Cytotoxic constituents of Bursera permollis

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.

Podophyllotoxin: History, Recent Advances and Future Prospects

Podophyllotoxin, along with its various derivatives and congeners are widely recognized as broad-spectrum pharmacologically active compounds. Etoposide, for instance, is the frontline chemotherapeutic drug used against various cancers due to its superior anticancer activity. It has recently been redeveloped for the purpose of treating cytokine storm in COVID-19 patients. Podophyllotoxin and its naturally occurring congeners have low bioavailability and almost all these initially discovered compounds cause systemic toxicity and development of drug resistance. Moreover, the production of synthetic derivatives that could suffice for the clinical limitations of these naturally occurring compounds is not economically feasible. These challenges demanded continuous devotions towards improving the druggability of these drugs and continue to seek structure-optimization strategies. The discovery of renewable sources including microbial origin for podophyllotoxin is another possible approach. This review focuses on the exigency of innovation and research required in the global R&D and pharmaceutical industry for podophyllotoxin and related compounds based on recent scientific findings and market predictions.

Cytotoxicity against Cholangiocarcinoma and HepG2 Cell Lines of Lignans from Hernandia nymphaeifolia

Eleven lignans (1-11) were isolated from the seed of Hernandia nymphaeifolia. Most of the lignans exhibited strong to moderate cytotoxicity against cholangiocarcinoma KKU-M156 and HepG2 cell lines. Compounds 4 and 8 showed cytotoxicity against the KKU-M156 cell line with IC50 values of 5.2 μ M (Emax 96%) and 5.4 (Emax 59%) μM, respectively. In the cases of cytotoxicity against the HepG2 cell line, compounds 2, 3, 4, and 8 showed cytotoxicity with IC50 values of 1.7 M (Emax 84%), 4.1 μM (Emax 74%), 4.5 μM (Emax 68%), and 5.2 μM (Emax 78%), respectively.

Cytotoxic podophyllotoxin type-lignans from the steam bark of Bursera fagaroides var. fagaroides

The hydroalcoholic extract of the steam bark of B. fagaroides var. fagaroides displayed potent cytotoxic activity against four cancer cell lines, namely KB (ED₅₀ = 9.6 × 10⁻² μg/mL), PC-3 (ED₅₀ = 2.5 × 10⁻¹ μg/mL), MCF-7 (ED₅₀ = 6.6 μg/mL), and HF-6 (ED₅₀ = 7.1 × 10⁻³ μg/mL). This extract also showed anti-tumour activity when assayed on mice inoculated with L5178Y lymphoma cells. Bioactivity-directed isolation of this extract, afforded seven podophyllotoxin-type lignans identified as podophyllotoxin (1), β-peltatin-A-methylether (2), 5′-desmethoxy-β-peltatin-A-methylether (3), desmethoxy-yatein (4), desoxypodophyllotoxin (5), burseranin (6), and acetyl podophyllotoxin (7) by 1D and 2DNMR and FAB-MS analyses, and comparison with reported values. All the isolated compounds showed potent cytotoxic activity in the cell lines tested, especially compound 3, which exhibited greater activity than camptothecin and podophyllotoxin against PC-3 (ED₅₀ = 1.0 × 10⁻⁵ μg/mL), and KB (ED₅₀ = 1.0 × 10⁻⁵ μg/mL). This is the first report of the isolation of podophyllotoxin and its acetate in a Bursera species.

Absolute configuration of podophyllotoxin related lignans from Bursera fagaroides using vibrational circular dichroism

The ethanol extract from the dried exudate of Bursera fagaroides (Burseraceae) showed significant cytotoxic activity in the HT-29 (human colon adenocarcinoma) test system. The extract provided four podophyllotoxin related lignans, identified as (7'R,8R,8'R)-(-)-deoxypodophyllotoxin (3), (7'R,8R,8'R)-(-)-morelensin (4), (8R,8'R)-(-)-yatein (5), and (8R,8'R)-(-)-5'-desmethoxyyatein (6), whose spectroscopic and chiroptical properties were compared with those of (7R,7'R,8R,8'R)-(-)-podophyllotoxin (1) and its acetyl derivative (2). Their absolute configurations were assigned by comparison of the vibrational circular dichroism spectra of 1 and 3 with those obtained by density functional theory calculations.

