Synthesis and biological evaluations of new analogs of 2-methoxyestradiol: Inhibitors of tubulin and angiogenesis

Effect of 2-methoxyestradiol treatment on early- and late-stage breast cancer progression in a mouse model

The prevalence of breast cancer (BC) continues to increase and is the leading cause of cancer deaths in many countries. Numerous in vitro and in vivo studies have demonstrated that 2-methoxyestradiol (2-ME) has antiproliferative and antiangiogenic effects in BC, thereby inhibiting tumour growth and metastasis. We compared the effect of 2-ME in early- and late-stage BC using a transgenic mouse model-FVB/N-Tg(MMTV-PyVT)-of spontaneously development of aggressive mammary carcinoma with lung metastasis. Mice received 100 mg/kg 2-ME treatment immediately when palpable mammary tumours were identified (early-stage BC; Experimental group 1) and 28 days after palpable mammary tumours were detected (late-stage BC; Experimental group 2). 2-ME was administered via oral gavage three times a week for 28 days after initiation of treatment, whereas control mice received the vehicle containing 10% dimethyl sulfoxide and 90% sunflower oil for the same duration as the treatment group. Mammary tumours were measured weekly over the 28 days and at termination, blood, mammary and lung tissue were collected for analysis. Mice with a tumour volume threshold of 4000 mm3 were killed before the treatment regime was completed. 2-ME treatment of early-stage BC led to lower levels of mammary tumour necrosis, whereas tumour mass and volume were increased. Additionally, necrotic lesions and anti-inflammatory CD163-expressing cells were more frequent in pulmonary metastatic tumours in this group. In contrast, 2-ME treatment of late-stage BC inhibited tumour growth over the 28-day period and resulted in increased CD3+ cell number and tumour necrosis. Furthermore, 2-ME treatment slowed down pulmonary metastasis but did not increase survival of late-stage BC mice. Besides late-stage tumour necrosis, none of the other results were statistically significant. This study demonstrates that 2-ME treatment has an antitumour effect on late-stage BC, however, with no increase in survival rate, whereas the treatment failed to demonstrate any benefit in early-stage BC.

Design, Synthesis, and Biological Evaluation of Pyrimidine Dihydroquinoxalinone Derivatives as Tubulin Colchicine Site-Binding Agents That Displayed Potent Anticancer Activity Both In Vitro and In Vivo

Polymerization of tubulin dimers to form microtubules is one of the key events in cell proliferation. The inhibition of this event has long been recognized as a potential treatment option for various types of cancer. Compound 1e was previously developed by our team as a potent inhibitor of tubulin polymerization that binds to the colchicine site. To further improve the potency and therapeutic properties of compound 1e, we hypothesized based on the X-ray crystal structure that modification of the pyrimidine dihydroquinoxalinone scaffold with additional hetero-atom (N, O, and S) substituents could allow the resulting new compounds to bind more tightly to the colchicine site and display greater efficacy in cancer therapy. We therefore synthesized a series of new pyrimidine dihydroquinoxalinone derivatives, compounds 10, 12b-c, 12e, 12h, and 12j-l, and evaluated their cytotoxicity and relative ability to inhibit proliferation, resulting in the discovery of new tubulin-polymerization inhibitors. Among these, the most potent new inhibitor was compound 12k, which exhibited high cytotoxic activity in vitro, a longer half-life than the parental compound in liver microsomes (IC50 = 0.2 nM, t 1/2 = >300 min), and significant potency against a wide range of cancer cell lines including those from melanoma and breast, pancreatic, and prostate cancers. High-resolution X-ray crystal structures of the best compounds in this scaffold series, 12e, 12j, and 12k, confirmed their direct binding to the colchicine site of tubulin and revealed their detailed molecular interactions. Further evaluation of 12k in vivo using a highly taxane-resistant prostate cancer xenograft model, PC-3/TxR, demonstrated the strong tumor growth inhibition at the low dose of 2.5 mg/kg (i.v., twice per week). Collectively, these results strongly support further preclinical evaluations of 12k as a potential candidate for development.

