A phase I and pharmacologic study of the MDR converter GF120918 in combination with doxorubicin in patients with advanced solid tumors

In vivo evaluation of P-glycoprotein and breast cancer resistance protein modulation in the brain using [(11)C]gefitinib

Gefitinib (Iressa) is a selective inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase. Recent studies confirmed that gefitinib interacted with the breast cancer resistance protein (BCRP) at submicromolar concentrations, whereas other multidrug transporters, including P-glycoprotein (P-gp), showed much lower reactivity toward gefitinib. Recently, many tracers for positron emission tomography (PET) have been prepared to study P-gp function in vivo; however, PET tracers had not been evaluated for both P-gp and BCRP modulation in the brain. Therefore, we evaluated in vivo brain penetration-mediated P-gp and BCRP in mice using [(11)C]gefitinib. Co-injection with gefitinib (over 50 mg/kg), a nonspecific P-gp modulator cyclosporin A (50 mg/kg), and the dual P-gp and BCRP modulator GF120918 (over 5 mg/kg) induced an increase in the brain uptake of [(11)C]gefitinib in mice 30 min after injection. In the PET study of mice, the radioactivity level in the brain with co-injection of GF120918 (5 mg/kg) was three- to fourfold higher than that in control after initial uptake. The radioactivity level in the brain in P-gp and Bcrp knockout mice was approximately eightfold higher than that in wild-type mice 60 min after injection. In conclusion, [(11)C]gefitinib is a promising PET tracer to evaluate the penetration of gefitinib into the brain by combined therapy with P-gp or BCRP modulators, and into brain tumors. Furthermore, PET study with GF120918 is a promising approach for evaluating brain penetration-mediated P-gp and BCRP.

Therapeutic options for triple-negative breast cancers with defective homologous recombination

Breast cancer is the most common malignancy among women in developed countries, affecting more than a million women per year worldwide. Over the last decades, our increasing understanding of breast cancer biology has led to the development of endocrine agents against hormone receptor-positive tumors and targeted therapeutics against HER2-expressing tumors. However, no targeted therapy is available for patients with triple-negative breast cancer, lacking expression of hormone receptors and HER2. Overlap between BRCA1-mutated breast cancers and triple-negative tumors suggests that an important part of the triple-negative tumors may respond to therapeutics targeting BRCA1-deficient cells. Here, we review the features shared between triple-negative, basal-like and BRCA1-related breast cancers. We also discuss the development of novel therapeutic strategies to target BRCA1-mutated tumors and triple-negative tumors with BRCA1-like features. Finally, we highlight the utility of mouse models for BRCA1-mutated breast cancer to optimize (combination) therapy and to understand drug resistance.

Multi-drug-resistance-reverting agents: 2-aryloxazole and 2-arylthiazole derivatives as potent BCRP or MRP1 inhibitors

2-Aryloxazole and 2-arylthiazole derivatives were evaluated for their inhibitory activity toward P-glycoprotein (P-gp) as well as their selectivity toward other ABC transporters involved in multi-drug resistance such as BCRP and MRP1. These derivatives have 6,7-dimethoxytetrahydroisoquinoline or cyclohexylpiperazine moieties, which are the same basic nuclei of the potent P-gp inhibitors MC70 (EC(50)=0.05 microM) and PB28 (EC(50)=0.55 microM), respectively. The results demonstrate that 2-aryloxazole and 2-arylthiazole derivatives, planned as cycloisosteres of MC70, were found to be less potent than the reference compound in inhibiting P-gp. These compounds were evaluated for their BCRP and MRP1 inhibitory activities. In particular, 6,7-dimethoxytetrahydroisoquinoline derivatives, unsubstituted, 3-Br, 3-Cl, and 3-OCH(3) 2-aryloxalzole derivatives showed the best BCRP inhibitory activity (EC(50) range: 0.24-0.46 microM). In contrast, all cyclohexylpiperazine derivatives except one (EC(50)=0.56 microM), showed decreased BCRP inhibitory activity. All compounds tested were unable to inhibit the MRP1 pump, with the exception of the 2-OCH(3) and 4-OCH(3) derivatives of the 6,7-dimethoxytetrahydroisoquinoline series, which displayed high MRP1 inhibitory activity (EC(50)=0.84 and 0.90 microM, respectively).

Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities

The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.

N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) as a chemical ATP-binding cassette transporter family G member 2 (Abcg2) knockout model to study nitrofurantoin transfer into milk

Genetic knockout mice studies suggested ATP-binding cassette transporter family G member 2 (ABCG2)/Abcg2 translocates nitrofurantoin at the mammary-blood barrier, resulting in drug accumulation in milk. The purpose of this study was to establish the role of Abcg2 in nitrofurantoin accumulation in rat milk using N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) as a "chemical knockout" equivalent. The inhibitory effect of GF120918 was verified in Madin-Darby canine kidney II cells stably expressing rat Abcg2 with Hoechst 33342 and nitrofurantoin flux in Transwells. Nitrofurantoin was infused (0.5 mg/h) in the absence and presence of GF120918 (10 mg/kg in dimethyl sulfoxide) to Sprague-Dawley lactating female rats using a balanced crossover design. Administration of GF120918 increased nitrofurantoin concentration in serum (from 443 +/- 51 to 650 +/- 120 ng/ml) and decreased concentration in milk (from 18.1 +/- 0.9 to 1.9 +/- 1.2 microg/ml), resulting in corresponding mean values for milk to serum concentration ratio (M/S) of 41.4 +/- 19.1 versus 3.04 +/- 2.27 in the absence and presence of GF120918 (p < 0.05), respectively. There was a decrease in systemic clearance with GF120918 (2.8 +/- 0.5 l/h/kg) compared with vehicle controls (4.1 +/- 0.5 l/h/kg; p < 0.05). Western blot analysis revealed good expression of Abcg2 and no P-glycoprotein (P-gp) expression in mammary gland, whereas immunohistochemistry confirmed the apical expression of Abcg2 in lactating mammary gland epithelia. Nitrofurantoin active transport into rat milk can be inhibited by GF120918 resulting in a 10-fold lower M/S. Although GF120918 inhibits both Abcg2 and P-gp, the high expression of Abcg2 and the absence of detectable P-gp expression in lactating mammary gland validate an important role for Abcg2 in nitrofurantoin accumulation in rat milk. GF120918 is particularly useful as a rat chemical knockout model to establish ABCG2's role in drug transfer into milk during breastfeeding.

Inhibition of P-glycoprotein (ABCB1)- and multidrug resistance-associated protein 1 (ABCC1)-mediated transport by the orally administered inhibitor, CBT-1((R))

Cellular expression of ATP-binding cassette (ABC) transport proteins, such as P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP1), or ABCG2, is known to confer a drug-resistant phenotype. Thus, the development of effective transporter inhibitors could be of value to cancer treatment. CBT-1 is a bisbenzylisoquinoline plant alkyloid currently in development as a Pgp inhibitor. We characterized its interactions with the three major ABC transporters associated with drug resistance - Pgp, MRP1 and ABCG2 - and compared it to other known inhibitors. CBT-1 completely inhibited rhodamine 123 transport from Pgp-overexpressing cells at a concentration of 1muM. Additionally, 1 microM completely reversed Pgp-mediated resistance to vinblastine, paclitaxel and depsipeptide in SW620 Ad20 cells. CBT-1 was found to compete [(125)I]-IAAP labeling of Pgp with an IC(50) of 0.14 microM, and low concentrations of CBT-1 (<1 microM) stimulated Pgp-mediated ATP hydrolysis. In MRP1-overexpressing cells, 10 microM CBT-1 was found to completely inhibit MRP1-mediated calcein transport. CBT-1 at 25 microM did not have a significant effect on ABCG2-mediated pheophorbide a transport. Serum levels of CBT-1 in samples obtained from eight patients receiving CBT-1 increased intracellular rhodamine 123 levels in CD56+ cells 2.1- to 5.7-fold in an ex vivo assay. CBT-1 is able to inhibit the ABC transporters Pgp and MRP1, making it an attractive candidate for clinical trials in cancers where Pgp and/or MRP1 might be overexpressed. Further clinical studies with CBT-1 are warranted.

