Colchicine and its analogues: recent findings

Novel Antineoplastic Inducers of Mitochondrial Apoptosis in Human Cancer Cells

I propose a new strategy to suppress human cancer completely with two entirely new drug compounds exploiting cancer's Warburg effect characterized by a defective mitochondrial aerobic respiration, substituted by cytosolic aerobic fermentation/glycolysis of D-(+)-glucose into L-(+)-lactic acid. The two essentially new drugs, compound 1 [P(op)T(est)162] and compound 3 (PT167), represent new highly symmetric, four-bladed propeller-shaped polyammonium cations. The in vitro antineoplastic highly efficacious drug compound 3 represents a covalent combination of compound 1 and compound 2 (PT166). The intermediate drug compound 2 is an entirely new colchic(in)oid derivative synthesized from colchicine. Compound 2's structure was determined using X-ray crystallography. Compound 1 and compound 3 were active in vitro versus 60 human cancer cell lines of the National Cancer Institute (NCI) Developmental Therapeutics Program (DTP) 60-cancer cell testing. Compound 1 and compound 3 not only stop the growth of cancer cells to ±0% (cancerostatic effect) but completely kill nearly all 60 cancer cells to a level of almost -100% (tumoricidal effect). Compound 1 and compound 3 induce mitochondrial apoptosis (under cytochrome c release) in all cancer cells tested by (re)activating (in most cancers impaired) p53 function, which results in a decrease in cancer's dysregulated cyclin D1 and an induction of the cell cycle-halting cyclin-dependent kinase inhibitor p21Waf1/p21Cip1.

Methanolic Extracts of D. viscosa Specifically Affect the Cytoskeleton and Exert an Antiproliferative Effect on Human Colorectal Cancer Cell Lines, According to Their Proliferation Rate

Numerous studies have reported the pharmacological effects exhibited by Dittrichia viscosa, (D. viscosa) including antioxidant, cytotoxic, antiproliferative, and anticancer properties. In our research, our primary objective was to validate a prescreening methodology aimed at identifying the fraction that demonstrates the most potent antiproliferative and anticancer effects. Specifically, we investigated the impact of various extract fractions on the cytoskeleton using a screening method involving transgenic plants. Tumors are inherently heterogeneous, and the components of the cytoskeleton, particularly tubulin, are considered a strategic target for antitumor agents. To take heterogeneity into account, we used different lines of colorectal cancer, specifically one of the most common cancers regardless of gender. In patients with metastasis, the effectiveness of chemotherapy has been limited by severe side effects and by the development of resistance. Additional therapies and antiproliferative molecules are therefore needed. In our study, we used colon-like cell lines characterized by the expression of gastrointestinal differentiation markers (such as the HT-29 cell line) and undifferentiated cell lines showing the positive regulation of epithelial-mesenchymal transition and TGFβ signatures (such as the DLD-1, SW480, and SW620 cell lines). We showed that all three of the D. viscosa extract fractions have an antiproliferative effect but the pre-screening on transgenic plants anticipated that the methanolic fraction may be the most promising, targeting the cytoskeleton specifically and possibly resulting in fewer side effects. Here, we show that the preliminary use of screening in transgenic plants expressing subcellular markers can significantly reduce costs and focus the advanced characterization only on the most promising therapeutic molecules.

Recent Advances of Tubulin Inhibitors Targeting the Colchicine Binding Site for Cancer Therapy

Cancer accounts for numerous deaths each year, and it is one of the most common causes of death worldwide, despite many breakthroughs in the discovery of novel anticancer candidates. Each new year the FDA approves the use of new drugs for cancer treatments. In the last years, the biological targets of anticancer agents have started to be clearer and one of these main targets is tubulin protein; this protein plays an essential role in cell division, as well as in intracellular transportation. The inhibition of microtubule formation by targeting tubulin protein induces cell death by apoptosis. In the last years, numerous novel structures were designed and synthesized to target tubulin, and this can be achieved by inhibiting the polymerization or depolymerization of the microtubules. In this review article, recent novel compounds that have antiproliferation activities against a panel of cancer cell lines that target tubulin are explored in detail. This review article emphasizes the recent developments of tubulin inhibitors, with insights into their antiproliferative and anti-tubulin activities. A full literature review shows that tubulin inhibitors are associated with properties in the inhibition of cancer cell line viability, inducing apoptosis, and good binding interaction with the colchicine binding site of tubulin. Furthermore, some drugs, such as cabazitaxel and fosbretabulin, have been approved by FDA in the last three years as tubulin inhibitors. The design and development of efficient tubulin inhibitors is progressively becoming a credible solution in treating many species of cancers.