Recent advances on synthesis and biological activities of C-17 aza-heterocycle derived steroids

Steroids modification for improving their biological activities is one of the most efficient and fruitful methods to develop novel medicines. Steroids with aza-heterocycles attaching to the C-17 owing various biological activities have received great attentions and some of the compounds are developed successfully as drugs. In this review, the research of the syntheses and biological activities of steroids bearing various aza-heterocycles published in the last 8 years is assembled, and some important structure-activity relationships (SARs) of active compounds are presented. According to the analysis of the literatures and our experiences in this field, the potential of aza-heterocyclic steroids as medicinal drugs is proposed.

Ergosterol analogs as inhibitors of cyclin dependent kinase 8

Five new compounds based on the structure of ergosterol have been prepared and tested for their ability to inhibit CDK8. The design of the compounds was inspired by the previous reported CDK8 inhibitors, cortistatin A, CCT251921 and Senexin A. The two most potent compounds, 16a and 16d, inhibited the target enzyme with K_d-values of 107 and 93 nM, respectively.

Triterpene glycosides and phenylpropane derivatives from Staurogyne concinnula possessing anti-angiogenic activity

After anti-angiogenic activity screening, the potential n-butanol layer partitioned from the ethanol extract of Staurogyne concinnula was conducted. Further purification by Diaion HP20 column and preparative HPLC chromatography, four undescribed triterpenoid saponin derivatives, along with the known baptisiasaponin I, and four known phenylpropanoid glycosides were isolated and characterized from n-butanol layer. The structures of isolated compounds were elucidated by ESI-MS, 1D, and 2D MNR data. Biological evaluation revealed that baptisiasaponin I possessed significant anti-angiogenic effects (IC₅₀ 4.0 ± 0.2 μM). Further mechanism of action of baptisiasaponin I by inhibition of integrin/FAK/paxillin signaling pathway and its downstream effectors as MMP2 and MMP9 are also presented.

Discovery of novel indole-1,2,4-triazole derivatives as tubulin polymerization inhibitors

A series of novel indole-1,2,4-triazole derivatives have been designed, synthesized, and evaluated as potential tubulin polymerization inhibitors. The top hit 12, bearing the 3,4,5-trimethoxyphenyl moiety, exhibited substantial anti-proliferative activity against HepG2, HeLa, MCF-7, and A549 cells in vitro with IC₅₀ values of 0.23 ± 0.08 μM, 0.15 ± 0.18 μM, 0.38 ± 0.12 μM, and 0.30 ± 0.13 μM, respectively. It also inhibited tubulin polymerization with the IC₅₀ value of 2.1 ± 0.12 μM, which was comparable with that of the positive controls. Furthermore, compound 12 regulated the expression of cell cycle-related proteins (Cyclin B1, Cdc25c, and Cdc2) and apoptosis-related proteins (Bcl-2, Bcl-x, and Mcl-1). Mechanistically, compound 12 could arrest cell cycle at the G2/M phase, thus induce an increase of apoptotic cell death. In addition, molecular docking hinted the possible interaction mode of compound 12 into the colchicine binding site of tubulin heterodimers. According to the applications of microtubule-targeting agents in both direct and synergistic cancer therapies, we hope this work might be of significance for future researches.

Arenarosides A-G, Polyhydroxylated Oleanane-Type Saponins from Polycarpaea arenaria and their Cytotoxic and Antiangiogenic Activities

Seven new polyhydroxylated oleanane-type triterpene saponins, arenarosides A-G (1-7), together with four known compounds, were isolated from an ethanol extract of the aerial parts of the Vietnamese plant Polycarpaea arenaria. The chemical structures of the newly isolated oleanane saponins were elucidated on the basis of spectroscopic and spectrometric analysis, especially 2D NMR and HRMS. Biological evaluation revealed that 3, 4, 6, and 7 showed moderate activities against four human cancer cell lines (A549, HTC116, PC3, and RT112) with IC₅₀ values of 6.0-9.9 μM, and 3, 4, 5, and 7 also displayed promising antiangiogenesis effects with IC₅₀ values <5 μM in the test system used. Among the isolates, arenaroside D (4) exhibited the most potent inhibitory effects, not only in cancer cell proliferation but also in angiogenic activities. Preliminary SAR studies revealed that the presence of an acetyl group at C-22 in oleanane-type triterpene saponins increases these bioactivities.

