Novel insights on [1,2]oxazolo[5,4-e]isoindoles on multidrug resistant acute myeloid leukemia cell line

A series of [1,2]oxazolo[5,4‐e]isoindole derivatives was evaluated against HL‐60 cell line and its multidrug resistance (MDR) variant, HL‐60R, resistant to doxorubicin and to other P‐gp substrates by overexpressing the efflux pump. They displayed antiproliferative activities, with IC₅₀ values ranging from 0.02 to 5.5 µM. In particular, the newly synthesized compound 4k produced synergistic effects in terms of cell growth inhibition and cell death induction either in combination with a Vinca alkaloid, Vinblastine, and a Taxane, Paclitaxel in HL‐60R cells. The study of the mechanism of action indicated that all compounds showed antimitotic activity through inhibition of tubulin polymerization. Thus, [1,2]oxazoles could represent a valuable tool to overcome MDR mechanism, confirming the potential use of this class of compounds.

Photopharmacology of Antimitotic Agents

Antimitotic agents such as the clinically approved vinca alkaloids, taxanes and epothilone can arrest cell growth during interphase and are therefore among the most important drugs available for treating cancer. These agents suppress microtubule dynamics and thus interfere with intracellular transport, inhibit cell proliferation and promote cell death. Because these drugs target biological processes that are essential to all cells, they face an additional challenge when compared to most other drug classes. General toxicity can limit the applicable dose and therefore reduce therapeutic benefits. Photopharmacology aims to avoid these side-effects by introducing compounds that can be applied globally to cells in their inactive form, then be selectively induced to bioactivity in targeted cells or tissue during a defined time window. This review discusses photoswitchable analogues of antimitotic agents that have been developed by combining different photoswitchable motifs with microtubule-stabilizing or microtubule-destabilizing agents.

Induction of adventitious shoots and tetraploids in Antirrhinum majus L. by treatment of antimitotic agents in vitro without plant growth regulators

We examined the effects of five antimitotic agents using Antirrhinum majus L. 'Maryland True Pink' on the induction of adventitious shoots resulted in increase of frequencies of chromosome doubling without plant growth regulators. Seeds were treated in vitro with 0, 16.5, 32.9, 65.8, 131.6, or 263.2 µM oryzalin (ORY), amiprofos-methyl (APM), butamifos (BUT), or propham (IPC) or 800, 1,600, 3,200, 6,400, or 12,800 µM colchicine (COL) for 7 day. ORY, COL and APM promoted induction of adventitious shoots on the hypocotyls at maximum frequencies of 57.6% with 16.5 µM ORY, 5.6% with 800 µM COL and 88.8% with 131.6 µM APM. ORY and COL also induced adventitious shoots on the epicotyls adjacent to the cotyledons, particularly at high concentrations, with a maximum frequency of 26.0% at 12,800 µM COL. APM treatment increased frequencies of tetraploids from 0.0 to 93.1%, with a positive correlation between the frequency and concentration. By contrast, ORY and COL induced tetraploids at frequencies of 16.0 to 54.6% and 4.0 to 59.4%, respectively, with peaks at both low and high concentrations of each. Correlation analysis revealed that frequencies of adventitious shoot formation could be useful as an index for the induction of tetraploids. These results showed that three of the antimitotic agents tested induced both adventitious shoot and tetraploid without plant growth regulators, indicating that antimitotic action may play a common role in the induction of adventitious shoot.

