Erratum: A novel selective AKR1C3-activated prodrug AST-3424/OBI-3424 exhibits broad anti-tumor activity.

[This corrects the article on p. 3645 in vol. 11, PMID: 34354865.].

Phase 1 dose-escalation study evaluating the safety, pharmacokinetics, and clinical activity of OBI-3424 in patients with advanced or metastatic solid tumors.

BACKGROUND: Report of a Phase 1 dose-escalation study of OBI-3424 monotherapy in patients with advanced solid tumors (NCT03592264). METHODS: A classic 3 + 3 design was used to determine the maximum tolerated dose and recommended Phase 2 dose (RP2D) of OBI-3424 administered intravenously, as a single agent, at doses of 1, 2, 4, 6, 8, or 12 mg/m2 (days 1 and 8 of a 21-day cycle, Schedule A) or 8, 10, 12, or 14 mg/m2 (day 1 of a 21-day cycle, Schedule B). RESULTS: Dose-limiting hematologic toxicities at 12 mg/m2 in Schedule A led to dose and schedule modifications (Schedule B). In Schedule B, maximum tolerated dose was not reached at the maximum dose tested (14 mg/m2). Grade ≥3 anemia was noted in 3/6 patients treated at 14 mg/m2; the RP2D was 12 mg/m2 (Schedule B). Grade ≥3 treatment-emergent adverse events were experienced by 19/39 (49%) and included anemia (41%) and thrombocytopenia (26%); three patients experienced serious treatment-emergent adverse events (grade ≥3 anemia and thrombocytopenia). One patient had a partial response and 21/33 (64%) had stable disease. CONCLUSIONS: The RP2D is 12 mg/m2 once every 3 weeks. OBI-3424 was well tolerated; dose-dependent, noncumulative thrombocytopenia and anemia were dose-limiting.

First-in-Human Study of OBI-999, a Globo H-Targeting Antibody-Drug Conjugate, in Patients With Advanced Solid Tumors.

PURPOSE: OBI-999 is a novel antibody-drug conjugate comprising the Globo H-targeting antibody (OBI-888) linked to the cytotoxic payload monomethyl auristatin E. OBI-999 demonstrated excellent dose-dependent tumor growth inhibition in breast, gastric, and pancreatic cancer xenograft models as well as a lung cancer patient-derived xenograft model. We conducted a phase I study of OBI-999 monotherapy in patients with advanced cancer (ClinicalTrials.gov identifier: NCT04084366). PATIENTS AND METHODS: OBI-999 was administered intravenously at doses of 0.4, 0.8, 1.2, and 1.6 mg/kg every 21 days as part of a 3 + 3 trial design. Primary end points were the incidence of dose-limiting toxicities and adverse events and determination of the maximum tolerated dose (MTD)/recommended phase II dose. RESULTS: Fifteen adult patients were treated. OBI-999 was well tolerated up to 1.2 mg/kg, the maximum tolerated dose. The most common treatment-emergent adverse events were neutropenia and anemia. OBI-999 exhibited nonlinear pharmacokinetics at all doses, with lower clearance at higher doses. The three patients treated at the 1.6 mg/kg dose level developed grade 4 neutropenia during cycles 1 and 2. Five (33.3%) patients had stable disease (SD) including one patient with adenoid cystic carcinoma of the oropharynx with SD for 13 cycles and one patient with gastroesophageal junction adenocarcinoma with SD for eight cycles. OBI-999 was well tolerated; however, dose-dependent, noncumulative neutropenia was dose-limiting. CONCLUSION: The recommended phase II dose was determined to be 1.2 mg/kg once every 3 weeks. A phase II cohort-expansion study is now enrolling patients with pancreatic, colorectal, and other cancers expressing high levels of Globo H.

A novel selective AKR1C3-activated prodrug AST-3424/OBI-3424 exhibits broad anti-tumor activity.

