Evaluation of dual P-gp-BCRP inhibitors as nanoparticle formulation

Applications of Nanotechnology-based Approaches to Overcome Multi-drug Resistance in Cancer

Cancer is one of the leading causes of death worldwide. Chemotherapy and radiation therapy are the major treatments used for the management of cancer. Multidrug resistance (MDR) is a major hindrance faced in the treatment of cancer and is also responsible for cancer relapse. To date, several studies have been carried out on strategies to overcome or reverse MDR in cancer. Unfortunately, the MDR reversing agents have been proven to have minimal clinical benefits, and eventually, no improvement has been made in therapeutic efficacy to date. Thus, several investigational studies have also focused on overcoming drug resistance rather than reversing the MDR. In this review, we focus primarily on nanoformulations regarded as a novel approach to overcome or bypass the MDR in cancer. The nanoformulation systems serve as an attractive strategy as these nanosized materials selectively get accumulated in tumor tissues, thereby improving the clinical outcomes of patients suffering from MDR cancer. In the current work, we present an overview of recent trends in the application of various nano-formulations, belonging to different mechanistic classes and functionalization like carbon nanotubes, carbon nanohorns, carbon nanospheres, liposomes, dendrimers, etc., to overcome MDR in cancer. A detailed overview of these techniques will help researchers in exploring the applicability of nanotechnologybased approaches to treat MDR.

Pyrimidine: A promising scaffold for optimization to develop the inhibitors of ABC transporters

The multidrug resistance (MDR) phenomenon in cancer cells is the major obstacle leading to failure of chemotherapy accompanied by the feature of intractable and recurrence of cancers. As significant contributors that cause MDR, ABC superfamily proteins can transport the chemotherapeutic drugs out of the tumor cells by the energy of adenosine triphosphate (ATP) hydrolysis, thereby reducing their intracellular accumulation. The ABC transports like ABCB1, ABCC1 and ABCG2 have been extensively studied to develop modulators for overcoming MDR. To date, no reversal agents have been successfully marketed for clinical application, and little information about the ABC proteins bound to specific inhibitors is known, which make the design of MDR inhibitors with potency, selectivity and low toxicity a major challenge. In recent years, it has been increasingly recognized that pyrimidine-based derivatives have the potential for reversing ABC-mediated MDR. In this review, we summarized the pyrimidine-based inhibitors of ABC transporters, and mainly focused on their structure optimizations, development strategies and structure-activity relationship studies in hope of providing a reference for medicinal chemists to develop new modulators of MDR with highly potency and fewer side effects.

Synthesis and biological evaluation of quinazoline derivatives - A SAR study of novel inhibitors of ABCG2

Multidrug resistance (MDR) is a major obstacle for effective chemotherapeutic treatment of cancer frequently leading to failure of the therapy. MDR is often associated with the overexpression of ABC transport proteins like ABCB1 or ABCG2 which efflux harmful substances out of cells at the cost of ATP hydrolysis. One way to overcome MDR is to apply potent inhibitors of ABC transporters to restore the sensitivity of the cells toward cytostatic agents. This study focusses on the synthesis and evaluation of novel 2,4-disubstituted quinazoline derivatives regarding the structure-activity-relationship (SAR), their ability to reverse MDR and their mode of interaction with ABCG2. Hence, the inhibitory potency and selectivity toward ABCG2 was determined. Moreover, the intrinsic cytotoxicity and the reversal of MDR were investigated. Interaction type studies with the substrate Hoechst 33342 and conformational analyses of ABCG2 with 5D3 monoclonal antibody were performed for a better understanding of the underlying mechanisms. In our study we could further enhance the inhibitory effect against ABCG2 (compound 31, IC₅₀: 55 nM) and identify the structural features that are crucial for inhibitory potency, the impact on transport activity and binding to the protein.

