Phytochemicals reverse P-glycoprotein mediated multidrug resistance via signal transduction pathways

P-glycoprotein, encoded by ATP-binding cassette transporters B1 gene (ABCB1), renders multidrug resistance (MDR) during cancer chemotherapy. Several synthetic small molecule inhibitors affect P-glycoprotein (P-gp) transport function in MDR tumor cells. However, inhibition of P-gp transport function adversely accumulates chemotherapeutic drugs in non-target normal tissues. Moreover, most small-molecule P-gp inhibitors failed in the clinical trials due to the low therapeutic window at the maximum tolerated dose. Therefore, downregulation of ABCB1-gene expression (P-gp) in tumor tissues seems to be a novel approach rather than inhibiting its transport function for the reversal of multidrug resistance (MDR). Several plant-derived phytochemicals modulate various signal transduction pathways and inhibit translocation of transcription factors, thereby reverses P-gp mediated MDR in tumor cells. Therefore, phytochemicals may be considered an alternative to synthetic small molecule P-gp inhibitors for the reversal of MDR in cancer cells. This review discussed the role of natural phytochemicals that modulate ABCB1 expression through various signal transduction pathways in MDR cancer cells. Therefore, modulating the cell signaling pathways by phytochemicals might play crucial roles in modulating ABCB1 gene expression and the reversal of MDR.

Cytotoxic and Anti-Inflammatory Sesquiterpenes from the Whole Plants of Centipeda minima

Sixteen new sesquiterpene lactones (1-16) along with 13 known analogues (17-29) were isolated from the whole plants of Centipeda minima. The structures of 1-16 were delineated by the combination of NMR spectroscopic experiments, HRESIMS, single-crystal X-ray diffraction analyses, and ECD spectra. Compounds 23-26 showed potent cytotoxicity against Hela, HCT-116, and HepG2 cells with IC₅₀ values of 0.8-2.6, 0.4-3.3, and 1.1-2.6 μM, respectively. Compounds 8, 15, and 24 exhibited significant inhibitory activity on the production of nitric oxide in the lipopolysaccharide-activated RAW 264.7 mouse macrophage cell line, with IC₅₀ values ranging from 0.1 to 0.2 μM.

Phenylethanol glycosides from the seeds of Aesculus chinensis var. chekiangensis

Three new phenylethanol glycosides (1-3) and one known analogue (4) were isolated from the seeds of Aesculus chinensis Bge. var. chekiangensis. To the best of our knowledge, this represents the first isolation of phenylethanol glycosides from the genus of Aesculus, which enriched its chemical composition. Structure elucidations were performed via extensive NMR and HRESIMS data together with comparison with literature data. Thereafter, the isolated compounds were assayed for their neuroprotective activities against CoCl₂-induced cytotoxicity in PC12 cells and compound 3 exhibited moderate activity.

MEG3 is restored by schisandrin A and represses tumor growth in choriocarcinoma cells

Schisandrin A (SchA) has been reported as a multidrug resistance-reversing agent; however, its antitumor effects have been rarely reported. Consequently, we attempted to explore whether SchA per se possesses an antitumor property in choriocarcinoma JEG-3 and BeWo cells and its potential mechanisms. JEG-3, BeWo, and HTR-8/SVneo cells were stimulated with SchA at different concentrations (10-100 μM), and cellular viability was evaluated with Cell Counting Kit-8. After stimulation with SchA, proliferation, apoptosis, migration, and invasion were detected by bromodeoxyuridine assay, Annexin V-fluorescein isothiocyanate/propidium iodide (Annexin V-FITC/PI) method, and a Transwell system, in JEG-3 cells transfected with short hairpin-RNA for maternally expressed 3. Western blot was performed to quantify protein. MEG3 was examined by a quantitative reverse transcription-polymerase chain reaction. MEG3 was downregulated in choriocarcinoma tissues. SchA diminished cellular viability, decreased proliferative activity, inhibited migratory and invasive behaviors, and repressed phosphorylation of regulators of phosphatidylinositol 3 kinase/protein kinase B/nuclear factor κB (PI3K/AKT/NF-κB) signaling cascade in gestational choriocarcinoma cells. MEG3 was upregulated by SchA in JEG-3 and BeWo cells. SchA exhibited little suppressive effects in JEG-3 cells lacking MEG3. Besides, the phosphorylation of transducers was evoked in MEG3-silenced JEG-3 cells despite stimulation with SchA. SchA administration repressed the growth of JEG-3 and BeWo cells by upregulating MEG3. Besides, SchA blocked PI3K/AKT/NF-κB signal cascade by elevating MEG3.

