Synthesis and biological evaluation of 4-aza-2,3-dihydropyridophenanthrolines as tubulin polymerization inhibitors

In Vitro Cytotoxicity and Apoptosis Inducing Evaluation of Novel Halogenated Isatin Derivatives

BACKGROUND

Isatin (1H-indole-2,3-dione) and its derivatives have been shown their responsibility in a wide range of biological activities. Among the range of beneficial properties, anticancer compounds were the most extensively highlighted and explored.

OBJECTIVE

Herein, we report the targeting effect of halogenated isatin derivatives on cancer cell mitochondria and their antiproliferative mechanism.

METHOD

A series of novel 5-halo-Isatin derivatives consisting 5-Amino-1,3,4-thiadiazole-2-thiol scaffold were synthesized and easily conducted in good yields through a condensation reaction between keto groups of Isatin and primary amine under alcoholic conditions, followed by S-benzylation. The compounds were fully characterized using spectroscopic methods such as 1H-NMR, FTIR, mass spectroscopy and then tested in vitro towards three cancer cell lines HT-29 (colon cancer), MCF-7 (breast cancer) and SKNMC (neuroblastoma). Apoptosis induction was investigated through assessment of caspase 3 and mitochondrial membrane potential.

RESULTS

The most potent compounds of 5b, 5r (IC50 = 18,13 µM) and 5n (IC50 = 20,17 µM) were found to show strong anticancer activity, especially for MCF7 cells. Further anticancer mechanism studies indicated that 5b and 5r induced apoptosis through the intrinsic mitochondrial pathway.

CONCLUSION

This research demonstrated that 5b and 5r have an anticancer property via the modulation of oxidative stress-mediated mitochondrial apoptosis and immune response, which deserves further studies on their clinical applications.

Synthesis of new tetronamides displaying inhibitory activity against bloom-forming cyanobacteria

BACKGROUND

The increasing frequency and intensity of cyanobacterial blooms pose a serious threat to aquatic ecosystems. These blooms produce potent toxins that can contaminate drinking water and endanger the life of wild and domestic animals as well as humans. Consequently, the development of effective methods for their control is a matter of high priority. We have previously shown that some γ-benzylidenebutenolides, related to the rubrolide family of natural products, are capable of inhibiting the photosynthetic electron transport chain (Hill reaction), a target of commercial herbicides. Here we report the synthesis and biological properties of a new class of rubrolide-inspired molecules featuring a tetronamide motif.

RESULTS

A total of 47 N-aryl tetronamides, including 38 aldol adducts, were prepared bearing phenyl, biphenyl, naphthyl, aliphatic and heteroaromatic groups. Some of the aldol adducts were dehydrated to the corresponding γ-benzylidenetetronamides, although satisfactory yields were obtained in only three cases (52-97%). None of the synthesized compounds were capable of blocking the Hill reaction. This notwithstanding, several aldol adducts equipped with a biphenyl substituent displayed excellent inhibitory activity against Synechococcus elongatus and other cyanobacterial strains (IC₅₀  = 1-5 μM). Further, these tetronamides were found to be essentially inactive against eukaryotic microorganisms.

CONCLUSION

Several newly synthesized biphenyl-containing tetronamides were shown to display potent and selective inhibitory activity against cyanobacteria. These compounds appear to exert their biological effects without interfering with the Hill reaction. As such, they represent novel leads in the search of environmentally benign agents for controlling cyanobacterial blooms. © 2019 Society of Chemical Industry.

