Modification of the phenyl ring B of phenyl 4-(2-oxoimidazolidin-1-yl)benzenesulfonates by pyridinyl moiety leads to novel antimitotics targeting the colchicine-binding site

A series of 8 novel pyridinyl 4-(2-oxoimidazolidin-1-yl)benzenesulfonates (PYRIB-SOs) were designed, prepared and evaluated for their mechanism of action. PYRIB-SOs were found to have antiproliferative activity in the nanomolar to submicromolar range on several breast cancer cell lines. Moreover, subsequent biofunctional assays indicated that the most potent PYRIB-SOs 1-3 act as antimitotics binding to the colchicine-binding site (C-BS) of α, β-tubulin and that they arrest the cell cycle progression in the G2/M phase. Microtubule immunofluorescence and tubulin polymerisation assay confirm that they disrupt the cytoskeleton through inhibition of tubulin polymerisation as observed with microtubule-destabilising agents. They also show good overall theoretical physicochemical, pharmacokinetic and druglike properties. Overall, these results show that PYRIB-SOs is a new family of promising antimitotics to be further studied in vivo for biopharmaceutical and pharmacodynamic evaluations.

Structure-Based Design and Synthesis of N-Substituted 3-Amino-β-Carboline Derivatives as Potent αβ-Tubulin Degradation Agents

So far, relatively few small molecules have been reported to promote tubulin degradation. Our previous studies have found that compound 2, a noncovalent colchicine-site ligand, was capable of promoting αβ-tubulin degradation. To further improve its antiproliferative activity, 66 derivatives or analogues of 2 were designed and synthesized based on 2-tubulin cocrystal structure. Among them, 12b displayed nanomolar potency against a variety of tumor cells, including paclitaxel- and adriamycin-resistant cell lines. 12b binds to the colchicine site and promotes αβ-tubulin degradation in a concentration-dependent manner via the ubiquitin-proteasome pathway. The X-ray crystal structure revealed that 12b binds in a similar manner as 2, but there is a slight conformation change of the B ring, which resulted in better interaction of 12b with surrounding residues. 12b effectively suppressed tumor growth at an i.v. dose of 40 mg/kg (3 times a week) on both A2780S (paclitaxel-sensitive) and A2780T (paclitaxel-resistant) ovarian xenograft models, with respective TGIs of 92.42 and 79.75% without obvious side effects, supporting its potential utility as a tumor-therapeutic compound.

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.

Structure modification and biological evaluation of indole-chalcone derivatives as anti-tumor agents through dual targeting tubulin and TrxR

Microtubule target agents (MTAs) are widely-used clinical anti-cancer drugs for decades, but the acquired drug resistance severely restricted their application. Thioredoxin reductases (TrxR) was reported to be overexpressed in most tumors and closely related to high risk of cancer recurrence and drug resistance, making it a potential target for anticancer drug discovery. Multi-target-directed ligands (MTDLs) by a single molecule provide a logical and alternative approach to drug combinations. In this work, based on the structure-activity relationships obtained in our previous study, some structure modifications were performed. On one hand, the retained skeleton structure of MTAs endowed its tubulin polymerization inhibition activity, on the other hand, the selenium-containing structure and α,β-unsaturated ketone moiety endowed the TrxR inhibition activity. As results, the newly obtained compounds exhibited superior anti-proliferative activities towards various human cancer cells and drug-resistance cells, and displayed high selectivity towards various human normal cells. The mechanism study revealed that the dual effect of cell cycle arrest triggered by targeting tubulin and the abnormal accumulation of ROS caused by TrxR inhibition eventually lead to cell apoptosis. Notably, compared with the MTA agents CA-4P, and the TrxR inhibitor Ethaselen, the optimized compound 14c, which served as dual-targeting inhibitor of tubulin and TrxR, exerted greatly improved in vivo anti-tumor activity. In summary, 14c deserved further consideration for cancer therapy.

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.

Discovery of new quinolines as potent colchicine binding site inhibitors: design, synthesis, docking studies, and anti-proliferative evaluation

Discovering of new anticancer agents with potential activity against tubulin polymerisation is still a promising approach. Colchicine binding site inhibitors are the most relevant anti-tubulin polymerisation agents. Thus, new quinoline derivatives have been designed and synthesised to possess the same essential pharmacophoric features of colchicine binding site inhibitors. The synthesised compounds were tested in vitro against a panel of three human cancer cell lines (HepG-2, HCT-116, and MCF-7) using colchicine as a positive control. Comparing to colchicine (IC50 = 7.40, 9.32, and 10.41 µM against HepG-2, HCT-116, and MCF-7, respectively), compounds 20, 21, 22, 23, 24, 25, 26, and 28 exhibited superior cytotoxic activities with IC50 values ranging from 1.78 to 9.19 µM. In order to sightsee the proposed mechanism of anti-proliferative activity, the most active members were further evaluated in vitro for their inhibitory activities against tubulin polymerisation. Compounds 21 and 32 exhibited the highest tubulin polymerisation inhibitory effect with IC50 values of 9.11 and 10.5 nM, respectively. Such members showed activities higher than that of colchicine (IC50 = 10.6 nM) and CA-4 (IC50 = 13.2 nM). The impact of the most promising compound 25 on cell cycle distribution was assessed. The results revealed that compound 25 can arrest the cell cycle at G2/M phase. Annexin V and PI double staining assay was carried out to explore the apoptotic effect of the synthesised compounds. Compound 25 induced apoptotic effect on HepG-2 thirteen times more than the control cells. To examine the binding pattern of the target compounds against the tubulin heterodimers active site, molecular docking studies were carried out.

Discovery of novel quinoline-based analogues of combretastatin A-4 as tubulin polymerisation inhibitors with apoptosis inducing activity and potent anticancer effect

A new series of quinoline derivatives of combretastatin A-4 have been designed, synthesised and demonstrated as tubulin polymerisation inhibitors. These novel compounds showed significant antiproliferative activities, among them, 12c exhibited the most potent inhibitory activity against different cancer cell lines (MCF-7, HL-60, HCT-116 and HeLa) with IC50 ranging from 0.010 to 0.042 µM, and with selectivity profile against MCF-10A non-cancer cells. Further mechanistic studies suggest that 12c can inhibit tubulin polymerisation and cell migration, leading to G2/M phase arrest. Besides, 12c induces apoptosis via a mitochondrial-dependant apoptosis pathway and caused reactive oxygen stress generation in MCF-7 cells. These results provide guidance for further rational development of potent tubulin polymerisation inhibitors for the treatment of cancer.HighlightsA novel series of quinoline derivatives of combretastatin A-4 have been designed and synthesised.Compound 12c showed significant antiproliferative activities against different cancer cell lines.Compound 12c effectively inhibited tubulin polymerisation and competed with [3H] colchicine in binding to tubulin.Compound 12c arrested the cell cycle at G2/M phase, effectively inducing apoptosis and inhibition of cell migration.

