Reversal effect of a macrocyclic bisbibenzyl plagiochin E on multidrug resistance in adriamycin-resistant K562/A02 cells

Synthesis and evaluation of folate-mediated targeting and poly (β-amino ester)-mediated pH-responsive delivery system of riccardin D based on the O-carboxymethylated chitosan micelles

This study aimed to combine the active targeting function of folate (FA) receptor-mediated endocytosis with the pH-responsive drug delivery of poly (ethylene glycol)-grafted-poly (-amino ester) copolymers (PEG-PAE) in cancer targeting therapy. Herein, O-carboxymethylated chitosan (OCMC) was grafted with hydrophobic deoxycholic acid (DOCA). Further, PEG-PAE and FA-conjugated DOCA modified OCMC were synthesized to develop the potential cancer-targeted carrier (PEG-PAE-DOMC-FA), for which the structure was investigated by 1H NMR and FTIR. Then riccardin D (RD) was successfully loaded for tumor-targeted drug delivery. The particle size, zeta potential, encapsulating efficiencies, and loading content profiles of PEG-PAE-DOMC-FA/RD showed a strong dependence on the environmental pH values. The cumulative release of PEG-PAE-DOMC-FA/RD at pH 5.0 (90.63 %) was higher than pH 7.4 (51.12 %), which also indicated the pH sensitivity. Moreover, a lower IC50 and higher coumarin-6 uptake were found because of the folate-receptor-mediated endocytosis. In pharmacokinetic study, PEG-PAE-DOMC-FA/RD significantly improved the mean retention time (MRT) and AUC(0-∞) from 7.89 h and 36.1 mg/L·h of control group to 10.03 h and 123.8 mg/L·h. In the xenograft mice model, stronger antitumor efficacy and lower toxicity were confirmed. In conclusion, the multi-functional micelles could be considered as a promising vehicle for delivering hydrophobic drugs to tumors.

Bis-bibenzyls, Bibenzyls, and Terpenoids in 33 Genera of the Marchantiophyta (Liverworts): Structures, Synthesis, and Bioactivity

The Marchantiophyta (liverworts) are rich sources of phenolic substances, especially cyclic and acyclic bis-bibenzyls, which are rare natural products in the plant kingdom, together with bibenzyls and characteristic terpenoids. At present, more than 125 bis-bibenzyls have been found in liverworts. They are biosynthesized from the dimerization of lunularic acid via dihydrocoumaric acid and prelunularin. The structurally unusual cyclic and acyclic bis-bibenzyls show various biological activities such as antimicrobial, antifungal, cytotoxic, muscle relaxation, antioxidant, tubulin polymerization inhibitory, and antitrypanosomal activities, among others. The present review article deals with the distribution and structure of bis-bibenzyls, bibenzyls, and several characteristic ent-sesqui- and diterpenoids in liverworts. Furthermore, the biosynthesis and total syntheses and biological activities of bis-bibenzyls are also surveyed.

Assessment of the Biological Effects of Pellia endiviifolia and its Constituents in Vitro

Liverworts are characterized by a high content of bioactive compounds reported to show antimicrobial, anticancer, and antioxidant properties. In this study, the biological effects of the methanol extract of the liverwort Pellia endiviifolia and its constituents, bis-bibenzyls perrottetin E, 10′-hydroxyperrottetin E, and 10,10′-dihydroxyperrottetin E, were investigated using human peripheral blood cells as a model system. The assessment of the investigated compounds comprised testing their genotoxicity, apoptotic potential, and redox modulating activities. The genotoxicity testing indicated that medium (25 µM) and high concentrations (100 µM) of the investigated compounds displayed genotoxic and antiproliferative effects in human lymphocytes as revealed by significant, concentration-dependent enhancement of the micronuclei incidence and decrease in the cytokinesis-block proliferation index compared to the control ( P < .001). Analysis of leukocyte apoptosis showed a substantial potential of all investigated compounds to induce apoptosis, which was not concentration-dependent. The P endiviifolia extract and perrottetin E demonstrated considerable pro-apoptotic potential, even at the lowest concentration (1 µM) applied. Evaluation of the redox modulating effects, which comprised measuring erythrocyte catalase activity and the lymphocyte malondialdehyde level, showed that the investigated compounds did not induce oxidative stress in human peripheral blood cells ( P > .05). The observed genotoxic, antiproliferative, and proapoptotic effects of the investigated compounds make them suitable for further comprehensive studies related to their possible applications as anticancer agents.

