Tubulin Binding Research Articles

Discovery of Novel Diarylamide N-Containing Heterocyclic Derivatives as New Tubulin Polymerization Inhibitors with Anti-Cancer Activity.

Tubulin has been regarded as an attractive and successful molecular target in cancer therapy and drug discovery. Vicinal diaryl is a simple scaffold found in many colchicine site tubulin inhibitors, which is also an important pharmacophoric point of tubulin binding and anti-cancer activity. As the continuation of our research work on colchicine binding site tubulin inhibitors, we designed and synthesized a series of diarylamide N-containing heterocyclic derivatives by the combination of vicinal diaryl core and N-containing heterocyclic skeletons into one hybrid though proper linkers. Among of these compounds, compound 15b containing a 5-methoxyindole group exhibited the most potent inhibitory activity against the tested three human cancer cell lines (MGC-803, PC-3 and EC-109) with IC50 values of 1.56 μM, 3.56 μM and 14.5 μM, respectively. Besides, the SARs of these compounds were preliminarily studied and summarized. The most active compound 15b produced the inhibition of tubulin polymerization in a dose-dependent manner and caused microtubule network disruption in MGC-803 cells. Therefore, compound 15b was identified as a novel tubulin polymerization inhibitor targeting the colchicine binding site. In addition, the results of molecular docking also suggested compound 15b could tightly bind into the colchicine binding site of β-tubulin.

Molecular determinants for α-tubulin methylation by SETD2

Post-translational modifications to tubulin are important for many microtubule-based functions inside cells. It was recently shown that methylation of tubulin by the histone methyltransferase SETD2 occurs on mitotic spindle microtubules during cell division, with its absence resulting in mitotic defects. However, the catalytic mechanism of methyl addition to tubulin is unclear. We used a truncated version of human wild type SETD2 (tSETD2) containing the catalytic SET and C-terminal Set2–Rpb1–interacting (SRI) domains to investigate the biochemical mechanism of tubulin methylation. We found that recombinant tSETD2 had a higher activity toward tubulin dimers than polymerized microtubules. Using recombinant single-isotype tubulin, we demonstrated that methylation was restricted to lysine 40 of α-tubulin. We then introduced pathogenic mutations into tSETD2 to probe the recognition of histone and tubulin substrates. A mutation in the catalytic domain (R1625C) allowed tSETD2 to bind to tubulin but not methylate it, whereas a mutation in the SRI domain (R2510H) caused loss of both tubulin binding and methylation. Further investigation of the role of the SRI domain in substrate binding found that mutations within this region had differential effects on the ability of tSETD2 to bind to tubulin versus the binding partner RNA polymerase II for methylating histones in vivo, suggesting distinct mechanisms for tubulin and histone methylation by SETD2. Finally, we found that substrate recognition also requires the negatively charged C-terminal tail of α-tubulin. Together, this study provides a framework for understanding how SETD2 serves as a dual methyltransferase for both histone and tubulin methylation.

Virtual and experimental high throughput screening of substituted hydrazones on β-Tubulin polymerization

Microtubule targeting agents that disrupt the dynamic functioning of the mitotic spindle are some of the best chemotherapeutic agents. Interruption of microtubule dynamics through polymerization or depolymerization causes cell arrest leading to apoptosis. We report a novel class of aroylhydrazones with anticancer properties. Tubulin inhibition studies were performed using both computational and biological methods. Docking and pharmacophore mapping showed efficient binding between the ligands and the protein. Tubulin inhibition assay showed the aroylhydrazones to be inhibitors of tubulin polymerization. DFT studies explains the geometrical and electronic properties of the compounds. Furthermore, anticancer studies using lung and liver cancer cell lines gave low IC50 values with the methyl substituted hydrazone MH-2 being the most potent. (IC50 of 0.0896 and 0.1040 µM respectively). The methyl group is responsible for the effective binding to the protein. Thus, a new class of tubulin binding agents have been identified as potential agents in cancer therapy.