Tertiary sulphonamide derivatives as dual acting small molecules that inhibit LSD1 and suppress tubulin polymerisation against liver cancer

A series of tertiary sulphonamide derivatives were synthesised and evaluated for their antiproliferative activity against liver cancer cell lines (SNU-475, HepG-2, and Bel-7402). Among these tertiary sulphonamides, compound 17a displayed the best anti-liver cancer activity against Bel-7402 cells with an IC50 value of 0.32 μM. Compound 17a could effectively inhibit tubulin polymerisation with an IC50 value of 1.27 μM. Meanwhile, it selectively suppressed LSD1 with an IC50 value of 63 nM. It also concentration-dependently inhibited migration against Bel-7402 cells. Importantly, tertiary sulphonamide 17a exhibited the potent antitumor activity in vivo. All these findings revealed that compound 17a might be a tertiary sulphonamide-based dual inhibitor of tubulin polymerisation and LSD1 to treat liver cancer.

Design, Synthesis, and Biological Evaluation of Stable Colchicine-Binding Site Tubulin Inhibitors 6-Aryl-2-benzoyl-pyridines as Potential Anticancer Agents

We previously reported a potent tubulin inhibitor CH-2-77. In this study, we optimized the structure of CH-2-77 by blocking metabolically labile sites and synthesized a series of CH-2-77 analogues. Two compounds, 40a and 60c, preserved the potency while improving the metabolic stability over CH-2-77 by 3- to 4-fold (46.8 and 29.4 vs 10.8 min in human microsomes). We determined the high-resolution X-ray crystal structures of 40a (resolution 2.3 Å) and 60c (resolution 2.6 Å) in complex with tubulin and confirmed their direct binding at the colchicine-binding site. In vitro, 60c maintained its mode of action by inhibiting tubulin polymerization and was effective against P-glycoprotein-mediated multiple drug resistance and taxol resistance. In vivo, 60c exhibited a strong inhibitory effect on tumor growth and metastasis in a taxol-resistant A375/TxR xenograft model without obvious toxicity. Collectively, this work showed that 60c is a promising lead compound for further development as a potential anticancer agent.

Pyrazoline derivatives as tubulin polymerization inhibitors with one hit for Vascular Endothelial Growth Factor Receptor 2 inhibition

In this work, to check the effect of the transposition of the rings in typical patterns, a series of pyrazoline derivatives 3a-3t bearing the characteristic 3,4,5-trimethoxy phenyl and thiophene moieties were synthesized and evaluated as tubulin polymerization inhibitors. Basically, as the concise output of our design, a majority of the synthesized compounds showed potency in inhibiting the tubulin polymerization. The top hit, 3q, exhibited potent anti-proliferation activity on cancer cell lines. It was comparable on tubulin-polymerization inhibition with the positive control Colchicine but lower toxic. The VEGFR2 inhibitory potency was introduced occasionally. The flow cytometry assay confirmed the apoptotic procedure and the confocal imaging revealed the tubulin-microtubule dynamics pattern. The anti-cancer mechanism of 3q was similar to Colchicine but not exactly the same on forming multi-polar spindles. The docking simulation visualized the possible binding patterns of 3q into tubulin and VEGFR2, respectively. The results inferred that further investigations on the transposition of the rings might lead to the improvement of tubulin polymerization inhibitory activity and the steadily introduction of the VEGFR2 inhibition.

Efficient Synthesis and Bioevaluation of Novel Dual Tubulin/Histone Deacetylase 3 Inhibitors as Potential Anticancer Agents

Novel dual HDAC3/tubulin inhibitors were designed and efficiently synthesized by combining the pharmacophores of SMART (tubulin inhibitor) and MS-275 (HDAC inhibitor), among which compound 15c was found to be the most potent and balanced HDAC3/tubulin dual inhibitor with high HDAC3 activity (IC50 = 30 nM) and selectivity (SI > 1000) as well as excellent antiproliferative potency against various cancer cell lines, including an HDAC-resistant gastric cancer cell line (YCC3/7) with IC50 values in the range of 30-144 nM. Compound 15c inhibited B16-F10 cancer cell migration and colony formation. In addition, 15c demonstrated significant in vivo antitumor efficacy in a B16-F10 melanoma tumor model with a better TGI (70.00%, 10 mg/kg) than that of the combination of MS-275 and SMART. Finally, 15c presented a safe cardiotoxicity profile and did not cause nephro-/hepatotoxicity. Collectively, this work shows that compound 15c represents a novel tubulin/HDAC3 dual-targeting agent deserving further investigation as a potential anticancer agent.

Design, Synthesis, and Bioactivity Evaluation of Dual-Target Inhibitors of Tubulin and Src Kinase Guided by Crystal Structure

Klisyri (KX01) is a dual tubulin/Src protein inhibitor that has shown potential therapeutic effects in several tumor models. However, a phase II clinical trial in patients with bone-metastatic castration-resistant prostate cancer was halted because of lack of efficacy. We previously reported that KX01 binds to the colchicine site of β-tubulin and its morpholine group lies close to α-tubulin's surface. Thus, we hypothesized that enhancing the interaction of KX01 with α-tubulin could increase tubulin inhibition and synthesized a series of KX01 derivatives directed by docking studies. Among these derivatives, 8a exhibited more than 10-fold antiproliferation activity in several tumor cells than KX01 and significantly improved in vivo antitumor effects. The X-ray crystal structure suggested that 8a both bound to the colchicine site and extended into the interior of α-tubulin to form potent interactions, presenting a novel binding mode. A potential clinical candidate for cancer therapy was identified in this study.

Synthesis and biological evaluation of new 2-methoxyestradiol derivatives: Potent inhibitors of angiogenesis and tubulin polymerization

Here, we report the structural optimization of a hit natural compound, 2-ME₂ (2-methoxyestradiol), which exhibited inhibitory activity but low potency on tubulin polymerization, anti- angiogenesis, MCF-7 proliferation and metastasis in vitro and in vivo. A novel series of 3,17-modified and 17-modified analogs of 2-ME₂ were synthesized and investigated for their antiproliferative activity against MCF-7 and another five different human cancer cell lines leading to the discovery of 9i. 9i bind to tubulin colchicine site tightly, inhibited tubulin polymerization and disrupted cellular microtubule networks. Cellular mechanism studies revealed that 9i could induce G2/M phase arrest by down-regulated expression of p-Cdc2, P21 and cell apoptosis by regulating apoptosis-related proteins (Parp, Caspase families) in a dose-dependent manner. Importantly, 9i significantly inhibited HUVEC tube formation, proliferation, migration and invasion. The inhibitory effect against angiogenesis in vivo was confirmed by zebrafish xenograft. Furthermore, 9i could effectively inhibit the proliferation and metastasis of MCF-7 cells in vitro and in zebrafish xenograft. The satisfactory physicochemical property and metabolic stability of 9i further indicated that it can act as a promising and potent anti-angiogenesis, inhibiting proliferation and metastasis of breast cancer agent via targeting tubulin colchicine binding site.

