Screening dietary flavonoids for the reversal of P-glycoprotein-mediated multidrug resistance in cancer

The Use of an Antioxidant Enables Accurate Evaluation of the Interaction of Curcumin on Organic Anion-Transporting Polypeptides 4C1 by Preventing Auto-Oxidation

Flavonoids have garnered attention because of their beneficial bioactivities. However, some flavonoids reportedly interact with drugs via transporters and may induce adverse drug reactions. This study investigated the effects of food ingredients on organic anion-transporting polypeptide (OATP) 4C1, which handles uremic toxins and some drugs, to understand the safety profile of food ingredients in renal drug excretion. Twenty-eight food ingredients, including flavonoids, were screened. We used ascorbic acid (AA) to prevent curcumin oxidative degradation in our method. Twelve compounds, including apigenin, daidzein, fisetin, genistein, isorhamnetin, kaempferol, luteolin, morin, quercetin, curcumin, resveratrol, and ellagic acid, altered OATP4C1-mediated transport. Kaempferol and curcumin strongly inhibited OATP4C1, and the Ki values of kaempferol (AA(-)), curcumin (AA(-)), and curcumin (AA(+)) were 25.1, 52.2, and 23.5 µM, respectively. The kinetic analysis revealed that these compounds affected OATP4C1 transport in a competitive manner. Antioxidant supplementation was determined to benefit transporter interaction studies investigating the effects of curcumin because the concentration-dependent curve evidently shifted in the presence of AA. In this study, we elucidated the food-drug interaction via OATP4C1 and indicated the utility of antioxidant usage. Our findings will provide essential information regarding food-drug interactions for both clinical practice and the commercial development of supplements.

Flavonoids as P-glycoprotein inhibitors for multidrug resistance in cancer: an in-silico approach

Cancer has become a leading cause of mortality due to non-communicable diseases after cardiovascular disease worldwide and is increasing day by day at a daunting pace. According to an estimate by 2040 there will be 28.4 million cancer cases. Occurrence of multidrug resistance has further worsened the scenario of available cancer treatment. Among different mechanisms of multidrug resistance efflux of xenobiotics by ABC transporter is of prime importance. P-glycoprotein (P-gp) is the major factor behind occurrence of multidrug resistance due to its wide distribution and invariably big binding cavity. Various generations of chemical inhibitors for P-gp have been designed and tested are not devoid of major side effects. Thus, in present study flavonoids a major class of natural compounds was virtually screened in order to find molecules which can be used as selective P-gp inhibitors to be used along with chemotherapeutics. After screening 4275 molecules from different classes of flavonoids i.e. flavan, flavanol, flavonone, flavone, anthocyanins, and isoflavone, through Glide docking top ten hit molecules were selected based on their binding affinity, binding energy calculation and pharmacokinetic properties. All the hit molecules were found to have docking score within the range of -11.202 to -9.699 kcal/mol showing very strong interaction with the amino acid residues of binding pocket. Whereas, dock score of standard P-gp inhibitor verapamil was -4.984 kcal/mol. The ligand and protein complex were found to be quite stable while run through molecular dynamics simulations.Communicated by Ramaswamy H. Sarma.

A computational-based approach to fabricate Ceritinib co-amorphous system using a novel co-former Rutin for bioavailability enhancement

In this study, we used molecular simulations to design Ceritinib (CRT) co-amorphous materials (CAMs) with concurrent improvement in solubility and bioavailability. Computational modeling enabled us to select the co-former by estimating the binding energy and intermolecular interactions. Rutin (RTH) was selected as a co-former for CRT CAMs using the solvent evaporation method to anticipate simultaneous improvement of solubility and bioavailability. The solid state characterization using DSC, XRPD, FT-IR, and a significant shift in Gordon Taylor experimental Tg values of co-amorphous materials revealed single amorphous phase formation and intermolecular interactions between CRT and RTH. The co-amorphous materials exhibited physical stability for up to 4 months under dry conditions (40 °C). Further, co-amorphous materials maintained the supersaturation for 24 hrs and improved solubility as well as dissolution of CRT. CRT:RTH 1:1 CAMs improved the permeability of CRT by 2 fold, estimated by employing the everted gut sac method. The solubility advantage of CAMs was also reflected in pharmacokinetic parameters, with a 3.1-fold and 2-fold improvement of CRT:RTH 2:1 in CRT exposure (AUC 0-t) and plasma concentration (Cmax) compared to the physical mixture, respectively.

Bioinformatic analysis of highly consumed phytochemicals as P-gp binders to overcome drug-resistance

Background and purpose

P-glycoprotein (P-gp) is an adenosine triphosphate (ATP)-dependent membrane efflux pump for protecting cells against xenobiotic compounds. Unfortunately, overexpressed P-gp in neoplastic cells prevents cell entry of numerous chemotherapeutic agents leading to multidrug resistance (MDR). MDR cells may be re-sensitized to chemotherapeutic drugs via P-gp inhibition/modulation. Side effects of synthetic P-gp inhibitors encouraged the development of natural products.

Experimental approach

Molecular docking and density functional theory (DFT) calculations were used as fast and accurate computational methods to explore a structure binding relationship of some dietary phytochemicals inside distinctive P-gp binding sites (modulatory/inhibitory). For this purpose, top-scored docked conformations were subjected to per-residue energy decomposition analysis in the B3LYP level of theory with a 6-31g (d, p) basis set by Gaussian98 package.

Findings/Results

Consecutive application of computational techniques revealed binding modes/affinities of nutritive phytochemicals within dominant binding sites of P-gp. Blind docking scores for best-ranked compounds were superior to verapamil and rhodamine-123. Pairwise amino acid decomposition of superior docked conformations revealed Tyr303 as an important P-gp binding residue. DFT-based induced polarization analysis revealed major electrostatic fluctuations at the atomistic level and confirmed larger effects for amino acids with energy-favored binding interactions. Conformational analysis exhibited that auraptene and 7,4',7'',4'''-tetra-O-methylamentoflavone might not necessarily interact to P-gp binding sites through minimum energy conformations.

Conclusion and implications

Although there are still many hurdles to overcome, obtained results may propose a few nutritive phytochemicals as potential P-gp binding agents. Moreover; top-scored derivatives may have the chance to exhibit tumor chemo-sensitizing effects.

Enhanced delivery of quercetin and doxorubicin using β-cyclodextrin polymer to overcome P-glycoprotein mediated multidrug resistance

In this study, we prepared a β-cyclodextrin polymer (β-CDP) co-loaded quercetin (QCT) and doxorubicin (DOX) nanocarrier (β-CDP/QD NCs) by freeze-dried method to combat P-glycoprotein (P-gp) mediated multidrug resistance (MDR) in KB-Ch^R 8-5 cancer cells. Various microscopic and spectroscopic techniques were employed to characterize the prepared nanocarrier. The molecular docking studies confirm the effective binding interactions of QCT and DOX with the synthesized β-CD polymer. The in vitro drug release study illustrates the sustainable release of DOX and QCT from the β-CDP nanocarrier. Further, we noticed that the QCT released from the β-CDP nanocarrier improved the intracellular availability of DOX via modulating P-gp drug efflux function in KB-Ch^R 8-5 cells and MCF-7/DOX cancer cells. Cell uptake results confirmed the successful internalization of DOX in KB-Ch^R 8-5 cells compared with free DOX. Cell-based assays such as nuclear condensation, alteration in the mitochondrial membrane potential (MMP), and apoptosis morphological changes confirmed the enhanced anticancer effect of β-CDP/QD NCs in the resistant cancer cells. Hence, QCT and DOX co-loaded β-CDP may be considered effective in achieving maximum cell death in the P-gp overexpressing MDR cancer cells.

