Hemi-synthesis and biological activity of new analogues of podophyllotoxin

Oxidative Transformations of Lignans

Numerous oxidative transformations of lignan structures have been reported in the literature. In this paper we present an overview on the current findings in the field. The focus is put on transformations targeting a specific structure, a specific reaction, or an interconversion of the lignan skeleton. Oxidative transformations related to biosynthesis, antioxidant measurements, and total syntheses are mostly excluded. Non-metal mediated as well as metal mediated oxidations are reported, and mechanisms based on hydrogen abstractions, epoxidations, hydroxylations, and radical reactions are discussed for the transformation and interconversion of lignan structures. Enzymatic oxidations, photooxidation, and electrochemical oxidations are also briefly reported.

Antitumor effect of Deoxypodophyllotoxin on human breast cancer xenograft transplanted in BALB/c nude mice model

Recently, biologically active compounds isolated from plants used in herbal medicine have been the center of interest. Deoxypodophyllotoxin (DPT), structurally closely related to the lignan podophyllotoxin, was found to be a potent antitumor and antiproliferative agent, in several tumor cells, in vitro. However, DPT has not been used clinically yet because of the lack of in vivo studies. This study is the first report demonstrating the antitumor effect of DPT on MDA-MB-231 human breast cancer xenografts in nude mice. DPT, significantly, inhibited the growth of MDA-MB-231 xenograft in BALB/c nude mice. The T/C value (the value of the relative tumor volume of treatment group compared to the control group) of groups treated with 5, 10, and 20 mg/kg of intravenous DPT-HP-β-CD was 42.87%, 34.04% and 9.63%, respectively, suggesting the positive antitumor activity of DPT. In addition, the antitumor effect of DPT-HP-β-CD (20 mg/kg) in human breast cancer MDA-MB-231 xenograft was more effective than etoposide (VP-16) (20 mg/kg) and docetaxel (20 mg/kg). These findings suggest that this drug is a promising chemotherapy candidate against human breast carcinoma.

Metal catalyst-free substitution of allylic and propargylic phosphates with diarylmethyl anions

Substitution of secondary allylic and propargylic phosphates with the anions derived from Ar₂CH₂ with BuLi or LDA proceeded regioselectively and stereoselectively without a metal catalyst, affording inversion products in good yields.

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.

A fragmentation study of two compounds related to 4'-demethylepipodophyllotoxin in negative ion electrospray ionization by MSn ion-trap time-of-flight mass spectrometry

High-resolution electrospray ionization multistage tandem mass spectrometry (MS 1-7) in negative ion mode was used to determine the accurate masses and fragmentation pathways of two compounds, 4'-demethylepipodophyllotoxin and 4'-demethyl-4-azido-4-deoxyepipodophyllotoxin, which are key intermediate compounds for the preparation of podophyllotoxin-type anti-cancer drugs. The deprotonated molecules [M-H]* of both compounds were readily observed in the conventional single-stage mass spectra due to the presence of the phenolic hydroxyl group in the molecules. Abundant information on the product ions was obtained from tandem mass spectra (MS 2-7) in negative ion mode. Based on the exact masses acquired from 14 different tandem mass spectra, a similar MSn fragmentation pathway was proposed for both compounds. A characteristic product ion produced in the MS 2-4 product ion scan experiments is the cyclohexylenetrione anion [M-H-2Me-RH]* or [M-H-RH-2Me]* at m/z 351 (C19H11O7) formed by the consecutive losses of two CH3 radicals at the 3'- and 5'-positions and the neutral loss of RH, where R = a 4-substituted group (-OH or -N3), from the [M-H]* ion. This anion may be considered as diagnostic for the presence of this type of compound. The other common cleavages are the neutral losses of CO at least two times in the MS 6,7 product ion spectra. The results of this work could serve as an effective tool for the detection or determination of other derivatives of 4'-demethyl-4beta-substituted podophyllotoxin, which are widely used as intermediates for the preparation of anti-tumor drugs.

Synthesis and biological evaluation of new 4beta-5-Fu-substituted 4'-demethylepipodophyllotoxin derivatives

A series of new 4beta-5-Fu-substituted 4'-demethylepipodophyllotoxin derivatives were synthesized and evaluated, together with some previously prepared ones, for their cytotoxic activities against four tumor cell lines (HL60, P388, A549 and BEL7402). Three of these compounds exhibited superior in vitro anticancer activity against P388 and A549 than the reference compound etoposide. In addition, the partition coefficients (P) of all the new and previously synthesized derivatives were determined.

