Gambogic acid as a non-competitive inhibitor of ATP-binding cassette transporter B1 reverses the multidrug resistance of human epithelial cancers by promoting ATP-binding cassette transporter B1 protein degradation

Non-Nutritive Sweeteners Acesulfame Potassium and Sucralose Are Competitive Inhibitors of the Human P-glycoprotein/Multidrug Resistance Protein 1 (PGP/MDR1)

Non-nutritive sweeteners (NNS) are popular sugar replacements used in foods, beverages, and medications. Although NNS are considered safe by regulatory organizations, their effects on physiological processes such as detoxification are incompletely understood. Previous studies revealed that the NNS sucralose (Sucr) altered P-glycoprotein (PGP) expression in rat colon. We also demonstrated that early-life exposure to NNS Sucr and acesulfame potassium (AceK) compromises mouse liver detoxification. Building upon these initial discoveries, we investigated the impact of AceK and Sucr on the PGP transporter in human cells to assess whether NNS influence its key role in cellular detoxification and drug metabolism. We showed that AceK and Sucr acted as PGP inhibitors, competing for the natural substrate-binding pocket of PGP. Most importantly, this was observed after exposure to concentrations of NNS within expected levels from common foods and beverage consumption. This may suggest risks for NNS consumers, either when taking medications that require PGP as the primary detoxification transporter or during exposure to toxic compounds.

The combination of nanotechnology and traditional Chinese medicine (TCM) inspires the modernization of TCM: review on nanotechnology in TCM-based drug delivery systems

Fast development of combination of nanotechnology with traditional Chinese medicine (TCM) broadens the field of application of TCM. Besides, it increases the research ideas and contributes to TCM modernization. As expected, TCM will be developed into the nanodrug delivery system by nanotechnology with careful design, which will enhance the medicinal value of TCM to cure and prevent disease based on benefits brought by nanometer scale. Here, formulations, relevant preparations methods, and characteristics of nano-TCM were introduced. In addition, the main excellent performances of nano-TCM were clearly elaborated. What is more, the review was intended to address the studies committed to application of nanotechnology in TCM over the years, including development of Chinese medicine active ingredients, complete TCM, and Chinese herbal compounds based on nanotechnology. Finally, this review discussed the safety of nano-TCM and presented future development trends in the way to realize the modernization of TCM. Overall, using the emerging nanotechnology in TCM is promising to promote progress of TCM in international platform. Recent researches on modernization of traditional Chinese medicine (TCM) urged by nanotechnology are introduced, and formulations, advantages, and applications of nano-TCM are reviewed to provide strong proofs.

Xanthones as P-glycoprotein modulators and their impact on drug bioavailability

Introduction: P-glycoprotein (P-gp) is an important efflux pump responsible for the extruding of many endogenous and exogenous substances out of the cells. P-gp can be modulated by different molecules - including xanthone derivatives - to surpass the multidrug resistance (MDR) phenomenon through P-gp inhibition, or to serve as an antidotal strategy in intoxication scenarios through P-gp induction/activation.Areas covered: This review provides a perspective on P-gp modulators, with particular focus on xanthonic derivatives, highlighting their ability to modulate P-gp expression and/or activity, and the potential impact of these effects on the pharmacokinetics, pharmacodynamics and toxicity of P-gp substrates.Expert opinion: Xanthones, of natural or synthetic origin, are able to modulate P-gp, interfering with its protein synthesis or with its mechanism of action, by decreasing or increasing its efflux capacity. These modulatory effects make the xanthonic scaffold a promising source of new derivatives with therapeutic potential. However, the mechanisms beyond the xanthones-mediated P-gp modulation and the chemical characteristics that make them more potent P-gp inhibitors or inducers/activators are still understudied. Furthermore, a new window of opportunity exists in the neuropathologies field, where xanthonic derivatives with potential to modulate P-gp should be further explored to optimize the prevention/treatment of brain pathologies.

Ligand decorated biodegradable nanomedicine in the treatment of cancer

Cancer is one of the major global health problems, responsible for the second-highest number of deaths. The genetic and epigenetic changes in the oncogenes or tumor suppressor genes alter the regulatory pathways leading to its onset and progression. Conventional methods are used in appropriate combinations for the treatment. Surgery effectively treats localized tumors; however, it fails to treat metastatic tumors, leading to a spread in other organs, causing a high recurrence rate and death. Among the different strategies, the nanocarriers-based approach is highly sought for, but its nonspecific delivery can cause a profound side effect on healthy cells. Targeted nanomedicine has the advantage of targeting cancer cells specifically by interacting with the receptors overexpressed on their surface, overcoming its non-specificity to target healthy cells. Nanocarriers prepared from biodegradable and biocompatible materials are decorated with different ligands by encapsulating therapeutic or diagnostic agents or both to target cancer cells overexpressing the receptors. Scientists are now utilizing a theranostic approach to simultaneously evaluate nanocarrier bio-distribution and its effect on the treatment regime. Herein, we have summarized the recent 5-year efforts in the development of the ligands decorated biodegradable nanocarriers, as a targeted nanomedicine approach, which has been highly promising in the treatment of cancer.

