SLCO1B1 Genetic Variation Influence on Atorvastatin Systemic Exposure in Pediatric Hypercholesterolemia

This clinical study examined the influence of SLCO1B1 c.521T>C (rs4149056) on plasma atorvastatin concentrations in pediatric hypercholesterolemia. The participants (8-21 years), including heterozygous (c.521T/C, n = 13), homozygous (c.521C/C, n = 2) and controls (c.521T/T, n = 13), completed a single-oral-dose pharmacokinetic study. Similar to in adults, the atorvastatin (AVA) area-under-concentration-time curve from 0 to 24 h (AUC0-24) was 1.7-fold and 2.8-fold higher in participants with c.521T/C and c.521C/C compared to the c.521T/T participants, respectively. The inter-individual variability in AVA exposure within these genotype groups ranged from 2.3 to 4.8-fold, indicating that additional factors contribute to the inter-individual variability in the AVA dose-exposure relationship. A multivariate model reinforced the SLCO1B1 c.521T>C variant as the central factor contributing to AVA systemic exposure in this pediatric cohort, accounting for ~65% of the variability in AVA AUC0-24. Furthermore, lower AVA lactone concentrations in participants with increased body mass index contributed to higher exposure within the c.521T/T and c.521T/C genotype groups. Collectively, these factors contributing to higher systemic exposure could increase the risk of toxicity and should be accounted for when individualizing the dosing of atorvastatin in eligible pediatric patients.

Clinical and Biomarker Results from Phase I/II Study of PI3K Inhibitor Alpelisib plus Nab-paclitaxel in HER2-Negative Metastatic Breast Cancer

PURPOSE

PIK3CA mutations are common in breast cancer and promote tumor progression and treatment resistance. We conducted a phase I/II trial of alpelisib (α-specific PI3K inhibitor) plus nab-paclitaxel in patients with HER2-negative metastatic breast cancer (MBC).

PATIENTS AND METHODS

Eligible patients had HER2-negative MBC with any number of prior chemotherapies. Phase I was 3+3 dose-escalation design with three dose levels of alpelisib (250, 300, and 350 mg) daily plus nab-paclitaxel 100 mg/m2 administered on days 1, 8, and 15 every 28 days. Phase II was according to Simon's two-stage design. PIK3CA mutations in tumor/circulating tumor DNA (ctDNA) were assessed. Primary endpoints were recommended phase II dose (RP2D) and objective response rate (ORR). Additional endpoints included safety, pharmacokinetics, progression-free survival (PFS), and association of PIK3CA mutation with outcomes.

RESULTS

A total of 43 patients were enrolled (phase I, n = 13 and phase II, n = 30). A total of 84% had visceral disease and 84% had prior taxane. No dose-limiting toxicities occurred in phase I. RP2D was alpelisib 350 mg daily plus nab-paclitaxel 100 mg/m2 on days 1, 8, and 15. Hyperglycemia (grade 3, 26% and grade 4, 0%), neutropenia (grade 3, 23% and grade 4, 7%), diarrhea (grade 3, 5% and grade 4, 0%), and rash (grade 3, 7% and grade 4, 0%) were the most common adverse events. Among 42 evaluable patients, ORR was 59% (complete response, 7% and partial response, 52%), 21% of whom had response lasting >12 months; median PFS was 8.7 months. A total of 40% of patients demonstrated tumor and/or ctDNA PIK3CA mutation; patients with tumor/ctDNA mutation demonstrated better PFS compared with those without mutation (11.9 vs. 7.5 months; HR, 0.44; P = 0.027). Patients with normal metabolic status had longer PFS compared with prediabetic/diabetic patients (12 vs. 7.5 months; P = 0.014). No pharmacokinetics interactions were detected.

CONCLUSIONS

The alpelisib plus nab-paclitaxel combination was well tolerated and shows encouraging efficacy, especially in patients with PIK3CA-mutated tumor/ctDNA. The impact of metabolic status on response to this combination merits further investigation.