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

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

Pinostrobin and Tectochrysin Conquer Multidrug-Resistant Cancer Cells via Inhibiting P-Glycoprotein ATPase

Enhanced drug efflux through ATP-binding cassette transporters, particularly P-glycoprotein (P-gp), is a key mechanism underlying multidrug resistance (MDR). In the present study, we investigated the inhibitory effects of pinostrobin and tectochrysin on P-gp in MDR cancer cells and the underlying mechanisms. Fluorescence substrate efflux assays, multidrug resistance 1 (MDR1) shift assays, P-gp ATPase activity assays, Western blotting, and docking simulation were performed. The potential of the test compounds for MDR reversal and the associated molecular mechanisms were investigated through cell viability assay, cell cycle analysis, apoptosis assay, and further determining the combination index. Results demonstrated that pinostrobin and tectochrysin were not the substrates of P-gp, nor did they affect the expression of this transporter. Both compounds noncompetitively inhibited the efflux of rhodamine 123 and doxorubicin through P-gp. Furthermore, they resensitized MDR cancer cells to chemotherapeutic drugs, such as vincristine, paclitaxel, and docetaxel; thus, they exhibited strong MDR reversal effects. Our findings indicate that pinostrobin and tectochrysin are effective P-gp inhibitors and promising candidates for resensitizing MDR cancer cells.

The effect of compatibility of Aconiti Radix and honey on the pharmacokinetics of five Aconitum alkaloids in rat plasma

Aconiti Radix (Chuanwu [CW]), is widely used for the treatment of the chronic and intractable diseases due to its remarkable curative effect. CW has been combined with honey for thousands of years to reduce toxicity and enhance efficacy. This study first clarified compatibility mechanism of CW co-used with honey using a comparative pharmacokinetic idea. We developed and validated a simple, sensitive, specific, and accurate UHPLC-MS/MS method to simultaneously determine five Aconitum alkaloids in rat plasma after oral administration of CW decoction and CW-honey concentrated solution. Pharmacokinetic parameters were significantly different between the two groups (P<0.01 and P<0.05). Compared with CW group, C_max and AUC_0→t were decreased in CW-honey group for three diester-diterpenoid alkaloids (hypaconitine, mesaconitine and aconitine); T_max and T_1/2 were prolonged. However, C_max and AUC_0→t were increased in CW-honey group for two monoester-diterpenoid alkaloids (benzoylaconine and benzoylmesaconine); T_max was shortened; T_1/2 was prolonged. These findings suggest that honey affected the pharmacokinetic behaviors of five Aconitum alkaloids. We speculate that the detoxification and synergism of honey might result from reducing the toxicity of diester-diterpenoid alkaloids and promoting the biological activity of monoester-diterpenoid alkaloids in vivo. This study provides a theoretical basis for the clinical use of CW combined with honey.

Effect of natural flavonoids to reverse P-glycoprotein-related multidrug resistance in breast cancer cell cultures

The aim of the research was to evaluate the influence of two P-glycoprotein (P-gp) inhibitors silymarin and quercetin on anticancer drug doxorubicin (DOX) and pegylated liposomal doxorubicin (PLD) delivery into breast cancer cells (2D cultures) and cancer cell spheroids (3D cultures) at different pH. The cytotoxicity of the compounds was assessed using MTT assay. Spheroids were generated using magnetic 3D Bioprinting method. The uptake of DOX and PLD into monolayer-cultured cells and spheroids was assessed by fluorescence microscopy. Both tested flavonoids did not increase DOX and PLD levels into monolayer-cultured 4T1 cells and 4T1 cell spheroids. However, both silymarin and quercetin enhanced DOX and PLD uptake into JC cell cultures. Silymarin and quercetin may modulate DOX and PLD transport into monolayer-cultured cells and three-dimensional cancer cell cultures depending on P-gp activity.

Efficacy of Flavonoids in Combating Fluconazole Resistant Oral Candidiasis

BACKGROUND

Candida is an opportunistic fungus often present in the oral mucosa. In the compromised immune system, it may become pathogenic and cause oral candidiasis. This infection is more common with Candida albicans; though, non-albicans Candida spp also have significant relevance. Current treatment guidelines include polyenes, azoles and echinocandins, where fluconazole is the primary therapeutic option. However, both inherited and acquired resistance to fluconazole is exhaustively reported. The development of resistance has resulted in the worsening of the original and re-emergence of new fungal diseases. Thus, the development of an anti-candidiasis therapy with a satisfactory outcome is the urgent need of the hour.

OBJECTIVE

This review article aims to stimulate the research in establishing the synergistic efficacy of various flavonoids with fluconazole to combat the resistance and develop an effective pharmacotherapy for the treatment of oral candidiasis. Further, in this article, we discuss in detail the mechanisms of action of fluconazole, along with the molecular basis of development of resistance in Candida species.

METHOD

PubMed and other databases were used for literature search.

RESULTS

The designing of natural drugs from the plant- derived phytochemicals are the promising alternates in modern medicine. The challenge today is the development of alternative anti- oral candidiasis drugs with increased efficacy, bioavailability and better outcome which can combat azole resistance. Identifying the flavonoids with potential antifungal action at low concentrations seems to meet the challenges.

CONCLUSION

Phyto-active constituents, either alone or in combination with conventional antibiotics may be an effective approach to deal with global antimicrobial resistance. The efficacy of herbal therapy for decades suggests that bacteria, fungi, and viruses may have a reduced ability to adapt and resistance to these natural antimicrobial regimes.

Transport and Interactions of Co-incubated Bi-functional Flavonoids through Inhibiting the Function of P-Glycoprotein (P-gp) Using KB/Multidrug-Resistant (MDR) Cells and Rat Everted Gut Sacs

This study aims to evaluate the interaction of flavonoid-flavonoid by inhibiting the function of P-glycoprotein (P-gp). The cellular uptake of seven substrates and eleven co-incubated inhibitors was measured in KB/MDR cells. The effect of galangin or morin on the absorption of silibinin or wogonin was carried out in the rat everted gut sacs. Docking was performed to evaluate the interactions between inhibitors and P-gp. Most substrates were greatly enhanced by at least five co-incubated inhibitors. Conversely, the increased uptake of substrates coincided with a decrease or without affecting the uptake of inhibitors, implying a competitive/non-competitive inhibition on P-gp. The enhancement effect by galangin or morin on the transport of silibinin or wogonin was verified in everted gut sacs. Docking explained the inhibition of flavonoids on P-gp by competitively binding to the ATP site. These results provide a strategy for increasing the absorption of flavonoids by co-administration.

A state-of-the-art review and prospective therapeutic applications of prenyl flavonoids as chemosensitizers against antifungal multidrug resistance in Candida albicans

Multidrug resistance (MDR) in the opportunistic pathogen Candida albicans is defined as non-susceptibility to at least one agent in two or more drug classes. This phenomenon has been increasingly reported since the rise in the incidence of fungal infections in immunocompromised patients at the end of the last century. After the discovery of efflux pump overexpression as a principal mechanism causing MDR in Candida strains, drug discovery targeting fungal efflux transporters has had a growing impact. Chemosensitization aims to enhance azole intracellular concentrations through combination therapy with transporter inhibitors. Consequently, the use of drug efflux inhibitors combined with the antifungal agent will sensitize the pathogen. As a result, the use of lower drug concentrations will reduce possible adverse effects on the host. Through an extensive revision of the literature, this review aims to provide an exhaustive and critical analysis of the studies carried out in the past two decades, regarding the chemosensitization strategy to cope with multidrug resistance in C. albicans. This work provides a deep analysis of the research about the inhibition of drug-efflux membrane transporters by prenylated flavonoids and the interactions of these phytocompounds with azole antifungals as an approach to chemosensitize multidrug-resistant C. albicans strains. We highlight the importance of prenylflavonoids and their particular chemical and pharmacological characteristics that make them excellent candidates with therapeutic potential as chemosensitizers. Finally, we propose the need for further research of prenyl flavonoids as inhibitors of drug-efflux mediated fungal resistance.