2,4,6-Substituted Quinazolines with Extraordinary Inhibitory Potency toward ABCG2

Several members of the ABC transporter superfamily play a decisive role in the development of multidrug resistance (MDR) in cancer. One of these MDR associated efflux transporters is ABCG2. One way to overcome this MDR is the coadministration of potent inhibitors of ABCG2. In this study, we identified novel inhibitors containing a 2,4,6-substituted quinazoline scaffold. Introduction of a 6-nitro function led to extraordinarily potent compounds that were highly selective for ABCG2 and also able to reverse the MDR toward the chemotherapeutic drugs SN-38 and mitoxantrone. The binding of substrate Hoechst 33342 and the two potent inhibitors 31 and 41 which differ in their mechanism of inhibition was rationalized using the recently published cryo-EM structures of ABCG2. For a better understanding of the interaction between the inhibitors and ABCG2, additional investigations regarding the ATPase activity, the interaction with Hoechst 33342, and with the conformational sensitive 5D3 antibody were carried out.

New Inhibitors of Breast Cancer Resistance Protein (ABCG2) Containing a 2,4-Disubstituted Pyridopyrimidine Scaffold

Multidrug resistance (MDR) occurring during cancer chemotherapy is a major obstacle for effectiveness and response to therapy and is often caused by ATP-binding cassette (ABC) efflux transporters. Belonging to the family of ABC transporters, breast cancer resistance protein is getting more and more in the spotlight of research. As a strategy to overcome MDR, inhibitors of ABC transporters were synthesized, which could be applied in combination with cytostatic drugs. For this purpose, 2,4-disubstituted pyridopyrimidine derivatives were synthesized. The investigations confirmed three key characteristics of good inhibitors: a low intrinsic cytotoxicity and a high potency and selectivity toward ABCG2. For selected compounds the interaction with ABCG2 was elucidated and their effect on ATPase activity and conformation sensitive 5D3 antibody binding was investigated. Their ability to reverse MDR in coadministration with the active metabolite of irinotecan and mitoxantron was confirmed.

9-Deazapurines as Broad-Spectrum Inhibitors of the ABC Transport Proteins P-Glycoprotein, Multidrug Resistance-Associated Protein 1, and Breast Cancer Resistance Protein

P-Glycoprotein (P-gp, ABCB1), multidrug resistance-associated protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, ABCG2) are the three major ABC transport proteins conferring resistance to many structurally diverse anticancer agents, leading to the phenomenon called multidrug resistance (MDR). Much effort has been put into the development of clinically useful compounds to reverse MDR. Broad-spectrum inhibitors of ABC transport proteins can be of great use in cancers that simultaneously coexpress two or three transporters. In this work, we continued our effort to generate new, potent, nontoxic, and multiply effective inhibitors of the three major ABC transporters. The best compound was active in a very low micromolar concentration range against all three transporters and restored sensitivity toward daunorubicin (P-gp and MRP1) and SN-38 (BCRP) in A2780/ADR (P-gp), H69AR (MRP1), and MDCK II BCRP (BCRP) cells. Additionally, the compound is a noncompetitive inhibitor of daunorubicin (MRP1), calcein AM (P-gp), and pheophorbide A (BCRP) transport.

Synthesis and biological investigation of 2,4-substituted quinazolines as highly potent inhibitors of breast cancer resistance protein (ABCG2)

Expression of ABCG2, a member of the ABC transporter superfamily, has been correlated to the clinical outcome of multiple cancers and is often associated with the occurrence of multidrug resistance (MDR) in chemotherapy. Inhibition of the transport protein by potent and selective inhibitors might be a way to treat cancer more efficiently and improve the therapy of cancer patients. Recently we reported the synthesis of new inhibitors based on a quinazoline scaffold. In the present study more structural variations were explored. Compounds with 3,4-dimethoxy groups and meta or para nitro substituents were found to be highly potent inhibitors of ABCG2. The most potent compound was more than five-fold more potent than Ko143, one of the best inhibitors of ABCG2. To determine the new compounds selectivity toward ABCG2 their inhibitory effects on ABCB1 and ABCC1 were also investigated identifying selective as well as broadspectrum inhibitors. Furthermore, intrinsic cytotoxicity and efficacy regarding the reversal of multidrug resistance toward SN-38 and mitoxantrone were explored. The most potent compounds were able to reverse the resistance toward the cytostatic agents with EC₅₀ values below 20 nM. Additionally, the type of interaction between inhibitors and the ABCG2 substrate Hoechst 33342 was investigated yielding competitive and non-competitive interactions suggesting different modes of binding. Finally the effect of the derivatives on vanadate-sensitive ATPase activity of ABCG2 was determined. According to the different effects on ATPase activity we conclude the existence of different binding sites. This study provides the structural requirements for high potency inhibition and elucidates the interaction with ABCG2 setting the basis for further studies.