Tubulin binding potentially clears up Bortezomib and Carfilzomib differential neurotoxic effect

Proteasome inhibitors (PIs) represent the gold standard in the treatment of multiple myeloma. Among PIs, Bortezomib (BTZ) is frequently used as first line therapy, but peripheral neuropathy (PN), occurring approximately in 50% of patients, impairs their life, representing a dose-limiting toxicity. Carfilzomib (CFZ), a second-generation PI, induces a significantly less severe PN. We investigated possible BTZ and CFZ off-targets able to explain their different neurotoxicity profiles. In order to identify the possible PIs off-targets we used the SPILLO-PBSS software that performs a structure-based in silico screening on a proteome-wide scale. Among the top-ranked off-targets of BTZ identified by SPILLO-PBSS we focused on tubulin which, by contrast, did not turn out to be an off-target of CFZ. We tested the hypothesis that the direct interaction between BTZ and microtubules would inhibit the tubulin alfa GTPase activity, thus reducing the microtubule catastrophe and consequently furthering the microtubules polymerization. This hypothesis was validated in a cell-free model, since BTZ (but not CFZ) reduces the concentration of the free phosphate released during GTP hydrolysis. Moreover, NMR binding studies clearly demonstrated that BTZ, unlike CFZ, is able to interact with both tubulin dimers and polymerized form. Our data suggest that different BTZ and CFZ neurotoxicity profiles are independent from their proteasome inhibition, as demonstrated in adult mice dorsal root ganglia primary sensory neurons, and, first, we demonstrate, in a cell free model, that BTZ is able to directly bind and perturb microtubules.

Rational design, chemical synthesis and cellular evaluation of novel 1,3-diynyl derivatives of noscapine as potent tubulin binding anticancer agents

We present a new class of derivatives of noscapine, 1,3-diynyl-noscapinoids of an antitussive plant alkaloid, noscapine based on our in silico efforts that binds tubulin and displays anticancer activity against a panel of breast cancer cells. Structure-activity analyses pointed the C-9 position of the isoquinoline ring which was modified by coupling of 1,3-diynyl structural motifs to rationally design and screened a series of novel 1,3-diynyl-noscapinoids (20–22) with robust binding affinity with tubulin. The selected 1,3-diynyl-noscapinoids, 20–22 revealed improved predicted binding energy of −6.568 kcal/mol for 20, -7.367 kcal/mol for 21 and -7.922 kcal/mol for 22, respectively in comparison to the lead molecule (−5.246 kcal/mol). These novel derivatives were chemically synthesized and validated their anticancer activity based on cellular studies using two human breast adenocarcinoma, MCF-7 and MDAMB-231, as well as with a panel of primary breast cancer cells isolated from patients. Interestingly, all these derivatives inhibited cellular proliferation in all the cancer cells that ranged between 6.2 to 38.9 μM, which is 6.7 to 1.5 fold lower than that of noscapine. Unlike previously reported derivatives of noscapine that arrests cells in the S-phase, these novel derivatives effectively inhibit proliferation of cancer cells, arrests cell cycle in the G2/M-phase followed by apoptosis and appearance of apoptotic cells. Thus, we conclude that 1,3-diynyl-noscapinoids have great potential to be a novel therapeutic agent for breast cancers.

Non-Invasive Evaluation of Acute Effects of Tubulin Binding Agents: A Review of Imaging Vascular Disruption in Tumors.

Tumor vasculature proliferates rapidly, generally lacks pericyte coverage, and is uniquely fragile making it an attractive therapeutic target. A subset of small-molecule tubulin binding agents cause disaggregation of the endothelial cytoskeleton leading to enhanced vascular permeability generating increased interstitial pressure. The resulting vascular collapse and ischemia cause downstream hypoxia, ultimately leading to cell death and necrosis. Thus, local damage generates massive amplification and tumor destruction. The tumor vasculature is readily accessed and potentially a common target irrespective of disease site in the body. Development of a therapeutic approach and particularly next generation agents benefits from effective non-invasive assays. Imaging technologies offer varying degrees of sophistication and ease of implementation. This review considers technological strengths and weaknesses with examples from our own laboratory. Methods reveal vascular extent and patency, as well as insights into tissue viability, proliferation and necrosis. Spatiotemporal resolution ranges from cellular microscopy to single slice tomography and full three-dimensional views of whole tumors and measurements can be sufficiently rapid to reveal acute changes or long-term outcomes. Since imaging is non-invasive, each tumor may serve as its own control making investigations particularly efficient and rigorous. The concept of tumor vascular disruption was proposed over 30 years ago and it remains an active area of research.

