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

Computational Study Into the Oxidative Ring-Closure Mechanism During the Biosynthesis of Deoxypodophyllotoxin

The nonheme iron dioxygenase deoxypodophyllotoxin synthase performs an oxidative ring-closure reaction as part of natural product synthesis in plants. How the enzyme enables the oxidative ring-closure reaction of (-)-yatein and avoids substrate hydroxylation remains unknown. To gain insight into the reaction mechanism and understand the details of the pathways leading to products and by-products we performed a comprehensive computational study. The work shows that substrate is bound tightly into the substrate binding pocket with the C7'-H bond closest to the iron(IV)-oxo species. The reaction proceeds through a radical mechanism starting with hydrogen atom abstraction from the C7'-H position followed by ring-closure and a final hydrogen transfer to form iron(II)-water and deoxypodophyllotoxin. Alternative mechanisms including substrate hydroxylation and an electron transfer pathway were explored but found to be higher in energy. The mechanism is guided by electrostatic perturbations of charged residues in the second-coordination sphere that prevent alternative pathways.

Comprehensive Review on Herbal Medicine: Emphasis on Current Therapy and Role of Phytoconstituents for Cancer Treatment

INTRODUCTION

Cancer poses a significant public health challenge in both developed and developing nations, with a rising global incidence of patients facing the threat of death due to abnormal cell proliferation.

AIM

Review explores the utilization of different parts of herbal medicinal plants and their active pharmaceutical constituents in the prevention and treatment of various types of cancer.

METHODOLOGY

Various anticancer medicinal plants have been identified, demonstrating their therapeutic effects by inhibiting cancer-stimulating enzymes and hormones, activating DNA repair processes, boosting the synthesis of protective stimulants, reducing the formation of free radicals, and enhancing individual immunity. Data for this study were gathered from diverse online bibliographic and databases, including Google, Google Scholar, Mendeley, Springer Link, Research Gate, and PubMed.

RESULT

Herbal drugs have a huge contribution to the inhibition of the progression of cancer.A large volume of clinical studies has reported the beneficial effects of herbal medicines on the survival, immune modulation, and quality of life (QOL) of cancer patients, when these herbal medicines are used in combination with conventional therapeutics.

CONCLUSION

The latest medicines for the clinical purpose (Above 50 %) are derived from herbal products. Furthermore, combination of these herbs with nanotechnology shows promise in treating specific carcinomas.

Chemistry and Biology of Podophyllotoxins: An Update

Podophyllotoxin is an aryltetralin lignan lactone derived from different plants of Podophyllum. It consists of five rings with four chiral centers, one trans-lactone and one aryl tetrahydronaphthalene skeleton with multiple modification sites. Moreover, podophyllotoxin and its derivatives showed lots of bioactivities, including anticancer, anti-inflammatory, antiviral, and insecticidal properties. The demand for podophyllotoxin and its derivatives is rising as a result of their high efficacy. As a continuation of our previous review (Chem. Eur. J., 2017, 23, 4467-4526), herein, total synthesis, biotransformation, structural modifications, bioactivities, and structure-activity relationships of podophyllotoxin and its derivatives from 2017 to 2022 are summarized. Meanwhile, a piece of update information on the origin of new podophyllotoxin analogues from plants from 2014 to 2022 was compiled. We hope that this review will provide a reference for future high value-added applications of podophyllotoxin and its analogues in the pharmaceutical and agricultural fields.

An Updated Insight into Phytomolecules and Novel Approaches used in the Management of Breast Cancer

Breast cancer is a widespread condition that kills more women from cancer-related causes than any other type of cancer globally. Women who have estrogen-dependent, initial metastatic breast cancer frequently receive treatment with surgery, radiation therapy, and chemotherapy. They may also get more specialized treatments like tamoxifen or aromatase inhibitors (anastrozole or letrozole). The World Health Organisation reported in 2012 that by 2030, breast cancer will be more common worldwide. There are several phytochemicals, such as isoflavones, coumestans, lignans, and prenylflavonoides. Isoflavones have been shown in studies to prevent the spread of breast cancer and to trigger apoptosis. Targeting BCs in metastatic breast cancer may be made possible by combining well-formulated phytochemicals in nanoparticles or other novel drug delivery agents with currently accepted endocrine and/or conventional chemotherapies. Cell signaling, regulation of cell cycles, oxidative stress action, and inflammation could be positively impacted by phytoconstituents. They have the ability to alter non-coding RNAs, to prevent the proliferation and regeneration of cancer cells. The availability of novel approaches helps in disease targeting, safety, effectiveness and efficacy. The current literature helps to know the available drugs i.e. phytoconstituents or novel drug delivery like nanoparticle, microsphere, micelles, liposomes and neosomes. The literature has been taken from PubMed, Google Scholar, SciFinder, or other internet sites.