Design, synthesis, and biological screening of a series of 4'-fluoro-benzotriazole-acrylonitrile derivatives as microtubule-destabilising agents (MDAs)

Introduction: Colchicine-binding site inhibitors are some of the most interesting ligands belonging to the wider family of microtubule-destabilising agents.Results: A novel series of 4'-fluoro-substituted ligands (5-13) was synthesised. The antiproliferative activity assays resulted in nM values for the new benzotriazole-acrylonitrile derivatives. Compound 5, the hit compound, showed an evident blockade of HeLa cell cycle in the G2-M phase, but also a pro-apoptotic potential, and an increase of early and late apoptotic cells in HeLa and MCF-7 cell cycle analysis. Confocal microscopy analysis showed a segmented shape and a collapse of the cytoskeleton, as well as a consistent cell shrinkage after administration of 5 at 100 nM. Derivative 5 was also proved to compete with colchicine at colchicine-binding site, lowering its activity against tubulin polymerisation. In addition, co-administration of 5 and doxorubicin in drug-resistant A375 melanoma cell line highlighted a synergic potential in terms of inhibition of cell viability.Discussion: The 4'-fluoro substitution of benzotriazole-acrylonitrile scaffold brought us a step forward in the optimisation process to obtain compound 5 as promising MDA antiproliferative agent at nanomolar concentration.

Design and discovery of new antiproliferative 1,2,4-triazin-3(2H)-ones as tubulin polymerization inhibitors targeting colchicine binding site

Thirty-five new colchicine binding site inhibitors have been designed and synthesized based on the 1,2,4-triazin-3(2H)-one nucleus. Such molecules were synthesized through a cascade reaction between readily accessible α-amino ketones and phenyl carbazate as a masked N-isocyanate precursor. The synthesized derivatives are cisoid restricted combretastatin A4 analogues containing 1,2,4-triazin-3(2H)-one in place of the olefinic bond, and they have the same essential pharmacophoric features of colchicine binding site inhibitors. The synthesized compounds were evaluated in vitro for their antiproliferative activities against a panel of three human cancer cell lines (MCF-7, HepG-2, and HCT-116), using colchicine as a positive control. Among them, two compounds 5i and 6i demonstrated a significant antiproliferative effect against all cell lines with IC₅₀ ranging from 8.2 - 18.2 µM. Further investigation was carried out for the most active cytotoxic agents as tubulin polymerization inhibitors. Compounds 5i and 6i effectively inhibited microtubule assembly with IC₅₀ values ranging from 3.9 to 7.8 µM. Tubulin polymerization assay results were found to be comparable with the cytotoxicity results. The cell cycle analysis revealed significant G2/M cell cycle arrest of the analogue 5i in HepG-2 cells. The most active compounds 4i, 4j, 5 g, 5i and 6i did not induce significant cell death in normal human lung cells Wl-38, suggesting their selectivity against cancer cells. Also, These compounds upregulated the level of active caspase-3 and boosted the levels of the pro-apoptotic protein Bax by five to seven folds in comparison to the control. Moreover, apoptosis analyses were conducted for compound 5i to evaluate its apoptotic potential. Finally, in silico studies were conducted to reveal the probable interaction with the colchicine binding site. ADME prediction study of the designed compounds showed that they are not only with promising tubulin polymerization inhibitory activity but also with favorable pharmacokinetic and drug-likeness properties.

