The multidrug resistance of tumour cells was reversed by tetrandrine in vitro and in xenografts derived from human breast adenocarcinoma MCF-7/adr cells

Natural products for combating multidrug resistance in cancer

Cancer cells frequently develop resistance to chemotherapeutic therapies and targeted drugs, which has been a significant challenge in cancer management. With the growing advances in technologies in isolation and identification of natural products, the potential of natural products in combating cancer multidrug resistance has received substantial attention. Importantly, natural products can impact multiple targets, which can be valuable in overcoming drug resistance from different perspectives. In the current review, we will describe the well-established mechanisms underlying multidrug resistance, and introduce natural products that could target these multidrug resistant mechanisms. Specifically, we will discuss natural compounds such as curcumin, resveratrol, baicalein, chrysin and more, and their potential roles in combating multidrug resistance. This review article aims to provide a systematic summary of recent advances of natural products in combating cancer drug resistance, and will provide rationales for novel drug discovery.

A Worldwide Bibliometric Analysis of Tetrandrine Research in Recent Two Decades

Background: Tetrandrine has been the focus of many studies in recent years. Currently, no bibliometric study in this field has been published. This study presents a bibliometric analysis of the articles on tetrandrine research from the WOS core database during the recent two decades.

Methods: Documents were retrieved for further bibliometric analysis based on the search terms: [TI = (Tetrandrine OR Sinomeninea OR Hanfangchin A) AND PY = (2000–2021)]. We used Microsoft Excel to conduct the frequency analysis, VOSviewer for data visualization, and RStudio for citation metrics and analysis. The standard bibliometric indicators such as the temporal trends and geographical distribution of publications and citations, prolific authors and co-authorship, keywords citation burst, preferred journals, top-cited articles, and important institutions were applied in this study.

Results: 490 documents were retrieved from WOS core database, the retrieved document type consists of 8 categories: 425 articles, 42 meeting abstracts, 8 reviews, 7 corrections, 3 editorial material, 2 proceedings paper, 1 letter, 1 retraction. Corrections and Retractions was excluded from this investigation, the left 482 document were included for furter bibliometric analysis.

Conclusion: Based on our findings, there was a continuous growth of publications on tetrandrine research for 22 years since 2000. China was the largest contributor to tetrandrine research, followed by the United States. The most influential author was Cheng Y (Natl Taiwan Univ Hosp). Acta Pharmacol Sin remained the main publication related to tetrandrine research. Chinese Academy of Sciences, is expected to be a good collaborating center in tetrandrine research. The use of tetrandrine in cancer treatment, could be the promising research subject areas to follow.

Cytotoxicity of synthetic derivatives against breast cancer and multi-drug resistant breast cancer cell lines: a literature-based perspective study

Cancer is the second most killer worldwide causing millions of people to lose their lives every year. In the case of women, breast cancer takes away the highest proportion of mortality rate than other cancers. Due to the mutation and resistance-building capacity of different breast cancer cell lines against conventional therapies, this death rate is on the verge of growth. New effective therapeutic compounds and treatment method is the best way to look out for in this critical time. For instance, new synthetic derivatives/ analogues synthesized from different compounds can be a ray of hope. Numerous synthetic compounds have been seen enhancing the apoptosis and autophagic pathway that directly exerts cytotoxicity towards different breast cancer cell lines. To cease the ever-growing resistance of multi-drug resistant cells against anti-breast cancer drugs (Doxorubicin, verapamil, tamoxifen) synthetic compounds may play a vital role by increasing effectivity, showing synergistic action. Many recent and previous studies have reported that synthetic derivatives hold potentials as an effective anti-breast cancer agent as they show great cytotoxicity towards cancer cells, thus can be used even vastly in the future in the field of breast cancer treatment. This review aims to identify the anti-breast cancer properties of several synthetic derivatives against different breast cancer and multi-drug-resistant breast cancer cell lines with their reported mechanism of action and effectivity.

Rutaecarpine Increases Anticancer Drug Sensitivity in Drug-Resistant Cells through MARCH8-Dependent ABCB1 Degradation

The overexpression of adenosine triphosphate (ATP)-binding cassette (ABC) subfamily B member 1 (ABCB1; P-glycoprotein; MDR1) in some types of cancer cells is one of the mechanisms responsible for the development of multidrug resistance (MDR), which leads to the failure of chemotherapy. Therefore, it is important to inhibit the activity or reduce the expression level of ABCB1 to maintain an effective intracellular level of chemotherapeutic drugs. In this study, we found that rutaecarpine, a bioactive alkaloid isolated from Evodia Rutaecarpa, has the capacity to reverse ABCB1-mediated MDR. Our data indicated that the reversal effect of rutaecarpine was related to the attenuation of the protein level of ABCB1. Mechanistically, we demonstrated that ABCB1 is a newly discovered substrate of E3 ubiquitin ligase membrane-associated RING-CH 8 (MARCH8). MARCH8 can interact with ABCB1 and promote its ubiquitination and degradation. In short, rutaecarpine increased the degradation of ABCB1 protein by upregulating the protein level of MARCH8, thereby antagonizing ABCB1-mediated MDR. Notably, the treatment of rutaecarpine combined with other anticancer drugs exhibits a therapeutic effect on transplanted tumors. Therefore, our study provides a potential chemotherapeutic strategy of co-administrating rutaecarpine with other conventional chemotherapeutic agents to overcome MDR and improve therapeutic effect.