MIL-1, a novel antitumor agent derived from natural product millepachine, acts as tubulin polymerization inhibitor for the treatment of hepatocellular carcinoma

Natural products are a large source of clinically effective antitumor drugs. Millepachine, a natural product derived from leguminous plants, was reported to display antitumor activity. In this study, the novel compound, (1H-indol-5-yl) (5-methoxy-2,2-dimethyl-2H-chromen-8-yl)methanone (MIL-1), was designed and synthesized by fusing millepachine and indole rings. MIL-1 exerted much better antitumor activity than millepachine, manifesting as a 24- to 201-fold increase in vitro cytotoxicity and a 2.4-fold increase in in vivo antitumor activity in hepatocellular cell lines-derived models. The immunofluorescence and HPLC detection revealed that MIL-1 was a potent microtubule targeting agent by interfering with the equilibrium of tubulin-microtubule dynamics and irreversibly binding to tubulin. MIL-1 displayed remarkable antitumor activity with an IC50 of 31-207 nM towards various human cancer cell lines derived from various organs and tissues, and it exerted no evidence of toxicity against normal cells. Mechanistic studies showed that MIL-1 arrested the cell cycle at G2/M phase and induced apoptosis by activating caspase-3 activity and reactive oxygen species (ROS) accumulation. Moreover, the superior antitumor effect of MIL-1 is worthy of further detailed study for the treatment of hepatocellular carcinoma (HCC).

Concise synthesis and biological evaluation of 2-Aryl-3-Anilinobenzo[b]thiophene derivatives as potent apoptosis-inducing agents

Many clinically used agents active in cancer chemotherapy exert their activity through the induction of cell death (apoptosis) by targeting microtubules, altering protein function or inhibiting DNA synthesis. The benzo[b]thiophene scaffold holds a pivotal place as a pharmacophore for the development of anticancer agents, and, in addition, this scaffold has many pharmacological activities. We have developed a flexible method for the construction of a new series of 2-aryl-3-(3,4,5-trimethoxyanilino)-6-methoxybenzo[b]thiophenes as potent antiproliferative agents, giving access to a wide range of substitution patterns at the 2-position of the 6-methoxybenzo[b]thiophene common intermediate. In the present study, all the synthesized compounds retained the 3-(3,4,5-trimethoxyanilino)-6-methoxybenzo[b]thiophene moiety, and the structure-activity relationship was examined by modification of the aryl group at its 2-position with electron-withdrawing (F) or electron-releasing (alkyl and alkoxy) groups. We found that small substituents, such as fluorine or methyl, could be placed in the para-position of the 2-phenyl ring, and these modifications only slightly reduced antiproliferative activity relative to the unsubstituted 2-phenyl analogue. Compounds 3a and 3b, bearing the phenyl and para-fluorophenyl at the 2-position of the 6-methoxybenzo[b]thiophene nucleus, respectively, exhibited the greatest antiproliferative activity among the tested compounds. The treatment of both Caco2 (not metastatic) and HCT-116 (metastatic) colon carcinoma cells with 3a or 3b triggered a significant induction of apoptosis as demonstrated by the increased expression of cleaved-poly(ADP-ribose) polymerase (PARP), receptor-interacting protein (RIP) and caspase-3 proteins. The same effect was not observed with non-transformed colon 841 CoN cells. A potential additional effect during mitosis for 3a in metastatic cells and for 3b in non-metastatic cells was also observed.

Synthesis, biological evaluation, and structure-activity relationships of new tubulin polymerization inhibitors based on 5-amino-1,2,4-triazole scaffold

Based on our previous research, thirty new 5-amino-1H-1,2,4-triazoles possessing 3,4,5-trimethoxyphenyl moiety were synthesized, and evaluated for antiproliferative activities. Among them, compounds IIa, IIIh, and IIIm demonstrated significant antiproliferative activities against a panel of tumor cell lines, and the promising compound IIIm dose-dependently caused G2/M phase arrest in HeLa cells. Furthermore, analogue IIa exhibited the most potent tubulinpolymerization inhibitory activity with an IC₅₀ value of 9.4 μM, and molecular modeling studies revealed that IIa formed stable interactions in the colchicine-binding site of tubulin, suggesting that 5-amino-1H-1,2,4-triazole scaffold has potential for further investigation to develop novel tubulin polymerization inhibitors with anticancer activity.

Indolyl-α-keto-1,3,4-oxadiazoles: Synthesis, anti-cell proliferation activity, and inhibition of tubulin polymerization

A series of novel indolyl-α-keto-1,3,4-oxadiazole derivatives have been synthesized by employing molecular iodine-mediated oxidative cyclization of acylhydrazones. In vitro anti cell proliferation activity of these derivatives against various cancer cells lines such as human lymphoblast (U937), leukemia (Jurkat & SB) and human breast (BT474) was investigated. Among the synthesized indolyl-α-keto-1,3,4-oxadiazoles 19a-p, only one compound (19e) exhibited significant antiproliferative activity against a panel of cell lines. The compound 19e with 3,4,5-trimethoxyphenyl motif, endowed strong cytotoxicity against U937, Jurkat, BT474 and SB cancer cells with IC₅₀ values of 7.1, 3.1, 4.1, and 0.8 µM, respectively. Molecular docking studies suggested a potential binding mode for 19e in the colchicine binding site of tubulin. When tested for in vitro tubulin polymerizaton, 19e inhibited tubulin polymezations (IC₅₀ = 10.66 µM) and induced apoptosis through caspase 3/7 activation. Further, the derivative 19e did not cause necrosis when measured using lactate dehydrogenase assay.

Discovery of novel CA-4 analogs as dual inhibitors of tubulin polymerization and PD-1/PD-L1 interaction for cancer treatment

A series of novel CA-4 analogs as dual inhibitors of tubulin polymerization and PD-1/PD-L1 were designed, synthesized and bio-evaluated. Among them, compound TP5 exhibited strongest inhibitory effects against five cancer cell lines with an IC50 value of 800 nM in HepG2 cells. In addition, mechanism studies revealed that TP5 could effectively inhibit tubulin polymerization, suppress HepG2 cells migration and colony formation, and cause cell arrest at G2/M phase and induce apoptosis. Furthermore, TP5 exhibited moderate anti-PD-1/PD-L1 activity with IC50 values of 48.76 μM in a homogenous time-resolved fluorescence (HTRF) assay. In vivo efficacy studies indicated that TP5 could significantly suppress tumor growth in an immune checkpoint humanized mouse model with a Tumor Growth Suppression (TGI) of 57.9% at 100 mg/kg without causing significant toxicity. Moreover, TP5 did not cause in vivo cardiotoxicity in BALB/c mice. These results suggest that the novel CA-4 analogs may serve as a starting point for developing more potent dual inhibitors of tubulin polymerization and PD-1/PD-L1.

