Antitumor agents. 113. New 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin and related compounds as potent inhibitors of human DNA topoisomerase II

Topoisomerase II inhibitors design: Early studies and new perspectives

The DNA topoisomerase enzymes are widely distributed throughout all spheres of life and are necessary for cell function. Numerous antibacterial and cancer chemotherapeutic drugs target the various topoisomerase enzymes because of their roles in maintaining DNA topology during DNA replication and transcription. Agents derived from natural products, like anthracyclines, epipodophyllotoxins and quinolones, have been widely used to treat a variety of cancers. A very active field of fundamental and clinical research is the selective targeting of topoisomerase II enzymes for cancer treatment. This thematic review summarizes the recent advances in the anticancer activity of the most potent topoisomerase II inhibitors (anthracyclines, epipodophyllotoxins and fluoroquinolones) their modes of action, and structure-activity relationships (SARs) organized chronologically in the last ten years from 2013 to 2023. The review also highlights the mechanism of action and SARs of promising new topoisomerase II inhibitors.

Podophyllotoxin and its derivatives: Potential anticancer agents of natural origin in cancer chemotherapy

The use of plant secondary metabolites has gained considerable attention among clinicians in the prevention and treatment of cancer. A secondary metabolite isolated mainly from the roots and rhizomes of Podophyllum species (Berberidaceae) is aryltetralin lignan - podophyllotoxin (PTOX). The purpose of this review is to discuss the therapeutic properties of PTOX as an important anticancer compound of natural origin. The relevant information regarding the antitumor mechanisms of podophyllotoxin and its derivatives were collected and analyzed from scientific databases. The results of the analysis showed PTOX exhibits potent cytotoxic activity; however, it cannot be used in its pure form due to its toxicity and generation of many side effects. Therefore, it practically remains clinically unusable. Currently, high effort is focused on attempts to synthesize analogs of PTOX that have better properties for therapeutic use e.g. etoposide (VP-16), teniposide, etopophos. PTOX derivatives are used as anticancer drugs which are showing additional immunosuppressive, antiviral, antioxidant, hypolipemic, and anti-inflammatory effects. In this review, attention is paid to the high potential of the usefulness of in vitro cultures of P. peltatum which can be a valuable source of lignans, including PTOX. In conclusion, the preclinical pharmacological studies in vitro and in vivo confirm the anticancer and chemotherapeutic potential of PTOX and its derivatives. In the future, clinical studies on human subjects are needed to certify the antitumor effects and the anticancer mechanisms to be certified and analyzed in more detail and to validate the experimental pharmacological preclinical studies.

Identification of Novel 4'-O-Demethyl-epipodophyllotoxin Derivatives as Antitumor Agents Targeting Topoisomerase II

C4 variation of 4'-O-demethyl-epipodophyllotoxin (DMEP) is an effective approach to optimize the antitumor spectra of this compound class. Accordingly, two series of novel DMEP derivatives were synthesized, and as expected, the antitumor spectra of these derivatives varied with different C4 substituents. Notably, most compounds showed significant inhibition against the etoposide (2)-resistant KBvin cells. Four of the compounds (11, 18, 27 and 28) induced protein-linked DNA break (PLDB) levels higher than those of GL-331 (6) and 2, and are assumed to be topoisomerase II (topo II) poisons more potent than 6 and 2. Compound 28, a potent topo II poison highly effective against KBvin cells, was further evaluated with a panel of tumor cells and was most active against HepG2. This compound also exhibited apparent in vivo antitumor efficacy in hepatoma 22 (H22) mouse model. The results indicated that C4 derivation of DMEP is a feasible approach to identify potent topo II inhibitors with optimized antitumor profiles.

