Biological evaluation of 9-thioansamitocin P3.

Highly cytotoxic maytansine derivatives are widely used in targeted tumor delivery. Structure-activity studies published earlier suggested the C9 carbinol to be a key element necessary to retain the potency. However, in 1984 a patent was published by Takeda in which the synthesis of 9-thioansamitocyn (AP3SH) was described and its activity in xenograft models was shown. In this article we summarize the results of an extended study of the anti-tumor properties of AP3SH. Like other maytansinoids, it induces apoptosis and arrests the cell cycle in the G2/M phase. It is metabolized in liver microsomes predominately by C3A4 isoform and doesn't inhibit any CYP isoforms except CYP3A4 (midazolam, IC50 7.84 µM). No hERG inhibition, CYP induction or mutagenicity in Ames tests were observed. AP3SH demonstrates high antiproliferative activity against 25 tumor cell lines and tumor growth inhibition in U937 xenograft model. Application of AP3SH as a cytotoxic payload in drug delivery system was demonstrated by us earlier.

The Suppressive Effect of Rebastinib on Triple-negative Breast Cancer Tumors Involves Multiple Mechanisms of Action.

BACKGROUND/AIM: High resistance of triple-negative breast cancer has prompted scientists to look for new targets susceptible to treatment. CDK16 has been suggested as a promising target whose inhibition can lead to tumor growth suppression. Rebastinib, a potent inhibitor of CDK16, has been reported to exhibit anti-tumor activity both in vitro and in vivo. MATERIALS AND METHODS: The anticancer activity of rebastinib was studied in vitro using cell proliferation, cell cycle arrest and cell apoptosis assays and in vivo in xenograft tumor models using MDA-MB-231 and MDA-MB-468-derived tumors. The safety and drug-like properties of rebastinib were assessed using a panel of Absorption, Distribution, Metabolism, and Excretion (ADME) assays, Ames tests, human Ether-a-go-go Related Gene (hERG) experiments and pharmacokinetic studies in mice and rats. RESULTS: Rebastinib demonstrates antitumor activity against breast cancer both in vitro and in vivo. However, the response of the tumor strongly depends on the type of triple-negative breast cancer. Rebastinib-induced cell cycle arrest was observed in G0/G1 phase suggesting a more complex mechanism than just CDK16 inhibition. ADME and PK studies confirmed the drug-like properties and reasonable safety of rebastinib. CONCLUSION: Our studies confirmed rebastinib to be a promising drug candidate for breast cancer treatment with high oral bioavailability and reasonable safety. Our data suggest that the mechanism of action of rebastinib is not limited to CDK16 inhibition but also involves other pathways. This does not diminish the importance of rebastinib as a drug candidate, but reveals the presence of several mechanisms, suggesting a wider scope of possible applications.

Age-related changes in hepatic expression and activity of drug metabolizing enzymes in male wild-type and breast cancer resistance protein knockout mice.

This study aimed to reveal age-related changes in the expression and activity of seven hepatic drug metabolizing enzymes (DMEs) in male wild-type and breast cancer resistance protein knockout (Bcrp1-/- ) FVB mice. The protein expression of four cytochrome P450 (Cyps) (Cyp3a11, 2d22, 2e1, and 1a2), and three UDP-glucuronosyltransferases (Ugts) (Ugt1a1, 1a6a, and 1a9) in liver microsomes of wild-type and Bcrp1-/- FVB mice at different ages were determined using a validated ultra high performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) method. The activities and mRNA levels of these DMEs were measured using the probe substrates method and real-time PCR, respectively. In the liver of wild-type FVB mice, Cyp3a11, 2d22, 2e1, 1a2, Ugt1a1, and 1a6a displayed maximum protein levels at 6-9 weeks of age. Cyp1a2, Ugt1a1, 1a6a, and 1a9 showed maximum activities at 6-9 weeks of age, whereas Cyp3a11, 2d22, and 2e1 showed maximum activities in 1-3-week-old mice. Additionally, most of the DMEs showed maximum mRNA levels in 17-week-old mice liver. Compared with wild-type FVB mice, the protein levels of these DMEs showed no significant changes in Bcrp1-/- FVB mice liver. However, the activity of Cyp2e1 was increased and that of Cyp2d22 was decreased. In conclusion, the seven hepatic DMEs in FVB mice liver showed significant alterations in an isoform-specific manner with increased age. Although the protein levels of these DMEs showed no significant changes, the activities of Cyp2e1 and 2d22 were changed in Bcrp1-/- mice.