Microtubule and tubulin binding and regulation of microtubule dynamics by the antibody drug conjugate (ADC) payload, monomethyl auristatin E (MMAE): Mechanistic insights into MMAE ADC peripheral neuropathy

Monomethyl auristatin E (MMAE) is a potent anti-cancer microtubule-targeting agent (MTA) used as a payload in three approved MMAE-containing antibody drug conjugates (ADCs) and multiple ADCs in clinical development to treat different types of cancers. Unfortunately, MMAE-ADCs can induce peripheral neuropathy, a frequent adverse event leading to treatment dose reduction or discontinuation and subsequent clinical termination of many MMAE-ADCs. MMAE-ADC-induced peripheral neuropathy is attributed to non-specific uptake of the ADC in peripheral nerves and release of MMAE, disrupting microtubules (MTs) and causing neurodegeneration. However, molecular mechanisms underlying MMAE and MMAE-ADC effects on MTs remain unclear. Here, we characterized MMAE-tubulin/MT interactions in reconstituted in vitro soluble tubulin or MT systems and evaluated MMAE and vcMMAE-ADCs in cultured human MCF7 cells. MMAE bound to soluble tubulin heterodimers with a maximum stoichiometry of ~1:1, bound abundantly along the length of pre-assembled MTs and with high affinity at MT ends, introduced structural defects, suppressed MT dynamics, and reduced the kinetics and extent of MT assembly while promoting tubulin ring formation. In cells, MMAE and MMAE-ADC (via nonspecific uptake) suppressed proliferation, mitosis and MT dynamics, and disrupted the MT network. Comparing MMAE action to other MTAs supports the hypothesis that peripheral neuropathy severity is determined by the precise mechanism(s) of each individual drug-MT interaction (location of binding, affinity, effects on morphology and dynamics). This work demonstrates that MMAE binds extensively to tubulin and MTs and causes severe MT dysregulation, providing convincing evidence that MMAE-mediated inhibition of MT-dependent axonal transport leads to severe peripheral neuropathy.

9-Arylimino noscapinoids as potent tubulin binding anticancer agent: chemical synthesis and cellular evaluation against breast tumour cells

ABSTRACT A library of 9-arylimino derivatives of noscapine was developed by coupling of Schiff base containing imine groups. Virtual screening using molecular docking with tubulin revealed three molecules, 12–14 that bind with high affinity. An improved predicted free energy of binding (FEB) of −5.390, −6.506 and −6.679 kcal/mol for the molecules 12–14 was found compared to noscapine (−5.135 kcal/mol). Furthermore, molecular dynamics simulation in combination with Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) revealed robust binding free energy of −166.03, −169.75 and −170.63 kcal/mol for the molecules 12, 13 and 14, respectively. These derivatives were strategically synthesized and experimentally validated for their anticancer activity. Tubulin binding assay revealed substantial binding of molecules 12–14 with purified tubulin. Further, their anticancer activity was demonstrated using two cancer cell lines (MCF-7 and MDAMB-231) and a panel of primary breast tumour cells. All these derivatives inhibited cellular proliferation in all the cancer cells that ranged between 30.1 and 5.8 µM, which is 1.7 to 7.52 fold lower than that of noscapine. Further, these novel derivatives arrest cell cycle in the G2/M-phase followed by induction of apoptosis. Thus, 9-arylimino noscapinoids 12–14 have a great potential to be a novel therapeutic agent for breast cancers.

Fisetin inhibits tau aggregation by interacting with the protein and preventing the formation of β-strands

Alzheimer's disease is a neurodegenerative disease which severely impacts the health of the elderly. Current treatments are only able to alleviate symptoms, but not prevent or cure the disease. The neurofibrillary tangles formed by tau protein aggregation are one of the defining characteristics of Alzheimer's disease, so tau protein has become a key target for the drug design. In this study, we show that fisetin, a plant-derived polyphenol compound, can inhibit aggregation of the tau fragment, K18, and can disaggregate tau K18 filaments in vitro. Meanwhile it is able to prevent the formation of tau aggregates in cells. Both experimental and computational studies indicate that fisetin could directly interact with tau K18 protein. The binding is mainly created by hydrogen bond and van der Waal force, prevents the formation of β-strands at the two hexapeptide motifs, and does not perturb the secondary structure or the tubulin binding ability of tau protein. In summary, fisetin might be a candidate for further development as a potential preventive or therapeutic drug for Alzheimer's disease.

