Modulation of P-glycoprotein activity by acridones and coumarins fromCitrus sinensis

Recent developments of P-glycoprotein inhibitors and its structure-activity relationship (SAR) studies

P-glycoprotein (P-gp) over-expression is a key factor in multi-drug resistance (MDR), which is a major factor in the failure of cancer treatment. P-gp inhibitors have been demonstrated to have powerful pharmacological properties and may be used as a therapeutic approach to overcome the MDR in cancer cells. Combining clinical investigations with biochemical and computational research may potentially lead to a clearer understanding of the pharmacological properties and the mechanisms of action of these P-gp inhibitors. The task of turning these discoveries into effective therapeutic candidates for a variety of malignancies, including resistant and metastatic kinds, falls on medicinal chemists. A variety of P-gp inhibitors with great potency, high selectivity, and minimal toxicity have been identified in recent years. The latest advances in drug design, characterization, structure-activity relationship (SAR) research, and modes of action of newly synthesized, powerful small molecules P-gp inhibitors over the previous ten years are highlighted in this review. P-gp transporter over-expression has been linked to MDR, therefore the development of P-gp inhibitors will expand our understanding of the processes and functions of P-gp-mediated drug efflux, which will be helpful for drug discovery and clinical cancer therapies.

A comprehensive review on acridone based derivatives as future anti-cancer agents and their structure activity relationships

The development of drug resistance and severe side-effects has reduced the clinical efficacy of the existing anti-cancer drugs available in the market. Thus, there is always a constant need to develop newer anti-cancer drugs with minimal adverse effects. Researchers all over the world have been focusing on various alternative strategies to discover novel, potent, and target specific molecules for cancer therapy. In this direction, several heterocyclic compounds are being explored but amongst them one promising heterocycle is acridone which has attracted the attention of medicinal chemists and gained huge biological importance as acridones are found to act on different therapeutically proven molecular targets, overcome ABC transporters mediated drug resistance and DNA intercalation in cancer cells. Some of these acridone derivatives have reached clinical studies as these heterocycles have shown huge potential in cancer therapeutics and imaging. Here, the authors have attempted to compile and make some recommendations of acridone based derivatives concerning their cancer biological targets and in vitro-cytotoxicity based on drug design and novelty to increase their therapeutic potential. This review also provides some important insights on the design, receptor targeting and future directions for the development of acridones as possible clinically effective anti-cancer agents.

Phytochemicals: Potential Lead Molecules for MDR Reversal

Multidrug resistance (MDR) is one of the main impediments in the treatment of cancers. MDR cancer cells are resistant to multiple anticancer drugs. One of the major mechanisms of MDR is the efflux of anticancer drugs by ABC transporters. Increased activity and overexpression of these transporters are important causes of drug efflux and, therefore, resistance to cancer chemotherapy. Overcoming MDR is a fundamental prerequisite for developing an efficient treatment of cancer. To date, various types of ABC transporter inhibitors have been employed but no effective anticancer drug is available at present, which can completely overcome MDR. Phytochemicals can reverse MDR in cancer cells via affecting the expression or activity of ABC transporters, and also through exerting synergistic interactions with anticancer drugs by addressing additional molecular targets. We have listed numerous phytochemicals which can affect the expression and activity of ABC transporters in MDR cancer cell lines. Phytochemicals in the groups of flavonoids, alkaloids, terpenes, carotenoids, stilbenoids, lignans, polyketides, and curcuminoids have been examined for MDR-reversing activity. The use of MDR-reversing phytochemicals with low toxicity to human in combination with effective anticancer agents may result in successful treatment of chemotherapy-resistant cancer. In this review, we summarize and discuss published evidence for natural products with MDR modulation abilities.

Natural products as multidrug resistance modulators in cancer

Cancer is a prominent cause of death globally. Currently, many drugs that are in clinical practice are having a high prevalence of side effect and multidrug resistance. Risk of tumors acquiring resistance to chemotherapy (multidrug resistance) remains a significant hurdle to the successful treatment of various types of cancer. Membrane-embedded drug transporters, generally overexpressed in cancer, are the leading cause among multiple mechanisms of multidrug resistance (MDR). P-glycoprotein (P-gp) also MDR1/ABCB1, multidrug resistance associated protein 1 (MRP1/ABCC1), MRP2 and breast cancer resistance protein (BCRP/ABCG2) are considered to be a prime factor for induction of MDR. To date, several chemical substances have been tested in a number of clinical trials for their MDR modulatory activity which are not having devoid of any side effects that necessitates to find newer and safer way to tackle the current problem of multidrug resistance in cancer. The present study systematically discusses the various classes of natural products i.e flavonoids, alkaloids, terpenoids, coumarins (from plants, marine, and microorganisms) as potential MDR modulators and/or as a source of promising lead compounds. Recently a bisbenzyl isoquinoline alkaloid namely tetrandrine, isolated from Chinese herb Stephania tetrandra (Han-Fang-Chi) is in clinical trials for its MDR reversal activity.

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

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

Tuberostemonine reverses multidrug resistance in chronic myelogenous leukemia cells K562/ADR

Objective: To investigate the reversal effect of tuberostemonine on MDR in myelogenous leukemia cells K562/ADR.

Methods: Human myelogenous leukemia cells K562 and their adriamycin-resistance cells K562/ADR were used. The growth curve of cells treated by tuberostemonine and the Non-toxic concentration of tuberostemonine were determined by MTT, Cell apoptosis was determined by MTT and flow cytometry. The expression of MDR1, Survivin and Livin was detected by RT-PCR. The activity of P-gp was detected by flow cytometry. Western blot was used to detect the expression of NF-κB and Survivin.