Sulfonation Disposition of Acacetin: In Vitro and in Vivo.

Acacetin, an important component of acacia honey, exerts extensive therapeutic effects on many cancers. However, the sulfonation disposition of acacetin has rarely been reported. Therefore, this study aimed to investigate the sulfonation disposition of acacetin systematically. The results showed that acacetin-7-sulfate was the main metabolite mediated primarily by sulfotransferases (SULT) 1A1. Dog liver S9 presented the highest formation rate of acacetin-7-sulfate. Compared with that in wild-type Friend Virus B (FVB) mice, plasma exposure of acacetin-7-sulfate decreased significantly in multidrug resistance protein 1 knockout (Mrp1-/-) mice vut increased clearly in breast cancer resistance protein knockout (Bcrp-/-) mice. In Caco-2 monolayers, the efflux and clearance of acacetin-7-sulfate was reduced distinctly by the BCRP inhibitor Ko143 on the apical side and by the MRP1 inhibitor MK571 on the basolateral side. In conclusion, acacetin sulfonation was mediated mostly by SULT1A1. Acacetin-7-sulfate was found to be transported mainly by BCRP and MRP1. Hence, SULT1A1, BCRP, and MRP1 are responsible for acacetin-7-sulfate exposure in vivo.

Sulfotransferases and Breast Cancer Resistance Protein Determine the Disposition of Calycosin in Vitro and in Vivo.

Sulfation is a key process of drug disposition that generally regulates drug effectiveness and toxicity. Calycosin derived from the dry root extract of Radix Astragali exhibits a variety of biological effects that easily undergo extensive phase II metabolism. However, the sulfation pathway of calycosin lacks information. We investigated the disposition mechanisms of calycosin sulfate in vitro and in vivo. We characterized the sulfation metabolism and excretion of calycosin using bidirectional transport studies. We confirmed that sulfate conjugate is breast cancer resistance protein (BCRP) substrate using the intestinal perfusion model and pharmacokinetics studies in Bcrp1-/- mice. Results showed that calycosin is rapidly and extensively metabolized to calycosin-3'-sulfate (C-3'-S) in the intestine and liver. The overexpression of BCRP led to a substantial increase (approximately 14-fold, p < 0.01) of excreted C-3'-S in the BCRP overexpressed Madin-Darby canine kidney II (MDCK II/BCRP) cells. The chemical inhibition of BCRP caused reduction (about 2-fold, p < 0.01) in C-3'-S apical excretion. Furthermore, in intestinal perfusion studies, the deletion of Bcrp1 significantly decreased C-3'-S excretion in the small intestine (82.6-90.6%, p < 0.01) and colon (97.6-98.2%, p < 0.01). In contrast, plasma level of C-3'-S was increased to 40-fold (p < 0.01) in Bcrp1-/- mice. In conclusion, calycosin undergoes an extensive sulfation metabolism and BCRP is a critical determinant to the disposition of C-3'-S.

Breast Cancer Resistance Protein and Multidrug Resistance Protein 2 Regulate the Disposition of Acacetin Glucuronides.