Cytotoxicity, in silico predictions and molecular studies for androstane heterocycle compounds revealed potential antitumor agent against lung cancer cells

The IL6/JAK2/STAT3 axis dysregulation and the related downstream pathways are a major contributor to the progression of non-small-cell lung carcinoma (NSCLC) and mainly affect apoptosis. Furthermore, tubulin inhibitors are potential chemotherapeutic agents against NSCLC. In this study, we have provided new molecular insights into the antiproliferative activity of six 3β-acetoxy-5α-androstane heterocycle compounds against NSCLC. The cell line A549, which represents a good model of NSCLC, was used to evaluate the antitumour activity of tested androstane derivatives, and non-cancerous gingival mesenchymal stem cell line (GMSC) were used to assess the specificity and toxicity of the tested compounds. Further on, molecular docking predictions were used to determine the molecular targets for the most promising cytotoxic compound. To assess apoptosis and cell cycle progression in treated A549 cells, flow cytometry was used. RT-qPCR and ELISA analyses were used to gain deep insights into cellular and molecular mechanisms. Results revealed that compound 4 has potential cytotoxicity on A549 cells, with lower IC₅₀ value (27.36 μM). Moreover, in silico, compound 4 showed a good binding affinity to JAK2 and tubulin-colchicine soblidotin molecular targets. This was further confirmed on the molecular level. Compound 4 has also led to apoptosis and increased fragmentation of DNA, and mitochondrial dysfunction. Our findings have provided good evidence that compound 4 may be a dual inhibitor of IL6/JAK2/STAT3 and tubulin formation in lung cancer. These findings support further molecular exploration of this androstane derivative as promising anti-lung cancer agent.Communicated by Ramaswamy H. Sarma.

Pd-catalyzed Suzuki-Miyaura couplings and evaluation of 13α-estrone derivatives as potential anticancer agents

13α-Estrones are of great value owing to their potent multiple bioactivity, including anticancer activity. 3-OH or 3-OBn derivatives of 2- or 4-[(subst.) phenyl]-13α-estrone as potential antiproliferative agents have been synthesized via facile, microwave-induced, Pd-catalyzed Suzuki-Miyaura coupling. 2- or 4-Halogenated 13α-estrone derivatives have been reacted with (4-subst.)phenylboronic acids using Pd(PPh₃)₄ as catalyst. The nature of para substituents at the introduced phenyl group did not influence the outcome of couplings. Certain newly synthesized compounds displayed substantial antiproliferative action against human adherent cancer cell lines of gynecological origin. Important structure-activity relationships were revealed, which might be helpful in the design of potent and selective anticancer derivatives based on the hormonally inactive 13α-estrane core.

Synthesis and Biological Evaluation of Analogs of Didehydroepiandrosterone as Potential New Anticancer Agents

The synthesis, cytotoxicity and inhibition of CDK8 by thirteen analogs of cortistatin A are reported. These efforts revealed that the analogs with either a 6- or 7-isoquinoline or 5-indole side chain in the 17-position are the most promising anti-proliferative agents. These compounds showed potent cytotoxic effects in CEM, HeLa and HMEC-1 cells. All three compounds exhibited IC₅₀ values < 10µM. The most interesting 10l analog exhibited an IC₅₀ value of 0.59 µM towards the human dermal microvascular endothelial cell line (HMEC-1), significantly lower than the reference standard 2-methoxyestradiol. At a concentration at 50 nM the most potent 10h compound reduced the activity of CDK8 to 35%.