Romidepsin (HDACi) plus cisplatin and nivolumab triplet combination in patients with metastatic triple negative breast cancer (mTNBC)

1076

Background: Histone deacetylase inhibitors (HDACi) upregulate genes involved in antigen presentation machinery and increase expression of natural killer group 2, member D ligands (NKG2DL), thus resulting in enhanced tumor cell recognition and response to PD-1/CTLA-4 blockade. Cisplatin and HDACi combination synergistically induces cytotoxicity, apoptosis, and DNA damage. This phase I-II trial investigated combination of romidepsin (HDACi) plus cisplatin and nivolumab (PD-1 inhibitor) in mTNBC. Patients and Methods: Eligible patients had mTNBC with any number of prior chemotherapies. Phase I was 3+3 dose-escalation design with three dose levels of romidepsin (8, 10, 12mg/m2, D2, 9) plus cisplatin 75mg/m2 D 1 every 21 days. Phase II treatment included romidepsin plus cisplatin plus nivolumab 360mg every 21 days and was designed according to Simon’s two stage minimax design. Primary endpoints were recommended phase 2 dose (RP2D) and objective response rate (ORR). Additional endpoints included safety, PFS, and pharmacokinetics. Results: 51 patients were enrolled (N=13 phase I, N=38 phase II) between 2015-2020. 69% had received ≥1 prior metastatic chemotherapy, 47% had prior platinum, 53% had liver metastasis, 12% had BRCA1/2 mutation, and 11% had PD-L1 positive disease. There were no dose limiting toxicities in phase I. The RP2D was romidepsin 12mg/m2 D2,9 + cisplatin 75mg/m2 D1 + nivolumab 360mg D1 every 21 days. Thrombocytopenia (G3:27%, G4:0%), neutropenia (G3:25%, G4:0%), anemia (G3:22%, G4:0%), nausea (G3:22%, G4:0%), and vomiting (G3:20%, G4:0%) were the most common grade 3/4 adverse events. 21% of patients had immune AEs (G3-4:8%). Among 34 evaluable phase II patients, ORR was 44% (Table), median PFS was 4.4 months, and 1-year PFS was 23%. Median OS was 10.3 months and 1-year OS was 43%. No pharmacokinetic interactions were detected with co-administration of romidepsin-cisplatin-nivolumab. Conclusions: The triplet combination of romidepsin plus cisplatin and nivolumab was well tolerated and shows encouraging efficacy in pretreated mTNBC, including in patients with PD-L1 negative disease and in those with liver metastasis. Correlative biomarker work is ongoing. This combination warrants further evaluation in larger studies. Clinical trial information: NCT02393794 .[Table: see text]

Preclinical Pharmacokinetics of Fosciclopirox, a Novel Treatment of Urothelial Cancers, in Rats and Dogs

Pharmacokinetic studies in rats and dogs were performed to characterize the in vivo performance of a novel prodrug, fosciclopirox. Ciclopirox olamine (CPX-O) is a marketed topical antifungal agent with demonstrated in vitro and in vivo preclinical anticancer activity in several solid tumor and hematologic malignancies. The oral route of administration for CPX-O is not feasible due to low bioavailability and dose-limiting gastrointestinal toxicities. To enable parenteral administration, the phosphoryl-oxymethyl ester of ciclopirox (CPX), fosciclopirox (CPX-POM), was synthesized and formulated as an injectable drug product. In rats and dogs, intravenous CPX-POM is rapidly and completely metabolized to its active metabolite, CPX. The bioavailability of the active metabolite is complete following CPX-POM administration. CPX and its inactive metabolite, ciclopirox glucuronide (CPX-G), are excreted in urine, resulting in delivery of drug to the entire urinary tract. The absolute bioavailability of CPX following subcutaneous administration of CPX-POM is excellent in rats and dogs, demonstrating the feasibility of this route of administration. These studies confirmed the oral bioavailability of CPX-O is quite low in rats and dogs compared with intravenous CPX-POM. Given its broad-spectrum anticancer activity in several solid tumor and hematologic cancers and renal elimination, CPX-POM is being developed for the treatment of urothelial cancer. The safety, dose tolerance, pharmacokinetics, and pharmacodynamics of intravenous CPX-POM are currently being characterized in a United States multicenter first-in-human Phase 1 clinical trial in patients with advanced solid tumors (NCT03348514).