The Lipoprotein Transport System in the Pathogenesis of Multiple Myeloma: Advances and Challenges

Multiple myeloma (MM) is an incurable neoplastic hematologic disorder characterized by malignant plasma cells, mainly in the bone marrow. MM is associated with multiple factors, such as lipid metabolism, obesity, and age-associated disease development. Although, the precise pathogenetic mechanisms remain unknown, abnormal lipid and lipoprotein levels have been reported in patients with MM. Interestingly, patients with higher APOA1 levels, the major apolipoprotein of high density lipoprotein (HDL), have better overall survival. The limited existing studies regarding serum lipoproteins in MM are inconclusive, and often contradictory. Nevertheless, it appears that deregulation of the lipoprotein transport system may facilitate the development of the disease. Here, we provide a critical review of the literature on the role of lipids and lipoproteins in MM pathophysiology. We also propose novel mechanisms, linking the development and progression of MM to the metabolism of blood lipoproteins. We anticipate that proteomic and lipidomic analyses of serum lipoproteins along with analyses of their functionality may improve our understanding and shed light on novel mechanistic aspects of MM pathophysiology.

Thirteen bisbenzylisoquinoline alkaloids in five Chinese medicinal plants: Botany, traditional uses, phytochemistry, pharmacokinetic and toxicity studies

RELEVANCE

Bisbenzylisoquinoline (BBIQ) alkaloids are generally present in plants of Berberidaceae, Monimiaceae and Ranunculaceae families in tropical and subtropical regions. Some species of these families are used in traditional Chinese medicine, with the effects of clearing away heat and detoxification, promoting dampness and defecation, and eliminating sores and swelling. This article offers essential data focusing on 13 representative BBIQ compounds, which are mainly extracted from five plants. The respective botany, traditional uses, phytochemistry, pharmacokinetics, and toxicity are summarized comprehensively. In addition, the ADME prediction of the 13 BBIQ alkaloids is compared and analyzed with the data obtained.

MATERIALS AND METHODS

We have conducted a systematic review of the botanical characteristics, traditional uses, phytochemistry, pharmacokinetics and toxicity of BBIQ alkaloids based on literatures collected from PubMed, Web of Science and Elsevier during 1999-2020. ACD/Percepta software was utilized to predict the pharmacokinetic parameters of BBIQ alkaloids and their affinity with enzymes and transporters.

RESULTS

Botany, traditional uses, phytochemistry, pharmacokinetic and toxicity of 13 alkaloids, namely, tetrandrine, dauricine, curine, trilobine, isotrilobine, cepharanthine, daurisoline, thalicarpine, thalidasine, isotetrandrine, liensinine, neferine and isoliensinine, have been summarized in this paper. It can't be denied that these alkaloids are important material basis of pharmacological effects of family Menispermaceae and others, and for traditional and local uses which has been basically reproduced in the current studies. The 13 BBIQ alkaloids in this paper showed strong affinity and inhibitory effect on P-glycoprotein (P-gp), with poor oral absorption and potent binding ability with plasma protein. BBIQ alkaloids represented by tetrandrine play a key role in regulating P-gp or reversing multidrug resistance (MDR) in a variety of tumors. The irrationality of their usage could pose a risk of poisoning in vivo, including renal and liver toxicity, which are related to the formation of quinone methide during metabolism.

CONCLUSION

Although there is no further clinical evaluation of BBIQ alkaloids as MDR reversal agents, their effects on P-gp should not be ignored. Considering their diverse distribution, pharmacokinetic characteristics and toxicity reported during clinical therapy, the quality standards in different plant species and the drug dosage remain unresolved problems.

Baicalensines A and B, Two Isoquinoline Alkaloids from the Roots of Thalictrum baicalense

Baicalensines A (1) and B (2) were isolated from the roots of Thalictrum baicalense and structurally characterized using spectroscopic data, ¹³C NMR calculations, and the CASE algorithm. Compound 1, representing a new class of alkaloid dimers, contains berberine conjugated to a ring-opened isoquinoline. Compound 2 is the first reported natural benzylisoquinoline bearing a formyl group at C-3. Plausible biosynthetic pathways are proposed. Compound 1 exerted moderate cytotoxicity against the Caco-2 and HL-60 cell lines.

Tetrandrine enhances antitumor effects of the histone deacetylase inhibitor MS-275 in human cancer in a Bax- and p53-dependent manner

MS-275 (Entinostat), is an oral histone deacetylase (HDAC) inhibitor with a high specificity for class 1 HDACs. As single agent, MS-275 exerts only modest antitumor activity against most solid malignancies. The use of MS-275 in combination with other anticancer agents is currently being evaluated to determine whether this approach can achieve superior therapeutic efficacy. Tetrandrine, a bisbenzylisoquinoline alkaloid isolated from the root of a Chinese medicinal herb, is safe and exhibits low toxicity, showing great potential to enhance chemotherapeutic efficacy. In the present study, we investigated the synergistic antitumor effects of MS-275 in combination with tetrandrine. Based on the results of in vitro experiments, the application of MS-275 in combination with tetrandrine induced selective apoptotic death in various cancer cells but spared normal cells. Mechanistically, the combination treatment induced a dramatic accumulation of reactive oxygen species (ROS), and a pretreatment with the ROS scavenger N-acetyl-L-cysteine (NAC) significantly prevented the cellular apoptosis induced by MS-275/tetrandrine. Moreover, molecular assays indicated that Bax and p53 were the key regulators of MS-275/tetrandrine induced apoptosis. The results of the in vivo studies were consistent with the results of the in vitro studies. Based on our findings, tetrandrine enhanced the antitumor effects of MS-275 in a Bax- and p53-dependent manner. The combination of MS-275 and tetrandrine may represent a novel and promising therapeutic strategy for cancer.

Tetrandrine: a review of its anticancer potentials, clinical settings, pharmacokinetics and drug delivery systems

OBJECTIVES

Tetrandrine, a natural bisbenzylisoquinoline alkaloid, possesses promising anticancer activities on diverse tumours. This review provides systematically organized information on cancers of tetrandrine in vivo and in vitro, discuss the related molecular mechanisms and put forward some new insights for the future investigations.