AST-3424/OBI-3424 (denoted by 3424) is a novel prodrug bis-alkylating agent activated by AKR1C3. AKR1C3 is overexpressed in many types of cancer, particularly in liver, non-small cell lung, gastric, renal and CRPC cancer. Currently 3424 is being studied in phase 1/2 clinical trials for the treatment of solid and hematologic cancers, and it represents potentially a novel, selective anti-cancer agent for multiple indications. In this study, AKR1C3-dependent activation of 3424 was investigated in vitro using recombinant human AKR1C3. AKR1C3-dependent cytotoxicity of 3424 was determined in a wide range of human cancer cell lines with different AKR1C3 expression levels. In addition, anti-tumor activity of 3424 was also investigated in a broad panel of CDX and PDX models. AKR1C3-dependent activation of prodrug 3424 was evident by monitoring the decrease of 3424 and generation of the active form, 2660. Kinetic analysis indicated that AKR1C3 exhibited higher catalytic efficiency towards 3424 compared to the physiological substrates. There was a strong correlation between 3424 cytotoxic potency and AKR1C3 expression. The racemic mixture induced DNA cross-linking in a concentration dependent manner. Tumor growth inhibition of 3424 was shown to be better than or comparable to the standard of care chemotherapy at clinically achievable doses as a single agent in various CDX models with high expression of AKR1C3, including liver HepG2, lung H460, castration-resistant prostate VCaP, gastric SNU-16, and kidney A498 cancer cell lines. The excellent anti-tumor efficacy of 3424 was further demonstrated in PDX models which have high level of AKR1C3 expression, but not in a model with low level of AKR1C3 expression. In the combination therapy, we showed that 3424 could enhance the efficacy of the standard care of chemotherapy in the CDX models. The results described here highlight that 3424 exhibits AKR1C3-dependent cytotoxicity in vitro and anti-tumor activity in vivo in a wide range of human cancer types, which support further development of 3424 as an anti-cancer agent for treating different types of cancers and the use of AKR1C3 as a biomarker to profile cancer patients and further guide patient selection for therapy with 3424.

Preclinical Studies of OBI-999: A Novel Globo H-Targeting Antibody-Drug Conjugate.

Globo H (GH), a hexasaccharide, is expressed at low levels in normal tissues but is highly expressed in multiple cancer types, rendering it a promising target for cancer immunotherapy. OBI-999, a novel antibody-drug conjugate, is derived from a conjugation of a GH-specific mAb with a monomethyl auristatin E (MMAE) payload through a site-specific ThioBridge and a cleavable linker. OBI-999 high homogeneity with a drug-to-antibody ratio of 4 (>95%) was achieved using ThioBridge. OBI-999 displayed GH-dependent cellular internalization and trafficked to endosome and lysosome within 1 and 5 hours, respectively. Furthermore, OBI-999 showed low nanomolar cytotoxicity in the assay with high GH expression on tumor cells and exhibited a bystander killing effect on tumor cells with minimal GH expression. Tissue distribution indicated that OBI-999 and free MMAE gradually accumulated in the tumor, reaching maximum level at 168 hours after treatment, whereas OBI-999 and free MMAE decreased quickly at 4 hours after treatment in normal organs. Maximum MMAE level in the tumor was 16-fold higher than in serum, suggesting that OBI-999 is stable during circulation and MMAE is selectively released in the tumor. Excellent tumor growth inhibition of OBI-999 was demonstrated in breast, gastric, and pancreatic cancer xenograft or lung patient-derived xenograft models in a dose-dependent manner. The highest nonseverely toxic dose in cynomolgus monkeys is 10 mg/kg determined by a 3-week repeated-dose toxicology study demonstrating an acceptable safety margin. Taken together, these results support further clinical development of OBI-999, which is currently in a phase I/II clinical study in multiple solid tumors (NCT04084366). OBI-999, the first GH-targeting ADC, displayed excellent tumor inhibition in animal models across multiple cancer types, including breast, gastric, pancreatic, and lung cancers, warranting further investigation in the treatment of solid tumors.

OBI-3424, a Novel AKR1C3-Activated Prodrug, Exhibits Potent Efficacy against Preclinical Models of T-ALL.