PURPOSE: To determine the mechanism responsible for acacetin glucuronide transport and the bioavailability of acacetin. METHODS: Area under the curve (AUC), clearance (CL), half-life (T1/2) and other pharmacokinetic parameters were determined by the pharmacokinetic model. The excretion of acacetin glucuronides was evaluated by the mouse intestinal perfusion model and the Caco-2 cell model. RESULTS: In pharmacokinetic studies, the bioavailability of acacetin in FVB mice was 1.3%. Acacetin was mostly exposed as acacetin glucuronides in plasma. AUC of acacetin-7-glucuronide (Aca-7-Glu) was 2-fold and 6-fold higher in Bcrp1 (-/-) mice and Mrp2 (-/-) mice, respectively. AUC of acacetin-5-glucuronide (Aca-5-Glu) was 2-fold higher in Bcrp1 (-/-) mice. In mouse intestinal perfusion, the excretion of Aca-7-Glu was decreased by 1-fold and 2-fold in Bcrp1 (-/-) and Mrp2 (-/-) mice, respectively. In Caco-2 cells, the efflux rates of Aca-7-Glu and Aca-5-Glu were significantly decreased by breast cancer resistance protein (BCRP) inhibitor Ko143 and multidrug resistance protein 2 (MRP2) inhibitor LTC4. The use of these inhibitors markedly increased the intracellular acacetin glucuronide content. CONCLUSIONS: BCRP and MRP2 regulated the in vivo disposition of acacetin glucuronides. The coupling of glucuronidation and efflux transport was probably the primary reason for the low bioavailability of acacetin.

High-Throughput and Reliable Isotope Label-free Approach for Profiling 24 Metabolic Enzymes in FVB Mice and Sex Differences.

FVB mice are extensively used in transgenic and pharmacokinetic research. In this study, a validated isotope label-free method was constructed using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to quantify 24 drug-metabolizing enzymes (DMEs) in FVB mice. The DMEs include cytochrome P450s (CYP450s/Cyp450s), UDP-glucuronsyltransferases (UGTs/Ugts), and sulfotransferases (SULTs/Sults), which catalyze a variety of reactions to detoxify xenobiotics and endobiotics. The proposed UHPLC-MS/MS method exhibited good range and high sensitivity for signature peptides, as well as acceptable accuracy, precision, and recovery. The protein expression profiles of the DMEs were determined in male and female mice. Overall, the major Cyps, Ugts, and Sults were expressed in male mice followed the rank order: Cyp2c29 > 2e1 > 3a11 > 1a2 > 2d22 > 27a1 > 2c39; Ugt2b5 > 2b1 > 1a6a > 1a9 > 1a1 > 2a3 > 1a2 > 1a5; and Sult1a1 > 3a > 1d1. In contrast, the rank order in female mice was Cyp2c29 > 2e1 > 2c39 > 2d22 > 3a11 > 1a2 > 27a1; Ugt1a6a > 2b5 > 1a1 > 2b1 > 2a3 > 1a9 > 1a5 > 1a2; and Sult1a1 > 3a1 > 1d1. Cyp2c29, Cyp1a2, Cyp27a1, Ugt2b1, Ugt2b5 and Ugt2b36 were male predominant, whereas Cyp2c39, Cyp2d22, Cyp7a1, Ugt1a1, Ugt1a5, Sult1a1, Sult3a1, and Sult1d1 were female predominant. This work could serve as a useful reference for the metabolic study of new drugs and for elucidating the effectiveness and toxicity of drugs. The method is stable, simple, and rapid for determining the expression of DMEs in animals.

Regioselective Glucuronidation of Diosmetin and Chrysoeriol by the Interplay of Glucuronidation and Transport in UGT1A9-Overexpressing HeLa Cells.

This study aimed to determine the reaction kinetics of the regioselective glucuronidation of diosmetin and chrysoeriol, two important methylated metabolites of luteolin, by human liver microsomes (HLMs) and uridine-5'-diphosphate glucuronosyltransferase (UGTs) enzymes. This study also investigated the effects of breast cancer resistance protein (BCRP) on the efflux of diosmetin and chrysoeriol glucuronides in HeLa cells overexpressing UGT1A9 (HeLa-UGT1A9). After incubation with HLMs in the presence of UDP-glucuronic acid, diosmetin and chrysoeriol gained two glucuronides each, and the OH-in each B ring of diosmetin and chrysoeriol was the preferable site for glucuronidation. Screening assays with 12 human expressed UGT enzymes and chemical-inhibition assays demonstrated that glucuronide formation was almost exclusively catalyzed by UGT1A1, UGT1A6, and UGT1A9. Importantly, in HeLa-UGT1A9, Ko143 significantly inhibited the efflux of diosmetin and chrysoeriol glucuronides and increased their intracellular levels in a dose-dependent manner. This observation suggested that BCRP-mediated excretion was the predominant pathway for diosmetin and chrysoeriol disposition. In conclusion, UGT1A1, UGT1A6, and UGT1A9 were the chief contributors to the regioselective glucuronidation of diosmetin and chrysoeriol in the liver. Moreover, cellular glucuronidation was significantly altered by inhibiting BCRP, revealing a notable interplay between glucuronidation and efflux transport. Diosmetin and chrysoeriol possibly have different effects on anti-cancer due to the difference of UGT isoforms in different cancer cells.

