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

Dual p38MAPK and MEK inhibition disrupts adaptive chemoresistance in mesenchymal glioblastoma to temozolomide

BACKGROUND

Precision treatment of glioblastoma is increasingly focused on molecular subtyping, with the mesenchymal subtype particularly resistant to temozolomide. Here, we aim to develop a targeted therapy for temozolomide resensitization in the mesenchymal subtype.

METHODS

We integrated kinomic profiles and kinase inhibitor screens from patient-derived proneural and mesenchymal glioma-propagating cells and public clinical datasets to identify key protein kinases implicated in temozolomide resistance. RNAseq, apoptosis assays, and comet assays were used to examine the role of p38MAPK signaling and adaptive chemoresistance in mesenchymal cells. The efficacy of dual p38MAPK and MEK/ERK inhibition using ralimetinib (selective orally active p38MAPK inhibitor; phase I/II for glioblastoma) and binimetinib (approved MEK1/2 inhibitor for melanoma; phase II for high-grade glioma) in primary and recurrent mesenchymal tumors was evaluated using an intracranial patient-derived tumor xenograft model, focusing on survival analysis.

RESULTS

Our transcriptomic-kinomic integrative analysis revealed p38MAPK as the prime target whose gene signature enables patient stratification based on their molecular subtypes and provides prognostic value. Repurposed p38MAPK inhibitors synergize favorably with temozolomide to promote intracellular retention of temozolomide and exacerbate DNA damage. Mesenchymal cells exhibit adaptive chemoresistance to p38MAPK inhibition through a pH-/calcium-mediated MEK/ERK pathway. Dual p38MAPK and MEK inhibition effectively maintain temozolomide sensitivity in primary and recurrent intracranial mesenchymal glioblastoma xenografts.

CONCLUSIONS

Temozolomide resistance in mesenchymal glioblastoma is associated with p38MAPK activation. Adaptive chemoresistance in p38MAPK-resistant cells is mediated by MEK/ERK signaling. Adjuvant therapy with dual p38MAPK and MEK inhibition prolongs temozolomide sensitivity, which can be developed into a precision therapy for the mesenchymal subtype.

Recent Advances in Doxorubicin Formulation to Enhance Pharmacokinetics and Tumor Targeting

Doxorubicin (DOX), a widely used drug in cancer chemotherapy, induces cell death via multiple intracellular interactions, generating reactive oxygen species and DNA-adducted configurations that induce apoptosis, topoisomerase II inhibition, and histone eviction. Despite its wide therapeutic efficacy in solid tumors, DOX often induces drug resistance and cardiotoxicity. It shows limited intestinal absorption because of low paracellular permeability and P-glycoprotein (P-gp)-mediated efflux. We reviewed various parenteral DOX formulations, such as liposomes, polymeric micelles, polymeric nanoparticles, and polymer-drug conjugates, under clinical use or trials to increase its therapeutic efficacy. To improve the bioavailability of DOX in intravenous and oral cancer treatment, studies have proposed a pH- or redox-sensitive and receptor-targeted system for overcoming DOX resistance and increasing therapeutic efficacy without causing DOX-induced toxicity. Multifunctional formulations of DOX with mucoadhesiveness and increased intestinal permeability through tight-junction modulation and P-gp inhibition have also been used as orally bioavailable DOX in the preclinical stage. The increasing trends of developing oral formulations from intravenous formulations, the application of mucoadhesive technology, permeation-enhancing technology, and pharmacokinetic modulation with functional excipients might facilitate the further development of oral DOX.

Cellular resistance mechanisms in cancer and the new approaches to overcome resistance mechanisms chemotherapy

Despite major advancements in cancer healing approaches over the last few decades, chemotherapy remains the most popular malignancy treatment. Chemotherapeutic drugs are classified into many kinds based on their mechanism of action. Multidrug resistance (MDR) is responsible for approximately 90% of fatalities in malignancy cases treated with standard chemotherapeutics or innovative targeted medicines. Many innovative prospective anti-cancer medicines displayed high anti-cancer efficacy in a single application. However, combining them with other medications improves cancer treatment efficacy. This supports the belief that a combination of drugs is significantly more effective than a single medicine. Due to the intricacy of MDR processes and the diversity of tumor illnesses, there will rarely be a single medicine that can be utilized to treat all types of cancer. Finding new medications that can reverse MDR in malignancy cells will augment efficacy of chemotherapeutic agents and allow us to treat cancers that are now incurable.