MDR in cancer: Addressing the underlying cellular alterations with the use of nanocarriers

Multidrug resistance (MDR) is associated with a wide range of pathological changes at different cellular and intracellular levels. Nanoparticles (NPs) have been extensively exploited as the carriers of MDR reversing payloads to resistant tumor cells. However, when properly formulated in terms of chemical composition and physicochemical properties, NPs can serve as beyond delivery systems and help overcome MDR even without carrying a load of chemosensitizers or MDR reversing molecular cargos. Whether serving as drug carriers or beyond, a wise design of the nanoparticulate systems to overcome the cellular and intracellular alterations underlying the resistance is imperative. Within the current review, we will initially discuss the cellular changes occurring in resistant cells and how such changes lead to chemotherapy failure and cancer cell survival. We will then focus on different mechanisms through which nanosystems with appropriate chemical composition and physicochemical properties can serve as MDR reversing units at different cellular and intracellular levels according to the changes that underlie the resistance. Finally, we will conclude by discussing logical grounds for a wise and rational design of MDR reversing nanoparticulate systems to improve the cancer therapeutic approaches.

Rutin, a Quercetin Glycoside, Restores Chemosensitivity in Human Breast Cancer Cells

Several studies have documented the ability of flavonoids to sensitize cancer cells to chemotherapeutics and reverse multidrug resistance by inhibition of efflux pumps (adenosine triphosphate-binding cassette transporters), apoptosis activation, and cell cycle arrest. In this study, the flavonoid rutin (quercetin 3-O-β-d-rutinoside) was investigated as chemosensitizer towards two different human epithelial breast cancer cell lines: (i) MB-MDA-231, selected as representative for triple-negative breast cancer and (ii) MCF-7 used as a well-characterized model of HER2-negative breast cancer. To assess the cytocompatibility of rutin against non-cancer cells, primary human mammary fibroblasts were used as control and non-target cells. In MDA-MB-231 cells, 20 μM rutin enhanced cytotoxicity related to cyclophosphamide and methotrexate. Rutin significantly (p < 0.05) increased the anticancer activity of both chemotherapeutics, at 24-48-72 h, and decreased the activity of the adenosine triphosphate-binding cassette transporters, namely, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). Flow cytometry analysis showed 20 μM and 50 μM rutin arrested cell cycle at G2/M and G0/G1 phases, respectively, significantly promoting cell apoptosis. Rutin, via non-selective inhibition of P-gp and BCRP pumps, efficiently reverses multidrug resistance and restores chemosensitivity to cyclophosphamide and cyclophosphamide of human chemoresistant, triple-negative breast cancer cells, successfully arresting cell cycle progression. Copyright © 2017 John Wiley & Sons, Ltd.

4-Anilino-2-pyridylquinazolines and -pyrimidines as Highly Potent and Nontoxic Inhibitors of Breast Cancer Resistance Protein (ABCG2)

Multidrug resistance (MDR) mediated by ATP-binding cassette (ABC) transport proteins remains a major problem in the chemotherapeutic treatment of cancer and might be overcome by inhibition of the transporter. Because of the lack of understanding, the complex mechanisms involved in the transport process, in particular for breast cancer resistance protein (BCRP/ABCG2), there is a persistent need for studies of inhibitors of ABCG2. In this study, we investigated a systematic series of 4-substituted-2-pyridylquinazolines in terms of their inhibitory potency as well as selectivity toward ABCG2. For comparison, the quinazoline scaffold was reduced to the significantly smaller 4-methylpyrimidine basic structure. Furthermore, the cytotoxicity and the ability to reverse MDR was tested with the chemotherapeutic agents SN-38 and mitoxantrone (MX). Interaction of the compounds with ABCG2 was investigated by a colorimetric ATPase assay. Enzyme kinetic studies were carried out with Hoechst 33342 as fluorescent dye and substrate of ABCG2 to elucidate the compounds binding modes.