Natural product inspired leads in the discovery of anticancer agents: an update

Natural products have emerged as major leads for the discovery and development of new anti-cancer drugs. The plant-derived anti-cancer drugs account for approximately 60% and the quest for new anti-cancer agents is in progress. Anti-cancer leads have been isolated from plants, animals, marine organisms, and microorganisms from time immemorial. The process of semisynthetic modifications of the parent lead has led to the generation of new anti-cancer agents with improved therapeutic efficacy and minimal side effects. The various chemo-informatics tools, bioinformatics, high-throughput screening, and combinatorial synthesis are able to deliver the new natural product lead molecules. Plant-derived anticancer agents in either late preclinical development or early clinical trials include taxol, vincristine, vinblastine, topotecan, irinotecan, etoposide, paclitaxel, and docetaxel. Similarly, anti-cancer agents from microbial sources include dactinomycin, bleomycin, mitomycin C, and doxorubicin. In this review, we highlighted the importance of natural products leads in the discovery and development of novel anti-cancer agents. The semisynthetic modifications of the parent lead to the new anti-cancer agent are also presented. Further, the leads in the preclinical settings with the potential to become effective anticancer agents are also reviewed.Communicated by Ramaswamy H. Sarma.

A recent antitumor story of podophyllotoxin derivatives targeting tubulin: an update (2017-2022)

So far, numerous tubulin-targeted podophyllotoxin congeners were designed and synthesized to overcome the poor water-solubility and improve the pharmaceutical characteristics. However, few studies are dedicated to exploring the interaction of tubulin with the downstream signal transduction pathways, which is important for gaining insight into the role of tubulin in the anticancer action of podophyllotoxin-based conjugates. In this review, we described a detailed account of all the advances on tubulin targeting-podophyllotoxin derivatives from 2017 and 2022 with in depth knowledge about their antitumor action and potential molecular signaling pathways directly involved in tubulin depolymerization, aiming to help researchers design and develop better anticancer drugs derived from podophyllotoxin. Moreover, we also discussed the associated challenges and future opportunities in this field. Short teaser Recent reviews summarized podophyllotoxin-based analogues, with interaction between tubulin and signal pathways being rarely involved. This review comprehensively sum up how podophyllotoxin derivatives targeting tubulin exert their antitumor action via potential molecular signaling pathways.

Anticancer plant-derivatives: deciphering their oncopreventive and therapeutic potential in molecular terms

Background

Over the years, phytomedicines have been widely used as natural modalities for the treatment and prevention of various diseases by different ethnic groups across the globe. Although, 25% of drugs in the USA contain at least one plant-derived therapeutic compound, currently there is a paucity of plant-derived active medicinal ingredients in the pharmaceutical industry. Scientific evidence-based translation of plant-derived ethnomedicines for their clinical application is an urgent need. The anticancer and associated properties (antioxidative, anti-inflammatory, pro-apoptotic and epithelial-mesenchymal transition (EMT) inhibition) of various plant extracts and phytochemicals have been elucidated earlier. Several of the plant derivatives are already in use under prophylactic/therapeutic settings against cancer and many are being investigated under different phases of clinical trials.

Main body

The purpose of this study is to systematically comprehend the progress made in the area of prophylactic and therapeutic potential of the anticancerous plant derivatives. Besides, we aim to understand their anticancer potential in terms of specific sub-phenomena, such as anti-oxidative, anti-inflammatory, pro-apoptotic and inhibition of EMT, with an insight of the molecules/pathways associated with them. The study also provides details of classes of anticancer compounds, their plant source(s) and the molecular pathway(s) targeted by them. In addition to the antioxidative and antiproliferative potentials of anticancer plant derivatives, this study emphasizes on their EMT-inhibition potential and other ‘anticancer related’ properties. The EMT is highlighted as a phenomenon of choice for targeting cancer due to its role in the induction of metastasis and drug resistance. Different phytochemicals in pre-clinical or clinical trials, with promising chemopreventive/anticancer activities have been enlisted and the plant compounds showing synergistic anticancer activity in combination with the existing drugs have been discussed. The review also unravels the need of carrying out pan-signalome studies for identifying the cardinal pathways modulated by phytomedicine(s), as in many cases, the molecular pathway(s) has/have been randomly studied.

Conclusion

This review systematically compiles the studies regarding the impact of various plant derivatives in different cancers and oncogenic processes, as tested in diverse experimental model systems. Availability of more comprehensive information on anticancer phyto-constituents, their relative abundance in crude drugs, pathways/molecules targeted by phytomedicines, their long-term toxicity data and information regarding their safe use under the combinatorial settings, would open greater avenues of their utilization in future against this dreaded disease.

Graphical Abstract

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.

Dimerizing cascades of enallenamides reveal the visible-light-promoted activation of cumulated C-C double bonds

The visible-light-promoted activation of conjugated C-C double bonds is well developed, while that of cumulated systems is underexplored. We present the feasibility of this challenging approach. The localization of a triplet on an allenamide arm can be favored over that on a conjugated alkene. Allenamides with an arylacryloyl arm dimerize at room temperature in the presence of visible light and an iridium(iii) photocatalyst. Two orthogonal polycyclizations took place and their outcome is entirely dictated by the substitution of the alkene partner. Both cascades afford complex molecular architectures with high selectivity. Products form through the ordered rearrangement of twelve π electrons, providing a [3.2.0] bicyclic unit tethered to a fused tricycle, whose formation included an aryl C-H functionalization step, using disubstituted alkenes. The outcome was reverted with trisubstituted ones, which gave rise to taxane-like bridged tricycles that had two six-membered lactams flanking a cyclooctane ring, which was established through the creation of four alternate C-C bonds.