Synthesis and Biological Activity of Ferrocenyl and Ruthenocenyl Analogues of Etoposide: Discovery of a Novel Dual Inhibitor of Topoisomerase II Activity and Tubulin Polymerization

Two series of the ferrocenyl and ruthenocenyl analogues of etoposide bearing 1,2,3-triazolyl or aminoalkyl linker were synthesized and evaluated for their cytotoxic properties, influence on the cell cycle, ability to induce tubulin polymerization, and inhibition of topoisomerase II activity. We found that the replacement of the etoposide carbohydrate moiety with a metallocenyl group led to organometallic conjugates exhibiting differentiated antiproliferative activity. Biological studies demonstrated that two ferrocenylalkylamino conjugates were notably more active than etoposide, with submicromolar or low-micromolar IC₅₀ values towards SW620, etoposide-resistant SW620E, and methotrexate-resistant SW620M cancer cell lines. Moreover, the simplest ferrocenylmethylamino conjugate exerted dual inhibitory action against tubulin polymerization and topoisomerase II activity while other studied compounds affected only topoisomerase II activity.

A colon-targeted podophyllotoxin nanoprodrug: synthesis, characterization, and supramolecular hydrogel formation for the drug combination

Making full use of the undeveloped bioactive natural product derivatives by selectively delivering them to target sites can effectively increase their druggability and reduce the wastage of resources. Azo-based prodrugs are widely regarded as an effective targeted delivery means for colon-related disease treatment. Herein, we report a new-type of azo-based nanoprodrug obtained from bioactive natural products, in which the readily available podophyllotoxin natural products are connected with methoxy polyethylene glycol (mPEG) via a multifunctional azobenzene group. The amphiphilic prodrug can form nanosized micelles in water and will be highly selectively activated by azoreductases, leading to the in situ generation of anticancer podophyllotoxin derivatives (AdP) in the colon after the cleavage of the azo bond. To satisfy the demand of drug carriers for cancer combination therapy in clinics, α-CD is further introduced into this nanoprodrug micelle system to form a supramolecular hydrogel via a cascade self-assembly strategy. Using imaging mass spectrometry (IMS), the colon-specific drug release ability of the hydrogel after oral administration is demonstrated at the molecular level. Finally, the nanoprodrug hydrogel is further used as a carrier to load a hydrophilic anti-cancer drug 5-FU during the hierarchical self-assembly process and to co-deliver AdP and 5-FU for the drug combination. The combination use of AdP and 5-FU provides enhanced cytotoxicity which indicates a significant synergistic interaction. This work offers a new way to enhance the therapeutic effect of nanoprodrugs via drug combination, and provides a new strategy for reusing bioactive natural products and their derivatives.

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.

Precisely Traceable Drug Delivery of Azoreductase-Responsive Prodrug for Colon Targeting via Multimodal Imaging

We report the development of an azoreductase-responsive prodrug AP-N═N-Cy in which the precursor compound AP, a readily available podophyllotoxin derivative, is linked with a NIR fluorophore (Cy) via a multifunctional azobenzene group. This type of azo-based prodrug can serve as not only an azoreductase-responsive NIR probe to real-time tracking of the drug delivery process but also a delivery platform for an anticancer compound (AdP). We have shown that cleavage of the multifunctional azobenzene group in AP-N═N-Cy only occurred in the presence of azoreductase, which specifically secretes in the colon, resulting in direct release of AdP through an in situ modification of a phenylamino group on the precursor AP. Moreover, introduction of the azobenzene group endows the prodrug with an unique fluorescence "off-on" property and served as a switch to "turn on" the fluorescence of Cy as consequence of a self-elimination reaction with breakage of an azo bond. Such a prodrug can be administered orally and exhibit high stability and low toxicity before arriving at the colon. In view of the synchronism of drug release and the fluorescence turn-on process, the fluorescence imaging method was utilized to precisely trace drug delivery in vitro, ex vivo, and in vivo. Distinguishingly, the biodistribution of AdP and Cy in various tissues was further precisely mapped at the molecular level using imaging mass spectrometry. To the best of our knowledge, this is the first time that the in vivo real-time precise tracking of the colon-specific drug release and biodistribution was reported via a multimodal imaging method.