KEY FINDINGS

Anticancer activities of tetrandrine have been reported comprehensively, including lung cancer, colon cancer, bladder cancer, prostate cancer, ovarian cancer, gastric cancer, breast cancer, pancreatic cancer, cervical cancer and liver cancer. The potential molecular mechanisms corresponding to the anticancer activities of tetrandrine might be related to induce cancer cell apoptosis, autophagy and cell cycle arrest, inhibit cell proliferation, migration and invasion, ameliorate metastasis and suppress tumour cell growth. Pharmaceutical applications of tetrandrine combined with nanoparticle delivery system including liposomes, microspheres and nanoparticles with better therapeutic efficiency have been designed and applied encapsulate tetrandrine to enhance its stability and efficacy in cancer treatment.

SUMMARY

Tetrandrine was proven to have definite antitumour activities. However, the safety, bioavailability and pharmacokinetic parameter studies on tetrandrine are very limited in animal models, especially in clinical settings. Our present review on anticancer potentials of tetrandrine would be necessary and highly beneficial for providing guidelines and directions for further research of tetrandrine.

Design, Synthesis of Novel Tetrandrine-14-l-Amino Acid and Tetrandrine-14-l-Amino Acid-Urea Derivatives as Potential Anti-Cancer Agents

Tetrandrine, a dibenzyltetrahydroisoquinoline alkaloid isolated from the root of the traditional Chinese medicinal plant Stephania tetrandra S. Moore, a member of the Menispermaceae, showed anti-cancer activity by inhibiting cell proliferation, preventing cell cycle progress and induction of cell death and autophagy. In this study, twelve tetrandrine-l-amino acid derivatives and twelve tetrandrine-14-l-amino acid-urea derivatives were designed and synthesized, using C14-aminotetrandrine as raw material. Then the preliminary in vitro anti-cancer activities of these derivatives against human breast cancer cell line MDA-MB-231, human leukemia cell lines HEL and K562 were evaluated. The in vitro cytotoxicity results showed that these derivatives exhibited potent inhibitory effects on cancer cell growth, and the primary structure-activity relationships were evaluated. Notably, compound 3f exhibited satisfactory anticancer activity against all three cancer cell lines, especially the HEL cell line, with the IC₅₀ value of 0.23 µM. Further research showed that 3f could induce G1/S cycle arrest and apoptosis in a dose- and time- dependent manner on the leukemia cell line HEL. The results suggested that 3f may be used as a potential anti-cancer agent for human leukemia.

Reversal of ABCB1-related multidrug resistance by ERK5-IN-1

Background

Inhibition of ABC transporters is considered the most effective way to circumvent multidrug resistance (MDR). In the present study, we evaluated the MDR modulatory potential of ERK5-IN-1, a potent extracelluar signal regulated kinase 5 (ERK5) inhibitor.

Methods

The cytotoxicity and MDR reversal effect of ERK5-IN-1 were assessed by MTT assay. The KBv200-inoculated nude mice xenograft model was used for the in vivo study. Doxorubicin efflux and accumulation were measured by flow cytometry. The modulation of ABCB1 activity was measured by colorimetric ATPase assay and [¹²⁵I]-iodoarylazidoprazosin (IAAP) photolabeling assay. Effect of ERK5-IN-1 on expression of ABCB1 and its downstream markers was measured by PCR and/or Western blot. Cell surface expression and subcellular localization of ABCB1 were tested by flow cytometry and immunofluorescence.

Results

Our results showed that ERK5-IN-1 significantly increased the sensitivity of vincristine, paclitaxel and doxorubicin in KBv200, MCF7/adr and HEK293/ABCB1 cells, respectively. This effect was not found in respective drug sensitive parental cell lines. Moreover, in vivo combination studies showed that ERK5-IN-1 effectively enhanced the antitumor activity of paclitaxel in KBv200 xenografts without causing addition toxicity. Mechanistically, ERK5-IN-1 increased intracellular accumulation of doxorubicin dose dependently by directly inhibiting the efflux function of ABCB1. ERK5-IN-1 stimulated the ABCB1 ATPase activity and inhibited the incorporation of [¹²⁵I]-iodoarylazidoprazosin (IAAP) into ABCB1 in a concentration-dependent manner. In addition, ERK5-IN-1 treatment neither altered the expression level of ABCB1 nor blocked the phosphorylation of downstream Akt or Erk1/2. No significant reversal effect was observed on ABCG2-, ABCC1-, MRP7- and LRP-mediated drug resistance.

Conclusions

Collectively, these results indicated that ERK5-IN-1 efficiently reversed ABCB1-mediated MDR by competitively inhibiting the ABCB1 drug efflux function. The use of ERK5-IN-1 to restore sensitivity to chemotherapy or to prevent resistance could be a potential treatment strategy for cancer patients.

Natural Products and Synthetic Analogs as a Source of Antitumor Drugs

Cancer is a heterogeneous disease and one of the major issues of health concern, especially for the public health system globally. Nature is a source of anticancer drugs with abundant pool of diverse chemicals and pharmacologically active compounds. In recent decade, some natural products and synthetic analogs have been investigated for the cancer treatment. This article presents the utilization of natural products as a source of antitumor drugs.

Interactions between artemisinin derivatives and P-glycoprotein

BACKGROUND

Artemisinin was isolated and identified in 1972, which was the starting point for a new era in antimalarial drug therapy. Furthermore, numerous studies have demonstrated that artemisinin and its derivatives exhibit considerable anticancer activity both in vitro, in vivo, and even in clinical Phase I/II trials. P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) is one of the most serious causes of chemotherapy failure in cancer treatment. Interestingly, many artemisinin derivatives exhibit excellent ability to overcome P-gp mediated MDR and even show collateral sensitivity against MDR cancer cells. Furthermore, some artemisinin derivatives show P-gp-mediated MDR reversal activity. Therefore, the interaction between P-gp and artemisinin derivatives is important to develop novel combination treatment protocols with artemisinin derivatives and established anticancer drugs that are P-gp substrates.

