A novel microtubule inhibitor 4SC-207 with anti-proliferative activity in taxane-resistant cells

Atropisomeric 1-phenylbenzimidazoles affecting microtubule organization: influence of axial chirality

Benzimidazoles are frequently used in medicinal chemistry. Their anticancer effect is among the most prominent biological activities exhibited by this scaffold. Although numerous benzimidazole derivatives have been synthesized, possible atropisomerism of ortho-substituted 1-phenylbenzimidazoles has been largely overlooked. The aim of this research was to synthesize a small library of novel atropisomeric benzimidazole derivatives and explore their biological activity in various cancer and normal human cell lines. The new unique structural motif provides an interesting 3D architecture with axial chirality, which further contributes to molecular complexity and specificity. Racemates and their separated atropisomers arrested the cell cycle, caused apoptosis, and affected microtubule organization in cancer cells in vitro at different intensities. Moreover, this phenomenon was also verified by the inhibition of endothelial cell migration. These results showed that (+)-atropisomers, especially 5n, exhibit a stronger effect and show promise as agents for cancer therapy.

A novel histone deacetylase inhibitor LT-548-133-1 induces apoptosis by inhibiting HDAC and interfering with microtubule assembly in MCF-7 cells

Many studies have indicated that histone deacetylase inhibitors (HDACis) have a significant antitumor effect in cancer. Here we report a compound named LT-548-133-1 that not only acts as an HDAC inhibitor but also interferes with microtubule assembly to inhibit MCF-7 cell proliferation and induce apoptosis. Consistent with Chidamide, LT-548-133-1 inhibited HDAC activity and increased histone H3 acetylation. But the difference is that it significantly induced cell cycle G2/M arrest while Chidamide caused G0/G1 arrest in MCF-7 cells. By Western blotting, we found the accumulation of CyclinB1 and phosphorylated histone H3 in LT-548-133-1 treated cells. Immunofluorescence based microtubule-repolymerization experiments and immunofluorescence staining of cell microtubules and nuclei showed that LT-548-133-1inhibited microtubule-repolymerization and induced mitotic abnormalities. The decreased expression of Bcl-2 and the increased expression of Bax, p53, p21, and cleaved-Caspase3 indicated the occurrence of apoptosis. Flow cytometry results also showed an increase in the proportion of apoptotic cells after administration of LT-548-133-1 or Chidamide. Therefore, we demonstrated that LT-548-133-1 could act as an HDAC inhibitor while inhibiting microtubule-repolymerization, causing mitosis to be arrested in G2/M. These two effects ultimately lead to proliferation inhibition and apoptosis of MCF-7 cells.

Synthesis and Biological Evaluation of New Antitubulin Agents Containing 2-(3',4',5'-trimethoxyanilino)-3,6-disubstituted-4,5,6,7-tetrahydrothieno[2,3-c]pyridine Scaffold

Two novel series of compounds based on the 4,5,6,7-tetrahydrothieno[2,3-c]pyridine and 4,5,6,7-tetrahydrobenzo[b]thiophene molecular skeleton, characterized by the presence of a 3′,4′,5′-trimethoxyanilino moiety and a cyano or an alkoxycarbonyl group at its 2- or 3-position, respectively, were designed, synthesized, and evaluated for antiproliferative activity on a panel of cancer cell lines and for selected highly active compounds, inhibition of tubulin polymerization, and cell cycle effects. We have identified the 2-(3′,4′,5′-trimethoxyanilino)-3-cyano-6-methoxycarbonyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine derivative 3a and its 6-ethoxycarbonyl homologue 3b as new antiproliferative agents that inhibit cancer cell growth with IC₅₀ values ranging from 1.1 to 4.7 μM against a panel of three cancer cell lines. Their interaction with tubulin at micromolar levels leads to the accumulation of cells in the G2/M phase of the cell cycle and to an apoptotic cell death. The cell apoptosis study found that compounds 3a and 3b were very effective in the induction of apoptosis in a dose-dependent manner. These two derivatives did not induce cell death in normal human peripheral blood mononuclear cells, suggesting that they may be selective against cancer cells. Molecular docking studies confirmed that the inhibitory activity of these molecules on tubulin polymerization derived from binding to the colchicine site.

Identification and characterization of SSE15206, a microtubule depolymerizing agent that overcomes multidrug resistance

Microtubules are highly dynamic structures that form spindle fibres during mitosis and are one of the most validated cancer targets. The success of drugs targeting microtubules, however, is often limited by the development of multidrug resistance. Here we describe the discovery and characterization of SSE15206, a pyrazolinethioamide derivative [3-phenyl-5-(3,4,5-trimethoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide] that has potent antiproliferative activities in cancer cell lines of different origins and overcomes resistance to microtubule-targeting agents. Treatment of cells with SSE15206 causes aberrant mitosis resulting in G2/M arrest due to incomplete spindle formation, a phenotype often associated with drugs that interfere with microtubule dynamics. SSE15206 inhibits microtubule polymerization both in biochemical and cellular assays by binding to colchicine site in tubulin as shown by docking and competition studies. Prolonged treatment of cells with the compound results in apoptotic cell death [increased Poly (ADP-ribose) polymerase cleavage and Annexin V/PI staining] accompanied by p53 induction. More importantly, we demonstrate that SSE15206 is able to overcome resistance to chemotherapeutic drugs in different cancer cell lines including multidrug-resistant KB-V1 and A2780-Pac-Res cell lines overexpressing MDR-1, making it a promising hit for the lead optimization studies to target multidrug resistance.

Novel cis-selective and non-epimerisable C3 hydroxy azapodophyllotoxins targeting microtubules in cancer cells

Podophyllotoxin (PT) and its clinically used analogues are known to be powerful antitumour agents. These compounds contain a trans fused strained γ-lactone system, a feature that correlates to the process of epimerisation, whereby the trans γ-lactone system of ring D opens and converts to the more thermodynamically stable cis epimer. Since these cis epimers are known to be either less active or lacking antitumour activity, epimerisation is an undesirable feature from a chemotherapeutic point of view. To circumvent this problem, considerable efforts have been reported, amongst which is the synthesis of azapodophyllotoxins where the stereocentres at C2 and C3 are removed in order to preclude epimerisation. Herein we report the identification of a novel C3 hydroxy, cis-selective γ-lactone configuration of ring C in the azapodophyllotoxin scaffold, through an efficient stereoselective multicomponent reaction (MCR) involving fluorinated and non-fluorinated aldehydes. This configuration releases the highly strained trans γ-lactone system in podophyllotoxin analogues into the more thermodynamically stable cis γ-lactone motif and yet retains significantly potent activity. These compounds were evaluated against the human cancer lines MCF-7 and 22Rv1 in vitro. Fourteen out of the seventeen tested compounds exhibited sub-micromolar activity with IC50 values in the range of 0.11-0.91 μM, which is comparable and in some cases better than the activity profile of etoposide in this assay. Interestingly, we obtained strong evidence from spectroscopic and X-ray data analyses that the previously reported structure of similar analogues is not accurate. Molecular modelling performed using the podophyllotoxin binding site on β tubulin revealed a novel binding mode of these analogues. Furthermore, sub-cellular study of our compounds using immunolabelling and confocal microscopy analyses showed strong microtubule disruptive activity, particularly in dividing cells.