Mechanistic analysis of carbon-carbon bond formation by deoxypodophyllotoxin synthase

The completion of the tetracyclic core of etoposide, classified by the World Health Organization as an essential medicine, by the Fe/2OG oxygenase deoxypodophyllotoxin synthase follows a hybrid radical-polar pathway not previously seen in other members of this enzyme class. The implication of a substrate-based benzylic carbocation in this mechanism will inform ongoing efforts to create analogs of this important drug with improved or emergent properties and represents a new route for resolution of the initial substrate radical that is common to members of the class. This study adds to our understanding on a growing number of biochemical transformations in which carbocation intermediates are likely to be crucial.

Deoxypodophyllotoxin contains a core of four fused rings (A to D) with three consecutive chiral centers, the last being created by the attachment of a peripheral trimethoxyphenyl ring (E) to ring C. Previous studies have suggested that the iron(II)- and 2-oxoglutarate–dependent (Fe/2OG) oxygenase, deoxypodophyllotoxin synthase (DPS), catalyzes the oxidative coupling of ring B and ring E to form ring C and complete the tetracyclic core. Despite recent efforts to deploy DPS in the preparation of deoxypodophyllotoxin analogs, the mechanism underlying the regio- and stereoselectivity of this cyclization event has not been elucidated. Herein, we report 1) two structures of DPS in complex with 2OG and (±)-yatein, 2) in vitro analysis of enzymatic reactivity with substrate analogs, and 3) model reactions addressing DPS’s catalytic mechanism. The results disfavor a prior proposal of on-pathway benzylic hydroxylation. Rather, the DPS-catalyzed cyclization likely proceeds by hydrogen atom abstraction from C7', oxidation of the benzylic radical to a carbocation, Friedel–Crafts-like ring closure, and rearomatization of ring B by C6 deprotonation. This mechanism adds to the known pathways for transformation of the carbon-centered radical in Fe/2OG enzymes and suggests what types of substrate modification are likely tolerable in DPS-catalyzed production of deoxypodophyllotoxin analogs.

Discovery of new quinolines as potent colchicine binding site inhibitors: design, synthesis, docking studies, and anti-proliferative evaluation

Discovering of new anticancer agents with potential activity against tubulin polymerisation is still a promising approach. Colchicine binding site inhibitors are the most relevant anti-tubulin polymerisation agents. Thus, new quinoline derivatives have been designed and synthesised to possess the same essential pharmacophoric features of colchicine binding site inhibitors. The synthesised compounds were tested in vitro against a panel of three human cancer cell lines (HepG-2, HCT-116, and MCF-7) using colchicine as a positive control. Comparing to colchicine (IC50 = 7.40, 9.32, and 10.41 µM against HepG-2, HCT-116, and MCF-7, respectively), compounds 20, 21, 22, 23, 24, 25, 26, and 28 exhibited superior cytotoxic activities with IC50 values ranging from 1.78 to 9.19 µM. In order to sightsee the proposed mechanism of anti-proliferative activity, the most active members were further evaluated in vitro for their inhibitory activities against tubulin polymerisation. Compounds 21 and 32 exhibited the highest tubulin polymerisation inhibitory effect with IC50 values of 9.11 and 10.5 nM, respectively. Such members showed activities higher than that of colchicine (IC50 = 10.6 nM) and CA-4 (IC50 = 13.2 nM). The impact of the most promising compound 25 on cell cycle distribution was assessed. The results revealed that compound 25 can arrest the cell cycle at G2/M phase. Annexin V and PI double staining assay was carried out to explore the apoptotic effect of the synthesised compounds. Compound 25 induced apoptotic effect on HepG-2 thirteen times more than the control cells. To examine the binding pattern of the target compounds against the tubulin heterodimers active site, molecular docking studies were carried out.

Exploring Multifunctional Bioactive Components from Podophyllum sinense Using Multi-Target Ultrafiltration

Podophyllum sinense (P. sinense) has been used as a traditional herbal medicine for ages due to its extensive pharmaceutical activities, including antiproliferative, anti-inflammatory, antiviral, insecticidal effects, etc. Nevertheless, the specific bioactive constituents responsible for its antiproliferative, anti-inflammatory, and antiviral activities remain elusive, owing to its complicated and diversified chemical components. In order to explore these specific bioactive components and their potential interaction targets, affinity ultrafiltration with multiple drug targets coupled with high performance liquid chromatography/mass spectrometry (UF–HPLC/MS) strategy was developed to rapidly screen out and identify bioactive compounds against four well-known drug targets that are correlated to the application of P. sinense as a traditional medicine, namely, Topo I, Topo II, COX-2, and ACE2. As a result, 7, 10, 6, and 7 phytochemicals were screened out as the potential Topo I, Topo II, COX-2, and ACE2 ligands, respectively. Further confirmation of these potential bioactive components with antiproliferative and COX-2 inhibitory assays in vitro was also implemented. Herein, diphyllin and podophyllotoxin with higher EF values demonstrated higher inhibitory rates against A549 and HT-29 cells as compared with those of 5-FU and etoposide. The IC₅₀ values of diphyllin were calculated at 6.46 ± 1.79 and 30.73 ± 0.56 μM on A549 and HT-29 cells, respectively. Moreover, diphyllin exhibited good COX-2 inhibitory activity with the IC₅₀ value at 1.29 ± 0.14 μM, whereas indomethacin was 1.22 ± 0.08 μM. In addition, those representative constituents with good affinity on Topo I, Topo II, COX-2, or ACE2, such as diphyllin, podophyllotoxin, and diphyllin O-glucoside, were further validated with molecular docking analysis. Above all, the integrated method of UF–HPLC/MS with multiple drug targets rapidly singled out multi-target bioactive components and partly elucidated their action mechanisms regarding its multiple pharmacological effects from P. sinense, which could provide valuable information about its further development for the new multi-target drug discovery from natural medicines.