Synthesis, characterization, and pharmacological evaluation of some metal complexes of quercetin as P-gp inhibitors

Background

Six different metal complexes of quercetin (Cu, Zn, Co, Vd, Mo, Ni) were synthesized, purified, and characterized by their physical and spectral (UV, IR) data. They were evaluated for their P-gp (permeability glycoprotein) inhibitory activity by in vitro everted sac method in rats. The apparent permeability of atorvastatin (P-gp substrate) from everted sac of the rat intestine was determined in control, standard (verapamil), and groups treated with quercetin-metal complexes. The drug contents were analyzed by validated RP-HPLC method using a mixture of acetonitrile and water (60:40 v/v) adjusted to pH 2.8 with phosphate buffer as mobile phase.

Results

In vitro studies revealed that the apparent permeability of atorvastatin (P-gp substrate) across the small intestine is much affected by the treatment with Cu/Co/Ni complexes of quercetin. The mean ± SD and apparent permeability of atorvastatin decreased after pre-treatment with these metal complexes.

Conclusions

The quercetin Cu/Co/Ni complexes could inhibit P-gp and increase the atorvastatin absorption. Hence, they could be considered P-gp inhibitors.

Cardamonin inhibits the expression of P-glycoprotein and enhances the anti-proliferation of paclitaxel on SKOV3-Taxol cells

Paclitaxel is widely used in the first-line treatment of ovarian cancer. Nevertheless, the development of acquired resistance to paclitaxel is a major obstacle for the therapy in clinic. Cardamonin is a novel anticancer chalcone which exhibits a wide range of pharmacological activities. However, the effect of cardamonin on paclitaxel-resistant ovarian cancer cells and its underlying molecular mechanisms are unknown. Here, we revealed whether cardamonin had a resensitivity for paclitaxel and furtherly explored the underlying mechanisms on SKOV3-Taxol cells. Our results showed that cardamonin combined with paclitaxel had a synergistic effect of anti-proliferation in SKOV3-Taxol cells, and CI was less than one. Cells apoptosis and G2/M phase arrest were enhanced by cardamonin with paclitaxel in a concentration-dependent way on SKOV3-Taxol cells (P < 0.05). Cardamonin significantly increased drug accumulation in SKOV3-Taxol cells (P < 0.05). Similar to verapamil, cardamonin decreased MDR1 mRNA and P-gp expression (P < 0.05). Cardamonin restrained NF-κB activation in SKOV3-Taxol cells (P < 0.05). Inhibitory effect of P-gp and NF-κB p65 (nuclear protein) expression was enhanced by cardamonin combined with PDTC, a NF-κB inhibitor. Cardamonin significantly inhibited the upregulation of NF-κB p65 (nuclear protein) and P-gp expression induced by TNF-α (P < 0.05). Taken together, cardamonin enhanced the effect of paclitaxel on inhibiting cell proliferation, inducing apoptosis and G2/M phase arrest, and then strengthened the cytotoxic effect of paclitaxel in SKOV3-Taxol cells. The mechanism might be involved in inhibition of P-gp efflux pump, reducing MDR1 mRNA and P-gp expression by cardamonin via suppression of NF-κB activation in SKOV3-Taxol cells.

Flavonoid-statin interactions causing myopathy and the possible significance of OATP transport, CYP450 metabolism and mevalonate synthesis

3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors, statins, are a primary treatment for hyperlipidemic cardiovascular diseases which are a leading global cause of death. Statin therapy is life saving and discontinuation due to adverse events such as myotoxicity may lead to unfavourable outcomes. There is no known mechanism for statin-induced myotoxicity although it is theorized that it is due to inhibition of downstream products of the HMG-CoA pathway. It is known that drug-drug interactions with conventional medicines exacerbate the risk of statin-induced myotoxicity, though little attention has been paid to herb-drug interactions with complementary medicines. Flavonoids are a class of phytochemicals which can be purchased as high dose supplements. There is evidence that flavonoids can raise statin plasma levels, increasing the risk of statin-induced myopathy. This could be due to pharmacokinetic interactions involving hepatic cytochrome 450 (CYP450) metabolism and organic anion transporter (OATP) absorption. There is also the potential for flavonoids to directly and indirectly inhibit HMG-CoA reductase which could contraindicate statin-therapy. This review aims to discuss what is currently known about the potential for high dose flavonoids to interact with the hepatic CYP450 metabolism, OATP uptake of statins or their ability to interact with HMG-CoA reductase. Flavonoids of particular interest will be covered and the difficulties of examining herbal products will be discussed throughout.

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.

Structure-activity relationship and mechanism of flavonoids on the inhibitory activity of P-glycoprotein (P-gp)-mediated transport of rhodamine123 and daunorubicin in P-gp overexpressed human mouth epidermal carcinoma (KB/MDR) cells

This study was aimed to investigate the inhibitory activity of flavonoids on P-glycoprotein (P-gp). Effects of 39 flavonoids on the cellular uptake (CU) of rhodamine123 (Rho) and daunomycin (DNR) were investigated in both parental KB and P-gp overexpressed KB/MDR cells. The inhibition mechanism of selected flavonoids was further investigated by measuring the ATPase activity and expression level of P-gp. Twelve flavonoids improved the uptake of Rho (↑Rho_F) and nineteen flavonoids increased the uptake of DNR (↑DNR_F) in KB/MDR cells with nine flavonoids overlapped. Structure-activity relationship (SAR) indicated that 8-OCH₃, and 2'-OH have a negative effect on Rho and DNR transport. Whereas 5-OH, 5-OCH₃, 6-OH, 7-OCH₃, 3'-OH, and 4'-OH, are essential for inhibition of flavonoids on P-gp and reversing the resistance of Rho and DNR. Eleven selected flavonoids significantly induced the basal P-gp-ATPase activity but much lower than that induced by verapamil. Tangeretin, galangin, kaempferol, quercetin, and morin significantly reversed the ATPase activity stimulated by verapamil. Six of eleven flavonoids significantly decreased P-gp expression, whereas three flavonoids slightly increased P-gp expression. These results provide valuable information that flavonoids can effectively reverse multidrug resistance of P-gp-mediated transport of nutraceutical and drugs by co-administration.

Does Oral Apigenin Have Real Potential for a Therapeutic Effect in the Context of Human Gastrointestinal and Other Cancers?

Apigenin (4′, 5, 7-trihydroxyflavone) is a plant flavone that has been found to have various actions against cancer cells. We evaluated available evidence to determine whether it is feasible for apigenin to have such effects in human patients.

Apigenin taken orally is systemically absorbed and recirculated by enterohepatic and local intestinal pathways. Its bioavailability is in the region of 30%. Once absorbed from the oral route it reaches maximal circulating concentration (C_max) after a time (T_max) of 0.5–2.5h, with an elimination half-life (T¹/₂) averaging 2.52 ± 0.56h.

Using a circulating concentration for efficacy of 1–5μmol/L as the target, we evaluated data from both human and rodent pharmacokinetic studies to determine if a therapeutic concentration would be feasible. We find that oral intake of dietary materials would require heroic ingestion amounts and is not feasible. However, use of supplements of semi-purified apigenin in capsule form could reach target blood levels using amounts that are within the range currently acceptable for other supplements and medications. Modified formulations or parenteral injection are suitable but may not be necessary.

Further work with direct studies of pharmacokinetics and clinical outcomes are necessary to fully evaluate whether apigenin will contribute to a useful clinical strategy, but given emerging evidence that it may interact beneficially with chemotherapeutic drugs, this is worthy of emphasis. In addition, more effective access to intestinal tissues from the oral route raises the possibility that apigenin may be of particular relevance to gastrointestinal disorders including colorectal cancer.