Mexican medicinal plants used for cancer treatment: pharmacological, phytochemical and ethnobotanical studies

AIM OF THE STUDY

This review provides a summary of Mexican medicinal flora in terms of ethnobotanical, pharmacology, and chemistry of natural products related to anticancer activity.

MATERIALS AND METHODS

Bibliographic investigation was carried out by analyzing recognized books and peer-reviewed papers, consulting worldwide accepted scientific databases from the last five decades. Mexican plants with attributed anti-cancer properties were classified into six groups: (a) plant extracts that have been evaluated for cytotoxic effects, (b) plant extracts that have documented anti-tumoral effects, (c) plants with active compounds tested on cancer cell lines, (d) plants with novel active compounds found only in Mexican species, (e) plants with active compounds that have been assayed on animal models and (f) plants with anti-cancer ethnopharmacological references but without scientific studies.

RESULTS

Three hundred plant species belonging to 90 botanical families used for cancer treatment have been recorded, of which only 181 have been experimentally analyzed. The remaining 119 plant species are in use in empirical treatment of diseases consistent with cancer symptomatology. Only 88 of the plant extracts experimentally studied in in vitro cellular models have demonstrated active cytotoxic effects in at least one cancer cell line, and 14 out of the 88 have also been tested in vivo with the results that one of them demonstrated anti-neoplasic effects. A total of 187 compounds, belonging to 19 types of plant secondary metabolites, have been isolated from 51 plant extracts with active cytotoxic effects, but only 77 of these compounds (41%) have demonstrated cytoxicity. Seventeen of these active principles have not been reported in other plant species. However, only 5 compounds have been evaluated in vivo, and 3 of them could be considered as active.

CONCLUSION

Clearly, this review indicates that it is time to increase the number of experimental studies and to begin to conduct clinical trials with those Mexican plants and its active compounds selected by in vitro and in vivo activities. Also, the mechanisms of action by which plant extracts and their active compounds exert anti-cancer effects remain to be studied.

Phenacetin Isolated from Bursera grandifolia, a Herbal Remedy with Antipyretic Properties

Bursera grandifolia and other related species have been used in traditional herbal medicine in Mexico and other Latin American countries for their analgesic, antipyretic and anti-inflammatory properties. From the chloroform extract of leaves of B. grandifolia, a substance was isolated and identified as phenacetin, a well known compound with widely tested analgesic and antipyretic properties. The structural identity of the compound was elucidated on the basis of chemical and spectroscopic evidence and by comparison with an authentic sample.

Relationships between inhibitory activity against a cancer cell line panel, profiles of plants collected, and compound classes isolated in an anticancer drug discovery project

In an attempt to determine the relationships between the plant profiles (country of collection, taxonomy, plant part) and the compound classes isolated with cytotoxic activity against a panel of human tumor cell lines, the data compiled from a 15-year anticancer drug-discovery project were subjected to an analysis of variance (ANOVA). The results indicate significant trends in cytotoxic activity relative to collection location, taxonomy, plant part, and compound classes isolated. Plant collections were made in tropical forests in six countries, with collections from Ecuador resulting in higher activity than those from Indonesia and Peru. Interestingly, collections from Florida were not statistically different than those from the countries with higher biodiversity. One hundred and forty-five families were represented in the collections, with the Clusiaceae, Elaeocarpaceae, Meliaceae, and Rubiaceae having low ED50 (half maximal effective dose) values. Especially active genera included Aglaia, Casearia, Exostema, Mallotus, and Trichosanthes. Roots and below-ground plant materials were significantly more active than above-ground materials. Cucurbitacins, flavaglines, anthraquinones, fatty acids, tropane alkaloids, lignans, and sesquiterpenoids were significantly more active than xanthones and oligorhamnosides. The results from this study should serve as a guide for future plant collection endeavors for anticancer drug discovery.