Cytotoxic, analgesic and anti-inflammatory activity of colchicine and its C-10 sulfur containing derivatives

10-Alkylthiocolchicines have been obtained and characterized by spectroscopic methods and their biological activities as: cytotoxic, anti-inflammatory and analgesic activities have been tested. Cytotoxic activity against SKOV-3 ovarian cell line for 10-alkylthiocolchicine analogues was reported and tested compounds showed to be more active than commonly used doxorubicin. Some of tested C-10 alkylthiolated colchicines have been found to exhibit cytotoxicity at levels comparable to that of the natural product-colchicine. 10-Methylthiocolchicine has IC50 = 8 nM and 10-ethylthiocolchicine has IC50 = 47 nM in comparison to colchicine IC50 = 37 nM. Moreover for 10-alkylthioderivatives apoptosis test, cyclin B1 and cell cycle tests were performed. 10-n-Butylthiocolchicine was tested for anti-inflammatory and analgesic activities it showed to produce analgesic rather than anti-inflammatory effect.

Design and synthesis of β-carboline and combretastatin derivatives as anti-neutrophilic inflammatory agents

A series of β-carboline derivatives was synthesized by the Pictet-Spengler reaction with or without the combretastatin skeleton. The structures of these derivatives were elucidated by spectroscopic techniques. All synthesized compounds were evaluated for their anti-inflammatory activity in human neutrophils. Among them, two compounds, NTU-228 and HK-72, showed significant inhibitory effects on N-formyl-Met-Leu-Phe (fMLF)-induced superoxide anion generation in human neutrophils with IC₅₀ values of 5.58 ± 0.56 and 2.81 ± 0.07 μM, respectively. Neither NTU-228 nor HK-72 caused cytotoxicity in human neutrophils. NTU-228 inhibited the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and intracellular Ca²⁺ levels ([Ca²⁺]_i) in fMLF-activated human neutrophils. Additionally, HK-72 selectively inhibited the fMLF-induced phosphorylation of p38 and [Ca²⁺]_i in human neutrophils. Molecular docking analysis showed a favorable binding affinity of HK-72 toward p38 MAPK. The proposed synthetic strategy opens up new opportunities for the synthesis of novel potential candidates against neutrophilic inflammation.

FB-15 inhibits MGC-803 cells growth by regulating energy metabolism

In this study, we scrutinized the anticancer effects of FB-15 on human gastric carcinoma MGC-803 cells in vitro and vivo, and its preliminary effect on tubulin and HIF-1α. We confirmed that FB-15 not only inhibited the proliferation of a large number of cells in a concentration and time-dependent manner but also inhibited proliferation of a single cell to form clones. FB-15 manifested little cytotoxicity for normal stomach cells GES-1. The flow cytometry analysis displayed that FB-15 induced apoptosis MGC-803 cells and mainly arrested cells in the S phase in a concentration-dependent manner. The results of the wound healing assay indicated that FB-15 suppressed cell migration. Furthermore, the western blotting showed that FB-15 down-regulated the expression of β3-tubulin and HIF-1α, consistent with Immunohistochemical assay. The binding modes of FB-15 with tubulin were clarified by molecular docking. FB-15 significantly suppressed the growth of MGC-803 gastric cancer tumors. The inhibitory effect of FB-15 on tumor growth was superior to 5-Fu. Taken together, these results provided evidence for FB-15 to be used as an effective anticancer drug candidate for gastric cancer.

Tubulin inhibitors: Discovery of a new scaffold targeting extra-binding residues within the colchicine site through anchoring substituents properly adapted to their pocket by a semi-flexible linker

Bis-hydrazides 13a-h were designed and synthesized as potential tubulin inhibitors selectively targeting the colchicine site between α- and β-tubulin subunits. The newly designed ring-B substituents were assisted at their ends by 'anchor groups' which are expected to exert binding interaction(s) with new additional amino acid residues in the colchicine site (beyond those amino acids previously reported to interact with reference inhibitors as CA-4 and colchicine). Conformational flexibility of bis-hydrazide linker assisted these 'extra-binding' properties through reliving ligands' strains in the final ligand-receptor complexes. Compound 13f displayed the most promising computational and biological study results in the series: MM/GBSA binding energy of -62.362 kcal/mol (extra-binding to Arg α:221, Thr β:353 & Lys β:254); 34% NCI-H522 cells' death (at 10 µM), IC₅₀ = 0.073 µM (MTT assay); significant cell cycle arrest at G2/M phase; 11.6% preG1 apoptosis induction and 83.1% in vitro tubulin inhibition (at concentration = IC₅₀). Future researchers in bis-hydrazide tubulin inhibitors are advised to consider the 2-chloro-N-(4-substituted-phenyl)acetamide derivatives as compound 13f due to extra-binding properties of their ring B.