Ellagic Acid and Schisandrins: Natural Biaryl Polyphenols with Therapeutic Potential to Overcome Multidrug Resistance in Cancer

Multidrug resistance (MDR) is one of the major clinical challenges in cancer treatment and compromises the effectiveness of conventional anticancer chemotherapeutics. Among known mechanisms of drug resistance, drug efflux via ATP binding cassette (ABC) transporters, namely P-glycoprotein (P-gp) has been characterized as a major mechanism of MDR. The primary function of ABC transporters is to regulate the transport of endogenous and exogenous small molecules across the membrane barrier in various tissues. P-gp and similar efflux pumps are associated with MDR because of their overexpression in many cancer types. One of the intensively studied approaches to overcome this mode of MDR involves development of small molecules to modulate P-gp activity. This strategy improves the sensitivity of cancer cells to anticancer drugs that are otherwise ineffective. Although multiple generations of P-gp inhibitors have been identified to date, reported compounds have demonstrated low clinical efficacy and adverse effects. More recently, natural polyphenols have emerged as a promising class of compounds to address P-gp linked MDR. This review highlights the chemical structure and anticancer activities of selected members of a structurally unique class of 'biaryl' polyphenols. The discussion focuses on the anticancer properties of ellagic acid, ellagic acid derivatives, and schisandrins. Research reports regarding their inherent anticancer activities and their ability to sensitize MDR cell lines towards conventional anticancer drugs are highlighted here. Additionally, a brief discussion about the axial chirality (i.e., atropisomerism) that may be introduced into these natural products for medicinal chemistry studies is also provided.

Incorporation of natural assumption to deal with cancer

The current state of the art for the use of natural ingredients for cancer therapy is by reviewing the publications and findings associated with cancer research with the employment of flavonoids. Cancer is the most furious disease making fear in the eyes of mankind. Though various treatment methods are prevalent, the patient's choices are shifting from synthetic treatment strategy to the natural ones. The plant-based metabolites are used very often in our life as a food additive and also as a medicine for primary health care. The safety profile and its efficacy add on advantage for the incorporation of the natural products separately or in combination as a remedy for cancer. Flavonoids, the plant-based metabolites are proven for their anti-inflammatory, anti-oxidant, and anti-cancer properties. Their chemotherapeutic and chemosensitizing power had made it interesting for the researchers to dig more on the health benefits of the flavonoids and incorporating it in a holistic approach, with its natural benefits to relieve the pain and the symptoms of the patient suffering from various medical conditions. The predominant approach for the management of cancer is by following safe and effective treatment modality. In this review, we mentioned the benefits of the flavonoids for the management of various cancers and its potency as a chemotherapeutic agent and as the chemosensitizer. Our mother nature had given remedies to cure various diseases in both human beings and animals by it; we just need to find out the sources and access to them.

Potential Herb-Drug Interactions in the Management of Age-Related Cognitive Dysfunction

Late-life mild cognitive impairment and dementia represent a significant burden on healthcare systems and a unique challenge to medicine due to the currently limited treatment options. Plant phytochemicals have been considered in alternative, or complementary, prevention and treatment strategies. Herbals are consumed as such, or as food supplements, whose consumption has recently increased. However, these products are not exempt from adverse effects and pharmacological interactions, presenting a special risk in aged, polymedicated individuals. Understanding pharmacokinetic and pharmacodynamic interactions is warranted to avoid undesirable adverse drug reactions, which may result in unwanted side-effects or therapeutic failure. The present study reviews the potential interactions between selected bioactive compounds (170) used by seniors for cognitive enhancement and representative drugs of 10 pharmacotherapeutic classes commonly prescribed to the middle-aged adults, often multimorbid and polymedicated, to anticipate and prevent risks arising from their co-administration. A literature review was conducted to identify mutual targets affected (inhibition/induction/substrate), the frequency of which was taken as a measure of potential interaction. Although a limited number of drugs were studied, from this work, interaction with other drugs affecting the same targets may be anticipated and prevented, constituting a valuable tool for healthcare professionals in clinical practice.

ABCB1 in dermatology: roles in skin diseases and their treatment

Adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1), also known as permeability glycoprotein, multidrug-resistant protein 1, or cluster of differentiation 243 (CD243), is a crucial protein for purging foreign substances from cells. The functions of ABCB1 have been investigated extensively for their roles in cancer, stem cells, and drug resistance. Abundant pharmacogenetic studies have been conducted on ABCB1 and its association with treatment responsiveness to various agents, particularly chemotherapeutic and immunomodulatory agents. However, its functions in the skin and implications on dermatotherapeutics are far less reported. In this article, we reviewed the roles of ABCB1 in dermatology. ABCB1 is expressed in the skin and its appendages during drug delivery and transport. It is associated with treatment responsiveness to various agents, including topical steroids, methotrexate, cyclosporine, azathioprine, antihistamines, antifungal agents, colchicine, tacrolimus, ivermectin, tetracycline, retinoid acids, and biologic agents. Moreover, genetic variation in ABCB1 is associated with the pathogenesis of several dermatoses, including psoriasis, atopic dermatitis, melanoma, bullous pemphigoid, Behçet disease, and lichen planus. Further investigation is warranted to elucidate the roles of ABCB1 in dermatology and the possibility of enhancing therapeutic efficacy through ABCB1 manipulation.

Suaeda vermiculata Aqueous-Ethanolic Extract-Based Mitigation of CCl4-Induced Hepatotoxicity in Rats, and HepG-2 and HepG-2/ADR Cell-Lines-Based Cytotoxicity Evaluations

Suaeda vermiculata, an edible halophytic plant, used by desert nomads to treat jaundice, was investigated for its hepatoprotective bioactivity and safety profile on its mother liquor aqueous-ethanolic extract. Upon LC-MS (Liquid Chromatography-Mass Spectrometry) analysis, the presence of several constituents including three major flavonoids, namely quercetin, quercetin-3-O-rutinoside, and kaempferol-O-(acetyl)-hexoside-pentoside were confirmed. The aqueous-ethanolic extract, rich in antioxidants, quenched the DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals, and also showed noticeable levels of radical scavenging capacity in ABTS (2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid) assay. For the hepatoprotective activity confirmation, the male rat groups were fed daily, for 7 days (n = 8/group, p.o.), either carboxyl methylcellulose (CMC) 0.5%, silymarin 200 mg/kg, the aqueous-ethanolic extract of the plant Suaeda vermiculata (100, 250, and 500 mg/kg extract), or quercetin (100 mg/kg) alone, and on day 7 of the administrations, all the animal groups, excluding a naïve (250 mg/kg aqueous-ethanolic extract-fed), and an intact animal group were induced hepatotoxicity by intraperitoneally administering carbon tetrachloride (CCl₄). All the animals were sacrificed after 24 h, and aspartate transaminase and alanine transaminase serum levels were observed, which were noted to be significantly decreased for the aqueous-ethanolic extract, silymarin, and quercetin-fed groups in comparison to the CMC-fed group (p < 0.0001). No noticeable adverse effects were observed on the liver, kidney, or heart's functions of the naïve (250 mg/kg) group. The aqueous-ethanolic extract was found to be safe in the acute toxicity (5 g/kg) test and showed hepatoprotection and safety at higher doses. Further upon, the cytotoxicity testings in HepG-2 and HepG-2/ADR (Adriamycin resistant) cell-lines were also investigated, and the IC₅₀ values were recorded at 56.19±2.55 µg/mL, and 78.40±0.32 µg/mL (p < 0.001, Relative Resistance RR 1.39), respectively, while the doxorubicin (Adriamycin) IC₅₀ values were found to be 1.3±0.064, and 4.77±1.05 µg/mL (p < 0.001, RR 3.67), respectively. The HepG-2/ADR cell-lines when tested in a combination of the aqueous-ethanolic extract with doxorubicin, a significant reversal in the doxorubicin's IC₅₀ value by 2.77 folds (p < 0.001, CI = 0.56) was noted as compared to the cytotoxicity test where the extract was absent. The mode of action for the reversal was determined to be synergistic in nature indicating the role of the aqueous-ethanolic extract.

