Studies on novel 4β-[(4-substituted)-1,2,3-triazol-1-yl] podophyllotoxins as potential anticancer agents

Chemistry and Biological Activities of Naturally Occurring and Structurally Modified Podophyllotoxins

Plants containing podophyllotoxin and its analogues have been used as folk medicines for centuries. The characteristic chemical structures and strong biological activities of this class of compounds attracted attention worldwide. Currently, more than ninety natural podophyllotoxins were isolated, and structure modifications of these molecules were performed to afford a variety of derivatives, which offered optimized anti-tumor activity. This review summarized up to date reports on natural occurring podophyllotoxins and their sources, structural modification and biological activities. Special attention was paid to both structural modification and optimized antitumor activity. It was noteworthy that etoposide, a derivative of podophyllotoxin, could prevent cytokine storm caused by the recent SARS-CoV-2 viral infection.

Insight Into the Molecular Mechanism of Podophyllotoxin Derivatives as Anticancer Drugs

Podophyllotoxin (PTOX) is a biologically active compound derived from the podophyllum plant, and both it and its derivatives possess excellent antitumor activity. The PTOX derivatives etoposide (VP-16) and teniposide (VM-26) have been approved by the U.S. Food and Drug Administration (FDA) for cancer treatment, but are far from perfect. Hence, numerous PTOX derivatives have been developed to address the major limitations of PTOX, such as systemic toxicity, drug resistance, and low bioavailability. Regarding their anticancer mechanism, extensive studies have revealed that PTOX derivatives can induce cell cycle G2/M arrest and DNA/RNA breaks by targeting tubulin and topoisomerase II, respectively. However, few studies are dedicated to exploring the interactions between PTOX derivatives and downstream cancer-related signaling pathways, which is reasonably important for gaining insight into the role of PTOX. This review provides a comprehensive analysis of the role of PTOX derivatives in the biological behavior of tumors and potential molecular signaling pathways, aiming to help researchers design and develop better PTOX derivatives.

2, 4, 5-Trideoxyhexopyranosides Derivatives of 4'- Demethylepipodophyllotoxin: De novo Synthesis and Anticancer Activity

BACKGROUND

Podophyllotoxin is a natural lignan which possesses anticancer and antiviral activities. Etoposide and teniposide are semisynthetic glycoside derivatives of podophyllotoxin and are increasingly used in cancer medicine.

OBJECTIVE

The present work was aimed to design and synthesize a series of 2, 4, 5-trideoxyhexopyranosides derivatives of 4'-demethylepipodophyllotoxin as novel anticancer agents.

METHODS

A divergent de novo synthesis of 2, 4, 5-trideoxyhexopyranosides derivatives of 4'-demethylepipodophyllotoxin has been established via palladium-catalyzed glycosylation. The abilities of synthesized glycosides to inhibit the growth of A549, HepG2, SH-SY5Y, KB/VCR and HeLa cancer cells were investigated by MTT assay. Flow cytometric analysis of cell cycle with propidium iodide DNA staining was employed to observe the effect of compound 5b on cancer cell cycle.

RESULTS

Twelve D and L monosaccharides derivatives 5a-5l have been efficiently synthesized in three steps from various pyranone building blocks employing de novo glycosylation strategy. D-monosaccharide 5b showed highest cytotoxicity on five cancer cell lines with the IC50 values from 0.9 to 6.7 mM. It caused HepG2 cycle arrest at G2/M phase in a concentration-dependent manner.

CONCLUSION

The present work leads to the development of novel 2, 4, 5-trideoxyhexopyranosides derivatives of 4'- demethylepipodophyllotoxin. The biological results suggested that the replacement of the glucosyl moiety of etoposide with 2, 4, 5-trideoxyhexopyranosyl is favorable to their cytotoxicity. D-monosaccharide 5b caused HepG2 cycle arrest at G2/M phase in a concentration-dependent manner.

The Effect of a Newly Synthesized Ferrocene Derivative against MCF-7 Breast Cancer Cells and Spheroid Stem Cells through ROS Production and Inhibition of JAK2/STAT3 Signaling Pathway

Background:

Breast Cancer Stem Cells (BCSCs) possess the ability of self-renewal and cellular heterogeneity, and therefore, play a key role in the initiation, propagation and clinical outcome of breast cancer. It has been shown that ferrocene complexes have remarkable potential as anticancer drugs.