Progress and challenges of multidrug resistance proteins in diseases

Chemotherapy remains the first choice for patients with advanced cancers when other treatments are ineffective. Multidrug resistance (MDR) is an unavoidable factor that negatively affects the effectiveness of cancer chemotherapy drugs. Researchers are trying to reduce MDR, improve the effectiveness of chemotherapeutic drugs, and alleviate patient suffering to positively contribute to disease treatment. MDR also occurs in inflammation and genetic disorders, which increases the difficulty of clinically beneficial treatments. The ATP-binding cassette (ABC) is an active transporter that plays an important role in the barrier and secretory functions of many normal cells. As the C subfamily in the ABC family, multidrug resistance proteins (MRPs/ABCCs) export a variety of antitumour drugs and are expressed in a variety of cancers. The present review summarises the role of MRPs in cancer and other diseases and recent research progress of MRP inhibitors to better examine the mechanism and function of MRPs, and establish a good relationship with clinical treatment.

Circumventing Doxorubicin Resistance Using Elastin-like Polypeptide Biopolymer-Mediated Drug Delivery

Although doxorubicin (dox), an anthracycline antibiotic, is widely used and effective in treating cancer, its treatment efficiency is limited by low blood plasma solubility, poor pharmacokinetics, and adverse side effects, including irreversible cardiotoxicity. Moreover, cancer cells often develop drug resistance over time, which decreases the efficacy of anti-cancer drugs, including dox. In this study, we examine a macromolecular drug delivery system for its ability to specifically deliver doxorubicin to cancer cells with and without drug resistance. This drug delivery system consists of a multi-part macromolecule, which includes the following: elastin-like polypeptide (ELP), cell penetrating peptide (CPP), a cleavable linker (releasing at low pH), and a derivative of doxorubicin. ELP is thermally responsive and improves drug solubility, while the CPP mediates cellular uptake of macromolecules. We compared cytotoxicity of two doxorubicin derivatives, where one is cleavable (DOXO) and contains a pH-sensitive linker and releases dox in an acidic environment, and the other is non-cleavable (ncDox) doxorubicin. Cytotoxicity, apoptosis, cell cycle distribution and mechanism of action of these constructs were tested and compared between dox-responsive MCF-7 and dox-resistant NCI/ADR cell lines. Dox delivered by the ELP construct is comparably toxic to both sensitive and drug resistant cell lines, compared to unconjugated doxorubicin, and given the pharmacokinetic and targeting benefits conveyed by conjugation to ELP, these biopolymers have potential to overcome dox resistance in vivo.

Inhibition of p38 MAPK increases the sensitivity of 5-fluorouracil-resistant SW480 human colon cancer cells to noscapine

A major cause of treatment failure in advanced colon cancer is resistance to chemotherapy. p38 mitogen-activated protein kinase (MAPK) has been associated with cellular apoptosis and plays an important role in multidrug resistance (MDR) in cancer cells. In the present study the effect of p38 MAPK on the sensitivity of 5-fluorouracil (5-FU)-resistant SW480 (SW480/5-FU) human colon cancer cells to noscapine was investigated. Following p38 MAPK interference, the inhibitory effect of noscapine on cell viability and proliferation was increased in the SW480/5-FU cells and there was also a decrease in the expression level of minichromosome maintenance proteins, recombinant Ki-67 and proliferating cell nuclear antigen. Inhibition of p38 MAPK also enhanced noscapine-induced G₁-phase cell cycle arrest in the SW480/5-FU cells and there was also a decrease in the protein and mRNA expression level of cyclin D, cyclin E and cyclin-dependent kinase 2, and an increase in the expression level of P57. Furthermore, p38 MAPK interference increased noscapine-induced apoptosis of the SW480/5-FU cells and there was an increase in the protein and mRNA expression level of caspases-3 and 8 and Bax, and decreased Bcl-2 expression level. The sensitivity of the SW480/5-FU cells to noscapine was also increased following p38 MAPK interference, as demonstrated by MDR inhibition via decreased Akt activity and reduced protein expression level of the MDR proteins P-glycoprotein, multidrug resistance protein 1 and ATP-binding cassette G2. These observations indicated that inhibition of p38 MAPK increased the sensitivity of the SW480/5-FU cells to noscapine by suppressing proliferation, induction of cell cycle arrest and apoptosis, and reversal of MDR in the SW480/5-FU cells.

