core structural scaffolds and helping to design new structures to fight against key disease-associated molecular targets based on available natural products are considered and briefly reviewed.

Chemical Space Expansion of Flavonoids: Induction of Mitotic Inhibition by Replacing Ring B with a 10π-Electron System, Benzo[b]thiophene

Natural products, which are enzymatically biosynthesized, have a broad range of biological activities. In particular, many flavonoids are known to contribute to human health with low toxicity. We previously reported that novel benzo[b]thiophenyl (BT) flavones with a 10π-electron BT ring B replacing the usual 6π-electron phenyl ring showed potent antiproliferative activity against human tumor cell lines. Interestingly, the activity profiles against cell cycle progression of the BT-flavones totally changed depending on the combination of substituents at the C-3 and C-5 positions. This finding encouraged an extension of these studies on the impact of BT to related flavonoids, such as chalcones, isoflavones, and aurones. Accordingly, 10 isoflavones, 29 chalcones, and four aurones were synthesized and evaluated for antiproliferative activity against five human tumor cell lines including a multi-drug-resistant cell line. Among these compounds, BT-isoflavone 7, BT-chalcones 48, 52, 57, 66, and 77, and BT-aurone 80 displayed significant antiproliferative effects against all tested tumor cell lines. The structure-antiproliferative activity relationships clearly demonstrated the importance of BT instead of phenyl as ring B for the isoflavone and chalcones, but not the aurones. Flow cytometry and immunocytochemical studies demonstrated that the active BT-flavonoids led to cell cycle arrest at the prometaphase by induction of multipolar spindle formation. The present studies should contribute greatly to the synthesis and functional analysis of biologically active flavonoid derivatives for chemical space expansion.

In Silico Exploration of Novel Tubulin Inhibitors: A Combination of Docking and Molecular Dynamics Simulations, Pharmacophore Modeling, and Virtual Screening

Microtubules play a critical role in mitosis and cell division and are regarded as an excellent target for anticancer therapy. Although microtubule-targeting agents have been widely used in the clinical treatment of different human cancers, their clinical application in cancer therapy is limited by both intrinsic and acquired drug resistance and adverse toxicities. In a previous work, we synthesized compound 9IV-c, ((E)-2-(3,4-dimethoxystyryl)-6,7,8-trimethoxy-N-(3,4,5-trimethoxyphenyl)quinoline-4-amine) that showed potent activity against multiple human tumor cell lines, by targeting spindle formation and/or the microtubule network. Accordingly, in this study, to identify potent tubulin inhibitors, at first, molecular docking and molecular dynamics studies of compound 9IV-c were performed into the colchicine binding site of tubulin; then, a pharmacophore model of the 9IV-c-tubulin complex was generated. The pharmacophore model was then validated by Güner-Henry (GH) scoring methods and receiver operating characteristic (ROC) analysis. The IBScreen database was searched by using this pharmacophore model as a screening query. Finally, five retrieved compounds were selected for molecular docking studies. These efforts identified two compounds (b and c) as potent tubulin inhibitors. Investigation of pharmacokinetic properties of these compounds (b and c) and compound 9IV-c displayed that ligand b has better drug characteristics compared to the other two ligands.

A novel synthetic microtubule inhibitor exerts antiproliferative effects in multidrug resistant cancer cells and cancer stem cells

The success of cancer chemotherapy is limited by multidrug resistance (MDR), which is mainly caused by P-glycoprotein (P-gp) overexpression. In the present study, we describe a novel microtubule inhibitor, 5-(N-methylmaleimid-3-yl)-chromone (SPC-160002), that can be used to overcome MDR. A synthetic chromone derivative, SPC-160002, showed a broad spectrum of anti-proliferative effects on various human cancer cells without affecting P-gp expression and its drug efflux function. Treatment with SPC-160002 arrested the cell cycle at the M phase, as evidenced using fluorescence-activated cell sorting analysis, and increased the levels of mitotic marker proteins, including cyclin B, pS10-H3, and chromosomal passenger complex. This mitotic arrest by SPC-160002 was mediated by promoting and stabilizing microtubule polymerization, similar to the mechanism observed in case of taxane-based drugs. Furthermore, SPC-160002 suppressed the growth and sphere-forming activity of cancer stem cells. Our data herein strongly suggest that SPC-160002, a novel microtubule inhibitor, can be used to overcome MDR and can serve as an attractive candidate for anticancer drugs.