Results: The effect of tuberostemonine on K562/ADR showed a dose-dependence, and 350μg/mL and 500μg/mL of tuberostemonine could inhibit the expression of MDR1 (P<0.05). While no function difference of P-gp was detected. With the increased concentration of tuberostemonine, the inhibitory effect were enhanced to the expression of NF-κB. Tuberostemonine combined with adriamycin could time-dependently inhibit the cell proliferation (P<0.05) and obviously promoted the cell apoptosis (P<0.05). Also the tuberostemonine could inhibit the expression of Survivin.

Conclusion: There are no direct relations between tuberostemonine and P-gp, but tuberostemonine could reverse the multidrug resistance of K562/ADR via down-regulating the expression of Nf-κB and inhibiting th1e expression of Survivin.

Advances in plant-based inhibitors of P-glycoprotein

Multidrug resistance (MDR) has emerged as the main problem in anti-cancer therapy. Although MDR involves complex factors and processes, the main pivot is the expression of multidrug efflux pumps. P-glycoprotein (P-gp) belongs to the family of adenosine triphosphate (ATP)-binding cassette (ABC) transporters. It functions in cellular detoxification, pumping a wide range of xenobiotic compounds out of the cell. An attractive therapeutic strategy for overcoming MDR is to inhibit the transport function of P-gp and thus, increase intracellular concentration of drugs. Recently, various types of P-gp inhibitors have been found and used in experiments. However, none of them has passed clinical trials due to their high side-effects. Hence, the search for alternatives, such as plant-based P-gp inhibitors have gained attention recently. Therefore, we give an overview of the source, function, structure and mechanism of plant-based P-gp inhibitors and give more attention to cancer-related studies. These products could be the future potential drug candidates for further research as P-gp inhibitors.

Inhibition of P-glycoprotein activity by limonin and other secondary metabolites from Citrus species in human colon and leukaemia cell lines

P-glycoprotein (P-gp), a membrane transporter encoded by the MDR1 gene in human cells, mediates drug efflux from cells and plays a major role in causing multidrug resistance; which is one of the most accepted mechanisms for failure of chemotherapy in cancer treatment. In this study, we investigated the effects of nine naturally occurring compounds isolated from Citrus jambhiri Lush and Citrus pyriformis Hassk (Rutaceae) for their potential to modulate the activity of P-gp in the multidrug-resistant human leukaemia cell line CEM/ADR5000. Limonin, deacetylnomilin, hesperidin, neohesperidin, stigmasterol and ss-sitosterol-O-glucoside inhibited the efflux of the P-gp substrate rhodamine 123 in a concentration-dependent manner. Some of these compounds were more active than verapamil, which was used as a positive control. Treatment of drug-resistant Caco-2 cells with the most active C. jambhiri and C. pyriformis compounds increased their sensitivity to doxorubicin and completely reversed doxorubicin resistance, which agrees with a decreased P-gp activity. Limonin was the most potent P-glycoprotein inhibitor - when it was applied at a non-toxic concentration of 20 microM, it significantly enhanced doxorubicin cytotoxicity 2.98-fold (P<0.001) and 2.2-fold (P<0.001) in Caco2 and CEM/ADR5000 cells, respectively. These isolated Citrus compounds could be considered as good candidates for the development of novel P-gp/MDR1 reversal agents which may enhance the accumulation and efficacy of chemotherapy agents.

Selective modulation of P-glycoprotein activity by steroidal saponines from Paris polyphylla

Bio-guided fractionation of the roots of Paris polyphylla (Trilliaceae), based on inhibition of P-glycoprotein-mediated daunorubicin efflux in K562/R7 cell line, led to isolation and identification of the three saponins 3-O-Rha(1-->2)[Ara(1-->4)]Glc-pennogenine, gracillin and polyphyllin D, and the two ecdysteroids 20-hydroxyecdysone and pinnatasterone. These compounds were tested for multidrug reversion on P-glycoprotein (ABCB1) with both drug-selected and transfected cell lines, and also on Breast Cancer Resistance Protein (BCRP/ABCG2). By contrast to a weak efficiency on BCRP, the three saponins displayed significant effects as inhibitors of P-glycoprotein-mediated drug efflux.

Chemical characterization of Citrus sinensis grafted on C. limonia and the effect of some isolated compounds on the growth of Xylella fastidiosa

Citrus sinensis grafted on C. limonia produces a considerable number of compounds that are not common in both plants developed from germination of seeds. The chemical profile of scion and rootstock differ notably for absence in the form of flavonoids and coumarins containing C5 prenyl groups attached to the carbon atoms of aromatic and heterocyclic systems or to oxygen. Only linear pyranocoumarins xanthyletin and xanthoxyletin were found in scion. This observation indicates that the prenylated compounds once biosynthesized in the roots could have been translocated to other organs. Xylella fastidiosa colonizes the xylem of plants causing diseases on several economically important crops such as citrus variegated chlorosis (CVC). A number of flavonoids, coumarins, alkaloids, dihydrocinnamic acid derivative, anacardic acid, triterpenes, and limonoids were tested for in vitro activity on the growth of Xylella fastidiosa. Azadirachtin A was the most active. Hesperidin, which occurs in great amounts in cells of the mesophyll of the affected leaves with CVC, showed a moderate activity suggesting that it can act as a good barrier for small-size colonies from X. fastidiosa.