Antimicrobial Peptide Reverses ABCB1-Mediated Chemotherapeutic Drug Resistance

Multidrug resistance (MDR) of tumor cells to chemotherapeutic agents is the main reason for the failure of cancer chemotherapy. Overexpression of ABCB1 transporter that actively pumps various drugs out of the cells has been considered a major contributing factor for MDR. Over the past decade, many antimicrobial peptides with antitumor activity have been identified or synthesized, and some antitumor peptides have entered the clinical practice. In this study, we report that peptide HX-12C has the effect of reversing ABCB1-mediated chemotherapy resistance. In ABCB1-overexpressing cells, nontoxic dose of peptide HX-12C inhibited drug resistance and increased the effective intracellular concentration of paclitaxel and other ABCB1 substrate drugs. The mechanism study showed that peptide HX-12C stimulated ABCB1 ATPase activity without changing the expression level and localization patterns of ABCB1. Molecular docking predicted the binding modes between peptide HX-12C and ABCB1. Overall, we found that peptide HX-12C reverses ABCB1-mediated MDR through interacting with ABCB1 and blocking its function without affecting the transporter's expression and cellular localization. Our findings suggest that this antimicrobial peptide may be used as a novel prospective cancer therapeutic strategy in combination with conventional anticancer agents.

Synergistic Effect of Tangeretin and Atorvastatin for Colon Cancer Combination Therapy: Targeted Delivery of These Dual Drugs Using RGD Peptide Decorated Nanocarriers

Purpose

Colorectal cancer (CRC) is the third most frequently diagnosed cancer and the fourth leading cause of cancer death over the world. Nano-sized drug delivery systems are used for the treatment of cancers. The aim of this study was to develop a tangeretin (TAGE) and atorvastatin (ATST) combined nano-system decorated with RGD (RGD-ATST/TAGE CNPs) for colon cancer combination therapy.

Materials and Methods

In this study, cyclized arginine-glycine-aspartic acid sequences (RGD) contained ligand was synthesized by conjugating cyclo (Arg-Gly-Asp-d-Phe-Lys) (cRGDfK) with D-α-tocopheryl succinate dichloromethane (TOSD) using polyethylene glycol (PEG) as a linker to obtain cRGDfK-PEG-TOSD. ATST and TAGE combined nano-systems: RGD-ATST/TAGE CNPs were prepared. The combination effects as well as antitumor effects of these two agents were evaluated on colon cancer cells and mice bearing cancer models.

Results

Drug entrapment efficiencies of nano-systems were high (around 90%), suggesting the good loading capacity. The release profiles of ATST or TAGE from RGD-ATST/TAGE CNPs followed Higuchi model. The RGD-decorated nano-system showed more obvious cytotoxicity on HT-29 cells than the undecorated nano-system, but no obvious difference was found on normal CCD-18 cells. The strongest synergism was observed when the weight ratio of ATST to TAGE was 1:1. In vivo biodistribution of RGD-ATST/TAGE CNPs in the tumor site is high and prominently inhibited the in vivo tumor growth.

Conclusion

The results demonstrated that RGD-ATST/TAGE CNPs showed the most significant synergistic therapeutic efficacy, exhibited no significant toxicity to major organs and tissues, and body weight of the treated mice was stable. Therefore, the combination nano-system is a promising platform for colon cancer therapy.

Kaempferol-Mediated Sensitization Enhances Chemotherapeutic Efficacy of Sorafenib Against Hepatocellular Carcinoma: An In Silico and In Vitro Approach

Purpose: Sorafenib is the sole FDA approved drug conventionally used for the treatment of advanced hepatocellular carcinoma (HCC). Despite of the beneficial use of sorafenib in the treatment of HCC, multidrug resistance still remains a challenge. HCC is inherently known as chemotherapy resistant tumor due to P-glycoprotein (P-gp)-mediated multidrug resistance. Methods: We studied the interaction energy of kaempferol with human multidrug resistance protein-1 (RCSB PDB ID: 2CBZ) using in silico method with the help of BIOVIA Discovery Studio. HepG2 and N1S1 liver cancer cell lines were treated in suitable cell culture media to evaluate the efficacy of kaempferol in chemo-sensitizing liver cancer cells towards the effect of sorafenib. Cell viability study was performed by MTT assay. Results: In silico analysis of kaempferol showed best docking score of 23.14 with Human Multi Drug Resistant Protein-1 (RCSB PDB ID: 2CBZ) compared with positive control verapamil. Inin-vitro condition, combination of sub-toxic concentrations of both kaempferol and sorafenib produced 50% cytotoxicity with concentration of 2.5 µM each which indicates that kaempferol has the ability to reverse the MDR by decreasing the over-expression of P-gp. Conclusion: Kaempferol is able to sensitize the HepG2 and N1S1 against the sub-toxic concentration of sorafenib. Hence, we consider that the efficacy of sorafenib chemotherapy can be enhanced by the significant approach of combining the sub-toxic concentrations of sorafenib with kaempferol. Thus, kaempferol can be used as a better candidate molecule along with sorafenib for enhancing its efficacy, if validated through preclinical studies.

Evaluation of the Effects of Maytenus ilicifolia on the Activities of Cytochrome P450 3A and P-glycoprotein

Background:

Maytenus ilicifolia is a Brazilian popular medicine commonly used to treat ulcer and gastritis. Despite the absence of toxicity regarding its consumption, possible interactions when co-administrated with conventional drugs, are unknown.

Objective:

This study aimed to evaluate the effects of M. ilicifolia extracts on Cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp) activities.

Method:

The extracts were obtained by infusion (MI) or turbo-extraction using hydro-acetonic solvent (MT70). The content of polyphenols in each extract was determined. To assess the modulation of M. ilicifolia on P-gp activity, the uptake of fexofenadine (FEX) by Caco-2 cells was investigated in the absence or presence of MI or MT70. The effect on CYP3A activity was evaluated by the co-administration of midazolam (MDZ) with each extract in male Wistar rats. The pharmacokinetic parameters of the drug were determined and compared with those from the control group. The content of total phenolic compounds, tannins, and flavonoids on MT70 extract was about double of that found in MI.

Results:

In the presence of the extracts, the uptake of the P-gp marker (FEX) by Caco-2 cells increased from 1.7 ± 0.4 ng.mg-1 protein (control) to 3.5 ± 0.2 ng.mg-1 protein (MI) and 4.4 ± 0.5 ng.mg-1 protein (MT70), respectively. When orally co-administrated with MDZ (substrate of CYP3A), the extracts augmented the AUC(0-∞) (Control: 911.7 ± 215.7 ng.h.mL-1; MI: 1947 ± 554.3 ng.h.mL-1; MT70: 2219.0 ± 506.3 ng.h.mL-1) and the Cmax (Control: 407.7 ± 90.4 ng.mL-1; MI: 1770.5 ± 764.5 ng.mL-1; MT70: 1987.2 ± 544.9 ng.mL-1) of the drug in rats indicating a 50% reduction of the oral Cl. No effect was observed when midazolam was given intravenously.

Conclusion:

The results suggest that M. ilicifolia can inhibit the intestinal metabolism and transport of drugs mediated by CYP3A and P-gp, respectively, however, the involvement of other transporters and the clinical relevance of such interaction still need to be clarified.

Wilforine resensitizes multidrug resistant cancer cells via competitive inhibition of P-glycoprotein

BACKGROUND AND PURPOSE

Multidrug resistance (MDR) remains the main obstacle in cancer treatment and overexpression of P-glycoprotein (P-gp) is one of the most common causes of chemoresistance. The development of novel P-gp inhibitors from natural products is a prospective strategy to combat MDR cancers. Among the natural sesquiterpene compounds, sesquiterpene pyridine alkaloids exhibit various biological properties. Therefore, in the present study, we evaluated the modulatory effects of wilforine on P-gp expression and function. The molecular mechanisms and kinetic models of wilforine-mediated P-gp inhibition were further investigated.