PURPOSE: OBI-3424 is a highly selective prodrug that is converted by aldo-keto reductase family 1 member C3 (AKR1C3) to a potent DNA-alkylating agent. OBI-3424 has entered clinical testing for hepatocellular carcinoma and castrate-resistant prostate cancer, and it represents a potentially novel treatment for acute lymphoblastic leukemia (ALL). EXPERIMENTAL DESIGN: We assessed AKR1C3 expression by RNA-Seq and immunoblotting, and evaluated the in vitro cytotoxicity of OBI-3424. We investigated the pharmacokinetics of OBI-3424 in mice and nonhuman primates, and assessed the in vivo efficacy of OBI-3424 against a large panel of patient-derived xenografts (PDX). RESULTS: AKR1C3 mRNA expression was significantly higher in primary T-lineage ALL (T-ALL; n = 264) than B-lineage ALL (B-ALL; n = 1,740; P < 0.0001), and OBI-3424 exerted potent cytotoxicity against T-ALL cell lines and PDXs. In vivo, OBI-3424 significantly prolonged the event-free survival (EFS) of nine of nine ALL PDXs by 17.1-77.8 days (treated/control values 2.5-14.0), and disease regression was observed in eight of nine PDXs. A significant reduction (P < 0.0001) in bone marrow infiltration at day 28 was observed in four of six evaluable T-ALL PDXs. The importance of AKR1C3 in the in vivo response to OBI-3424 was verified using a B-ALL PDX that had been lentivirally transduced to stably overexpress AKR1C3. OBI-3424 combined with nelarabine resulted in prolongation of mouse EFS compared with each single agent alone in two T-ALL PDXs. CONCLUSIONS: OBI-3424 exerted profound in vivo efficacy against T-ALL PDXs derived predominantly from aggressive and fatal disease, and therefore may represent a novel treatment for aggressive and chemoresistant T-ALL in an AKR1C3 biomarker-driven clinical trial.

Analysis of the pharmacokinetics and metabolism of aloe-emodin following intravenous and oral administrations in rats.

Aloe-emodin, a natural polyphenolic anthraquinone, has shown various beneficial bioactivities in vitro. The aim of this study was to investigate the pharmacokinetics and metabolism of aloe-emodin. Aloe-emodin was intravenously and orally administered to rats. The concentrations of aloe-emodin and rhein, a metabolite of aloe-emodin, were determined by HPLC method prior to and after hydrolysis with ß-glucuronidase and sulfatase/ß-glucuronidase. The results showed that the systemic exposures of aloe-emodin and its metabolites were ranked as aloe-emodin glucuronides (G) > rhein sulfates (S) > aloe-emodin > rhein and rhein G when aloe-emodin was given intravenously. In contrast, when aloe-emodin was administered orally, the parent form of aloe-emodin was not absorbed per se, and the systemic exposures of its metabolites were ranked as aloe-emodin G > rhein G > rhein. In conclusion, the metabolites of aloe-emodin are more important than the parent form for the bioactivities in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Increased Systemic Exposure of Methotrexate by a Polyphenol-Rich Herb via Modulation on Efflux Transporters Multidrug Resistance-Associated Protein 2 and Breast Cancer Resistance Protein.

Scutellariae radix (SR, roots of Scutellaria baicalensis Georgi), a popular Chinese medicine, contains plenty of flavonoids such as baicalin, wogonoside, baicalein, and wogonin. Methotrexate (MTX), an important immunosuppressant with a narrow therapeutic index, is a substrate of multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP). This study investigated the effect of SR on MTX pharmacokinetics and the underlying mechanisms. Rats were orally administered MTX alone and with 1.0 or 2.0 g/kg of SR. The serum concentrations of MTX were determined by a fluorescence polarization immunoassay. Cell models were used to explore the involvement of MRP2 and BCRP in the interaction. The results showed that 1.0 g/kg of SR significantly increased Cmax, AUC(0-30), AUC(0-2880), and mean residence time (MRT) of MTX by 50%, 45%, 501%, and 347%, respectively, and 2.0 g/kg of SR significantly enhanced the AUC(0-2880) and MRT by 242% and 293%, respectively, but decreased AUC(0-30) by 41%. Cell line studies indicated that SR activated the BCRP-mediated efflux transport, whereas the serum metabolites of SR inhibited both the BCRP- and MRP2-mediated efflux transports. In conclusion, SR ingestion increased the systemic exposure and MRT of MTX via modulation on MRP2 and BCRP.