α-Trifluoromethyl Chalcones as Potent Anticancer Agents for Androgen Receptor-Independent Prostate Cancer

α-Trifluoromethyl chalcones were prepared and evaluated for their antiproliferative activities against androgen-independent prostate cancer cell lines as well as five additional types of human tumor cell lines. The most potent chalcone 5 showed superior antitumor activity in vivo with both oral and intraperitoneal administration at 3 mg/kg. Cell-based mechanism of action studies demonstrated that 5 induced cell accumulation at sub-G1 and G2/M phases without interfering with microtubule polymerization. Furthermore, several cancer cell growth-related proteins were identified by using chalcone 5 as a bait for the affinity purification of binding proteins.

Bicyclic Chalcones as Mitotic Inhibitors for Overcoming Androgen Receptor-Independent and Multidrug-Resistant Prostate Cancer

To improve the biological effects of the lead compound 5'-chloro-2,2'-dihydroxychalcone (Cl-DHC), bicyclic aromatic chalcones were designed, synthesized, and evaluated against androgen-independent prostate cancer (PCa) DU145 and PC-3 cell proliferation. Newly synthesized bi-naphthyl derivatives 2 and 3 suppressed the proliferation of these two cell lines and also taxane-resistant prostate cancer cell lines at a submicromolar level. The two compounds were 4-18 times more potent than the parent molecule Cl-DHC. A structure-activity relationship analysis revealed that the orientation of the 10π-electron ring-A naphthalene had a significant effect on the activity. Mode-of-action studies in KB-VIN cells demonstrated that 2 and 3 arrested cells in mitosis at prometaphase and metaphase followed by induction of sub-G1 accumulation. Thus, 2 and 3 have good potential as leads for continued development of treatments for cancers especially for not only androgen-independent PCa but also multidrug-resistant tumors.

Synthesis and biological evaluation of oxazinonaphthalene-3-one derivatives as potential anticancer agents and tubulin inhibitors

Objectives

In the present study, a new series of oxazinonaphthalene-3-one analogs was designed and synthesized as novel tubulin inhibitors.

Materials and Methods

The cytotoxic activity of the synthesized compounds was evaluated against four human cancer cell lines including A2780 (human ovarian carcinoma), A2780/RCIS (cisplatin resistant human ovarian carcinoma), MCF-7 (human breast cancer cells), and MCF-7/MX (mitoxantrone resistant human breast cancer cells), those compounds which demonstrated the most antiproliferative activity in the MTT test were selected to investigate their tubulin inhibition activity and their effects on cell cycle arrest (at the G2/M phase). Moreover, molecular docking studies of the selected compounds in the catalytic site of tubulin (PDB ID: 4O2B) were carried out to describe the results of biological experiments.

Results

Most of our compounds exhibited significant to moderate cytotoxic activity against four human cancer cell lines. Among them, Compounds 4d, 5c, and 5g, possessing trimethoxy phenyl, showed the most antiproliferative activity with IC50 values ranging from 4.47 to 52.8 μM.

Conclusion

The flow cytometric analysis of A2780 cancer cell line treated with compounds 4d, 5c, and 5g showed that these compounds induced cell cycle arrest at the G2/M phase. Compound 5g, the most antiproliferative compound, inhibited tubulin polymerization in a dose-dependent manner. Molecular docking studies of 5g into the colchicine-binding site of tubulin displayed a possible mode of interaction between this compound and tubulin.