PURPOSE

This systematic review provides an updated overview on the interaction between artemisinin derivatives and P-gp and the effect of artemisinin derivatives on the P-gp expression level.

RESULTS

Artemisinin derivatives exhibit multi-specific interactions with P-gp. The currently used artemisinin derivatives are not transported by P-gp. However, some of novel synthetized artemisinin derivatives exhibit P-gp substrate properties. Furthermore, many artemisinin derivatives act as P-gp inhibitors, which exhibit the potential to reverse MDR towards clinically used anticancer drugs.

CONCLUSION

Therefore, studies on the interaction between artemisinin derivatives and P-gp provide important information for the development of novel anti-cancer artemisinin derivatives to reverse P-gp mediated MDR and for the design of rational artemisinin-based combination therapies against cancer.

Discovery of aromatic amides with triazole-core as potent reversal agents against P-glycoprotein-mediated multidrug resistance

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is a major impediment for clinical cancer therapy. 19 novel aromatic amides with triazole-core as MDR reversal agents were designed and synthesized via click chemistry to reverse MDR. Among them, compound 42 was identified as the most promising candidate with high potency (EC₅₀ = 78.1 ± 5.4 nM), low cytotoxity (SI > 1282) and persistent duration in reversing doxorubicin (DOX) resistance in K562/A02 cells. 42 also enhanced the potency of other P-gp associated cytotoxic agents with different structures. In further study, remarkably increased intracellular accumulation of Rh123 and DOX in K562/A02 cells was achieved by compound 42, while CYP3A4 activity had no change by compound 42. These results indicate that compound 42 as a relatively safe modulator of P-gp-mediated MDR has good potential for further development.

Antitumor activity of arsenite in combination with tetrandrine against human breast cancer cell line MDA-MB-231 in vitro and in vivo

Background

Triple-negative breast cancer (TNBC) is one of the most difficult subtypes of breast cancer to treat due to its aggressive, metastatic behavior, and a lack of a targeted therapy. Trivalent arsenic derivatives (arsenite, As^III) with remarkable clinical efficacy in acute promyelocytic leukemia has been demonstrated to exhibit inhibitory effect against breast cancer cells. To provide novel insight into the development of new therapeutic strategies, antitumor activity of As^III and tetrandrine (Tetra), a Chinese plant-derived alkaloid, against the TNBC cell line MDA-MB-231 in vitro and in vivo was investigated.

Methods

Cytotoxicity was evaluated using cell viability, lactate dehydrogenase leakage and cell cycle assay. Alterations of genes related to cell proliferation and death were analyzed using western blotting. In vivo antitumor activity of As^III alone or in combination with Tetra was studied using MDA-MB-231 xenografts in nude mice.

Results

Synergistic cytotoxic effects of two drugs were observed in the cells. In vivo study also showed that co-administration of As^III and Tetra significantly reduced tumor volume and weight, directly supporting its in vitro antitumor activity. No deaths and reduction of body-weight were observed after a long-term co-administration, indicating its good tolerability. S-phase arrest associated with the upregulation of FOXO3a, p27 along with decreased Cyclin D1 expression was observed in the cells treated with the combined regimen. A substantial upregulated p21 expression and downregulated phospho-FOXO3a and Cyclin D1 expression was observed in the tumor tissues of mice co-administered with As^III and Tetra. Autophagy induction was observed in the combination treatment in vitro and in vivo. The addition of wortmannin, a potent autophagy inhibitor, significantly rescued MDA-MB-231 cells from their cytotoxicity of As^III and Tetra.

Conclusions

S-phase arrest, autophagic and necrotic cell death contribute to the cytocidal effects of the combined regimen of As^III and Tetra. Considering our previous study showing synergistic cytotoxic effects of the combined regimen in estrogen receptor-positive breast cancer cell line MCF-7, these results suggest that development of the combination regimen of As^III plus Tetra may offer many benefits to patients with different types of breast cancer.

The Effects of Synthetically Modified Natural Compounds on ABC Transporters

Multidrug resistance (MDR) is a major hurdle which must be overcome to effectively treat cancer. ATP-binding cassette transporters (ABC transporters) play pivotal roles in drug absorption and disposition, and overexpression of ABC transporters has been shown to attenuate cellular/tissue drug accumulation and thus increase MDR across a variety of cancers. Overcoming MDR is one desired approach to improving the survival rate of patients. To date, a number of modulators have been identified which block the function and/or decrease the expression of ABC transporters, thereby restoring the efficacy of a range of anticancer drugs. However, clinical MDR reversal agents have thus far proven ineffective and/or toxic. The need for new, effective, well-tolerated and nontoxic compounds has led to the development of natural compounds and their derivatives to ameliorate MDR. This review evaluates whether synthetically modifying natural compounds is a viable strategy to generate potent, nontoxic, ABC transporter inhibitors which may potentially reverse MDR.

Tetrandrine enhances the antifungal activity of fluconazole in a murine model of disseminated candidiasis

BACKGROUND

Tetrandrine (TET), a bis-benzylisoquinoline alkaloid isolated from the Chinese medicinal herb Stephaniae tetrandrae, has a long history in Chinese clinical applications as an anti-inflammatory or anti-arrhythmic agent in the treatment of diverse diseases. In our previous study, TET exhibited the synergisitic action on azoles against pathogenic fungi.

PURPOSE

In the current study, we examined whether TET can enhance the antifungal activity of FLC against disseminated candidiasis in mice.

