Wai-Leng Lee

Phytoagents for Cancer Management: Regulation of Nucleic Acid Oxidation, ROS, and Related Mechanisms

Accumulation of oxidized nucleic acids causes genomic instability leading to senescence, apoptosis, and tumorigenesis. Phytoagents are known to reduce the risk of cancer development; whether such effects are through regulating the extent of nucleic acid oxidation remains unclear. Here, we outlined the role of reactive oxygen species in nucleic acid oxidation as a driving force in cancer progression. The consequential relationship between genome instability and cancer progression highlights the importance of modulation of cellular redox level in cancer management. Current epidemiological and experimental evidence demonstrate the effects and modes of action of phytoagents in nucleic acid oxidation and provide rationales for the use of phytoagents as chemopreventive or therapeutic agents. Vitamins and various phytoagents antagonize carcinogen-triggered oxidative stress by scavenging free radicals and/or activating endogenous defence systems such as Nrf2-regulated antioxidant genes or pathways. Moreover, metal ion chelation by phytoagents helps to attenuate oxidative DNA damage caused by transition metal ions. Besides, the prooxidant effects of some phytoagents pose selective cytotoxicity on cancer cells and shed light on a new strategy of cancer therapy. The “double-edged sword” role of phytoagents as redox regulators in nucleic acid oxidation and their possible roles in cancer prevention or therapy are discussed in this review.

Deoxyelephantopin impedes mammary adenocarcinoma cell motility by inhibiting calpain-mediated adhesion dynamics and inducing reactive oxygen species and aggresome formation.

We previously showed that deoxyelephantopin (DET), a plant sesquiterpene lactone, exhibits more profound suppression than paclitaxel (PTX) of lung metastasis of mammary adenocarcinoma TS/A cells in mice. Proteomics studies suggest that DET affects actin cytoskeletal protein networks and downregulates calpain-mediated proteolysis of several actin-associated proteins, whereas PTX mainly interferes with microtubule proteins. Here, DET was observed to significantly deregulate adhesion formation in TS/A cells, probably through inhibition of m-calpain activity. Epithelial growth factor (EGF)-mediated activation of Rho GTPase Rac1 and formation of lamellipodia in TS/A cells were remarkably suppressed by DET treatment. Further, DET impaired vesicular trafficking of EGF and induced protein carbonylation and formation of centrosomal aggregates in TS/A cells. DET-induced reactive oxygen species were observed to be the upstream stimulus for the formation of centrosomal ubiquitinated protein aggregates that might subsequently restrict cancer cell motility. PTX, however, caused dramatic morphological changes, interfered with microtubule networking, and moderately inhibited calpain-mediated cytoskeletal and focal adhesion protein cleavage in TS/A cells. This study provides novel mechanistic insights into the pharmacological action of DET against metastatic mammary cell migration and suggests that modulation of oxidative stress might be a potential strategy for treatment of metastatic breast cancer.

Novel sesquiterpene lactone analogues as potent anti-breast cancer agents

Triple‐negative breast cancer (TNBC) is associated with high grade, metastatic phenotype, younger patient age, and poor prognosis. The discovery of an effective anti‐TNBC agent has been a challenge in oncology. In this study, fifty‐eight ester derivatives (DETDs) with a novel sesquiterpene dilactone skeleton were organically synthesized from a bioactive natural product deoxyelephantopin (DET). Among them, DETD‐35 showed potent antiproliferative activities against a panel of breast cancer cell lines including TNBC cell line MDA‐MB‐231, without inhibiting normal mammary cells M10. DETD‐35 exhibited a better effect than parental DET on inhibiting migration, invasion, and motility of MDA‐MB‐231 cells in a concentration‐dependent manner. Comparative study of DETD‐35, DET and chemotherapeutic drug paclitaxel (PTX) showed that PTX mainly caused a typical time‐dependent G2/M cell‐cycle arrest, while DETD‐35 or DET treatment induced cell apoptosis. In vivo efficacy of DETD‐35 was evaluated using a lung metastatic MDA‐MB‐231 xenograft mouse model. DETD‐35 significantly suppressed metastatic pulmonary foci information along with the expression level of VEGF and COX‐2 in SCID mice. DETD‐35 also showed a synergistic antitumor effect with PTX in vitro and in vivo. This study suggests that the novel compound DETD‐35 may have a potential to be further developed into a therapeutic or adjuvant agent for chemotherapy against metastatic TNBC.