CD44 targeted redox-triggered self-assembly with magnetic enhanced EPR effects for effective amplification of gambogic acid to treat triple-negative breast cancer

Gambogic acid (GA) is a natural anti-tumor drug whose application is restricted by its poor aqueous solubility and inefficient bioavailability. Developing nanomaterials with excellent biocompatibility can amplify the therapeutic effects of GA. In this study, a tumor-targeted redox controllable self-assembled nano-system with magnetic enhanced EPR effects (mPEG-HA/CSO-SS-Hex/SPION/GA) was developed to improve the anticancer efficacy of GA. The nano-system is constituted by three layers: the outer layer is mono-aminated poly(ethylene glycol) grafted hyaluronic acid (mPEG-HA), which can target the CD44 receptor in breast cancer cells; the middle layer consists of disulfide linked hexadecanol (Hex) and chitosan oligosaccharide (CSO) to control the drug release by reduction response; the core layer is superparamagnetic iron oxide nanoparticles (SPION), which can enhance the EPR effect by magnetic guidance and contribute to GA entrapment. Different experiments were performed to characterize the complex self-assembly, and the cytotoxicity, pharmacokinetics, and in vivo antitumor activity of the self-assembly were investigated to evaluate its anti-tumor effects. The results revealed that mPEG-HA/CSO-SS-Hex/SPION/GA is an excellent nanosystem with appropriate size and sensitive responsiveness; it can accumulate in tumor sites and achieve excellent therapeutic effects on triple-negative breast cancer (TNBC). In summary, a CD44-targeted redox-triggered self-assembly nanosystem with magnetic enhanced EPR effects was developed for effective amplification of GA; it has potential to act as an effective carrier in drug delivery for chemotherapy of TNBC.

Dual Inhibitors as a New Challenge for Cancer Multidrug Resistance Treatment

BACKGROUND

Dual-targeting in cancer treatment by a single drug is an unconventional approach in relation to drug combinations. The rationale for the development of dualtargeting agents is to overcome incomplete efficacy and drug resistance frequently present when applying individual targeting agents. Consequently, -a more favorable outcome of cancer treatment is expected with dual-targeting strategies.

METHODS

We reviewed the literature, concentrating on the association between clinically relevant and/or novel dual inhibitors with the potential to modulate multidrug resistant phenotype of cancer cells, particularly the activity of P-glycoprotein. A balanced analysis of content was performed to emphasize the most important findings and optimize the structure of this review.

RESULTS

Two-hundred and forty-five papers were included in the review. The introductory part was interpreted by 9 papers. Tyrosine kinase inhibitors' role in the inhibition of Pglycoprotein and chemosensitization was illustrated by 87 papers. The contribution of naturalbased compounds in overcoming multidrug resistance was reviewed using 92 papers, while specific dual inhibitors acting against microtubule assembling and/or topoisomerases were described with 55 papers. Eleven papers gave an insight into a novel and less explored approach with hybrid drugs. Their influence on P-glycoprotein and multidrug resistance was also evaluated.

CONCLUSION

These findings bring into focus rational anticancer strategies with dual-targeting agents. Most evaluated synthetic and natural drugs showed a great potential in chemosensitization. Further steps in this direction are needed for the optimization of anticancer treatment.

Gambogic acid increases the sensitivity to paclitaxel in drug‑resistant triple‑negative breast cancer via the SHH signaling pathway

Paclitaxel is the most frequently used therapy regimen for triple-negative breast cancer (TNBC). However, chemoresistance frequently occurs, leading to enhanced failure rates of chemotherapy in TNBC; therefore, novel biological therapies are urgently needed. Gambogic acid (GA) has potent anticancer effects and inhibits tumor growth in several types of human cancer. However, the effects of GA on paclitaxel-resistant TNBC remain unknown. In the present study, the Cell Counting Kit-8 assay was used to examine the effect of GA and/or paclitaxel on the viability of TNBC cells; flow cytometry was used to examine the effects of GA on cell apoptosis; and western blotting and reverse transcription-quantitative PCR were used to determine the effects of GA on the expression of sonic hedgehog (SHH) signaling pathway target genes. The present results indicated that GA significantly inhibited the viability and enhanced the rate of apoptosis in paclitaxel-resistant MDA-MB-231 cells via activating the SHH signaling pathway. In vivo experiments confirmed that GA treatment enhanced the sensitivity of MDA-MB-231 cells to paclitaxel via the SHH signaling pathway. In conclusion, the combination of GA with paclitaxel may increase the antitumor effects on paclitaxel-resistant TNBC via downregulating the SHH signaling pathway.

A novel redox/pH dual-responsive and hyaluronic acid-decorated multifunctional magnetic complex micelle for targeted gambogic acid delivery for the treatment of triple negative breast cancer

Gambogic acid (GA) is a naturally derived potent anticancer agent with extremely poor biocompatibility. In the present study, a novel of redox/pH dual-responsive multifunctional magnetic complex micelle (sPEG/HA/CSO-SS-Hex/Fe₃O₄/GA), which consisted of a reducible hexadecanol-modified chitosan oligosaccharide polymer micelle (CSO-SS-Hex) coated with hyaluronic acid (HA) and DCA grafted sheddable PEG-PLL (sPEG) copolymers and loaded with gambogic acid (GA) and Fe₃O₄ nanoparticles were developed for parenteral delivery for the treatment of triple negative breast cancer (TNBC). The ex vivo study showed that the sPEG shielded cationic HA/CSO-SS-Hex/Fe₃O₄/GA core at physiological pH but quickly shed off to re-expose the core due to its charge reversible property. The sPEG/HA/CSO-SS-Hex/Fe₃O₄/GA micelles effectively facilitated tumor-targeted GA delivery by HA, which is a targeting ligand for CD44 receptor of TNBC cells, meanwhile increase GA uptake at the acidic condition but diminished the drug uptake at neutral pH. The in vitro cellular uptake study and in vivo biodistribution and antitumor activity of the formulations were determined, all results showed that the complex micelle enhanced TNBC tumor cellular uptake and fast drug release due to the combined effect of magnet targeting, CD44 receptor-mediated internalization and redox/pH dual-responsive drug release. Hence, tumor-targeted delivery of GA with redox/pH dual-responsive multifunctional magnetic complex micelle sPEG/HA/CSO-SS-Hex/Fe₃O₄/GA might have potential implications for the chemotherapy of TNBC.

Hyaluronic acid-decorated redox-sensitive chitosan micelles for tumor-specific intracellular delivery of gambogic acid

Introduction: Herein, a hyaluronic acid (HA)-coated redox-sensitive chitosan-based nanoparticle, HA(HECS-ss-OA)/GA, was successfully developed for tumor-specific intracellular rapid delivery of gambogic acid (GA).