METHODS

The human P-gp stable expression cells (ABCB1/Flp-In^TM-293) and human cervical cancer cells (sensitive: HeLaS3; MDR: KBvin) were used. The cell viability was assessed by SRB assay. The inhibitory effect of wilforine on P-gp efflux and the underlying mechanism were evaluated by assays for calcein-AM uptake, rhodamine123 and doxorubicin efflux, ATPase activity, real-time quantitative RT-PCR, apoptosis, and cell cycle analysis. Molecular docking was performed by the docking software CDOCKER with BIOVIA Discovery Studio 4.5 (D.S. 4.5).

RESULTS

We found that wilforine significantly inhibited the efflux activity of P-gp in a concentration-dependent manner. Further kinetic analysis demonstrated that wilforine significantly inhibited P-gp efflux function by competitive inhibition and stimulated the basal P-gp ATPase activity. In addition, wilforine re-sensitized MDR cancer cells to chemotherapeutic drugs. The docking model indicated that wilforine was bound to residues of P-gp such as LEU884, LYS887, THR176 and ASN172.

CONCLUSION

These results suggest a novel future therapeutic strategy for MDR cancer using wilforine as an adjuvant treatment with chemotherapy.

Quercetin overcomes colon cancer cells resistance to chemotherapy by inhibiting solute carrier family 1, member 5 transporter

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) remains a significant impediment to the success of cancer chemotherapy. The natural flavonoid Quercetin (Que) has been reported to be able to inhibit P-gp-mediated MDR in various cancer cells. However, the MDR reversal effect of Que on human colon cancer cells and its mechanism at the metabolic level requires further clarification. This study was designed to provide a better understanding of the MDR reversal effect of Que. Our present results showed that 33 μM of Que significantly improved the cytotoxicity of doxorubicin (Dox) to P-gp-overexpressed SW620/Ad300 cells by proliferation and apoptpsis assay. Further mechanism studies demonstrated that Que inhibited the ATP-driven transport activity of P-gp, which in turn increased the intracellular accumulation of Dox. The metabolomics studies based on UPLC-MS/MS analysis revealed that Que could reverse the MDR by significantly blocking D-glutamine and D-glutamate metabolism, and the underlying mechanism is that Que down-regulated the expression of the glutamine transporter solute sarrier family 1, member 5 (SLC1A5) in SW620/Ad300 cells. This is the first time to report that Que was a SLC1A5 inhibitor, which could be served as a template compound to potentially develop novel P-gp-mediated MDR reversal modulators in cancer chemotherapy.

Kaempferol modulates TCDD- and t-BHQ-induced drug-metabolizing enzymes and luteolin enhances this effect

The expression of drug-metabolizing enzymes is deeply involved in chemical-induced cancer progression and prevention. The aryl hydrocarbon receptor (AhR) induces phase I, and certain phase II drug-metabolizing enzymes after the binding of ligands, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We have previously demonstrated that luteolin inhibited TCDD-induced AhR transformation, and modulated the expression of drug-metabolizing enzymes through not only the AhR, but also the nuclear factor-erythroid-2-related factor 2 (Nrf2). We have examined the effect of kaempferol on the expression of drug-metabolizing enzymes through modulation of the AhR- and Nrf2-pathways, and the effect of co-treatment with kaempferol and luteolin. Kaempferol dose-dependently inhibited not only the TCDD-induced expression of phase I and phase II drug-metabolizing enzymes, but also the tertiary butylhydroquinone (t-BHQ)-induced expression of phase II drug-metabolizing enzymes, by modulating the AhR- and Nrf2-pathways. Co-treatment with kaempferol and luteolin enhanced the inhibitory effect on the expression of drug-metabolizing enzymes, compared with either kaempferol or luteolin alone. Moreover, co-treatment with kaempferol and luteolin increased the cellular levels of kaempferol without affecting the levels of luteolin. An in vivo study was also performed and the results demonstrated that co-treatment with kaempferol and luteolin enhanced the inhibition of benzo[a]pyrene-induced drug-metabolizing enzymes compared with either kaempferol or luteolin alone, in the liver of ICR mice. These results suggest that luteolin promoted the incorporation of kaempferol into hepatocytes and enhanced the inhibitory effect of kaempferol on chemical-induced drug-metabolizing enzymes. Thus, luteolin enhances the kaempferol-inhibited expression of drug-metabolizing enzymes.

Defying Multidrug Resistance! Modulation of Related Transporters by Flavonoids and Flavonolignans

Multidrug resistance (MDR) is a major challenge for the 21th century in both cancer chemotherapy and antibiotic treatment of bacterial infections. Efflux pumps and transport proteins play an important role in MDR. Compounds displaying inhibitory activity toward these proteins are prospective for adjuvant treatment of such conditions. Natural low-cost and nontoxic flavonoids, thanks to their vast structural diversity, offer a great pool of lead structures with broad possibility of chemical derivatizations. Various flavonoids were found to reverse both antineoplastic and bacterial multidrug resistance by inhibiting Adenosine triphosphate Binding Cassette (ABC)-transporters (human P-glycoprotein, multidrug resistance-associated protein MRP-1, breast cancer resistance protein, and bacterial ABC transporters), as well as other bacterial drug efflux pumps: major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR) and resistance-nodulation-cell-division (RND) transporters, and glucose transporters. Flavonoids and particularly flavonolignans are therefore highly prospective compounds for defying multidrug resistance.

Quercetin reverses docetaxel resistance in prostate cancer via androgen receptor and PI3K/Akt signaling pathways

Docetaxel is the first-line chemotherapy agent for metastatic prostate cancer. However, the emergence of resistance diminishes its efficacy and limits the survival benefit. Quercetin is a dietary flavonoid which has been shown to have multiple anti-cancer effects. Also, quercetin has been reported to reverse chemo-resistance in many other cancers. This study was to determine whether quercetin could reverse docetaxel resistance in prostate cancer cells and xenograft models, thereby exploring the underlying mechanism. Depending on the docetaxel-resistant cells (LNCaP/R, PC-3/R) which were established from docetaxel-sensitive cells (LNCaP, PC-3), it was demonstrated that quercetin could reverse docetaxel resistance in prostate cancer on proliferation, colony formation, migration, invasion and apoptosis. Although single docetaxel application had little effect on docetaxel-resistant cells, combining docetaxel with quercetin was significantly effective. Combination therapy could maximally inhibited PI3K/Akt pathway and promoted apoptosis. As shown by in-vivo study, xenograft tumors treated by docetaxel with quercetin had poorest growth. Then, to investigate the underlying mechanisms, the differences among parental cells, docetaxel-resistant subclones and quercetin treated resistant subclones were evaluated. It was found that docetaxel-resistant subclones had stronger activation of androgen receptor and PI3K/Akt pathway, more remarkable mesenchymal and stem-like cell phenotypes, and more P-gp expression than that of parental cells. Interestingly, quercetin could reverse these transformations. Our data revealed that quercetin had docetaxel-resistance reversal effect both in vitro and in vivo and provided in-depth support for clinical use of quercetin in docetaxel-resistant prostate cancer.