Rhubarb decreased the systemic exposure of cyclosporine, a probe substrate of P-glycoprotein and CYP 3A.

1. Rhubarb, rhizome of Rheum palmatum L. (RP), is an important herb in clinical Chinese medicine. 2. Cyclosporine (CSP) is an immunosuppressant with narrow therapeutic window. The oral bioavailability of CSP was associated with P-glycoprotein (P-gp) and CYP 3A4. CSP was used as a probe substrate to investigate the in vivo modulation effects of RP on P-gp and CYP 3A. 3. Rats were orally administered 2.5 mg/kg of CSP with and without 0.25 and 1.0 g/kg of RP. The blood CSP concentration was determined by a specific monoclonal fluorescence polarization immunoassay. 4. Both dosages of RP significantly decreased the Cmax and AUC0-t of CSP in rats. Mechanism studies indicated that RP activated the functions of P-gp and CYP 3A. 5. RP ingestion reduced the systemic exposure of CSP through activating P-gp and CYP 3A.

Interaction of rhubarb and methotrexate in rats: in vivo and ex vivo approaches.

Rhubarb, the rhizome of Rheum palmatum L. (RP), is a popular herb used in Chinese medicine prescriptions. RP contains a variety of polyphenolic anthraquinones, such as aloe-emodin, rhein, emodin and chrysophanol. Our previous study found that the anthraquinones in RP existed predominantly as glucuronides/sulfates in the bloodstream, which were putative substrates of MRPs. Methotrexate (MTX) is a widely used immunosuppressant and anticancer agent, but it has a narrow therapeutic index. The transcellular transport of MTX is mediated by multidrug resistance associated proteins (MRPs). This study investigated the effects of coadministration of RP on MTX pharmacokinetics in rats. The possible involvement of MRP 2 was verified by using cell models and various typical MRP 2 substrates. The results showed that coadministration of 0.5 mg/kg of RP significantly increased the AUC 0-t and MRT of MTX by 307% and 364%, and 1.0 g/kg of RP significantly increased the AUC 0-t and MRT of MTX by 602% and 419%, respectively. Cell line studies indicated that the activity of MRP 2 was inhibited by the metabolites of RP and rhein. In conclusion, concomitant administration of RP markedly increased the systemic exposure of MTX via inhibiting MRP 2-mediated excretion.

Potential risk of mulberry-drug interaction: modulation on P-glycoprotein and cytochrome P450 3A.

Mulberry is a fruit containing polyphenol antioxidants. Cyclosporine (CSP), a potent immunosuppressant with a narrow therapeutic range, is widely used in transplant patients. This study investigated the effect of co-administration of mulberry on the bioavailability of CSP, a probe drug of P-glycoprotein (P-gp)/cytochrome P450 3A4 (CYP 3A4), in rats and relevant mechanisms. CSP (2.5 mg/kg) was orally administered with and without a single dose or the seventh dose of mulberry (2 g/kg) to rats. The results showed that a single dose of mulberry significantly decreased the area under the curve of concentration (AUC(0-540)) and the maximum blood concentration (Cmax) of CSP by 53.2 and 65.8%, respectively. Repeated dosing of mulberry significantly decreased the AUC(0-540) and Cmax of CSP by 23.7 and 39.7%, respectively. Mechanism studies indicated that mulberry significantly increased the activities of P-gp and CYP 3A. In conclusion, mulberry significantly reduced the bioavailability of CSP through activating the functions of P-gp and CYP 3A.