Bioactive Triterpenoid Saponins From the Seeds of Aesculus chinensis Bge. var. chekiangensis

Phytochemical investigation of Aesculus chinensis Bge. var. chekiangensis (Hu et Fang) Fang obtained 33 triterpenoid saponins, including 14 new ones, aesculiside C–P (1–14). The structure elucidations were performed through comprehensive MS, 1D and 2D-NMR analysis, and their absolute configuration was unambiguously determined by X-ray diffraction analysis as well as Mo₂(OAc)₄-induced ECD method for the first time. All the substances were examined for their cytotoxic activities against three tumor cell lines, Hep G2, HCT-116, and MGC-803. Of these, compounds 8, 9, 14–16, 18, and 22 exhibited potent cytotoxicities against all cell lines with IC₅₀ of 2–21 μM, while compounds 3, 6, 7, 17–19, 20, 24, and 28 depicted moderate activity (IC₅₀ 13 to >40 μM). On these bases, the preliminary structure-activity correlations were also discussed. Meanwhile the neuroprotective properties of triterpenoid saponins from Aesculus genus were evaluated for the first time. Among them, compounds 1, 4, 12, 20, 22, 25, 29, and 31 exhibited moderate activities against C_OCl₂-induced PC12 cell injury.

New Indole Glycosides from Aesculus chinensis var. chekiangensis and Their Neuroprotective Activities

The dried seeds of Aesculus chinensis Bge. var. chekiangensis (Hu et Fang) Fang, called “Suo Luo Zi”, have been used in traditional Chinese medicine. Nevertheless, most studies have been focused on components of less polarity fractions. In this research, twelve indoles, including six new indole glycosides (1–6) as well as six known analogs were isolated from the polar portion which has been seldom studied. This is the first description of N-glucosylated indoles obtained from the genus of Aesculus. Structures of the new compounds (1–6) were elucidated based on comprehensive interpretation of HRESIMS, 1D and 2D NMR. Additionally, the neuroprotective activities of the N-glucosylated indoles were evaluated for the first time indicating that compounds 1–5 and 9–10 exhibited moderate neuroprotective activities. Further cytotoxicity tests of isolates 1–10 on three human tumor cell lines suggested that none of these compounds were cytotoxic (IC₅₀ > 50 μM).

Pseudoprotodioscin inhibits SREBPs and microRNA 33a/b levels and reduces the gene expression regarding the synthesis of cholesterol and triglycerides

The extract of Dioscorea zingiberensis C.H. Wright rhizomes is found to be effective in the therapy of cardiovascular disease. Steroidal saponins make substantial contribution. Previous study has proposed that methylprotodioscin (MP) may promote cholesterol efflux by increasing ABCA1 expression. But the other main saponins ingredients are not referred to. The aim of the present work was to reveal the effect and mechanism of protodioscin (PD), MP and pseudoprotodioscin (PPD) on the synthesis-related gene expression of cholesterol and triglycerides. MTT assay apoptosis assay with annexin AV-APC and 7-AAD double staining were performed. MicroRNA assay and qRT-PCR were used to analyze the gene expression which regulates synthesis of cholesterol and triglycerides. Western blot was to demonstrate the levels of target proteins. Cholesterol efflux assay was executed to study the stimulative effect of saponins on cholesterol efflux. In Hep G2 cells, PPD increased ABCA1 protein and mRNA levels, and promoted the effluxion of ApoA-1-mediated cholesterol. The underlying mechanisms involved that PPD inhibited SREBP1c and SREBP2 transcription by decreasing microRNA 33a/b levels. This procedure reciprocally led to the increase of ABCA1 levels. In THP-1 macrophages, PPD showed the similar effect, which reduced HMGCR, FAS and ACC mRNA levels and promoted low density lipoprotein receptor by decreasing the PCSK9 levels. These studies demonstrated that PPD is a potential agent for cholesterol efflux, SREBPs and microRNA 33a/b inhibition, which related to the gene expression for the synthesis of cholesterol and triglycerides.