Synthesis and Anticancer Activity of Mitotic-Specific 3,4-Dihydropyridine-2(1H)-thiones

Most anticancer drugs target mitosis as the most crucial and fragile period of rapidly dividing cancer cells. However the limitations of classical chemotherapeutics drive the search for new more effective and selective compounds. For this purpose structural modifications of the previously characterized pyridine aalog (S1) were incorporated aiming to obtain an antimitotic inhibitor of satisfactory and specific anticancer activity. Structure-activity relationship analysis of the compounds against a panel of cancer cell lines allowed to select a compound with a thiophene ring at C5 of a 3,4-dihydropyridine-2(1H)-thione (S22) with promising antiproliferative activity (IC50 equal 1.71 ± 0.58 µM) and selectivity (SI = 21.09) against melanoma A375 cells. Moreover, all three of the most active compounds from the antiproliferative study, namely S1, S19 and S22 showed better selectivity against A375 cells than reference drug, suggesting their possible lower toxicity and wider therapeutic index. As further study revealed, selected compounds inhibited tubulin polymerization via colchicine binding site in dose dependent manner, leading to aberrant mitotic spindle formation, cell cycle arrest and apoptosis. Summarizing, the current study showed that among obtained mitotic-specific inhibitors analogue with thiophene ring showed the highest antiproliferative activity and selectivity against cancer cells.

CAP rigidification of MS-275 and chidamide leads to enhanced antiproliferative effects mediated through HDAC1, 2 and tubulin polymerization inhibition

The study focuses on the prudent design and synthesis of anilide type class I HDAC inhibitors employing a functionalized pyrrolo[2,3-d]pyrimidine skeleton as the surface recognition part. Utilization of the bicyclic aromatic ring to fabricate the target compounds was envisioned to confer rigidity to the chemical architecture of MS-275 and chidamide. In-vitro enzymatic and cellular assays led to the identification of compound 7 as a potent inhibitor of HDAC1 and 2 isoform that exerted substantial cell growth inhibitory effects against human breast MDA-MB-231, cervical HeLa, breast MDA-MB-468, colorectal DLD1, and colorectal HCT116 cell lines with an IC₅₀ values of 0.05-0.47 μM, better than MS-275 and chidamide. In addition, the anilide 7 was also endowed with a superior antiproliferative profile than MS275 and chidamide towards the human cutaneous T cell lymphoma (HH and HuT78), leukemia (HL60 and KG-1), and HDACi sensitive/resistant gastric cell lines (YCC11 and YCC3/7). Exhaustive exploration of the construct 7 confirmed it to be a microtubule-targeting agent that could trigger the cell-cycle arrest in mitosis. In pursuit of extracting the benefits of evidenced microtubule-destabilizing activity of the anilide 7, it was further evaluated against non-small-cell lung cancer cell lines as well as the multiple-drug resistant uterine cancer cell line (MES-SA/Dx5) and overwhelmingly positive results in context of inhibitory effects were attained. Furthermore, molecular modelling studies were performed and some key interactions of the anilide 7 with the amino acid residues of the active site of HDAC1 isoform and tubulin were figured out.

A facile synthesis of diaryl pyrroles led to the discovery of potent colchicine site antimitotic agents

Three different series of cis-restricted analogues of combretastatin A-4 (CA-4), corresponding to thirty-nine molecules that contained a pyrrole nucleus interposed between the two aryl rings, were prepared by a palladium-mediated coupling approach and evaluated for their antiproliferative activity against six human cancer cell lines. In the two series of 1,2-diaryl pyrrole derivatives, results suggested that the presence of the 3',4',5'-trimethoxyphenyl moiety at the N-1 position of the pyrrole ring was more favorable for antiproliferative activity. In the series of 3,4-diarylpyrrole analogues, three compounds (11i-k) exhibited maximal antiproliferative activity, showing excellent antiproliferative activity against the CA-4 resistant HT-29 cells. Inhibition of tubulin polymerization of selected 1,2 pyrrole derivatives (9a, 9c, 9o and 10a) was similar to that observed with CA-4, while the isomeric 3,4-pyrrole analogues 11i-k were generally from 1.5- to 2-fold more active than CA-4. Compounds 11j and 11k were the only compounds that showed activity as inhibitors of colchicine binding comparable to that CA-4. Compound 11j had biological properties consistent with its intracellular target being tubulin. This compound was able to block the cell cycle in metaphase and to induce significant apoptosis at a concentration of 25 nM, following the mitochondrial pathway, with low toxicity for normal cells. More importantly, compound 11j exerted activity in vivo superior to that of CA-4P, being able to significantly reduce tumor growth in a syngeneic murine tumor model even at the lower dose tested (5.0 mg/kg).

A novel series of benzothiazepine derivatives as tubulin polymerization inhibitors with anti-tumor potency

In this work, a series of diaryl benzo[b][1,4]thiazepine derivatives D1-D36 were synthesized and screened as tubulin polymerization inhibitors with anti-tumor potency. They were designed by introducing the seven-member ring benzothiazepine as the linker for CA-4 modification for the first time. Among them, the hit compound D8 showed potential on inhibiting the growth of several cancer cell lines (IC₅₀ values: 1.48 μM for HeLa, 1.47 μM for MCF-7, 1.52 μM for HT29 and 1.94 μM for A549), being comparable with the positive controls Colchicine and CA-4P. The calculated IC₅₀ value of D8 as an tubulin polymerization inhibitor was 1.20 μM. The results of the flow cytometry assay revealed that D8 could induce the mitotic catastrophe and the death of living cancer cells. D8 also indicated the anti-vascular activity. The possible binding pattern was implied by docking simulation, inferring the possibility of introducing interactions with the nearby tubulin chain. Since the novel structural trial has been conducted with preliminary discussion, this work might stimulate new ideas in further modification of tubulin-related anti-cancer agents and therapeutic approaches.

Tubulin inhibitory activity of a novel colchicine-binding compounds based on a dinaphthospiropyranran scaffold

Spiropyrans have been investigated for their thermo- and photochromic characteristics, but their biotherapeutic properties have not been addressed. We report anti-proliferative properties of a novel dinaphthospiropyran analogue (1). The compound 1 was synthesized by a simple and expedient method using a one-pot acid-catalyzed aldol condensation of 2-hydroxy-1-naphthaldehyde with 4-piperidone followed by an acetalization reaction. Compound 1 was submitted to anticancer drug screen in the National Cancer Institute's panel of 60 human tumor cell lines. The average concentration of 1 to inhibit 50% cell growth was 5.4 ± 0.23 µM. All cell lines responded at almost the same concentration, suggesting that the action of 1 is not selective for cancer of origin. COMPARE analysis of dose-response data revealed interaction with tubulin as the possible mechanism of action of 1. At molecular level, 1 induced tubulin reorganization in colon cancer HCT-116 cells. Under cell-free conditions, the efficacy of 1 to inhibit tubulin polymerization was comparable to that of paclitaxel and vinblastine. Molecular docking showed that compound 1 binds to the colchicine-binding site of tubulin. We conclude that dinaphthospiropyrans present a novel scaffold for the development of tubulin inhibitors.