Pharmacokinetics and Relative Bioavailability of Flavonoids between Two Dosage Forms of Gegen-Qinlian-Tang in Rats.

Gegen-Qinlian-Tang (GQT), a popular Chinese medicine prescription, consists of Puerariae Radix, Scutellariae Radix, Coptidis Rhizoma, and Glycyrrhizae Radix. This study investigated the pharmacokinetics of GQT in rats and compared the bioavailability between two dosage forms, that is, traditional decoction (TD) and concentrated powder (CP). Rats were given TD and CP of GQT in a crossover design, and blood samples were withdrawn at predetermined time points. The quantitation methods of ten constituents in two dosage forms of GQT and in serum specimen using HPLC were developed and validated in this study. The pharmacokinetic parameters were calculated using noncompartment model. The results showed that daidzein, baicalein, wogonin, berberine, palmatine, and coptisine were not found in the circulation, whereas the sulfates/glucuronides of daidzein, baicalein, and wogonin were the major forms after oral administration of GQT. Comparison between two dosage forms indicated that the AUC(0-t) of daidzein sulfates/glucuronides after administration of CP was significantly lower than that of TD by 28.9%, whereas the bioavailabilities of baicalin/baicalein and wogonoside/wogonin were comparable between two dosage forms. In conclusion, the major flavonoids of GQT were extensively metabolized into sulfates/glucuronides and present as the major molecules in the circulation. TD of GQT revealed higher bioavailability of daidzin/daidzein than CP.

Steady-state pharmacokinetics and tissue distribution of anthraquinones of Rhei Rhizoma in rats.

AIM OF THE STUDY: Rhei Rhizoma, the rhizome of Rheum palmatum L. (RP), is a popular herb in clinical Chinese medicine. RP is abundant in polyphenolic anthraquinones, which have been reported to show various beneficial bioactivities. This study investigated the pharmacokinetics and tissue distribution of anthraquinones following seven-dose administration of RP decoction to rats. MATERIALS AND METHODS: Six Sprague-Dawley rats were given 2.0 g/kg of RP twice daily for seven doses and blood samples were collected at designated time after the 7th dose. Another six rats were sacrificed at 30 min after the 7th dose and organs including liver, kidney, lung and brain were collected. Serum and tissue specimens were assayed by HPLC before and after hydrolysis with ß-glucuronidase and sulfatase, respectively. RESULTS: Pharmacokinetic analysis indicated that the anthraquinones in serum mainly presented as glucuronides/sulfates and contained higher ratio of sulfates when compared with single-dose administration of RP. Contrary to the finding in serum, tissue analysis discovered mainly free form of anthraquinone in most organs assayed, such as aloe-emodin and rhein in kidney, liver, lung; emodin in liver, lung; trace of chrysophanol in kidney and liver. In all brains, neither free forms nor their glucuronides/sulfates have been detected. CONCLUSIONS: The glucuronides/sulfates of anthraquinones were the major forms in bloodstream, whereas the free forms of most anthraquinones were predominant in kidney and liver.

Suppression on metastasis by rhubarb through modulation on MMP-2 and uPA in human A549 lung adenocarcinoma: an ex vivo approach.

AIM OF THE STUDY: The aim of this study is to determine and identify the possible molecular mechanisms of anti-cancer effect of rhubarb under the physiologically achievable concentrations by using an ex vivo approach. MATERIALS AND METHODS: Rats were orally administered rhubarb decoction and then serum metabolites were extracted, prepared and characterized to assay for the following in vitro study. The MTT assay, zymography analysis, wound healing assay, RT-PCR, and Western blot analysis were used to reveal molecular events of rhubarb metabolites in this study. Experimental metastasis model was used to investigate the in vivo anti-metastatic efficacy of rhubarb. RESULTS: Our results demonstrated that cell line mobility was strongly inhibited and the enzymatic activity of MMP-2 decreased following culture with the rhubarb serum metabolite in human lung adenocarcinoma A549 cells. Further experiments demonstrated that the downregulation of MMP-2 enzymatic activity act through both transcriptional and post-translational mechanisms. NF-κB/c-Jun and uPA were observed involving in the inhibition of MMP-2 transcription and post-translational modification, respectively, in A549 cells treated with rhubarb serum metabolite. Further animal experiments demonstrated a significant reduction in lung metastatic colonies in rhubarb-treated mice, suggesting that rhubarb contain enriched active components that block cancer metastasis. CONCLUSIONS: Our studies, both in vitro and in vivo, clearly demonstrated the anti-tumor effect of rhubarb in an experimental setting of achievable physiological concentrations and also provide possible molecular mechanisms of anti-metastatic mechanisms by rhubarb treatment.