Materials and methods: The redox-sensitive polymer, HECS-ss-OA, was prepared through a well-controlled synthesis procedure with a satisfactory reproducibility and stable resulted surface properties of the assembled cationic micelles. GA was solubilized into the inner core of HECS-ss-OA micelles, while HA was employed to coat outside HECS-ss-OA/GA for CD44-mediated active targeting along with protection from cation-associated in vivo defects. The desirable redox-sensitivity of HA(HECS-ss-OA)/GA was demonstrated by morphology and particle size changes alongside in vitro drug release of nanoparticles in different simulated reducing environments.

Results: The results of flow cytometry and confocal microscopy confirmed the HA-receptor mediated cellular uptake and burst drug release in highly reducing cytosol of HA(HECS-ss-OA)/GA. Consequently, HA(HECS-ss-OA)/GA showed the highest apoptosis induction and cytotoxicity over the non-sensitive (HA(HECS-cc-OA)/GA) and HA un-coated (HECS-ss-OA/GA) controls against A549 NSCLC model both in vitro and in vivo. Furthermore, a diminished systemic cytotoxicity was observed in HA(HECS-ss-OA)/GA treated mice compared with those treated by HA un-coated cationic ones and GA solution.

Traditional Chinese medicine-combination therapies utilizing nanotechnology-based targeted delivery systems: a new strategy for antitumor treatment

Cancer is a major public health problem, and is now the world’s leading cause of death. Traditional Chinese medicine (TCM)-combination therapy is a new treatment approach and a vital therapeutic strategy for cancer, as it exhibits promising antitumor potential. Nano-targeted drug-delivery systems have remarkable advantages and allow the development of TCM-combination therapies by systematically controlling drug release and delivering drugs to solid tumors. In this review, the anticancer activity of TCM compounds is introduced. The combined use of TCM for antitumor treatment is analyzed and summarized. These combination therapies, using a single nanocarrier system, namely codelivery, are analyzed, issues that require attention are determined, and future perspectives are identified. We carried out a systematic review of >280 studies published in PubMed since 1985 (no patents involved), in order to provide a few basic considerations in terms of the design principles and management of targeted nanotechnology-based TCM-combination therapies.

Gambogic acid reverses oxaliplatin resistance in colorectal cancer by increasing intracellular platinum levels

Resistance to oxaliplatin (L-OHP) is a major obstacle to successful chemotherapy in colorectal cancer (CRC). In the present study, the ability of gambogic acid (GA) to reverse L-OHP resistance in CRC LoVo cells was investigated. L-OHP-resistant LoVo/L-OHP cells were established by exposing them to increasing concentrations of L-OHP. GA-reversed L-OHP-sensitive LoVo/L-OHP/GA cells were established by exposure to 0.5 µmol/l GA for 2 weeks. A Cell Counting Kit-8 assay was used to assess levels of proliferation. Flow cytometry was applied to detect apoptosis rates. Transwell assays were used to analyse invasion. Inductively coupled plasma mass spectrometry was used to determine intracellular platinum (Pt) content. Western blot analysis was used to reveal the protein levels of Human copper transporter 1 (hCTR1), Copper-transporting p-type adenosine triphosphatases 1 (ATP7A) and Copper-transporting p-type adenosine triphosphatases 2 (ATP7B). LoVo/L-OHP and LoVo/L-OHP/GA cell lines were successfully established, and it was identified that L-OHP inhibited the proliferation of LoVo, LoVo/L-OHP and LoVo/L-OHP/GA cells in a dose-dependent manner. Compared with the parent LoVo cells, the anti-apoptosis and invasion properties of LoVo/L-OHP cells were enhanced, and were reversed by GA treatment. Intracellular Pt content was highest in the LoVo cells, followed by LoVo/L-OHP/GA cells, and then lowest in the LoVo/L-OHP cells. Downregulated hCTP1 and upregulated ATP7A and ATP7B were associated with L-OHP resistance, and GA reversed the resistance by increasing levels of hCTR1 and decreasing levels of ATP7A and ATP7B. In conclusion, GA has the potential ability to reverse L-OHP resistance in CRC cells by increasing intracellular Pt content, which it achieves by increasing hCTR1 levels and decreasing ATP7A and ATP7B levels. GA may represent a promising treatment agent for L-OHP resistance.

Research Progress on Reversing Multidrug Resistance in Tumors by Using Chinese Medicine

Multidrug resistance (MDR) is a major cause of cancer chemotherapy failure, and it is important to develop suitable reversal agents to overcome MDR. A majority of chemical reversal agents have acceptable reversal effects. However, the toxicity and adverse reactions associated with these agents restricts their clinical use. Chinese medicines (CMs) have lower toxicities and adverse reactions and are associated with multiple components, multiple targets and reduced toxicity. CMs have several advantages and could reverse MDR, decrease drug dosage, enhance patient compliance and increase efficacy. This review summarizes the current progress of CM reversal agents..

Bromodomain‑containing protein 4 is critical for the antiproliferative and pro‑apoptotic effects of gambogic acid in anaplastic thyroid cancer

Gambogic acid (GA) has been widely used as an anticancer drug for different tumors, including thyroid cancer. However, the potential function and molecular mechanisms of GA in anaplastic thyroid cancer (ATC) has not been illustrated thus far. The aim of the present study was to demonstrate the antitumor effects of GA on ATC cells and investigate its underlying molecular mechanisms. The results revealed that GA significantly decreased the viability and proliferation, as well as induced cell apoptosis in ATC cell lines. Next, it was demonstrated that GA decreased the expression of bromodomain‑containing protein 4 (BRD4), which has been reported to function as an oncogene in various types of cancer. BRD4 expression was significantly higher in ATC tissues compared with that in adjacent normal thyroid tissues. In addition, BRD4 silencing significantly repressed the cell viability and proliferation, and increased the cell apoptotic rate in vitro, while it also delayed the tumor growth in vivo. Notably, ectopic BRD4 expression significantly weakened the biological effects of GA on ATC cells in vitro and in vivo, which suggested that GA served its anticancer functions partially via downregulating BRD4. In conclusion, BRD4, functioning as an oncogene in ATC, is important for the antiproliferative and pro‑apoptotic effects of GA.