METHODS

BALB/c mice were inoculated intravenously with FLC-sensitive or FLC-resistant strains of Candida albicans, randomized and treated intraperitoneally with different doses of TET and/or FLC daily for 7 days. The treatment effectiveness, fungal burdens and the levels of the IFN-γ, IL-10, TGF-β1 and IL-17A are determined in serum by ELISA and in the kidney by Real-time RT-PCR methods.

RESULTS

We found that treatment with 45, 30 and 15 mg/kg of TET, enhanced the antifungal activities of a sub-critical dose (0.4 or 5 mg/kg) and minimal dose (0.8 or 10 mg/kg) of FLC against FLC-sensitive and FLC-resistant (respectively) infected mice. In the resistant strains the resistance mechanisms included MDR1 overexpression-and CDR1/CDR2 overexpression. Furthermore, when animals were treated with a sub-high dose (1.6-3.2 and 20-30 mg/kg) of FLC in the presence of fixed amounts of TET at 45, 30 and 15 mg/kg, the therapeutic doses of FLC could be substantially reduced in all strains tested. The findings in infected animal are consistent with the conclusion that TET exerts a synergistic effect on FLC against C. albicans by fractional inhibitory concentration index (FICI) and time-killing test in vitro.

CONCLUSION

In summary, our data indicate that TET will enhance the antifungal activity of FLC against C. albicans infection in disseminated mice model.

Tetrandrine, a Chinese plant-derived alkaloid, is a potential candidate for cancer chemotherapy

Cancer is a disease caused by the abnormal proliferation and differentiation of cells governed by tumorigenic factors. Chemotherapy is one of the major cancer treatment strategies, and it functions by targeting the physiological capabilities of cancer cells, including sustained proliferation and angiogenesis, the evasion of programmed cell death, tissue invasion and metastasis. Remarkably, natural products have garnered increased attention in the chemotherapy drug discovery field because they are biologically friendly and have high therapeutic effects. Tetrandrine, isolated from the root of Stephania tetrandra S Moore, is a traditional Chinese clinical agent for silicosis, autoimmune disorders, inflammatory pulmonary diseases, cardiovascular diseases and hypertension. Recently, the novel anti-tumor effects of tetrandrine have been widely investigated. More impressive is that tetrandrine affects multiple biological activities of cancer cells, including the inhibition of proliferation, angiogenesis, migration, and invasion; the induction of apoptosis and autophagy; the reversal of multidrug resistance (MDR); and the enhancement of radiation sensitization. This review focuses on introducing the latest information about the anti-tumor effects of tetrandrine on various cancers and its underlying mechanism. Moreover, we discuss the nanoparticle delivery system being developed for tetrandrine and the anti-tumor effects of other bisbenzylisoquinoline alkaloid derivatives on cancer cells. All current evidence demonstrates that tetrandrine is a promising candidate as a cancer chemotherapeutic.

A vascular disrupting agent overcomes tumor multidrug resistance by skewing macrophage polarity toward the M1 phenotype

Multidrug resistance (MDR) mediated by ATP-binding cassette (ABC) transporters is the major obstacle for chemotherapeutic success. Although attempts have been made to circumvent ABC transporter-mediated MDR in past decades, there is still no effective agent in clinic. Here, we identified a vascular disrupting agent, Z-GP-DAVLBH, that significantly inhibited the growth of multidrug-resistant human hepatoma HepG2/ADM and human breast cancer MCF-7/ADR tumor xenografts, although these cells were insensitive to Z-GP-DAVLBH in vitro. Z-GP-DAVLBH increased the secretion of granulocyte-macrophage colony-stimulating factor in tumor tissues and serum of tumor-bearing mice to skew tumor-associated macrophages from the pro-tumor M2 phenotype to the antitumor M1 phenotype, thereby contributing to the induction of HepG2/ADM and MCF-7/ADR cell apoptosis. Our findings shed new light on the underlying mechanisms of VDAs in the treatment of drug-resistant tumors and provide strong evidence that Z-GP-DAVLBH should be a promising agent for overcoming MDR.

Tetrandrine and cancer - An overview on the molecular approach

Tetrandrine has been known in the treatment of tuberculosis, hyperglycemia, negative ionotropic and chronotropic effects on myocardium, malaria, cancer and fever since years together. It has been known that, tetrandrine could modulate multiple signaling molecules such as kinases of cell cycle and rat sarcoma (RAS) pathway along with proteins of tumor suppressor genes, autophagy related, β-catenins, caspases, and death receptors. Moreover, tetrandrine exhibited reversal of drug resistance by modulating P-glyco protein (P-gp) expression levels in different cancers which is an added advantage of this compound compared to other chemotherapy drugs. Though, bioavailability of tetrandrine is a limiting factor, the anticancer activity was observed in animal models without changing any pharmacokinetic parameters. In the present review, role of tetrandrine as kinase inhibitor, inducer of autophagy and caspase pathways and suppressor of RAS mediated cell proliferation were discussed along with inhibition of angiogenesis. It has also been discussed that how tetrandrine potentiate anticancer effect in different types of cancers by modulating multidrug resistance under in vitro and in vivo trials including the available literature on the clinical trials.

Natural alkaloids as P-gp inhibitors for multidrug resistance reversal in cancer

The biggest challenge associated with cancer chemotherapy is the development of cross multi-drug resistance to almost all anti-cancer agents upon chronic treatment. The major contributing factor for this resistance is efflux of the drugs by the p-glycoprotein pump. Over the years, inhibitors of this pump have been discovered to administer them in combination with chemotherapeutic agents. The clinical failure of first and second generation P-gp inhibitors (such as verapamil and cyclosporine analogs) has led to the discovery of third generation potent P-gp inhibitors (tariquidar, zosuquidar, laniquidar). Most of these inhibitors are nitrogenous compounds and recently a natural alkaloid CBT-01^® (tetrandrine) has advanced to the clinical phase. CBT-01 demonstrated positive results in Phase-I study in combination with paclitaxel, which warranted conducting it's Phase II/III trial. Apart from this, there exist a large number of natural alkaloids possessing potent inhibition of P-gp efflux pump and other related pumps responsible for the development of resistance. Despite the extensive contribution of alkaloids in this area, has never been reviewed. The present review provides a comprehensive account on natural alkaloids possessing P-gp inhibition activity and their potential for multidrug resistance reversal in cancer.

