Design, synthesis, in vitro and in vivo biological evaluation of 2-amino-3-aroylbenzo[b]furan derivatives as highly potent tubulin polymerization inhibitors

Progress in Electrochemically Empowered C-O Bond Formation: Unveiling the Pathway of Efficient Green Synthesis

(C-X) bonds (X=C, N, O) are the main backbone for making different skeleton in the organic synthetic transformations. Among all the sustainable techniques, electro-organic synthesis for C-X bond formation is the advanced tool as it offers a greener and more cost-effective approach to chemical reactions by utilizing electrons as reagents. In this review, we want to explore the recent advancements in electrochemical C-O bond formation. The electrochemically driven C-O bond formation represents an emerging and exciting area of research. In this context, electrochemical techniques offers numerous advantages, including higher yields, cost-efficient production, and simplified work-up procedures. This method enables the continuous and consistent formation of C-O bonds in molecules, significantly enhancing overall reaction yields. Furthermore, both intramolecular and intermolecular C-O bond forming reaction provided valuable products of O-containing acyclic/cyclic analogue. Hence, carbonyl (C=O), ether -O-), and ester (-COOR) functionalization in both cyclic/acyclic analogues have been prepared continuously via this innovative pathway. In this context, we want to discuss one-decade electrochemical synthetic pathways of various C-O bond contains functional group in chronological manner. This review focused on all the synthetic aspects including mechanistic path and has also mentioned overall critical finding regarding the C-O bond formation via electrochemical pathways.

Microtubule destabilising activity of selected 7-methoxy-2-phenylbenzo[b]furan derivative against primary and metastatic melanoma cells

Herein, we report the results of anticancer screening of two 2-phenylbenzo[b]furan derivatives functionalised at the 3-position with 4-hydroxy-3,5-dimethoxybenzoyl (BF2) or 3,4,5-trimethoxybenzoyl (BF3) against 60 different cancer cell lines. The results confirmed the anticancer potential of the tested compounds against different cancer cell types, especially colon cancer, brain cancer and melanoma. BF3 was defined as the most potent (also as a tubulin polymerisation inhibitor). Its anticancer activity against melanoma cell lines that originated from different stages, i.e., primary skin-derived A375 and metastatic WM9/MDA-MB-435S, was evaluated (as the clinical success of melanoma therapy strictly depends on the disease stage). Moreover, to determine the BF3 mode of action and its effect on cell proliferation, intracellular microtubule networks, cell cycle phase distribution and apoptosis were evaluated. Our study revealed that BF3 inhibited cell proliferation in a dose-dependent manner, with IC50 yielding 0.09 ± 0.01 μM, 0.11 ± 0.01 μM and 0.18 ± 0.05 μM for A375, MDA-MB435S and WM9, respectively. The strong antiproliferative activity of compound BF3 correlated well with its inhibitory effect on tubulin polymerisation. Molecular docking proved that BF3 belongs to the colchicine binding site inhibitors (CBSIs), and experimental studies revealed that it disturbs cell cycle progression leading to G2/M arrest and apoptosis.

Development of tubulin polymerization inhibitors as anticancer agents

INTRODUCTION

Microtubules are intracellular, filamentous, polymeric structures that extend throughout the cytoplasm, composed of α-tubulin and β-tubulin subunits. They regulate many cellular functions including cell polarity, cell shape, mitosis, intracellular transport, cell signaling, gene expression, cell integrity, and are associated with tumorigenesis. Inhibition of tubulin polymerization within tumor cells represents a crucial focus in the pursuit of developing anticancer treatments.

AREAS COVERED

This review focuses on the natural product and their synthetic congeners as tubulin inhibitors along with their site of interaction on tubulin. This review also covers the developed novel tubulin inhibitors and important patents focusing on the development of tubulin inhibition for cancer treatment reported from 2018 to 2023. The scientific and patent literature has been searched on PubMed, Espacenet, ScienceDirect, and Patent Guru from 2018-2023.