Euryops pectinatus L. Flower Extract Inhibits P-glycoprotein and Reverses Multi-Drug Resistance in Cancer Cells: A Mechanistic Study

Euryops pectinatus is a South African ornamental plant belonging to family Asteraceae. The present work evaluates the cytotoxic activity and phytochemical profile of the flower extract. Metabolite profiling was performed using HPLC-PDA-ESI-MS/MS. Total phenolics and flavonoids content were assessed. Cytotoxicity was evaluated against 6 different cancer cell lines using MTT assay. The possible underlying mechanism was proposed. We analyzed whether the extract could overcome the resistance of multidrug-resistant cancer cells for doxorubicin. The effect of combination of E. pectinatus with doxorubicin was also studied. Additionally, the potential inhibitory activity of the identified phytochemicals to PB1 protein was analyzed using in silico molecular docking. Twenty-five compounds were tentatively identified. Total phenolic and flavonoid contents represented 49.41 ± 0.66 and 23.37 ± 0.23 µg/mg dried flower extract, respectively. The extract showed selective cytotoxicity against Caco2 cells but its main effect goes beyond mere cytotoxicity. It showed strong inhibition of P-glycoprotein, which helps to overcome multidrug resistance to classical chemotherapeutic agents. In silico molecular docking showed that dicaffeoyl quinic acid, kaempferol-O-rutinoside, rutin, and isorhamnetin-O-rutinoside exhibited the most potent inhibitory activity to PB1 involved in tumor progression. Euryops pectinatus flower heads could have promising selective cytotoxicity alone or in combination with other chemotherapeutic agents to counteract multidrug resistance.

Medicinal chemistry strategies to discover P-glycoprotein inhibitors: An update

The presence of multidrug resistance (MDR) in malignant tumors is one of the primary causes of treatment failure in cancer chemotherapy. The overexpression of the ATP binding cassette (ABC) transporter, P-glycoprotein (P-gp), which significantly increases the efflux of certain anticancer drugs from tumor cells, produces MDR. Therefore, inhibition of P-gp may represent a viable therapeutic strategy to overcome cancer MDR. Over the past 4 decades, many compounds with P-gp inhibitory efficacy (referred to as first- and second-generation P-gp inhibitors) have been identified or synthesized. However, these compounds were not successful in clinical trials due to a lack of efficacy and/or untoward toxicity. Subsequently, third- and fourth-generation P-gp inhibitors were developed but dedicated clinical trials did not indicate a significant therapeutic effect. In recent years, an extraordinary array of highly potent, selective, and low-toxicity P-gp inhibitors have been reported. Herein, we provide a comprehensive review of the synthetic and natural products that have specific inhibitory activity on P-gp drug efflux as well as promising chemosensitizing efficacy in MDR cancer cells. The present review focuses primarily on the structural features, design strategies, and structure-activity relationships (SAR) of these compounds.

Prediction of P-glycoprotein inhibitors with machine learning classification models and 3D-RISM-KH theory based solvation energy descriptors

Development of novel in silico methods for questing novel PgP inhibitors is crucial for the reversal of multi-drug resistance in cancer therapy. Here, we report machine learning based binary classification schemes to identify the PgP inhibitors from non-inhibitors using molecular solvation theory with excellent accuracy and precision. The excess chemical potential and partial molar volume in various solvents are calculated for PgP± (PgP inhibitors and non-inhibitors) compounds with the statistical-mechanical based three-dimensional reference interaction site model with the Kovalenko-Hirata closure approximation (3D-RISM-KH molecular theory of solvation). The statistical importance analysis of descriptors identified the 3D-RISM-KH based descriptors as top molecular descriptors for classification. Among the constructed classification models, the support vector machine predicted the test set of Pgp± compounds with highest accuracy and precision of ~ 97% for test set. The validation of models confirms the robustness of state-of-the-art molecular solvation theory based descriptors in identification of the Pgp± compounds.

Flavonoids as P-gp Inhibitors: A Systematic Review of SARs

P-glycoprotein, also known as ABCB1 in the ABC transporter family, confers the simultaneous resistance of metastatic cancer cells towards various anticancer drugs with different targets and diverse chemical structures. The exploration of safe and specific inhibitors of this pump has always been the pursuit of scientists for the past four decades. Naturally occurring flavonoids as benzopyrone derivatives were recognized as a class of nontoxic inhibitors of P-gp. The recent advent of synthetic flavonoid dimer FD18, as a potent P-gp modulator in reversing multidrug resistance both in vitro and in vivo, specifically targeted the pseudodimeric structure of the drug transporter and represented a new generation of inhibitors with high transporter binding affinity and low toxicity. This review concerned the recent updates on the structure-activity relationships of flavonoids as P-gp inhibitors, the molecular mechanisms of their action and their ability to overcome P-gp-mediated MDR in preclinical studies. It had crucial implications on the discovery of new drug candidates that modulated the efflux of ABC transporters and also provided some clues for the future development in this promising area.

Tackling drug resistance with efflux pump inhibitors: from bacteria to cancerous cells

Drug resistance is a serious concern in a clinical setting jeopardizing treatment for both infectious agents and cancers alike. The wide-spread emergence of multi-drug resistant (MDR) phenotypes from bacteria to cancerous cells necessitates the need to target resistance mechanisms and prevent the emergence of resistant mutants. Drug efflux seems to be one of the preferred approaches embraced by both microbial and mammalian cells alike, to thwart the action of chemotherapeutic agents thereby leading to a drug resistant phenotype. Relative to microbes, which predominantly employs proton motive force (PMF) powered, Major Facilitator Superfamily (MFS)/Resistance Nodulation and Division (RND) classes of efflux pumps to efflux drugs, cancerous cells preferentially use ATP fuelled ATP binding cassette (ABC) transporters to extrude chemotherapeutic agents. The prevalence, evolutionary characteristics and overlapping functions of ABC transporters have been highlighted in this review. Additionally, we outline the role of ABC pumps in conferring MDR phenotype to both bacteria and cancerous cells and underscore the importance of efflux pump inhibitors (EPI) to mitigate drug resistance. Based on the literature reports and analysis, we reason out feasibility of employing bacteria as a tool to screen for EPI's targeting ABC pumps of cancerous cells.

Reversal of Multidrug Resistance in Cancer by Multi-Functional Flavonoids

Multidrug resistance (MDR) resulting from different defensive mechanisms in cancer is one of the major obstacles of clinical treatment. To circumvent MDR many reversal agents have been developed, but most of them fail in clinical trials due to severely adverse effects. Recently, certain natural products have been reported to overcome MDR, including flavonoids which are abundant in plants, foods, and herbs. The structure of flavonoids can be abbreviated as C6-C3-C6 (C for carbon), and further categorized into flavonoids, iso-flavonoids and neo-flavonoids, according to their structural backbones. Flavonoids possess multiple bioactivities, and a growing body of research has indicated that both flavonoids and iso-flavonoids can either kill or re-sensitize conventional chemotherapeutics to resistant cancer cells. Here, we summarize the research and discuss the underlying mechanisms, concluding that these flavonoids do not function as specific regulators of target proteins, but rather as multi-functional agents that negatively regulate the key factors contributing to MDR.

Quantitative Structure⁻Activity Relationships for the Flavonoid-Mediated Inhibition of P-Glycoprotein in KB/MDR1 Cells

P-glycoprotein (P-gp) serves as a therapeutic target for the development of inhibitors to overcome multidrug resistance (MDR) in cancer cells. In order to enhance the uptake of chemotherapy drugs, larger amounts of P-gp inhibitors are required. Besides several chemically synthesized P-gp inhibitors, flavonoids as P-gp inhibitors are being investigated, with their advantages including abundance in our daily diet and a low toxicity. The cytotoxicity of daunorubicin (as a substrate of P-gp) to KB/MDR1 cells and the parental KB cells was measured in the presence or absence of flavonoids. A two-dimensional quantitative structure–activity relationship (2D-QSAR) model was built with a high cross-validation coefficient (Q²) value of 0.829. Descriptors including vsurf_DW23, E_sol, Dipole and vsurf_G were determined to be related to the inhibitory activity of flavonoids. The lack of 2,3-double bond, 3′-OH, 4′-OH and the increased number of methoxylated substitutions were shown to be beneficial for the inhibition of P-gp. These results are important for the screening of flavonoids for inhibitory activity on P-gp.

