Design, synthesis and anticancer properties of isocombretapyridines as potent colchicine binding site inhibitors

The Potential Strategies for Overcoming Multidrug Resistance and Reducing Side Effects of Monomer Tubulin Inhibitors for Cancer Therapy

BACKGROUND

Tubulin is an essential target in tumor therapy, and this is attributed to its ability to target MT dynamics and interfere with critical cellular functions, including mitosis, cell signaling, and intracellular trafficking. Several tubulin inhibitors have been approved for clinical application. However, the shortcomings, such as drug resistance and toxic side effects, limit its clinical application. Compared with single-target drugs, multi-target drugs can effectively improve efficacy to reduce side effects and overcome the development of drug resistance. Tubulin protein degraders do not require high concentrations and can be recycled. After degradation, the protein needs to be resynthesized to regain function, which significantly delays the development of drug resistance.

METHODS

Using SciFinder® as a tool, the publications about tubulin-based dual-target inhibitors and tubulin degraders were surveyed with an exclusion of those published as patents.

RESULTS

This study presents the research progress of tubulin-based dual-target inhibitors and tubulin degraders as antitumor agents to provide a reference for developing and applying more efficient drugs for cancer therapy.

CONCLUSION

The multi-target inhibitors and protein degraders have shown a development prospect to overcome multidrug resistance and reduce side effects in the treatment of tumors. Currently, the design of dual-target inhibitors for tubulin needs to be further optimized, and it is worth further clarifying the detailed mechanism of protein degradation.

Discovery of a Dual Tubulin and Neuropilin-1 (NRP1) Inhibitor with Potent In Vivo Anti-Tumor Activity via Pharmacophore-based Docking Screening, Structure Optimization, and Biological Evaluation

Dual inhibition of tubulin and neuropilin-1 (NRP1) may become an effective method for cancer treatment by simultaneously killing tumor cells and inhibiting tumor angiogenesis. Herein, we identified dual tubulin/NRP1-targeting inhibitor TN-2, which exhibited good inhibitory activity against both tubulin polymerization (IC50 = 0.71 ± 0.03 μM) and NRP1 (IC50 = 0.85 ± 0.04 μM). Importantly, it significantly inhibited the viability of several human prostate tumor cell lines. Further mechanism studies indicated that TN-2 could inhibit tubulin polymerization and cause G2/M arrest, thereby inducing cell apoptosis. It could also suppress cell tube formation, migration, and invasion. Moreover, TN-2 showed obvious antitumor effects on the PC-3 cell-derived xenograft model with negligible side effects and good pharmacokinetic profiles. These data demonstrate that TN-2 could be a promising dual-target chemotherapeutic agent for the treatment of prostate cancer.

Discovery and biological evaluation of 4,6-pyrimidine analogues with potential anticancer agents as novel colchicine binding site inhibitors

Novel 4,6-pyrimidine analogues were designed and synthesized as colchicine binding site inhibitors (CBSIs) with potent antiproliferative activities. Among them, compound 17j has the most potent activities against 6 human cancer cell lines with IC₅₀ values from 1.1 nM to 4.4 nM, which was 76 times higher than the lead compound 3 in A549 cells. The co-crystal structure of 17j in complex with tubulin confirms the key binding mode at the colchicine binding site. Moreover, 17j inhibited the tubulin polymerization in biochemical assays, depolymerized cellular microtubules, induced the G2/M arrest, inhibited the cell migration, and promoted the initiation of apoptosis. In vivo, 17j effectively inhibits primary tumor growth with tumor growth inhibition rates of 42.51% (5 mg/kg) and 65.42% (10 mg/kg) in A549 xenograft model. Taken together, 17j represents a promising new generation of CBSIs.

An update on the recent advances and discovery of novel tubulin colchicine binding inhibitors

Microtubules, formed by α- and β-tubulin heterodimer, are considered as a major target to prevent the proliferation of tumor cells. Microtubule-targeted agents have become increasingly effective anticancer drugs. However, due to the relatively sophisticated chemical structure of taxane and vinblastine, their application has faced numerous obstacles. Conversely, the structure of colchicine binding site inhibitors (CBSIs) is much easier to be modified. Moreover, CBSIs have strong antiproliferative effect on multidrug-resistant tumor cells and have become the mainstream research orientation of microtubule-targeted agents. This review focuses mainly on the recent advances of CBSIs during 2017-2022, attempts to depict their biological activities to analyze the structure-activity relationships and offers new perspectives for designing next generation of novel CBSIs.