Bis-Bibenzyls from the Liverwort Pellia endiviifolia and Their Biological Activity

Based on previous investigations where bis-bibenzyls isolated from liverworts showed various biological activities (cytotoxic, antimicrobial, and antiviral), we investigated their cytotoxic activity in several human cancer cell lines. From the methylene-chloride/methanol extract of the liverwort Pellia endiviifolia, three bis-bibenzyls of the perrottetin type were isolated, namely perrottetin E, 10′-hydroxyperrottetin E, and 10,10′-dihydroxyperrottetin E. The last two were found for the first time in this species. Their structures were resolved using 1D and 2D NMR, as well as by comparison with data in the literature. Cytotoxic activity of the isolated compounds was tested on three human leukemia cell lines, HL-60 (acute promyelocytic leukemia cells), U-937 (acute monocytic leukemia cells), and K-562 (human chronic myelogenous leukemia cells), as well as on human embryonal teratocarcinoma cell line (NT2/D1) and human glioblastoma cell lines A-172 and U-251, and compared to the previously isolated bis-bibenzyls (perrottetins) of similar structure. The isolated compounds exhibited modest activity against leukemia cells and significant activity against NT2/D1 and A-172. Overall, the most active cytotoxic compounds in this investigation were perrottetin E (1), isolated in this work from Pellia endiviifolia, and perrottetin F phenanthrene derivative (7), previously isolated from Lunularia cruciata and added for a comparison of their cytotoxic activity.

Bibenzyls and bisbybenzyls of bryophytic origin as promising source of novel therapeutics: pharmacology, synthesis and structure-activity

BACKGROUND

The amphibian, non-vascular, gametophyte-dominant, bio-indicator class, bryophytes; with their wide ranges of habitat have attained importance due to their promising medicinal attributions and therapeutic role; mostly aided by presence of aromatic bibenzyl and bisbybenzyl class of compounds. Bibenzyls are steroidal ethane derivatives, resembling the structural moiety of bioactive dihydro-stilbenoids or iso-quinoline alkaloids. These stress triggered secondary metabolites are the by-products of the flavonoid biosynthetic pathway. Different classes of bryophytes (Bryophyta, Marchantiophyta and Anthocerotophyta) possess different subtypes of bibenzyls and dimeric bisbibenzyls. Among the liverwort, hornwort and mosses, former one is mostly enriched with bibenzyl type constituents as per the extensive study conducted for phytochemical deposit. Considering macrocyclic and acyclic group of bibenzyls and bisbybenzyls, generally marchantin type compounds are reported vividly for significant biological activity that includes neuro-nephro-cardio-protection besides anti-allergic, anti-microbial, anti-apoptotic and cytotoxic activities studied on in-vitro and in-vivo models or on cell lines.

RESULT

The critical analysis of reported chemical and pharmaceutical attributions of bibenzyls and bis-bibenzyls yielded detailed report on this compound class along with their application, mode of action, natural source, techniques of synthesis, extraction procedure, isolation and characterization. Further, the structure activity relationship studies and bioactivity of bibenzyls derived from non-bryophytic origin were also summarized.

CONCLUSION

This review encompasses prospective biological application of botanical reservoir of this primarily ignored, primeval land plant group where recent technical advances has paved the way for qualitative and quantitative isolation and estimation of novel compounds as well as marker components to study their impact on environment, as bio-control agents and as key leads in future drug designing. Graphical abstract.

Antiproliferative and Antimicrobial Activities of Selected Bryophytes

One-hundred and sixty-eight aqueous and organic extracts of 42 selected bryophyte species were screened in vitro for antiproliferative activity on a panel of human gynecological cancer cell lines containing HeLa (cervix epithelial adenocarcinoma), A2780 (ovarian carcinoma), and T47D (invasive ductal breast carcinoma) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and for antibacterial activity on 11 strains using the disc-diffusion method. A total of 99 extracts derived from 41 species exerted ≥25% inhibition of proliferation of at least one of the cancer cell lines at 10 μg/mL. In the cases of Brachythecium rutabulum, Encalypta streptocarpa, Climacium dendroides, Neckera besseri, Pleurozium schreberi, and Pseudoleskeella nervosa, more than one extract was active in the antiproliferative assay, whereas the highest activity was observed in the case of Paraleucobryum longifolium. From the tested families, Brachytheciaceae and Amblystegiaceae provided the highest number of antiproliferative extracts. Only 19 samples of 15 taxa showed moderate antibacterial activity, including the most active Plagiomnium cuspidatum, being active on 8 tested strains. Methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus were the most susceptible to the assayed species. This is the first report on the bioactivities of these 14 species.