Rational Design of Azastatin as a Potential ADC Payload with Reduced Bystander Killing

Auristatins are a class of ultrapotent microtubule inhibitors, whose growing clinical popularity in oncology is based upon their use as payloads in antibody-drug conjugates (ADCs). The most widely utilized auristatin, MMAE, has however been shown to cause apoptosis in non-pathological cells proximal to the tumour ("bystander killing"). Herein, we introduce azastatins, a new class of auristatin derivatives encompassing a side chain amine for antibody conjugation. The synthesis of Cbz-azastatin methyl ester, which included the C2-elongation and diastereoselective reduction of two proteinogenic amino acids as key transformations, was accomplished in 22 steps and 0.76 % overall yield. While Cbz-protected azastatin methyl ester (0.13-3.0 nM) inhibited proliferation more potently than MMAE (0.47-6.5 nM), removal of the Cbz-group yielded dramatically increased IC50 -values (9.8-170 nM). We attribute the reduced apparent cytotoxicity of the deprotected azastatin methyl esters to a lack of membrane permeability. These results clearly establish the azastatins as a novel class of cytotoxic payloads ideally suited for use in next-generation ADC development.

Computational modeling and target synthesis of monomethoxy-substituted o-diphenylisoxazoles with unexpectedly high antimitotic microtubule destabilizing activity

The ability of monomethoxy-substituted o-diphenylisoxazoles 2a-d to interact with the colchicine site of tubulin was predicted using computational modeling, docking studies, and calculation of binding affinity. The respective molecules were synthesized in high yields by three steps reaction using easily available benzaldehydes, acetophenones, and arylnitromethanes as starting material. The calculated antitubulin effect was confirmed in vivo in a sea urchin embryo model. Compounds 2a and 2c showed high antimitotic microtubule destabilizing activity compared to that of CA4. Isoxazole 2a also exhibited significant cytotoxicity against human cancer cells in NCI60 screen. For the first time, isoxazole-linked CA4 derivatives 2a and 2c with only one methoxy substituent were identified as potent antimitotic microtubule destabilizing agents. These molecules could be considered as promising structures for further optimization.

Synthesis, biological evaluation, and molecular docking analysis of phenstatin based indole linked chalcones as anticancer agents and tubulin polymerization inhibitors

A library of new phenstatin based indole linked chalcone compounds (9a-z and 9aa-ad) were designed and synthesized. Of these, compound 9a with 1-methyl, 2- and 3-methoxy substituents in the aromatic ring was efficacious against the human oral cancer cell line SCC-29B, spheroids, and in a mouse xenograft model of oral cancer AW13516. Compound 9a exhibited anti-cancer activity through disrupting cellular integrity and affecting glucose metabolism-which is a hallmark of cancer. The cellular architecture was affected by inhibition of tubulin polymerization as observed by an immunofluorescence assay on 9a-treated SCC-29B cells. An in vitro tubulin polymerization kinetics assay provided evidence of direct interaction of 9a with tubulin. This physical interaction between tubulin and compound 9a was further confirmed by Surface Plasmon Resonance (SPR) analysis. Molecular docking experiments and validations revealed that compound 9a interacts and binds at the colchicine binding site of tubulin and at active sites of key enzymes in the glucose metabolism pathway. Based on in silico modeling, biophysical interactions, and pre-clinical observations, 9a consisting of phenstatin based indole-chalcone scaffolds, can be considered as an attractive tubulin polymerization inhibitor candidate for developing anti-cancer therapeutics.

Anti-proliferative potential of triphenyl substituted pyrimidines against MDA-MB-231, HCT-116 and HT-29 cancer cell lines

A series of triphenyl substituted pyrimidines as analogous of colchicine and combretastatin A-4 was synthesized and evaluated for the antiproliferative potential. The compounds were screened against MDA-MB-231, HCT-116 and HT-29 cell lines using MTT assay. Most of the compounds displayed antiproliferative activity in low to sub micro molar concentration. Amongst the synthesized derivatives, compounds HK-2, HK-10 and HK-13 were found to be effective against all the three cancer cell lines. HK-2 exhibited IC₅₀ values of 3.39 µM, 4.78 µM and 4.23 µM, HK-10 showed IC₅₀ values of 0.81 µM, 5.89 µM, 4.96 µM and HK-13 showed IC₅₀ values 3.24 µM, 4.93 µM and 4.73 µM against MDA-MB-231, HCT-116 and HT-29 cancer cell lines, respectively. HK-10 was found to be the most potent compound in the series with IC₅₀ values of 0.81 µM against MDA-MB-231. In the cell cycle analysis, HK-2 and HK-10 showed cell arrest at G2/M phase of the cell cycle while HK-13 inhibited cell growth at the G1/G0 phase. All the three compounds showed cell death induced through apoptosis. In the docking studies, HK-2, HK-10 and HK-13 were found to fit well in the colchicine binding site of the tubulin. Some of the compounds in the current series were found to be promising against all the three cancer cell lines and may act as potent leads for further development.

Synthesis and biological evaluation of substituted N-(2-(1H-benzo[d]imidazol-2-yl)phenyl)cinnamides as tubulin polymerization inhibitors

A new series of N-(2-(1H-benzo[d]imidazol-2-yl)phenyl) cinnamides was prepared and evaluated for their in vitro cytotoxic activity using various cancer cell lines viz. A549 (human non-small cell lung cancer), MDA-MB-231 (human triple negative breast cancer), B16-F10 (mouse melanoma), BT-474 (human breast cancer), and 4 T1 (mouse triple negative breast cancer). In the series of tested compounds, 12h showed potent cytotoxic activity against non-small cell lung cancer cell line with IC₅₀ value of 0.29 ± 0.02 µM. The cytoxicity of most potent compound 12h was also tested on NRK-52E (normal rat kidney epithelial cell line) and showed less cytotoxicity compared to cancer cells. Tubulin polymerization assay indicated that the compound 12h was able to impede the cell division by inhibiting tubulin polymerization. Moreover, molecular docking study also suggested the binding of 12h at the colchicine-binding site of the tubulin protein. Cell cycle analysis revealed that the compound 12h arrests G2/M phase. In addition, 12h induced apoptosis in A549 cell lines was evaluated by various staining studies like acridine orange, DAPI, analysis of mitochondrial membrane potential, annexin V-FITC, and DCFDA assays.