Podofilox suppresses gastric cancer cell proliferation by regulating cell cycle arrest and the c-Myc/ATG10 axis

Gastric cancer (GC) is a malignancy for which effective therapeutic drugs are limited. Podofilox exhibits antitumor effects in various types of cancer; however, whether it may inhibit GC growth remains unknown. The aim of the present study was to investigate the role of podofilox in GC. Cell Counting Kit-8, colony formation and cell cycle assays were used to detect the role of podofilox on cellular proliferation and the cell cycle, respectively. A microarray was used to detect the transcriptional changes induced by podofilox in GC cells. The results of the present study demonstrated that podofilox inhibited GC cell proliferation and colony formation. The half maximal inhibitory concentration of podofilox in AGS and HGC-27 cells was 2.327 and 1.981 nM, respectively. In addition, treatment with podofilox induced G₀/G₁ cell cycle arrest. Molecular analysis based on microarray data demonstrated that podofilox altered the expression levels of genes involved in the cell cycle, c-Myc and p53 signaling. Autophagy-related 10 (ATG10), which was highly expressed in GC tissues, was also downregulated by podofilox, as demonstrated by the results of the microarray analysis and immunoblotting. To determine the involvement of ATG10 in GC, ATG10 was knocked down in GC cells by small interfering RNA, which suppressed the proliferation and colony formation of GC cells compared with those observed in the control-transfected cells. Taken together, the results of the present study suggested that podofilox may inhibit GC cell proliferation by preventing the cell cycle progression and regulating the c-Myc/ATG10 signaling pathway.

Peperomin E Induces Apoptosis and Cytoprotective Autophagy in Human Prostate Cancer DU145 Cells In Vitro and In Vivo

Peperomin E was first isolated from Peperomia dindygulensis, an anticarcinogenic herb, and exhibited anticancer activity in many cancer cell lines. To date, it is unknown whether peperomin E has an effect on human prostate cancer DU145 cells in vitro and in vivo. In this study, we used MTT to assess the proliferation inhibition activity of peperomin E in DU145 cells in vitro and observed the cell morphological changes by a phase contrast microscope. A DU145 cell xenograft tumor mouse model was used to evaluate the efficacy of peperomin E in vivo. Apoptosis rates were measured by flow cytometry, and protein expression levels were analyzed by western blot. The results showed that peperomin E significantly inhibited the proliferation of DU145 cells in vitro and reduced the weight and volume of tumors in vivo. Peperomin E also significantly induced the apoptosis and autophagic response of DU145 cells. The autophagic inhibitors LY294002 and chloroquine enhanced peperomin E-mediated inhibition of DU145 cell proliferation and induction of DU145 cell apoptosis. The results also showed that the Akt/mTOR pathway participated in peperomin E-induced autophagy in DU145 cells. In summary, our finding showed that peperomin E had an effect on DU145 cells in vitro and in a nude mouse DU145 cell xenograft model in vivo, demonstrated that peperomin E could significantly induce apoptosis and the autophagic response in DU145 cells and that autophagy played a cytoprotective role in peperomin E-treated DU145 cells. These results suggest that the combination of peperomin E treatment and autophagic inhibition has potential for the treatment of prostate cancer.

[Conjugate of podophyllotoxin with chlorambucil: synthesis, biological testing and molecular modeling]

In the present work we have studied a novel conjugate of the DNA alkylating agent chlorambucil with podophyllotoxin, a ligand of the colchicine binding site in tubulin. The target compound was obtained by Steglich esterification of podophyllotoxin with the percentage yield of 41%. Results of biotesting carried out on the carcinoma A549 cell line revealed that at a concentration of 2 μM the conjugate caused full depolymerization of microtubules without any other effect on free tubulin. The conjugate inhibited proliferation (IC50=135±30 nM) and growth (EC50=240±30 nM) of A549 cells. The data of computer molecular docking of the novel compound into the 3D model of the colchicine binding site in α,β-tubulin and molecular dynamics modelling allowed to explain the observed difference in effects of chlorambucil-podophyllotoxin and chlorambucil-colchicine conjugates on microtubules.

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.