EXPERT OPINION

Tubulin is one of the promising targets explored extensively for drug discovery. Compounds binding in the colchicine site could be given importance because they can elude resistance mediated by the P-glycoprotein efflux pump and no colchicine site binding inhibitor is approved by FDA so far. The research on the development of antibody drug conjugates (ADCs) for tubluin polymerization inhibition could be significant strategy for cancer treatment.

Synthesis and Biological Studies of Benzo[b]furan Derivatives: A Review from 2011 to 2022

The importance of the benzo[b]furan motif becomes evident in the remarkable results of numerous biological investigations, establishing its potential as a robust therapeutic option. This review presents an overview of the synthesis of and exhaustive biological studies conducted on benzo[b]furan derivatives from 2011 to 2022, accentuating their exceptional promise as anticancer, antibacterial, and antifungal agents. Initially, the discussion focuses on chemical synthesis, molecular docking simulations, and both in vitro and in vivo studies. Additionally, we provide an analysis of the intricate interplay between structure and activity, thereby facilitating comparisons and profoundly emphasizing the applications of the benzo[b]furan motif within the realms of drug discovery and medicinal chemistry.

Discovery of novel 6-p-tolyl-3-(3,4,5-trimethoxybenzyl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine derivative as a potent tubulin inhibitor with promising in vivo antitumor activity

Building on our prior research, a novel series of trimethoxyphenoxymethyl- and trimethoxybenzyl-substituted triazolothiadiazine compounds has been designed and achieved successfully via a direct ring-closing strategy. Initial biological evaluation illustrated that the most active derivative B₅ exhibited significant cell growth inhibitory activity toward HeLa, HT-29, and A549 giving the IC₅₀ values of 0.046, 0.57, and 0.96 μM, respectively, which are greater or similar with CA-4. The mechanism study revealed that B₅ caused the G₂/M phase arrest, induced cell apoptosis in HeLa cells in a concentration-dependent manner, and also showed potent tubulin polymerization inhibitory effect. Meanwhile, B₅ exerted significant antivascular activity in the wound-healing and tube formation assays. Most importantly, B₅ remarkably inhibited tumor growth without obvious signs of toxicity in A549-xenograft mice model. These observations indicate that 6-p-tolyl-3-(3,4,5-trimethoxybenzyl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine might be considered as the potential lead compound to develop highly efficient anticancer agents with potent selectivity over normal human cells.

Anticancer therapeutic potential of benzofuran scaffolds

Benzofuran moiety is the main component of many biologically active natural and synthetic heterocycles. These heterocycles have unique therapeutic potentials and are involved in various clinical drugs. The reported results confirmed the extraordinary inhibitory potency of such benzofurans against a panel of human cancer cell lines compared with a wide array of reference anticancer drugs. Several publications about the anticancer potencies of benzofuran-based heterocycles were encountered. The recent developments of anticancer activities of both natural and synthetic benzofuran scaffolds during 2019-2022 are thoroughly covered. Many of the described benzofurans are promising candidates for development as anticancer agents based on their outstanding inhibitory potency against a panel of human cancer cells compared with reference anticancer drugs. These findings encourage medicinal chemists to explore new areas to improve human health and reduce suffering.

Design, synthesis, and bioevaluation of imidazo [1,2-a] pyrazine derivatives as tubulin polymerization inhibitors with potent anticancer activities

Through structural optimization and ring fusion strategy, we designed a series of novel imidazo[1,2-a]pyrazine derivatives as potential tubulin inhibitors. These compounds displayed potent anti-proliferative activities (micromolar to nanomolar) against a panel of cancer cell lines (including HepG-2, HCT-116, A549 and MDA-MB-231 cells). Among them, compound TB-25 exhibited the strongest inhibitory effects against HCT-116 cells with an IC₅₀ of 23 nM. Mechanism studies revealed that TB-25 could effectively inhibit tubulin polymerization in vitro, and destroy the dynamic equilibrium of microtubules in HCT-116 cells. In addition, TB-25 dose-dependently induced G2/M phase cell cycle arrest and apoptosis in HCT-116 cells. Furthermore, TB-25 suppressed HCT-116 cell migration in a concentration-dependent manner. Finally, molecular docking showed that TB-25 fitted well in the colchicine binding site of tubulin and overlapped nicely with CA-4. Collectively, these results suggest that TB-25 represents a promising tubulin inhibitor deserving further investigation.

