Microtubins: a novel class of small synthetic microtubule targeting drugs that inhibit cancer cell proliferation

Triazolo-linked benzimidazoles as tubulin polymerization inhibitors and DNA intercalators: Design, synthesis, cytotoxicity, and docking studies

A simple "click" protocol was employed in the quest of synthesizing 1,2,3-triazole-linked benzimidazoles as promising anticancer agents on various human cancer cell lines such as A549, HCT116, SK-Mel-28, HT-29, and MCF-7. Compound 12j demonstrated significant cytotoxic potential towards SK-Mel-28 cancer cells (IC₅₀ : 4.17 ± 0.09 µM) and displayed no cytotoxicity (IC₅₀ : > 100 µM) against normal human BEAS-2B cells inferring its safety towards normal healthy cells. Further to comprehend the underlying apoptosis mechanisms, AO/EB, dichlorodihydrofluorescein diacetate (DCFDA), and 4',6-diamidino-2-phenylindole (DAPI) staining were performed, which revealed the nuclear and morphological alterations. Compound 12j displayed impairment in cellular migration and inhibited colony formation. The annexin V binding assay and JC-1 were implemented to evaluate the scope of apoptosis and the loss of the mitochondrial transmembrane potential in SK-Mel-28 cells. Cell-cycle analysis revealed that compound 12j arrested the cells at the G2/M phase in a dose-dependent manner. Target-based assays established the inhibition of tubulin polymerization by 12j at an IC₅₀ value of 5.65  ± 0.05 μM and its effective binding with circulating tumor DNA as a DNA intercalator. The detailed binding interactions of 12j with tubulin and DNA were examined by docking studies on PDB ID: 3E22 and DNA hexamer (PDB ID: 1NAB), respectively.

Role of microtubule dynamics in Wallerian degeneration and nerve regeneration after peripheral nerve injury

Wallerian degeneration, the progressive disintegration of distal axons and myelin that occurs after peripheral nerve injury, is essential for creating a permissive microenvironment for nerve regeneration, and involves cytoskeletal reconstruction. However, it is unclear whether microtubule dynamics play a role in this process. To address this, we treated cultured sciatic nerve explants, an in vitro model of Wallerian degeneration, with the microtubule-targeting agents paclitaxel and nocodazole. We found that paclitaxel-induced microtubule stabilization promoted axon and myelin degeneration and Schwann cell dedifferentiation, whereas nocodazole-induced microtubule destabilization inhibited these processes. Evaluation of an in vivo model of peripheral nerve injury showed that treatment with paclitaxel or nocodazole accelerated or attenuated axonal regeneration, as well as functional recovery of nerve conduction and target muscle and motor behavior, respectively. These results suggest that microtubule dynamics participate in peripheral nerve regeneration after injury by affecting Wallerian degeneration. This study was approved by the Animal Care and Use Committee of Southern Medical University, China (approval No. SMU-L2015081) on October 15, 2015.

Antibody-drug conjugates: an evolving approach for melanoma treatment

Melanoma continues to be an aggressive and deadly form of skin cancer while therapeutic options are continuously developing in an effort to provide long-term solutions for patients. Immunotherapeutic strategies incorporating antibody-drug conjugates (ADCs) have seen varied levels of success across tumor types and represent a promising approach for melanoma. This review will explore the successes of FDA-approved ADCs to date compared to the ongoing efforts of melanoma-targeting ADCs. The challenges and opportunities for future therapeutic development are also examined to distinguish how ADCs may better impact individuals with malignancies such as melanoma.

MID1 and MID2 regulate cell migration and epithelial-mesenchymal transition via modulating Wnt/β-catenin signaling

Background

The ubiquitin E3 ligase activity has been ascribed to MID1, the causative gene of X-linked OS, and its homologue, MID2. Both alpha4, the common MID protein partner, and PP2Ac in MID-alpha4-PP2Ac complexes can be ubiquitylated. Ubiquitylation of alpha4 converted its function toward PP2Ac from protective to destructive, while PP2A also affected MID protein phosphorylation and their subsequent trafficking on microtubules. It was believed that disruption of the function of MID1-alpha4-PP2A complex was vital to the pathogenesis of craniofacial malformation, the most prominent clinical manifestation of OS, although the detailed molecular mechanisms was not unravelled.

Methods

The cellular level of PP2A and phosphor-PP2A in cells overexpressing MID1/MID2 or in cells with siRNA mediated MID1/MID2 gene silencing was analyzed using Western blot. The Wnt signaling in these cells was further monitored using TCF/LEF luciferase reporter assay and the cellular level of β-catenin was also verified using western blot. Given the crosstalk of E-cadherin and Wnt via the common effector β-catenin, the potential influences of MID1/MID2 on the cell migration and epithelial-mesenchymal transition (EMT) were investigated using wound healing assay and immunofluorescence for E-cadherin and vimentin, respectively.

Results

Here, we presented the increased phosphorylation of PP2Ac in cells overexpressing MID1/MID2, and vice versa, in vitro, while the cellular level of total PP2Ac was unaffected. In addition, β-catenin, the effector of canonical Wnt signaling, was downregulated in cells overexpressing MID1/MID2 and upregulated in cells with siRNA mediated MID1/MID2 gene silencing. Down-regulated Wnt/β-catenin signaling by Okadaic acid, a specific inhibitor of PP2A, was partially rescued by siRNA mediated MID1/MID2 gene silencing. In consistent, an activated EMT and accelerated cell migration in cells with MID1/MID2 gene silencing were observed, and vice versa.

