Conjugates of podophyllotoxin and norcantharidin as dual inhibitors of topoisomeraseⅡ and protein phosphatase 2A

Strategies for Solubility and Bioavailability Enhancement and Toxicity Reduction of Norcantharidin

Cantharidin (CTD) is the main active ingredient isolated from Mylabris, and norcantharidin (NCTD) is a demethylated derivative of CTD, which has similar antitumor activity to CTD and lower toxicity than CTD. However, the clinical use of NCTD is limited due to its poor solubility, low bioavailability, and toxic effects on normal cells. To overcome these shortcomings, researchers have explored a number of strategies, such as chemical structural modifications, microsphere dispersion systems, and nanodrug delivery systems. This review summarizes the structure-activity relationship of NCTD and novel strategies to improve the solubility and bioavailability of NCTD as well as reduce the toxicity. This review can provide evidence for further research of NCTD.

Design and Synthesis of Novel Podophyllotoxins Hybrids and the Effects of Different Functional Groups on Cytotoxicity

Development of novel anticancer therapeutic candidates is one of the key challenges in medicinal chemistry. Podophyllotoxin and its derivatives, as a potent cytotoxic agent, have been at the center of extensive chemical amendment and pharmacological investigation. Herein, a new series of podophyllotoxin-N-sulfonyl amidine hybrids (4a–4v, 5a–5f) were synthesized by a CuAAC/ring-opening procedure. All the synthesized podophyllotoxins derivatives were evaluated for in vitro cytotoxic activity against a panel of human lung (A-549) cancer cell lines. Different substituents’, or functional groups’ antiproliferative activities were discussed. The –CF₃ group performed best (IC₅₀: 1.65 μM) and exhibited more potent activity than etoposide. Furthermore, molecular docking and dynamics studies were also conducted for active compounds and the results were in good agreement with the observed IC₅₀ values.

Identification of novel topoisomerase II alpha inhibitors by virtual screening, molecular docking, and bioassay

Breast cancer is one of the most common tumors, and its treatment still leaves room for improvement. Topoisomerase II alpha is a potential target for the treatment of human diseases such as breast cancer. In this article, we attempted to discover a novel anticancer drug. We have used the topoisomerase II alpha protein-Homo sapiens (Human) to hierarchically screen the Maybridge database. Based on their docking score, the top hit compounds have been assayed for inhibition in a topoisomerase II pBR322 DNA relaxation assay in vitro. Candidate compound 6 (CP6) was found to have the best inhibitory effect for topoisomerase II among the 20 tested compounds. In addition, CP6 had potent cytotoxicity against eight tested tumor cell lines. At the same time, CP6 was shown to have potential anti-multidrug resistance capabilities. This study identifies CP6, which can contribute to the development of new topoisomerase II inhibitors as anticancer agents.

Antifungal Activity and DNA Topoisomerase Inhibition of Hydrolysable Tannins from Punica granatum L

Punica granatum L. (pomegranate) fruit is known to be an important source of bioactive phenolic compounds belonging to hydrolysable tannins. Pomegranate extracts have shown antifungal activity, but the compounds responsible for this activity and their mechanism/s of action have not been completely elucidated up to now. The aim of the present study was the investigation of the inhibition ability of a selection of pomegranate phenolic compounds (i.e., punicalagin, punicalin, ellagic acid, gallic acid) on both plant and human fungal pathogens. In addition, the biological target of punicalagin was identified here for the first time. The antifungal activity of pomegranate phenolics was evaluated by means of Agar Disk Diffusion Assay and minimum inhibitory concentration (MIC) evaluation. A chemoinformatic analysis predicted for the first time topoisomerases I and II as potential biological targets of punicalagin, and this prediction was confirmed by in vitro inhibition assays. Concerning phytopathogens, all the tested compounds were effective, often similarly to the fungicide imazalil at the label dose. Particularly, punicalagin showed the lowest MIC for Alternaria alternata and Botrytis cinerea, whereas punicalin was the most active compound in terms of growth control extent. As for human pathogens, punicalagin was the most active compound among the tested ones against Candida albicans reference strains, as well as against the clinically isolates. UHPLC coupled with HRMS indicated that C. albicans, similarly to the phytopathogen Coniella granati, is able to hydrolyze both punicalagin and punicalin as a response to the fungal attack. Punicalagin showed a strong inhibitory activity, with IC₅₀ values of 9.0 and 4.6 µM against C. albicans topoisomerases I and II, respectively. Altogether, the results provide evidence that punicalagin is a valuable candidate to be further exploited as an antifungal agent in particular against human fungal infections.