Novel effect and the mechanistic insights of fruiting body extract of medicinal fungus Antrodia cinnamomea against T47D breast cancer.

INTRODUCTION Tamoxifen, an anti-oestrogenic drug for estrogen receptor positive (ER+) breast cancer, was observed to stimulate tumor growth or drug resistance in patients. Antrodia cinnamomea (AC), a precious medicinal fungus has been traditionally used as a folk remedy for cancers in Asian countries. The objective of this study was to investigate the bioefficacy and the underlying molecular mechanisms of the AC fruiting bodies extracts (AC-3E) against human ER+ T47D breast cancer cells, and compare the effect with that of tamoxifen. METHODS Cell proliferation, migration, TUNEL assay, western blotting, time-lapse confocal microscopy analyses, chorioallantoic membrane assay, and a xenograft BALB/c nude mouse system were used in this study. Chemical fingerprinting of AC-3E was established using LC-MS. RESULTS AC-3E attenuated T47D breast cancer cell activity by deregulating the PI3K/Akt/mTOR signaling pathway and key cell-cycle mediators, and inducing apoptosis. AC-3E also effectively inhibited tube-like structures of endothelial cells, blood vessel branching and microvessel formation ex vivo and in vivo. Significant preventive and therapeutic effects against T47D mammary tumor growth of AC-3E was observed comparable or superior to tamoxifen treatment in xenograft BALB/c nude mice. Dehydroeburicoic acid (2) was characterized as the main chemical constituent in AC-3E against breast cancer. CONCLUSION This study suggests that AC-3E extracts can be employed as a double-barreled approach to treat human ER+ breast cancer by attacking both cancer cells and tumor-associated blood vessel cells.

Targeting Membrane Lipid a Potential Cancer Cure

Cancer mortality and morbidity is projected to increase significantly over the next few decades. Current chemotherapeutic strategies have significant limitations, and there is great interest in seeking novel therapies which are capable of specifically targeting cancer cells. Given that fundamental differences exist between the cellular membranes of healthy cells and tumor cells, novel therapies based on targeting membrane lipids in cancer cells is a promising approach that deserves attention in the field of anticancer drug development. Phosphatidylethanolamine (PE), a lipid membrane component which exists only in the inner leaflet of cell membrane under normal circumstances, has increased surface representation on the outer membrane of tumor cells with disrupted membrane asymmetry. PE thus represents a potential chemotherapeutic target as the higher exposure of PE on the membrane surface of cancer cells. This feature as well as a high degree of expression of PE on endothelial cells in tumor vasculature, makes PE an attractive molecular target for future cancer interventions. There have already been several small molecules and membrane-active peptides identified which bind specifically to the PE molecules on the cancer cell membrane, subsequently inducing membrane disruption leading to cell lysis. This approach opens up a new front in the battle against cancer, and is of particular interest as it may be a strategy that may be prove effective against tumors that respond poorly to current chemotherapeutic agents. We aim to highlight the evidence suggesting that PE is a strong candidate to be explored as a potential molecular target for membrane targeted novel anticancer therapy.