Rhinacanthin-C enhances chemosensitivity of breast cancer cells via the downregulation of P-glycoprotein through inhibition of Akt/NF-kappa B signaling pathway

Introduction: High expression of P-glycoprotein (P-gp) has been linked to multidrug resistance (MDR) and chemotherapeutic failure. Previously, we demonstrated that rhinacanthin-C, a naphthoquinone from Rhinacanthus nasutus, was able to enhance the cytotoxicity of doxorubicin against breast cancer MCF-7 cells via direct P-gp inhibition. In this study, we looked at its effect on P-gp downregulation and the mechanism involved in the resistance of MCF-7 cells to doxorubicin. Methods: Doxorubicin-resistant MCF-7 (MCF-7/DOX) cells were exposed to rhinacanthin-C for 24-48 hours prior to the assessment of their chemosensitivity via MTT assay, P-gp activity via calcein-AM uptake assay, P-gp expression, and signaling via qRT-PCR and western blot analyses. Results: Pretreatment with 1 µM of rhinacanthin-C for 48 hours significantly enhanced cytotoxicity of doxorubicin, as well as camptothecin and etoposide, to MCF-7/DOX cells. In the rhinacanthin-C-treated cells, reduction of MDR1 mRNA and P-gp levels and increased intracellular calcein were observed. Moreover, phosphorylation of Akt, NF-ᴋB and IκB-α, along with YB-1 expression, significantly decreased after 24-hour treatment with rhinacanthin-C. In contrast, the naphthoquinone had no effect on expression levels of ERK1/2 and phosphorylated ERK1/2 under similar conditions. Conclusion: Rhinacanthin-C, at a non-cytotoxic concentration (1 µM), could downregulate P-gp expression in MCF-7/DOX cells via the inhibition of the Akt/NF-ᴋB signaling pathway and YB-1 expression. Long-term exposure to this natural naphthoquinone may increase the chemosensitivity of cancer cells with MDR phenotype.

Cinnamophilin overcomes cancer multi-drug resistance via allosterically modulating human P-glycoprotein on both drug binding sites and ATPase binding sites

Cancer multi-drug resistance (MDR) caused by P-glycoprotein (P-gp) efflux is a critical unresolved clinical concern. The present study analyzed the effect of cinnamophilin on P-gp inhibition and MDR reversion. The effect of cinnamophilin on P-gp was investigated through drug efflux assay, ATPase assay, MDR1 shift assay, and molecular docking. The cancer MDR-reversing ability and mechanisms were analyzed through cytotoxicity and combination index (CI), cell cycle, and apoptosis experiments. P-gp efflux function was significantly inhibited by cinnamophilin without influencing the drug's expression or conformation. Cinnamophilin uncompetitively inhibited the efflux of doxorubicin and rhodamine 123 and exhibited a distinct binding behavior compared with verapamil, the P-gp standard inhibitor. The half maximal inhibitory concentration of cinnamophilin for doxorubicin and rhodamine 123 efflux was 12.47 and 11.59 μM, respectively. In regard to P-gp energy consumption, verapamil-stimulated ATPase activity was further enhanced by cinnamophilin at concentrations of 0.1, 1, 10, and 20 μM. In terms of MDR reversion, cinnamophilin demonstrated synergistic cytotoxic effects when combined with docetaxel, vincristine, or paclitaxel. The CI was < 0.7 in all experimental combination treatments. The present study showed that cinnamophilin possesses P-gp-modulating effects and cancer MDR resensitizing ability.