Gatorbulin-1, a distinct cyclodepsipeptide chemotype, targets a seventh tubulin pharmacological site

Tubulin-targeted chemotherapy has proven to be a successful and wide spectrum strategy against solid and liquid malignancies. Therefore, new ways to modulate this essential protein could lead to new antitumoral pharmacological approaches. Currently known tubulin agents bind to six distinct sites at α/β-tubulin either promoting microtubule stabilization or depolymerization. We have discovered a seventh binding site at the tubulin intradimer interface where a novel microtubule-destabilizing cyclodepsipeptide, termed gatorbulin-1 (GB1), binds. GB1 has a unique chemotype produced by a marine cyanobacterium. We have elucidated this dual, chemical and mechanistic, novelty through multidimensional characterization, starting with bioactivity-guided natural product isolation and multinuclei NMR-based structure determination, revealing the modified pentapeptide with a functionally critical hydroxamate group; and validation by total synthesis. We have investigated the pharmacology using isogenic cancer cell screening, cellular profiling, and complementary phenotypic assays, and unveiled the underlying molecular mechanism by in vitro biochemical studies and high-resolution structural determination of the α/β-tubulin-GB1 complex.

In silico design of novel tubulin binding 9-arylimino derivatives of noscapine, their chemical synthesis and cellular activity as potent anticancer agents against breast cancer

We present a series of 9-arylimino derivatives of noscapine (an antitussive plant alkaloid) that binds to tubulin and displaying anticancer activity against a panel of breast cancer cells. These compounds were rationally designed by coupling of Schiff base containing imine groups at position-9 of the isoquinoline ring of noscapine. Based on a combination of Glide docking and free energy of binding (FEB) calculation, we have screened a panel of three 9-compounds, 12–14 with improved binding affinity with tubulin compared to noscapine. The predicted FEB is −6.166 kcal/mol for 12, −6.411 kcal/mol for 13 and −7.512 kcal/mol for 14. In contrast, the predicted FRB of noscapine is −5.135 kcal/mol. These novel derivatives were strategically synthesized and validated their anticancer activity based on cellular studies using two human breast adenocarcinoma, MCF-7 and MDAMB-231, as well as with a panel of primary breast tumor cells isolated from patients. Interestingly, all these derivatives inhibited cellular proliferation in all the cancer cells that ranged between 3.6 and 26.4 µM, which is 11.02–2.03 fold lower than that of noscapine. Unlike previously reported derivatives of noscapine that arrest cells in the S-phase, these novel derivatives effectively inhibit proliferation of cancer cells, arrest the cell cycle in the G2/M-phase and induced apoptosis. Thus, we conclude that 9-arylimino derivatives of noscapine have great potential to be a novel therapeutic agent for breast cancers. Communicated by Ramaswamy H. Sarma

Design, Synthesis, and Biological Evaluation of Tubulysin Analogues, Linker-Drugs, and Antibody-Drug Conjugates, Insights into Structure-Activity Relationships, and Tubulysin-Tubulin Binding Derived from X-ray Crystallographic Analysis.

Molecular design, synthesis, and biological evaluation of tubulysin analogues, linker-drugs, and antibody-drug conjugates are described. Among the new discoveries reported is the identification of new potent analogues within the tubulysin family that carry a C11 alkyl ether substituent, rather than the usual ester structural motif at that position, a fact that endows the former with higher plasma stability than that of the latter. Also described herein are X-ray crystallographic analysis studies of two tubulin-tubulysin complexes formed within the α/β interface between two tubulin heterodimers and two highly potent tubulysin analogues, one of which exhibited a different binding mode to the one previously reported for tubulysin M. The X-ray crystallographic analysis-derived new insights into the binding modes of these tubulysin analogues explain their potencies and provide inspiration for further design, synthesis, and biological investigations within this class of antitumor agents. A number of these analogues were conjugated as payloads with appropriate linkers at different sites allowing their attachment onto targeting antibodies for cancer therapies. A number of such antibody-drug conjugates were constructed and tested, both in vivo and in vitro, leading to the identification of at least one promising ADC (Herceptin-LD3), warranting further investigations.