Abstract P6-11-08: Safety and efficacy results from phase I study of BYL 719 plus nab-paclitaxel in HER 2 negative metastatic breast cancer

Introduction

Mutations/deregulations in the phosphatidylinositol-3-kinase (PI3K) pathway are common in breast cancer, Inhibition of the PI3K pathway is recognized as a promising target for the treatment of breast cancer. Although taxanes are effective early on in advanced stage breast cancer, resistance often develops. It has been demonstrated that activation of the PI3K/AKT pathway confers resistance to paclitaxel, and in preclinical models, concomitant inhibition of the PI3K pathway enhances the efficacy of taxanes. BYL719 is a potent oral, class I PI3K inhibitor which strongly inhibits the PI3K alpha isoforms and is significantly less active against the other class I isoforms. Targeting the alpha isoform of PI3K is expected to improve the therapeutic window over inhibitors with less isoform specificity. Nab-Paclitaxel is a solvent-free, nanoparticle, albumin-based paclitaxel which takes advantage of the antitumor activity of paclitaxel while decreasing the toxicities typically associated with the solvent (Cremophor) used to administer the most common formulation of paclitaxel.

Methods

A 3+3 dose-escalation design evaluated three dose levels of BYL719 (250mg, 300mg, and 350mg) administered PO once daily (D1-28) with nab-Paclitaxel (100 mg/m2 intravenously D 1, 8, 15) every 28 days in patients with metastatic HER 2 negative breast cancer. The aims of the study were to 1) determine the recommended phase II dose (RPTD) of BYL719 + nab-Paclitaxel, 2) assess pharmacokinetics of BYL and nab-paclitaxel, and 3) assess preliminary efficacy.

Results

10 patients were enrolled at 3 dose levels of BYL719 and 3 patients were enrolled in expansion cohort at the RPTD of BYL719 of 350 mg PO daily plus nab-paclitaxel 100mg/m2 (D 1, 8, 15). Median age was 61years; 54% (7/13) of patients were hormone receptor positive and 46% (6/13) triple negative. 85% (11/13) had visceral disease, 69% (9/13) had received prior chemotherapy for metastatic disease and 85% (11/13) had received prior taxane in adjuvant/metastatic setting. There were no DLTs in the three cohorts and the MTD of BYL was not reached. Hyperglycemia (G3:31%, G4:0%) and neutropenia (G3:15%, G4:8%), were the most common grade 3/4 adverse events. There were no Grade 3/4 diarrhea or rash. Best overall response for 12 patients was 58% (7/12) (complete response=1, partial response=6), and an additional 33% (4/12) demonstrated stable disease. Objective responses were noted in both hormone positive and triple negative disease. Median duration of response is 6.5 months (range 2-14 months). No pharmacokinetic interactions were detected when BYL and nab-paclitaxel were co-administered.

Discussion:

This phase I study demonstrates that combination of BYL719 and nab-paclitaxel was well tolerated and shows encouraging efficacy in metastatic HER2 negative breast cancer. Enrollment in the phase II portion of the trial at the RPTD (BYL719 350mg PO daily plus nab-paclitaxel 100mg/m2 D1,8,15 every 28 days) continues. Ongoing analysis of PI3K pathway alterations in tumor and cfDNA will be correlated with clinical response.

Citation Format: Sharma P, Abramson VG, O'Dea A, Lewis S, Scott JN, Ward J, De Jong JA, Lehn C, Brown AR, Williamson SK, Perez RP, Komiya T, Godwin AK, Reed GA, Khan QJ. Safety and efficacy results from phase I study of BYL 719 plus nab-paclitaxel in HER 2 negative metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-11-08.

