Characterization of a Potent, Selective, and Safe Inhibitor, Ac15(Az8)2, in Reversing Multidrug Resistance Mediated by Breast Cancer Resistance Protein (BCRP/ABCG2).

Overexpression of breast cancer resistance transporter (BCRP/ABCG2) in cancers has been explained for the failure of chemotherapy in clinic. Inhibition of the transport activity of BCRP during chemotherapy should reverse multidrug resistance. In this study, a triazole-bridged flavonoid dimer Ac15(Az8)2 was identified as a potent, nontoxic, and selective BCRP inhibitor. Using BCRP-overexpressing cell lines, its EC50 for reversing BCRP-mediated topotecan resistance was 3 nM in MCF7/MX100 and 72 nM in S1M180 in vitro. Mechanistic studies revealed that Ac15(Az8)2 restored intracellular drug accumulation by inhibiting BCRP-ATPase activity and drug efflux. It did not down-regulate the cell surface BCRP level to enhance drug retention. It was not a transport substrate of BCRP and showed a non-competitive relationship with DOX in binding to BCRP. A pharmacokinetic study revealed that I.P. administration of 45 mg/kg of Ac15(Az8)2 resulted in plasma concentration above its EC50 (72 nM) for longer than 24 h. It increased the AUC of topotecan by 2-fold. In an in vivo model of BCRP-overexpressing S1M180 xenograft in Balb/c nude mice, it significantly reversed BCRP-mediated topotecan resistance and inhibited tumor growth by 40% with no serious body weight loss or death incidence. Moreover, it also increased the topotecan level in the S1M180 xenograft by 2-fold. Our results suggest that Ac15(Az8)2 is a promising candidate for further investigation into combination therapy for treating BCRP-overexpressing cancers.

Flavonoid Monomers as Potent, Nontoxic, and Selective Modulators of the Breast Cancer Resistance Protein (ABCG2).

We synthesize various substituted triazole-containing flavonoids and identify potent, nontoxic, and highly selective BCRP inhibitors. Ac18Az8, Ac32Az19, and Ac36Az9 possess m-methoxycarbonylbenzyloxy substitution at C-3 of the flavone moiety and substituted triazole at C-4' of the B-ring. They show low toxicity (IC50 toward L929 > 100 µM), potent BCRP-inhibitory activity (EC50 = 1-15 nM), and high BCRP selectivity (BCRP selectivity over MRP1 and P-gp > 67-714). They inhibit the efflux activity of BCRP, elevate the intracellular drug accumulation, and restore the drug sensitivity of BCRP-overexpressing cells. Like Ko143, Ac32Az19 remarkably exhibits a 100% 5D3 shift, indicating that it can bind and cause a conformational change of BCRP. Moreover, it significantly reduces the abundance of functional BCRP dimers/oligomers by half to retain more mitoxantrone in the BCRP-overexpressing cell line and that may account for its inhibitory activity. They are promising candidates to be developed into combination therapy to overcome MDR cancers with BCRP overexpression.

Triazole Bridged Flavonoid Dimers as Potent, Nontoxic, and Highly Selective Breast Cancer Resistance Protein (BCRP/ABCG2) Inhibitors.

The present work describes the syntheses of diverse triazole bridged flavonoid dimers and identifies potent, nontoxic, and highly selective BCRP inhibitors. A homodimer, Ac22(Az8)2, with m-methoxycarbonylbenzyloxy substitution at C-3 of the flavone moieties and a bis-triazole-containing linker (21 atoms between the two flavones) showed low toxicity (IC50 toward L929, 3T3, and HFF-1 > 100 µM), potent BCRP-inhibitory activity (EC50 = 1-2 nM), and high BCRP selectivity (BCRP selectivity over MRP1 and P-gp > 455-909). Ac22(Az8)2 inhibits BCRP-ATPase activity, blocks the drug efflux activity of BCRP, elevates the intracellular drug accumulation, and finally restores the drug sensitivity of BCRP-overexpressing cells. It does not down-regulate the surface BCRP protein expression to enhance the drug retention. Therefore, Ac22(Az8)2 and similar flavonoid dimers appear to be promising candidates for further development into combination therapy to overcome MDR cancers with BCRP overexpression.