Novel podophyllotoxin and benzothiazole derivative induces transitional morphological and functional changes in HaCaT cells

Podophyllotoxin (PPT) is an antimitotic drug used topically in the treatment of anogenital warts. Due to its toxicity it cannot be administered systemically as an anticancer agent. However, modified PPT derivatives such as etoposide and teniposide are used clinically as systemic agents. Thus, we invented novel PPT derivative KL3 that was synthesized by photocyclization. Earlier we have shown that KL3 has an anticancer effect in various cell lines. Here we compared the toxicity of KL3 vs PPT on non-cancerous normal human keratinocytes (HaCaT) and peripheral blood mononuclear cells (PBMC) showing that KL3 is less toxic than PPT to non-cancerous cells. At concentrations that neither induced cell death, nor affected cell cycle, KL3 in HaCaT cells evoked transient ultrastructural features of ER stress, swelling of mitochondria and elongation of cytoplasmic processes. Those changes partially reversed with prolonged incubation while features of autophagy were induced. PPT in equivalent concentrations induced HaCaT cell death by cell cycle arrest, intrinsic apoptosis and finally disintegration of cell membranes followed by secondary necrosis. In conclusion, we show that the KL3 derivative of PPT in contrast to PPT allows repair of normal keratinocytes and triggers mechanisms that restore non-tumor cell homeostasis.

Status and Challenges of Plant-Anticancer Compounds in Cancer Treatment

Nowadays, cancer is one of the deadliest diseases in the world, which has been estimated to cause 9.9 million deaths in 2020. Conventional treatments for cancer commonly involve mono-chemotherapy or a combination of radiotherapy and mono-chemotherapy. However, the negative side effects of these approaches have been extensively reported and have prompted the search of new therapeutic drugs. In this context, scientific community started to look for innovative sources of anticancer compounds in natural sources, including traditional plants. Currently, numerous studies have evaluated the anticancer properties of natural compounds derived from plants, both in vitro and in vivo. In pre-clinical stages, some promising compounds could be mentioned, such as the sulforaphane or different phenolic compounds. On the other hand, some phytochemicals obtained positive results in clinical stages and were further approved for cancer treatment, such as vinca alkaloids or the paclitaxel. Nevertheless, these compounds are not exempt of limitations, such as low solubility, restricted effect on their own, negative side-effects, etc. This review aims to compile the information about the current phytochemicals used for cancer treatment and also promising candidates, main action mechanisms and also reported limitations. In this sense, some strategies to face the limitations have been considered, such as nano-based formulations to improve solubility or chemical modification to reduce toxicity. In conclusion, although more research is still necessary to develop more efficient and safe phytochemical drugs, more of these compounds might be used in future cancer therapies.

Design and Synthesis of 4-O-Podophyllotoxin Sulfamate Derivatives as Potential Cytotoxic Agents

4-O-Podophyllotoxin sulfamate derivatives were prepared using the natural lignan podophyllotoxin. The prepared compounds were afforded by reacting O-sulfonyl chloride podophyllotoxin with ammonia or aminoaryl/heteroaryl motif. Biological evaluation was performed in human breast cancer (MCF7), ovarian cancer (A2780), colon adenocarcinoma (HT29), and normal lung fibroblast (MRC5) cell lines. Compound 3 exhibited potent inhibitory activity and good selectivity margin. Compounds 2, 3, and 7 exerted apoptotic effect in MCF7 cells in a dose-dependent manner. The cytotoxicity of the verified compounds was inferior to that of podophyllotoxin.

Novel Hybrids of Podophyllotoxin and Coumarin Inhibit the Growth and Migration of Human Oral Squamous Carcinoma Cells

Oral squamous cell carcinoma is the most common malignancy of oral tumor. In this study, two novel hybrids of podophyllotoxin and coumarin were designed using molecular hybridization strategy and synthesized. Pharmacological evaluation showed that the potent compound 12b inhibited the proliferation of three human oral squamous carcinoma cell lines with nanomolar IC₅₀ values, as well as displayed less toxicity on normal cells. Mechanistic studies indicated that 12b triggered HSC-2 cell apoptosis, induced cell cycle arrest, and inhibited cell migration. Moreover, 12b could disturb the microtubule network via binding into the tubulin. It was noteworthy that induction of autophagy by 12b was associated with the upregulation of Beclin1, as well as LC3-II. Furthermore, 12b significantly stimulated the AMPK pathway and restrained the AKT/mTOR pathway in HSC-2 cells. These results indicated that compound 12b was a promising candidate for further investigation.

Microenvironmental Determinants of Breast Cancer Metastasis: Focus on the Crucial Interplay Between Estrogen and Insulin/Insulin-Like Growth Factor Signaling