Discovery of a Novel Vascular Disrupting Agent Inhibiting Tubulin Polymerization and HDACs with Potent Antitumor Effects

Most vascular disrupting agents (VDAs) fail to prevent the regrowth of blood vessels at the edge of tumors, causing tumor rebound and relapse. Herein, a series of novel multifunctional vascular disrupting agents (VDAs) capable of inhibiting microtubule polymerization and histone deacetylases (HDACs) were designed and synthesized using the tubulin polymerization inhibitor TH-0 as the lead compound. Among them, compound TH-6 exhibited the most potent antiproliferative activity (IC₅₀ = 18-30 nM) against a panel of cancer cell lines. As expected, TH-6 inhibited tubulin assembly and increased the acetylation level of HDAC substrate proteins in HepG2 cells. Further in vivo antitumor assay displayed that TH-6 effectively inhibited tumor growth with no apparent toxicity. More importantly, TH-6 disrupted both the internal and peripheral tumor vasculatures, which contributed to the persistent tumor inhibitory effects after drug withdrawal. Altogether, TH-6 deserves to be further investigated for the new approach to clinical cancer therapy.

A novel tubulin inhibitor, 6h, suppresses tumor-associated angiogenesis and shows potent antitumor activity against non-small cell lung cancers

Tumor angiogenesis is closely associated with the metastasis and progression of non-small cell lung cancer (NSCLC), a highly vascularized solid tumor. However, novel therapeutics are lacking for the treatment of this cancer. Here, we developed a series of 2-aryl-4-(3,4,5-trimethoxy-benzoyl)-5-substituted-1,2,3-triazol analogs (6a-6x) as tubulin colchicine-binding site inhibitors, aiming to find a novel promising drug candidate for NSCLC treatment. We first identified 2-(2-fluorophenyl)-3-(3,4,5-trimethoxybenzoyl)-5-(3-hydroxyazetidin-1-yl)-2H-1,2,3-triazole (6h) as a hit compound, which inhibited angiogenesis induced by NSCLC cells both in vivo and in vitro. In addition, our data showed that 6h could tightly bind to the colchicine-binding site of tubulin and inhibit tubulin polymerization. We also found that 6h could effectively induce G2/M cell cycle arrest of A549 and H460 cells, inhibit cell proliferation, and induce apoptosis. Furthermore, we showed 6h had the potential to inhibit the migration and invasion of NSCLC cells, two basic characteristics of tumor metastasis. Finally, we found 6h could effectively inhibit tumor progression in A549 xenograft mouse models with minimal toxicity. Taken together, these findings provide strong evidence for the development of 6h as a promising microtubule colchicine-binding site inhibitor for NSCLC treatment.

Indazole-based microtubule-targeting agents as potential candidates for anticancer drugs discovery

Tremendous research is focused on developing novel drug candidates targeting microtubules to inhibit their function in several cellular processes, including cell division. In this regard, several indazole derivatives were sought to target the colchicine binding site on the β-tubulin, a crucial protein required to form microtubules, to develop microtubule targeting agents. Even though there are several reviews on the indazole-based compounds, none of them focused on using indazole scaffold to develop microtubule targeting agents. Therefore, this review aims to present the advances in research on compounds containing indazole scaffolds as microtubule targeting agents based on the articles published in the last two decades. Among the articles reviewed, we found that compounds 6 and 7 showed the lowest IC₅₀ values of 0.6 ∼ 0.9 nM in the cell line studies, making them the strongest indazole derivatives that target microtubules. The compounds 30, 31, 37 (IC₅₀ = ∼ 1 nM) and compounds 8, 38 (IC₅₀ = ∼ 2 nM) have proved to be potent microtubule inhibitors. The compounds 18, 31, 44, 45 also showed strong anticancer activity (IC₅₀ = ∼ 8 nM). It is important to notice that except for compounds 9, 12, 13, 15, and SRF, the top activity compounds including 6, 7, 8, 10, 11, 30, 31, 37, 44, and 45 contain 3,4,5‑trimethoxyphenyl substitution similar to that of colchicine. Therefore, it appears that the 3,4,5‑trimethoxyphenyl substituent on the indazole scaffold is crucial for targeting CBS.

Design, synthesis and bioevaluation of 6-aryl-1-(3,4,5-trimethoxyphenyl)-1H-benzo[d]imidazoles as tubulin polymerization inhibitors

A series of new 6-aryl-1-(3,4,5-trimethoxyphenyl)-1H-benzo[d]imidazoles as tubulin polymerization inhibitors targeting the colchicine-binding site were designed to restrict bioactive configuration of (Z,E)-vinylogous CA-4. All of the target compounds were synthesized and then evaluated for their in vitro antiproliferative activities. Among them, 2a exhibited the most potent activities against three cancer cell lines with IC₅₀ values in the range of 0.037-0.20 μM. Further mechanism studies revealed that 2a inhibited tubulin polymerization, disrupted cell microtubule networks, arrested the cell cycle at G2/M phase, induced apoptosis and hindered cancer cell migration. Moreover, 2a displayed significant in vivo antitumor efficacy in 4T1-xenograft mice model with tumor growth inhibition rate of 52% at the dose of 2.5 mg/kg. Colchicine competition assay and the docking model of 2a in complex with tubulin showed that 2a acted at the colchicine-binding site.