A Novel Method to Construct 2-Aminobenzofurans via [4 + 1] Cycloaddition Reaction of In Situ Generated Ortho-Quinone Methides with Isocyanides

A new approach for the synthesis of 2-aminobenzofurans has been described via Sc(OTf)₃ mediated formal cycloaddition of isocyanides with the in situ generated ortho-quinone methides (o-QMs) from o-hydroxybenzhydryl alcohol. Notably, as a class of readily available and highly active intermediates, o-QMs were first used in the construction of benzofurans. This [4 + 1] cycloaddition reaction provides a straightforward and efficient methodology for the construction of 2-aminobenzofurans scaffold in good yield (up to 93% yield) under mild conditions.

Synthesis of 2-Aminofurans and 2-Aminothiophenes through Elemental Sulfur-Promoted Switchable Redox Condensation Reaction of Enaminones with Methylene Nitriles

Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5-annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, eco-friendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.

Targeting the tumor microenvironment by an enzyme-responsive prodrug of tubulin destabilizer for triple-negative breast cancer therapy with high safety

In response to the long-term potential toxicity concerns of tubulin destabilizer, an enzyme-responsive prodrug therapy for triple-negative breast cancer was developed based on the different β-glucuronidase levels between tumor and normal tissues in this study. All the prodrugs synthesized herein showed remarkable stability in phosphate buffer and bovine serum solution, among which 17a was found to be more susceptible to enzymatic cleavage. 17a exhibited excellent selectivity between the in vitro antiproliferative activities against β-glucuronidase-pretreated and -untreated cancer cells (IC₅₀ (+Enz) = 8.9-15.7 nM, IC₅₀ (-Enz) > 50 μM), along with favorable liver microsomal metabolic stability and improved aqueous solubility. Furthermore, as a candidate prodrug 17a showed potent antitumor efficacy in MDA-MB-231 xenograft mouse model without causing perceptible injury to organs. Importantly, 17a exhibited superior safety profiles with higher LD₅₀ value and no perceivable cardiotoxicity, which was a major dose-limiting adverse effect for the parent compound 1. These salient toxicity-reduced effects of 17a would merit further in-depth assessment of this compound for preclinical therapeutic usages.

Electrochemically-mediated C–H functionalization of allenes and 1,3-dicarbonyl compounds to construct tetrasubstituted furans

We reported an electrocatalytic C–H activation method to construct novel highly functionalized tetrasubstituted furan derivatives, which uses allenes and 1,3-dicarbonyl compounds as substrates.

Synthesis and structure-activity relationships of 5-phenyloxazole-2-carboxylic acid derivatives as novel inhibitors of tubulin polymerization

A series of 5-phenyloxazole-2-carboxylic acid derivatives were synthesized, and their structure-activity relationships (SARs) were studied. N,5-diphenyloxazole-2-carboxamides 6, 7, and 9, which mimicked ABT751, showed improved cytotoxicity compared with ABT751. Compound 9 exhibited the highest antiproliferative activities against Hela A549, and HepG2 cancer cell lines, with IC₅₀ values of 0.78, 1.08, and 1.27 μM, respectively. Furthermore, compound 9 showed selectivity for human cancer cells over normal cells, and this selectivity was greater than those of ABT751 and colchicine. Preliminary mechanism studies suggested that compound 9 inhibited tubulin polymerization and led to cell cycle arrest at G₂/M phase. Molecular docking studies indicated that compound 9 bound to the colchicine binding site of tubulin. Our findings provided insights into useful SARs for further structural modification of inhibitors of tubulin polymerization.