Targeting cancer stem cells

Recent evidence has demonstrated the existence of a small subset of the tumour mass that is wholly responsible for the sustained growth and propagation of the tumour. This cancer stem cell (CSC) compartment is also likely to be responsible both for disease relapse and the resistance to therapy that often accompanies relapse. The evidence for CSCs in various malignancies is presented. The failure of existing therapeutics to eradicate CSCs suggests that they are relatively resistant to present cancer treatments. This resistance may reflect the preservation of normal stem cell protective mechanisms, such as an increased expression of drug efflux pumps or alterations in apoptotic, cell cycle and DNA repair mechanisms. Targeting these mechanisms, and taking advantage of potential differences in the biology of normal stem cells and CSCs, such as differences in surface phenotype, self renewal/quiescence and stem cell-niche interactions are discussed and preliminary preclinical or clinical data are presented. Finally, the authors give their opinion of the direction in which one must travel to successfully target the CSC and improve treatment outcomes in malignant disease.

Pharmacokinetic considerations in the treatment of CNS tumours

Despite aggressive therapy, the majority of primary and metastatic brain tumour patients have a poor prognosis with brief survival periods. This is because of the different pharmacokinetic parameters of systemically administered chemotherapeutic agents between the brain and the rest of the body. Specifically, before systemically administered drugs can distribute into the CNS, they must cross two membrane barriers, the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB). To some extent, these structures function to exclude xenobiotics, such as anticancer drugs, from the brain. An understanding of these unique barriers is essential to predict when and how systemically administered drugs will be transported to the brain. Specifically, factors such as physiological variables (e.g. blood flow), physicochemical properties of the drug (e.g. molecular weight), as well as influx and efflux transporter expression at the BBB and BCB (e.g. adenosine triphosphate-binding cassette transporters) determine what compounds reach the CNS. A large body of preclinical and clinical research exists regarding brain penetration of anticancer agents. In most cases, a surrogate endpoint (i.e. CSF to plasma area under the concentration-time curve [AUC] ratio) is used to describe how effectively agents can be transported into the CNS. Some agents, such as the topoisomerase I inhibitor, topotecan, have high CSF to plasma AUC ratios, making them valid therapeutic options for primary and metastatic brain tumours. In contrast, other agents like the oral tyrosine kinase inhibitor, imatinib, have a low CSF to plasma AUC ratio. Knowledge of these data can have important clinical implications. For example, it is now known that chronic myelogenous leukaemia patients treated with imatinib might need additional CNS prophylaxis. Since most anticancer agents have limited brain penetration, new pharmacological approaches are needed to enhance delivery into the brain. BBB disruption, regional administration of chemotherapy and transporter modulation are all currently being evaluated in an effort to improve therapeutic outcomes. Additionally, since many chemotherapeutic agents are metabolised by the cytochrome P450 3A enzyme system, minimising drug interactions by avoiding concomitant drug therapies that are also metabolised through this system may potentially enhance outcomes. Specifically, the use of non-enzyme-inducing antiepileptic drugs and curtailing nonessential corticosteroid use may have an impact.