Glucoside Derivatives Of Podophyllotoxin: Synthesis, Physicochemical Properties, And Cytotoxicity

Background

Widespread concern of the side effects and the broad-spectrum anticancer property of podophyllotoxin as an antitumor agent highlight the need for the development of new podophyllotoxin derivatives. Although some per-butyrylated glucosides of podophyllotoxin and 4β-triazolyl-podophyllotoxin glycosides show good anticancer activity, the per-acetylated/free of podophyllotoxin glucosides and their per-acetylated are not well studied.

Methods

A few glucoside derivatives of PPT were synthesized and evaluated for their in vitro cytotoxic activities against five human cancer cell lines, HL-60 (leukemia), SMMC-7721 (hepatoma), A-549 (lung cancer), MCF-7 (breast cancer), and SW480 (colon cancer), as well as the normal human pulmonary epithelial cell line (BEAS-2B). In addition, we investigated the structure–activity relationship and the physicochemical property–anticancer activity relationship of these compounds.

Results

Compound 6b shows the highest cytotoxic potency against all five cancer cell lines tested, with IC₅₀ values ranging from 3.27±0.21 to 11.37±0.52 μM. We have also found that 6b displays higher selectivity than the etoposide except in the case of HL-60 cell line. The active compounds possess similar physicochemical properties: MSA > 900, %PSA < 20, ClogP > 2, MW > 700 Da, and RB > 10.

Conclusion

We synthesized several glucoside derivatives of PPT and tested their cytotoxicity. Among them, compound 6b showed the highest cytotoxicity. Further studies including selectivity of active compounds have shown that the selectivity indexes of 6b are much greater than the etoposide except in the case of HL-60 cell line. The active compounds possessed similar physicochemical properties. This study indicates that active glucoside analogs of podophyllotoxin have potential as lead compounds for developing novel anticancer agents.

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.

Design, synthesis, and evaluation of DNA topoisomerase II-targeted nucleosides

We developed novel nucleoside-based topoisomerase II selective inhibitors and showed that small structural units, such as catechols, are essential for DNA topoisomerase II inhibitory activity. Moreover, nucleoside analogues containing TBS and 1,3-dithian moieties had potent and selective DNA topoisomerase II inhibitory activities. In further experiments, compound 25b having a beta configuration of the thymine moiety showed relatively strong growth inhibitory activity against cancer cell lines, and was more potent against all cancer cell lines than compound 26b, which carries a thymine moiety in the alpha configuration.

Tertiary amine mediated targeted therapy against metastatic lung cancer

In this work, two tertiary amine-derived 4'-demethylepipodophyllotoxin (DMEP) conjugates (DC and DP) have been designed and synthesized using N,N,N'-trimethyl-N'-(4-carboxyl benzyl)-1,3-propanediamine (CPDM) and 4-(4-methylpiperazinomethyl)benzoic acid (PBA) as the targeting ligands. Both DC and DP exhibited strong in vitro cytotoxicity against small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cell lines. Cellular uptake efficiencies of DC and DP in human alveolar type II epithelial cells were significantly enhanced compared to DMEP and etoposide (VP-16), which were demonstrated to be concentration-, time- and energy-dependent. The active transport process of DC and DP might be mediated by organic cation transporters (OCTs). After systemic administration in mice, both DC and DP selectively accumulated in the lung, displaying the highest C_max and AUC_0-t values of all tested tissues. Compared with DMEP and VP-16, DC and DP remarkably reduced the lung weight and the number of lung metastases of B16 melanoma in mice, and further prolonged the survival of tumor-bearing mice. Also, DC and DP exhibited comparable levels of cell cycle arrest and cell apoptosis. Furthermore, DC and DP demonstrated minimum toxicity towards vital organs and reduced gastrointestinal injury compared to DMEP and VP-16. Taken together, tertiary amine-derived moieties such as CPDM and PBA represent an efficient yet safe strategy to achieve lung-targeted drug delivery.

