Potent ABCG2 Inhibitors Research Articles

Dorsomorphin attenuates ABCG2-mediated multidrug resistance in colorectal cancer

Colorectal cancer is a common malignant tumor with high mortality, for which chemotherapy resistance is one of the main reasons. The high expression of ABCG2 in the cancer cells and expulsion of anticancer drugs directly cause multidrug resistance (MDR). Therefore, the development of new ABCG2 inhibitors that block the active causes of MDR may provide a strategy for the treatment of colorectal cancer. In this study, we find that dorsomorphin (also known as compound C or BML-275) potently inhibits the transporter activity of ABCG2, thereby preserving the chemotherapeutic agents mitoxantrone and doxorubicin to antagonize MDR in ABCG2-overexpressing colorectal cancer cells. Additionally, dorsomorphin does not alter ABCG2 protein expression. The results of molecular docking studies show that dorsomorphin is bound stably to the ABCG2-binding pocket, suggesting that dorsomorphin is a potent ABCG2 inhibitor that attenuates ABCG2-mediated MDR in colorectal cancer.

Enhanced reversal of ABCG2-mediated drug resistance by replacing a phenyl ring in baicalein with a meta-carborane.

Success of chemotherapy is often hampered by multidrug resistance. One mechanism for drug resistance is the elimination of anticancer drugs through drug transporters, such as breast cancer resistance protein (BCRP; also known as ABCG2), and causes a poor 5-year survival rate of human patients. Co-treatment of chemotherapeutics and natural compounds, such as baicalein, is used to prevent chemotherapeutic resistance but is limited by rapid metabolism. Boron-based clusters as meta-carborane are very promising phenyl mimetics to increase target affinity; we therefore investigated the replacement of a phenyl ring in baicalein by a meta-carborane to improve its affinity towards the human ABCG2 efflux transporter. Baicalein strongly inhibited the ABCG2-mediated efflux and caused a fivefold increase in mitoxantrone cytotoxicity. Whereas the baicalein derivative 5,6,7-trimethoxyflavone inhibited ABCG2 efflux activity in a concentration of 5 μm without reversing mitoxantrone resistance, its carborane analogue 5,6,7-trimethoxyborcalein significantly enhanced the inhibitory effects in nanomolar ranges (0.1 μm) and caused a stronger increase in mitoxantrone toxicity reaching similar values as Ko143, a potent ABCG2 inhibitor. Overall, in silico docking and in vitro studies demonstrated that the modification of baicalein with meta-carborane and three methoxy substituents leads to an enhanced reversal of ABCG2-mediated drug resistance. Thus, this seems to be a promising basis for the development of efficient ABCG2 inhibitors.

In Vitro and In Vivo Evaluation of ABCG2 (BCRP) Inhibitors Derived from Ko143.

Breast cancer resistance protein (BCRP, ABCG2) is an efflux transporter that plays a crucial role in multidrug resistance to antineoplastic drugs. Ko143, an analogue of the natural product fumitremorgin C, is a potent inhibitor of ABCG2 but is rapidly hydrolyzed to an inactive metabolite in vivo. To identify ABCG2 inhibitors with improved metabolic stability, we have assessed a series of Ko143 analogues for their ability to inhibit ABCG2-mediated transport in ABCG2-transduced MDCK II cells and determined the stability of the most potent compounds in liver microsomes. The most promising analogues were evaluated in vivo by positron emission tomography. In vitro, three of the tested analogues were potent ABCG2 inhibitors and stable in microsomes. In vivo, they increased the distribution of the ABCG2/ABCB1 substrate [11C]tariquidar to the brain both in wild-type (with Abcb1a/b transport blocked by tariquidar) and Abcb1a/b(-/-) mice. One analogue was more potent than Ko143 in both animal models.

Characterization of Potent ABCG2 Inhibitor Derived from Chromone: From the Mechanism of Inhibition to Human Extracellular Vesicles for Drug Delivery.