Multiple cation-doped linear polymers toward ATP sensing and a cell imaging application

A set of multiple cation-doped linear polymers (abbreviated as OPY-1,2-BE, OPY-1,4-BB, OPY-1,8-BO, OPY-1,4-OBB) synthesized from a dipyridine derivative (OPY) and dibrominated compounds were employed as fluorescent probes for adenosine triphosphate (ATP) sensing.

Inclusion complex from cyclodextrin-grafted hyaluronic acid and pseudo protein as biodegradable nano-delivery vehicle for gambogic acid

β-Cyclodextrin can form inclusion complex with a series of guest molecules including phenyl moieties, and has gained considerable popularity in the study of supramolecular nanostructure. In this study, a biodegradable nanocomplex (HA(CD)-4Phe4 nanocomplex) was developed from β-cyclodextrin grafted hyaluronic acid (HA) and phenylalanine based poly(ester amide). The phenylalanine based poly(ester amide) is a biodegradable pseudo protein which provides the encapsulation capacity for gambogic acid (GA), a naturally-derived chemotherapeutic which has been effectively employed to treat multidrug resistant tumor. The therapeutic potency of free GA is limited due to its poor solubility in water and the lack of tumor-selective toxicity. The nanocomplex carrier enhanced the solubility and availability of GA in aqueous media, and the HA component enabled the targeted delivery to tumor cells with overexpression of CD44 receptors. In the presence of hyaluronidase, the release of GA from the nanocomplex was significantly accelerated, due to the enzymatic biodegradation of the carrier. Compared to free GA, GA-loaded nanocomplex exhibited improved cytotoxicity in MDA-MB-435/MDR multidrug resistant melanoma cells, and induced enhanced level of apoptosis and mitochondrial depolarization, at low concentration of GA (1-2µM). The nanocomplex enhanced the therapeutic potency of GA, especially when diluted in physiological environment. In addition, suppressed matrix metalloproteinase activity was also detected in MDA-MB-435/MDR cells treated by GA-loaded nanocomplex, which demonstrated its potency in the inhibition of tumor metastasis. The in vitro data suggested that HA(CD)-4Phe4 nanocomplex could provide a promising alternative in the treatment of multidrug resistant tumor cells.

STATEMENT OF SIGNIFICANCE

Gambogic acid (GA), naturally derived from genus Garcinia trees, exhibited significant cytotoxic activity against multiple types of tumors with resistance to traditional chemotherapeutics. Unfortunately, the poor solubility of GA in conventional pharmaceutical solvents and non-targeted distribution in normal tissues greatly limited its therapeutic potency. To overcome the challenges, we develop a nanoplatform from the supramolecular assembly of β-cyclodextrin grafted hyaluronic acid (HA) and phenylalanine based pseudo protein. The pseudo protein in the nanocomplex provided the hydrophobic interaction and loading capacity for GA, while the HA component targeted the overexpressed CD44 receptor and improved the selective endocytosis in multidrug resistant melanoma cells. The supramolecular nanocomplex provide a promising platform for the delivery of hydrophobic chemotherapeutics to improve the bioavailability and efficiency.

Gambogic acid sensitizes gemcitabine efficacy in pancreatic cancer by reducing the expression of ribonucleotide reductase subunit-M2 (RRM2)

Background

Pancreatic cancer is susceptible to gemcitabine resistance, and patients receive less benefit from gemcitabine chemotherapy. Previous studies report that gambogic acid possesses antineoplastic properties; however, to our knowledge, there have been no specific studies on its effects in pancreatic cancer. Therefore, the purpose of this study was to explore whether increases the sensitivity of pancreatic cancer to gemcitabine, and determine the synergistic effects of gambogic acid and gemcitabine against pancreatic cancer.

Methods

The effects of gambogic acid on cell viability, the cell cycle, and apoptosis were assessed using 4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) and flow cytometry in pancreatic cancer cell lines. Protein expression was detected by western blot analysis and mRNA expression was detected using q-PCR. A xenograft tumor model of pancreatic cancer was used to investigate the synergistic effects of gambogic acid and gemcitabine.

Results

Gambogic acid effectively inhibited the growth of pancreatic cancer cell lines by inducing S-phase cell cycle arrest and apoptosis. Synergistic activity of gambogic acid combined with gemcitabine was observed in PANC-1 and BxPC-3 cells based on the results of MTT, colony formation, and apoptosis assays. Western blot results demonstrated that gambogic acid sensitized gemcitabine-induced apoptosis by enhancing the expression of cleaved caspase-3, cleaved caspase-9, cleaved-PARP, and Bax, and reducing the expression of Bcl-2. In particular, gambogic acid reduced the expression of the ribonucleotide reductase subunit-M2 (RRM2) protein and mRNA, a trend that correlated with resistance to gemcitabine through inhibition of the extracellular signal-regulated kinase (ERK)/E2F1 signaling pathway. Treatment with gambogic acid and gemcitabine significantly repressed tumor growth in the xenograft pancreatic cancer model. Immunohistochemistry results demonstrated a downregulation of p-ERK, E2F1, and RRM2 in mice receiving gambogic acid treatment and combination treatment.