Discovery of Novel Flavonoid Dimers To Reverse Multidrug Resistance Protein 1 (MRP1, ABCC1) Mediated Drug Resistance in Cancers Using a High Throughput Platform with "Click Chemistry".

A 300-member flavonoid dimer library of multidrug resistance-associated protein 1 (MRP1, ABCC1) modulators was rapidly assembled using "click chemistry". Subsequent high-throughput screening has led to the discovery of highly potent (EC50 ranging from 53 to 298 nM) and safe (selective indexes ranging from >190 to >1887) MRP1 modulators. Some dimers have potency about 6.5- to 36-fold and 64- to 358-fold higher than the well-known MRP1 inhibitors, verapamil, and MK571, respectively. They inhibited DOX efflux and restored intracellular DOX concentration. The most potent modulator, Ac3Az11, was predicted to bind to the bipartite substrate-binding site of MRP1 in a competitive manner. Moreover, it provided sufficient concentration to maintain its plasma level above its in vitro EC50 (53 nM for DOX) for about 90 min. Overall, we demonstrate that "click chemistry" coupled with high throughput screening is a rapid, reliable, and efficient tool in the discovery of compounds having potent MRP1-modualting activity.

(-)-Epiafzelechin Protects against Ovariectomy-induced Bone Loss in Adult Mice and Modulate Osteoblastic and Osteoclastic Functions In Vitro.

The present study was designed to characterize the bone protective effects of (-)-epiafzelechin (EAF), a flavan-3-ol, in mature ovariectomized mice model and its ability to stimulate osteoblastic activity and inhibit osteoclastic activity. Mature C57BL/6 mice (three to four months old) were either ovariectomised (OVX) or sham-operated and subjected to treatment (vehicle, 17ß-oestradiol (E2, 200 µg/kg/day) or EAF (500 µg/kg/day) orally for six weeks. EAF and E2 significantly reduced urinary calcium (Ca) excretion, serum osteocalcin (OCN), and urinary deoxy-pyridinoline (DPD); increased bone mineral density (BMD); and improved micro-architectural properties in OVX mice. EAF significantly increased cell viability, alkaline phosphatise (ALP) activity, and collagen content, as well as runt-related transcriptional factor 2 (Runx2) mRNA expression in murine osteoblastic MC3T3-E1 cells. In addition, EAF significantly reduced the viability of osteoclast precursor murine leukemia monocyte RAW 264.7 cells and tartrate-resistant acid phosphatase (TRAP) activities in mature osteoclastic RAW 264.7 cells. EAF is a bioactive flavan-3-ol that protects estrogen deficiency-induced bone loss in OVX mice and exerts direct modulating effects in bone cells in vitro.

A New Class of Safe, Potent, and Specific P-gp Modulator: Flavonoid Dimer FD18 Reverses P-gp-Mediated Multidrug Resistance in Human Breast Xenograft in Vivo.

Flavonoid dimer FD18 is a new class of dimeric P-gp modulator that can reverse cancer drug resistance. FD18 is a potent (EC50 = 148 nM for paclitaxel), safe (selective index = 574), and selective P-glycoprotein (P-gp) modulator. FD18 can modulate multidrug resistance toward paclitaxel, vinblastine, vincristine, doxorubicin, daunorubicin, and mitoxantrone in human breast cancer LCC6MDR in vitro. FD18 (1 µM) can revert chemosensitivity of LCC6MDR back to parental LCC6 level. FD18 was 11- to 46-fold more potent than verapamil. FD18 (1 µM) can increase accumulation of doxorubicin by 2.7-fold, daunorubicin (2.1-fold), and rhodamine 123 (5.2-fold) in LCC6MDR. FD18 inhibited P-gp-mediated doxorubicin efflux and has no effect on influx. FD18 at 1 µM did not affect the protein expression level of P-gp. Pharmacokinetics studies indicated that intraperitoneal administration of 45 mg/kg FD18 was enough to maintain a plasma level above EC50 (148 nM) for more than 600 min. Toxicity studies with FD18 (90 mg/kg, i.p. for 12 times in 22 days) with paclitaxel (12 mg/kg, i.v. for 12 times in 22 days) revealed no obvious toxicity or death in mice. In vivo efficacy studies indicated that FD18 (45 mg/kg, i.p. for 12 times in 22 days) together with paclitaxel (12 mg/kg, i.v. for 12 times in 22 days) resulted in a 46% reduction in LCC6MDR xenograft volume (n = 11; 648 ± 84 mm(3)) compared to paclitaxel control (n = 8; 1201 ± 118 mm(3)). There were no animal deaths or significant drop in body weight and vital organ wet weight. FD18 can increase paclitaxel accumulation in LCC6MDR xenograft by 1.8- to 2.2-fold. The present study suggests that FD18 represents a new class of safe and potent P-gp modulator in vivo.