Nanotechnology in Glycomics: Applications in Diagnostics, Therapy, Imaging, and Separation Processes

This review comprehensively covers the most recent achievements (from 2013) in the successful integration of nanomaterials in the field of glycomics. The first part of the paper addresses the beneficial properties of nanomaterials for the construction of biosensors, bioanalytical devices, and protocols for the detection of various analytes, including viruses and whole cells, together with their key characteristics. The second part of the review focuses on the application of nanomaterials integrated with glycans for various biomedical applications, that is, vaccines against viral and bacterial infections and cancer cells, as therapeutic agents, for in vivo imaging and nuclear magnetic resonance imaging, and for selective drug delivery. The final part of the review describes various ways in which glycan enrichment can be effectively done using nanomaterials, molecularly imprinted polymers with polymer thickness controlled at the nanoscale, with a subsequent analysis of glycans by mass spectrometry. A short section describing an active glycoprofiling by microengines (microrockets) is covered as well.

Overcoming multidrug resistance through co-delivery of ROS-generating nano-machinery in cancer therapeutics

The use of nanotechnology to overcome multidrug resistance (MDR) in cancer cells has been predominant. Herein, we report the conjugation of copper(ii)-doxorubicin complexes on the surfaces of layered double hydroxide nanoparticles (LDHs) along with ascorbic acid intercalation in the gallery space to demonstrate synergistic effects to conquer MDR. The pH-sensitive release of doxorubicin (Dox) and the sustained release of ascorbic acid (AA) generate high amounts of hydrogen peroxide intracellularly that concomitantly results in conversion to cytotoxic free radicals through a copper(ii)-catalyzed Fenton-like reaction. Therefore, the combination of the chemotherapeutic agent (Dox) and free radical attack can devastate the MDR for effective cancer treatment through the co-delivery system.

The Role of Eukaryotic and Prokaryotic ABC Transporter Family in Failure of Chemotherapy

Over the years chemotherapy failure has been a vital research topic as researchers have been striving to discover reasons behind it. The extensive studies carried out on chemotherapeutic agents confirm that resistance to chemotherapy is a major reason for treatment failure. “Resistance to chemotherapy,” however, is a comprehensive phrase that refers to a variety of different mechanisms in which ATP-binding cassette (ABC) mediated efflux dominates. The ABC is one of the largest gene superfamily of transporters among both eukaryotes and prokaryotes; it represents a variety of genes that code for proteins, which perform countless functions, including drug efflux – a natural process that protects cells from foreign chemicals. Up to date, chemotherapy failure due to ABC drug efflux is an active research topic that continuously provides further evidence on multiple drug resistance (MDR), aiding scientists in tackling and overcoming this issue. This review focuses on drug resistance by ABC efflux transporters in human, viral, parasitic, fungal and bacterial cells and highlights the importance of the MDR permeability glycoprotein being the mutual ABC transporter among all studied organisms. Current developments and future directions to overcome this problem are also discussed.

Synthesis and Biological Evaluation of 4-Anilino-quinazolines and -quinolines as Inhibitors of Breast Cancer Resistance Protein (ABCG2)

Chemotherapeutic treatment of cancer often fails due to overexpression of the ATP-binding cassette (ABC) transport proteins, like ABCG2, triggering active efflux of various structurally unrelated drugs. This so-called multidrug resistance (MDR) may be reversed by selective, potent, and nontoxic inhibitors of ABCG2. As only a few potent inhibitors are known, new compounds based on a 4-substituted-2-phenylquinazoline scaffold were investigated. Substitution with hydroxy, cyano, nitro, acetamido, and fluoro led to high inhibitory activities toward ABCG2. The ability to reverse MDR of the most active compounds was confirmed in a MTT efficacy assay. Moreover, a negligibly low intrinsic cytotoxicity was found resulting in a high therapeutic ratio. Investigations of the inhibitory activity toward ABCB1 and ABCC1 yielded a high selectivity toward ABCG2 for the quinazoline compounds. Quinoline-based analogues showed lower inhibitory activity and selectivity. The study yielded a variety of promising compounds, some with superior properties compared to those of the standard inhibitor Ko143.