Objective:

The present study was conducted to investigate the effects of a novel ferrocene complex, 1- ferrocenyl-3-(4-methylsulfonylphenyl)propen-1-one (FMSP) on MCF-7 breast cancer cell line and its derived mammospheres with cancer stem cell properties.

Methods:

Mammospheres were developed from MCF-7 cells and validated by the evaluation of CD44 and CD24 cell surface markers by flow cytometry as well as of the expression of genes that are associated with stem cell properties by real-time PCR. Cells viability was assessed by a soluble tetrazolium salt (MTS) after the treatment of cells with various concentrations of FMSP. Apoptosis was evaluated by flow cytometry analysis of annexin V and PI labeling of cells. Reactive Oxygen Species (ROS) production was measured using a cellpermeable, oxidant-sensitive fluorescence probe (carboxy-H2DCFDA). The involvement of the JAK2/STAT3 pathway was also investigated by western blotting.

Results:

FMSP could successfully prevent mammosphere formation from differentiated MCF-7 cells and significantly down-regulated the expression of genes involved in the production of the stem cell properties including Wnt1, Notch1, β -catenin, SOX2, CXCR4 and ALDH1A1. FMSP decreased cell viability in both MCF-7 cells and spheroid cells, although MCF-10A cells were unaffected by this compound. Apoptosis was also dramatically induced by FMSP, via ROS production but independent of CD95 activation. Phosphorylation levels of JAK2 and STAT3 were also found to be significantly attenuated even in the presence of IL-6, the putative activator of the JAK/STAT pathway.

Conclusion:

FMSP can effectively target BCSCs via ROS production and modulation of major signaling pathways that contribute to the stemness of breast cancer cells, and therefore, might be considered a promising anticancer agent after in vivo studies.

Divergent de novo synthesis of 2,4,5-trideoxyhexopyranosides derivatives of podophyllotoxin as anticancer agents

Aim: Identification of new anticancer glycosidic derivatives of podophyllotoxin. Methods: 14 podophyllotoxin D- and L-monosaccharides have been synthesized in three steps employing de novo glycosylation strategy, and their abilities to inhibit the growth of HeLa, HepG2, MCF-7, A549 and MDA-MB-231 cancer cells were investigated by MTT assay. Molecular docking study of compound 5j with tubulin was performed. Immunofluorescence was applied for detecting the inhibitory effect of 5j on tubulin polymerization. Results & conclusion: Most of synthesized compounds showed strong cytotoxicity activity against five cancer cell lines. Compound 5j possessed the highest cytotoxicity with the IC50 values from 41.6 to 95.2 nM, and could concentration-dependently inhibit polymerization of the microtubule cytoskeleton of MCF-7 cells. Molecular docking disclosed that sugar moiety-dedicated hydrogen bond endowed 5j a higher binding affinity for tubulin.

Synthesis of podophyllotoxin-glycosyl triazoles via click protocol mediated by silver (I)-N-heterocyclic carbenes and their anticancer evaluation as topoisomerase-II inhibitors

Herein we report the regioselective synthesis of podophyllotoxin-Glycosyl triazole hybrids catalysed by Ag(I)-N-heterocyclic carbene (Ag(I)-NHC) in a short reaction time (∼30 min) at ambient conditions. In principle, it is the first report of Click alkyne-azide cycloaddition catalysed by Ag(I)-NHC catalyst and moreover, this new methodology yielded good results when compared with traditional CuAAC in terms of reaction time and selectivity. The synthesised compounds were further explored for in vitro anticancer activity against four human cancer cell lines Du145, HeLa, A-549, and MCF-7 and found that these synthesised compounds possess significant anticancer activity. Further, the compounds 5a and 5e were identified as promising leads due to their better activity across all cell lines than that of the standard drug etoposide. Molecular docking studies of 5a & 5e with DNA Topoisomerase-II were revealed that the free energy calculations of active compounds were in good agreement with observed IC₅₀ values.

Synthesis and anticancer activity of dimeric podophyllotoxin derivatives

Background

Podophyllotoxin is a potent cytotoxic agent and serves as a useful lead compound for the development of antitumor drugs. Several podophyllotoxin-derived antitumor agents, including etoposide, are currently in clinical use; however, their therapeutic efficacy is often limited due to side effects and the development of resistance by cancer cells. Previous studies have shown that 4β-1,2,3-triazole derivatives of podophyllotoxin exhibit more potent anticancer activity and better binding to topoisomerase-II than etoposide. The effect of dimerization of such derivatives on the anticancer activity has not been studied.