Synthesis of substituted phenanthrene-9-benzimidazole conjugates: Cytotoxicity evaluation and apoptosis inducing studies

A series of new phenanthrene-9-benzimidazole conjugates has been synthesized by condensing phenanthrene aldehydes with various substituted o-phenylenediamines. The title compounds were evaluated for their in vitro cytotoxic potential against various human cancer cell lines like breast (BT-549), prostate (PC-3 and DU145), triple negative breast cancer (MDA-MB-453), and human colon cancer (HCT-116 and HCT-15) cells. Among the tested compounds, 10o displayed significant in vitro cytotoxic activity against PC-3 prostate cancer cells with an IC₅₀ value of 6.32 ± 0.09 μM. Further, the cell cycle analysis indicated that it blocks G2/M phase of the cell cycle in a dose dependent manner. In order to determine the effect of the compound 10o on cell viability; phase contrast microscopy, AO/EB staining, DAPI staining, and DCFDA staining studies were performed. In these studies, apoptotic features were clearly observed indicating that the compound inhibited cell proliferation by apoptosis. JC-1 staining and annexin binding assays indicated the extent of apoptosis in PC-3 cells. Further, relative viscosity measurements and molecular docking studies indicated that these compounds bind to DNA by intercalation.

Recent Advances in the Chemistry and Biology of Podophyllotoxins

Podophyllotoxin and its related aryltetralin cyclolignans belong to a family of important products that exhibit various biological properties (e.g., cytotoxic, insecticidal, antifungal, antiviral, anti-inflammatory, neurotoxic, immunosuppressive, antirheumatic, antioxidative, antispasmogenic, and hypolipidemic activities). This Review provides a survey of podophyllotoxin and its analogues isolated from plants. In particular, recent developments in the elegant total chemical synthesis, structural modifications, biosynthesis, and biotransformation of podophyllotoxin and its analogues are summarized. Moreover, a deoxypodophyllotoxin-based chemosensor for selective detection of mercury ion is described. In addition to the most active podophyllotoxin derivatives in each series against human cancer cell lines and insect pests listed in the tables, the structure-activity relationships of podophyllotoxin derivatives as cytotoxic and insecticidal agents are also outlined. Future prospects and further developments in this area are covered at the end of the Review. We believe that this Review will provide necessary information for synthetic, medicinal, and pesticidal chemistry researchers who are interested in the chemistry and biology of podophyllotoxins.

Discovery of a Series of Acridinones as Mechanism-Based Tubulin Assembly Inhibitors with Anticancer Activity

Microtubules play critical roles in vital cell processes, including cell growth, division, and migration. Microtubule-targeting small molecules are chemotherapeutic agents that are widely used in the treatment of cancer. Many of these compounds are structurally complex natural products (e.g., paclitaxel, vinblastine, and vincristine) with multiple stereogenic centers. Because of the scarcity of their natural sources and the difficulty of their partial or total synthesis, as well as problems related to their bioavailability, toxicity, and resistance, there is an urgent need for novel microtubule binding agents that are effective for treating cancer but do not have these disadvantages. In the present work, our lead discovery effort toward less structurally complex synthetic compounds led to the discovery of a series of acridinones inspired by the structure of podophyllotoxin, a natural product with important microtubule assembly inhibitory activity, as novel mechanism-based tubulin assembly inhibitors with potent anticancer properties and low toxicity. The compounds were evaluated in vitro by wound healing assays employing the metastatic and triple negative breast cancer cell line MDA-MB-231. Four compounds with IC₅₀ values between 0.294 and 1.7 μM were identified. These compounds showed selective cytotoxicity against MDA-MB-231 and DU-145 cancer cell lines and promoted cell cycle arrest in G₂/M phase and apoptosis. Consistent with molecular modeling results, the acridinones inhibited tubulin assembly in in vitro polymerization assays with IC₅₀ values between 0.9 and 13 μM. Their binding to the colchicine-binding site of tubulin was confirmed through competitive assays.

Thermodynamically driven, syn-selective vinylogous aldol reaction of tetronamides

A stereoselective vinylogous aldol reaction of N-monosubstituted tetronamides with aldehydes is described.

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

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

Synthesis and biological evaluation of 4β-benzoxazolepodophyllotoxin hybrids as DNA topoisomerase-II targeting anticancer agents

A series of new 4β-benzoxazolepodophyllotoxin compounds (9a–j) were prepared and screened for molecular modelling and cytotoxicity against various human tumour cell lines. Cell apoptosis evaluation was performed using Hoechst staining.