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.

Novel Aza-podophyllotoxin derivative induces oxidative phosphorylation and cell death via AMPK activation in triple-negative breast cancer

BACKGROUND

To circumvent Warburg effect, several clinical trials for different cancers are utilising a combinatorial approach using metabolic reprogramming and chemotherapeutic agents including metformin. The majority of these metabolic interventions work via indirectly activating AMP-activated protein kinase (AMPK) to alter cellular metabolism in favour of oxidative phosphorylation over aerobic glycolysis. The effect of these drugs is dependent on glycaemic and insulin conditions.  Therefore, development of small molecules, which can activate AMPK, irrespective of the energy state, may be a better approach for triple-negative breast cancer (TNBC) treatment.

METHODS

Therapeutic effect of SU212 on TNBC cells was examined using in vitro and in vivo models.

RESULTS

We developed and characterised the efficacy of novel AMPK activator (SU212) that selectively induces oxidative phosphorylation and decreases glycolysis in TNBC cells, while not affecting these pathways in normal cells.   SU212 accomplished this metabolic reprogramming by activating AMPK independent of energy stress and irrespective of the glycaemic/insulin state. This leads to mitotic phase arrest and apoptosis in TNBC cells. In vivo, SU212 inhibits tumour growth, cancer progression and metastasis.

CONCLUSIONS

SU212 directly activates AMPK in TNBC cells, but does not hamper glucose metabolism in normal cells. Our study provides compelling preclinical data for further development of SU212 for the treatment of TNBC.

Antitumor potential of the protein phosphatase inhibitor, cantharidin, and selected derivatives

Cantharidin is a potent natural protein phosphatase monoterpene anhydride inhibitor secreted by several species of blister beetle, with its demethylated anhydride analogue, (S)-palasonin, occurring as a constituent of the higher plant Butea frondosa. Cantharidin shows both potent protein phosphatase inhibitory and cancer cell cytotoxic activities, but possible preclinical development of this anhydride has been limited thus far by its toxicity. Thus, several synthetic derivatives of cantharidin have been prepared, of which some compounds exhibit improved antitumor potential and may have use as lead compounds. In the present review, the potential antitumor activity, structure-activity relationships, and development of cantharidin-based anticancer drug conjugates are summarized, with protein phosphatase-related and other types of mechanisms of action discussed. Protein phosphatases play a key role in the tumor microenvironment, and thus described herein is also the potential for developing new tumor microenvironment-targeted cancer chemotherapeutic agents, based on cantharidin and its naturally occurring analogues and synthetic derivatives.

Norcantharidin: research advances in pharmaceutical activities and derivatives in recent years