Targeting autophagy augments the activity of DHA-E3 to overcome p-gp mediated multi-drug resistance

Multidrug resistance (MDR) is a major obstacle for successful chemotherapy treatment. Searching for effective MDR modulators and combining them with anticancer drug therapies has been a promising strategy against clinical MDR. In our previous study, we have found that DHA-E3, a synthetic derivative of DHA, has the ability to modulate the function of P-glycoprotein (P-gp) and reverse MDR in cancer cells. In this study, we further evaluated the reversal effect of DHA-E3 on MDR and explored its mechanism of action in vitro. Our findings showed that DHA-E3 significantly potentiated the cytotoxicity of vincristine(VCR) and adriamycin(ADR) in the P-gp over-expressing KB/VCR and A02 cells. The mechanistic study found that DHA-E3 increased the intracellular accumulation of ADR and rhodamine-123 by directly inhibiting the drug-transport activity of P-gp. In the present study, we found that DHA-E3 not only reversed MDR, but also induced autophagy in MDR cancer cells. To determine whether DHA-E3-induced autophagy is an adaptive survival response or contributes to cell death, we manipulated autophagic activity using autophagy inhibitor 3-MA or siRNA targeting Beclin1. We found that the reversal activity of DHA-E3 was significantly exacerbated in the presence of 3-MA or blocking the expression of Beclin1. These results suggest that DHA-E3 is capable of reversing MDR, induction of autophagy represents a defense mechanism and inhibiting this process may be an effective strategy to augment the reversal activity of reversal agents.

Reversal of the multidrug resistance of human ileocecal adenocarcinoma cells by acetyl-11-keto-β-boswellic acid via downregulation of P-glycoprotein signals

Multidrug resistance (MDR) represents a clinical obstacle to cancer chemotherapy since it causes cancer recurrence and metastasis. Acetyl-11-keto-β-boswellic acid (AKBA), an active ingredient derived from the plant Boswellia serrata, has been found to inhibit the growth of a wide variety of tumor cells, including glioma, colorectal cancer, leukemia, human melanoma, hepatocellular carcinoma, and prostate cancer cells. However, the actions of AKBA in multidrug-resistant cancer cells have not been fully elucidated. The current study examined the reversal of MDR by AKBA in a human ileocecal adenocarcinoma cell line with vincristine-induced resistance, HCT-8/VCR. A 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay indicated that cytotoxicity increased drastically and the IC50 of VCR in HCT-8/VCR cells decreased in the presence of AKBA. AKBA had a maximum "fold reversal" of MDR (FR) of 9.19-fold. In addition, HCT-8/VCR cells treated with AKBA and VCR exhibited a higher percentage of apoptotic tumor cells according to flow cytometry. The reversal of MDR by AKBA was evident in an intracellular increase in Rhodamine (Rh123), indicating that the activity of P-glycoprotein (P-gp) was blocked. Furthermore, AKBA inhibited the expression of P-gp and decreased levels of expression of multidrug resistance gene 1 in HCT-8/VCR cells. The current results indicated that AKBA might be a potential agent to reverse MDR in human ileocecal adenocarcinoma.

Design, synthesis and biological evaluation of novel triazole-core reversal agents against P-glycoprotein-mediated multidrug resistance

We designed and synthesized a novel series of P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) inhibitors bearing a triazolphenethyl–tetrahydroisoquinoline scaffold through click chemistry.

Novel isatin derivatives of podophyllotoxin: synthesis and cytotoxic evaluation against human leukaemia cancer cells as potent anti-MDR agents

Compound8cexhibited cytotoxicity at nanomolar range; induced G2/M cell cycle arrest accompanied by apoptosis and down-regulated the levels of Pgp, MRP-1 and GST-π.