Crystal structure of human PACRG in complex with MEIG1 reveals roles in axoneme formation and tubulin binding

The Parkin co-regulated gene protein (PACRG) binds at the inner junction between doublet microtubules of the axoneme, a structure found in flagella and cilia. PACRG binds to the adaptor protein meiosis expressed gene 1 (MEIG1), but how they bind to microtubules is unknown. Here, we report the crystal structure of human PACRG in complex with MEIG1. PACRG adopts a helical repeat fold with a loop that interacts with MEIG1. Using the structure of the axonemal doublet microtubule from the protozoan Chlamydomonas reinhardtii and single-molecule fluorescence microscopy, we propose that PACRG binds to microtubules while simultaneously recruiting free tubulin to catalyze formation of the inner junction. We show that the homologous PACRG-like protein also mediates dual tubulin interactions but does not bind MEIG1. Our findings establish a framework to assess the function of the PACRG family of proteins and MEIG1 in regulating axoneme assembly.

Microtubule Growth Is Slowed through Transient Exposure of GDP Tubulin

Microtubule plus-end growth dynamics are determined by a kinetic race dictated by tubulin on- and off-rates at the microtubule tip. The apparent tubulin on- and off-rates can be estimated by measuring the mean plus-end growth rate across a range of free tubulin concentrations. However, when growth phases are studied at higher temporal resolution, fluctuations around the average growth rate are observed, implying more complex dynamics. To understand growth dynamics at the microtubule plus-end, we used Interference Reflection Microscopy (IRM) to quantify time-dependent variations in microtubule growth using GMPCPP, a non-hydrolyzable GTP analog. We found an expected linear dependence of the average growth rate on tubulin concentration. However, there was also a linear relationship between growth variance and tubulin concentration. Utilizing these measured values, we were able to constrain a biochemical model of microtubule growth with an on-rate of 0.7/ μM/pf/s. To determine the degree to which growth in GMPCPP mimics the GTP cap, we repeated the measurements in GTP. We again found a linear dependence of the average growth rate on tubulin; but found a much higher tubulin-dependent growth variance than expected from the GMPCPP experiments. When the growth variance was normalized to growth rate for each condition, there was a 5-fold increase in the relative growth variance in GTP compared to GMPCPP. This result suggests that GTP hydrolysis impacts tubulin binding kinetics at the microtubule plus-end. Consistent with this hypothesis, we then artificially varied the hydrolysis rates from 0 to 0.15 s−1 in the biochemical model. Increasing the hydrolysis rate increased the growth variance, and transient suppression of growth coincided with increasing numbers of exposed GDP tubulin at the plus-end. This work suggests that during growth, exposure of terminal GDP tubulin slows growth until a terminal GTP is restored.

Experiments in the EpiDerm 3D Skin In Vitro Model and Minipigs In Vivo Indicate Comparatively Lower In Vivo Skin Sensitivity of Topically Applied Aneugenic Compounds.

Risk management of in vitro aneugens for topically applied compounds is not clearly defined because there is no validated methodology to accurately measure compound concentration in proliferating stratum basale keratinocytes of the skin. Here, we experimentally tested several known aneugens in the EpiDerm reconstructed human skin in vitro micronucleus assay and compared the results to flow cytometric mechanistic biomarkers (phospho-H3; MPM2, DNA content). We then evaluated similar biomarkers (Ki-67, nuclear area) using immunohistochemistry in skin sections of minipigs following topical exposure the potent aneugens, colchicine, and hesperadin. Data from the EpiDerm model showed positive micronucleus responses for all aneugens tested following topical or direct media dosing with similar sensitivity when adjusted for applied dose. Quantitative benchmark dose-response analysis exhibited increases in the mitotic index biomarkers phospho-H3 and MPM2 for tubulin binders and polyploidy for aurora kinase inhibitors are at least as sensitive as the micronucleus endpoint. By comparison, the aneugens tested did not induce histopathological changes, increases in Ki-67 immunolabeling or nuclear area in skin sections from the in vivo minipig study at doses in significant excess of those eliciting a response in vitro. Results indicate the EpiDerm in vitro micronucleus assay is suitable for the hazard identification of aneugens. The lack of response in the minipig studies indicates that the barrier function of the minipig skin, which is comparable to human skin, protects from the effects of aneugens in vivo. These results provide a basis for conducting additional studies in the future to further refine this understanding.