Inhibition of ABC transporters is a promising approach to overcome multidrug resistance in cancer. Herein, we report the characterization of a potent ABCG2 inhibitor, namely, chromone 4a (C4a). Molecular docking and in vitro assays using ABCG2 and P-glycoprotein (P-gp) expressing membrane vesicles of insect cells revealed that C4a interacts with both transporters, while showing selectivity toward ABCG2 using cell-based transport assays. C4a inhibited the ABCG2-mediated efflux of different substrates and molecular dynamic simulations demonstrated that C4a binds in the Ko143-binding pocket. Liposomes and extracellular vesicles (EVs) of Giardia intestinalis and human blood were used to successfully bypass the poor water solubility and delivery of C4a as assessed by inhibition of the ABCG2 function. Human blood EVs also promoted delivery of the well-known P-gp inhibitor, elacridar. Here, for the first time, we demonstrated the potential use of plasma circulating EVs for drug delivery of hydrophobic drugs targeting membrane proteins.

Design, synthesis, and biological evaluation of phenylurea indole derivatives as ABCG2 inhibitors

Three series of phenylurea indole derivatives were synthesized with potent inhibitory activities on ABCG2 with simple and efficient synthetic routes. Among these compounds, four phenylurea indole derivatives 3c-3f with extended π system were discovered as the most potent ABCG2 inhibitors, while these compounds showed no inhibition on ABCB1. Compounds 3c and 3f were selected for further investigation to explore the mechanisms of action on reversing ABCG2-mediated multidrug resistance (MDR). The results revealed that compounds 3c and 3f increased the accumulation of mitoxantrone (MX) in ABCG2-overexpressing cells, but they did not alter the expression level or localization of ABCG2 in cells. In addition, both 3c and 3f significantly stimulated the ATP hydrolysis of ABCG2 transporter indicating that they can be competitive substrates of ABCG2 transporter, and thereby increase the accumulation of mitoxantrone in ABCG2-overexpressing H460/MX20 cells. Both 3c and 3f was docked into the drug-binding site of the human ABCG2 transporter protein (PDB 6FFC) with high affinities. This study showed that extending the π system of phenylurea indole derivatives enhanced their inhibitory activities on ABCG2, which may provide a clue for the further research to discover more potent ABCG2 inhibitors.

Characterization of potent ABCG2 inhibitor derived from chromone: from the mechanism of inhibition to a pharmaceutical formulation based on extracellular vesicles

Characterization of potent ABCG2 inhibitor derived from chromone: from the mechanism of inhibition to a pharmaceutical formulation based on extracellular vesicles

Tetrahydroquinoline/4,5-Dihydroisoxazole Molecular Hybrids as Inhibitors of Breast Cancer Resistance Protein (BCRP/ABCG2).

Multidrug resistance (MDR) is one of the major factors in the failure of many chemotherapy approaches. In cancer cells, MDR is mainly associated with the expression of ABC transporters such as P‐glycoprotein, MRP1 and ABCG2. Despite major efforts to develop new selective and potent inhibitors of ABC drug transporters, no ABCG2‐specific inhibitors for clinical use are yet available. Here, we report the evaluation of sixteen tetrahydroquinoline/4,5‐dihydroisoxazole derivatives as a new class of ABCG2 inhibitors. The affinity of the five best inhibitors was further investigated by the vanadate‐sensitive ATPase assay. Molecular modelling data, proposing a potential binding mode, suggest that they can inhibit the ABCG2 activity by binding on site S1, previously reported as inhibitors binding region, as well targeting site S2, a selective region for substrates, and by specifically interacting with residues Asn436, Gln398, and Leu555. Altogether, this study provided new insights into THQ/4,5‐dihydroisoxazole molecular hybrids, generating great potential for the development of novel most potent ABCG2 inhibitors.