ABC transporter expression in hematopoietic stem cells and the role in AML drug resistance

ATP-binding cassette (ABC) transporters are known to play an important role in human physiology, toxicology, pharmacology, and numerous disorders including acute myeloid leukemia (AML). In AML only a few cells have properties allowing for ongoing proliferation and for expansion of this malignant disorder. These very primitive cells, referred to as leukemic stem cells, reside mostly in a quiescent cell cycle state. These cells have the capacity of self-renewal and are likely characterized by a high expression of a number of ABC transporters. In addition, over-expression of certain ABC transporters in leukemic cells has been associated with poor treatment outcome in AML patients. Therefore, to be able to improve diagnostics and therapies for AML patients, it may be important to better characterize this quiescent stem cell population. Particularly knowledge of the biology of highly expressed ABC transporters in these primitive leukemic cells might provide new insights to improve therapeutic options. This review provides an overview about ABC transporters and AML in general and particularly of the ABC transporters involved in multidrug resistance and cholesterol metabolism in primitive normal and leukemic cells.

Tetrandrine achieved plasma concentrations capable of reversing MDR in vitro and had no apparent effect on doxorubicin pharmacokinetics in mice

PURPOSE

Tetrandrine (Tet), a multidrug resistant (MDR) modulator, was a potential candidate for use in cancer therapy and exhibited potent biological activity in vitro and in vivo when combined with anticancer agents such as doxorubicin, paclitaxel. Our aims were to determine whether serum concentration of Tet, which was capable of blocking P-gp in vitro, could be safely achieved in mice and whether Tet induced pharmacokinetic alterations in serum doxorubicin disposition in mice.

METHODS

Tet of 30 mg/kg dose used to reverse MDR was administrated intraperitoneally in mice. Plasma Tet and serum doxorubicin concentration were analyzed by HPLC. CYP 3A4 activity was examined by HPLC with the substrate of nifedipine.

RESULTS

More than 1 micromol/L of Tet could at least tenfold reverse MDR in vitro. The plasma peak concentration of Tet was about 2 micromol/L and not less than 1 micromol/L until 18 h following Tet administration (i.p.) at 30 mg/kg. These suggested that the concentrations of Tet that were sufficient to inhibit P-gp might be achieved in mice receiving 30 mg/kg of Tet. Importantly, no significant difference was demonstrated between the doxorubicin pharmacokinetic parameters obtained in mice received doxorubicin only and doxorubicin plus Tet. This implied that Tet of 30 mg/kg did not alter the profiles of pharmacokinetics of doxorubicin including the clearance and AUC of doxorubicin. Furthermore, Tet did not significantly affect on CYP 3A4 activity in human liver microsomes until more than 25 micromol/L.

CONCLUSIONS

Tet at the tested dose of combination treatment could achieve plasma concentrations that reversed MDR in experimental models and it had no apparent effect on doxorubicin pharmacokinetics in mice and CYP 3A4 activity in human liver microsomes.

Combination of suboptimal doses of inhibitors targeting different domains of LtrMDR1 efficiently overcomes resistance of Leishmania spp. to Miltefosine by inhibiting drug efflux

Miltefosine (hexadecylphosphocholine) is the first orally active drug approved for the treatment of leishmaniasis. We have previously shown the involvement of LtrMDR1, a P-glycoprotein-like transporter belonging to the ATP-binding cassette superfamily, in miltefosine resistance in Leishmania. Here we show that overexpression of LtrMDR1 increases miltefosine efflux, leading to a decrease in drug accumulation in the parasites. Although LtrMDR1 modulation might be an efficient way to overcome this resistance, a main drawback associated with the use of P-glycoprotein inhibitors is related to their intrinsic toxicity. In order to diminish possible side effects, we have combined suboptimal doses of modulators targeting both the cytosolic and transmembrane domains of LtrMDR1. Preliminary structure-activity relationships have allowed us to design a new and potent flavonoid derivative with high affinity for the cytosolic nucleotide-binding domains. As modulators directed to the transmembrane domains, we have selected one of the most potent dihydro-beta-agarofuran sesquiterpenes described, and we have also studied the effects of two of the most promising, latest-developed modulators of human P-glycoprotein, zosuquidar (LY335979) and elacridar (GF120918). The results show that this combinatorial strategy efficiently overcomes P-glycoprotein-mediated parasite miltefosine resistance by increasing intracellular miltefosine accumulation without any side effect in the parental, sensitive, Leishmania line and in different mammalian cell lines.