Strategies for the Optimization of Natural Leads to Anticancer Drugs or Drug Candidates

Natural products have made significant contribution to cancer chemotherapy over the past decades and remain an indispensable source of molecular and mechanistic diversity for anticancer drug discovery. More often than not, natural products may serve as leads for further drug development rather than as effective anticancer drugs by themselves. Generally, optimization of natural leads into anticancer drugs or drug candidates should not only address drug efficacy, but also improve absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles and chemical accessibility associated with the natural leads. Optimization strategies involve direct chemical manipulation of functional groups, structure-activity relationship directed optimization and pharmacophore-oriented molecular design based on the natural templates. Both fundamental medicinal chemistry principles (e.g., bioisosterism) and state-of-the-art computer-aided drug design techniques (e.g., structure-based design) can be applied to facilitate optimization efforts. In this review, the strategies to optimize natural leads to anticancer drugs or drug candidates are illustrated with examples and described according to their purposes. Furthermore, successful case studies on lead optimization of bioactive compounds performed in the Natural Products Research Laboratories at UNC are highlighted.

Design, synthesis, and cytotoxicity of perbutyrylated glycosides of 4β-triazolopodophyllotoxin derivatives

A series of novel perbutyrylated glycosides of 4β-triazolopodophyllotoxin derivatives were synthesized by utilizing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Evaluation of cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using the MTT assay shows that some of these glycosylated derivatives have good anticancer activity. Among the synthesized compounds, compound 21a shows the highest activity, with IC₅₀ values ranging from 0.49 to 6.70 μM, which is more potent than the control drugs etoposide and cisplatin. Compound 21a is characterized by a perbutyrylated α-D(+)-galactosyl residue, the absence of an additional linking spacer between the sugar residue and the triazole ring, as well as a 4'-OH group on the E ring of the podophyllotoxin scaffold.

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.

Semi-synthesis and anti-lung cancer activity evaluation of aryl dihydrothiazol acyl podophyllotoxin ester derivatives

S12, the best anticancer agent among the 17 podophyllotoxin derivatives, showed a proliferative inhibition effect via inhibiting tubulin polymerization.

Novel DNA topoisomerase IIα inhibitors from combined ligand- and structure-based virtual screening

DNA topoisomerases are enzymes responsible for the relaxation of DNA torsional strain, as well as for the untangling of DNA duplexes after replication, and are important cancer drug targets. One class of topoisomerase inhibitors, “poisons”, binds to the transient enzyme-DNA complex which occurs during the mechanism of action, and inhibits the religation of DNA. This ultimately leads to the accumulation of DNA double strand breaks and cell death. Different types of topoisomerases occur in human cells and several poisons of topoisomerase I and II are widely used clinically. However, their use is compromised by a variety of side effects. Recent studies confirm that the inhibition of the α-isoform of topoisomerase II is responsible for the cytotoxic effect, whereas the inhibition of the β-isoform leads to development of adverse drug reactions. Thus, the discovery of agents selective for topoisomerase IIα is an important strategy for the development of topoisomerase II poisons with improved clinical profiles. Here, we present a computer-aided drug design study leading to the identification of structurally novel topoisomerase IIα poisons. The study combines ligand- and structure-based drug design methods including pharmacophore models, homology modelling, docking, and virtual screening of the National Cancer Institute compound database. From the 8 compounds identified from the computational work, 6 were tested for their capacity to poison topoisomerase II in vitro: 4 showed selective inhibitory activity for the α- over the β-isoform and 3 of these exhibited cytotoxic activity. Thus, our study confirms the applicability of computer-aided methods for the discovery of novel topoisomerase II poisons, and presents compounds which could be investigated further as selective topoisomerase IIα inhibitors.

Synthesis and biological evaluation of podophyllotoxin congeners as tubulin polymerization inhibitors

A series of new podophyllotoxin derivatives containing structural modifications at C-7, C-8, and C-9 were synthesized and evaluated for their cytotoxic activity against three human cancer cell lines. All the synthesized compounds showed significant growth inhibition with GI50 values in micromolar levels while some of the compounds were several times more potent against MCF-7 and HeLa cell lines than MIAPACA cell line. Three compounds (12a, 12d and 12e) emerged as potent compounds with broad spectrum of cytotoxic activity against all the tested cell lines with GI50 values in the range of 0.01-2.1 μM. These compounds induce microtubule depolymerization and arrests cells at the G2/M phase of the cell cycle. Moreover, compounds 12d and 12e disrupted microtubule network and accumulated tubulin in the soluble fraction in a similar manner to their parent podophyllotoxin scaffold. In addition, structure activity relationship studies within the series were also discussed. Molecular docking studies of these compounds into the colchicine-binding site of tubulin, revealed possible mode of inhibition by these compounds.