Metabolism and pharmacokinetics of san-huang-xie-xin-tang, a polyphenol-rich chinese medicine formula, in rats and ex-vivo antioxidant activity.

San-Huang-Xie-Xin-Tang (SHXXT), a widely used Chinese herbal formula, consists of rhizomes of Rheum officinale, roots of Scutellaria baicalensis and rhizomes of Coptis chinesis. This study investigated the metabolism and pharmacokinetics of polyphenols in SHXXT, including baicalin, baicalein, wogonin, emodin, aloe-emodin, rhein and chrysophanol. The quantitation methods of SHXXT decoction and rat serum using high performance liquid chromatography were developed and validated in this study. After oral administration of SHXXT decoction to rats, the parent forms of various constituents and their conjugated metabolites in serum were determined before and after hydrolysis with ß-glucuronidase and sulfatase. The results showed that only free form of rhein can be quantitated, whereas the parent forms of coptisine, palmatine, berberine, baicalein, wogonin, emodin, aloe-emodin and chrysophanol were not detected in serum. The glucuronides of baicalein, wogonin, emodin, aloe-emodin, rhein and chrysophanol were the predominant forms in bloodstream. In order to evaluate the in vivo antioxidant activity of SHXXT, the serum metabolite of SHXXT was prepared, characterized and followed by evaluation of the effect on AAPH-induced hemolysis. The results indicated that metabolites of SHXXT exhibited significant free radical scavenging activity. We suggest that biologists redirect their focus to the bioactivity of the conjugated metabolites of these polyphenols.

Potential ex vivo immunomodulatory effects of San-Huang-Xie-Xin-Tang and its component herbs on mice and humans.

AIM OF THE STUDY: San-Huang-Xie-Xin-Tang (SHXXT), an important Chinese medicine formula, contains Rhei Rhizoma (RR), Scutellariae Radix (SR) and Coptidis Rhizoma (CR). RR and SR are abundant in anthraquinone and flavonoid polyphenols. Pharmacokinetic study of SHXXT indicated that glucuronides were the predominant forms of polyphenols in rats. MATERIALS AND METHODS: As an extension of pharmacokinetic study, the serum metabolites of SHXXT, RR, SR and CR were prepared from rats and quantitated, then the immunomodulation effects were examined by culturing these serum metabolites with murine and human immune cells. RESULTS: The results indicated that the inhibitions on nitric oxide (NO) and cytokine production from mitogen-activated peritoneal macrophages by the serum metabolites of SHXXT, RR, SR and CR were through reducing the protein expression of inducible NO synthase (iNOS) and the IC(50) were 0.8%, 1.5%, 3.0% and 0.8% of their blood concentrations, respectively. In addition, the serum metabolites of SHXXT, RR, SR and CR significantly decreased the ratios of interferon-gamma (IFN-gamma) to interleukin (IL)-4 in mitogen-stimulated mice spleen cells and human peripheral blood mononuclear cells (PBMCs). Moreover, the serum metabolites of SHXXT and SR significantly arrested the mitogen-stimulated mice spleen cells at G2/M stage. CONCLUSIONS: In conclusion, the serum metabolites of SHXXT and the component herbs exerted promising modulation activities on the immune functions and the cell cycle distribution of mice and human immune cells. We suggest that SHXXT is a promising remedy for immunomodulation through Th1/Th2 regulation.

Differences in pharmacokinetics and ex vivo antioxidant activity following intravenous and oral administrations of emodin to rats.