New CDK8 inhibitors as potential anti-leukemic agents - Design, synthesis and biological evaluation

Cyclin-dependent kinase 8 (CDK8) plays a vital role in regulating cell transcription either through its association with the mediator complex or by the phosphorylation of transcription factors. CDK8-mediated activation of oncogenes has proved to be important in a variety of cancer types including hematological malignancies. We have designed and synthesized a series of new synthetic steroids. The compounds were evaluated as CDK8 inhibitors in vitro. The three most potent compounds exhibit K_d-values towards CDK8 in the low nanomolar range (3.5-18 nM). Furthermore, the compounds displayed selectivity for CDK8 in a panel of 465 different kinases. The cell studies indicated a selectivity to kill AML-cancer cell lines compared to normal cell lines.

Anti-Cancer Activity of Novel Dihydrotestosterone-Derived Ring A-Condensed Pyrazoles on Androgen Non-Responsive Prostate Cancer Cell Lines

Regioselective synthesis of novel ring A-fused arylpyrazoles of dihydrotestosterone (DHT) was carried out in two steps under facile reaction conditions. Aldol condensation of DHT with acetaldehyde afforded a 2-ethylidene derivative regio- and stereo-selectively, which was reacted with different arylhydrazines in the presence of iodine via microwave-assisted oxidative cyclization reactions. The 17-keto analogs of steroidal pyrazoles were also synthesized by simple oxidation in order to enlarge the compound library available for pharmacological studies and to obtain structure–activity relationship. The antiproliferative activities of the structurally related heteroaromatic compounds were tested in vitro on human cervical and breast adenocarcinoma cell lines (HeLa, MCF-7 and MDA-MB-231) and on two androgen-independent malignant prostate carcinoma cell lines (PC-3 and DU 145). Based on primary cytotoxicity screens and IC₅₀ assessment, a structure-function relationship was identified, as derivatives carrying a hydroxyl group on C-17 exhibit stronger activity compared to the 17-one counterparts. Cancer cell selectivity of the derivatives was also determined using non-cancerous MRC-5 cells. Furthermore, the proapoptotic effects of some selected derivatives were verified on androgen therapy refractive p53-deficient PC-3 cells. The present study concludes that novel DHT-derived arylpyrazoles exert cancer cell specific antiproliferative activity and activate apoptosis in PC-3 cells.

Synthesis, molecular modeling and biological evaluation of potent analogs of 2-methoxyestradiol

The endogenous steroid 2-methoxyestradiol (1) has attracted a great interest as a lead compound towards the development of new anti-cancer drugs. Herein, the synthesis, molecular modeling, anti-proliferative and anti-angiogenic effects of ten 2-ethyl and four 2-methoxy analogs of estradiol are reported. The ethyl group was introduced to the steroid A-ring using a novel Friedel-Crafts alkylation protocol. Several analogs displayed potent anti-proliferative activity with IC₅₀-values in the submicromolar range towards the CEM human leukemia cancer cell line. As such, all of these compounds proved to be more active than the lead compound 2-methoxyestradiol (1) in these cells. The six most cytostatic analogs were also tested as anti-angiogenic agents using an in vitro tube formation assay. The IC₅₀-values were determined to be in the range of 0.1 μM ± 0.03 and 1.1 μM ± 0.2. These six compounds were also modest inhibitors against tubulin polymerization with the most potent inhibitor was 14b (IC₅₀ = 2.1 ± 0.1 μM). Binding studies using N,N'-ethylene-bis(iodoacetamide) revealed that neither14a or 14b binds to the colchicine binding site in the tubulin protein, in contrast to 2-methoxyestradiol (1). These observations were supported by molecular modeling studies. Results from a MDA-MB-231 cell cycle assay showed that both 10e and 14b gave accumulation in the G2/M phase resulting in induction of apoptosis. The results presented herein shows that the novel analogs reported exhibit their anticancer effects via several modes of action.