Schizandrin A inhibits proliferation, migration and invasion of thyroid cancer cell line TPC-1 by down regulation of microRNA-429

OBJECTIVE

Schizandrin A (SchA) exerts anticancer potential. However, the effects of SchA on thyroid cancer (TC) have not been clear illuminated. Therefore, we investigated the effects of SchA on TC cell line TPC-1 and the underlying mechanisms.

METHODS

TPC-1 cells were treated with SchA and/or transfected with miR-429 mimic, anti-miR-429 and their corresponding negative controls (NC). Cell viability, proliferation, migration, invasion and cell apoptosis were examined by CCK-8 assay, bromodeoxyuridine, modified two-chamber migration assay, Millicell Hanging Cell Culture and flow cytometry analysis, respectively. The expression of miR-429, p16, Cyclin D1, cyclin-dependent kinases 4 (CDK4), matrix metalloprotein (MMP)-2, MMP-9 and Vimentin was detected by qRT-PCR. All protein expression was examined by western blot.

RESULTS

SchA inhibited cell proliferation, metastasis and induced cell apoptosis. Moreover, SchA negatively regulated miR-429 expression. Treatment with miR-429 mimic and SchA reversed the results led by SchA and NC. Furthermore, the phosphorylation β-catenin, mitogen-activated protein kinase (MEK) and extracellular signal-regulated kinase (ERK) were statistically down-regulated by SchA while co-treatment with miR-429 mimic and SchA led to the opposite trend. Moreover, miR-429 knockdown showed contrary results.

CONCLUSION

SchA inhibits cell proliferation, migration, invasion and inactivates Wnt/β-catenin and MEK/ERK signaling pathways by down regulating miR-429.

Vielanin P enhances the cytotoxicity of doxorubicin via the inhibition of PI3K/Nrf2-stimulated MRP1 expression in MCF-7 and K562 DOX-resistant cell lines

BACKGROUND

Cancer cells that are resistant to structurally and mechanically unrelated anticancer drugs are said to have multidrug resistance (MDR). The overexpression of the ATP-binding cassette (ABC) transporter is one of the most important mechanisms of MDR. Vielanin P (VP), a dimeric guaiane from the leaves of Xylopia vielana, has the potential to reverse multidrug resistance.

PURPOSE

To evaluate the meroterpenoid compound VP as a low cytotoxicity MDR regulator and the related mechanisms.

METHODS

Cell viability was determined by CCK-8 and MTT assays. Apoptosis and the accumulation of doxorubicin (DOX) and 5(6)-carboxyfluorescein diacetate (CFDA) were determined by flow cytometry. We determined mRNA levels by quantitative real-time polymerase chain reaction (qRT-PCR). Protein levels were analyzed by Western blotting and immunofluorescence.

RESULTS

In the MCF-7 and K562 DOX-resistant cell lines, VP treatment (10 μM or 20 μM) enhanced the activity of chemotherapeutic agents. We found that VP selectively inhibited MRP1 mRNA but not MDR1 mRNA. VP enhanced DOX-induced apoptosis and reduced colony formation in the presence of DOX in drug-resistant cells. Moreover, VP increased the accumulation of DOX and the MRP1-specific substrate CFDA. In addition, VP reversed MRP1 protein levels and the accumulation of DOX and CFDA in MRP1-overexpressing MCF-7 and K562 cells. Thus, the mechanism of MDR reversal by VP is MRP1-dependent. Furthermore, we found that the inhibitory effect of VP on MRP1 is PI3K/Nrf2-dependent.

CONCLUSION

These results support the potential therapeutic value of VP as an MDR-reversal agent by inhibiting MRP1 via PI3K/Nrf2 signaling.