Synergistic cytotoxic effects of arsenite and tetrandrine in human breast cancer cell line MCF-7

To provide novel insight into the development of new therapeutic strategies to combat breast cancer using trivalent arsenic (AsIII)-based combination therapy, the cytotoxicity of a combination of AsIII and tetrandrine (Tetra), a Chinese plant-derived alkaloid, was investigated in the human breast cancer cell line MCF-7. Cytotoxicity was evaluated using cell viability, colony formation, wound healing, lactate dehydrogenase leakage and cell cycle assay. Alterations of genes associated with cell proliferation and death were analyzed using real-time PCR and western blotting. Intracellular arsenic accumulation (As[i]) was also determined. Tetra significantly enhanced the cytotoxicity of AsIII in MCF-7 cells in a synergistic manner. The combined treatment upregulated the expression level of FOXO3a, and subsequently resulted in a concomitant increase in the expression levels of p21, p27, and decrease of cycline D1, which occurred in parallel with G0/G1 phase arrest. Autophagy induction was also observed in the combination treatment. Importantly, combining AsIII with Tetra exhibited a synergistic inhibitory effect on the expression level of survivin. Furthermore, enhanced As[i] along with synergistic cytotoxicity was observed in MCF-7 cells treated with AsIII combined with Tetra or Ko134, an inhibitor of breast cancer resistance protein (BCRP), suggesting that Tetra or the BCRP inhibitor probably intervened in the occurrence of resistance to arsenic therapy by enhancing the As[i] via modulation of multidrug efflux transporters. These results may provide a rational molecular basis for the combination regimen of AsIII plus Tetra, facilitating the development of AsIII-based anticancer strategies and combination therapies for patients with solid tumors, especially breast cancer.

Targeted Drug Delivery in Cancer Therapy

Chemotherapy has been the main modality of treatment for cancer patients; however, its success rate remains low, primarily due to limited accessibility of drugs to the tumor tissue, their intolerable toxicity, development of multi-drug resistance, and the dynamic heterogeneous biology of the growing tumors. Better understanding of tumor biology in recent years and new targeted drug delivery approaches that are being explored using different nanosystems and bioconjugates provide optimism in developing successful cancer therapy. This article reviews the possibilities and challenges for targeted drug delivery in cancer therapy.

An AS1411 aptamer-conjugated liposomal system containing a bubble-generating agent for tumor-specific chemotherapy that overcomes multidrug resistance

Recent research in chemotherapy has prioritized overcoming the multidrug resistance (MDR) of cancer cells. In this work, liposomes that contain doxorubicin (DOX) and ammonium bicarbonate (ABC, a bubble-generating agent) are prepared and functionalized with an antinucleolin aptamer (AS1411 liposomes) to target DOX-resistant breast cancer cells (MCF-7/ADR), which overexpress nucleolin receptors. Free DOX and liposomes without functionalization with AS1411 (plain liposomes) were used as controls. The results of molecular dynamic simulations suggest that AS1411 functionalization may promote the affinity and specific binding of liposomes to the nucleolin receptors, enhancing their subsequent uptake by tumor cells, whereas plain liposomes enter cells with difficulty. Upon mild heating, the decomposition of ABC that is encapsulated in the liposomes enables the immediate activation of generation of CO2 bubbles, creating permeable defects in their lipid bilayers, and ultimately facilitating the swift intracellular release of DOX. In vivo studies in nude mice that bear tumors demonstrate that the active targeting of AS1411 liposomes can substantially increase the accumulation of DOX in the tumor tissues relative to free DOX or passively targeted plain liposomes, inhibiting tumor growth and reducing systemic side effects, including cardiotoxicity. The above findings indicate that liposomes that are functionalized with AS1411 represent an attractive therapeutic alternative for overcoming the MDR effect, and support a potentially effective strategy for cancer therapy.

Butorphanol, a synthetic opioid, sensitizes ABCB1-mediated multidrug resistance via inhibition of the efflux function of ABCB1 in leukemia cells

Multidrug resistance (MDR) remains a formidable challenge in the use of chemotherapy and represents a powerful obstacle to the treatment of leukemia. ATP-binding cassette subfamily B member 1 (ABCB1) is a recognized factor which causes MDR and is closely related to poor outcome and relapse in leukemia. Ongoing research concerning the strategy for inhibiting the abnormally high activity of the ABCB1 transporter is critically needed. In the present study, we sought to elucidate the interaction between ABCB1 transporter and butorphanol. Our results showed that butorphanol significantly antagonized ABCB1-mediated drug efflux and increased the intracellular drug concentration by inhibiting the transport activity of ABCB1 in leukemia cells. Mechanistic investigations demonstrated that butorphanol did not alter the protein expression or localization of ABCB1 in HL60/VCR and K562/ADR cells. Furthermore, homology modeling indicated that butorphanol could fit into the large drug-binding cavity of ABCB1 and form a binding conformation. In conclusion, butorphanol reversed the ABCB1-mediated MDR in leukemia cells by directly suppressing the efflux activity of ABCB1.