Conclusions

These results demonstrate that gambogic acid sensitizes pancreatic cancer cells to gemcitabine in vitro and in vivo by inhibiting the activation of the ERK/E2F1/RRM2 signaling pathway. The results also indicate that gambogic acid treatment combined with gemcitabine might be a promising chemotherapy strategy for pancreatic cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0579-0) contains supplementary material, which is available to authorized users.

Natural Products as Alternative Choices for P-Glycoprotein (P-gp) Inhibition

Multidrug resistance (MDR) is regarded as one of the bottlenecks of successful clinical treatment for numerous chemotherapeutic agents. Multiple key regulators are alleged to be responsible for MDR and making the treatment regimens ineffective. In this review, we discuss MDR in relation to P-glycoprotein (P-gp) and its down-regulation by natural bioactive molecules. P-gp, a unique ATP-dependent membrane transport protein, is one of those key regulators which are present in the lining of the colon, endothelial cells of the blood brain barrier (BBB), bile duct, adrenal gland, kidney tubules, small intestine, pancreatic ducts and in many other tissues like heart, lungs, spleen, skeletal muscles, etc. Due to its diverse tissue distribution, P-gp is a novel protective barrier to stop the intake of xenobiotics into the human body. Over-expression of P-gp leads to decreased intracellular accretion of many chemotherapeutic agents thus assisting in the development of MDR. Eventually, the effectiveness of these drugs is decreased. P-gp inhibitors act by altering intracellular ATP levels which are the source of energy and/or by affecting membrane contours to increase permeability. However, the use of synthetic inhibitors is known to cause serious toxicities. For this reason, the search for more potent and less toxic P-gp inhibitors of natural origin is underway. The present review aims to recapitulate the research findings on bioactive constituents of natural origin with P-gp inhibition characteristics. Natural bioactive constituents with P-gp modulating effects offer great potential for semi-synthetic modification to produce new scaffolds which could serve as valuable investigative tools to recognize the function of complex ABC transporters apart from evading the systemic toxicities shown by synthetic counterparts. Despite the many published scientific findings encompassing P-gp inhibitors, however, this article stand alones because it provides a vivid picture to the readers pertaining to Pgp inhibitors obtained from natural sources coupled with their mode of action and structures. It provides first-hand information to the scientists working in the field of drug discovery to further synthesise and discover new P-gp inhibitors with less toxicity and more efficacies.

An overview of anticancer activity of Garcinia and Hypericum

Cancer is one of the leading causes of death worldwide (approximately 8.2 million cases/year) and, over the next two decades, a 70% increase in new cancer cases is expected. Through analysis of the available drugs between the years of 1930 and 2014, it was found that 48% were either natural products or their derivatives. This proportion increased to 66% when semi-synthetic products were included. The family Clusiaceae Juss. (Malpighiales) includes approximately 1000 species distributed throughout all tropical and temperate regions. The phytochemical profile of this family includes many chemicals with interesting pharmacological activities, including anticancer activities. This study includes an overview of the in vitro and in vivo anticancer activity of secondary metabolites from Garcinia and Hypericum and the mechanisms involved in this activity. Hypericum no longer belong to Clusiaceae family, but was considered in the past by taxonomists, due to similarities with this family. Research in the area has shown that several compounds belonging to different chemical classes exhibit activity in several tumor cell lines in different experimental models. This review shows the significant antineoplasic activity of these compounds, in particular of these two genera and validates the importance of natural products in the search for anticancer drugs.

A 20(S)-protopanoxadiol derivative overcomes multi-drug resistance by antagonizing ATP-binding cassette subfamily B member 1 transporter function

In cancer cells, failure of chemotherapy is often caused by the ATP-binding cassette subfamily B member 1 (ABCB1), and few drugs have been successfully developed to overcome ABCB1-mediated multi-drug resistance (MDR). To suppress ABCB1 activity, we previously designed and synthesized a new series of derivatives based on 20(S)-protopanoxadiol (PPD). In the present study, we investigated the role of PPD derivatives in the function of ABC transporters. Non-toxic concentrations of the PPD derivative PPD12 sensitized ABCB1-overexpressing cells to their anti-cancer substrates better than either the parental PPD or inactive PPD11. PPD12 increased intracellular accumulation of adriamycin and rhodamine123 in resistant cancer cells. Although PPD12 did not suppress the expression of ABCB1 mRNA or protein, it stimulated the activity of ABCB1 ATPase. Because PPD12 is a competitive inhibitor, it was predicted to bind to the large hydrophobic cavity of homology-modeled human ABCB1. PPD12 also enhanced the efficacy of adriamycin against ABCB1-overexpressing KB/VCR xenografts in nude mice. In conclusion, PPD12 enhances the efficacy of substrate drugs in ABCB1-overexpressing cancer cells. These findings suggest that a combination therapy consisting of PPD12 with conventional chemotherapeutic agents may be an effective treatment for ABCB1-mediated MDR cancer patients.

Role of gambogic acid and NaI131 in A549/DDP cells

Resistance to platinum in tumor tissue is a considerable barrier against effective lung cancer treatment. Radionuclide therapy is the primary adjuvant treatment, however, the toxic side effects limit its dosage in the clinical setting. Therefore, the present study aimed to determine whether an NaI¹³¹ radiosensitizer could help reduce the toxic side effects of radionuclide therapy. In vitro experiments were conducted to determine whether NaI¹³¹ can inhibit platinum resistance in A549/DDP cells, which are cisplatin-resistant non-small cell lung cancer cells, and whether gambogic acid (GA) is an effective NaI¹³¹ radiosensitizer. Cell proliferation following drug intervention was analyzed using MTT and isobolographic analysis. Apoptosis was assessed by flow cytometry. In addition, the mechanisms of drug intervention were analyzed by measuring the expression of P-glycoprotein (P-gP), B cell lymphoma 2 (Bcl-2), Bcl2-associated X protein (Bax) and P53 using western blot analysis and immunocytochemistry. According to isobolographic analysis, a low concentration of NaI¹³¹ combined with GA had a synergistic effect on the inhibition of A549/DDP cell proliferation, which was consistent with an increased rate of apoptosis. Furthermore, the overexpression of Bax, and the downregulation of P-gP, P53 and Bcl-2 observed demonstrated the potential mechanism(s) of NaI¹³¹ and GA intervention. NaI¹³¹ may induce apoptosis in A549/DDP cells by regulating apoptosis-related proteins. A low concentration combination of NaI¹³¹ and GA was able to significantly inhibit A549/DDP cell proliferation and induce cell apoptosis. Thus, the two drugs appear to have a synergistic effect on apoptosis of A549/DDP cells.