Stability of Drugs, Drug Candidates, and Metabolites in Blood and Plasma

Determination of drug or drug metabolite concentrations in biological samples, particularly in serum or plasma, is fundamental to describing the relationships between administered dose, route of administration, and time after dose for achieving the optimal clinical response. While a well-characterized, accurate analytical method is needed to define these parameters, it must also be established that the analyte concentration in the sample at the time of analysis is identical to the concentration at sample acquisition. This is necessitated by the fact that drugs and their metabolites are susceptible to degradation in samples due to metabolism or to physical and chemical processes, resulting in a lower measured concentration than was in the original sample. Careful examination of analyte stability during processing and storage and, if necessary, adjustment of procedures and conditions to maximize stability, are a critical component of method validation to ensure the accuracy of the data. The protocols provided in this unit address the stability of the analytes in whole blood and blood-derived samples prior to sample preparation for analysis. Issues addressed include sample acquisition, processing of whole blood, and storage of blood-derived samples. © 2016 by John Wiley & Sons, Inc.

A Phase 1 study of intravenous infusions of tigecycline in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) cells meet the higher energy, metabolic, and signaling demands of the cell by increasing mitochondrial biogenesis and mitochondrial protein translation. Blocking mitochondrial protein synthesis through genetic and chemical approaches kills human AML cells at all stages of development in vitro and in vivo. Tigecycline is an antimicrobial that we found inhibits mitochondrial protein synthesis in AML cells. Therefore, we conducted a phase 1 dose‐escalation study of tigecycline administered intravenously daily 5 of 7 days for 2 weeks to patients with AML. A total of 27 adult patients with relapsed and refractory AML were enrolled in this study with 42 cycles being administered over seven dose levels (50–350 mg/day). Two patients experienced DLTs related to tigecycline at the 350 mg/day level resulting in a maximal tolerated dose of tigecycline of 300 mg as a once daily infusion. Pharmacokinetic experiments showed that tigecycline had a markedly shorter half‐life in these patients than reported for noncancer patients. No significant pharmacodynamic changes or clinical responses were observed. Thus, we have defined the safety of once daily tigecycline in patients with refractory AML. Future studies should focus on schedules of the drug that permit more sustained target inhibition.

Tolerability and pharmacokinetics of oxaloacetate 100 mg capsules in Alzheimer's subjects

Bioenergetics and bioenergetic-related functions are altered in Alzheimer's disease (AD) subjects. These alterations represent therapeutic targets and provide an underlying rationale for modifying brain bioenergetics in AD-affected persons. Preclinical studies in cultured cells and mice found that administering oxaloacetate (OAA), a Krebs cycle and gluconeogenesis intermediate, enhanced bioenergetic fluxes and upregulated some brain bioenergetic infrastructure-related parameters. We therefore conducted a study to provide initial data on the tolerability and pharmacokinetics of OAA in AD subjects. Six AD subjects received OAA 100 mg capsules twice a day for one month. The intervention was well-tolerated. Blood level measurements following ingestion of a 100 mg OAA capsule showed modest increases in OAA concentrations, but pharmacokinetic analyses were complicated by relatively high amounts of endogenous OAA. We conclude that OAA 100 mg capsules twice per day for one month are safe in AD subjects but do not result in a consistent and clear increase in the OAA blood level, thus necessitating future clinical studies to evaluate higher doses.

H1-antihistamines exacerbate high-fat diet-induced hepatic steatosis in wild-type but not in apolipoprotein E knockout mice