Rare dimeric guaianes from Xylopia vielana and their multidrug resistance reversal activity

Thirteen undescribed dimeric guaianes were isolated from the leaves of Xylopia vielana Pierre. Their structures were elucidated by NMR spectroscopy and mass spectrometry, and the absolute configurations of vielanins G-Q were determined by a combination of the circular dichroism (CD) exciton chirality method, chemical conversion, and electronic CD (ECD) spectroscopy analysis. Vielaninors A and B are the first examples of trinor-guaiane-dimers. Multidrug resistance reversal activity assay of the isolates was evaluated in doxorubicin-resistant human breast cancer cells. Vielanins H, K-M, P, and Q were noncytotoxic and enhanced the cytotoxicity of doxorubicin by 2.1-41.6-fold at 10 μM.

Andalucin from Artemisia lannta suppresses the neuroinflammation via the promotion of Nrf2-mediated HO-1 levels by blocking the p65-p300 interaction in LPS-activated BV2 microglia

BACKGROUND

Neuroinflammation plays an important role in many neurodegenerative conditions such as Alzheimer's disease (AD) and Parkinson disease (PD). Andalucin (ADL), a sesquiterpene lactone from Artemisia lannta, has been reported to exhibit NO inhibition in vitro. However, the effect of ADL on microglia-mediated neuroinflammation has not been investigated.

PURPOSE

This study was designed to determine the anti-neuroinflammatory effect of ADL against LPS-activated BV2 microglial cells and to explore the underlying mechanisms.

METHODS

The production of pro-inflammatory mediators and cytokines were measured by ELISA. The relevant mechanisms were analyzed by qRT-PCR, Luciferase assay, Western blot and Co-immunoprecipitation Assay.

RESULTS

ADL inhibited the LPS-induced release of NO, PGE₂, TNF-α, IL-6 and IL-1β. In addition, ADL reduced the mRNA and protein levels of iNOS and COX-2. Mechanism studies found that ADL activated Nrf2/HO-1 signaling pathway and suppressed NF-κB signaling pathway. Further investigation showed that the stimulative effect of ADL on Nrf2 transcriptional activity and the inhibitory effect of ADL on RelA transcriptional activity were due to its regulation on p300-Nrf2/p65 interaction.

CONCLUSION

ADL displayed anti-neuroinflammatory activity in LPS-activated BV2 cells. The mechanism concerns its regulatory effect on the crosstalk between Nrf2 and p65.

Combining GRP78 suppression and MK2206-induced Akt inhibition decreases doxorubicin-induced P-glycoprotein expression and mitigates chemoresistance in human osteosarcoma

P-glycoprotein (P-gp) overexpression is associated with poor prognosis and drug-resistance in osteosarcoma (OS), but the underlying mechanisms remain incompletely understood. Here, we examined the regulation of P-gp, GRP78, and phospho-Akt in doxorubicin (DOX)-treated OS cells. DOX induced P-gp expression, which was associated with increased GRP78 levels and Akt activation in vitro and in vivo. Functional analysis showed that Akt induces P-gp and GRP78 expression, which contributes to the DOX-induced Akt activation. Examination of the relationship between Akt and GRP78 demonstrated that GRP78 suppression attenuates the Akt activity in OS parental sensitive and resistant cells, indicating that GRP78 is required for full Akt activity. Inhibition of Akt activity using MK2206 decreased GRP78 expression in OS cells, which enhanced the inhibitory effect of MK2206 on P-gp expression. GRP78 knockdown combined with MK2206 suppressed the development of DOX resistance in OS cells and inhibited the in vivo tumor growth in the presence of DOX. These results support the development of novel therapeutic strategies that target GRP78 and Akt to sensitize OS cells for chemotherapy.

Schisandrin A reverses doxorubicin-resistant human breast cancer cell line by the inhibition of P65 and Stat3 phosphorylation

BACKGROUND

Multidrug resistance (MDR) in breast cancer therapy occurs frequently. Thus, anti-MDR agents from natural products or synthetic compounds were tested extensively. We have also explored the reverse effect and mechanism of Schisandrin A (Sch A), a natural product, on MCF-7 breast cancer doxorubicin (DOX)-resistant subline MCF-7/DOX.