Heterocyclic-Fused Pyrimidines as Novel Tubulin Polymerization Inhibitors Targeting the Colchicine Binding Site: Structural Basis and Antitumor Efficacy

We report the design, synthesis, and biological evaluation of heterocyclic-fused pyrimidines as tubulin polymerization inhibitors targeting the colchicine binding site with significantly improved therapeutic index. Additionally, for the first time, we report high-resolution X-ray crystal structures for the best compounds in this scaffold, 4a, 4b, 6a, and 8b. These structures not only confirm their direct binding to the colchicine site in tubulin and reveal their detailed molecular interactions but also contrast the previously published proposed binding mode. Compounds 4a and 6a significantly inhibited tumor growth in an A375 melanoma xenograft model and were accompanied by elevated levels of apoptosis and disruption of tumor vasculature. Finally, we demonstrated that compound 4a significantly overcame clinically relevant multidrug resistance in a paclitaxel resistant PC-3/TxR prostate cancer xenograft model. Collectively, these studies provide preclinical and structural proof of concept to support the continued development of this scaffold as a new generation of tubulin inhibitors.

Synthesis of imidazo-thiadiazole linked indolinone conjugates and evaluated their microtubule network disrupting and apoptosis inducing ability

A series of imidazo[2,1-b][1,3,4]thiadiazole linked indolinone conjugates were synthesized and investigated for antiproliferative activity in different human cancer cell lines by changing various substitutions at indolinone and phenyl ring systems. Among them conjugates 7, 14 and 15 were exhibited potent antiproliferative activity with GI₅₀ values from 0.13 to 3.8 μΜ and evaluated for cell cycle analysis, tubulin polymerization assay and apoptosis. Treatment with 7, 14 and 15 were resulted in accumulation of cells in G2/M phase, inhibition of tubulin assembly, disruption of microtubule network. Inhibition of tubulin polymerization was further supported by Western blot analysis. In addition, the conjugates (7, 14 and 15) also showed apoptosis in HeLa cell line, detailed biological studies such as Hoechst 33,258 staining, DNA fragmentation and caspase-3 assays suggested that these compounds induce cell death by apoptosis. Docking studies revealed that these compounds (7, 14 and 15) bind with αAsn101, αThr179, αSer178, βCys241, βLys254 and βLys352 in the colchicine-binding site of the tubulin.

Regioselective monoalkylation of 17β-estradiol for the synthesis of cytotoxic estrogens

The regioselective synthesis of estrogens and their derivatives continues to be of interest. Most reported syntheses require multistep protocols associated with poor overall yield and lack of regioselectivity. New preparative protocols are still desired. Herein, 11 2-alkylated 17β-estradiol analogs were synthesized in a highly regioselective manner. The products were obtained using a convenient, one pot and high-yielding protocol. The anti-proliferative activity of the compounds was tested in human T-cell leukemia (CEM), human cervix carcinoma (HeLa) and human dermal microvascular endothelial (HMEC-1) cells.

Synthesis, molecular docking and biological evaluation of 1-phenylsulphonyl-2-(1-methylindol-3-yl)-benzimidazole derivatives as novel potential tubulin assembling inhibitors

A series of new 1-phenylsulphonyl-2-(1-methylindol-3-yl)-benzimidazole derivatives were designed, synthesized and evaluated as potential inhibitors of tubulin polymerization and anthropic cancer cell lines. Among them, compound 33 displayed the most potent tubulin polymerization inhibitory activity in vitro (IC₅₀  = 1.41 μM) and strong antiproliferative activities against A549, Hela, HepG2 and MCF-7 cell lines in vitro with GI₅₀ value of 1.6, 2.7, 2.9 and 4.3 μM, respectively, comparable with the positive control colchicine (GI₅₀ value of 4.1, 7.2, 9.5 and 14.5 μM, respectively) and CA-4 (GI₅₀ value of 2.2, 4.3, 6.4 and 11.4 μM, respectively). Simultaneously, we evaluated that compound 33 could effectively induce apoptosis of A549 associated with G2/M phase cell cycle arrest. Immunofluorescence microscopy also clearly indicated compound 33 a potent antimicrotubule agent. Docking simulation showed that compound 33 could bind tightly with the colchicine-binding site and act as a tubulin inhibitor. Three-dimensional-QSAR model was also built to provide more pharmacophore understanding that could be used to design new agents with more potent tubulin assembling inhibitory activity in the future.