Mechanistic basis of breast cancer resistance protein inhibition by new indeno[1,2-b]indoles

The ATP-binding cassette transporter ABCG2 mediates the efflux of several chemotherapeutic drugs, contributing to the development of multidrug resistance (MDR) in many cancers. The most promising strategy to overcome ABCG2-mediated MDR is the use of specific inhibitors. Despite many efforts, the identification of new potent and specific ABCG2 inhibitors remains urgent. In this study, a structural optimization of indeno[1,2-b]indole was performed and a new generation of 18 compounds was synthesized and tested as ABCG2 inhibitors. Most compounds showed ABCG2 inhibition with IC50 values below 0.5 µM. The ratio between cytotoxicity (IG50) and ABCG2 inhibition potency (IC50) was used to identify the best inhibitors. In addition, it was observed that some indeno[1,2-b]indole derivatives produced complete inhibition, while others only partially inhibited the transport function of ABCG2. All indeno[1,2-b]indole derivatives are not transported by ABCG2, and even the partial inhibitors are able to fully chemosensitize cancer cells overexpressing ABCG2. The high affinity of these indeno[1,2-b]indole derivatives was confirmed by the strong stimulatory effect on ABCG2 ATPase activity. These compounds did not affect the binding of conformation-sensitive antibody 5D3 binding, but stabilized the protein structure, as revealed by the thermostabilization assay. Finally, a docking study showed the indeno[1,2-b]indole derivatives share the same binding site as the substrate estrone-3-sulfate.

Water-soluble inhibitors of ABCG2 (BCRP) - A fragment-based and computational approach.

A good balance between hydrophilicity and lipophilicity is a prerequisite for all bioactive compounds. If the hydrophilicity of a compound is low, its solubility in water will be meager. Many drug development failures have been attributed to poor aqueous solubility. ABCG2 inhibitors are especially prone to be insoluble since they have to address the extremely large and hydrophobic multidrug binding site in ABCG2. For instance, our previous, tariquidar-related ABCG2 inhibitor UR-MB108 (1) showed high potency (79nM), but very low aqueous solubility (78nM). To discover novel potent ABCG2 inhibitors with improved solubility we pursued a fragment-based approach. Substructures of 1 were optimized and the fragments 'enlarged' to obtain inhibitors, supported by molecular docking studies. Synthesis was achieved, i.a., via Sonogashira coupling, click chemistry and amide coupling. A kinetic solubility assay revealed that 1 and most novel inhibitors did not precipitate during the short time period of the applied biological assays. The solubility of the compounds in aqueous media at equilibrium was investigated in a thermodynamic solubility assay, where UR-Ant116 (40), UR-Ant121 (41), UR-Ant131 (48) and UR-Ant132 (49) excelled with solubilities between 1μM and 1.5μM - an up to 19-fold improvement compared to 1. Moreover, these novel N-phenyl-chromone-2-carboxamides inhibited ABCG2 in a Hoechst 33342 transport assay with potencies in the low three-digit nanomolar range, reversed MDR in cancer cells, were non-toxic and proved stable in blood plasma. All properties make them attractive candidates for invitro assays requiring long-term incubation and invivo studies, both needing sufficient solubility at equilibrium. 41 and 49 were highly ABCG2-selective, a precondition for developing PET tracers. The triple ABCB1/C1/G2 inhibitor 40 qualifies for potential therapeutic applications, given the concerted role of the three transporter subtypes at many tissue barriers, e.g. the BBB.

Tariquidar-related triazoles as potent, selective and stable inhibitors of ABCG2 (BCRP)

