Comparison of carbon-sulfur and carbon-amine bond in therapeutic drug: 4β-S-aromatic heterocyclic podophyllum derivatives display antitumor activity

Podophyllotoxin derivatives-tubulin complex reveals a potential binding site of tubulin polymerization inhibitors in α-tubulin adjacent to colchicine site

The colchicine site of β-tubulin has been proven to be essential binding sites of microtubule polymerization inhibitors. Recent studies implied that GTP pocket of α-tubulin adjacent to colchicine sites is a potential binding site for developing tubulin polymerization inhibitors. However, the structural basis for which type of structural fragments was more beneficial for enhancing the affinity of α-tubulin is still unclear. Here, podophyllotoxin derivatives-tubulin complex crystals indicated that heterocyclic with the highly electronegative and small steric hindrance was conducive to change configuration and enhance the affinity of the residues in GTP pocket of α-tubulin. Triazole with lone-pairs electrons and small steric hindrance exhibited the strongest affinity for enhancing affinity of podophyllotoxin derivatives by forming two hydrogen bonds with αT5 Ser178. Pyrimidine with the secondary strong affinity could bind Asn101 to make the αH7 configuration deflection, which reduces the stability of tubulin result in its depolymerization. Conversely, 4β-quinoline-podophyllotoxin with the weakest affinity did not interact with α-tubulin. The molecular dynamics simulation and protein thermal shift results showed that 4β-triazole-podophyllotoxin-tubulin was the most stable mainly due to two hydrogen bonds and the higher van der Waals force. This work provided a structural basis of the potential binding sites for extending the α/β-tubulin dual-binding sites inhibitors design strategy.

Synthesis and Antimicrobial Activity of Some New Substituted Quinoxalines

A number of new symmetrically and asymmetrically 2,3-disubstituted quinoxalines were synthesized through functionalization of 2,3-dichloroquinoxaline (2,3-DCQ) with a variety of sulfur and/or nitrogen nucleophiles. The structures of the obtained compounds were established based on their spectral data and elemental analysis. The antimicrobial activity for the prepared compounds was investigated against four bacterial species and two fungal strains. The symmetrically disubstituted quinoxalines 2, 3, 4, and 5 displayed the most significant antibacterial activity, while compounds 6a, 6b, and the pentacyclic compound 10 showed considerable antifungal activity. Furthermore, compounds 3f, 6b showed broad antimicrobial spectrum against most of the tested strains.

Antitumor activity of a novel dual functional podophyllotoxin derivative involved PI3K/AKT/mTOR pathway

The progression of cancer through local expansion and metastasis is well recognized, but preventing these characteristic cancer processes is challenging. To this end, a new strategy is required. In this study, we presented a novel dual functional podophyllotoxin derivative, 2-pyridinealdehyde hydrazone dithiocarbamate S-propionate podophyllotoxin ester (PtoxPdp), which inhibited both matrix metalloproteinases and Topoisomerase II. This new podophyllotoxin derivative exhibited significant anti-proliferative, anti-metastatic that correlated with the downregulation of matrix metalloproteinase. In a xenograft animal local expansion model, PtoxPdp was superior to etoposide in tumor repression. A preliminary mechanistic study revealed that PtoxPdp induced apoptosis and autophagy via the PI3K/AKT/mTOR pathway. Furthermore, PtoxPdp could also inhibit epithelial-mesenchymal transition, which was achieved by downregulating both PI3K/AKT/mTOR and NF-κB/Snail pathways. Taken together, our results reveal that PtoxPdp is a promising antitumor drug candidate.

Increasing the distance between two monomers of topoisomerase IIβ under the action of antitumor agent 4β-sulfur-(benzimidazole) 4'-demethylepipodophyllotoxin

Topoisomerases II (Top2s) are a group of essential enzymes involved in replication, transcription, chromosome condensation, and segregation via altering DNA topology. The mechanism of the Top2s poisons such as etoposide (VP-16) was reported as stabilizing the Top2-DNA complex and engendering permanent DNA breakage. As the structurally similar compound of VP-16, a novel 4β-sulfur-substituted 4′-demethylepipodophyllotoxin (DMEP) derivative (compound C-Bi) with superior antitumor activity was developed in our previous study. To understand the structural basis of the compound action, the crystal structure (2.54 Å) of human Top2 β-isoform (hTop2β) cleavage complexes stabilized by compound C-Bi was determined. However, compound C-Bi was not visible in the crystal structure. Through the comparison of the structures of hTop2β-DNA-etoposide ternary complex and hTop2β-DNA binary complex, it could be observed that the distance between drug-binding sites Arg503 of the two monomers was 26.62 Å in hTop2β-DNA-etoposide ternary complex and 34.54 Å in hTop2β-DNA binary complex, respectively. Significant twist were observed in the DNA chains of binary complex. It suggested that compound C-Bi played antitumor roles through increasing spacing of hTop2β monomers. The changes in hTop2β structure further caused double changes in the torsional direction and migration distance of the DNA chains, resulting in impeding religation of DNA.