Antifungal, anticancer, and docking studies of colchiceine complexes with monovalent metal cation salts

Complexes of colchiceine with monovalent cation perchlorates and iodides have been obtained and characterized by spectroscopic methods. DFT and spectroscopic studies reveal that the dihedral angle ω_1-1a-12-12a , crucial for colchicine biological mechanism of action, that is, binding to tubulins depends on the diameter of the complexed metal cation. Biological tests indicated no antifungal properties of colchicine (it was active only toward A.pullulans), in contrast to its derivative-(colchiceine). Complexation of colchiceine with metal cations improved significantly the antifungal potency, even below MIC <1 μg/ml. The colchiceine complexes were more potent than colchiceine, and some of them were even more potent than the fungicidal standard IPBC. The highest potency of colchiceine complexes was noted against A. pullulans (MIC = 0.5 μg/ml). In contrast to the findings concerning antifungal potency, the anticancer studies showed complexes of colchicine more active (~IC₅₀  = 2 nM) than those of colchiceine (~IC₅₀  = 6 μM). MDA-MB-231 breast cancer cell lines and human lung fibroblasts CCD39Lu were also tested.

Phenotypic Drug Screening for Dysferlinopathy Using Patient-Derived Induced Pluripotent Stem Cells

Dysferlinopathy is a progressive muscle disorder that includes limb‐girdle muscular dystrophy type 2B and Miyoshi myopathy (MM). It is caused by mutations in the dysferlin (DYSF) gene, whose function is to reseal the muscular membrane. Treatment with proteasome inhibitor MG‐132 has been shown to increase misfolded dysferlin in fibroblasts, allowing them to recover their membrane resealing function. Here, we developed a screening system based on myocytes from MM patient‐derived induced pluripotent stem cells. According to the screening, nocodazole was found to effectively increase the level of dysferlin in cells, which, in turn, enhanced membrane resealing following injury by laser irradiation. Moreover, the increase was due to microtubule disorganization and involved autophagy rather than the proteasome degradation pathway. These findings suggest that increasing the amount of misfolded dysferlin using small molecules could represent an effective future clinical treatment for dysferlinopathy. stem cells translational medicine2019;8:1017–1029

Troponoid Atropisomerism: Studies on the Configurational Stability of Tropone-Amide Chiral Axes

Configurationally stable, atropisomeric motifs are an important structural element in a number of molecules, including chiral ligands, catalysts, and molecular devices. Thus, understanding features that stabilize chiral axes is of fundamental interest throughout the chemical sciences. The following details the high rotational barriers about the Ar-C(O) bond of tropone amides, which significantly exceed those of analogous benzamides. These studies are supported by both experimental and computational rotational barrier measurements. We also report the resolution of an axially chiral α-hydroxytropolone amide into its individual atropisomers, and demonstrate its configurational stability at physiological pH and temperatures over 24 h.

Design, synthesis, and preliminary biological evaluation of 3′,4′,5′-trimethoxy flavonoid salicylate derivatives as potential anti-tumor agents

According to the combination principle, target compounds were designed; compound10vmight be a promising multiple target anti-tumor agent candidate.