In Vivo Exposure of Kaempferol Is Driven by Phase II Metabolic Enzymes and Efflux Transporters.

Kaempferol is a well-known flavonoid; however, it lacks extensive pharmacokinetic studies. Phase II metabolic enzymes and efflux transporters play an important role in the disposition of flavonoids. This study aimed to investigate the mechanism by which phase II metabolic enzymes and efflux transporters determine the in vivo exposure of kaempferol. Pharmacokinetic analysis in Sprague-Dawley rats revealed that kaempferol was mostly biotransformed to conjugates, namely, kaempferol-3-glucuronide (K-3-G), kaempferol-7-glucuronide (K-7-G), and kaempferol-7-sulfate, in plasma. K-3-G represented the major metabolite. Compared with that in wild-type mice, pharmacokinetics in knockout FVB mice demonstrated that the absence of multidrug resistance protein 2 (MRP2) and breast cancer resistance protein (BCRP) significantly increased the area under the curve (AUC) of the conjugates. The lack of MRP1 resulted in a much lower AUC of the conjugates. Intestinal perfusion in rats revealed that the glucuronide conjugates were mainly excreted in the small intestine, but 7-sulfate was mainly excreted in the colon. In Caco-2 monolayers, K-7-G efflux toward the apical (AP) side was significantly higher than K-3-G efflux. In contrast, K-3-G efflux toward the basolateral (BL) side was significantly higher than K-7-G efflux. The BL-to-AP efflux was significantly reduced in the presence of the MRP2 inhibitor LTC4. The AP-to-BL efflux was significantly decreased in the presence of the BL-side MRPs inhibitor MK571. The BCRP inhibitor Ko143 decreased the glucuronide conjugate efflux. Therefore, kaempferol is mainly exposed as K-3-G in vivo, which is driven by phase II metabolic enzymes and efflux transporters (i.e., BCRP and MRPs).

Species- and gender-dependent differences in the glucuronidation of a flavonoid glucoside and its aglycone determined using expressed UGT enzymes and microsomes.

Flavonoids occur naturally as glucosides and aglycones. Their common phenolic hydroxyl groups may trigger extensive UDP-glucuronosyltransferase (UGT)- catalysed metabolism. Unlike aglycones, glucosides contain glucose moieties. However, the influence of these glucose moieties on glucuronidation of glucosides and aglycones remains unclear. In this study, the flavonoid glucoside tilianin and its aglycone acacetin were used as model compounds. The glucuronidation characteristics and enzyme kinetics of tilianin and acacetin were compared using human UGT isoforms, liver microsomes and intestinal microsomes obtained from different animal species. Tilianin and acacetin were metabolized into different glucuronides, with UGT1A8 produced as the main isoform. Assessment of enzyme kinetics in UGT1A8, human liver microsomes and human intestinal microsomes revealed that compared with tilianin, acacetin displayed lower Km (0.6-, 0.7- and 0.6-fold, respectively), higher Vmax (20-, 60- and 230-fold, respectively) and higher clearance (30-, 80- and 300-fold, respectively). Furthermore, glucuronidation of acacetin and tilianin showed significant species- and gender-dependent differences. In conclusion, glucuronidation of flavonoid aglycones is faster than that of glucosides in the intestine and the liver. Understanding the metabolism and species- and gender-dependent differences between glucosides and aglycones is crucial for the development of drugs from flavonoids.