The combination of the tubulin binding small molecule PTC596 and proteasome inhibitors suppresses the growth of myeloma cells

The novel small molecule PTC596 inhibits microtubule polymerization and its clinical development has been initiated for some solid cancers. We herein investigated the preclinical efficacy of PTC596 alone and in combination with proteasome inhibitors in the treatment of multiple myeloma (MM). PTC596 inhibited the proliferation of MM cell lines as well as primary MM samples in vitro, and this was confirmed with MM cell lines in vivo. PTC596 synergized with bortezomib or carfilzomib to inhibit the growth of MM cells in vitro. The combination treatment of PTC596 with bortezomib exerted synergistic effects in a xenograft model of human MM cell lines in immunodeficient mice and exhibited acceptable tolerability. Mechanistically, treatment with PTC596 induced cell cycle arrest at G2/M phase followed by apoptotic cell death, associated with the inhibition of microtubule polymerization. RNA sequence analysis also revealed that PTC596 and the combination with bortezomib affected the cell cycle and apoptosis in MM cells. Importantly, endoplasmic reticulum stress induced by bortezomib was enhanced by PTC596, providing an underlying mechanism of action of the combination therapy. Our results indicate that PTC596 alone and in combination with proteasome inhibition are potential novel therapeutic options to improve outcomes in patients with MM.

Identification of candidate genes and pathways in dexmedetomidine-induced neuroprotection in rats using RNA sequencing and bioinformatics analysis.

Traumatic brain injury (TBI) is a major cause of disability worldwide, without definitive and effective intervention. Dexmedetomidine (DEX) has a neuroprotective effect against TBI; however, the detailed mechanism underlying this effect remains unclear. Ten male Sprague Dawley rats were used to establish a TBI model. The rats were randomly divided into two groups: the TBI group (TBI, control group) and the DEX treatment group (DEX). The next day, the neurological function of the rats were evaluated by the modified neurological severity score (mNSS). Then, the rats were sacrificed, and RNA sequencing was performed to identify differentially expressed messenger RNAs (mRNAs) and microRNAs (miRNAs) in brain tissue samples. Additionally, we performed a bioinformatics analysis to explore the candidate genes and pathways that might play important roles in DEX-induced neuroprotection. The most significantly differentially expressed miRNAs and possible hub genes were validated by quantitate reverse transcription-polymerase chain reaction (qRT-PCR) using more samples. In the DEX group, 517 mRNAs (352 up-regulated and 165 down-regulated) and 35 miRNAs (18 up-regulated and 17 down-regulated) were differentially expressed compared to the TBI group. Gene Ontology analysis revealed the up-regulated mRNAs to be significantly enriched in microtubule-based movement or processes, microtubule and tubulin binding. Kyoto Encyclopedia of Genes and Genomes analysis showed that these up-regulated mRNAs were significantly enriched in the B-cell receptor signaling pathway as well as the cell cycle pathway. Also, Lyn and Cdk1 were found to be associated with the B-cell receptor signaling and cell cycle pathways, respectively. Furthermore, the down-regulated miRNAs were significantly enriched in cellular components, although no significant Gene Ontology terms or KEGG pathways were found for the down-regulated mRNAs or up-regulated miRNAs. Differentially expressed mRNAs and miRNAs were identified after the administration of DEX in a TBI rat model. The B-cell receptor signaling pathway and the cell cycle pathway might be involved in the neuroprotective effect of DEX against TBI, Lyn and Cdk1 might be hub genes.