Fluorinated derivatives of 2-phenyl-3-hydroxy-4(1H)-quinolinone as tubulin polymerization inhibitors

We have synthesized a series of 2-phenyl-3-hydroxy-4(1H)-quinolinone derivatives substituted with one or more fluorine atoms on the quinolone backbone as well as on phenyl ring. The derivatives bearing more fluorine atoms were subjected to modification by nucleophilic substitutions by thiophenol, morpholine, and piperazine derivative. We have tested the prepared compounds in cytotoxic activity assay against cancer cell lines. Four derivatives exhibited micromolar values of IC₅₀ against some of the cancer cell lines, and we have subjected them to cell cycle analysis on CCRF-CEM. Moreover, most active 7-fluoro-3-hydroxy-2-phenyl-6-(phenylthio)quinolin-4(1H)-one inhibits mitosis progression. Cell cycle analysis, in vitro tubulin polymerization assay, and tubulin imaging in cells indicated that the anticancer activity of thiophenol derivative is associated with its ability to inhibit microtubule formation.

Synthesis, biological evaluation and molecular docking studies of new amides of 4-chlorothiocolchicine as anticancer agents

Colchicine belongs to a large group of microtubule polymerization inhibitors. Although the anti-cancer activity of colchicine and its derivatives has been established, none of them has found commercial application in cancer treatment due to side effects. Therefore, we designed and synthesized a series of six triple-modified 4-chlorothiocolchicine analogues with amide moieties and one urea derivative. These novel derivatives were tested against several different cancer cell lines (A549, MCF-7, LoVo, LoVo/DX) and primary acute lymphoblastic leukemia (ALL) cells and they showed activity in the nanomolar range. The obtained IC₅₀ values for novel derivatives were lower than those obtained for unmodified colchicine and common anticancer drugs such as doxorubicin and cisplatin. Further studies of colchicine and selected analogues were undertaken to indicate that they induced apoptotic cell death in ALL-5 cells. We also performed in silico studies to predict binding modes of the 4-chlorothiocolchicine derivatives to different β tubulin isotypes. The results indicate that select triple-modified 4-chlorothiocolchicine derivatives represent highly promising novel cancer chemotherapeutics.

Dual-functional conjugates improving cancer immunochemotherapy by inhibiting tubulin polymerization and indoleamine-2,3-dioxygenase

A series of novel conjugates comprising tublin and IDO inhibitors were designed, synthesized and evaluated for their antiproliferative activity. Among them, HI5, composed of combretastatin A-4 (CA-4) and (D)-1-methyltryptophan (D-MT) by a linker, exhibited the most potent antitumor activity, in particular with higher IC₅₀ value (0.07 μM) than CA-4 (0.21 μM) against HeLa cancer cell line. Mechanism studies indicated that HI5 can inhibit tubulin polymerization and cell migration, cause G2/M phase arrest, concurrent induce apoptosis via the mitochondrial dependent apoptosis pathway and cause reactive oxidative stress generation in HeLa cells. Furthermore, HI5 can inhibit IDO expression and decrease kynurenine production, leading to stimulating T cells activation and proliferation to enhance antitumor immunity in vitro. Interestingly, HI5 can effectively limit the tumor growth in the HeLa xenograft mice models without causing significant loss of body weight. Consequently, such a conjugation can be a potent and safe immunochemotherapeutic method for improving cancer therapy.

Design, synthesis and biological evaluation of novel vicinal diaryl-substituted 1H-Pyrazole analogues of combretastatin A-4 as highly potent tubulin polymerization inhibitors

A series of 3-(3',4',5'-trimethoxyphenyl)-4-substituted 1H-pyrazole and their related 3-aryl-4-(3',4',5'-trimethoxyphenyl)-1-H-pyrazole regioisomeric derivatives, prepared as cis-rigidified combretastatin A-4 (CA-4) analogues, were synthesized and evaluated for their in vitro antiproliferative against six different cancer cell lines and, for selected highly active compounds, inhibitory effects on tubulin polymerization, cell cycle effects and in vivo potency. We retained the 3',4',5'-trimethoxyphenyl moiety as ring A throughout the present investigation, and a structure-activity relationship (SAR) information was obtained by adding electron-withdrawing (OCF₃, CF₃) or electron-releasing (alkyl and alkoxy) groups on the second aryl ring, corresponding to the B-ring of CA-4, either at the 3- or 4-position of the pyrazole nucleus. In addition, the B-ring was replaced with a benzo[b]thien-2-yl moiety. For many of the compounds, their activity was greater than, or comparable with, that of CA-4. Maximal activity was observed with the two regioisomeric derivatives characterized by the presence of a 4-ethoxyphenyl and a 3',4',5'-trimethoxyphenyl group at the C-3 and C-4 positions, and vice versa, of the 1H-pyrazole ring. The data showed that the 3',4',5'-trimethoxyphenyl moiety can be moved from the 3- to the 4-position of the 1H-pyrazole ring without significantly affecting antiproliferative activity. The most active derivatives bound to the colchicine site of tubulin and inhibited tubulin polymerization at submicromolar concentrations. In vivo experiments, on an orthotopic murine mammary tumor, revealed that 4c inhibited tumor growth even at low concentrations (5 mg/kg) compared to CA-4P (30 mg/kg).

Synthesis, Microtubule-Binding Affinity, and Antiproliferative Activity of New Epothilone Analogs and of an EGFR-Targeted Epothilone-Peptide Conjugate

A new simplified, epoxide-free epothilone analog was prepared incorporating an N-(2-hydroxyethyl)-benzimidazole side chain, which binds to microtubules with high affinity and inhibits cancer cell growth in vitro with nM potency. Building on this scaffold, a disulfide-linked conjugate with the purported EGFR-binding (EGFR, epidermal growth factor receptor) peptide GE11 was then prepared. The conjugate retained significant microtubule-binding affinity, in spite of the size of the peptide attached to the benzimidazole side chain. The antiproliferative activity of the conjugate was significantly lower than for the parent scaffold and, surprisingly, was independent of the EGFR expression status of cells. Our data indicate that the disulfide-based conjugation with the GE11 peptide is not a viable approach for effective tumor-targeting of highly potent epothilones and probably not for other cytotoxics.

Synthesis and in Vitro Bioactivity of Polyunsaturated Fatty Acid Conjugates of Combretastatin A-4

Combretastatin A-4 (CA-4) (1) is a plant-derived anticancer agent binding to the tubulin colchicine site. Polyunsaturated fatty acids (PUFAs) are readily taken up by cancer cells and have been used to improve cell targeting. In the present study, four CA-4-PUFA conjugates were synthesized by coupling combretastatin A-4 (1) with several polyunsaturated fatty acids. The conjugates (2a-d) were characterized using spectroscopic methods. Their cytotoxicity was evaluated against human breast cancer cells (MCF-7), and the inhibition of tubulin polymerization was determined in vitro. All conjugates influenced tubulin polymerization, with the arachidonic acid conjugate (2c) displaying cytotoxicity similar in potency to the natural product CA-4 (1).