Inhibition of AKT/FoxO3a signaling induced PUMA expression in response to p53-independent cytotoxic effects of H1: A derivative of tetrandrine

PUMA (p53 unregulated modulator of apoptosis), a BH3-only Bcl-2 family member, can be induced by p53-dependent and p53-independent manners. It plays an important role as regulator of cellular apoptosis. Herein, we evaluate the effects of H1 (a derivative of tetrandrine) on induction of PUMA and underlie its potential mechanism in p53-independent cytotoxic response. Anti-proliferative activity and evidently cytotoxic activity of H1 were observed in wild-type and p53 null cells. Further studies demonstrated that H1 resulted in an increase of cleaved PARP, decease of survivin and elevation of p-H2AX. What is more, H1 significantly induced PUMA expression in a concentration- and time-dependent manner and caused an increase of Bax/Bcl-2 ratio in p53 null cells. Of note, knockdown of PUMA attenuated cytotoxic activity of H1. Further studies demonstrated that inhibition of AKT/FoxO3a signaling contributed to H1-mediated PUMA induction. Targeted suppression of AKT/FoxO3a signaling by siRNA could overcome H1-mediated PUMA induction. In addition, H1 significantly suppressed NF-κB activity and caused an increase of early apoptotic and late apoptotic cells, and elevated caspase-3 activity. Taken together, we found that inhibition of AKT/FoxO3a signaling may contribute to H1-mediated PUMA induction, suggesting that inhibition of AKT/FoxO3a signaling result in PUMA expression in response to p53-independent cytotoxic effects of H1.

Ganoderma lucidum derived ganoderenic acid B reverses ABCB1-mediated multidrug resistance in HepG2/ADM cells

Chemotherapy is one of the most common therapeutic option for metastatic tumors and hematological malignancies. ABCB1-mediated multidrug resistance is the major obstacle for chemotherapy. Natural products with diversified structures are ideal source of ABCB1 modulators. Ganoderenic acid B, a lanostane-type triterpene isolated from Ganoderma lucidum, exhibited potent reversal effect on ABCB1-mediated multidrug resistance of HepG2/ADM cells to doxorubicin, vincristine and paclitaxel. Similarly, ganoderenic acid B could also significantly reverse the resistance of ABCB1-overexpressing MCF-7/ADR cells to doxorubicin. Furthermore, ganoderenic acid B notably enhanced intracellular accumulation of rhodamine-123 in HepG2/ADM cells through inhibition of its efflux. ABCB1 siRNA interference assay indicated that the reversal activity of ganoderenic acid B was dependent on ABCB1. Further mechanistic investigations found that ganoderenic acid B did not alter the expression level of ABCB1 and the activity of ABCB1 ATPase. Molecular docking model displayed that the positions of ganoderenic acid B binding to ABCB1 were different from the region of verapamil interacted with ABCB1. Collectively, ganoderenic acid B can enhance the cytotoxicity of chemotherapeutics towards ABCB1-mediated MDR cancer cells via inhibition of the transport function of ABCB1. These findings provide evidence that ganoderenic acid B has the potential to be developed into an ABCB1-mediated multidrug resistance reversal agent.

Phospholipid-modified PEI-based nanocarriers for in vivo siRNA therapeutics against multidrug-resistant tumors

Multidrug resistance (MDR) mediated by P-glycoprotein overexpression in solid tumors is a major factor in the failure of many forms of chemotherapy. Here we evaluated phospholipid-modified, low-molecular-weight polyethylenimine (DOPE-PEI) nanocarriers for intravenous delivery of anti-P-pg siRNA to tumors with the final goal of modulating MDR in breast cancer. First, we studied the biodistribution of DOPE-PEI nanocarriers and the effect of PEG coating in a subcutaneous breast tumor model. Four hours postinjection, PEGylated carriers showed an 8% injected dose (ID) accumulation in solid tumor via the enhanced permeability and retention effect and 22% ID in serum due to a prolonged, PEG-mediated circulation. Second, we established the therapeutic efficacy and safety of DOPE-PEI/siRNA-mediated P-gp downregulation in combination with doxorubicin (Dox) chemotherapy in MCF-7/MDR xenografts. Weekly injection of siRNA nanopreparations and Dox for up to 5 weeks sensitized the tumors to otherwise non-effective doses of Dox and decreased the tumor volume by threefold vs controls. This therapeutic improvement in response to Dox was attributed to the significant, sequence-specific P-gp downregulation in excised tumors mediated by the DOPE-PEI formulations.

Reversal of P-glycoprotein-mediated multidrug resistance by the novel tetrandrine derivative W6

Overexpression of ATP-dependent efflux pump P-glycoprotein (P-gp) is the main cause of multidrug resistance (MDR) and chemotherapy failure in cancer treatment. Inhibition of P-gp-mediated drug efflux is an effective way to overcome cancer drug resistance. The present study investigated the reversal effect of the novel tetrandrine derivative W6 on P-gp-mediated MDR. KBv200, MCF-7/adr and their parental sensitive cell lines KB, MCF-7 were used for reversal study. The intracellular accumulation with P-gp substrates of doxorubicin was determined by flow cytometry. The expression of P-gp and ERK1/2 was investigated by western blot and real-time-PCR (RT-PCR) analysis. ATPase activity of P-gp was performed by P-gp-Glo(TM) assay systems. In comparison with P-gp-negative parental cells, W6 produced a favorable reversal effect in the MDR cells, as determined using the MTT assay. W6 significantly and dose-dependently increased intracellular accumulation of P-gp substrate doxorubicin (DOX) in P-gp overexpressing KBv200 cells, and also inhibited the ATPase activity of P-gp. W6 inhibited P-gp expression in KBv200 cells in a time-dependent manner, but it had no effect on MDR1 expression. In addition, W6 significantly decreased the ERK1/2 activation in KBv200 cells. Our results showed that W6 effectively reversed P-gp-mediated MDR by inhibiting the transport function and expression of P-gp, demonstrating the potential clinical utility of W6.