We examined the effects of two over-the-counter H1-antihistamines on the progression of fatty liver disease in male C57Bl/6 wild-type and apolipoprotein E (ApoE)-/- mice. Mice were fed a high-fat diet (HFD) for 3 mo, together with administration of either cetirizine (4 mg/kg body wt) or fexofenadine (40 mg/kg body wt) in drinking water. Antihistamine treatments increased body weight gain, gonadal fat deposition, liver weight, and hepatic steatosis in wild-type mice but not in ApoE-/- mice. Lobular inflammation, acute inflammation, and necrosis were not affected by H1-antihistamines in either genotype. Serum biomarkers of liver injury tended to increase in antihistamine-treated wild-type mice. Serum level of glucose was increased by fexofenadine, whereas lipase was increased by cetirizine. H1-antihistamines reduced the mRNA expression of ApoE and carbohydrate response element-binding protein in wild-type mice, without altering the mRNA expression of sterol regulatory element-binding protein 1c, fatty acid synthase, or ApoB100, in either genotype. Fexofenadine increased both triglycerides and cholesterol ester, whereas cetirizine increased only cholesterol ester in liver, with a concomitant decrease in serum triglycerides by both antihistamines in wild-type mice. Antihistamines increased hepatic levels of conjugated bile acids in wild-type mice, with the effect being significant in fexofenadine-treated animals. The increase was associated with changes in the expression of organic anion transport polypeptide 1b2 and bile salt export pump. These results suggest that H1-antihistamines increase the progression of fatty liver disease in wild-type mice, and there seems to be an association between the severity of disease, presence of ApoE, and increase in hepatic bile acid levels.

Chronic ingestion of H1-antihistamines increase progression of atherosclerosis in apolipoprotein E-/- mice

Although increased serum histamine levels and H1R expression in the plaque are seen in atherosclerosis, it is not known whether H1R activation is a causative factor in the development of the disease, or is a host defense response to atherogenic signals. In order to elucidate how pharmacological inhibition of histamine receptor 1 (H1R) signaling affects atherogenesis, we administered either cetirizine (1 and 4 mg/kg. b.w) or fexofenadine (10 and 40 mg/kg. b.w) to ApoE^−/− mice maintained on a high fat diet for three months. Mice ingesting a low dose of cetirizine or fexofenadine had significantly higher plaque coverage in the aorta and cross-sectional lesion area at the aortic root. Surprisingly, the higher doses of cetirizine or fexofenadine did not enhance atherosclerotic lesion coverage over the controls. The low dose of fexofenadine, but not cetirizine, increased serum LDL cholesterol. Interestingly, the expression of iNOS and eNOS mRNA was increased in aortas of mice on high doses of cetirizine or fexofenadine. This may be a compensatory nitric oxide (NO)-mediated vasodilatory mechanism that accounts for the lack of increase in the progression of atherosclerosis. Although the administration of cetirizine did not alter blood pressure between the groups, there was a positive correlation between blood pressure and lesion/media ratio at the aortic root in mice receiving the low dose of cetirizine. However, this association was not observed in mice treated with the high dose of cetirizine or either doses of fexofenadine. The macrophages or T lymphocytes densities were not altered by low doses of H1-antihistamines, whereas, high doses decreased the number of macrophages but not T lymphocytes. The number of mast cells was decreased only in mice treated with low dose of fexofenadine. These results demonstrate that chronic ingestion of low therapeutic doses of cetirizine or fexofenadine enhance progression of atherosclerosis.

Oral ciclopirox olamine displays biological activity in a phase I study in patients with advanced hematologic malignancies

The antimycotic ciclopirox olamine is an intracellular iron chelator that has anticancer activity in vitro and in vivo. We developed an oral formulation of ciclopirox olamine and conducted the first-in-human phase I study of this drug in patients with relapsed or refractory hematologic malignancies (Trial registration ID: NCT00990587). Patients were treated with 5-80 mg/m² oral ciclopirox olamine once daily for five days in 21-day treatment cycles. Pharmacokinetic and pharmacodynamic companion studies were performed in a subset of patients. Following definition of the half-life of ciclopirox olamine, an additional cohort was enrolled and treated with 80 mg/m² ciclopirox olamine four times daily. Adverse events and clinical response were monitored throughout the trial. Twenty-three patients received study treatment. Ciclopirox was rapidly absorbed and cleared with a short half-life. Plasma concentrations of an inactive ciclopirox glucuronide metabolite were greater than those of ciclopirox. Repression of survivin expression was observed in peripheral blood cells isolated from patients treated once daily with ciclopirox olamine at doses greater than 10 mg/m², demonstrating biological activity of the drug. Dose-limiting gastrointestinal toxicities were observed in patients receiving 80 mg/m² four times daily, and no dose limiting toxicity was observed at 40 mg/m² once daily. Hematologic improvement was observed in two patients. Once-daily dosing of oral ciclopirox olamine was well tolerated in patients with relapsed or refractory hematologic malignancies, and further optimization of dosing regimens is warranted in this patient population.