METHODS

MTT assay was performed to measure the viability of MCF-7 cells to assess the reverse effect of Sch A. Western blot analysis was used to study the protein levels. Laser scanning confocal microscopy was performed to detect the intercellular DOX and Rhodamine 123 accumulation. The qRT-PCR was used to analysis the target gene expression. Dual-luciferase reporter assay was performed to test the transcriptional activity of P-glycoprotein (P-gp).

RESULTS

Sch A, at the concentration of 20 µM, showed selective reverse effect (better than the positive control, verapamil at 5 µM) on MCF-7/DOX cell line but not on BEL-7402/DOX, Hep G2/DOX, and K-562/DOX cells. In addition, Sch A enhanced DOX-induced cleavage of Caspase-9 and PARP levels by increasing intracellular DOX accumulation and inhibiting P-gp function. Furthermore, Sch A selectively suppressed P-gp at gene and protein levels in MCF-7/DOX cells which express high level of MDR1 but not MRP1, MRP3, or BCRP. Besides, Sch A showed inhibitory effect on P-gp transcriptional activity. Sch A significantly reduced p-IκB-α (Ser32) and p-Stat3 (Tyr705) levels which mediate P-gp expression. In addition, Stat3 knockdown enhanced the reverse effect of siP65. The combined effect of siStat3 and siP65 was better than Sch A single treatment in MCF-7/DOX cells.

CONCLUSION

Sch A specifically reverses P-gp-mediated DOX resistance in MCF-7/DOX cells by blocking P-gp, NF-κB, and Stat3 signaling. Inhibition of P65 and Stat3 shows potent anti-MDR effect on MCF-7/DOX cells.

Tomentodione M sensitizes multidrug resistant cancer cells by decreasing P-glycoprotein via inhibition of p38 MAPK signaling

In this study, we investigated the mechanism by which tomentodione M (TTM), a novel natural syncarpic acid-conjugated monoterpene, reversed multi-drug resistance (MDR) in cancer cells. TTM increased the cytotoxicity of chemotherapeutic drugs such as docetaxel and doxorubicin in MCF-7/MDR and K562/MDR cells in a dose- and time-dependent manner. TTM reduced colony formation and enhanced apoptosis in docetaxel-treated MCF-7/MDR and K562/MDR cells, and it enhanced intracellular accumulation of doxorubicin and rhodamine 123 in MDR cancer cells by reducing drug efflux mediated by P-gp. TTM decreased expression of both P-gp mRNA and protein by inhibiting p38 MAPK signaling. Similarly, the p38 MAPK inhibitor SB203580 reversed MDR in cancer cells by decreasing P-gp expression. Conversely, p38 MAPK-overexpressing MCF-7 and K562 cells showed higher P-gp expression than controls. These observations indicate that TTM reverses MDR in cancer cells by decreasing P-gp expression via p38 MAPK inhibition.

Isolation, Structure Elucidation, and Absolute Configuration of Syncarpic Acid-Conjugated Terpenoids from Rhodomyrtus tomentosa

Three new syncarpic acid-conjugated sesquiterpenoids, tomentodiones E-G (1-3), and six new syncarpic acid-conjugated monoterpenoids, tomentodiones H-M (4-9), were isolated from the leaves of Rhodomyrtus tomentosa. Compounds 1-3 represent the first examples of β-calacorene-based meroterpenoids. Their structures and absolute configurations were determined by a combination of NMR and ECD spectroscopy and X-ray diffraction analysis. On the basis of ECD data analysis for isolated and synthesized compounds, an empirical rule was proposed to determine the absolute configuration at C-7' of syncarpic acid-conjugated terpenoids. Additionally, a study of the reversal effect of multidrug resistance in doxorubicin-resistant human breast cancer cells showed that the noncytotoxic (+)-4 exerted the strongest potentiation effect of doxorubicin susceptibility, with an enhancement of 16.5-fold at a concentration of 30 μM.