Methods

Two moieties of podophyllotoxin were linked at the C-4 position via 1,2,3-triazole rings to give a series of novel dimeric podophyllotoxin derivatives. 4β-Azido-substituted podophyllotoxin derivatives (23 and 24) were coupled with various dipropargyl functionalized linkers by utilizing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction to provide dimeric products in very good yield. The in vitro anticancer activity of the synthesized compounds was evaluated by MTT assay against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW480). The normal BEAS-2B (lung) cell line was also included for study in order to evaluate the cancer selectivity of the most active compound as compared with normal cells.

Results

A group of 16 dimeric podophyllotoxin derivatives with different linkers were synthesized and structurally characterized. Most compounds do not show significant cytotoxicity (IC₅₀ > 40 mM) against all five cancer cell lines. However, one compound (29) which bears a perbutyrylated glucose residue on the glycerol linker is highly potent against all five cancer cell lines tested, with IC₅₀ values ranging from 0.43 to 3.50 μM. This compound (29) also shows good selectivity towards cancer cell lines as compared with the normal BEAS-2B (lung) cell line, showing selectivity indexes from 4.4 to 35.7.

Conclusion

The anticancer activity of dimeric podophyllotoxin derivatives is generally speaking not improved as compared to their monomeric counterparts, and the potency of these dimeric derivatives can be largely affected by the nature of the linker between the two moieties. Among the synthesized derivatives, compound 29 is significantly more cytotoxic and selective towards cancer cells than etoposide and cisplatin, which are currently in clinical use. Compound 29 is a promising anticancer drug and needs further studies.

What Has Come out from Phytomedicines and Herbal Edibles for the Treatment of Cancer?

Several modern treatment strategies have been adopted to combat cancer with the aim of minimizing toxicity. Medicinal plant-based compounds with the potential to treat cancer have been widely studied in preclinical research and have elicited many innovations in cutting-edge clinical research. In parallel, researchers have eagerly tried to decrease the toxicity of current chemotherapeutic agents either by combining them with herbals or in using herbals alone. The aim of this article is to present an update of medicinal plants and their bioactive compounds, or mere changes in the bioactive compounds, along with herbal edibles, which display efficacy against diverse cancer cells and in anticancer therapy. It describes the basic mechanism(s) of action of phytochemicals used either alone or in combination therapy with other phytochemicals or herbal edibles. This review also highlights the remarkable synergistic effects that arise between certain herbals and chemotherapeutic agents used in oncology. The anticancer phytochemicals used in clinical research are also described; furthermore, we discuss our own experience related to semisynthetic derivatives, which are developed based on phytochemicals. Overall, this compilation is intended to facilitate research and development projects on phytopharmaceuticals for successful anticancer drug discovery.

Mechanism of antiproliferative action of a new d-secoestrone-triazole derivative in cervical cancer cells and its effect on cancer cell motility

Cervical cancer is the fourth most frequently diagnosed tumor and the fourth leading cause of cancer death in females worldwide. Cervical cancer is predominantly related with human papilloma virus (HPV) infection, with the most oncogenic types being HPV-18 and -16. Our previous studies demonstrated that some d-secoestrone derivatives exert pronounced antiproliferative activity. The aim of the current investigation was to characterize the mechanism of action of d-secoestrone-triazole (D-SET) on three cervical cancer cell lines with different pathological backgrounds. The growth-inhibitory effects of D-SET were determined by a standard MTT assay. We have found that D-SET exerts a pronounced growth-inhibitory effect on HPV 18-positive HeLa and HPV-negative C-33 A cells, but it has no substantial inhibitory activity on HPV 16-positive SiHa or on intact fibroblast MRC-5 cell lines. After 24h incubation, cells showed the morphological and biochemical signs of apoptosis determined by fluorescent double staining, flow cytometry and caspase-3 activity assay. Besides the elevation of the ratio of cells in the subG1 phase, flow cytometric analysis revealed a cell cycle arrest at G2/M in both HeLa and C-33 A cell lines. To distinguish the G2/M cell population immunocytochemical flow cytometric analysis was performed on HeLa cells. The results show that D-SET significantly increases the ratio of phosphorylated histone H3, indicating cell accumulation in the M phase. Additionally, D-SET significantly increased the maximum rate of microtube formation measured by an in vitro tubulin polymerization assay. Besides its direct antiproliferative activity, the antimigratory property of D-SET has been investigated. Our results demonstrate that D-SET significantly inhibits the migration and invasion of HeLa cells after 24h incubation. These results suggests that D-SET is a potent antiproliferative agent against HPV 16+ and HPV-negative cervical cancer cell lines, with an efficacious motility-inhibiting activity against HPV 16+ cells. Accordingly D-SET can be regarded as a potential drug candidate with a promising new mechanism of action among the antiproliferative steroids, potentially allowing for the design of novel anticancer agents.