Current Perspectives on Taxanes: Focus on Their Bioactivity, Delivery and Combination Therapy

Taxanes, mainly paclitaxel and docetaxel, the microtubule stabilizers, have been well known for being the first-line therapy for breast cancer for more than the last thirty years. Moreover, they have been also used for the treatment of ovarian, hormone-refractory prostate, head and neck, and non-small cell lung carcinomas. Even though paclitaxel and docetaxel significantly enhance the overall survival rate of cancer patients, there are some limitations of their use, such as very poor water solubility and the occurrence of severe side effects. However, this is what pushes the research on these microtubule-stabilizing agents further and yields novel taxane derivatives with significantly improved properties. Therefore, this review article brings recent advances reported in taxane research mainly in the last two years. We focused especially on recent methods of taxane isolation, their mechanism of action, development of their novel derivatives, formulations, and improved tumor-targeted drug delivery. Since cancer cell chemoresistance can be an unsurpassable hurdle in taxane administration, a significant part of this review article has been also devoted to combination therapy of taxanes in cancer treatment. Last but not least, we summarize ongoing clinical trials on these compounds and bring a perspective of advancements in this field.

Synthesis and Antiproliferative Screening Of Novel Analogs of Regioselectively Demethylated Colchicine and Thiocolchicine

Colchicine, a pseudoalkaloid isolated from Colchicum autumnale, has been identified as a potent anticancer agent because of its strong antimitotic activity. It was shown that colchicine modifications by regioselective demethylation affected its biological properties. For demethylated colchicine analogs, 10-demethylcolchicine (colchiceine, 1) and 1-demethylthiocolchicine (3), a series of 12 colchicine derivatives including 5 novel esters (2b–c and 4b–d) and 4 carbonates (2e–f and 4e–f) were synthesized. The antiproliferative activity assay, together with in silico evaluation of physicochemical properties, confirmed attractive biological profiles for all obtained compounds. The substitutions of H-donor and H-acceptor sites at C1 in thiocolchicine position provide an efficient control of the hydration affinity and solubility, as demonstrated for anhydrate 3, hemihydrate 4e and monohydrate 4a.

A Novel Class of N-Sulfonyl and N-Sulfamoyl Noscapine Derivatives that Promote Mitotic Arrest in Cancer Cells

Noscapine displays weak anticancer efficacy and numerous research efforts have attempted to generate more potent noscapine analogues. These modifications included the replacement of the N-methyl group in the 6'-position with a range of substituents, where N-ethylcarbamoyl substitution was observed to possess enhanced anticancer activity. Herein, we describe advances in this area, namely the synthesis and pharmacological evaluation of a series of N-sulfonyl and N-sulfamoyl noscapine derivatives. A number of these sulfonyl-containing noscapinoids demonstrated improved activities compared to noscapine. ((R)-5-((S)-4,5-Dimethoxy-1,3-dihydroisobenzofuran-1-yl)-4-methoxy-6-((1-methyl-1H-imidazol-4-yl)sulfonyl)-5,6,7,8-tetrahydro[1,3]dioxolo[4,5-g]isoquinoline) (14 q) displayed sub-micromolar activities of 560, 980, 271 and 443 nM against MCF-7, PANC-1, MDA-MB-435 and SK-MEL-5 cells, respectively. This antiproliferative effect was also maintained against drug-resistant NCI/Adr^RES cells despite high expression of the multidrug efflux pump, P-glycoprotein.

Natural products as new antimitotic compounds for anticancer drug development

Cell cycle control genes are frequently mutated in cancer cells, which usually display higher rates of proliferation than normal cells. Dysregulated mitosis leads to genomic instability, which contributes to tumor progression and aggressiveness. Many drugs that disrupt mitosis have been studied because they induce cell cycle arrest and tumor cell death. These antitumor compounds are referred to as antimitotics. Vinca alkaloids and taxanes are natural products that target microtubules and inhibit mitosis, and their derivatives are among the most commonly used drugs in cancer therapy worldwide. However, severe adverse effects such as neuropathies are frequently observed during treatment with microtubule-targeting agents. Many efforts have been directed at developing improved antimitotics with increased specificity and decreased likelihood of inducing side effects. These new drugs generally target specific components of mitotic regulation that are mainly or exclusively expressed during cell division, such as kinases, motor proteins and multiprotein complexes. Such small molecules are now in preclinical studies and clinical trials, and many are products or derivatives from natural sources. In this review, we focused on the most promising targets for the development of antimitotics and discussed the advantages and disadvantages of these targets. We also highlighted the novel natural antimitotic agents under investigation by our research group, including combretastatins, withanolides and pterocarpans, which show the potential to circumvent the main issues in antimitotic therapy.