5'-Chloro-2,2'-dihydroxychalcone and related flavanoids as treatments for prostate cancer

Several flavonoids and their biosynthetic precursor chalcones were designed and synthesized to improve the biological effects of the lead compound 2'-hydroxyflavonone against androgen receptor (AR)-dependent transcriptional stimulation. Newly synthesized chalcones 19 and 26 suppressed AR-dependent transcription as well as DHT-dependent growth stimulation at a low micromolar level. These compounds were also effective against ligand-independent constitutively active mutant AR derived from castration-resistant PCa (CRPC). Compounds 19 and 26 showed broad spectrum antiproliferative activity at 5-10 μM against multiple tumor cell lines including androgen-independent and taxane-resistant prostate cancer as well as a multidrug-resistant subline. Mode of action studies suggested that 19 induced sub-G1 accumulation in PC-3 cells by disrupting the microtubule network without affecting cell cycle progression. Furthermore, the in vivo effectiveness of chalcone 19 was confirmed in a xenograft model antitumor assay. Thus, chalcone 19 has the potential to be a bifunctional lead for treatment of AR-dependent PCa at lower doses as well as AR-independent PCa, including CRPC, at higher doses.

Corymbulosins I-W, Cytotoxic Clerodane Diterpenes from the Bark of Laetia corymbulosa

The isolation studies of a crude MeOH/CH₂Cl₂ (1:1) extract (N005829) of the bark of Laetia corymbulosa yielded 15 new clerodane diterpenes, designated corymbulosins I-W (1-15), as well as four known diterpenes, 16-19. The structures of 1-15 were characterized on the basis of extensive 1D and 2D NMR and HRMS analyses. The absolute configurations of newly isolated compounds 1-15, as well as known 16-19, which were reported previously with only relative configurations, were determined through ECD experiments, X-ray analysis, chemical methods, including Mosher esterification, and comparison of their spectroscopic data. The isolated compounds were evaluated for cytotoxicity against human cancer cell lines. Flow cytometric and immunocytochemical observations of cells treated with cytotoxic clerodanes demonstrated that the chromatin was fragmented and dispersed with formation of apoptotic microtubules.

Synthesis, biological evaluation and molecular docking studies of a new series of chalcones containing naphthalene moiety as anticancer agents

A series of chalcones containing naphthalene moiety 4a-4p have been synthesized, characterized by ¹H NMR and ¹³C NMR and evaluated for their in vitro anticancer activity. The majority of the screened compounds displayed potent anticancer activity against both HCT116 and HepG2 human cancer cell lines. Among the series, compound 4h with a diethylamino group at the para position of the phenyl ring exhibited the most potent anticancer activity against HCT116 and HepG2 cell lines with IC₅₀ values of 1.20 ± 0.07 and 1.02 ± 0.04 μM, respectively. The preliminary structure-activity relationship has been summarized. Tubulin polymerization experiments indicated that 4h effectively inhibited tubulin polymerization and flow cytometric assay revealed that 4h arrests HepG2 cells at the G2/M phase in a dose-dependent manner. Furthermore, molecular docking studies suggested that 4h binds to the colchicine binding site of tubulin.

Tabercorymines A and B, Two Vobasinyl-Ibogan-Type Bisindole Alkaloids from Tabernaemontana corymbosa

Tabercorymines A (1) and B (2), two new vobasinyl-ibogan-type bisindole alkaloids with an unprecedented skeleton, were isolated from Tabernaemontana corymbosa. Their structures were established by a combination of spectroscopic data, chemical transformation, single-crystal X-ray diffraction, and ECD calculation. Compound 1 represents a novel bisindole alkaloid, characterized by a caged heteropentacyclic ring system incorporating an unprecedented C-7/C-20 bond in the vobasinyl unit. Alkaloids 1 and 2 showed potent antiproliferative activity against several human cancer cell lines, including vincristine-resistant KB.