Tariquidar derivatives have been described as potent and selective ABCG2 inhibitors. However, their susceptibility to hydrolysis limits their applicability. The current study comprises the synthesis and characterization of novel tariquidar-related inhibitors, obtained by bioisosteric replacement of the labile moieties in our previous tariquidar analog UR-ME22-1 (9). CuAAC (“click” reaction) gave convenient access to a triazole core as a substitute for the labile amide group and the labile ester moiety was replaced by different acyl groups in a Sugasawa reaction. A stability assay proved the enhancement of the stability in blood plasma. Compounds UR-MB108 (57) and UR-MB136 (59) inhibited ABCG2 in a Hoechst 33342 transport assay with an IC50 value of about 80 nM and belong to the most potent ABCG2 inhibitors described so far. Compound 57 was highly selective, whereas its PEGylated analog 59 showed some potency at ABCB1. Both 57 and 59 produced an ABCG2 ATPase-depressing effect which is in agreement with our precedent cryo-EM study identifying 59 as an ATPase inhibitor that exerts its effect via locking the inward-facing conformation. Thermostabilization of ABCG2 by 57 and 59 can be taken as a hint to comparable binding to ABCG2. As reference substances, compounds 57 and 59 allow additional mechanistic studies on ABCG2 inhibition. Due to their stability in blood plasma, they are also applicable in vivo. The highly specific inhibitor 57 is suited for PET labeling, helping to further elucidate the (patho)physiological role of ABCG2, e.g. at the BBB.

Enasidenib Drives Maturation of Human Erythroid Precursors Independently of IDH2

Acute Myeloid Leukemia (AML) remains one of the most difficult cancers to treat, with a 30% 2-year survival rate. High-throughput sequencing of AML patients has identified mutations, including FLT3, IDH1, and IDH2, for which targeted therapies have been developed. Enasidenib is an FDA-approved, first-in-class agent that preferentially inhibits IDH2-mutant activity and reduces levels of the oncometabolite 2-HG, inducing differentiation of IDH2-mutated blasts. Interestingly, greater than 50% of enasidenib-treated patients who had no objective clinical response still demonstrated improvement in their peripheral blood counts and reached RBC transfusion independence. The mechanism underlying this phenomenon is unknown but is of great clinical relevance given the high transfusion dependence and anemia-associated complications universally associated with AML. Thus, we sought to investigate how enasidenib drives normal hematopoiesis to improve quality of life and reduce morbidity in AML patients. In this study, we demonstrate that enasidenib enhances erythropoiesis from normal CD34+ hematopoietic stem and progenitor cells (HSPCs) derived from cord blood (CB) and bone marrow. Enasidenib doubled the proportion and total number of mature CD71+/GPA+ erythroblasts after 8 days of culture with EPO, SCF, and IL-3. In the presence of EPO, enasidenib induced a gene signature characteristic of maturing erythrocytes, with increased expression of GATA1 (1.3 fold), EPOR (2 fold), and KLF1 (1.4 fold), and decreased PU.1 (0.5 fold) and GATA2 (0.7 fold). Enasidenib-treated progenitor cells further demonstrated increased hemoglobin production (1.9 fold) and morphologic characteristics of increased erythroid maturation. Next, we sought to determine if enasidenib augments erythroid differentiation through IDH2 and IDH2-dependent pathways. First, we found that other IDH inhibitors (AG-120, AGI-6780, and AG-881) did not increase erythropoiesis at doses ranging from 1-10μM. As expected for normal HSPCs, 2-HG was not present at detectable levels in either the DMSO or enasidenib-treated conditions, and addition of 2-HG (50, 200μM) did not affect the ability of enasidenib to increase the proportion of CD71+GPA+ cells. Because it is possible that enasidenib acts through inhibition of wild-type IDH2, we generated CRISPR-Cas9 engineered IDH2 knockout (KO) CD34+ cells and treated them with enasidenib. Similar to wildtype cells, IDH2 KO CB CD34+ cells demonstrated a 3.4-fold increase in %CD71+GPA+ erythroid cells. Thus, enasidenib augments erythropoiesis independently of both mutant and wildtype IDH2 pathways. We then investigated the progenitor population that enasidenib acts on to drive erythroid maturation. Enasidenib did not increase the number of BFU-E or CFU-E colonies or the proportion of BFU-E (IL3R-CD34+CD36-) and CFU-E (IL3R-CD34-CD36+) progenitors in colony forming or liquid culture assays, respectively, leading us to conclude that enasidenib acts on more mature erythroid progenitors. Indeed, treating sorted mature CD71+ erythroid progenitors with enasidenib increased %CD71+GPA+ cells compared to DMSO control, whereas enasidenib treatment of CD71- early erythroid progenitors showed no effect. These observations provide evidence that enasidenib acts on CD71+ erythroid progenitors to increase late-stage erythroid differentiation. Given that CD71 allows for iron uptake into erythroid progenitors, we hypothesized that enasidenib modulates the heme biosynthesis pathway. Enasidenib inhibited the ABCG2 transporter, which effluxes protoporphyrin IX (PPIX), the direct precursor to heme, from the mitochondria and cytosol. Inhibition of ABCG2 by enasidenib could lead to PPIX accumulation within the cell, driving increased heme synthesis. To investigate this hypothesis, we treated cells with 20μM Ko143, a potent ABCG2 inhibitor, and observed a similar increase in %CD71+GPA+ cells as seen with enasidenib. Measurement of PPIX autofluorescence by flow cytometry and microscopy revealed an increase of PPIX in enasidenib-treated cells by 1.2-fold. Together, our data suggests that enasidenib drives maturation of CD71+ erythroid precursors independently of wildtype or mutant IDH2. Our results position enasidenib as a promising therapy to stimulate erythropoiesis and provide the basis for a clinical trial using enasidenib to improve anemia in a wide array of clinical contexts. Disclosures Majeti: Forty Seven Inc.: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; BioMarin: Consultancy.