Plant-based anticancer molecules: a chemical and biological profile of some important leads

A number of natural products, with diverse chemical structures, have been isolated as anticancer agents. Several potential lead molecules such as camptothecin, vincristine, vinblastine, taxol, podophyllotoxin, combretastatins, etc. have been isolated from plants and many of them have been modified to yield better analogues for activity, toxicity or solubility. Several successful molecules like topotecan, irinotecan, taxotere, etoposide, teniposide, etc. also have emerged as drugs upon modification of these natural leads and many more are yet to come. In this review, the authors have focused on four important anticancer leads, that is, camptothecin, taxol, combretastatin A-4 and podophyllotoxin. Their chemistry, structure and activity relationships, biological activities, modes of action, analogue synthesis and future prospects have been discussed.

Cytotoxicity, apoptosis induction, and mitotic arrest by a novel podophyllotoxin glucoside, 4DPG, in tumor cells

AIM

To define the in vitro cytotoxic activities of 4-demethyl-picropodophyllotoxin 7'-O-beta-D-glucopyranoside (4DPG), a new podophyllotoxin glucoside.

METHODS

Antiproliferation activity was measured in several tumor cell lines by using the microculture tetrazolium MTT assays. Cell cycle distribution was analyzed using flow cytometry and mitosis index assays. Furthermore, transmission electron microscopy, TUNEL, DNA agarose electrophoresis, and activated caspase-3 were used to analyze the induction of apoptotic cell death. Moreover, intracellular changes in the cytoskeleton were detected using immunocytochemistry.

RESULTS

4DPG effectively inhibited the proliferation of cancer cells (HeLa, CNE, SH-SY5Y, and K562 cell lines). For the K562 cell line, the antiproliferation effect of 4DPG was much more potent than that of etoposide (IC50 value: 7.79 x 10(-9) mol/L for 4DPG vs 2.23 x 10(-5) mol/L for etoposide). Further, 4DPG blocked the cell cycle in the mitotic phase. The induction of apoptosis and elevated levels of activated caspase-3 were confirmed in cells treated with 4DPG. The microtubule skeleton of HeLa cells was disrupted immediately after treatment with 4DPG.

CONCLUSION

The cytotoxicity of 4DPG is due to its inhibition of the microtubule assembly of cancer cells at a low concentration, thus inducing apoptosis. These properties qualify 4DPG to be a potential antitumor drug.

Podophyllotoxin: distribution, sources, applications and new cytotoxic derivatives

Several podophyllotoxin derivatives modified in the A, B, C, D and E rings were prepared from podophyllotoxin and methyl isoxazopodophyllic acid and evaluated for their cytotoxicity on several neoplastic cell lines. Chemical transformations performed on these compounds have yielded derivatives more potent and more selective that the parent compound. Most of the compounds maintained their cytotoxicity at the microM level. Distribution, biosynthesis, production, biotechnology, applications and synthesis have also been reviewed.

Cytotoxic and cytostatic activity of erlangerins from Commiphora erlangeriana

The resin of Commiphora erlangeriana is known to be poisonous to humans and animals and has traditionally been used as an arrow poison. Since recent phytochemical studies on this plant material has identified four major lignans (named, Erlangerins A to D) that closely relate to the structure of podophyllotoxin, it was hypothesised that the well known poisoning effect of the resin could in part be due to direct toxicity to mammalian cells. Hence, the toxicity of Erlangerins was studied by measuring the viability of two human (HeLa and EAhy926) and two murine (L929 and RAW 264.7) cell lines. As assessed by the MTT assay, the effect of Erlangerin C and D closely follow the activity profile of podophyllotoxin: they induced a concentration-dependent cytotoxicity in the murine macrophage cells (RAW 264.7) and a cytostatic effect in HeLa, EAhy926 and L929 cells. In contrast, Erlangerins A and B suppressed cell viability at relatively higher concentrations (EC(50) values higher than 3 micro M as compared with nM concentration range for Erlangerins C and D and podophyllotoxin) and their activity appears to be consistent with a cytotoxic mode of action in all cell lines studied. The structure-activity-relationship established from the study is discussed.