An Overview of the Current Development of Phytoremedies for Breast Cancer

Breast cancer is one of the main causes of death by cancer in women, with an alarming year-by-year increase in incidence. Conventional cancer therapies, including surgery, radiotherapy, chemotherapy, endocrine therapy, and targeted therapy, play an important role in the treatment of breast cancer; however, drug resistance, severe side effect, and high recurrent rate significantly limit the effectiveness of current clinical treatments. Plant-based system has been used for treatment or prevention of various human diseases throughout history. The pressing need for development of new therapeutic or preventive agents for breast cancer has spurred the search for bioactive phytocompounds with novel modes of action. In this chapter, we review the current limitation of conventional chemo- or targeted-therapeutic drugs for breast cancer, and summarize some potential novel phytoagents discovered from dietary vegetables or traditional herbal medicines as alternative options or future medicine for breast cancer. We explore the mechanistic insights of these natural phytoagents against various types of breast cancer and discuss their therapeutic potential, alone or in combination, with current clinical drugs.

Chapter 4 - Taxol, Camptothecin and Beyond for Cancer Therapy

Abstract Plants produce a remarkably diverse array of metabolites, many of which have evolved to confer effectiveness against microbial attack, resist environmental stress or function as signalling molecules in interplant communication. Further, botanical preparations have been used for treating and preventing various human diseases throughout history. More than half of the current anti-cancer drugs in clinical use are natural products or their derivatives, and many are plant-derived agents. Two renowned examples of plant-based drugs used for humans are paclitaxel and camptothecin (CPT). Paclitaxel (taxol), originally identified from Pacific yew Taxus brevifolia Nutt, and its semi-synthesized analogues docetaxel (Taxotere®), and CPT, originally identified from Camptotheca acuminata Decne, a native tree to China, as well as its more water-soluble derivatives topotecan (Hycamtin) and irinotecan or CPT-11 (Camptosar), are used as chemotherapeutic drugs for various cancers. This review offers a current and integrative account of the two representative chemotherapeutic phytoagents paclitaxel and CPT in terms of their discovery, development of authentic compounds and improvement by synthetic chemistry approaches, as well as their mechanisms of action and clinical applications. We also discuss the bench-side or clinically observed drug resistance and adverse side effects of both drugs, which are the major drawbacks to their use for cancer. Despite intensive efforts and substantial advances in improving treatment, cancer is still a life-threatening and leading cause of death, especially with recurring, metastatic or drug-resistant tumours. The successful experiences with the discovery and development of paclitaxel and CPT as anti-cancer drugs have been significant milestones for the design of alternative strategies and remedies from plant-derived agents in cancer management.

Copper supplementation amplifies the anti-tumor effect of curcumin in oral cancer cells

BACKGROUND Oral cancer is the sixth most common cancer worldwide and 90% of oral malignancies are caused by oral squamous cell carcinoma (OSCC). Curcumin, a phytocompound derived from turmeric (Curcuma longa) was observed to have anti-cancer activity which can be developed as an alternative treatment option for OSCC. However, OSCC cells with various clinical-pathological features respond differentially to curcumin treatment. HYPOTHESIS Intracellular copper levels have been reported to correlate with tumor pathogenesis and affect the sensitivity of cancer cells to cytotoxic chemotherapy. We hypothesized that intracellular copper levels may affect the sensitivity of oral cancer cells to curcumin. METHODS We analysed the correlation between intracellular copper levels and response to curcumin treatment in a panel of OSCC cell lines derived from oral cancer patients. Exogenous copper was supplemented in curcumin insensitive cell lines to observe the effect of copper on curcumin-mediated inhibition of cell viability and migration, as well as induction of oxidative stress and apoptosis. Protein markers of cell migration and oxidative stress were also analysed using Western blotting. RESULTS Concentrations of curcumin which inhibited 50% OSCC cell viability (IC50) was reduced up to 5 times in the presence of 250 µM copper. Increased copper level in curcumin-treated OSCC cells was accompanied by the induction of intracellular ROS and increased level of Nrf2 which regulates oxidative stress responses in cells. Supplemental copper also inhibited migration of curcumin-treated cells with enhanced level of E-cadherin and decreased vimentin, indications of suppressed epithelial-mesenchymal transition. Early apoptosis was observed in combined treatment but not in treatment with curcumin or copper alone. CONCLUSION Supplement of copper significantly enhanced the inhibitory effect of curcumin treatment on migration and viability of oral cancer cells. Together, these findings provide molecular insight into the role of copper in overcoming insensitivity of oral cancer cells to curcumin treatment, suggesting a new strategy for cancer therapy.