Design, Synthesis, and Antipoliferative Activities of Novel Substituted Imidazole-Thione Linked Benzotriazole Derivatives

A new series of benzotriazole moiety bearing substituted imidazol-2-thiones at N1 has been designed, synthesized and evaluated for in vitro anticancer activity against the different cancer cell lines MCF-7(breast cancer), HL-60 (Human promyelocytic leukemia), and HCT-116 (colon cancer). Most of the benzotriazole analogues exhibited promising antiproliferative activity against tested cancer cell lines. Among all the synthesized compounds, BI9 showed potent activity against the cancer cell lines such as MCF-7, HL-60 and HCT-116 with IC₅₀ 3.57, 0.40 and 2.63 µM, respectively. Compound BI9 was taken up for elaborate biological studies and the HL-60 cells in the cell cycle were arrested in G₂/M phase. Compound BI9 showed remarkable inhibition of tubulin polymerization with the colchicine binding site of tubulin. In addition, compound BI9 promoted apoptosis by regulating the expression of pro-apoptotic protein BAX and anti-apoptotic proteins Bcl-2. These results provide guidance for further rational development of potent tubulin polymerization inhibitors for the treatment of cancer.

Discovery of novel N-benzylbenzamide derivatives as tubulin polymerization inhibitors with potent antitumor activities

A series of novel N-benzylbenzamide derivatives were designed and synthesized as tubulin polymerization inhibitors. Among fifty-one target compounds, compound 20b exhibited significant antiproliferative activities with IC₅₀ values ranging from 12 to 27 nM against several cancer cell lines, and possessed good plasma stability and satisfactory physicochemical properties. Mechanism studies demonstrated that 20b bound to the colchicine binding site and displayed potent anti-vascular activity. Notably, the corresponding disodium phosphate 20b-P exhibited an excellent safety profile with the LD₅₀ value of 599.7 mg/kg (i.v. injection), meanwhile, it significantly inhibited tumor growth and decreased microvessel density in liver cancer cell H22 allograft mouse model without obvious toxicity. Collectively, 20b and 20b-P are novel promising anti-tubulin agents with more druggable properties and deserve to be further investigated for cancer therapy.

SAR Investigation and Discovery of Water-Soluble 1-Methyl-1,4-dihydroindeno[1,2-c]pyrazoles as Potent Tubulin Polymerization Inhibitors

Taking the previously discovered 1-methyl-1,4-dihydroindeno[1,2c]pyrazol derivative LL01 as a lead, systematic structural modifications were made at the phenolic 6- and 7-positions and the aniline at the 3-position of the indenopyrazole core to investigate the SARs and to improve water solubility. Among the designed indenopyrazoles ID01-ID33, a series of potent MTAs were identified. As the hydrochloride salt(s), ID09 and ID33 showed excellent aqueous solubility and favorable Log P value and displayed noteworthily low nanomolar potency against a variety of tumor cells, including those taxol-resistant ones. They inhibited tubulin polymerization, disrupted cellular microtubule networks by targeting the colchicine site, and promoted HepG2 cell cycle arrest and cell apoptosis. In the HepG2 xenograft mouse model, ID09 and ID33 effectively inhibited tumor growth at an oral dose of 25 mg/kg. At an intravenous (iv) injection dose of 10 mg/kg every other day, ID09 suppressed tumor growth by 68% without obvious toxicity.

Methylsulfanylpyridine based diheteroaryl isocombretastatin analogs as potent anti-proliferative agents

Isocombretastatins are the not isomerizable 1,1-diarylethene isomers of combretastatins. Both families of antimitotics are poorly soluble and new analogs with improved water solubility are needed. The ubiquitous 3,4,5-trimethoxyphenyl ring and most of its replacements contribute to the solubility problem. 39 new compounds belonging to two series of isocombretastatin analogs with 2-chloro-6-methylsulfanyl-4-pyridinyl or 2,6-bis(methylsulfanyl)-4-pyridinyl moieties replacing the 3,4,5-trimethoxyphenyl have been synthesized and their antimitotic activity and aqueous solubility have been studied. We show here that 2-chloro-6-methylsulfanylpyridines are more successful replacements than 2,6-bis(methylsulfanyl)pyridines, giving highly potent tubulin inhibitors and cytotoxic compounds with improved water solubilities. The optimal combination is with indole rings carrying polar substitutions at the three position. The resulting diheteroaryl isocombretastatin analogs showed potent cytotoxic activity against human cancer cell lines caused by tubulin inhibition, as shown by in vitro tubulin polymerization inhibitory assays, cell cycle analysis, and confocal microscopy studies. Cell cycle analysis also showed apoptotic responses following G₂/M arrest after treatment. Conformational analysis and docking studies were applied to propose binding modes of the compounds at the colchicine site of tubulin and were in good agreement with the observed SAR. 2-Chloro-6-methylsulfanylpyridines represent a new and successful trimethoxyphenyl ring substitution for the development of improved colchicine site ligands.