7-Deacetyl-10-alkylthiocolchicine derivatives - new compounds with potent anticancer and fungicidal activity

A series of new semi-synthetic 7-deacetyl-10-alkylthiocolchicne derivatives with ethyl, n-propyl, i-propyl and n-butyl substituents were synthesised and characterised by spectroscopic methods, elemental analysis, DFT calculations and molecular docking simulations. All the synthesized compounds have been tested for fungicidal and anticancer activities against SKOV-3, LoVo, MCF-7, MDA-MB-231 and the lung-derived fibroblast CCD39Lu. All the new colchicine derivatives exhibit significantly higher cytotoxicity towards the SKOV-3 tumour cell line than the natural product - colchicine. The most effective cytotoxic agents were 7-deacetyl-10-n-buthylthiocolchicine and 7-deacetyl-10-i-propylthiocolchicine. Among all the compounds tested, 7-deacetyl-10-n-buthylthiocolchicine exhibited the highest fungicidal activity. Molecular modeling indicated that several mutations found in the β-tubulin unit of the tested fungal strains are crucial for antifungal activity and selectivity of 7-deacetyl-10-n-buthylthiocolchicine. The obtained results may be useful for the development of selective colchicine derivatives as effective fungicidal and/or anticancer drugs.

Recent advances in trimethoxyphenyl (TMP) based tubulin inhibitors targeting the colchicine binding site

Microtubules (composed of α- and β-tubulin heterodimers) play a pivotal role in mitosis and cell division, and are regarded as an excellent target for chemotherapeutic agents to treat cancer. There are four unique binding sites in tubulin to which taxanes, vinca alkaloids, laulimalide and colchicine bind respectively. While several tubulin inhibitors that bind to the taxane or vinca alkaloid binding sites have been approved by FDA, currently there are no FDA approved tubulin inhibitors targeting the colchicine binding site. Tubulin inhibitors that bind to the colchicine binding site have therapeutic advantages over taxanes and vinca alkaloids, for example, they can be administered orally, have less drug-drug interaction potential, and are less prone to develop multi-drug resistance. Typically, tubulin inhibitors that bind to the colchicine binding site bear the trimethoxyphenyl (TMP) moiety which is essential for interaction with tubulin. Over the last decade, a variety of molecules bearing the TMP moiety have been designed and synthesized as tubulin inhibitors for cancer treatment. In this review, we focus on the TMP analogs that are designed based on CA-4, indole, chalcone, colchicine and natural product scaffolds which are known to interact with the colchicine binding site in tubulin. The challenges and future direction of the TMP based tubulin inhibitors are also discussed in detail.

Colchicine prodrugs and codrugs: Chemistry and bioactivities

Antimitotic colchicine possesses low therapeutic index due to high toxicity effects in non-target cell. However, diverse colchicine analogs have been derivatized as intentions for toxicity reduction and structure-activity relationship (SAR) studying. Hybrid system of colchicine structure with nontoxic biofunctional compounds modified further affords a new entity in chemical structure with enhanced activity and selectivity. Moreover, nanocarrier formulation strategies have been used for colchicine delivery. This review paper focuses on colchicine nanoformulation, chemical synthesis of colchicine prodrugs and codrugs with different linkers, highlights linker chemical nature and biological activity of synthesized compounds. Additionally, classification of colchicine prodrugs based on type of conjugates is discussed, as biopolymers prodrugs, fluorescent prodrug, metal complexes prodrug, metal-labile prodrug and bioconjugate prodrug. Finally, we briefly summarized the biological importance of colchicine nanoformulation, colchicine prodrugs and codrugs.

Total Synthesis of (±)-Allocolchicine and Its Analogues Using Co-Catalyzed Alkyne [2 + 2 + 2]-Cyclotrimerization

The total synthesis of (±)-allocolchicine has been completed by employing cobalt-catalyzed alkyne [2 + 2 + 2]-cyclotrimerization as the key reaction. The essential diyne has been synthesized from easily available 3,4,5-trimethoxybenzaldehyde following simple chemical transformations. In general, the cycloaddition gave a mixture of C(9) and C(10) isomers thus allowing the synthesis of both allocolchicine and its C(10)-carboxylate. Because this cycloaddition was employed at the penultimate stage, it allowed the synthesis of various analogues having the diverse functionality at C(9) and/or C(10) of ring C.