FZD1 activates protein kinase C delta-mediated drug-resistance in multidrug-resistant MES-SA/Dx5 cancer cells

Multidrug-resistant (MDR) cancer is a major clinical problem in chemotherapy of cancer patients. We have noted inappropriate PKCδ hypomethylation and overexpression of genes in the PKCδ/AP-1 pathway in the human uterus sarcoma drug-resistant cell line, MES-SA/Dx5 cells, which also overexpress p-glycoprotein (ABCB1). Recent studies have indicated that FZD1 is overexpressed in both multidrug-resistant cancer cell lines and in clinical tumor samples. These data have led us to hypothesize that the FZD1-mediated PKCδ signal-transduction pathway may play an important role in drug resistance in MES-SA/Dx5 cells. In this work, the PKCδ inhibitor Rottlerin was found to reduce ABCB1 expression and to inhibit the MDR drug pumping ability in the MES-SA/Dx5 cells when compared with the doxorubicin-sensitive parental cell line, MES-SA. PKCδ was up-regulated with concurrent up-regulation of the mRNA levels of the AP-1-related factors, c-JUN and c-FOS. Activation of AP-1 also correlated with up-regulation of the AP-1 downstream genes HGF and EGR1. Furthermore, AP-1 activities were reduced and the AP-1 downstream genes were down-regulated in Rottlerin-treated or PKCδ shRNA-transfected cells. MES-SA/Dx5 cells were resensitized to doxorubicin-induced toxicity by co-treatment with doxorubicin and Rottlerin or PKCδ shRNA. In addition, cell viability and drug pump-out ability were significantly reduced in the FZD1 inhibitor curcumin-treated and FZD1 shRNA-knockdown MES-SA/Dx5 cells, indicating involvement of PKCδ in FZD1-modulated ABCB1 expression pathway. Taken together, our data demonstrate that FZD1 regulates PKCδ, and the PKCδ/AP-1 signalling transduction pathway plays an important role in drug resistance in MES-SA/Dx5 cells.

Secondary metabolites from the Chinese liverwort Cephaloziella kiaeri

Sixteen new clerodane diterpenoids, cephaloziellins A-P (1-16), and two known analogues (17 and 18) were isolated from an EtOH extract of the Chinese liverwort Cephaloziella kiaeri. The structures of the new compounds were elucidated from extensive spectroscopic data (IR, UV, HRESIMS, 1D NMR, and 2D NMR), and the structures of 5, 9, and 15 were confirmed by single-crystal X-ray diffraction analyses. The absolute configurations of all new compounds were established by comparing experimental and calculated electronic circular dichroism spectra.

Phytochemical and biological studies of bryophytes

The bryophytes contain the Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerotophyta (hornworts). Of these, the Marchantiophyta have a cellular oil body which produce a number of mono-, sesqui- and di-terpenoids, aromatic compounds like bibenzyl, bis-bibenzyls and acetogenins. Most sesqui- and di-terpenoids obtained from liverworts are enantiomers of those found in higher plants. Many of these compounds display a characteristic odor, and can have interesting biological activities. These include: allergenic contact dermatitis, antimicrobial, antifungal and antiviral, cytotoxic, insecticidal, insect antifeedant, superoxide anion radical release, 5-lipoxygenase, calmodulin, hyaluronidase, cyclooxygenase, DNA polymerase β, and α-glucosidase and NO production inhibitory, antioxidant, piscicidal, neurotrophic and muscle relaxing activities among others. Each liverwort biosynthesizes unique components, which are valuable for their chemotaxonomic classification. Typical chemical structures and biological activity of the selected liverwort constituents as well as the hemi- and total synthesis of some biologically active compounds are summarized.

In vitro and in vivo evaluation of riccardin D nanosuspensions with different particle size

Riccardin D (RD) is a novel compound extracted from Chinese liverwort Marchantia polymorpha L. It exhibits various anticancer activities and can be used during lung cancer treatment. However, the compound's low solubility hinders its development. Recently nanosuspension has been developed as one of the most promising formulations for poorly water-soluble drugs. In order to understand the dissolution behavior of riccardin D in vitro and in vivo, two nanosuspensions of riccardin D with markedly different sizes were prepared. The particle size of nanosuspension A prepared by bottom-up method was 184.1±3.15 nm, while that of nanosuspension B prepared by top-down method was 815.4±9.65 nm. The main purpose of this study was to investigate the effects of particle size on pharmacokinetics and tissue distribution after intravenous administration. Riccardin D dissolving in organic solution was studied as control group. In pharmacokinetics study in Wistar rats, nanosuspension A showed properties similar to the control group, while nanosuspension B exhibited rather different properties. In tissue distribution research on Kunming strain mice, nanosuspension A had a multi-peak phenomenon because of reticulate endothelial system (RES) while nanosuspension B showed a high uptake in RES organs that passively target to the lungs. In conclusion, particle size of riccardin D nanosuspensions had obvious effects on pharmacokinetics and tissue distribution.