Regiospecific Synthesis of 1,4,5-Trisubstituted 1,2,3-Triazoles via Enolate–Azide Cycloaddition between 1,3-Dicarbonyl Compounds and Aryl Azides

A cycloaddition reaction at room temperature between aryl azides and 1,3-dicarbonyl compounds in the presence of potassium carbonate in dimethylsulphoxide yielded 10 4-ethoxycarbonyl-1-aryl-5-methyl-1 H-1,2,3-triazoles and seven other closely-related compounds. The 1,2,3-triazoles, nine of which are new, were obtained in good to high yields and only the 1,4-regioisomers were formed.

Promise of Retinoic Acid-Triazolyl Derivatives in Promoting Differentiation of Neuroblastoma Cells

Retinoic acid induces differentiation in various types of cells including skeletal myoblasts and neuroblasts and maintains differentiation of epithelial cells. The present study demonstrates synthesis and screening of a library of retinoic acid-triazolyl derivatives for their differentiation potential on neuroblastoma cells. Click chemistry approach using copper(I)-catalyzed azide-alkyne cycloaddition was adopted for the preparation of these derivatives. The neurite outgrowth promoting potential of retinoic acid-triazolyl derivatives was studied on neuroblastoma cells. Morphological examination revealed that compounds 8a, 8e, 8f, and 8k, among the various derivatives screened, exhibited promising neurite-outgrowth inducing activity at a concentration of 10 μM compared to undifferentiated and retinoic acid treated cells. Further on, to confirm this differentiation potential of these compounds, neuroblastoma cells were probed for expression of neuronal markers such as NF-H and NeuN. The results revealed a marked increase in the NF-H and NeuN protein expression when treated with 8a, 8e, 8f, and 8k compared to undifferentiated and retinoic acid treated cells. Thus, these compounds could act as potential leads in inducing neuronal differentiation for future studies.

Triazole linked mono carbonyl curcumin-isatin bifunctional hybrids as novel anti tubulin agents: Design, synthesis, biological evaluation and molecular modeling studies

Keeping in view the limitations associated with currently available anticancer drugs, molecular hybrids of mono carbonyl curcumin and isatin tethered by triazole ring have been synthesized and evaluated for in vitro cytotoxicity against THP-1, COLO-205, HCT-116, A549, HeLa, CAKI-I, PC-3, MiaPaca-2 human cancer cell lines. The results revealed that the compounds SA-1 to SA-9, SB-2, SB-3, SB-4, SB-7 and SC-2 showed a good range of IC50 values against THP-1, COLO-205, HCT-116 and PC-3 cell lines, while the other four cell lines among these were found to be almost resistant. Structure activity relationship revealed that the nature of Ring X and substitution at position R influences the activity. Methoxy substituted phenyl ring as Ring X and H as R were found to be the ideal structural features. The most potent compounds (SA-2, SA-3, SA-4, SA-7) were further tested for tubulin inhibition. Compound SA-2 was found to significantly inhibit the tubulin polymerization (IC50=1.2 μM against HCT-116). Compound SA-2, moreover, lead to the disruption of microtubules as confirmed by immunofluorescence technique. The significant cytotoxicity and tubulin inhibition by SA-2 was streamlined by molecular modeling studies where it was docked at the curcumin binding site of tubulin.

Design, synthesis, and biological and docking studies of novel epipodophyllotoxin–chalcone hybrids as potential anticancer agents

Click-chemistry based design and efficient synthesis of podophyllotoxin–chalcone conjugates as potential topoisomerase-II inhibitors towards the development of better anticancer leads.