Development of a UPLC-MS/MS bioanalytical method for the pharmacokinetic study of (-)-epiafzelechin, a flavan-3-ol with osteoprotective activity, in C57BL/6J mice.

(-)-Epiafzelechin is a flavan-3-ol commonly found in plant source. Biological studies suggested that (-)-epiafzelechin may have anti-inflammatory, anti-oxidant and bone-protective effect. However, it's in vivo efficacy remains to be demonstrated. A specific detection method for (-)-epiafzelechin was successfully developed by using UPLC-MS/MS to quantify the amount of (-)-epiafzelechin present in mice plasma after a liquid-liquid extraction by ethyl acetate. The separation was achieved by using a reversed-phase C18 column with a 16 min gradient elution protocol consisting of water (0.1%, v/v, formic acid) and 0-70% ACN (0.1%, v/v, formic acid). The lower limit of quantitation for (-)-epiafzelechin was found to be 12.5 ng/mL. This method exhibited a good linearity (r(2)=0.992). The intra-day and inter-day precision were within 12%, while the accuracy was between 97.6 and 113. 4%. A quantity of 10mg/kg synthetic (-)-epiafzelechin was administered to C57BL/6J mice by intravenous (i.v.) and intraperitoneal (i.p.) injections and the blood was collected at different time points. The plasma was then analyzed by the UPLC-MS/MS method, and the plasma drug concentration-time curves for i.v. and i.p. (-)-epiafzelechin injection were constructed. The maximum concentrations (Cmax) of (-)-epiafzelechin in blood by i.v. and i.p. injection were found to be 10.6 and 6.0 µg/mL, respectively, while the time for reaching Cmax in i.p. injection was found to be 15 min. The distribution half-lives of (-)-epiafzelechin after i.v. and i.p. injection were found to be 7.0 and 12.6 min, respectively. Some of the PK parameters were found to be similar in both i.v. and i.p. injections of (-)-epiafzelechin owing to its high solubility in water.

Synthetic and mechanistic studies of indium-mediated allylation of imines in ionic liquids.

Aldimines derived from aryl and non-enolizable aliphatic aldehydes were allylated with allyl bromide mediated by indium powder in [bpy][BF4] (bpy = N-butylpyridine) to give good yields of the corresponding homoallylic amines. Selective formation of monoallylated amines can be achieved by varying the amount of bromide ion additive in the form of [bpy][Br]. The transient organoindium intermediates, allylindium(I) and allylindium(III) dibromide formed in the reaction, were studied by NMR spectroscopy to explain the selectivity.

Grignard reagents in ionic liquids.

Grignard reagents were generated from magnesium and organic iodides in the ionic liquid n-butylpyridinium tetrafluoroborate, [bpy][BF4], and they showed different reactivity from classical Grignard reagents in organic solvents.

Formation and reactions of alkylzinc reagents in room-temperature ionic liquids.

[reaction: see text] The presence of a suitable amount of bromide or chloride ions was found to be critical in forming the alkylzinc reagents from alkyl iodides and zinc metal in the room-temperature ionic liquid, N-butylpyridinium tetrafluoroborate. Beta-hydride transfer in the reactions of butylzinc reagents with aldehydes can also be reduced by a bromide ion.