Mechanism Underlying the Reversal of Drug Resistance in P-Glycoprotein-Expressing Leukemia Cells by Pinoresinol and the Study of a Derivative

P-glycoprotein (P-gp) is a membrane protein associated with multidrug resistance (MDR) due to its key role in mediating the traffic of chemotherapeutic drugs outside cancer cells, leading to a cellular response that hinders efforts toward successful therapy. With the aim of finding agents that circumvent the MDR phenotype mediated by P-gp, 15 compounds isolated from native and naturalized plants of Argentina were screened. Among these, the non-cytotoxic lignan (±) pinoresinol successfully restored sensitivity to doxorubicin from 7 μM in the P-gp overexpressed human myelogenous leukemia cells, Lucena 1. This resistance-reversing effect was confirmed by competitively increasing the intracellular doxorubicin accumulation and by significantly inhibiting the efflux of doxorubicin and, to a lesser extent, that of rhodamine 123. The activity obtained was similar to that observed with verapamil. No such results were observed in the sensitive parental K562 cell line. To gain deeper insight into the mode of action of pinoresinol, its effect on P-gp function and expression was examined. The docking simulations indicated that the lignan bound to P-gp at the apex of the V-shaped transmembrane cavity, involving transmembrane helices 4, 5, and 6, and partially overlapped the binding region of tariquidar, which was used as a positive control. These results would shed some light on the nature of its interaction with P-gp at molecular level and merit further mechanistic and kinetic studies. In addition, it showed a maximum 29% activation of ATP hydrolysis and antagonized verapamil-stimulated ATPase activity with an IC₅₀ of 20.9 μM. On the other hand, pinoresinol decreased the presence of P-gp in the cell surface. Derivatives of pinoresinol with improved activity were identified by docking studies. The most promising one, the non-cytotoxic 1-acetoxypinoresinol, caused a reversion of doxorubicin resistance from 0.11 μM and thus higher activity than the lead compound. It also caused a significant increase in doxorubicin accumulation. Results were similar to those observed with verapamil. The results obtained positioned these compounds as potential candidates for effective agents to overcome P-gp-mediated MDR, leading to better outcomes for leukemia chemotherapy.

Protection by Huang-Lian-Jie-Du decoction and its constituent herbs of lipopolysaccharide-induced acute kidney injury

Sepsis, characterized by systemic inflammation, often leads to end-organ dysfunction, such as acute kidney injury (AKI). Despite of the severity and frequency of septic AKI in clinic, its pathogenesis is still poorly understood. Combined with histopathology evaluations, mortality assessments, biochemical evaluations, reverse transcription (RT) reaction and quantitative real-time PCR, and western blot, 1H NMR-based metabolomics approach was applied to investigate effects of Huang-Lian-Jie-Du-Decotion (HLJDD), a traditional Chinese medicine prescription, and its four component herbs on lipopolysaccharide (LPS)-induced septic AKI and the underlying mechanism. LPS induced kidney dysfunction via activation of NF-κB and mitogen-activated protein kinases (MAPKs), by excessive production of IL-6, tumor necrosis factor-α, inducible nitric oxide synthase, and COX-2, producing perturbance in energy metabolism and oxidative stress. HLJDD and its component herbs could effectively inhibit LPS-induced AKI in mice by inhibiting NF-κB and MAPK activation and activating the Akt/HO-1 pathway, and by markedly ameliorating disturbances in oxidative stress and energy metabolism induced by LPS. The four-component herbs could complement each other.