Synthesis of a 3-(α-styryl)benzo[b]-thiophene library via bromocyclization of alkynes and palladium-catalyzed to sylhydrazones cross-couplings: evaluation as antitubulin agents

A library of functionalized 3-(α-styryl)-benzo[b]thiophenes, endowed with a high level of molecular diversity, was efficiently synthesized by applying a synthetic sequence that allowed introduction of various substituents on aromatic A, B, and C-rings. The strategy developed involves the synthesis of 3-bromobenzo[b]thiophene derivatives through a bromocyclization step of methylthio-containing alkynes using N-methylpyrrolidin-2-one hydrotribromide reagent (MPHT). Further coupling of 3-bromobenzothiophenes under palladium-catalysis with N-tosylhydrazones efficiently furnished 2-aryl-3-(α-styryl)benzo[b]thiophene derivatives. The antiproliferative properties of target compounds were studied. Among them, compound 5m has demonstrated submicromolar cytotoxic activity against HCT-116 cell line, and inhibited the polymerization of tubulin at micromolar level comparable to that of CA-4.

AG11, a novel dichloroflavanone derivative with anti-mitotic activity towards human bladder cancer cells

BACKGROUND

New chemotherapy drugs should be investigated to improve survival of patients with advanced bladder cancer. Here, we report the synthesis and evaluation of AG11, a new flavanone derivative obtained through cyclization of its chalcone precursor CB11.

MATERIALS AND METHODS

The effect of AG11 on cell viability was evaluated by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide assay and apoptotic cell death was analyzed by flow cytometry. Finally, the effect of AG11 on tubulin polymerization in vitro and microtubule distribution across the cells was investigated.

RESULTS

AG11 was found to have an IC50 (half-maximal inhibitory concentration) of 4.6 μM and its inhibitory effect on RT4 cells proliferation is associated with a cell-cycle arrest in G2+M phases followed by apoptosis after a 48 h treatment. AG11 prevented polymerization of purified tubulin in a concentration-dependent manner in vitro and disrupted mitotic spindle formation in cells.

CONCLUSION

AG11 appears to be an attractive scaffold for further development of a structurally simpler new anti-microtubule agents.

Beta class II tubulin predominates in normal and tumor breast tissues

BACKGROUND

Antimitotic chemotherapeutic agents target tubulin, the major protein in mitotic spindles. Tubulin isotype composition is thought to be both diagnostic of tumor progression and a determinant of the cellular response to chemotherapy. This implies that there is a difference in isotype composition between normal and tumor tissues.

METHODS

To determine whether such a difference occurs in breast tissues, total tubulin was fractionated from lysates of paired normal and tumor breast tissues, and the amounts of beta-tubulin classes I + IV, II, and III were measured by competitive enzyme-linked immunosorbent assay (ELISA). Only primary tumor tissues, before chemotherapy, were examined. Her2/neu protein amplification occurs in about 30% of breast tumors and is considered a marker for poor prognosis. To gain insight into whether tubulin isotype levels might be correlated with prognosis, ELISAs were used to quantify Her2/neu protein levels in these tissues.

RESULTS

Beta-tubulin isotype distributions in normal and tumor breast tissues were similar. The most abundant beta-tubulin isotypes in these tissues were beta-tubulin classes II and I + IV. Her2/neu levels in tumor tissues were 5-30-fold those in normal tissues, although there was no correlation between the Her2/neu biomarker and tubulin isotype levels.

CONCLUSION

These results suggest that tubulin isotype levels, alone or in combination with Her2/neu protein levels, might not be diagnostic of tumorigenesis in breast cancer. However, the presence of a broad distribution of these tubulin isotypes (for example, 40-75% beta-tubulin class II) in breast tissue, in conjunction with other factors, might still be relevant to disease progression and cellular response to antimitotic drugs.