The development and progression of the great majority of breast cancers (BCs) are mainly dependent on the biological action elicited by estrogens through the classical estrogen receptor (ER), as well as the alternate receptor named G-protein–coupled estrogen receptor (GPER). In addition to estrogens, other hormones and growth factors, including the insulin and insulin-like growth factor system (IIGFs), play a role in BC. IIGFs cooperates with estrogen signaling to generate a multilevel cross-communication that ultimately facilitates the transition toward aggressive and life-threatening BC phenotypes. In this regard, the majority of BC deaths are correlated with the formation of metastatic lesions at distant sites. A thorough scrutiny of the biological and biochemical events orchestrating metastasis formation and dissemination has shown that virtually all cell types within the tumor microenvironment work closely with BC cells to seed cancerous units at distant sites. By establishing an intricate scheme of paracrine interactions that lead to the expression of genes involved in metastasis initiation, progression, and virulence, the cross-talk between BC cells and the surrounding microenvironmental components does dictate tumor fate and patients’ prognosis. Following (i) a description of the main microenvironmental events prompting BC metastases and (ii) a concise overview of estrogen and the IIGFs signaling and their major regulatory functions in BC, here we provide a comprehensive analysis of the most recent findings on the role of these transduction pathways toward metastatic dissemination. In particular, we focused our attention on the main microenvironmental targets of the estrogen-IIGFs interplay, and we recapitulated relevant molecular nodes that orientate shared biological responses fostering the metastatic program. On the basis of available studies, we propose that a functional cross-talk between estrogens and IIGFs, by affecting the BC microenvironment, may contribute to the metastatic process and may be regarded as a novel target for combination therapies aimed at preventing the metastatic evolution.

Picropodophyllotoxin, an Epimer of Podophyllotoxin, Causes Apoptosis of Human Esophageal Squamous Cell Carcinoma Cells Through ROS-Mediated JNK/P38 MAPK Pathways

Esophageal squamous cell carcinoma (ESCC), a major histologic type of esophageal cancer, is one of the frequent causes of cancer-related death worldwide. Picropodophyllotoxin (PPT) is the main component of Podophyllum hexandrum root with antitumor activity via apoptosis-mediated mechanisms in several cancer cells. However, the underlying mechanism of the PPT effects in apoptosis induction in cancer remains ambiguous. Hence, in this study, we evaluate the anti-cancer effects of PPT in apoptotic signaling pathway-related mechanisms in ESCC cells. First, to verify the effect of PPT on ESCC cell viability, we employed an MTT assay. PPT inhibited the viability of ESCC cells in time- and dose-dependent manners. PPT induced G2/M phase cell cycle arrest and annexin V-stained cell apoptosis through the activation of the c-Jun N-terminal kinase (JNK)/p38 pathways. Furthermore, the treatment of KYSE 30 and KYSE 450 ESCC cells with PPT induced apoptosis involving the regulation of endoplasmic reticulum stress- and apoptosis-related proteins by reactive oxygen species (ROS) generation, the loss of mitochondrial membrane potential, and multi-caspase activation. In conclusion, our results indicate that the apoptotic effect of PPT on ESCC cells has the potential to become a new anti-cancer drug by increasing ROS levels and inducing the JNK/p38 signaling pathways.

Phytochemicals as Potential Anticancer Drugs: Time to Ponder Nature's Bounty

Medicinal plants have been used from the beginning of human civilization, which is mostly evident from the ancient script and traditional herbal medicine recipe. Despite the historically enriched demonstration about the use of plant as therapeutics, the pharmaceutical industries lack interest on phytochemical research compared with synthetic drug. Mostly, the absence of information about plant-based medicinal therapeutics is responsible to draw the attention of researchers to think about natural products as potential drug for detrimental diseases, such as cancer. This review will cover about clinically successful plant-based anticancer drugs and underappreciated, but potential, drugs to bridge the information gap between plant biologists and clinical researchers. Additionally, unprecedented advancement of synthetic chemistry, omics study to pin point the target genes/proteins, and efficient drug delivery system have made it easier for researchers to develop a phytochemical as an efficient anticancer drug.

Effect of 3-O-acetylaleuritolic acid from in vitro-cultured Drosera spatulata on cancer cells survival and migration

BACKGROUND

Drosera spatulata is a source of many compounds such as naphthoquinones, phenolic acids, flavonoids, anthocyanins, and naphthalene derivatives. Unfortunately, the information regarding the biological activity and chemical profile of those compounds is still incomplete. Herein, we investigated the biological activity of 3-O-acetylaleuritolic acid (3-O-AAA) in cancer cell lines.

METHODS

The cell viability of HeLa, HT-29, MCF7, and MCF12A cells was assessed using MTT assay. Proliferation potential was assessed using the clonogenic assay and flow cytometry. Migration modulation was tested using a scratch assay. Protein expression was analyzed by immunoblotting.

RESULTS

3-O-AAA significantly inhibited the growth of all tested tumor cells. The results of the colony formation assay suggested cytostatic properties of the studied compound. The scratch assay showed that 3-O-AAA was an efficient migration inhibitor in a dose-dependent manner. Moreover, it caused modulation of mTOR, beclin1, and Atg5 proteins suggesting a possible role of the compound in autophagy induction.

CONCLUSION

Collectively, these results demonstrated that 3-O-AAA inhibited the proliferation and migration of cancer cell lines as well as contributed to autophagy induction showing some anticancer properties.