Discovery of oral-available resveratrol-caffeic acid based hybrids inhibiting acetylated and phosphorylated STAT3 protein

Constitutive activation of STAT3 has been found in a wide variety of cancers and demonstrated as a very attractive therapeutic target. Disrupting both acetylation and phosphorylation of STAT3 protein was hypothesized to greatly deactivate STAT3, therefore, treating cancers. To demonstrate the hypothesis, two series of novel resveratrol-caffeic acid hybrids were designed aiming to regulate both acetylation and phosphorylation of STAT3 protein, which is also the first report of the synthetic inhibitors simultaneously regulating two biological reactions of STAT3 to our knowledge. Most of these compounds were demonstrated with preferential antitumor activity with low IC₅₀ values against two cancer cell lines. Particularly, compound 7d was found as an excellent STAT3 inhibitor with over 50-fold better potency than resveratrol and caffeic acid. Meanwhile, the novel derivatives significantly inhibited the proliferation and induced the apoptosis of tumor cells. Molecular docking further disclosed the binding modes of STAT3 with the inhibitors. In addition, compound 7d orally and significantly suppressed breast cancer 4T1 xenograft tumor growth in vivo, indicating its great potential as an efficacious drug candidate for human cancer therapy.

Involucratusins A-H: Unusual Cadinane Dimers from Stahlianthus involucratus with Multidrug Resistance Reversal Activity

Three novel cadinane dimers, involucratusins A–C (1–3), five unique nor-cadinane-dimers, involucratusins D–H (4–8), together with a known compound (9) were isolated from the rhizomes of Stahlianthus involucratus. Their challenging structures and absolute configurations were determined by spectroscopic data, CD experimentation, chemical conversions and single-crystal X-ray diffraction. Compounds 1–3 are unusual cadinane dimers with new connection and novel cores. Compound 4 is a unique nor-cadinane-dimer, and 5 and 6 are two pairs of hemiketal racemates with novel dinor-cadinane-dimer backbone. Compounds 7 and 8 represent unusual dodecanor-cadinane-dimer and tetradecanor-cadinane-dimer carbon skeletons, respectively. The possible biogenetic pathways of 1–8 were proposed, involving nucleophilic addition, S_N2 nucleophilic displacement, [3 + 3] benzannulation, oxidative cleavage, decarboxylation, and oxidative phenol coupling reactions. Multidrug resistance (MDR) reversal activity assay of the isolates were evaluated in doxorubicin-resistant human breast cancer cells (MCF-7/DOX). The combined use of these novel cadinane dimers at a concentration of 10 μM increased the cytotoxicity of doxorubicin by 2.2–5.8-fold. It is the first report about the MDR reversal activity of cadinane dimers.

Novel ginkgolide B derivative attenuated the function and expression of P-glycoprotein at the blood–brain barrier, presenting brain-targeting ability

The effects of ginkgolide B derivative (GBD) and GB on P-glycoprotein efflux function and expression level were studied to explain GBD's brain-targeting behavior.

Polyphyllin I induced-apoptosis is enhanced by inhibition of autophagy in human hepatocellular carcinoma cells

BACKGROUND

Polyphyllin I (PPI), a bioactive phytochemical isolated from the rhizoma of Paris polyphyllin, exerts preclinical anticancer efficacy in various cancer models. However, the effects of PPI on regulatory human hepatocellular carcinoma (HCC) cell proliferation and its underlying mechanisms remain unknown.

PURPOSE

This study investigated the antiproliferation effect of PPI on HCC cells and its underlying mechanisms.

METHODS

Cell viability was measured by MTT assay. Cell death, apoptosis and acidic vesicular organelles (AVOs) formation were determined by flow cytometry. Protein levels were analyzed by Western blot analysis.

RESULTS

PPI induced apoptosis through the caspase-dependent pathway and activated autophagy through the PI3K/AKT/mTOR pathway. Blockade of autophagy by pharmacological inhibitors or RNA interference enhanced the cytotoxicity and antiproliferation effects of PPI. Moreover, chloroquine (CQ) enhanced the antiproliferation effect of PPI on HCC cells via the caspase-dependent apoptosis pathway by inhibiting protective autophagy. Therefore, the combination therapy of CQ and PPI exhibited synergistic effects on HCC cells compared with CQ or PPI alone.

CONCLUSION

The current findings strongly indicate that PPI can induce protective autophagy in HCC cells, thereby providing a novel target in potentiating the anticancer effects of PPI and other chemotherapeutic drugs in liver cancer treatment. Moreover, the combination therapy of CQ and PPI is an effective and promising candidate to be further developed as therapeutic agents in the treatment of liver cancer.