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.

Design, synthesis and cytotoxic activity of novel sulfonylurea derivatives of podophyllotoxin

Three series of novel sulfonylurea podophyllotoxin derivatives were designed, synthesized, and evaluated for in vitro cytotoxicity against four tumor cell lines (A-549, DU-145, KB and KBvin). Compounds 14c (IC₅₀: 1.41-1.76 μM) and 14e (IC₅₀: 1.72-2.01 μM) showed superior cytotoxic activity compared with etoposide (IC₅₀: 2.03 to >20 μM), a clinically available anticancer drug. Significantly, most of the compounds exhibited comparable cytotoxicity against the drug-resistant tumor cell line KBvin, while etoposide lost activity completely. Preliminary structure-activity relationship (SAR) correlations indicated that the 4'-O-methyl functionality in podophyllotoxin analogues may be essential to maintain cytotoxic activity, while an arylsulfonylurea side chain at podophyllotoxin's 4β position can significantly improve cytotoxic activity.

Synthesis and anticancer activity of heteroaromatic linked 4β-amido podophyllotoxins as apoptotic inducing agents

A series of different heteroaromatic linked 4β-amidopodophyllotoxin conjugates (16a-i, 17a-i and 18a-d) were synthesized and evaluated for anticancer activity against five human cancer cell lines. Among the series, one of the compound 17g showed significant antiproliferative activity in A549 (lung cancer) cell line. Flow cytometric analysis showed that 17g arrested the cell cycle in the G2/M phase leading to caspase-3 dependent apoptotic cell death. Further, Hoechst 33258 staining and DNA fragmentation assay also suggests that 17g induces cell death by apoptosis.

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.

Synthesis and antitumor activity of novel podophyllotoxin derivatives against multidrug-resistant cancer cells

Seven novel 4β-N-substituted podophyllotoxin derivatives with indole rings were prepared and evaluated for cytotoxicity against human cancer cell lines HeLa, KB, KBV, K562, and K562/AO2. Most of them demonstrated improved antitumor activity and weak multidrug resistance compared to the drugs currently available.

Synthesis of Novel Functionalized 4-Aza-2,3-Didehydropodophyllotoxin Derivatives with Potential Antitumor Activity

Novel arylamino alcohols were synthesized and these alcohols were used to prepare 12 novel N-(2-hydroxy-ethyl)-2,3-didehydroazapodophyllotoxins, in one step, by simple reflux in ethanol. Isolated yields in the range of 50-70% were obtained.

Development of predictive quantitative structure-activity relationship models of epipodophyllotoxin derivatives

Epipodophyllotoxins are the most important anticancer drugs used in chemotherapy for various types of cancers. To further, improve their clinical efficacy a large number of epipodophyllotoxin derivatives have been synthesized and tested over the years. In this study, a quantitative structure-activity relationship (QSAR) model has been developed between percentage of cellular protein-DNA complex formation and structural properties by considering a data set of 130 epipodophyllotoxin analogues. A systematic stepwise searching approach of zero tests, missing value test, simple correlation test, multicollinearity test, and genetic algorithm method of variable selection was used to generate the model. A statistically significant model (r((train))(2) = 0.721; q(cv)(2) = 0.678) was obtained with descriptors such as solvent-accessible surface area, heat of formation, Balaban index, number of atom classes, and sum of E-state index of atoms. The robustness of the QSAR models was characterized by the values of the internal leave-one-out cross-validated regression coefficient (q(cv)(2)) for the training set and r((test))(2) for the test set. The root mean square error between the experimental and predicted percentage of cellular protein-DNA complex formation (PCPDCF) was 0.194 and r((test))(2) = 0.689, revealing good predictability of the QSAR model.