Bioactive constituents from roots of Bursera tonkinensis

Bioassay directed-fractionation led to isolation of 12 compounds from the roots of Bursera tonkinensis Guillaum (Burseraceae), including burselignan, bursephenylpropane, and burseneolignan. Of the 12 compounds, only 4'-demethyldesoxypodophyllotoxin exhibited significant cytotoxic activities against KB, Col2 and LNCaP cell lines.

Flow cytometric estimation on cytotoxic activity of leaf extracts from seashore plants in subtropical Japan: isolation, quantification and cytotoxic action of (-)-deoxypodophyllotoxin

The cytotoxic activity of methanol extracts of leaves collected from 39 seashore plants in Iriomote Island, subtropical Japan was examined on human leukaemia cells (K562 cells) using a flow cytometer with two fluorescent probes, ethidium bromide and annexin V-FITC. Five extracts (10 microg/mL) from Hernandia nymphaeaefolia, Cerbera manghas, Pongamia pinnata, Morus australis var. glabra and Thespesia populnea greatly inhibited the growth of K562 cells. When the concentration was decreased to 1 microg/mL, only one extract from H. nymphaeaefolia still inhibited the cell growth. A cytotoxic compound was isolated from the leaves by bioassay-guided fractionation and was identified as (-)-deoxypodophyllotoxin (DPT). The fresh leaves of H. nymphaeaefolia contained a remarkably high amount of DPT (0.21 +/- 0.07% of fresh leaf weight), being clarified by a quantitative HPLC analysis. DPT at 70-80 pM started to inhibit the growth of K562 cells in an all-or-none fashion and at 100 pM or more it produced complete inhibition in all cases. Therefore, the slope of the dose-response curve was very steep. DPT at 100 pM or more decreased the cell viability to 50%-60% and increased the number of cells undergoing apoptosis (annexin V-positive cells). The results indicate that DPT contributes to the cytotoxic action of the extract from the leaves of H. nymphaeaefolia on K562 cells.

Novel action of lignans isolated from Hernandia nymphaeifolia on Ca(2+) signaling in renal tubular cells

The effect of five lignans, epi-aschantin, epi-magnolin, epi-yangambin, deoxypodophyllotoxin and yatein, isolated from Hernandia nymphaeifolia on Ca(2+) signaling in Madin-Darby canine kidney cells was examined using fura-2 as a Ca(2+) indicator. These lignans at concentrations between 10 and 100 microM increased [Ca(2+)](i) in a concentration-dependent manner. Removal of extracellular Ca(2+) abolished the Ca(2+) signals evoked by 50 microM of the lignans. La(3+)(50 microM) abolished the Ca(2+) signals induced by 100 microM of epi-aschantin, epi-magnolin and epi-yangambin, and 20 microM deoxypodophyllotoxin, but inhibited by 60% 50 microM yatein-induced responses. All five lignans (50-100 microM) inhibited by 42-65% thapsigargin-induced capacitative Ca(2+) entry, and inhibited by 23-61% thapsigargin-induced intracellular Ca(2+) release. Epi-yangambin (100 microM), epi-magnolin (100 microM), and epi-aschantin (100 microM) inhibited by 8-38% 10 microM ATP-induced Ca(2+) release. Trypan blue exclusion revealed that incubation with deoxypodophyllotoxin or yatein (but not the other lignans) decreased cell viability in a concentration-dependent manner. Together, the results suggest that, in renal tubular cells, these lignans exert multiple actions on Ca(2+) signaling. They caused Ca(2+) influx but reduced thapsigargin-induced capacitative Ca(2+) entry and also thapsigargin- and ATP-induced Ca(2+) release. Additionally, deoxypodophyllotoxin and yatein may be cytotoxic.