Conclusions

The results in this study indicated roles for MID1 and MID2 in regulating cell migration/EMT via modulating Wnt/β-catenin signaling, which might help to understand the molecular etiology of the facial abnormalities that are usually the consequences of defective neural crest cells migration and EMT at the early stage of craniofacial development.

Complex Formation with Monomeric α-Tubulin and Importin 13 Fosters c-Jun Protein Stability and Is Required for c-Jun's Nuclear Translocation and Activity

Microtubules are highly dynamic structures, which consist of α- and β-tubulin heterodimers. They are essential for a number of cellular processes, including intracellular trafficking and mitosis. Tubulin-binding chemotherapeutics are used to treat different types of tumors, including malignant melanoma. The transcription factor c-Jun is a central driver of melanoma development and progression. Here, we identify the microtubule network as a main regulator of c-Jun activity. Monomeric α-tubulin fosters c-Jun protein stability by protein-protein interaction. In addition, this complex formation is necessary for c-Jun's nuclear localization sequence binding to importin 13, and consequent nuclear import and activity of c-Jun. A reduction in monomeric α-tubulin levels by treatment with the chemotherapeutic paclitaxel resulted in a decline in the nuclear accumulation of c-Jun in melanoma cells in an experimental murine model and in patients' tissues. These findings add important knowledge to the mechanism of the action of microtubule-targeting drugs and indicate the newly discovered regulation of c-Jun by the microtubule cytoskeleton as a novel therapeutic target for melanoma and potentially also other types of cancer.

Systematic Review on Cytotoxic and Anticancer Potential of N-Substituted Isatins as Novel Class of Compounds Useful in Multidrug-Resistant Cancer Therapy: In Silico and In Vitro Analysis

As the emergence of resistance to clinical cancer treatments poses a significant problem in cancer management, there is a constant need to explore novel anticancer agents which have the ability to overcome multidrug resistance (MDR) mechanisms. The search for the development of novel isatin-based antitumor agents accelerated after the approval by the Food and Drug Administration (FDA) of sunitinib malate, a C-3 isatin derivative, as a multitargeted receptor tyrosine kinase inhibitor. However, it is interesting to note that, over the last decade, various N-substituted analogs of isatin with intact carbonyl functionalities have been found to show more promising anticancer potential than its C-3 derivatives. Microtubule-targeting agents are a class of anticancer drugs which affect mitosis by targeting microtubules and suppressing their dynamic behavior. This review presents a systematic compilation of the in vitro cytotoxic and anticancer properties of various N-substituted isatins and illustrates their mechanism of action to overcome MDR by acting as microtubule-destabilizing agents. Predictions of the biological activities and cytotoxic effects of potential N-substituted isatins against various cancer cell lines have also been performed using the PASS computer-aided drug discovery program. Findings from such in vitro and in silico studies will act as a guide for the development of structure-activity relationship and will facilitate the design and exploration of more potent analogs of isatin with high potency and lower side effects for treatment of drug-resistant cancer. Mechanism of action of N-substituted isatin as microtubule-destabilizing agent on tumor cells. N-Substituted isatins bind to colchicine binding site on β-tubulin, which inhibits microtubule polymerization and thereby destabilizes microtubule dynamics, resulting in mitotic arrest leading to tumor cell growth suppression.

Camptothecin induces mitotic arrest through Mad2-Cdc20 complex by activating the JNK-mediated Sp1 pathway

Camptothecin (CPT) is a popular therapeutic agent that targets topoisomerase I. Our findings demonstrated that CPT-induced microtubule polymerization results in markedly increased histone H3 phosphorylation. CPT also enhanced interactions between the mitotic checkpoint proteins, Mad2 and Cdc20, and thereby increased mitotic arrest. Transient knockdown of Mad2 completely restored cell cycle progression from CPT-induced mitotic arrest, while simultaneously reduced cyclin B1 and Cdk1 expression. Moreover, we found that c-Jun N-terminal kinase (JNK) acts upstream of Sp1, which upregulates p21-mediated mitotic arrest in response to CPT; furthermore, knockdown of p21 restored cell cycle progression, while inhibition of Cdks completely restored cell cycle progression from CPT-induced mitotic arrest. We hypothesized that, during mitotic arrest in response to CPT, cell survival signaling blocks apoptosis, thereby enhancing mitotic arrest. As expected, a caspase-9 inhibitor, z-LEHD-FMK, and an autophagy inhibitor, 3-methyladenine (3 MA), significantly diminished CPT-induced mitotic arrest. On the other hand, when Mad2 was depleted, z-LEHD-FMK and 3 MA markedly increased apoptosis, and restored cell cycle progression. Taken together, these results suggest that CPT decodes the action of topoisomerase I-mediated tubulin targeting drugs, leading to mitotic arrest by upregulating Mad2 through the JNK-mediated Sp1 pathway and autophagy formation from tubulin polymerization.