Tubulin Inhibitors: A Chemoinformatic Analysis Using Cell-Based Data

Inhibiting the tubulin-microtubules (Tub-Mts) system is a classic and rational approach for treating different types of cancers. A large amount of data on inhibitors in the clinic supports Tub-Mts as a validated target. However, most of the inhibitors reported thus far have been developed around common chemical scaffolds covering a narrow region of the chemical space with limited innovation. This manuscript aims to discuss the first activity landscape and scaffold content analysis of an assembled and curated cell-based database of 851 Tub-Mts inhibitors with reported activity against five cancer cell lines and the Tub-Mts system. The structure-bioactivity relationships of the Tub-Mts system inhibitors were further explored using constellations plots. This recently developed methodology enables the rapid but quantitative assessment of analog series enriched with active compounds. The constellations plots identified promising analog series with high average biological activity that could be the starting points of new and more potent Tub-Mts inhibitors.

Deciphering the key heterocyclic scaffolds in targeting microtubules, kinases and carbonic anhydrases for cancer drug development

Heterocyclic scaffolds are widely utilized for drug design by taking into account the molecular structure of therapeutic targets that are related to a broad spectrum of ailments, including tumors. Such compounds display various covalent and non-covalent interactions with the specific residues of the target proteins while causing their inhibition. There is a substantial number of heterocyclic compounds approved for cancer treatment, and these compounds function by interacting with different therapeutic targets involved in tumorogenesis. In this review, we trace and emphasize the privileged heterocyclic pharmacophores that have immense potency against several essential chemotherapeutic tumor targets: microtubules, kinases and carbonic anhydrases. Potent compounds currently undergoing pre-clinical and clinical studies have also been assessed for ascertaining the effective class of chemical scaffolds that have significant therapeutic potential against multiple malignancies. In addition, we also describe briefly the role of heterocyclic compounds in various chemotherapy regimens. The optimized molecular hybridization of delineated motifs may result in the discovery of more active anticancer therapeutics and circumvent the development of resistance by specific targets in the future.

Discovery of highly potent tubulin polymerization inhibitors: Design, synthesis, and structure-activity relationships of novel 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidines

By removing 5-methyl and 6-acetyl groups in our previously reported compound 3, we designed a series of novel 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidine derivatives as potential tubulin polymerization inhibitors. Among them, compound 5e displayed low nanomolar antiproliferative efficacy on HeLa cells which was 166-fold higher than the lead analogue 3. Interestingly, 5e displayed significant selectivity in inhibiting cancer cells over HEK-293 (normal human embryonic kidney cells). In addition, 5e dose-dependently arrested HeLa in G2/M phase through the alterations of the expression levels of p-cdc2 and cyclin B1, and caused HeLa cells apoptosis by regulation of expressions of cleaved PARP. Further evidence demonstrated that 5e effectively inhibited tubulin polymerization and was 3-fold more powerful than positive control CA-4. Moreover, molecular docking analysis indicated that 5e overlapped well with CA-4 in the colchicine-binding site. These studies demonstrated that 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidine skeleton might be used as the leading unit to develop novel tubulin polymerization inhibitors as potential anticancer agents.

Structure-activity relationships and antiproliferative effects of 1,2,3,4-4H-quinoxaline derivatives as tubulin polymerization inhibitors

Colchicine binding site inhibitors (CBSIs) hold great potential for the treatment of various tumors and they can overcome multidrug resistance which the existing tubulin inhibitors such as paclitaxel and vinorelbine are faced with. Herein, we report the design, synthesis and biological evaluation of a series of tetrahydro-quinoxaline derivatives as colchicine binding site inhibitors. All the synthesized compounds were evaluated for their in vitro antiproliferative activities against HT-29 and Hela cancer cell lines, and most of the target compounds demonstrated moderate to strong activities towards two tumor cell lines. In addition, the structure-activity relationships of these derivatives were also discussed. Among them, compounds 11a and 11b showed the most potent activities. Moreover, compound 11a inhibited the tubulin polymerization in both cell-free and cellular assays. Further profiling of compound 11a revealed that it arrested cell cycle in G2/M and induced cell apoptosis in a dose-dependent manner. Furthermore, molecular docking study proved that compound 11a acted on the colchicine binding site. Therefore, 11a is a promising candidate for the discovery of colchicine binding site inhibitors.