Silymarin as a flavonoid-type P-glycoprotein inhibitor with impact on the pharmacokinetics of carbamazepine, oxcarbazepine and phenytoin in rats

P-glycoprotein (P-gp) is an efflux transporter involved in drug-resistant epilepsy and some flavonoids have been targeted as effective P-gp inhibitors. Herein, we assessed the impact of silymarin on the pharmacokinetics of three antiepileptic drugs (AEDs) in rats. Animals were pretreated with silymarin, verapamil (positive control) or vehicle (negative control) 1 h before AEDs administration (carbamazepine (25 mg/kg), oxcarbazepine (OXC) (50 mg/kg), or phenytoin (100 mg/kg)). Multiple blood samples were collected after AED dosing, and a non-compartmental analysis was performed. An independent study was also conducted to investigate the effects of silymarin on the OXC plasma-to-brain distribution. Silymarin altered the pharmacokinetics of OXC, increasing its peak plasma concentration by 50% and its extent of systemic exposure by 41%, which had also impact on brain drug concentrations. These findings support that the co-administration of silymarin and OXC should continue to be explored as a strategy to reverse the pharmacoresistance in epilepsy.

Tenulin and isotenulin inhibit P-glycoprotein function and overcome multidrug resistance in cancer cells

BACKGROUND

Multidrug resistance (MDR) in cancer is one of the main obstacles in treatment with chemotherapy. Drug efflux through P-glycoprotein is the major mechanism involved in MDR. A potential strategy to provide the best possible clinical outcomes is to develop P-glycoprotein (P-gp) inhibitors from natural products.

PURPOSE

The present study investigated the effects of the natural sesquiterpene lactone tenulin and its derivative isotenulin on human P-gp; the mechanisms of kinetic interactions were also explored.

METHODS

The human P-gp (ABCB1/Flp-In™-293) stable expression cells were established by using the Flp-In™ system. The effects of tenulin and isotenulin on cell viability were evaluated by SRB assays in established cell lines, sensitive cancer cell line (HeLaS3), and resistant cancer cell line (KB-vin). The transporter inhibition ability was evaluated by calcein-AM uptake assays. The P-gp inhibition kinetics of tenulin and isotenulin were evaluated by rhodamine123 and doxorubicin efflux assays. The ATPase activity was evaluated with the Pgp-Glo™ Assay System.

RESULTS

Tenulin and isotenulin significantly inhibited the P-gp efflux function by stimulating P-gp ATPase activity. Tenulin and isotenulin interacted with the effluxes of rhodamine 123 and doxorubicin through a competitive and noncompetitive mechanism, respectively. The combinations of tenulin and isotenulin with chemotherapeutic drugs significantly resensitized MDR cancer cells.

CONCLUSION

These results suggested that tenulin and isotenulin are potential candidates to be developed for synergistic treatment of MDR cancers.

MIX2: A Novel Natural Multi-Component Modulator of Multidrug-Resistance and Hallmarks of Cancer Cells

Multidrug resistance is one of the key barriers suppressing the effectiveness of drug therapies of malignant tumors. Here, we report a study on the effect of a mix of natural extracts (MIX2) prepared from fresh fruits of Prunus spinosa, Crataegus monogyna, Sorbus aucuparia, and Euonymus europaeus on the classic hallmarks of cancer cells and the expression of multidrug resistance proteins. In the studies, HeLa and T98G cell lines, and classic methods of molecular biology, including RT-qPCR, Western blot, flow cytometry, and confocal imaging, were used. Additionally, migration, adhesion, and proliferation assays were performed. The obtained results indicate that the MIX2 cocktail presents strong anti-cancer properties. MIX2 is not toxic, but at the same time significantly alters the migration, proliferation, and adhesion of tumor cells. Furthermore, it was found that cells exposed to the mixture presented a significantly reduced expression level of genes associated with MDR, including ABCB1, which encodes for glycoprotein P. In vitro data showed that MIX2 effectively sensitizes tumor cells to doxorubicin. We postulate that modulation of the multidrug resistance phenotype of tumors with the use of MIX2 may be considered as a safe and applicable tool in sustaining drug delivery therapies of malignancies.

Flavonoids modulate multidrug resistance through wnt signaling in P-glycoprotein overexpressing cell lines

BACKGROUND

Wnt signaling has been linked with P-glycoprotein (P-gp) overexpression and which was mainly mediated by β-catenin nuclear translocation. Flavonoids have already been reported as modulators of the Wnt/β-catenin pathway and hence they may serve as promising agents in the reversal of P-gp mediated cancer multi drug resistance (MDR).

METHODS

In this study, we screened selected flavonoids against Wnt/β-catenin signaling molecules. The binding interaction of flavonoids (theaflavin, quercetin, rutin, epicatechin 3 gallate and tamarixetin) with GSK 3β was determined by molecular docking. Flavonoids on P-gp expression and the components of Wnt signaling in drug-resistant KBCH^R8-5 cells were analyzed by western blotting and qRT-PCR. The MDR reversal potential of these selected flavonoids against P-gp mediated drug resistance was analyzed by cytotoxicity assay in KBCH^R8-5 and MCF7/ADR cell lines. The chemosensitizing potential of flavonoids was further analyzed by observing cell cycle arrest in KBCH^R8-5 cells.

RESULTS

In this study, we observed that the components of Wnt/β-catenin pathway such as Wnt and GSK 3β were activated in multidrug resistant KBCH^R8-5 cell lines. All the flavonoids selected in this study significantly decreased the expression of Wnt and GSK 3β in KBCH^R8-5 cells and subsequently modulates P-gp overexpression in this drug-resistant cell line. Further, we observed that these flavonoids considerably decreased the doxorubicin resistance in KBCH^R8-5 and MCF7/ADR cell lines. The MDR reversal potential of flavonoids were found to be in the order of theaflavin > quercetin > rutin > epicatechin 3 gallate > tamarixetin. Moreover, we observed that flavonoids pretreatment significantly induced the doxorubicin-mediated arrest at the phase of G2/M. Further, the combinations of doxorubicin with flavonoids significantly modulate the expression of drug response genes in KBCH^R8-5 cells.

CONCLUSION

The present findings illustrate that the studied flavonoids significantly enhances doxorubicin-mediated cell death through modulating P-gp expression pattern by targeting Wnt/β-catenin signaling in drug-resistant KBCH^R8-5 cells.

Taxifolin Resensitizes Multidrug Resistance Cancer Cells via Uncompetitive Inhibition of P-Glycoprotein Function

P-glycoprotein (P-gp) effluxes lots of chemotherapeutic agents and leads to multidrug resistance (MDR) in cancer treatments. The development of P-gp inhibitors from natural products provide a potential strategy for the beneficial clinical outcomes. This study aimed to evaluate the effects of the natural flavonoid taxifolin, luteolin, (-)-gallocatechin, and (-)-catechin on human P-gp activity. The kinetic interactions and underlying mechanisms of taxifolin-mediated transporter inhibition were further investigated. The transporter inhibition ability was evaluated in human P-gp stable expression cells (ABCB1/Flp-InTM-293) by calcein-AM uptake assays. The kinetics study for P-gp inhibition was evaluated by doxorubicin and rhodamine123 efflux assays. The MDR reversal ability of taxifolin were performed by SRB assays to detect the cell viability in sensitive cancer cell line (HeLaS3), and resistant cancer cell line (KB-vin). Cell cycle analysis and ABCB1 real-time RT-PCR were used for mechanical exploration. The results demonstrated that taxifolin decreased ABCB1 expression in a concentration-dependent manner. The function of P-gp was inhibited by taxifolin through uncompetitive inhibition of rhodamine 123 and doxorubicin efflux. The combination of taxifolin significantly resensitized MDR cancer cells to chemotherapeutic agents. These results suggested that taxifolin may be considered as a potential P-gp modulator for synergistic treatment of MDR cancers.