Podophyllotoxin Isolated from Podophyllum peltatum Induces G2/M Phase Arrest and Mitochondrial-Mediated Apoptosis in Esophageal Squamous Cell Carcinoma Cells

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers in East Asia and is the seventh leading cause of cancer deaths. Podophyllotoxin (PT), a cyclolignan isolated from podophyllum peltatum, exhibits anti-cancer effects at the cellular level. This study investigated the underlying mechanism of anti-cancer effects induced by PT in ESCC cells. Exposure to increasing concentrations of PT led to a significant decrease in the growth and anchorage-independent colony numbers of ESCC cells. PT showed high anticancer efficacy against a panel of four types of ESCC cells, including KYSE 30, KYSE 70, KYSE 410, KYSE 450, and KYSE 510 by IC50 at values ranges from 0.17 to 0.3 μM. We also found that PT treatment induced G2/M phase arrest in the cell cycle and accumulation of the sub-G1 population, as well as apoptosis. Exposure to PT triggered a significant synthesis of reactive oxygen species (ROS), a loss of mitochondrial membrane potential (MMP), and activation of various caspases. Furthermore, PT increased the levels of phosphorylated c-Jun N-terminal kinase (JNK), p38, and the expression of Endoplasmic reticulum (ER) stress marker proteins via ROS generation. An increase in the level of pro-apoptotic proteins and a reduction in the anti-apoptotic protein level induced ESCC cell death via the loss of MMP. Additionally, the release of cytochrome c into the cytosol with Apaf-1 induced the activation of multi-caspases. In conclusion, our results revealed that PT resulted in apoptosis of ESCC cells by modulating ROS-mediated mitochondrial and ER stress-dependent mechanisms. Therefore, PT is a promising therapeutic candidate as an anti-cancer drug against ESCC for clinical use.

Synthesis and Biological Evaluation of 4β-N-Acetylamino Substituted Podophyllotoxin Derivatives as Novel Anticancer Agents

A series of novel podophyllotoxin derivatives obtained by 4β-N-acetylamino substitution at C-4 position was designed, synthesized, and evaluated for in vitro cytotoxicity against four human cancer cell lines (EC-9706, HeLA, T-24 and H460) and a normal human epidermal cell line (HaCaT). The cytotoxicity test indicated that most of the derivatives displayed potent anticancer activities. In particular, compound 12h showed high activity with IC₅₀ values ranging from 1.2 to 22.8 μM, with much better cytotoxic activity than the control drug etoposide (IC₅₀: 8.4 to 78.2 μM). Compound 12j exhibited a promising cytotoxicity and selectivity profile against T24 and HaCaT cell lines with IC₅₀ values of 2.7 and 49.1 μM, respectively. Compound 12g displayed potent cytotoxicity against HeLA and T24 cells with low activity against HaCaT cells. According to the results of fluorescence-activated cell sorting (FACS) analysis, 12g induced cell cycle arrest in the G2/M phase accompanied by apoptosis in T24 and HeLA cells. Furthermore, the docking studies showed possible interactions between human DNA topoisomerase IIα and 12g. These results suggest that 12g merits further optimization and development as a new podophyllotoxin-derived lead compound.

[Podophyllotoxin analogue with bicyclo[3.2.1]octane moiety annelated with indole: synthesis, molecular modeling, and biological testing]

C4-Ester derivatives of the anticancer agent podophyllotoxin with bridged moieties can either inhibit polymerization of alpha,beta-tubulin with the formation of microtubules (analogously to the parent molecule) or cause an unusual effect of "curling and shortening" of the microtubules (MT). In order to predict the effect of bridged podophyllotoxin derivatives on the MT network using computer molecular modeling it is desirable to enhance the structural diversity of their bridged substituents. In the present work we synthesized novel podophyllotoxin ester with bicyclo[3.2.1]octane moiety annelated with indole core. The target compound was obtained by Steglich esterification of podophyllotoxin by rac-exo-(indolo[2,3-b])bicyclo[3.2.1]oct-2-ene-6-carboxylic acid as diastereomeric (6RS,8SR,9RS) mixture, which could not be separated by thin layer or preparative column chromatography on silica gel. Results of biotesting of 4-O-{(6R,8S,9R)-5,6,7,8,9,10-hexahydro-6,9-methanocyclohepto[b]indol-8-ylcarbonyl}-Lpodophyllotoxin on the carcinoma A549 cells proved its ability to cause full depolymerization of microtubules without curling effect at a concentration 10 μM. Cytotoxicity value of the compound estimated in MTT test was in a high nanomolar concentration interval (EC50=710±30 nM). Computer molecular docking of both isomers of novel compound and earlier synthesized podophyllotoxin esters with bridged moieties into the 3D model of the colchicine domain in alpha,beta-tubulin revealed the difference in positions of the bridge moieties of new compound and MT-curling ligands and allowed to hypothesize that the atypical action on MT might be caused by positioning of their bridge groups near the GTP binding site in alpha-tubulin.

A comprehensive review of topoisomerase inhibitors as anticancer agents in the past decade

The topoisomerase enzymes play an important role in DNA metabolism, and searching for enzyme inhibitors is an important target in the search for new anticancer drugs. Discovery of new anticancer chemotherapeutical capable of inhibiting topoisomerase enzymes is highlighted in anticancer research. Therefore, biologists, organic chemists and medicinal chemists all around the world have been identifying, designing, synthesizing and evaluating a variety of novel bioactive molecules targeting topoisomerase. This review summarizes types of topoisomerase inhibitors in the past decade, and divides them into nine classes by structural characteristics, including N-heterocycles compounds, quinone derivatives, flavonoids derivatives, coumarin derivatives, lignan derivatives, polyphenol derivatives, diterpenes derivatives, fatty acids derivatives, and metal complexes. Then we discussed the application prospect and development of these anticancer compounds, as well as concluded parts of their structural-activity relationships. We believe this review would be invaluable in helping to further search potential topoisomerase inhibition as antitumor agent in clinical usage.