Emodin, a natural anthraquinone polyphenol, has been reported to possess promising in vitro antioxidation, anticancer and anti-inflammatory activities. Whether the in vitro bioactivities can predict in vivo effects remained an unanswered question without understanding emodin pharmacokinetics in animals. To fill this blank, this study investigated the biological fate of emodin in rats. Emodin was intravenously (5.0 mg/kg) and orally (20.0 and 40.0 mg/kg) administered to rats. Blood samples were assayed by HPLC before and after hydrolysis with sulfatase and beta-glucuronidase. It is observed that after intravenous bolus of emodin, the parent form of emodin declined rapidly, and emodin glucuronides, omega-hydroxyemodin (omega-OHE) and omega-OHE sulfates/glucuronides all emerged instantaneously. In contrast, when emodin was given orally, emodin glucuronides were exclusively present in serum, whereas emodin, omega-OHE and omega-OHE sulfates/glucuronides were not detected. In order to evaluate the in vivo antioxidation activity, the serum metabolites of emodin following intravenous and oral administrations were prepared from rats and characterized, followed by investigating the effects on 2,2'-azobis(2-amidinopropane hydrochloride)-induced hemolysis. The results suggested that the serum metabolites of oral emodin exhibited more promising free radical scavenging activity than those of intravenous emodin and emodin parent form. We suggest biologists to redirect their targets to emodin glucuronide.

Metabolism and pharmacokinetics of anthraquinones in Rheum palmatum in rats and ex vivo antioxidant activity.

Anthraquinones are a major group of polyphenols in the rhizome of Rheum palmatum L. (RP). This study investigated the metabolism and pharmacokinetics of anthraqinones in RP decoction in rats. The concentrations of four anthraquinones including aloe-emodin, rhein, emodin, chrysophanol, and their glycosides in the decoction were quantitated by HPLC before and after acid hydrolysis with the results indicating that the anthraquinones mainly existed as the glycoside form except for rhein. Rats were orally administered RP decoction and blood samples were assayed by HPLC before and after treatments with sulfatase and beta-glucuronidase. It was found that the glucuronides of aloe-emodin, rhein, emodin and chrysophanol were predominant in the blood, whereas their aglycones were not detected except for rhein. In conclusion, the anthraquinones were subject to a rapid and extensive conjugation metabolism in rats and the serum metabolites of RP exhibited a potential free radical scavenging effect on AAPH-induced hemolysis at pharmacologically relevant concentrations.

Metabolism and pharmacokinetics of 3,3',4',7-tetrahydroxyflavone (fisetin), 5-hydroxyflavone, and 7-hydroxyflavone and antihemolysis effects of fisetin and its serum metabolites.

3,3',4',7-Tetrahydroxyflavone (fisetin) has shown various beneficial bioactivities. This study investigated the metabolism and pharmacokinetics of fisetin, 5-hydroxyflavone (5-OH-flavone), and 7-hydroxyflavone (7-OH-flavone) in male Sprague-Dawley rats. Blood was withdrawn via cardiopuncture and assayed by HPLC before and after hydrolysis with sulfatase and beta-glucuronidase. The results indicated that after intravenous administration of fisetin (10 mg/kg of bw), fisetin declined rapidly and fisetin sulfates/glucuronides emerged instantaneously. When fisetin (50 mg/kg of bw) was given orally, fisetin parent form was transiently present in serum only during the absorption phase, whereas fisetin sulfates/glucuronides predominated. The serum metabolites of fisetin showed less potent inhibition on 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced hemolysis than fisetin. Following oral administrations of 40 mg/kg of bw of 5-OH-flavone and 7-OH-flavone, the glucuronide of 5-OH-flavone and the sulfate/glucuronide of 7-OH-flavone were found in serum, whereas no traces of parent forms were detected. In conclusion, fisetin and 7-OH-flavone were rapidly and extensively biotransformed into their sulfate/glucuronide, whereas 5-OH-flavone was exclusively metabolized to glucuronide.