Exploring new Horizons in overcoming P-glycoprotein-mediated multidrug-resistant breast cancer via nanoscale drug delivery platforms

The high probability (13%) of women developing breast cancer in their lifetimes in America is exacerbated by the emergence of multidrug resistance after exposure to first-line chemotherapeutic agents. Permeation glycoprotein (P-gp)-mediated drug efflux is widely recognized as the major driver of this resistance. Initial in vitro and in vivo investigations of the co-delivery of chemotherapeutic agents and P-gp inhibitors have yielded satisfactory results; however, these results have not translated to clinical settings. The systemic delivery of multiple agents causes adverse effects and drug-drug interactions, and diminishes patient compliance. Nanocarrier-based site-specific delivery has recently gained substantial attention among researchers for its promise in circumventing the pitfalls associated with conventional therapy. In this review article, we focus on nanocarrier-based co-delivery approaches encompassing a wide range of P-gp inhibitors along with chemotherapeutic agents. We discuss the contributions of active targeting and stimuli responsive systems in imparting site-specific cytotoxicity and reducing both the dose and adverse effects.

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.

Quercitrin alleviates cartilage extracellular matrix degradation and delays ACLT rat osteoarthritis development: An in vivo and in vitro study

Introduction: Disruptions of extracellular matrix (ECM) degradation homeostasis play a significant role in the pathogenesis of osteoarthritis (OA). Matrix metalloproteinase 13 (MMP13) and collagen Ⅱ are important components of ECM. Earlier we found that quercitrin could significantly decrease MMP13 gene expression and increase collagen Ⅱ gene expression in IL-1β-induced rat chondrocytes and human chondrosarcoma (SW1353) cells. Objectives: The effects and mechanism of quercitrin on OA were explored. Methods: Molecular mechanisms of quercitrin on OA were studied in vitro in primary chondrocytes and SW1353 cells. An anterior cruciate ligament transection (ACLT) rat model of OA was used to investigate the effect of quercitrin in vivo. Micro-CT analysis and Safranin O-Fast Green Staining of knee joint samples were performed to observe the damage degree of tibial subchondral bone. Immunohistochemistry of knee joint samples were conducted to observe the protein level of MMP13, collagen Ⅱ and p110α in articular cartilage. Results: In vitro, quercitrin promoted cell proliferation and delayed ECM degradation by regulating MMP13 and collagen II gene and protein expressions. Moreover, quercitrin activated the Phosphatidylinositol 3-kinase p110α (p110α)/AKT/mTOR signaling pathway by targeting p110α. We also firstly showed that the gene expression level of p110α was remarkably decreased in cartilage of OA patients. The results showed that intra-articular injection of quercitrin increased bone volume/tissue volume of tibial subchondral bone and cartilage thickness and reduced the Osteoarthritis Research Society International scores in OA rats. Meanwhile, immunohistochemical results showed that quercitrin exerted anti-OA effect by delaying ECM degradation. Conclusion: These findings suggested that quercitrin may be a prospective disease-modifying OA drug for prevention and treatment of early stage OA.

Inhibitory Activity of 8 Alkaloids on P-gp and Their Distribution in Chinese Uncaria Species

P-glycoprotein (P-gp) inhibition conduces to improving the ability of chemicals to cross through blood-brain barrier (BBB). The hook-bearing branch of Uncaria is used as a traditional herbal medicine for the treatment of hypertension, headache, stroke, and Alzheimer’s disease in recent years. In this study, the inhibitory effects of 8 alkaloids sourced from Uncaria plants on P-gp were evaluated. Meanwhile, the content of 8 alkaloids in 8 Chinese Uncaria species was quantified simultaneously by high-performance liquid chromatography analysis. Western blotting, real-time quantitative reverse transcription-polymerase chain reaction, and flow cytometry were used to evaluate the P-gp levels in MCF-7/adriamycin-resistant (ADR) cells. It was shown that hirsuteine and hirsutine, selected from 8 candidate alkaloids, could remarkably suppressed P-gp level and function in MCF-7/ADR cells when using Verapamil as positive control. By tracking their chemical distribution in 8 Chinese Uncaria species, we found that hirsuteine and hirsutine were much more abundant in Uncaria rhynchophylla and Uncaria hirsuta than in any other 6 species. And a chemical content profile of these alkaloids was plotted within 8 Chinese species.