Synthesis of macrocyclic bisbibenzyl derivatives and their anticancer effects as anti-tubulin agents

Based on the core skeleton of the total synthesized bisbibenzyl marchantin C, riccardin D and plagiochin E, a series of brominated and aminomethylated derivatives of above three bisbibenzyls have been synthesized and their cytotoxic activity against KB, MCF-7 and PC3 cell lines has been preliminary evaluated. The bio-test results revealed that the brominated derivatives 21, 22, 24, 25 and 28 exhibited excellent antiproliferative activity, with IC(50) value lower than their parent compounds. As a most potent microtubule depolymerization agent, compound 28 was found to arrest cells at the G(2)/M phase of the cell cycle as determined by the flow cytometry assay in PC3 cell line. The remarkable biological profile and novel structure of these bisbibenzyl derivatives make them possible as promising candidates for clinical development as chemotherapeutic agents.

Doxorubicin-loaded PEG-PCL copolymer micelles enhance cytotoxicity and intracellular accumulation of doxorubicin in adriamycin-resistant tumor cells

Background

Multidrug resistance remains a major obstacle to successful cancer chemotherapy. Some chemical multidrug resistance inhibitors, such as ciclosporin and verapamil, have been reported to reverse resistance in tumor cells. However, the accompanying side effects have limited their clinical application. In this study, we have developed a novel drug delivery system, ie, a polyethyleneglycol-polycaprolactone (PEG-PCL) copolymer micelle encapsulating doxorubicin, in order to circumvent drug resistance in adriamycin-resistant K562 tumor cells.

Methods

Doxorubicin-loaded diblock copolymer PEG-PCL micelles were developed, and the physicochemical properties of these micelles, and accumulation and cytotoxicity of doxorubicin in adriamycin-resistant K562 tumor cells were studied.

Results

Doxorubicin-loaded micelles were prepared using a solvent evaporation method with a diameter of 36 nm and a zeta potential of +13.8 mV. The entrapment efficiency of doxorubicin was 48.6% ± 2.3%. The micelles showed sustained release, increased uptake, and cellular cytotoxicity, as well as decreased efflux of doxorubicin in adriamycin-resistant K562 tumor cells.

Conclusion

This study suggests that PEG-PCL micelles have the potential to reverse multidrug resistance in tumor cells.

Reversal effects of two new milbemycin compounds on multidrug resistance in MCF-7/adr cells in vitro

Development of agents to overcome multidrug resistance (MDR) is important in cancer chemotherapy, and the overexpression of P-glycoprotein (P-gp) is one of the major mechanisms of MDR. In this paper, we evaluated the effects of two new milbemycin compounds, milbemycin β(14) and secomilbemycin D, isolated from fermentation broth of S. bingchenggensis on reversing MDR of adriamycin-resistant human breast carcinoma (MCF-7/adr) cells. We observed that the both milbemycins (5 μM) showed strong potency to increase adriamycin cytotoxicity toward MCF-7/adr cells with reversal fold (RF) of 13.5 and 10.59, respectively. In addition, the mechanisms of milbemycins on reversing P-gp-mediated MDR demonstrated that they significantly increased the accumulations of adriamycin and Rh123 via inhibiting P-gp efflux in MCF-7/adr cells. Furthermore, the results also revealed that milbemycin β(14) and secomilbemycin D could regulate down the expression of P-gp, but not affect the expression of MDR1 gene. In conclusion, our observations suggest that the two new milbemycin compounds probably represent the promising agents for reversing MDR in cancer therapy.

Dihydroptychantol A, a macrocyclic bisbibenzyl derivative, induces autophagy and following apoptosis associated with p53 pathway in human osteosarcoma U2OS cells

Dihydroptychantol A (DHA), a novel macrocyclic bisbibenzyl compound extracted from liverwort Asterella angusta, has antifungal and multi-drug resistance reversal properties. Here, the chemically synthesized DHA was employed to test its anti-cancer activities in human osteosarcoma U2OS cells. Our results demonstrated that DHA induced autophagy followed by apoptotic cell death accompanied with G₂/M-phase cell cycle arrest in U2OS cells. DHA-induced autophagy was morphologically characterized by the formation of double membrane-bound autophagic vacuoles recognizable at the ultrastructural level. DHA also increased the levels of LC3-II, a marker of autophagy. Surprisingly, DHA-mediated apoptotic cell death was potentiated by the autophagy inhibitor 3-methyladenine, suggesting that autophagy may play a protective role that impedes the eventual cell death. Furthermore, p53 was shown to be involved in DHA-mediated autophagy and apoptosis. In this connection, DHA increased nuclear expression of p53, induced p53 phosphorylation, and upregulated p53 target gene p21(Waf1/Cip1). In contrast, cytoplasmic p53 was reduced by DHA, which contributed to the stimulation of autophagy. In relation to the cell cycle, DHA decreased the expression of cyclin B₁, a cyclin required for progression through the G₂/M phase. Taken together, DHA induces G₂/M-phase cell cycle arrest and apoptosis in U2OS cells. DHA-induced apoptosis was preceded by the induction of protective autophagy. DHA-mediated autophagy and apoptosis are associated with the cytoplasmic and nuclear functions of p53.