The combination of quinazoline and chalcone moieties leads to novel potent heterodimeric modulators of breast cancer resistance protein (BCRP/ABCG2)

During the last decade it has been found that chalcones and quinazolines are promising inhibitors of ABCG2. The combination of these two scaffolds offers a new class of heterocyclic compounds with potentially high inhibitory activity against ABCG2. For this purpose we investigated 22 different heterodimeric derivatives. In this series only methoxy groups were used as substituents as these had been proven superior for inhibitory activity of chalcones. All compounds were tested for their inhibitory activity, specificity and cytotoxicity. The most potent ABCG2 inhibitor in this series showed an IC50 value of 0.19 μM. It possesses low cytotoxicity (GI50 = 93 μM), the ability to reverse MDR and is nearly selective toward ABCG2. Most compounds containing dimethoxy groups showed slight activity against ABCB1 too. Among these three compounds (17, 19 and 24) showed even higher activity toward ABCB1 than ABCG2. All inhibitors were further screened for their effect on basal ATPase activity. Although the basal ATPase activity was partially stimulated, the compounds were not transported by ABCG2. Thus, quinazoline-chalcones are a new class of effective ABCG2 inhibitors.

Nanostructured lipid-carrageenan hybrid carriers (NLCCs) for controlled delivery of mitoxantrone hydrochloride to enhance anticancer activity bypassing the BCRP-mediated efflux

Novel nanostructured lipid-carrageenan hybrid carriers (NLCCs) were exploited for controlled delivery of water soluble chemotherapeutic agent mitoxantrone hydrochloride (MTO) with high loading capacity, sustained release property, and potential for improving oral bioavailability and antitumor efficacy. By introducing the negative polymer of carrageenan, MTO was highly incorporated into NLCCs with encapsulation efficiency of 95.8% by electrostatic interaction. In vivo pharmacokinetics of MTO solution (MTO-Sol) and MTO-NLCCs in rats demonstrated that the apparent bioavailability of MTO-NLCCs was increased to approximate 3.5-fold compared to that of MTO-Sol. The cytotoxicity investigations by MTT method indicated that NLCCs could significantly enhanced the antitumor efficacy against resistant MCF-7/MX cells. The relative cellular association of MTO-NLCCs was 9.2-fold higher than that of MTO-Sol in breast cancer resistance protein (BCRP) over-expressing MCF-7/MX cells, implying that BCRP-mediated drug efflux was diminished by the introduction of NLCCs. The endocytosis inhibition study implied that the NLCCs entered the MCF-7/MX cells by clathrin-mediated endocytosis process, which can bypass the efflux of MTO mediated by BCRP. The new developed NLCCs provide an effective strategy for oral delivery of water-soluble MTO with improved encapsulation efficiency, oral bioavailability, and cytotoxicity against resistant breast cancer cells.

Development, Maintenance, and Reversal of Multiple Drug Resistance: At the Crossroads of TFPI1, ABC Transporters, and HIF1

Early detection and improved therapies for many cancers are enhancing survival rates. Although many cytotoxic therapies are approved for aggressive or metastatic cancer; response rates are low and acquisition of de novo resistance is virtually universal. For decades; chemotherapeutic treatments for cancer have included anthracyclines such as Doxorubicin (DOX); and its use in aggressive tumors appears to remain a viable option; but drug resistance arises against DOX; as for all other classes of compounds. Our recent work suggests the anticoagulant protein Tissue Factor Pathway Inhibitor 1α (TFPI1α) plays a role in driving the development of multiple drug resistance (MDR); but not maintenance; of the MDR state. Other factors; such as the ABC transporter drug efflux pumps MDR-1/P-gp (ABCB1) and BCRP (ABCG2); are required for MDR maintenance; as well as development. The patient population struggling with therapeutic resistance specifically requires novel treatment options to resensitize these tumor cells to therapy. In this review we discuss the development, maintenance, and reversal of MDR as three distinct phases of cancer biology. Possible means to exploit these stages to reverse MDR will be explored. Early molecular detection of MDR cancers before clinical failure has the potential to offer new approaches to fighting MDR cancer.