Abstract 25: Identifying new inhibitors of ABCG2 by high-throughput screening

Abstract Background: ABCG2, also known as breast cancer resistance protein (BCRP), is a member of the ATP-binding cassette (ABC)-family of membrane transport proteins associated with multidrug resistance (MDR). No ABCG2 inhibitor has shown clinical significance yet. Aim: To identify novel inhibitors of ABCG2 by high-throughput screening. Material & Methods: After higher expression of ABCG2 in HCT-116/BCRP cells was confirmed by flow cytometry (FACSVerse) using 5D3 antibody, high-throughput fluorescent cell-based assay was performed with the original chemical library of Tohoku University containing about 6000 compounds using ABCG2-specific fluorescent substrate, Pheophorbide a (PhA) in HCT-116/BCRP cells overexpressing ABCG2. Ko143, a potent ABCG2 inhibitor, was used as positive control. Fluorescence intensity in the cells was read by a fluorescence plate reader (SpectraMax M2e) in bottom read mode, with 395 nm excitation, 670 nm emission. To validate the results, flow cytometry assay was performed with 10 µM PhA in HCT-116/BCRP cells. The fluorescence intensity was analyzed by flow cytometry (FACSVerse). Results: Fluorescenct cell-based assay with high-throughput screening could detect 23 candidate compounds, which showed higher fluorescence intensity as positive control Ko143 showed. Then, these 23 compounds were validated with flow cytometry assays. The flow cytometry assays revealed that 16 compounds increased fluorescence intensity of PhA in HCT-116/BCRP cells in dose dependent manner, suggesting that these candidate compounds inhibited transport function of ABCG2. Among 16 compounds, 6 compounds showed further inhibitory effect for transport function of ABCG2 as equivalent to that of Ko143. Conclusion: These 6 compounds may provide a basis for further investigation of ABCG2 function. Citation Format: Shoji Kokubo, Shinobu Ohnuma, Hideaki Karasawa, Akihiro Yamamura, Hideyuki Suzuki, Megumi Murakami, Norihiko Sugisawa, Keigo Kanehara, Keisuke Sato, Takanori Ishida, Takashi Kamei, Takeshi Naitoh, Michiaki Unno. Identifying new inhibitors of ABCG2 by high-throughput screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 25.