Riccardin D, a novel macrocyclic bisbibenzyl, induces apoptosis of human leukemia cells by targeting DNA topoisomerase II

We studied the effect of riccardin D, a macrocyclic bisbibenzyl, which was isolated from the Chinese liverwort plant, on human leukemia cells and the underlying molecular mechanism. Riccardin D had a significant antiproliferative effect on human leukemia cell lines HL-60, K562 and its multidrug resistant (MDR) counterpart K562/A02 cells, but showed no effect on the topoisomerase-II-deficient HL-60/MX2 cells, as measured by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. The pBR322 DNA relaxation assay revealed that riccardin D selectively inhibited the activity of topoisomerase II (topo II). The suppression of topo II activity by riccardin D was stronger than that of etoposide, a known topo II inhibitor. After treatment with riccardin D, nuclear extracts of leukemia K562 and K562/A02 cells left the majority of pBR322 DNA in a supercoiled form. Further examination showed that riccardin D effectively induced HL-60, K562 and K562/A02 apoptosis as evidenced by externalization of phosphatidylserine and formation of DNA ladder fragments. The activation of cytochrome c, caspase-9, caspase-3 and cleaved poly ADP-ribose polymerase (PARP) was also enhanced, as estimated by Western blot analysis. By contrast, riccardin D was unable to induce apoptosis in the topoisomerase-II-deficient HL-60/MX2 cells, indicating that the induction of apoptosis by riccardin D was due to the inhibition of topo II activity. In addition, riccardin D was able to significantly decrease P-glycoprotein (P-gp) expression in K562/A02 cells. Taken together, our data demonstrate that riccardin D is a novel DNA topo II inhibitor which can induce apoptosis of human leukemia cells and that it has therapeutic potential for both regular and MDR strains of leukemia cells.

Modulation of P-glycoprotein activity by the substituted quinoxalinone compound QA3 in adriamycin-resistant K562/A02 cells

QA3 is a derivative of the substituted 1,3-dimethyl-1H-quinoxalin-2-ones, which are compounds that may selectively antagonize P-glycoprotein (P-gp) in multidrug resistance (MDR) cancer cells. Our previous work identified QA3 as a candidate compound for reversing MDR in cancer cells. In the present study, we found that QA3 significantly decreases the intracellular level of ATP, stimulates ATPase activity in membrane microsomes and decreases protein kinase C (PKC) activity. These results indicated that QA3 inhibits P-gp activity by blocking ATP hydrolysis and ATP regeneration. Furthermore, QA3 triggered and increased adriamycin-induced K562/A02 cell apoptosis as evidenced by Annexin V-FITC plus PI staining.Western blot analysis showed that the levels of cleaved caspase-9 and cleaved caspase-3 proteins increased, and similarly, the levels of procaspase-9 and procaspase-3 decreased after QA3 treatment. Consequently, poly ADP-ribose polymerase (PARP) activity increased as evidenced by the presence of the PARP cleavage product in K562/A02 cells. QA3 also enhanced the potency of adriamycin against K562/A02 cells as demonstrated by increased apoptosis and activation of caspase-9,-3 and PARP. These data support the observation that P-gp activity is inhibited after QA3 treatment. Moreover, these results indicate that QA3 is a novel MDR reversal agent with potent inhibitory action against P-gp MDR cancer cells.