c-Jun NH2-terminal kinase-induced proteasomal degradation of c-FLIPL/S and Bcl2 sensitize prostate cancer cells to Fas- and mitochondria-mediated apoptosis by tetrandrine

Tetrandrine, a constituent of Chinese herb Stephania tetrandra, causes cell death in prostate cancer, but the molecular mechanisms leading to apoptosis is not known. Here we demonstrated that tetrandrine selectively inhibits the growth of prostate cancer PC3 and DU145 cells compared to normal prostate epithelial PWR-1E cells. Tetrandrine-induced cell death in prostate cancer cells is caused by reactive oxygen species (ROS)-mediated activation of c-Jun NH2-terminal kinase (JNK1/2). JNK1/2-mediated proteasomal degradation of c-FLIPL/S and Bcl2 proteins are key events in the sensitization of prostate cancer cells to Fas- and mitochondria-mediated apoptosis by tetrandrine. Tetrandrine-induced JNK1/2 activation caused the translocation of Bax to mitochondria by disrupting its association with Bcl2 which was accompanied by collapse of mitochondrial membrane potential (MMP), cytosolic release of cytochrome c and Smac, and apoptotic cell death. Additionally, tetrandrine-induced JNK1/2 activation increased the phosphorylation of Bcl2 at Ser70 and facilitated its degradation via the ubiquitin-mediated proteasomal pathway. In parallel, tetrandrine-mediated ROS generation also caused the induction of ligand-independent Fas-mediated apoptosis by activating procaspase-8 and Bid cleavage. Inhibition of procaspase-8 activation attenuated the cleavage of Bid, loss of MMP and caspase-3 activation suggest that tetrandrine-induced Fas-mediated apoptosis is associated with the mitochondrial pathway. Furthermore, most of the signaling effects of tetrandrine on apoptosis were significantly attenuated in the presence of antioxidant N-acetyl-l-cysteine, thereby confirming the involvement of ROS in these events. In conclusion, the results of the present study indicate that tetrandrine-induced apoptosis in prostate cancer cells is initiated by ROS generation and that both intrinsic and extrinsic pathway contributes to cell death.

The co-delivery of a low-dose P-glycoprotein inhibitor with doxorubicin sterically stabilized liposomes against breast cancer with low P-glycoprotein expression

Introduction

P-glycoprotein (P-gp) inhibitors are usually used to treat tumors that overexpress P-gps. However, most common types of breast cancers, such as Luminal A, are low-P-gp expressing, at least during the initial phases of treatment. Therefore, it would be interesting to know if P-gp inhibitors are still useful in treating low-P-gp-expressing tumors.

Methods

In the study reported here, the human breast-cancer cell line MCF-7, chosen as a model of Luminal A, was found to be low-P-gp expressing. We designed a novel doxorubicin (DOX) sterically stabilized liposome system co-loaded with the low-dose P-gp inhibitor cyclosporine A (CsA) (DOX/CsA/SSL).

Results

The co-delivery system showed good size uniformity, high encapsulation efficiency, and a desirable release profile. The cell-uptake and cytotoxicity studies demonstrated that CsA could significantly enhance the intracellular accumulation and toxicity of free DOX and the liposomal DOX in MCF-7 cells. The confocal microscopy and in vivo imaging study confirmed the intracellular and in vivo targeting effect of DOX/CsA/SSL, respectively. Finally, the in vivo study proved that DOX/CsA/SSL could achieve significantly better antitumor effect against MCF-7 tumor than controls, without inducing obvious systemic toxicity.

Conclusion

This study demonstrated that the co-delivery of a low-dose P-gp inhibitor and liposomal DOX could improve the therapy of low-P-gp-expressing cancer, which is of significance in clinical tumor therapy.

The novel bis-benzylisoquinoline PY35 reverses P-glycoprotein-mediated multidrug resistance

Multidrug resistance (MDR) to chemotherapeutic drugs is the main cause of chemotherapy failure in cancer treatment, and it generally results from expression of ATP-dependent efflux pump P-glycoprotein (P-gp). MDR reversal agents typically act by inhibiting the drug efflux activity of P-gp, thereby increasing intracellular drug levels. PY35 is a novel 5-substituted tetrandrine (Tet) derivative (CN Application No. 201210238709.6). The present study was performed to investigate the ability of PY35 to reverse P-gp-mediated MDR and its mechanism in resistant K562/Adriamycin (ADM), MCF-7/ADM cells and their sensitive cell lines K562 and MCF-7. The ability of PY35 to reverse drug resistance was evaluated by MTT assay. The results showed that PY35 can reverse MDR more effectively than the drug prototype‑Tet. The P-gp function was assessed by the Rhodamine 123 (Rho-123; a P-gp substrate) uptake assay with flow cytometry (FCM) and laser scanning confocal microscopes (LSCM); it showed that the MDR cells pumped Rho-123 out the cells, while their sensitive cells scarcely showed efflux. The presence of PY35 efficiently decreased the efflux of the Rho-123, showing that PY35 can reverse P-gp-mediated MDR by increasing the intracellular concentration of Rho-123. The intracellular accumulation of ADM was analyzed by FCM and showed that the coadministration of PY35 and ADM had clearer accumulation than the treatment of Tet and ADM, and was also more evident than treatment with only ADM. The effect of PY35 on the expression of P-gp was assessed by western blotting. The results indicated that PY35 does not inhibit the expression level of the P-gp. This study indicated that PY35 can effectively reverse P-gp-mediated MDR, not by inhibiting the expression of P-gp, but by the coadministration of PY35 and ADM that could increase the intracellular accumulation of drugs. Thus, PY35 may be a potential inhibitor to overcome drug resistance.