Synthesis, Evaluation for Cytotoxicity and Molecular Docking Studies of Benzo[c]furan-Chalcones for Potential to Inhibit Tubulin Polymerization and/or EGFR-Tyrosine Kinase Phosphorylation

A series of 2-arylbenzo[c]furan-chalcone hybrids 3a⁻y have been synthesized and evaluated for antiproliferative effects against the human breast cancer (MCF-7) cell line and for its potential to induce apoptosis and also to inhibit tubulin polymerization and/or epidermal growth factor receptor-tyrosine kinase (EGFR-TK) phosphorylation. Most of these compounds exhibited moderate to significant antigrowth effects in vitro against the MCF-7 cell line when compared to the reference standard actinomycin D. The capabilities of the most cytotoxic benzofuran-chalcone hybrids 3b and 3i, to induce apoptosis, have been evaluated by Annexin V-Cy3 SYTOX staining and caspase-3 activation. The experimental and molecular docking results suggest that the title compounds have the potential to exhibit inhibitory effects against tubulin polymerization and epidermal growth factor receptor tyrosine kinase (EGFR-TK) phosphorylation. The modeled structures of representative compounds displayed hydrophobic interactions as well as hydrogen and/or halogen bonding with the protein residues. These interactions are probably responsible for the observed increased binding affinity for the two receptors and their significant antigrowth effect against the MCF-7 cell line.

High-affinity ligands of the colchicine domain in tubulin based on a structure-guided design

Microtubule-targeting agents that bind at the colchicine-site of tubulin are of particular interest in antitumoral therapy due to their dual mechanism of action as antimitotics and vascular disrupting agents. Cyclohexanediones derivatives have been described as a new family of colchicine-domain binders with an association constant to tubulin similar to that of colchicine. Here, the high-resolution structures of tubulin in complex with cyclohexanediones TUB015 and TUB075 were solved by X-ray crystallography. A detailed analysis of the tubulin-TUB075 interaction by means of computational affinity maps allowed the identification of two additional regions at the binding site that were addressed with the design and synthesis of a new series of cyclohexanediones with a distal 2-substituted benzofurane. These new compounds showed potent antiproliferative activity with IC50 values in the nM range, arrested cell cycle progression at the G2/M phase and induced apoptosis at sub μM concentrations. Moreover, they caused the destruction of a preformed vascular network in vitro and inhibited the migration of endothelial cells at non-toxic concentrations. Finally, these compounds displayed high affinity for tubulin as substantiated by a K b value of 2.87 × 108 M-1 which, to the best of our knowledge, represents the highest binding constant measured to date for a colchicine-domain ligand.

The Design and Development of Potent Small Molecules as Anticancer Agents Targeting EGFR TK and Tubulin Polymerization

Some novel anthranilate diamides derivatives 4a–e, 6a–c and 9a–d were designed and synthesized to be evaluated for their in vitro anticancer activity. Structures of all newly synthesized compounds were confirmed by infra-red (IR), high-resolution mass (HR-MS) spectra, ¹H nuclear magnetic resonance (NMR) and ¹³C nuclear magnetic resonance (NMR) analyses. Cytotoxic screening was performed according to (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium (MTT) assay method using erlotinib as a reference drug against two different types of breast cancer cells. The molecular docking study was performed for representative compounds against two targets, epidermal growth factor receptor (EGFR) and tubulin in colchicine binding site to assess their binding affinities in order to rationalize their anticancer activity in a qualitative way. The data obtained from the molecular modeling was correlated with that obtained from the biological screening. These data showed considerable anticancer activity for these newly synthesized compounds. Biological data for most of the anthranilate diamide showed excellent activity with nanomolar or sub nanomolar half maximal inhibitory concentration (IC₅₀) values against tumor cells. EGFR tyrosine kinase (TK) inhibition assay, tubulin inhibition assay and apoptosis analysis were performed for selected compounds to get more details about their mechanism of action. Extensive structure activity relationship (SAR) analyses were also carried out.

Rational design and synthesis of 2-anilinopyridinyl-benzothiazole Schiff bases as antimitotic agents

Based on our previous results and literature precedence, a series of 2-anilinopyridinyl-benzothiazole Schiff bases were rationally designed by performing molecular modeling experiments on some selected molecules. The binding energies of the docked molecules were better than the E7010, and the Schiff base with trimethoxy group on benzothiazole moiety, 4y was the best. This was followed by the synthesis of a series of the designed molecules by a convenient synthetic route and evaluation of their anticancer potential. Most of the compounds have shown significant growth inhibition against the tested cell lines and the compound 4y exhibited good antiproliferative activity with a GI₅₀ value of 3.8µM specifically against the cell line DU145. In agreement with the docking results, 4y exerted cytotoxicity by the disruption of the microtubule dynamics by inhibiting tubulin polymerization via effective binding into colchicine domain, comparable to E7010. Detailed binding modes of 4y with colchicine binding site of tubulin were studied by molecular docking. Furthermore, 4y induced apoptosis as evidenced by biological studies like mitochondrial membrane potential, caspase-3, and Annexin V-FITC assays.

Synthesis and bioevaluation of N,4-diaryl-1,3-thiazole-2-amines as tubulin inhibitors with potent antiproliferative activity

A series of N,4-diaryl-1,3-thiazole-2-amines containing three aromatic rings with an amino linker were designed and synthesized as tubulin inhibitors and evaluated for their antiproliferative activity in three human cancer cell lines. Most of the target compounds displayed moderate antiproliferative activity, and N-(2,4-dimethoxyphenyl)-4-(4-methoxyphenyl)-1,3-thiazol-2-amine (10s) was determined to be the most potent compound. Tubulin polymerization and immunostaining experiments revealed that 10s potently inhibited tubulin polymerization and disrupted tubulin microtubule dynamics in a manner similar to CA-4. Moreover, 10s effectively induced SGC-7901 cell cycle arrest at the G₂/M phase in both concentration- and time-dependent manners. The molecular docking results revealed that 10s could bind to the colchicine binding site of tubulin.

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.

Synthesis, anti-cancer evaluation of benzenesulfonamide derivatives as potent tubulin-targeting agents

A series of benzenesulfonamide derivatives were synthesized and evaluated for their anti-proliferative activity and interaction with tubulin. These new derivatives showed significant activities against cellular proliferative and tubulin polymerization. Compound BA-3b proved to be the most potent compound with IC50 value ranging from 0.007 to 0.036 μM against seven cancer cell lines, and three drug-resistant cancer cell lines, which indicated a promising anti-cancer agent. The target tubulin was also verified by dynamic tubulin polymerization assay and tubulin intensity assay.