Benzoyl indoles with metabolic stability as reversal agents for ABCG2-mediated multidrug resistance

Ko143, a potent ABCG2 inhibitor that reverses multidrug resistance in cancer, cannot be used clinically due to its unsuitable metabolic stability. We identified benzoyl indoles as reversal agents that reversed ABCG2-mediated multidrug resistance (MDR), with synthetic tractability and enhanced metabolic stability compared to Ko143. Bisbenzoyl indole 2 and monobenzoyl indole 8 significantly increased the accumulation of mitoxantrone (MX) in ABCG2-overexpressing NCI–H460/MX20 cells, and sensitized NCI–H460/MX20 cells to mitoxantrone. Mechanistic studies were conducted by [3H]-MX accumulation assay, Western blot analysis, immunofluorescence analysis and ABCG2 ATPase assay. The results revealed that the reversal efficacies of compounds 2 and 8 were not due to an alteration in the expression level or localization of ABCG2 in ABCG2-overexpressing cell lines. Instead, compounds 2 and 8 significantly stimulated the ATP hydrolysis of ABCG2 transporter, suggesting that these compounds could be competitive substrates of ABCG2 transporter. Overall, the results of our study indicated that compounds 2 and 8 significantly reversed ABCG2-mediated MDR by blocking the efflux of anticancer drugs.

Synthesis and Investigation of Tetrahydro-β-carboline Derivatives as Inhibitors of the Breast Cancer Resistance Protein (ABCG2).

The breast cancer resistance protein (ABCG2) transports chemotherapeutic drugs out of cells, which makes it a major player in mediating multidrug resistance (MDR) of cancer cells. To overcome this mechanism, inhibitors of ABCG2 can be used. Only a few potent and selective ABCG2 inhibitors have been discovered, i.e., fumitremorgin C (FTC), Ko143, and the alkaloid harmine, which contain a tetrahydro-β-carboline or β-carboline backbone, respectively. However, toxicity and or instability prevent their use in vivo. Therefore, there is a need for further potent inhibitors. We synthesized and pharmacologically investigated 37 tetrahydro-β-carboline derivatives. The inhibitory activity of two compounds (51, 52) is comparable to that of Ko143, and they are selective for ABCG2 over ABCB1. Furthermore, they are able to reverse the ABCG2-mediated resistance toward SN-38 and inhibit the ATPase activity. The cytotoxicity data show that their inhibitory effect is substantially higher than their toxicity.

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.

Pyrimido[1″,2″:1,5]pyrazolo[3,4-b]quinolines: Novel compounds that reverse ABCG2-mediated resistance in cancer cells

Overexpression of ATP-binding cassette transporter (ABC) subfamily G2 in cancer cells is known to elicit a MDR phenotype, ultimately resulting in cancer chemotherapy failure. Here, we report, for the first time, the effect of eight novel pyrimido[1″,2″:1,5]pyrazolo[3,4-b]quinoline (IND) derivatives that inhibit ABCG2 transporter restoring cancer cell chemosensitivity. IND -4, -5, -6, -7, and -8, at 10 µM, and nilotinib at 5 µM, significantly potentiated (8–10 fold) the cytotoxicity of the ABCG2 substrates mitoxantrone (MX) and doxorubicin in HEK293 cells overexpressing ABCG2 transporter, MX (~14 fold) in MX-resistant NCI-H460/MX-20 small cell lung cancer, and of topotecan (~7 fold) in S1-M1-80 colon cancer cells which all stably expressing ABCG2. In contrast, cytotoxicity of cisplatin, which is not an ABCG2 substrate, was not altered. IND-5,-6,-7, and -8 significantly increased the accumulation of rhodamine-123 in multidrug resistant NCI-H460/MX-20 cells overexpressing ABCG2. Both IND-7 and -8, the most potent ABCG2 inhibitors, had the highest affinities for the binding sites of ABCG2 in modeling studies. In conclusion, the beneficial actions of new class of agents warrant further development as potential MDR reversal agents for clinical anticancer agents that suffer from ABCG2-mediated MDR insensitivity.