Simultaneous delivery of doxorubicin and GG918 (Elacridar) by new polymer-lipid hybrid nanoparticles (PLN) for enhanced treatment of multidrug-resistant breast cancer

Multidrug-resistant (MDR) cancer may be treated using combinations of encapsulated cytotoxic drugs and chemosensitizers. To optimize for the effectiveness of this combinational approach, novel polymer-lipid hybrid nanoparticle (PLN) formulations capable of delivering a cytotoxic drug, doxorubicin (Dox), a chemosensitizer, GG918, or their combination were prepared. Both acute and long-term anticancer activities of various combinations of Dox and GG918 in solution or PLN form were evaluated in a human MDR breast cancer cell line (MDA435/LCC6/MDR1) using trypan blue exclusion and clonogenic assays. Cellular Dox uptake and drug distribution within the cells were determined by fluoremetry and fluorescence microscopy. The results showed that the encapsulation efficiencies of Dox and GG918 in PLN were up to 89% and were not compromised by co-encapsulation of the two agents. Of various combinational treatment approaches, the Dox and GG918 co-encapsulated PLN formulation ((DG)n) demonstrated the greatest Dox uptake and anticancer activity to the MDR cells, while co-administration of two single-agent loaded PLN was least effective. Fluorescence microscopy indicated cellular internalization of (DG)n. These findings suggest that in addition to the total drug concentrations, the simultaneous delivery of Dox and GG918 to the same cellular location is critical in determining the therapeutic effectiveness of this anticancer drug-chemosensitizer combination.

Increased MDR1 expression in normal and malignant peripheral blood mononuclear cells obtained from patients receiving depsipeptide (FR901228, FK228, NSC630176)

The increased expression of markers associated with a differentiated phenotype, such as P-glycoprotein (Pgp), follows treatment with histone deacetylase inhibitors. Because depsipeptide (FR901228, FK228, NSC630176) is a substrate for Pgp, up-regulation of the gene that encodes it, MDR1, would mean that depsipeptide induces its own mechanism of resistance. To examine the effect of depsipeptide on expression of ATP-binding cassette transporters associated with multidrug resistance, the kidney cancer cell lines 108, 121, 127, and 143 were treated with depsipeptide and evaluated by quantitative reverse transcription-PCR. Increased levels of MDR1 (1.3- to 6.3-fold) and ABCG2 (3.2- to 11.1-fold) but not MRP1 (0.9- to 1.3-fold) were observed. The induced Pgp transported the fluorescent substrates rhodamine 123, bisantrene, calcein-AM, BODIPY-vinblastine, and BODIPY-paclitaxel. In normal peripheral blood mononuclear cells (PBMC) and circulating tumor cells obtained from patients receiving depsipeptide, increased levels of histone H3 acetylation were found. We next examined MDR1 levels in normal and malignant PBMCs obtained from 15 patients enrolled in clinical trials with depsipeptide and detected up to a 6-fold increase in normal PBMCs and up to an 8-fold increase in circulating tumor cells after depsipeptide administration. In one patient with Sézary syndrome, increased MDR1 gene expression was accompanied by increased cell surface Pgp expression in circulating Sézary cells as determined by measurement of MRK-16 staining by flow cytometry. These studies suggest that depsipeptide induces its own mechanism of resistance and thus provide a basis for clinical trials evaluating depsipeptide in combination with a Pgp inhibitor.

Drug delivery across the blood–brain barrier: why is it difficult? how to measure and improve it?

The development of drugs that act in the CNS has been significantly impeded by the difficulty of delivering them across the blood-brain barrier (BBB). This article aims to provide the reader with a critical overview of important issues in the discovery and development of drugs that need to enter the brain to elicit pharmacological activity, focusing particularly on i) the role of drug transporters in brain permeation and how to manipulate them to enhance drug brain bioavailability; ii) the successful application, limitations and challenges of commonly used in vitro and in vivo methodologies for measuring drug transport across the BBB, and iii) a discussion of recently developed strategies (e.g., modulation of efflux transporters by chemical inhibitors and the employment of delivery vectors taking advantage of native transport systems at the BBB) for facilitating drug penetration into the brain.