Recent progress on C-4-modified podophyllotoxin analogs as potent antitumor agents

Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water-soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C-4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure-activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL-331, TOP-53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide-related drugs and provides detailed coverage of the current status and recent development of C-4-modified PPT analogs as anticancer clinical trial candidates.

Synthesis and cytotoxic evaluation of novel ester-triazole-linked triterpenoid-AZT conjugates

Betulinic acid and analogous naturally occurring triterpenoid acids were transformed into the corresponding propargyl esters and subsequently deployed as substrates for a click chemistry-mediated coupling with azidothymidine (AZT) en route to novel 1,2,3-triazole-tethered triterpenoid-AZT conjugates. Twelve new hybrids were thus prepared and assessed in terms of their cytotoxic activity, revealing an interesting anticancer activity of five triterpenoid-AZT hybrids on KB and Hep-G2 tumor cell lines.

Synthesis of novel spin-labeled podophyllotoxin derivatives as potential antineoplastic agents: Part XXV

A series of novel spin-labeled 4β-[(4-substituted)-1,2,3-triazol-1-yl]podophyllotoxin derivatives (17a-h) were firstly designed and synthesized with significant regioselectivity by employing Cu(I) catalyzed click approach, and evaluated for cytotoxicity against four human tumor cell lines (A-549, DU145, KB, and KBvin). Among them, compound 17h displayed the highest cytotoxic activity against the tumor cell lines tested. Significantly, compound 17h showed superior cytotoxic activity compared with etoposide (IC₅₀ 6.30 to>10 μM), a clinically available anticancer drug. Significant activity toward the drug resistant KBvin cell line revealed promising future for compound 17h as a new generation of epipodophyllotoxin-derived antitumor clinical trial candidate.

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.

Synthesis and biological evaluation of ursolic acid-triazolyl derivatives as potential anti-cancer agents

A series of ursolic acid-1-phenyl-1H-[1,2,3]triazol-4-ylmethylester congeners have been designed and synthesized in an attempt to develop potent antitumor agents. A regioselective approach using Huisgen 1,3-dipolar cycloaddition reaction of ursolic acid-alkyne derivative with various aromatic azides was employed to target an array of triazolyl derivatives in an efficient manner. Their structures were confirmed by using (1)H NMR, (13)C NMR, IR and MS analysis. All the compounds were evaluated for anti-cancer activity against a panel of four human cancer cell lines including A-549 (lung), MCF-7 (breast), HCT-116 (colon), THP-1 (leukemia) and a normal human epithelial cell line (FR-2) using sulforhodamine-B assay. The pharmacological results showed that most of the compounds displayed high level of antitumor activities against the tested cancer cell lines compared with ursolic acid. Compounds 7b, 7g, 7p and 7r were found to be the most potent compounds in this study.

Synthesis and cytotoxic activity on human cancer cells of carbamate derivatives of 4β-(1,2,3-triazol-1-yl)podophyllotoxin

Carbamate derivatives of 4β-(1,2,3-triazol-1-yl)podophyllotoxin were synthesized by means of click chemistry, and their cytotoxicities against human cancer cell lines HL-60, A-549, HeLa, and HCT-8 were evaluated. Some compounds were more potent than the anticancer drug etoposide. 4'-O-Demethyl-4β-[(4-hydroxymethyl)-1,2,3-triazol-1-yl]-4-deoxypodophyllotoxin cyclopentyl carbamate, the most potent compound, induced cell cycle arrest in the G2/M phase accompanied by apoptosis in A-549 cells. Furthermore, this compound inhibited the formation of microtubules in A-549 cells and caused the inhibition of DNA topoisomerase-II.

Synthesis and biological evaluation of 4α/4β-imidazolyl podophyllotoxin analogues as antitumor agents

A series of 4α/4β-imidazolyl podophyllotoxin analogues have been designed and synthesized. All of the compounds were evaluated for their anticancer activity against a panel of three human cancer cell lines. Within the cell lines tested, some of the synthesized compounds showed promising anticancer activity. Compound 12, in particular, exhibited remarkable cytotoxicity, demonstrating effects against all tumor cell lines, including the K562/ADM cell line.