Current Advances of Tubulin Inhibitors in Nanoparticle Drug Delivery and Vascular Disruption/Angiogenesis

Extensive research over the last decade has resulted in a number of highly potent tubulin polymerization inhibitors acting either as microtubule stabilizing agents (MSAs) or microtubule destabilizing agents (MDAs). These inhibitors have potent cytotoxicity against a broad spectrum of human tumor cell lines. In addition to cytotoxicity, a number of these tubulin inhibitors have exhibited abilities to inhibit formation of new blood vessels as well as disrupt existing blood vessels. Tubulin inhibitors as a vascular disrupting agents (VDAs), mainly from the MDA family, induce rapid tumor vessel occlusion and massive tumor necrosis. Thus, tubulin inhibitors have become increasingly popular in the field of tumor vasculature. However, their pharmaceutical application is halted by a number of limitations including poor solubility and toxicity. Thus, recently, there has been considerable interests in the nanoparticle drug delivery of tubulin inhibitors to circumvent those limitations. This article reviews recent advances in nanoparticle based drug delivery for tubulin inhibitors as well as their tumor vasculature disruption properties.

Recent Advances in chemistry and pharmacology of 2-methoxyestradiol: An anticancer investigational drug

2-Methoxyestradiol (2ME2), an estrogen hormone metabolite is a potential cancer chemotherapeutic agent. Presently, it is an investigational drug under various phases of clinical trials alone or in combination therapy. Its anticancer activity has been attributed to its antitubulin, antiangiogenic, pro-apoptotic and ROS induction properties. This anticancer drug candidate has been explored extensively in last twenty years for its detailed chemistry and pharmacology. Present review is an update of its chemistry and biological activity. It also extends an assessment of potential of 2ME2 and its analogues as possible anticancer drug in future.

Synthesis, biological evaluation and molecular docking studies of novel 1-(4,5-dihydro-1H-pyrazol-1-yl)ethanone-containing 1-methylindol derivatives as potential tubulin assembling inhibitors

A series of novel compounds (6a–6v) containing 1-methylindol and 1-(4,5-dihydro-1H-pyrazol-1-yl)ethanone skeleton were designed, synthesized and evaluated as potential anticancer agents.

Synthesis, biological evaluation, and molecular docking studies of novel 1-benzene acyl-2-(1-methylindol-3-yl)-benzimidazole derivatives as potential tubulin polymerization inhibitors

A series of 1-benzene acyl-2-(1-methylindol-3-yl)-benzimidazole derivatives were designed, synthesized and evaluated as potential tubulin polymerization inhibitors and for the cytotoxicity against anthropic cancer cell lines. Among the novel compounds, compound 11f was demonstrated the most potent tubulin polymerization inhibitory activity (IC50 = 1.5 μM) and antiproliferative activity against A549, HepG2 and MCF-7 (GI50 = 2.4, 3.8 and 5.1 μM, respectively), which was compared with the positive control colchicine and CA-4. We also evaluated that compound 11f could effectively induce apoptosis of A549 associated with G2/M phase cell cycle arrest. Docking simulation and 3D-QSAR model in these studies provided more information that could be applied to design new molecules with more potent tubulin inhibitory activity.

Synthesis, biological evaluation and molecular modeling of new analogs of the anti-cancer agent 2-methoxyestradiol: potent inhibitors of angiogenesis

Structural-activity studies on the steroid 2-methoxyestradiol revealed a new analog that exhibited potent inhibition of angiogenesis and cytotoxic effects.