Nanomedicine-based combination of gambogic acid and retinoic acid chlorochalcone for enhanced anticancer efficacy in osteosarcoma

In this study, gambogic acid (GA) and retinoic acid chlorochalcone (RACC) co-loaded glycol chitosan nanoparticle was successfully developed and studied for its therapeutic efficacy against osteosarcoma cancer cells. The GA/RACC loaded glycol chitosan nanoparticles (RGNP) was nanosized and exhibited a controlled release of drug in either pH 7.4 and pH 5.0. Owing to the strong positive charge on the RGNP surface, efficiency cellular uptake was observed in cancer cells. Moreover, a synergistic combination of GA and RACC were effectively suppressed the tumor growth progression. The half maximal inhibitory concentration (IC50) values in MG63 cells were 0.89μg/ml and 0.35μg/ml for GA and RGNP after 24h. The results clearly suggest the synergist effect of GA and RACC in effectively inhibiting the cancer cell proliferation. The RGNP as expected induced a remarkably higher apoptosis of cancer cells with ∼28%. Overall, combination of GA and RACC encapsulated in a nanocarrier could be an effective strategy to treat osteosarcoma. Future studies will focus on the in vivo evaluation of GA/RACC-loaded polymeric nanoparticles.

Combination of gambogic acid with cisplatin enhances the antitumor effects on cisplatin-resistant lung cancer cells by downregulating MRP2 and LRP expression

Cisplatin resistance is a main clinical problem of lung cancer therapy. Gambogic acid (GA) could prohibit the proliferation of a variety of human cancer cells. However, the effects of GA on cisplatin-resistant lung cancer are still unclear. The objective of the present study was to find out the antitumor effects of GA on cisplatin-resistant human lung cancer A549/DDP cells and further explore its underlying mechanisms. Cell Counting Kit-8 assay was used to observe the impacts of GA and/or cisplatin on the proliferation of lung cancer cells; flow cytometry was used to detect the effects of GA on cell cycle and apoptosis; Western blot was used to examine the effects of GA on the expression of lung resistance protein (LRP) and multidrug resistance-associated protein 2 (MRP2) protein in A549/DDP cells. Our results showed that GA dose- and time-dependently prohibited the proliferation and induced significant cell apoptosis in A549 and A549/DDP cells. GA also induced G0/G1 arrest in both A549/DDP and A549 cells. Moreover, GA upregulated protein expression level of cleaved caspase-3 and Bax and downregulated protein expression level of pro-caspase-9 and Bcl-2 in time- and dose-dependent way in A549/DDP cells. GA combined with cisplatin enhanced the cells apoptotic rate and reduced the cisplatin resistance index in A549/DDP cells. In addition, GA reduced the MRP2 and LRP protein expression level in A549/DDP cells. GA inhibits the proliferation, induces cell cycle arrest and apoptosis in A549/DDP cells. Combination of GA with cisplatin enhances the antitumor effects on cisplatin-resistant lung cancer cells by downregulating MRP2 and LRP expression.

Proteomic and bioinformatic analyses of possible target-related proteins of gambogic acid in human breast carcinoma MDA-MB-231 cells

Gambogic acid (GA) is an anticancer agent in phase ‖b clinical trial in China but its mechanism of action has not been fully clarified. The present study was designed to search the possible target-related proteins of GA in cancer cells using proteomic method and establish possible network using bioinformatic analysis. Cytotoxicity and anti-migration effects of GA in MDA-MB-231 cells were checked using MTT assay, flow cytometry, wound migration assay, and chamber migration assay. Possible target-related proteins of GA at early (3 h) and late stage (24 h) of treatment were searched using a proteomic technology, two-dimensional electrophoresis (2-DE). The possible network of GA was established using bioinformatic analysis. The intracellular expression levels of vimentin, keratin 18, and calumenin were determined using Western blotting. GA inhibited cell proliferation and induced cell cycle arrest at G2/M phase and apoptosis in MDA-MB-231 cells. Additionally, GA exhibited anti-migration effects at non-toxic doses. In 2-DE analysis, totally 23 possible GA targeted proteins were found, including those with functions in cytoskeleton and transport, regulation of redox state, metabolism, ubiquitin-proteasome system, transcription and translation, protein transport and modification, and cytokine. Network analysis of these proteins suggested that cytoskeleton-related proteins might play important roles in the effects of GA. Results of Western blotting confirmed the cleavage of vimentin, increase in keratin 18, and decrease in calumenin levels in GA-treated cells. In summary, GA is a multi-target compound and its anti-cancer effects may be based on several target-related proteins such as cytoskeleton-related proteins.