Microbial Catalyzed Regio-Selective Demethylation of Colchicine by Streptomyces griseus ATCC 13273

Colchicinoids and their derivatives are of great importance in pharmaceutical applications, and colchicine is usually used as the first choice for the treatment of gout. To expand the structural diversities and clinical application of colchicinoids, many attempts have been established for the derivatives with better activity or less toxicity. Herein, in this paper, we report a direct microbial transformation of colchicine into 2-O-demethyl-colchicine (M1) and 3-O-demethl-colchicine (M2) by Streptomyces griseus ATCC 13273. It is noteworthy that when DMF was used as co-solvent, the yield of M1 and M2 could reach up to 51 and 31%, respectively. All the structures of the metabolites were elucidated unambiguously by ESI-MS, ¹H-NMR, ¹³C-NMR, and 2D-NMR spectroscopy.

New imidazoquinoxaline derivatives: Synthesis, biological evaluation on melanoma, effect on tubulin polymerization and structure-activity relationships

Microtubules are considered as important targets of anticancer therapy. EAPB0503 and its structural imidazo[1,2-a]quinoxaline derivatives are major microtubule-interfering agents with potent anticancer activity. In this study, the synthesis of several new derivatives of EAPB0503 is described, and the anticancer efficacy of 13 novel derivatives on A375 human melanoma cell line is reported. All new compounds show significant antiproliferative activity with IC50 in the range of 0.077-122μM against human melanoma cell line (A375). Direct inhibition of tubulin polymerization assay in vitro is also assessed. Results show that compounds 6b, 6e, 6g, and EAPB0503 highly inhibit tubulin polymerization with percentages of inhibition of 99%, 98%, 90%, and 84% respectively. Structure-activity relationship studies within the series are also discussed in line with molecular docking studies into the colchicine-binding site of tubulin.

New Colchicine-Derived Triazoles and Their Influence on Cytotoxicity and Microtubule Morphology

A series of new colchicinoids with a variable triazole unit at C-7 was synthesized through Cu(I)-catalyzed 1,3-dipolar cycloaddition (click-chemistry) of a colchicine-derived azide with various alkynes and the cytotoxicity against THP-1 and Jurkat cancer cell lines was used for structural optimization. Three particularly active compounds (IC50 ≤ 5 nM) were additionally investigated with respect to their efficacy against relevant solid tumor cell lines (HeLa, A549, and SK MES 1). Besides distorting the microtubule morphology by tubulin depolymerization, one compound also exhibited a pronounced centrosome declustering effect in triple negative breast cancer cells (MDA-MB-231) and nonsmall cell lung cancer cells (H1975).

Colchicine derivatives with potent anticancer activity and reduced P-glycoprotein induction liability

Colchicine (1), a nature-derived microtubule polymerization inhibitor, develops multi-drug resistance in tumor cells due to its P-gp substrate and induction activity, which in turn leads to its rapid efflux from tumor cells. This auto-induction of the efflux of colchicine remains a major challenge to medicinal chemists. Based on structure-based molecular modeling, a series of new colchicine derivatives were designed and synthesized with a potential for reduced P-gp induction liability. Screening of the prepared derivatives for P-gp induction activity revealed that a number of derivatives possess remarkably lower P-gp-induction activity (>90% intracellular accumulation of rhodamine 123 in LS-180 cells) compared to the parent natural product colchicine (62% Rh123 accumulation in LS-180 cells). The reduced P-gp-induction activity of new derivatives may be due to their reduced ability to interact and change the conformation of P-gp. The synthesized derivatives were then screened for antiproliferative activity against two colon cancer cell lines including HCT-116 and Colo-205. The derivative 4o showed potent cytotoxicity in HCT-116 cells with IC50 of 0.04 μM with significantly reduced P-gp induction liability. Compound 4o also inhibited microtubule assembly and induced expression of pro-apoptotic protein p21. In an Ehrlich solid tumor mice model, compound 4o showed 38% TGI with no mortality at 2 mg kg(-1) dose (oral). Compound 4o, with potent in vitro and in vivo anticancer activity, significantly reduced P-gp induction activity and its excellent physicochemical and pharmacokinetic properties open up new opportunities for the colchicine scaffold.

Drug–tubulin interactions interrogated by transient absorption spectroscopy

The triplet excited state of complexed COL and MTC gives well defined transient spectra undetectable in the absence of TU.