Design, Synthesis and Biological Evaluation of Novel Spin-Labeled Derivatives of Podophyllotoxin

In order to design new antitumor drugs and study the relationship between antitumor and antioxidative activity of spin-labeled derivatives of podophyllotoxin, five novel pyrroline spin-labeled 4β-N-substituted-amino acid-4′-O-demethylepipodo-phyllotoxin compounds (11a-e) (Scheme 2) were synthesized and evaluated. Their cytotoxicity against three tumor cell lines (human lung carcinoma A-549, human leukemia cell HL-60 and multiple myeloma RPMI-8226) has been evaluated using a MTT-based assay in vitro. Also, we determined malondialdehyde (MDA) in liver and kidney homogenate of SD rats by the TBA method. The five new compounds showed either superior or comparable inhibitory activity against A-549, HL-60 and RPMI-8226 cell lines compared with etoposide (VP-16, 2), and all the tested compounds showed more significant antioxidant activities than VP-16. Furthermore, the partition coefficients were measured and preliminary structure-activity relationships are presented.

Plant-derived natural product research aimed at new drug discovery

Many important bioactive compounds have been discovered from natural sources using bioactivity-directed fractionation and isolation (BDFl) [Balunas MJ, Kinghorn AD (2005) Drug discovery from medicinal plants. Life Sci 78:431-441]. Continuing discovery has also been facilitated by the recent development of new bioassay methods. These bioactive compounds are mostly plant secondary metabolites, and many naturally occurring pure compounds have become medicines, dietary supplements, and other useful commercial products. Active lead compounds can also be further modified to enhance the biological profiles and developed as clinical trial candidates. In this review, the authors will summarize research on many different useful compounds isolated or developed from plants with emphasis placed on those recently discovered by the authors' laboratories as antitumor and anti-HIV clinical trial candidates.

A review on plant-derived natural products and their analogs with anti-tumor activity

Traditional medicines, including Chinese herbal formulations, can serve as the source of potential new drugs, and initial research focuses on the isolation of bioactive lead compound(s). The development of novel plant-derived natural products and their analogs for anticancer activity details efforts to synthesize new derivatives based on bioactivity- and mechanism of action-directed isolation and characterization coupled with rational drug design - based modification. Also, the anticancer activity of certain natural products and their analogs can be enhanced by synthesizing new derivatives based on active pharmacophore models; drug resistance and solubility and metabolic limitations can be overcome by appropriate molecular modifications; and new biological properties or mechanisms of action can be added by combining other functional groups or molecules. Preclinical screening for in vitro human cell line panels and selected in vivo xenograft testing then identifies the most promising drug development targets.

Synthesis and biological evaluation of new spin-labeled derivatives of podophyllotoxin

In order to find compounds with superior bioactivity and less toxicity, a series of spin-labeled podophyllotoxin derivatives were synthesized and tested for the partition coefficients and cytotoxicity against P-388 and A-549. Furthermore, we also determined antioxidant activities of target molecular in tissues of SD rats by the TBA method. Results revealed that most synthesized compounds showed more significant cytotoxicity against P-388 and A-549 in vitro than VP-16. Among them, 9d exhibited most potent cytotoxicity against P-388 and A-549 cells (IC50 is <0.01 and 0.13 microM, respectively). Also, the antioxidative activities showed that the modified compounds of 4'-demethylepipodophyllotoxin (9a-d and 10a-c) are higher than those of podophyllotoxin series (8a-d). The relationship between the cytotoxicity and antioxidative activity discussed.

Synthesis and biological evaluation of new 4beta-anilino- and 4beta-imido-substituted podophyllotoxin congeners

A series of C-4-anilino- and C-4-imido-substituted new podophyllotoxin congeners have been designed, synthesized, and evaluated for their cytotoxicity and DNA topoisomerase-II (topo-II) inhibition potential. Some of these compounds have exhibited promising in vitro anticancer and topo-II inhibition activity.