Synthesis of 2-aminobenzofurans via base-mediated [3 + 2] annulation of N-phenoxy amides with gem-difluoroalkenes

Efficient metal-free [3 + 2] annulation of N-phenoxy amides with gem-difluoroalkenes has been realized for the assembly of 2-aminobenzofuran derivatives with potent cytotoxicity against cancer cell lines and application potential for DELs.

Furan-Conjugated Tripeptides as Potent Antitumor Drugs

Cervical cancer is among the leading causes of death in women. Chemotherapy options available for cervical cancer include highly cytotoxic drugs such as taxol, cisplatin, 5-florouracil, and doxorubicin, which are not specific. In the current study, we have identified a new peptide conjugate (Fur⁴-2-Nal³-Ala²-Phe¹-CONH₂) (conjugate 4), from screening of a small library of tripeptide-conjugates of furan, as highly potent anticancer compound against human cervical cancer cells (HeLa cells) (IC₅₀ = 0.15 ± 0.05 µg/mL or 0.28 +/- 0.09 µM). Peptides were constructed on Rink amide resin from C- to N-terminus followed by capping by α-furoic acid moiety. The synthesized peptides were purified by recycling RP-HPLC, and structures of all the peptides were confirmed by using FABMS/ESIMS, ¹H- NMR, ¹³C-NMR, and HR-FABMS. Conjugate 4 was furthermore found to be specifically active against human cervical cancer cells since it did not inhibit the proliferation of other human normal cells (HUVEC (human umbilical vein endothelial cells) and IMR-90 (normal human fibroblasts)), and cancer cells tested (HUVEC, MCF-7, and MDA-MB-231 cells), as well as in mice 3T3 cells (normal fibroblasts). This study revealed a good structure activity relationship of various peptide conjugates. Conjugate 4 in branched forms (4a and 4b) were also synthesized and evaluated against HeLa cells, and results revealed that both were inactive. Atomic force microscopy (AFM) studies and staining with rhodamine 123 and propidium iodide (PI) revealed that conjugate 4 possesses a membranolytic effect and causes the loss of mitochondrial membrane potential.

Synthesis and in vitro and in vivo biological evaluation of novel derivatives of flexicaulin A as antiproliferative agents

As our research focuses on anticancer drugs, a series of novel derivatives of flexicaulin A (FA), an ent-kaurene diterpene, condensed with an aromatic ring were synthesized, and their antiproliferative activities against four human cancer cell lines (TE-1, EC109, MCF-7, and MGC-803) were evaluated. The activities of most of the new compounds were better than those of FA. Compound 2y exhibited the best activity with an IC50 value reaching 0.13 μM against oesophageal cancer cells (EC109 cells). The IC50 values for 2y in normal cells (GES-1 cells and HUVECs) were 0.52 μM and 0.49 μM, respectively. Subsequent mechanistic investigations found that compound 2y can inhibit the proliferation of cancer cells and cell cloning. In addition, 2y could reduce the mitochondrial membrane potential, increase the apoptosis rate, and increase the ROS level in EC109 cells. Moreover, 2y can upregulate the expression of ROS/JNK pathway-related proteins (p-ASK1, p-MKK4, p-JNK, and p-Cjun (ser63)) and pro-apoptotic proteins (Bax, Bad, and Bim). In vivo experiments showed that 2y can inhibit tumour growth in nude mice. The mechanism involves an increase in protein expression in the ROS pathway, leading to changes in apoptosis-related proteins. In addition, compound 2y shows low toxicity. These results indicate that compound 2y holds promising potential as an antiproliferative agent.