6H2L, a novel synthetic derivative of bifendate, induces apoptosis in hepatoma cells via mitochondrial and MAPK pathway

Hepatocellular carcinoma (HCC) is a major cause of cancer-related death worldwide. Our previous study indicated that 6H2L, a novel synthetic bifendate derivative, shows multidrug resistance reversal activity, while its antitumor effect has not been revealed. Here, the potent antitumor effects of 6H2L on hepatoma cells both in vitro and in vivo were investigated. 6H2L inhibited cell viability of HepG2 and SMMC-7721 cells with less sensitivity to normal human liver L-02 cells. 6H2L induced apoptosis in hepatoma cells. It upregulated Bax expression, while simultaneously decreasing Bcl-2 expression. Further elucidation of the mechanism revealed that 6H2L induced mitochondrial dysfunction, with transmitochondrial membrane potential collapse and cytochrome c release, which activated caspase-9 and caspase-3 and subsequently cleaved PARP, suggesting that 6H2L induced apoptosis via triggering mitochondrial pathway. Moreover, 6H2L decreased the phosphorylation of ERK1/2, whereas it increased the expression of p-JNK and p-p38. Then, specific inhibitors of the mitogen-activated protein kinase (MAPK) pathway were employed to confirm the roles of the MAPK pathway in the apoptosis-inducing effects of 6H2L. Additionally, 6H2L obviously inhibited the tumor growth in H22-bearing ICR mice. Meanwhile, 6H2L remarkably up-regulated Bax while suppressing Bcl-2 in tumors. Importantly, neither significant weight loss, white blood cell (WBC) count, nor histopathological abnormalities of major organs were observed in the mice receiving 6H2L treatment, indicating that 6H2L exerted strong anticancer activities with low toxicity in vivo. In contrast, fluorouracil inhibited tumor growth with significant decreased body weight and WBC count. Taken together, these results suggested 6H2L is a potential therapeutic candidate for HCC.

2-Deoxy-D-glucose enhances the anti-cancer effects of idarubicin on idarubicin-resistant P388 leukemia cells

Cancer cells switch from mitochondrial oxidative phosphorylation to glycolysis, even in the presence of normal oxygen concentrations. Inhibition of the glycolytic pathway is therefore a critical strategy in cancer therapy. A non-metabolic glucose analog, 2-deoxy-D-glucose (2-DG), has been the focus of research on glycolytic inhibitors for use in cancer treatment. The current study examined the anti-cancer effects of 2-DG on idarubicin (IDA)-resistant P388 (P388/IDA) leukemia cells. P388/IDA cells were established following continuous exposure of IDA to P388 cells. Characterization of P388/IDA cells revealed increased lactate production and glucose consumption compared with P388 parent cells. The results of a cell viability assay determined that 2-DG induces higher toxicity in P388/IDA cells compared with P388 cells. Although 2-DG also exhibits endoplasmic reticulum (ER) stress-inducing activity, the cytotoxic effect of the ER stress inducer, tunicamycin, on P388/IDA cells was lower than that of P388 cells. A combination of 2-DG and IDA enhanced P388/IDA cell death compared with each agent alone. The results indicated that P388 cells activated glycolysis after acquiring IDA resistance and therefore, inhibition of the glycolytic pathway via 2-DG might be a useful strategy for cancer therapy against IDA- resistant leukemia cells.