HZ08, a great regulator to reverse multidrug resistance via cycle arrest and apoptosis sensitization in MCF-7/ADM

In early studies, it was demonstrated that R-HZ08, S-HZ08 and the racemate had strong reverse efficacy of multidrug resistance in vitro and in vivo (Yan et al., 2008b). The effect was supposed to have direct interaction with multidrug resistance-associated protein (MRP1) in MCF-7/ADM and P-glycoprotein in K562/A02. According to our latest study, we found HZ08 could enhance chemotherapy induced apoptosis by synergistic action on reactive oxygen species generation, GSH depletion, mitochondrial membrane potential depolarization, cytochrome c release and caspase activation. Moreover, the potential selective effect of HZ08 on resistant cells suggested that HZ08 have specific targets for resistance reversal via apoptosis regulation. Therefore, we traced individual influence of HZ08, not only on apoptosis pathway per se but also on apoptosis related intracellular regulation systems. Then we found HZ08 could increase cells in G(0)/G(1) phase and regulate apoptosis related proteins (Bcl-2, Bax) as well as upstream functional molecules (c-Myc and c-Fos), which are usually abnormal in malignancy and responsible for multidrug resistance in MCF-7/ADM. Thereby, chemotherapy induced apoptosis was promoted. R-HZ08 showed better effect than S-HZ08 or the racemate did in most of targets above. Furthermore, HZ08 did not change the concentration of intracellular Ca(2+) which means it would not have side effect as verapamil does. Considering multidrug resistance is multifactorial, HZ08, especially R-HZ08, which could sensitize apoptosis by multiple improvements of upstream malignant characters, will be a promising drug to enhance the effect of chemotherapy in the treatment of multidrug resistant tumor.

Anti-proliferative and pro-apoptotic effects of tectorigenin on hepatic stellate cells

AIM

To investigate the effect of tectorigenin on proliferation and apoptosis of hepatic stellate cells (HSC)-T6 cells.

METHODS

HSC-T6 cells were incubated with tectorigenin at different concentrations, and their proliferation was assessed by bromodeoxyuridine incorporation assay. Apoptosis was detected by flow cytometry assay with Hoechst 33342 staining. Also, generation of reactive oxygen species (ROS), intracellular [Ca(2+)](i), potential of mitochondrial membrane, activities of cytochrome c and caspase-9 and -3 were investigated to explore a conceivable apoptotic pathway.

RESULTS

Tectorigenin suppressed the proliferation of HSC-T6 cells and induced apoptosis of HSC-T6 cells in a time- and dose-dependent manner. Tectorigenin at the concentration of 100 microg/mL greatly inhibited the viability of HSC-T6 cells and induced the condensation of chromatin and fragmentation of nuclei. When treated for 48 h, the percentage of cell growth and apoptosis reached 46.3% +/- 2.37% (P = 0.004) and 50.67% +/- 3.24% (P = 0.003), respectively. Furthermore, tectorigenin-induced apoptosis of HSC-T6 cells was associated with the generation of ROS, increased intracellular [Ca(2+)](i), loss of mitochondrial membrane potential, translocation of cytochrome c, and activation of caspase-9 and -3.

CONCLUSION

Tectorigenin inhibits proliferation of HSC-T6 cells and induces apoptosis of HSC-T6 cells.

Reversal of P-glycoprotein-mediated multidrug resistance in vitro by milbemycin compounds in adriamycin-resistant human breast carcinoma (MCF-7/adr) cells

The effects of milbemycin A(4) (MB A(4)), milbemycin oxime A(4) (MBO A(4)) and milbemycin beta(1) (MB beta(1)) on reversing multidrug resistance (MDR) of tumor cells were firstly conducted according to the following research, including MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay, the accumulation of adriamycin, the accumulation and efflux of rhodamine 123 (Rh123), the regulations of MDR1 gene, and expression of P-gp. The three milbemycins (5muM) showed strong potency to increase adriamycin cytotoxicity toward adriamycin-resistant human breast carcinoma cells MCF-7/adr with reversal fold (RF) of 21.42, 19.06 and 14.89, respectively. In addition, the mechanisms of milbemycins on P-glycoprotein (P-gp)-mediated MDR demonstrated that the milbemycins significantly increased the intracellular accumulations of adriamycin and Rh123 via inhibiting P-gp transport function. Based on the analysis of the P-gp and MDR1 gene expression using flow cytometry and RT-PCR, the results revealed that milbemycin compounds, particularly MB A(4), could regulate down the expression of the P-gp and MDR1 gene. These findings suggest that the milbemycins probably represent promising agents for overcoming MDR in cancer therapy, and especially MB A(4) is better modulator with the lowest toxicity.

Cyclic bisbibenzyls induce growth arrest and apoptosis of human prostate cancer PC3 cells

AIM

To investigate the cytotoxic effects of four cyclic bisbibenzyls, Riccardin C (Ric), Pakyonol (Pak), Marchantin M (Mar), and Plagiochin E (Pla) against chemoresistant prostate cancer PC3 cells.