Inducing cell cycle arrest and apoptosis by dimercaptosuccinic acid modified Fe3O4 magnetic nanoparticles combined with nontoxic concentration of bortezomib and gambogic acid in RPMI-8226 cells

The purpose of this study was to determine the potential benefits of combination therapy using dimercaptosuccinic acid modified iron oxide (DMSA-Fe₃O₄) magnetic nanoparticles (MNPs) combined with nontoxic concentration of bortezomib (BTZ) and gambogic acid (GA) on multiple myeloma (MM) RPMI-8226 cells and possible underlying mechanisms. The effects of BTZ-GA-loaded MNP-Fe₃O₄ (BTZ-GA/MNPs) on cell proliferation were assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,4,-diphenyltetrazolium bromide (MTT) method. Cell cycle and apoptosis were detected using the terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) assay and flow cytometry (FCM). Furthermore, DMSA-Fe₃O₄ MNPs were characterized in terms of distribution, apoptotic morphology, and cellular uptake by transmission electron microscopy (TEM) and 4,6-diamidino-2-phenylindole (DAPI) staining. Subsequently, the effect of BTZ-GA/MNPs combination on PI3K/Akt activation and apoptotic-related protein were appraised by Western blotting. MTT assay and hematoxylin and eosin (HE) staining were applied to elevate the functions of BTZ-GA/MNPs combination on the tumor xenograft model and tumor necrosis. The results of this study revealed that the majority of MNPs were quasi-spherical and the MNPs taken up by cells were located in the endosome vesicles of cytoplasm. Nontoxic concentration of BTZ-GA/MNPs increased G₂/M phase cell cycle arrest and induced apoptosis in RPMI-8226 cells. Furthermore, the combination of BTZ-GA/MNPs activated phosphorylated Akt levels, Caspase-3, and Bax expression, and down-regulated the PI3K and Bcl-2 levels significantly. Meanwhile, the in vivo tumor xenograft model indicated that the treatment of BTZ-GA/MNPs decreased the tumor growth and volume and induced cell apoptosis and necrosis. These findings suggest that chemotherapeutic agents polymerized MNPs-Fe₃O₄ with GA could serve as a better alternative for targeted therapeutic approaches to treat multiple myeloma.

Fine-tuning vitamin E-containing telodendrimers for efficient delivery of gambogic acid in colon cancer treatment

Certain natural products such as gambogic acid (GA) exhibit potent antitumor effects. Unfortunately, administration of these natural products is limited by their poor solubility in conventional pharmaceutical solvents. In this study, a series of telodendrimers, composed of linear polyethylene glycol (PEG)-blocking-dendritic oligomer of cholic acid (CA) and vitamin E (VE), have been designed with architectures optimized for efficient delivery of GA and other natural anticancer compounds. Two of the telodendrimers with segregated CA and VE domains self-assembled into stable cylindrical and/or spherical nanoparticles (NPs) after being loaded with GA as observed under transmission electron microscopy (TEM), which correlated with the dynamic light scattering (DLS) analysis of sub-30 nm particle sizes. A very high GA loading capacity (3:10 drug/polymer w/w) and sustained drug release were achieved with the optimized telodendrimers. These novel nanoformulations of GA were found to exhibit similar in vitro cytotoxic activity against colon cancer cells as the free drug. Near-infrared fluorescence small animal imaging revealed preferential accumulation of GA-loaded NPs into tumor tissue. The optimized nanoformulation of GA achieved superior antitumor efficacy compared to GA-Cremophor EL formulation at equivalent doses in HT-29 human colon cancer xenograft mouse models. Given the mild adverse effects associated with this natural compound and the enhanced anticancer effects via tumor targeted telodendrimer delivery, the optimized GA nanoformulation is a promising alternative to the traditional chemotherapy in colon cancer treatment.

A new strategy for TiO2 whiskers mediated multi-mode cancer treatment

Traditional Chinese medicine (TCM) which functions as chemotherapeutic or adjuvantly chemotherapeutic agents has been drawing a great many eyeballs for its easy obtain and significant antitumor effects accompanied with less toxic and side effects. PDT (photodynamic therapy) utilizes the fact that certain compounds coined as photosensitizers, when exposed to light of a specific wavelength, are capable of generating cytotoxic reactive oxygen species (ROS) such as hydroxyl radical, hydrogen peroxide, and superoxide to kill cancer cells. Combinations of cancer therapeutic modalities are studied to improve the efficacy of treatment. This study aimed to explore a new strategy of coupling of titanium dioxide whiskers (TiO2 Ws) with the anticancer drug gambogic acid (GA) in photodynamic therapy. The nanocomposites were coined as GA-TiO2. The combination of TiO2 Ws with GA induced a remarkable enhancement in antitumor activity estimated by MTT assay, nuclear DAPI staining, and flow cytometry. Furthermore, the possible signaling pathway was explored by reverse transcription polymerase chain reaction (RT-PCR) and Western blot assay. These results identify TiO2 Ws of good biocompatibility and photocatalytic activity. In human leukemia cells (K562 cells), TiO2 Ws could obviously increase the intracellular concentration of GA and enhance its potential antitumor efficiency, suggesting that TiO2 Ws could act as an efficient drug delivery carrier targeting GA to carcinoma cells. Moreover, photodynamic GA-TiO2 nanocomposites could induce an evident reinforcement in antitumor activity with UV illumination. These results reveal that such modality combinations put forward a promising proposal in cancer therapy.

Integrated traditional Chinese and western medicine modulator for overcoming the multidrug resistance with carbon nanotubes

GA/Dox/P-gp Ab-CNTs, integrated specific targeting, P-gp inhibitor and chemotherapeutic agent, could represent a promising modulator for overcoming tumor MDR.

PEG–PLGA–PLL nanoparticles in combination with gambogic acid for reversing multidrug resistance of K562/A02 cells to daunorubicin

The present chemotherapy in malignancy treatment, including leukaemia, is plagued by one main problem: multidrug resistance (MDR) which is often related to excessive expression of adenosine triphosphate-dependent efflux pump.