Divergent Dynamic Kinetic Resolution of a Racemic Mixture of Four Stereoisomers via N-Heterocyclic Carbene Organocatalysis

Racemic mixtures of four stereoisomers are easily formed via many fundamental organic transformations, but the direct utilities of these mixtures have been less studied and remain large challenges to date. In this work, we introduce a new method, i.e., divergent dynamic kinetic resolution, to achieve the separation of racemic mixtures of four stereoisomers. The hypothesis was proved by using a N-heterocyclic carbene-catalyzed benzoin reaction, which afforded two separable diastereomeric products bearing three consecutive stereocenters with good to excellent enantioselectivties. We believe that this resolution protocol will find applications in more transformations.

Combined In Vitro Studies and in Silico Target Fishing for the Evaluation of the Biological Activities of Diphylleia cymosa and Podophyllum hexandrum

This paper reports the in silico prediction of biological activities of lignans from Diphylleia cymosa and Podophyllum hexandrum combined with an in vitro bioassays. The extracts from the leaves, roots and rhizomes of both species were evaluated for their antibacterial, anticholinesterasic, antioxidant and cytotoxic activities. A group of 27 lignans was selected for biological activities prediction using the Active-IT system with 1987 ligand-based bioactivity models. The in silico approach was properly validated and several ethnopharmacological uses and known biological activities were confirmed, whilst others should be investigated for new drugs with potential clinical use. The extracts from roots of D. cymosa and from rhizomes and roots of P. hexandrum were very effective against Bacillus cereus and Staphylococcus aureus, while podophyllotoxin inhibited the growth of Staphylococcus aureus and Escherichia coli. D. cymosa leaves and roots showed anticholinesterasic and antioxidant activities, respectively. The evaluated extracts showed to be moderately toxic to THP-1 cells. The chromatographic characterization indicated that podophyllotoxin was the major constituent of P. hexandrum extract while kaempferol and its hexoside were the main constituents of D. cymosa leaves and roots, respectively. These results suggest that the podophyllotoxin could be the major antibacterial lignan, while flavonoids could be responsible for the antioxidant activity.

Bulnesia sarmientoi Supercritical Fluid Extract Exhibits Necroptotic Effects and Anti-Metastatic Activity on Lung Cancer Cells

Bulnesia sarmientoi (BS) has long been used as an analgesic, wound-healing and anti-inflammatory medicinal plant. The aqueous extract of its bark has been demonstrated to have anti-cancer activity. This study investigated the anti-proliferative and anti-metastatic effects of BS supercritical fluid extract (BSE) on the A549 and H661 lung cancer cell lines. The cytotoxicity on cancer cells was assessed by an MTT assay. After 72 h treatment of A549 and H661 cells, the IC₅₀ values were 18.1 and 24.7 μg/mL, respectively. The cytotoxicity on MRC-5 normal cells was relatively lower (IC₅₀ = 61.1 μg/mL). BSE arrested lung cancer cells at the S and G₂/M growth phase. Necrosis of A549 and H661 cells was detected by flow cytometry with Annexin V-FITC/PI double staining. Moreover, the cytotoxic effect of BSE on cancer cells was significantly reverted by Nec-1 pretreatment, and BSE induced TNF-α and RIP-1 expression in the absence of caspase-8 activity. These evidences further support that BSE exhibited necroptotic effects on lung cancer cells. By wound healing and Boyden chamber assays, the inhibitory effects of BSE on the migration and invasion of lung cancer cells were elucidated. Furthermore, the chemical composition of BSE was examined by gas chromatography-mass analysis where ten constituents of BSE were identified. α-Guaiene, (−)-guaiol and β-caryophyllene are responsible for most of the cytotoxic activity of BSE against these two cancer cell lines. Since BSE possesses significant cytotoxicity and anti-metastatic activity on A549 and H661 cells, it may serve as a potential target for the treatment of lung cancer.

Anticancer Activity of Natural Compounds from Plant and Marine Environment

This paper describes the substances of plant and marine origin that have anticancer properties. The chemical structure of the molecules of these substances, their properties, mechanisms of action, their structure⁻activity relationships, along with their anticancer properties and their potential as chemotherapeutic drugs are discussed in this paper. This paper presents natural substances from plants, animals, and their aquatic environments. These substances include the vinca alkaloids, mistletoe plant extracts, podophyllotoxin derivatives, taxanes, camptothecin, combretastatin, and others including geniposide, colchicine, artesunate, homoharringtonine, salvicine, ellipticine, roscovitine, maytanasin, tapsigargin, and bruceantin. Compounds (psammaplin, didemnin, dolastin, ecteinascidin, and halichondrin) isolated from the marine plants and animals such as microalgae, cyanobacteria, heterotrophic bacteria, invertebrates (e.g., sponges, tunicates, and soft corals) as well as certain other substances that have been tested on cells and experimental animals and used in human chemotherapy.