Design, synthesis, and biological evaluation of new series of pyrrol-2(3H)-one and pyridazin-3(2H)-one derivatives as tubulin polymerization inhibitors

A potential microtubule destabilizing series of new thirty-five Pyrrol-2-one, Pyridazin-3(2H)-one and Pyridazin-3(2H)-one/oxime derivatives has been synthesized and tested for their antiproliferative activity against a panel of 60 human cancer cell lines. Compounds IVc, IVg and IVf showed a broad spectrum of growth inhibitory activity against cancer cell lines representing renal, cancer of lung, colon, central nervous system, ovary, and kidney. Among them, compound IVg was found to have broad spectrum anti-tumor activity against the tested nine tumor subpanels with selectivity ratios ranging between 0.21 and 3.77 at the GI50 level. In vitro assaying revealed tubulin polymerization inhibition by all active compounds IVc, IVg and IVf. The results of the docking study revealed nice fitting of compounds IVc, IVf, and IVg into CA-4 binding site in tubulin. The three compounds exhibited high binding affinities (ΔGb = −12.49 to −12.99 kcal/mol) toward tubulin compared to CA-4 (−8.87 kcal/mol). Investigation of the binding modes of the three compounds IVc, IVf, and IVg revealed that they interacted mainly hydrophobically with tubulin and similar binding orientations to that of CA-4. These observations suggest that tubulin is a possible target for these compounds.

Design, synthesis, and biological evaluation of novel 5,6,7-trimethoxy quinolines as potential anticancer agents and tubulin polymerization inhibitors.

Objective(s):Microtubules have key roles in essential cellular processes such as mitosis, cell motion, and intracellular organelle transport. Increasing interest has been given to tubulin binding compounds after the introduction of taxanes into clinical oncology. The object of this study was synthesis and biological evaluation of novel 5,6,7-trimethoxy quinolines as tubulin inhibitors.Materials and Methods:The cytotoxicity of the newly synthesized compounds was assessed against different human cancer cell lines including MCF-7, A2780, MCF-7/MX, A2780/RCIS, and normal cells. Compounds demonstrating the most antiproliferative activity, were chosen to examine their tubulin inhibition activity and their ability to arrest the cell cycle and induce apoptosis. Molecular docking studies and molecular dynamics simulation of compound 7e in the catalytic site of tubulin were performed. Results:Most of the synthesized quinolines showed moderate to significant cytotoxic activity against human cancer cells. Compounds 7e and 7f, possessing N-(4-benzoyl phenyl) and N-(4-phenoxy phenyl), respectively, exhibited the most antiproliferative activity more potent than the other compounds and exhibited similar antiproliferative activity on both resistant and parental cancer cells.Conclusion:Flow cytometry analysis of A2780, A2780/RCIS, MCF-7, and MCF-7/MX cancer cells treated with 7e and 7f exhibited that these compounds arrested the cell cycle (at the G2/M phase) and induced cellular apoptosis in A2780 cancer cells. These quinolines inhibited tubulin polymerization in a way resembling that of CA-4. Molecular dynamics simulation and molecular docking studies of compound 7e into the binding site of tubulin displayed the probable interactions of 7e with the binding site of tubulin.

Potential of medicinal plant compounds to targeting Tau protein in the therapy of Alzheimer’s disease– A review

Alzheimer’s disease (AD) is a devastative neurodegenerative disorder with complex etiology. AD is characterized by blood-brain barrier disruption, oxidative stress, mitochondrial impairment, neuro- inflammation, hypo-metabolism; it decreases in acetylcholine levels and a reduction of cerebral blood flow. It is also not solely the end-product of aberrantly processed, misfolded, and aggregated oligomeric amyloid- beta peptides but hyper phosphorylated Tau (tubulin binding protein) which formed senile plaque and intracellular neurofibrillary tangles respectively. However, despite the long-term and worldwide effort for a more effective therapy, the only available treatment is a symptomatic use of acetylcholinesterase inhibitors and memantine. Then, many researchers focused their attention to modulate amyloid-beta peptides. These therapeutic approaches as well as those based on cholinergic or amyloid theory have not brought the desired benefits yet. Thus, the main features related with the Tau pathology found in AD are Tau phosphorylation and aggregation. Based on the biochemically diverse range of pathological Tau protein, a number of approaches have been proposed to develop new potential therapeutics like inhibition of Tau phosphorylation, proteolysis and aggregation; promotion of intra- and extracellular Tau clearance and stabilization of microtubules (MTs). Medicinal plants have been used in different systems of medicine and exhibited their powerful roles in the management and cure of memory disorders. This review paper discusses the potential of medicinal plant molecules to targeting Tau protein in Alzheimer’s disease therapy.