Mechanisms of Multidrug Resistance in Cancer Chemotherapy

Cancer is one of the main causes of death worldwide. Despite the significant development of methods of cancer healing during the past decades, chemotherapy still remains the main method for cancer treatment. Depending on the mechanism of action, commonly used chemotherapeutic agents can be divided into several classes (antimetabolites, alkylating agents, mitotic spindle inhibitors, topoisomerase inhibitors, and others). Multidrug resistance (MDR) is responsible for over 90% of deaths in cancer patients receiving traditional chemotherapeutics or novel targeted drugs. The mechanisms of MDR include elevated metabolism of xenobiotics, enhanced efflux of drugs, growth factors, increased DNA repair capacity, and genetic factors (gene mutations, amplifications, and epigenetic alterations). Rapidly increasing numbers of biomedical studies are focused on designing chemotherapeutics that are able to evade or reverse MDR. The aim of this review is not only to demonstrate the latest data on the mechanisms of cellular resistance to anticancer agents currently used in clinical treatment but also to present the mechanisms of action of novel potential antitumor drugs which have been designed to overcome these resistance mechanisms. Better understanding of the mechanisms of MDR and targets of novel chemotherapy agents should provide guidance for future research concerning new effective strategies in cancer treatment.

Cordycepin Resensitizes T24R2 Cisplatin-Resistant Human Bladder Cancer Cells to Cisplatin by Inactivating Ets-1 Dependent MDR1 Transcription

Tumor cell resistance to anti-cancer drugs is a major obstacle in tumor therapy. In this study, we investigated the mechanism of cordycepin-mediated resensitization to cisplatin in T24R2 cells, a T24-derived cell line. Treatment with cordycepin or cisplatin (2 μg/mL) alone failed to induce cell death in T24R2 cells, but combination treatment with these drugs significantly induced apoptosis through mitochondrial pathways, including depolarization of mitochondrial membranes, decrease in anti-apoptotic proteins Bcl-2, Bcl-xL, and Mcl-1, and increase in pro-apoptotic proteins Bak and Bax. High expression levels of MDR1 were the cause of cisplatin resistance in T24R2 cells, and cordycepin significantly reduced MDR1 expression through inhibition of MDR1 promoter activity. MDR1 promoter activity was dependent on transcription factor Ets-1 in T24R2 cells. Although correlation exists between MDR1 and Ets-1 expression in bladder cancer patients, active Ets-1, Thr38 phosphorylated form (pThr38), was critical to induce MDR1 expression. Cordycepin decreased pThr-38 Ets-1 levels and reduced MDR1 transcription, probably through its effects on PI3K signaling, inducing the resensitization of T24R2 cells to cisplatin. The results suggest that cordycepin effectively resensitizes cisplatin-resistant bladder cancer cells to cisplatin, thus serving as a potential strategy for treatment of cancer in patients with resistance to anti-cancer drugs.

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.

Isolation and Synthesis of Novel Meroterpenoids from Rhodomyrtus tomentosa: Investigation of a Reactive Enetrione Intermediate

Rhodomyrtusials A-C, the first examples of triketone-sesquiterpene meroterpenoids featuring a unique 6/5/5/9/4 fused pentacyclic ring system were isolated from Rhodomyrtus tomentosa, along with several biogenetically-related dihydropyran isomers. Two bis-furans and one dihydropyran isomer showed acetylcholinesterase (AChE) inhibitory activity. Structures of the isolates were unambiguously established by a combination of spectroscopic data, ECD analysis, and total synthesis. Bioinspired total syntheses of six isolates were achieved in six steps utilizing a reactive enetrione intermediate generated in situ from a readily available hydroxy-endoperoxide precursor.

The Health Beneficial Properties of Rhodomyrtus tomentosa as Potential Functional Food

Rhodomyrtus tomentosa (Aiton) Hassk. is a flowering plant belonging to the family Myrtaceae, native to southern and southeastern Asia. It has been used in traditional Vietnamese, Chinese, and Malaysian medicine for a long time for the treatment of diarrhea, dysentery, gynecopathy, stomachache, and wound healing. Moreover, R. tomentosa is used to make various food products such as wine, tea, and jam. Notably, R. tomentosa has been known to contain structurally diverse and biologically active metabolites, thus serving as a potential resource for exploring novel functional agents. Up to now, numerous phenolic and terpenoid compounds from the leaves, root, or fruits of R. tomentosa have been identified, and their biological activities such as antioxidant, antibacterial, anti-inflammatory, and anticancer have been evidenced. In this contribution, an overview of R. tomentosa and its health beneficial properties was focused on and emphasized.