Natural antitubulin agents: importance of 3,4,5-trimethoxyphenyl fragment

Microtubules are polar cytoskeletal filaments assembled from head-to-tail and comprised of lateral associations of α/β-tubulin heterodimers that play key role in various cellular processes. Because of their vital role in mitosis and various other cellular processes, microtubules have been attractive targets for several disease conditions and especially for cancer. Antitubulin is the most successful class of antimitotic agents in cancer chemotherapeutics. The target recognition of antimitotic agents as a ligand is not much explored so far. However, 3,4,5-trimethoxyphenyl fragment has been much highlighted and discussed in such type of interactions. In this review, some of the most important naturally occurring antimitotic agents and their interactions with microtubules are discussed with a special emphasis on the role of 3,4,5-trimethoxyphenyl unit. At last, some emerging naturally occurring antimitotic agents have also been tabulated.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for anticancer hybrids

A Hybrid drug which comprises the incorporation of two drug pharmacophores in one single molecule are basically designed to interact with multiple targets or to amplify its effect through action on another bio target as one single molecule or to counterbalance the known side effects associated with the other hybrid part(.) The present review article offers a detailed account of the design strategies employed for the synthesis of anticancer agents via molecular hybridization techniques. Over the years, the researchers have employed this technique to discover some promising chemical architectures displaying significant anticancer profiles. Molecular hybridization as a tool has been particularly utilized for targeting tubulin protein as exemplified through the number of research papers. The microtubule inhibitors such as taxol, colchicine, chalcones, combretasatin, phenstatins and vinca alkaloids have been utilized as one of the functionality of the hybrids and promising results have been obtained in most of the cases with some of the tubulin based hybrids exhibiting anticancer activity at nanomolar level. Linkage with steroids as biological carrier vector for anticancer drugs and the inclusion of pyrrolo [2,1-c] [1,4]benzodiazepines (PBDs), a family of DNA interactive antitumor antibiotics derived from Streptomyces species in hybrid structure based drug design has also emerged as a potential strategy. Various heteroaryl based hybrids in particular isatin and coumarins have also been designed and reported to posses' remarkable inhibitory potential. Apart from presenting the design strategies, the article also highlights the structure activity relationship along with mechanistic insights revealed during the biological evaluation of the hybrids.

Biotransformation of colchicinoids into their corresponding 3-O-glucosyl derivatives by selected strains of Bacillus megaterium

Natural colchicinoids and their semisynthetic derivatives are important active ingredients for pharmaceutical applications. Thiocolchicoside (3-demethoxy-3-glucosyloxythiocolchicine) is used in several countries as standard therapy for the treatment of diseases of the muscle-skeletal system, due to its potent antiinflammatory and myorelaxant properties. Manufacturing of thiocolchicoside requires a key step, the regioselective demethylation and glucosylation of chemically derivative thiocolchicine. High selectivity and efficiency of this transformation cannot be achieved in a satisfactory way with a chemical approach. In particular, the chemical demethylation, a part from requiring toxic and aggressive reagents, generates a complex mixture of products with no industrial usefulness. We report herein an efficient, direct and green biotransformation of thiocolchicine into thiocolchicoside, performed by a specific strain of Bacillus megaterium. The same process, with minor modifications, can be used to convert the by-product 3-O-demethyl-thiocolchicine into thiocolchicoside. In addition, we describe the B. megaterium strain selection process and the best conditions for this effective double biotransformation. The final product has a pharmaceutical quality, and the process has been industrialised.

Drugs that target dynamic microtubules: a new molecular perspective

Microtubules have long been considered an ideal target for anticancer drugs because of the essential role they play in mitosis, forming the dynamic spindle apparatus. As such, there is a wide variety of compounds currently in clinical use and in development that act as antimitotic agents by altering microtubule dynamics. Although these diverse molecules are known to affect microtubule dynamics upon binding to one of the three established drug domains (taxane, vinca alkaloid, or colchicine site), the exact mechanism by which each drug works is still an area of intense speculation and research. In this study, we review the effects of microtubule-binding chemotherapeutic agents from a new perspective, considering how their mode of binding induces conformational changes and alters biological function relative to the molecular vectors of microtubule assembly or disassembly. These "biological vectors" can thus be used as a spatiotemporal context to describe molecular mechanisms by which microtubule-targeting drugs work.