Gastrointestinal Bezoar Stones: Current Knowledge and Future Perspective on the Potential of Plant-Derived Phytobezoar in Cancer Treatment

Bezoar stone formation is an infrequent event in the gastrointestinal (GI) system due to the chemical reaction between stomach bile and the high intake of nondigestible food materials. There are mainly four types of GI bezoars: trichobezoar, lactobezoar, pharmacobezoar, and phytobezoar, and formations of these bezoars in humans are physical disorders which require clinical treatments. Intriguingly, phytobezoars such as Calculus bovis obtained from ox/cattle have been used in China as medicine since 2000 years ago. Modern science found C. bovis possesses antioxidant and anti-inflammatory properties, and identification of its chemical constituent led to successful synthesis of the artificial medicinal bezoar. Phytobezoars, major type of GI bezoar, can also be found in animals besides ox/cattle, and these bezoars have been traditionally used to treat against poison, and more recently those obtained from porcupines are used by Asian Chinese to treat cancer. However, to date, medicinal values of porcupine bezoars lack scientific proof. Therefore, understanding on the factors that lead to bezoar formation in the GI tract, identification of their chemical composition, and elucidation of underlying physiological mechanism modulated by phytobezoars are important to provide guidance in their usage in treating various ailments including cancer. In this chapter, the development of different bezoar stones in the GI tract is summarized on the pharmacological action of phytobezoars C. bovis, and porcupine bezoar is presented on the medicinal values of these phytobezoars. Moreover, distinct composition and classification of plant materials found in the phytobezoars and their potential benefits in cancer treatment are also discussed.

Antioxidant and intracellular reactive oxygen species/reactive nitrogen species scavenging activities of three porcupine bezoars from Hystrix brachyura

Background: Porcupine dates are phytobezoar stones that are used in Traditional Chinese Medicine (TCM) treatments against cancer, postsurgical recovery, dengue fever, etc. The medicinal values have not been scientifically investigated due to the availability and high pricing of the dates. Objectives: This paper represents the first report on the phytochemical content, in vitro antioxidant and intracellular reactive oxygen species (ROS)/reactive nitrogen species (RNS) scavenging properties of the extracts of three porcupine dates: grassy date (GD), black date (BD), and powdery date (PD). Materials and Methods: Dried samples were extracted with methanol and lyophilized. Samples were screened for phytochemical constituents, in vitro antioxidant assays based on total phenolic content (TPC), free radical scavenging, and ferric reducing power (FRP) as well as intracellular ROS and RNS scavenging properties. Results: Phytochemical screening and total tannins assay revealed that tannins, cardiac glycosides, and terpenoids were found in all porcupine dates with tannins forming the major portion of the TPC. In comparison to GD, BD and PD were found to contain significantly high TPC, radical scavenging activity, and FRP. At 200 μg/ml, BD and PD remarkably scavenged 2, 2-azobis (2-amidinopropane) dihydrochloride-induced ROS in RAW264.7 cells and significantly reduced nitric oxide in lipopolysaccharide-stimulated cells. Conclusion: Overall, BD and PD exhibited promising in vitro antioxidant as well as intracellular ROS/RNS scavenging properties. Abbreviations Used: TCM: Traditional Chinese Medicine, BD: Black date, GD: Grassy date, PD: Powdery date, TPC: Total phenolic content, FRS: Free radical scavenging, FRP: Ferric reducing power, NO: Nitric oxide, ROS: Reactive oxygen species, RNS: Reactive nitrogen species, GAE: Gallic acid equivalent, AAE: Ascorbic acid equivalent, PVPP: Polyvinylpolypyrrolidone, DCFH-DA: Dichloro-dihydro-fluorescein diacetate, AAPH: 2, 2-azobis (2-amidinopropane) dihydrochloride, LPS: Lipopolysaccharide