Identification of a Novel Polyamine Scaffold With Potent Efflux Pump Inhibition Activity Toward Multi-Drug Resistant Bacterial Pathogens

We have previously reported the use of combinatorial chemistry to identify broad-spectrum antibacterial agents. Herein, we extend our analysis of this technology toward the discovery of anti-resistance molecules, focusing on efflux pump inhibitors. Using high-throughput screening against multi-drug resistant Pseudomonas aeruginosa, we identified a polyamine scaffold that demonstrated strong efflux pump inhibition without possessing antibacterial effects. We determined that these molecules were most effective with an amine functionality at R1 and benzene functionalities at R2 and R3. From a library of 188 compounds, we studied the properties of 5 lead agents in detail, observing a fivefold to eightfold decrease in the 90% effective concentration of tetracycline, chloramphenicol, and aztreonam toward P. aeruginosa isolates. Additionally, we determined that our molecules were not only active toward P. aeruginosa, but toward Acinetobacter baumannii and Staphylococcus aureus as well. The specificity of our molecules to efflux pump inhibition was confirmed using ethidium bromide accumulation assays, and in studies with strains that displayed varying abilities in their efflux potential. When assessing off target effects we observed no disruption of bacterial membrane polarity, no general toxicity toward mammalian cells, and no inhibition of calcium channel activity in human kidney cells. Finally, combination treatment with our lead agents engendered a marked increase in the bactericidal capacity of tetracycline, and significantly decreased viability within P. aeruginosa biofilms. As such, we report a unique polyamine scaffold that has strong potential for the future development of novel and broadly active efflux pump inhibitors targeting multi-drug resistant bacterial infections.

Multilevel induction of apoptosis by microtubule-interfering inhibitors 4β-S-aromatic heterocyclic podophyllum derivatives causing multi-fold mitochondrial depolarization and PKA signaling pathways in HeLa cells

Herein is a first effort to study effect of carbon-sulfur (C-S) and carbon-nitrogen (C-N) bonds modification on the antitumor activity of the podophyllum derivatives in HeLa cells. Compared with the derivative modified by the C-N bond, the C-S bond modification exhibited superior antitumor activity by further causing significant mitochondria depolarization from three signaling pathway. First, a large number of microtubules were depolymerized by 4β-S-heterocyclic substituted podophyllum derivatives. The increasing free tubulin bond with voltage-dependent anion-selective channel (VDAC). Second, cAMP-dependent protein kinase A (PKA) was activated by 4β-S-heterocyclic substituted podophyllum derivatives. And then the activated PKA further caused significantly mitochondria depolarization. Third, the activated PKA also activated c-Jun N-terminal kinase (JNK) and further deceased MMP by improving the level of reactive oxygen species. Understanding the molecular events that contribute to drug-induced tumors apoptosis should provide a paradigm for a more rational approach to antitumor drug design.

Synthesis and Antiproliferative Activity of Novel All-Trans-Retinoic Acid-Podophyllotoxin Conjugate towards Human Gastric Cancer Cells

With the purpose of creating a multifunctional drug for gastric cancer treatment, a novel all-trans-retinoic acid (ATRA) conjugate with podophyllotoxin (PPT) was designed and synthesized, and its in vitro antiproliferative activity was evaluated against human gastric cancer cell lines using CCK-8 assay. The conjugate, P-A, exhibited significant anticancer activity against MKN-45 and BGC-823 cells with IC₅₀ values of 0.419 ± 0.032 and 0.202 ± 0.055 μM, respectively. Moreover, P-A efficiently triggered cell cycle arrest and induced apoptosis in MKN-45 and BGC-823 cells due to modulation of cell cycle arrest- (CDK1, CDK2, CyclinA and CyclinB1) and apoptosis- (cleaved caspase-3, -8 and -9) related proteins, respectively. Further mechanism studies revealed that P-A could increase the expression levels of RARα and RARβ, and decrease the level of RARγ in MKN-45 and BGC-823 cells. Finally, P-A inhibited the ERK1/2 and AKT signaling in the above two cancer cell lines. More importantly, the underlying mechanisms of P-A were similar to those of precursor PPT but different with the other precursor ATRA. Together, the conjugate P-A was a promising candidate for the potential treatment of human gastric cancer.