Anandamide protects HT22 cells exposed to hydrogen peroxide by inhibiting CB1 receptor-mediated type 2 NADPH oxidase

Background. Endogenous cannabinoid anandamide (AEA) protects neurons from oxidative injury in rodent models; however the mechanism of AEA-induced neuroprotection remains to be determined. Activation of neuronal NADPH oxidase 2 (Nox2) contributes to oxidative damage of the brain, and inhibition of Nox2 can attenuate cerebral oxidative stress. We aimed to determine whether the neuronal Nox2 was involved in protection mediated by AEA. Methods. The mouse hippocampal neuron cell line HT22 was exposed to hydrogen peroxide (H₂O₂) to mimic oxidative injury of neurons. The protective effect of AEA was assessed by measuring cell metabolic activity, apoptosis, lactate dehydrogenase (LDH) release, cellular morphology, intracellular reactive oxygen species (ROS), and antioxidant and oxidant levels and Nox2 expression. Results. HT22 cells exposed to H₂O₂ demonstrated morphological changes, decreased LDH release, reduced metabolic activity, increased levels of intracellular ROS and oxidized glutathione (GSSG), reduced levels of superoxide dismutase (SOD), and reduced glutathione (GSH) and increased expression of Nox2. AEA prevented these effects, a property abolished by simultaneous administration of CB1 antagonist AM251 or CB1-siRNA. Conclusion. Nox2 inhibition is involved in AEA-induced cytoprotection against oxidative stress through CB1 activation in HT22 cells.

Nanoparticle delivery and combination therapy of gambogic acid and all-trans retinoic acid

In order to enhance the in vivo codelivery efficiency of gambogic acid (GA) and all-trans retinoic acid (ATRA), our strategy was to entrap GA in the self-assembled nanoparticles based on amphiphilic hyaluronic acid (HA)-ATRA (HRA) conjugate. In this way, GA and ATRA were loaded simultaneously in a nanocarrier and codelivered into the tumor cell through HA receptor-mediated endocytosis. GA-loaded HRA nanoparticles (GA-HRA) were prepared by a dialysis method, and their physicochemical characteristics were investigated as well. GA-HRA exhibited a high drug loading capacity (31.1%), had a particle size in the range of 100–150 nm, and good biocompatibility. HRA nanoparticles were effectively internalized by MCF-7 cells and translocated into the nucleus in a time-dependent manner. The in vivo imaging analysis demonstrated that the fluorescent signals in the tumor were markedly increased with DiR-loaded nanoparticles after intravenous administration compared to free DiR solution, suggesting it has excellent tumor targeting properties. More importantly, GA-HRA exhibited excellent in vivo efficacy with dramatically reduced toxicity. In conclusion, with the assistance of HRA nanoparticles, GA and ATRA can successfully realize an effective combination chemotherapy as well as tumor-targeted delivery.

Gambogic acid synergistically potentiates cisplatin-induced apoptosis in non-small-cell lung cancer through suppressing NF-κB and MAPK/HO-1 signalling

Background:

Gambogic acid (GA) has been reported to have potent anticancer activity and is authorised to be tested in phase II clinical trials for treatment of non-small-cell lung cancer (NSCLC). The present study aims to investigate whether GA would be synergistic with cisplatin (CDDP) against the NSCLC.

Methods:

1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), combination index (CI) isobologram, western blot, quantitative PCR, flow cytometry, electrophoretic mobility shift assay, xenograft tumour models and terminal deoxynucleotide transferase-mediated dUTP nick-end labelling analysis were used in this study.

Results:

The cell viability results showed that sequential CDDP-GA treatment resulted in a strong synergistic action in A549, NCI-H460, and NCI-H1299 cell lines, whereas the reverse sequence and simultaneous treatments led to a slight synergistic or additive action. Increased sub-G1 phase cells and enhanced PARP cleavage demonstrated that the sequence of CDDP-GA treatment markedly increased apoptosis in comparison with other treatments. Furthermore, the sequential combination could enhance the activation of caspase-3, -8, and 9, increase the expression of Fas and Bax, and decrease the expression of Bcl-2, survivin and X-inhibitor of apoptosis protein (X-IAP) in A549 and NCI-H460 cell lines. In addition, increased apoptosis was correlated with enhanced reactive oxygen species generation. Importantly, it was found that, followed by CDDP treatment, GA could inhibit NF-κB and mitogen-activated protein kinase (MAPK)/heme oxygenase-1 (HO-1) signalling pathways, which have been validated to reduce ROS release and confer CDDP resistance. The roles of NF-κB and MAPK pathways were further confirmed by using specific inhibitors, which significantly increased ROS release and apoptosis induced by the sequential combination of CDDP and GA. Moreover, our results indicated that the combination of CDDP and GA exerted increased antitumour effects on A549 xenograft models through inhibiting NF-κB, HO-1, and subsequently inducing apoptosis.

Conclusion:

Gambogic acid sensitises lung cancer cells to CDDP in vitro and in vivo in NSCLC through inactivation of NF-κB and MAPK/HO-1 signalling pathways, providing a rationale for the combined use of CDDP and GA in lung cancer chemotherapy.

20(S)-Protopanaxadiol (PPD) analogues chemosensitize multidrug-resistant cancer cells to clinical anticancer drugs

Novel 20(S)-protopanoxadiol (PPD) analogues were designed, synthesized, and evaluated for the chemosensitizing activity against a multidrug resistant (MDR) cell line (KBvcr) overexpressing P-glycoprotein (P-gp). Structure-activity relationship analysis showed that aromatic substituted aliphatic amine at the 24-positions (groups V) effectively and significantly sensitized P-gp overexpressing multidrug resistant (MDR) cells to anticancer drugs, such as docetaxel (DOC), vincristine (VCR), and adriamycin (ADM). PPD derivatives 12 and 18 showed 1.3-2.6 times more effective reversal ability than verapamil (VER) for DOC and VCR. Importantly, no cytotoxicity was observed by the active PPD analogues (5μM) against both non-MDR and MDR cells, suggesting that PPD analogues serve as novel lead compounds toward a potent and safe resistance modulator. Moreover, a preliminary mechanism study demonstrated that the chemosensitizing activity of PPD analogues results from inhibition of P-glycoprotein (P-gp) overexpressed in MDR cancer cells.