Cantharidin (CTD) is the main bioactive component of Cantharides, which is called Banmao in Traditional Chinese Medicine (TCM). Norcantharidin (NCTD) is a structural modifier of CTD. To compare with CTD, NCTD has lighter side effects and stronger bioactivity in anti-cancer through inhibiting cell proliferation, causing apoptosis and autophagy, overwhelming migration and metastasis, affecting immunity as well as lymphangiogenesis. Examples of these effects include suppressing Protein Phosphatase 2A and modulating Wnt/beta catenin signal, with Caspase family proteins, AMPK pathway and c-Met/EGFR pathway involving respectively. Moreover, NCTD has the effects of immune enhancement, anti-platelet aggregation and inhibition of renal interstitial fibrosis with distinct signaling pathways. The immunological effects induced by NCTD are related to the regulation of macrophage polarization and LPS-mediated immune response. The antiplatelet activity that NCTD induced is relevant to the inhibition of platelet signaling and the downregulation of α2 integrin. Furthermore, some of novel derivatives designed and synthesized artificially show stronger biological activities (e.g., anticancer effect, enzyme inhibition effect, antioxidant effect) and lower toxicity than NCTD itself. Plenty of literatures have reported various pharmacological effects of NCTD, particularly the anticancer effect, which has been widely concerned in clinical application and laboratory research. In this review, the pharmaceutical activities and derivatives of NCTD are discussed, which can be reference for further study.

Recent advances of podophyllotoxin/epipodophyllotoxin hybrids in anticancer activity, mode of action, and structure-activity relationship: An update (2010-2020)

Podophyllotoxins and epipodophyllotoxins, possess excellent activity against both drug-sensitive and drug-resistant even multidrug-resistant cancer cells via inhibition of tubulin polymerization. Several podophyllotoxin/epipodophyllotoxin derivatives such as etoposide and teniposide have already been applied for cancer therapy, revealing their potential as putative anticancer drugs. Hybridization of podophyllotoxin/epipodophyllotoxin moiety with other anticancer pharmacophores is a promising strategy to develop novel drug candidates so as to overcome drug resistance and improve the specificity, and numerous of podophyllotoxin/epipodophyllotoxin hybrids exhibit excellent in vitro antiproliferative and in vivo anticancer potency. This review emphasizes the recent development of podophyllotoxin/epipodophyllotoxin hybrids with potential application for cancer therapy covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design as well as structure-activity relationships were also summarized.

Radiosensitization of Head and Neck Squamous Cell Carcinoma (HNSCC) by a Podophyllotoxin

Surgical resection and radiotherapy are an effective treatment in many head and neck squamous cell carcinomas (HNSCC), but in others, the development of radiotherapy resistance limits treatment efficacy and permits disease progression. We developed a novel multiwell radiation dosing method to increase the throughput of our investigation of the activity of a novel podophyllotoxin SU093 in acting as a radiosensitizer in the HNSCC models FaDu and SCC-25. These in vitro studies showed that combining SU093 with 5 Grays ionizing radiation acted synergistically to increase HNSCC apoptosis and decrease its proliferation via inhibition of Nuclear factor, erythroid 2 like 2 (Nrf2), a key effector of the DNA damage response induced by ionizing radiation. Combined treatment reduced in vitro migration in a simulated wounding model while also promoting cell cycle arrest at the G2/M phase. These findings validate the potential of SU093 as a synergistic radiosensitizing agent for use in combination with localized radiotherapy in treatment resistant HNSCC.

Podophyllotoxin derivatives as an excellent anticancer aspirant for future chemotherapy: A key current imminent needs

Cancer is one of the leading groups of threatened caused by abnormal state cell growth and second leading diseases involved in the major global death. To treat this, research looking for promising anticancer drugs from natural resource, or synthesized novel molecules by diverse group of scientists worldwide. Currently, drugs get into clinical practices and showing side effects with target actions which in turn leading to multidrug resistance unknowingly. Podophyllotoxin, a naturally occurring lignan and with hybrids have become one of the most attractive subjects due to their broad spectrum of pharmacological activities. Podophyllotoxin derivatives have been the centre of attention of extensive chemical amendment and pharmacological investigation in modern decades. Mainly, the innovation of the semi-synthetic anticancer drugs etoposide and teniposide has stimulated prolonged research interest in this structural phenotype. The present review focuses mainly onnew anticancer drugs from podophyllotoxin analogs, mechanism of action and their structure-activity relationships (SAR) as potential anticancer candidates for future discovery of suitable drug candidates.