New derivatives of silybin and 2,3-dehydrosilybin and their cytotoxic and P-glycoprotein modulatory activity

Large series of O-alkyl derivatives (methyl and benzyl) of silybin and 2,3-dehydrosilybin was prepared. Selective alkylation of the silybin molecule was systematically investigated. For the first time we present here, for example, preparation of 19-nor-2,3-dehydrosilybin. All prepared silybin/2,3-dehydrosilybin derivatives were tested for cytotoxicity on a panel of drugs sensitive against multidrug resistant cell lines and the ability to inhibit P-glycoprotein mediated efflux activity. We have identified effective and relatively non-cytotoxic inhibitors of P-gp derived from 2,3-dehydrosilybin. Some of them were more effective inhibitors at concentrations lower than a standard P-gp efflux inhibitor cyclosporin A. Another group of 2,3-dehydrosilybin derivatives also had better inhibitory effects on P-gp efflux but a cytotoxicity comparable with that of parent 2,3-dehydrosilybin. Structural requirements for improving inhibitory activity and reducing toxicity of 2,3-dehydrosilybin were established. Effect of E-ring substitution as well as an influence of the substituent size at the C-7-OH position of A-ring on P-gp-inhibitory activity was evaluated for the first time in this study.

In vitro andin vivo evaluation of WK-X-34, a novel inhibitor of P-glycoprotein and BCRP, using radio imaging techniques

Overexpression of the multidrug resistance proteins P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) results in treatment failure of many malignancies including ovarian cancer. Dual inhibition of Pgp and BCRP may restore the sensitivity of resistant cells to anticancer drugs. We report the synthesis and characterization of a novel anthranilic-acid based Pgp and BCRP modulator, WK-X-34. In vitro inhibition of Pgp activity was evaluated using 99mTc-Sestamibi and daunorubicin accumulation in Pgp overexpressing human ovarian cancer cells (A2780/Adr) and its sensitive counterpart (A2780/wt). Interaction with BCRP was examined with a mitoxantrone-efflux assay in BCRP-overexpressing MCF7/mx cells, with flow cytometry. Interactions with the multidrug resistance associated proteins (MRP) were evaluated in transfected MRP1, MRP2 and MRP3 cell lines, using a 5-CFDA efflux assay. In vivo 99mTc-Sestamibi imaging of human ovarian cancer xenografts was used to evaluate the in vivo efficacy of WK-X-34 in mice. Daunorubicin accumulation in A2780/Adr cells was inhibited by WK-X-34 at nanomolar concentrations (IC50: 82.1 +/- 6 nM). WK-X-34 inhibited mitoxantrone accumulation in BCRP-overexpressing cells at micromolar concentrations (IC50 = 26.5 +/- 4.6 microM), whereas WK-X-34 did not significantly alter 5-CFDA accumulation in MRP transfected cells. In vivo, uptake of 99mTc-Sestamibi was significantly increased in A2780/Adr xenograft tumors, brain and intestine (AUCs(0-4h) 136%, 147% and 138%; p < 0.05) in mice dosed with WK-X-34 (20 mg/kg i.p.). WK-X-34 selectively modulates Pgp and BCRP in vitro and in vivo in multidrug resistant ovarian cancer cells, and thus may have potential utility in the treatment of multidrug resistant tumors.

Disulfiram, an old drug with new potential therapeutic uses for human cancers and fungal infections

Disulfiram, a drug used to treat alcoholism, has recently been indicated to play a primary as well as an adjuvant role in the treatment of many cancers and in the reversal of fungal drug-resistance. This review discusses the molecular mechanism of action of disulfiram and its potential use in the treatment of human cancers and fungal infections.