Synthesis of 4β-triazole-podophyllotoxin derivatives by azide-alkyne cycloaddition and biological evaluation as potential antitumor agents

A representative synthetic process of derivatizing the natural product podophyllotoxin utilizing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) is described including molecular design, reaction optimization and X-ray structure confirmation. Evaluation of cytotoxicity against human cancer cell lines (Hela, K562 and K562/A02) using MTT assay proves that these triazole derivatives have good antitumor activities. High activities toward the drug resistant K562/A02 cell line reveal promising future for these derivatives. The rarely prepared 1,5-disubstituted triazole isomers, which would be omitted by the "click chemistry", were found to have superior cytotoxicities to that of the 1,4-disubstituted isomers.

Novel tandem biotransformation process for the biosynthesis of a novel compound, 4-(2,3,5,6-tetramethylpyrazine-1)-4'-demethylepipodophyllotoxin

According to the structure of podophyllotoxin and its structure-function relationship, a novel tandem biotransformation process was developed for the directional modification of the podophyllotoxin structure to directionally synthesize a novel compound, 4-(2,3,5,6-tetramethylpyrazine-1)-4'-demethylepipodophyllotoxin (4-TMP-DMEP). In this novel tandem biotransformation process, the starting substrate of podophyllotoxin was biotransformed into 4'-demethylepipodophyllotoxin (product 1) with the demethylation of the methoxyl group at the 4' position by Gibberella fujikuroi SH-f13, which was screened out from Shennongjia prime forest humus soil (Hubei, China). 4'-Demethylepipodophyllotoxin (product 1) was then biotransformed into 4'-demethylpodophyllotoxone (product 2) with the oxidation of the hydroxyl group at the 4 position by Alternaria alternata S-f6, which was screened out from the gathered Dysosma versipellis plants in the Wuhan Botanical Garden, Chinese Academy of Sciences. Finally, 4'-demethylpodophyllotoxone (product 2) and ligustrazine were linked with a transamination reaction to synthesize the target product 4-TMP-DMEP (product 3) by Alternaria alternata S-f6. Compared with podophyllotoxin (i.e., a 50% effective concentration [EC(50)] of 529 μM), the EC(50) of 4-TMP-DMEP against the tumor cell line BGC-823 (i.e., 0.11 μM) was significantly reduced by 5,199 times. Simultaneously, the EC(50) of 4-TMP-DMEP against the normal human proximal tubular epithelial cell line HK-2 (i.e., 0.40 μM) was 66 times higher than that of podophyllotoxin (i.e., 0.006 μM). Furthermore, compared with podophyllotoxin (i.e., log P = 0.34), the water solubility of 4-TMP-DMEP (i.e., log P = 0.66) was significantly enhanced by 94%. For the first time, the novel compound 4-TMP-DMEP with superior antitumor activity was directionally synthesized from podophyllotoxin by the novel tandem biotransformation process developed in this work.

Synthesis and antitumor activity of novel aroylthiourea derivatives of podophyllotoxin

A novel series of 4β-[(4-substituted) aroylthiourea] derivatives of podophyllotoxin were synthesized and their abilities to inhibit the growth of cancer cells were investigated by MTT assay. Compound 4a possessed the highest cytotoxicity on HepG2, A549 and HCT-116 cancer cell lines with the IC(50) values of 0.1 μM. Apoptosis in HCT-116 cells induced by compound 4a was observed by Hoechst33342-Propidium iodide (PI) and acridine orange (AO)-ethidium bromide (EB) double staining assays. DNA flow cytometric analysis revealed that 4a induced cell cycle arrest at G2/M phase and kDNA decatenation assay indicated that 4a inhibited topoisomerase IIα-mediated kDNA decatenation. Our results indicated that compound 4a possessed promising antitumor activity, which need to be studied further.

4-Des-oxy-4β-(4-methoxy-carbonyl-1,2,3-triazol-1-yl)podophyllotoxin dichloro-methane solvate

In the title compound {systematic name: methyl 1-[12-oxo-10-(3,4,5-trimethoxy-phen-yl)-4,6,13-trioxa-tetra-cyclo-[7.7.0.0(3,7).0(11,15)]hexa-deca-1,3(7),8-trien-16-yl]-1H-1,2,3-triazole-4-carboxyl-ate dichloro-methane solvate}, C(26)H(25)N(3)O(9)·CH(2)Cl(2), the tetra-hydro-furan ring and the six-membered ring fused to it both display envelope conformations.