Structural Insights into the Inhibition of Tubulin by the Antitumor Agent 4β-(1,2,4-triazol-3-ylthio)-4-deoxypodophyllotoxin

The colchicine domain is widely recognized as the binding site of microtubule depolymerization agents for anticancer drug design. Almost all of the drugs targeting the colchicine domain have been confirmed to bind to the tubulin β-subunit. Here we studied a crystal structure (2.3 Å) of the complex between tubulin and 4β-(1,2,4-triazol-3-ylthio)-4-deoxypodophyllotoxin (compound 1S) with superior antitumor activity, which was designed on the basis of the colchicine domain and synthesized in our previous work. A distinct binding model of the colchicine domain was found in the complexes of tubulin with compound 1S. From a comparison of the crystal structures of tubulin-compound 1S and tubulin-colchicine complexes, the side chains of the T7 loop of β-tubulin flip outward and the T5 loop of α-tubulin changes its conformation. It has been shown that the β-subunit T7 loop reversibly participates in resistance to straightening that opposes microtubule assembly by flipping in and out. Together with the biochemical results from compound 1S, the structural data highlight the main contributors in the α-subunits and the colchicine domain β-subunits: the dual-target binding sites in the α-T7 loop and β-H7-T7 loop of tubulin. Compound 1S can synchronously bind to αβ-tubulin. The structures also highlight common features for the design and development of novel potent microtubule destabilizing agents.

Novel Beta-Tubulin-Immobilized Nanoparticles Affinity Material for Screening β-Tubulin Inhibitors from a Complex Mixture

In order to efficiently screen and isolate β-tubulin inhibitors, β-tubulin was immobilized on core-shell PMMA/CS (poly(methyl methacrylate)/Chitosan) nanoparticles to produce a new type of immobilized affinity material named β-tubulin-immobilized nanoparticles (β-TIN). The selectivity and adsorption performance of β-TIN were characterized using various control drugs. The β-TIN, the paclitaxel molecularly imprinted ploymers (MIP), and the C18 adsorbing material were compared for selectivity and enrichment ratio. Microtubule-targeting antitumor compounds were screened and isolated from a typical Chinese medicine, Chloranthus multistachys, by β-TIN. Three active compounds (curcolnol, zedoarofuran, and codonolactone) in Chloranthus multistachys extract were captured successfully. Microscale thermophoresis demonstrated that these three compounds strongly bind to β-tubulin, and the dissociation constants (K_d) between the three active compounds and β-tubulin were 1820 ± 0.68 nM, 1640 ± 0.52 nM, and 284 ± 1.00 nM, respectively. Moreover, the binding affinity between codonolactone and β-tubulin was greater than that between paclitaxel and β-tubulin. The antitumor activities of the three compounds were confirmed by the microtubule inhibition model, and the results showed a similar antitumor mechanism as paclitaxel. Molecular dynamics simulations were performed to preliminarily investigate the potential binding sites and the structure-activity relationship between the three active molecules and β-tubulin. Our study is the first to report the use of this novel material which is highly efficient in capturing low-content β-tubulin inhibitors from a complex mixture. The three screened compounds exhibited potential antineoplastic activity, and these lead compounds utilize a new mechanism of action with promising development prospects. Because β-TIN is easily prepared, displays excellent adsorption and selectivity for targets, and can effectively maintain the steric conformation and activities of target proteins, it will be very useful in the screening of lead compounds for different drug target proteins.

Synthesis and cytotoxicity of novel artemisinin derivatives containing sulfur atoms

Ten novel artemisinin derivatives containing sulfur atoms were designed and synthesized and their structures were confirmed by (1)H NMR, (13)C NMR and HRMS technologies in this study. All compounds were reported for the first time. The in vitro cytotoxicity against PC-3, SGC-7901, A549 and MDA-MB-435s cancer cell lines was evaluated by MTT assay. Compounds 4a and 4f displayed potent antitumor activity against PC-3, SGC-7901 and A549 cells with IC50 ranging from 1.6 to 30.5 μM, which values are compared to that of 5-FU (IC50 from 6.8 to 42.5 μM). Compounds 4a and 4f showed high specificity towards human lung cancer A549 cells compared to normal human hepatic L-02 cells with selectivity index of 16.1 and 50.1 respectively. Our promising findings indicated that the compounds 4a and 4f could stand as potential lead compounds for further investigation.

Esterification of Ginsenoside Rh2 Enhanced Its Cellular Uptake and Antitumor Activity in Human HepG2 Cells

Our previous research had indicated that the octyl ester derivative of ginsenoside Rh2 (Rh2-O) might have a higher bioavailability than Rh2 in the Caco-2 cell line. The aim of this study was to investigate the cellular uptake and antitumor effects of Rh2-O in human HepG2 cells as well as its underlying mechanism compared with Rh2. Results showed that Rh2-O exhibited a higher cellular uptake (63.24%) than Rh2 (36.76%) when incubated with HepG2 cells for 24 h. Rh2-O possessed a dose- and time-dependent inhibitory effect against the proliferation of HepG2 cells. The IC50 value of Rh2-O for inhibition of HepG2 cell proliferation was 20.15 μM, which was roughly half the value of Rh2. Rh2-O induced apoptosis of HepG2 cells through a mitochondrial-mediated intrinsic pathway. In addition, the accumulation of ROS was detected in Rh2-O-treated HepG2 cells, which participated in the apoptosis of HepG2 cells. Conclusively, the findings above all suggested that Rh2-O as well as Rh2 inducing HepG2 cells apoptosis might involve similar mechanisms; however, Rh2-O had better antitumor activities than Rh2, probably due to its higher cellular uptake.