MBL-II-141, a chromone derivative, enhances irinotecan (CPT-11) anticancer efficiency in ABCG2-positive xenografts

ABCG2 is responsible for the multidrug resistance (MDR) phenotype, and strongly modulates cancer outcomes. Its high expression at a number of physiological barriers, including blood-brain and intestinal barriers, impacts on drug pharmacokinetics parameters. We characterized MBL-II-141, a specific and potent ABCG2 inhibitor. Combination of 10 mg/kg MBL-II-141 with the anticancer agent CPT-11 completely blocked the growth of 90% freshly implanted ABCG2-positive tumors. Moreover, the same combination slowed the growth of already established tumors. As required for preclinical development, we defined the main pharmacokinetics parameters of MBL-II-141 and its influence on the kinetics of CPT-11 and its active metabolite SN-38 in mice. MBL-II-141 distribution into the brain occurred at a low, but detectable, level. Interestingly, preliminary data suggested that MBL-II-141 is well tolerated (at 50 mg/kg) and absorbed upon force-feeding. MBL-II-141 induced a potent sensitization of ABCG2-positive xenografts to CPT-11 through in vivo ABCG2 inhibition. MBL-II-141 strongly increased CPT-11 levels in the brain, and therefore would be a valuable agent to improve drug distribution into the brain to efficiently treat aggressive gliomas. Safety and other pharmacological data strongly support the reglementary preclinical development of MBL-II-141.

Symmetric Bis-chalcones as a New Type of Breast Cancer Resistance Protein Inhibitors with a Mechanism Different from That of Chromones

Potent ABCG2 inhibitors were recently identified as asymmetric chromones with different types of substituents. We here synthesized symmetric bis-chalcones that were differently substituted and screened for their ability to inhibit mitoxantrone efflux from ABCG2-transfected HEK293 cells. Potent bis-chalcone inhibitors were identified, the efficiency depending on both position of the central ketone groups and the number and positions of lateral methoxy substituents. The best derivative, namely, 1p, was selective for ABCG2 over P-glycoprotein and MRP1, appeared not to be transported by ABCG2, and was at least as active on various drug-selected cancer cells overexpressing ABCG2. Compound 1p stimulated the ABCG2 basal ATPase activity by contrast to a chromone lead that inhibited it, suggesting different mechanisms of interaction. Combination of both types of inhibitors produced synergistic effects, leading to complete inhibition at very low concentrations.

Quinoline Carboxamide‐Type ABCG2 Modulators: Indole and Quinoline Moieties as Anilide Replacements

ABC, it's easy as 1 2 3! Bioisosteric replacement of the anilide core by an indole moiety considerably increased stability and gave potent and selective ABCG2 (BCRP) inhibitors. Some compounds are superior to the reference substances fumitremorgin C and Ko143 in terms of potency and efficacy and are the most potent ABCG2 modulators reported so far.

Synthesis and ABCG2 Inhibitory Activity of Novel Fumitremorgin C Analogs – Specificity and Structure Activity Correlations

The Ko family of fumitremorgin C analogs are potent and selective ABCG2 inhibitors. However, the most potent Ko compounds carry an ester linkage in their side-chain that makes them chemically and metabolically less stable. We have synthesized 16 tricyclic and 28 tetracyclic novel analogs devoid of ester linkages and tested them for ABCG2 inhibition potency and specificity. Unlike in the tricyclic analog group, potent ABCG2 inhibitory compounds were found among the tetracyclic analogs. The most potent compounds carried the 3S,6S,12aS configuration. We observed a marked stereospecificity as compounds with the 3S,6S,12aS configuration were at least 18-fold more potent inhibitors than their diastereoisomeric pairs with a 3S,6R,12aS configuration. This stereospecificity was not observed in ABCB1 and ABCC1 inhibition. Therefore, a single chiral center confers specificity for ABCG2 over ABCB1 and ABCC1. This is quite unexpected considering the large multivalent drug binding site these transporters harbor.