Quantitative analysis of the effect of tubulin isotype expression on sensitivity of cancer cell lines to a set of novel colchicine derivatives

BACKGROUND

A maximum entropy approach is proposed to predict the cytotoxic effects of a panel of colchicine derivatives in several human cancer cell lines. Data was obtained from cytotoxicity assays performed with 21 drug molecules from the same family of colchicine compounds and correlate these results with independent tubulin isoform expression measurements for several cancer cell lines. The maximum entropy method is then used in conjunction with computed relative binding energy values for each of the drug molecules against tubulin isotypes to which these compounds bind with different affinities.

RESULTS

We have found by using our analysis that alphabetaI and alphabetaIII tubulin isoforms are the most important isoforms in establishing predictive response of cancer cell sensitivity to colchicine derivatives. However, since alphabetaI tubulin is widely distributed in the human body, targeting it would lead to severe adverse side effects. Consequently, we have identified tubulin isotype alphabetaIII as the most important molecular target for inhibition of microtubule polymerization and hence cancer cell cytotoxicity. Tubulin isotypes alphabetaI and alphabetaII are concluded to be secondary targets.

CONCLUSIONS

The benefit of being able to correlate expression levels of specific tubulin isotypes and the resultant cell death effect is that it will enable us to better understand the origin of drug resistance and hence design optimal structures for the elimination of cancer cells. The conclusion of the study described herein identifies tubulin isotype alphabetaIII as a target for optimized chemotherapy drug design.

Computational design and biological testing of highly cytotoxic colchicine ring A modifications

Microtubules are the primary target for many anti-cancer drugs, the majority of which bind specifically to beta-tubulin. The existence of several beta-tubulin isotypes, coupled with their varied expression in normal and cancerous cells provides a platform upon which to construct selective chemotherapeutic agents. We have examined five prevalent human beta-tubulin isotypes and identified the colchicine-binding site as the most promising for drug design based on specificity. Using this binding site as a template, we have designed several colchicine derivatives and computationally probed them for affinity to the beta-tubulin isotypes. These compounds were synthesized and subjected to cytotoxicity assays to determine their effectiveness against several cancerous cell lines. We observed a correlation between computational-binding predictions and experimentally determined IC(50) values, demonstrating the utility of computational screening in the design of more effective colchicine derivatives. The most promising derivative exhibited an IC(50) approximately threefold lower than values previously reported for either colchicine or paclitaxel, demonstrating the utility of computational design and assessment of binding to tubulin.

Microtubule dynamics as a target in oncology

Drugs that affect microtubule dynamics, including the taxanes and vinca alkaloids, have been a mainstay in the treatment of leukemias and solid tumors for decades. New, more effective microtubule-targeting agents continue to enter into clinical trials and some, including the epothilone ixapebilone, have been approved for use. In contrast, several other drugs of this class with promising preclinical data were later shown to be ineffective or intolerable in animal models or clinical trials. In this review, we discuss the molecular mechanisms as well as preclinical and clinical results for a variety of microtubule-targeting agents in various stages of development. We also offer a frank discussion of which microtubule-targeting agents are amenable to further development based on their availability, efficacy and toxic profile.

Isolation, structure elucidation and cytotoxic evaluation of endiandrin B from the Australian rainforest plant Endiandra anthropophagorum

Chemical investigations of the DCM extract from the roots of Endiandra anthropophagorum resulted in the isolation of a new cyclobutane lignan endiandrin B (1), together with the known natural products, endiandrin A (2), and (-)-dihydroguaiaretic acid (3). The structure of 1 was determined by extensive spectroscopic analyses, and confirmed by single crystal X-ray crystallography. Methylation of 1 using diazomethane afforded the previously reported natural product, cinbalansan (4). All compounds were evaluated for their cytotoxicity towards human lung carcinoma cells (A549) using high-content screening. (-)-Dihydroguaiaretic acid (3) was found to be the most potent cytotoxin against the A549 lung carcinoma cell line, with an IC(50) value of 7.49 microM.