METHODS

Cell growth was assayed by MTT method, and apoptotic related protein Bcl-2 and Bax, poly(ADP-ribose) polymerase (PARP) were examined by Western blotting. Cell cycle and apoptosis of PC3 cells were evaluated with flow cytometry and morphologic examinations.

RESULTS

The four compounds inhibited proliferation and elicited cell death in a dose- and time-dependent manner with IC(50) values of 3.22 micromol/L for Ric, 7.98 micromol/L for Pak, 5.45 micromol/L for Mar, and 5.99 micromol/L for Pla, respectively. Furthermore, exposed to these chemicals caused a decrease in the antiapoptotic protein Bcl-2 and an increase in proapoptotic Bax expression. PARP cleavage and caspase-3 activity were also observed.

CONCLUSION

The results suggest that cyclic bisbibenzyls could be used for the development of novel therapeutic chemicals against prostate cancer.

Reversal of P-glycoprotein-mediated multidrug resistance in vitro by doramectin and nemadectin

Objectives

Multidrug resistance (MDR) is a serious obstacle encountered in cancer treatment. This study was performed to explore the reversal of MDR by doramectin from the avermectin family and nemadectin belonging to the milbemycin family.

Methods

The MTT assay was used to evaluate the abilities of the two compounds to reverse drug resistance in adriamycin-resistant human breast carcinoma cells (MCF-7/adr). Intracellular accumulation of adriamycin was determined by HPLC. The effects of the two compounds on inhibiting P-glycoprotein (P-gp) efflux was demonstrated by accumulation of rhodamine 123 in MCF-7/adr cells. To investigate the mechanism of reversal by the two compounds, the expressions of P-gp and the MDR1 gene encoding P-gp were tested by flow cytometry and reverse-transcriptase PCR.

Key findings

Doramectin and nemadectin at the high dose of 8 μmol/l significantly increased the sensitivity of MCF-7/adr cells to adriamycin by 49.35- and 23.97-fold, respectively. They also increased the intracellular accumulation of adriamycin and rhodamine 123 in MCF-7/adr cells in a dose-dependent manner. Expression of both P-gp and MDR1 were down-regulated.

Conclusions

Doramectin and nemadectin are promising agents for overcoming MDR in cancer therapy. Doramectin was more potent in reversing MDR.

Ring strain and total syntheses of modified macrocycles of the isoplagiochin type

Macrocycles of the bisbibenzyl-type are natural products that are found exclusively in bryophytes (liverworts). The molecular framework of the subtype "isoplagiochin" is of substantial structural interest because of the chirality of the entire molecule, which arises from two biaryl axes in combination with two helical two-carbon units in a cyclic arrangement. From a structural as well as a synthetic point of view we report on the total synthesis of compounds which possess more rigid two-carbon biaryl bridges like stilbene (E or Z) or even tolane moieties which were introduced starting with a Sonogashira protocol. The McMurry method proved to be a powerful tool for the cyclization to these considerably ring-strained macrocycles.

Reversal of multidrug resistance by curcumin through FA/BRCA pathway in multiple myeloma cell line MOLP-2/R

Most patients with multiple myeloma (MM) will relapse eventually due to the acquired multidrug resistance (MDR). The objective of this study was to explore the reversal effect of curcumin on the MDR of human MM cell line, MOLP-2/R, and analyze the role of Fanconi anemia (FA)/BRCA pathway in this process. MOLP-2/R was selected by stepwise exposure of parental MOLP-2 cells to increasing concentrations of melphalan. The MTT assay was used to detect the reversal ratio of curcumin. The FANCD2 monoubiquitination expression was detected by western blotting to explore the role of FA/BRCA pathway. Cell cycle, apoptosis, and intracellular drug concentration were analyzed by flow cytometry. The results indicated that combination of melphalan with curcumin had stronger effects on the proliferation inhibition, inducement of apoptosis, G2/M phase arrest, and enhancement of intracellular drug concentration than melphalan alone in MOLP-2/R cells. These effects were accompanied with inhibition of FA/BRCA pathway by down regulation of FANCD2 protein monoubiquitination in a dose-dependent manner. In conclusion, curcumin reversed multidrug resistance of MOLP-2/R through inhibition of FA/BRCA pathway. The possible mechanisms include (1) reduction of DNA damage repair and stimulation of apoptosis of tumor cells through inhibition of FA/BRCA pathway, which is important for DNA repair, and (2) achievement of high concentration in target cells. Curcumin may be a safe reversal agent of multidrug resistance with low-dose DNA cross-linking agents.