Synthesis and Biological Evaluation of N-[2-(4-Hydroxyphenylamino)-pyridin-3-yl]-4-methoxy-benzenesulfonamide (ABT-751) Tricyclic Analogues as Antimitotic and Antivascular Agents with Potent in Vivo Antitumor Activity

Benzopyridothiadiazepine (2a) and benzopyridooxathiazepine (2b) were modified to produce tricyclic quinazolinone 15-18 or benzothiadiazine 26-27 derivatives. These compounds were evaluated in cytotoxicity and tubulin inhibition assays and led to potent inhibitors of tubulin polymerization. N-[2(4-Methoxyphenyl)ethyl]-1,2-dihydro-pyrimidino[2,1-b]quinazolin-6-one (16a) exhibited the best in vitro cytotoxic activity (GI50 10-66.9 nM) against the NCI 60 human tumor cell line and significant potency against tubulin assembly (IC50 0.812 μM). In mechanism studies, 16a was shown to block cell cycle in G2/M phase and to disrupt microtubule formation and displayed good antivascular properties as inhibition of cell migration, invasion, and endothelial tube formation. Compound 16a was evaluated in C57BL/6 mouse melanoma B16F10 xenograft model to validate its antitumor activity, in comparison with reference ABT-751 (1). Compound 16a displayed strong in vivo antitumor and antivascular activities at a dose of 5 mg/kg without obvious toxicity, whereas 1 needed a 10-fold higher concentration to reach similar effects.

Dioxol and dihydrodioxin analogs of 2- and 3-phenylacetonitriles as potent anti-cancer agents with nanomolar activity against a variety of human cancer cells

A small library of (Z)-2-(benzo[d][1,3]dioxol-5-yl) and (Z)-2,3-dihydrobenzo[b][1,4]dioxin-6-yl analogs of 2- and 3-phenylacetonitriles has been synthesized and evaluated for their anti-cancer activities against a panel of 60 human cancer cell lines. The dihydrodioxin analog 3j and dioxol analogs 5e and 7e exhibited the most potent anti-cancer activity of all the analogs synthesized in this study, with GI50 values of <100 nM against almost all of the cell lines in the human cancer cell panel. Of these three, only compound 3j inhibited tubulin polymerization to any degree in vitro. The binding modes of 3j and the structurally related tubulin-inhibitor DMU-212 were determined by virtual docking studies with tubulin dimer. Compound 3j docked at the colchicine-binding site at the dimer interface of tubulin. The Full-Fitness (FF) score of 3j was observed to be substantially higher than DMU-212, which agrees well with the observed anti-cancer potency (GI50 values). The mechanism by which dioxol analogs 5e and 7e exert their cytotoxic effects remains unknown at this stage, but it is unlikely that they affect tubulin dynamics. Nevertheless, these findings suggest that both dioxol and dihydrodioxin analogs of phenylacrylonitrile may have potential for development as clinical candidates to treat a variety of human cancers.

Engineered kinesin motor proteins amenable to small-molecule inhibition

The human genome encodes 45 kinesin motor proteins that drive cell division, cell motility, intracellular trafficking and ciliary function. Determining the cellular function of each kinesin would benefit from specific small-molecule inhibitors. However, screens have yielded only a few specific inhibitors. Here we present a novel chemical-genetic approach to engineer kinesin motors that can carry out the function of the wild-type motor yet can also be efficiently inhibited by small, cell-permeable molecules. Using kinesin-1 as a prototype, we develop two independent strategies to generate inhibitable motors, and characterize the resulting inhibition in single-molecule assays and in cells. We further apply these two strategies to create analogously inhibitable kinesin-3 motors. These inhibitable motors will be of great utility to study the functions of specific kinesins in a dynamic manner in cells and animals. Furthermore, these strategies can be used to generate inhibitable versions of any motor protein of interest.

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 of aryl dihydrothiazol acyl shikonin ester derivatives as anticancer agents through microtubule stabilization

The high incidence of cancer and the side effects of traditional anticancer drugs motivate the search for new and more effective anticancer drugs. In this study, we synthesized 17 kinds of aryl dihydrothiazol acyl shikonin ester derivatives and evaluated their anticancer activity through MTT assay. Among them, C13 showed better antiproliferation activity with IC50=3.14 ± 0.21 μM against HeLa cells than shikonin (IC50=5.75 ± 0.47 μM). We then performed PI staining assay, cell cycle distribution, and cell apoptosis analysis for C13 and found that it can cause cell arrest in G2/M phase, which leads to cell apoptosis. This derivative can also reduce the adhesive ability of HeLa cells. Docking simulation and confocal microscopy assay results further indicated that C13 could bind well to the tubulin at paclitaxel binding site, leading to tubulin polymerization and mitotic disruption.

Design, Synthesis and Biological Evaluation of 1,4-Disubstituted-3,4-dihydroisoquinoline Compounds as New Tubulin Polymerization Inhibitors

A series of 1,4-disubstituted-3,4-dihydroisoquinoline derivatives designed as tubulin polymerization inhibitors were synthesized. Their cytotoxic activities against the CEM leukemia cell line were evaluated. Most of them displayed moderate cytotoxic activities, and compounds 21 and 32 showed good activities with IC50 of 4.10 and 0.64 μM, respectively. The most potent compound 32 was further confirmed to be able to inhibit tubulin polymerization, and its hypothetical binding mode with tubulin was obtained by molecular docking.

Synthesis and structure-activity relationship of 4-azaheterocycle benzenesulfonamide derivatives as new microtubule-targeting agents

A series of 1-sulfonyl indolines was synthesized and evaluated for antiproliferative activity. The most potent compounds 9 a and 9 e showed significant cytotoxicity (IC50 in the range of 0.055-0.105 and 0.039-0.112 μM, respectively) against four human cancer cell lines HCT116, PC3, HepG2 and SK-OV-3. The structure-activity relationship of this series of sulfonamides, including the influence of azaheterocycle rings, substituent at the different positions of indoline, and the cyclopropane moiety, was described.

Selected hybrid natural products as tubulin modulators

Modulators of microtubule dynamics have received increasing attention because of their potential to stop cancer growth. Although it belongs to the category of complex protein-protein interactions (PPIs), which are generally considered difficult to modulate through small molecules, the use of microtubule is considered a well-validated target. There are a number of bioactive natural products and related compounds that are currently in use as drugs or in clinical trials as next generation anti-cancer agents. The present review article is focused on two such bioactive natural products, epothilone and halichondrin B, and covers some of the key papers published after 2005 that outline various synthetic approaches to obtain next generation structural analogs as well as the synthesis of hybrid compounds.

Synthesis, cytotoxic effects and tubulin polymerization inhibition of 1,4-disubstituted 1,2,3-triazole analogs of 2-methoxyestradiol

Thirteen 1,4-disubstituted 1,2,3-triazole analogs of 2-methoxyestradiol were prepared and tested for their cytotoxic and tubulin polymerization inhibition effects. Two compounds, 11j and 11k, exhibited anti-proliferative effects at low micromolar concentrations. The two analogs 11j and 11k also inhibited tubulin assembly with IC50 values of 8.1 and 5.9μM, respectively.