Effects of menthol on the pharmacokinetics of bupropion among Black smokers

INTRODUCTION

Despite the widespread use of mentholated cigarettes, lower cessation rates, and disproportionately high smoking-related morbidity among Blacks, the possible role of menthol in smokers' response to pharmacotherapy has not been well-studied. This study examined the effects of menthol on the pharmacokinetic (PK) profiles of bupropion and its principal metabolites, hydroxybupropion, threohydrobupropion, and erythrohydrobupropion among Black smokers.

METHODS

After a 7-day placebo run-in period, participants received 150 mg bid sustained-release bupropion for 20-25 days. Blood samples were drawn for PK analysis on 2 occasions, 10-15 days after the commencement of bupropion while participants were still smoking (smoking phase) and at days 20-25 when they were asked not to smoke (nonsmoking phase).

RESULTS

18 smokers of nonmenthol cigarettes and 23 smokers of menthol cigarettes were enrolled in this study. No differences were found by menthol smoking status in the Cmax and area under the plasma concentration versus time curve (AUC) of bupropion and its metabolites in the smoking or nonsmoking phases. However, among menthol smokers, the AUC ratios of metabolite/bupropion were lower in the nonsmoking phase compared with the smoking phase (hydro/bup = 31.49 ± 18.84 vs. 22.95 ± 13.27, p = .04; erythro/bup = 1.99 ± 1.02 vs. 1.76 ± 0.75, p = .016; threo/bup = 11.77 ± 8.90 vs. 10.44 ± 5.63, p = .034). No significant differences were found in the metabolite/bup ratios between smoking and nonsmoking conditions among nonmenthol smokers.

CONCLUSIONS

We did not find a significant effect of menthol compared with nonmenthol cigarette smoking on the PKs of bupropion and metabolites at steady state. More research is needed to advance the understanding of mechanisms underlying disparities in smoking cessation outcomes related to smoking of menthol cigarettes.

Quantification of the transporter substrate fexofenadine in cell lysates by liquid chromatography/tandem mass spectrometry

Drug-drug interactions at transporters present a significant and under-investigated clinical problem. Investigations of specific transporter functions and screening for potential drug-drug interactions, both in vitro and especially in vivo, will require validated experimental probes. Fexofenadine, an approved, well-tolerated drug, is a promising probe for studies of membrane transporter function. Although fexofenadine pharmacokinetics are known to be controlled by transporters, the contributions of individual transporters have not been defined. We have developed a rapid, specific, and sensitive analytical method for quantitation of fexofenadine to support this work. This liquid chromatography/tandem mass spectrometry (LC/MS/MS) method quantifies fexofenadine in cell lysates from in vitro studies using cetirizine as the internal standard. Cell lysates were prepared for analysis by acetonitrile precipitation. Analytes were then separated by gradient reversed-phase chromatography and analyzed by tandem mass spectrometry using the m/z 502.17/466.2 transition for fexofenadine and m/z 389.02/201.1 for cetirizine. The method exhibited a linear dynamic range of 1-500 ng/mL for fexofenadine in cell lysates. The lower limit of quantification was 1 ng/mL with a relative standard deviation of less than 5%. Intra- and inter-day precision and accuracy were within the limits presented in the FDA guidelines for bioanalysis. We also will validate this method to support not only the quantification of fexofenadine, but also other probe drugs for drug-drug interaction studies. This method for quantification will facilitate the use of fexofenadine as a probe drug for characterization of transporter activity.

Buspirone, fexofenadine, and omeprazole: quantification of probe drugs and their metabolites in human plasma

Probe drugs are critical tools for the measurement of drug metabolism and transport activities in human subjects. Often several probe drugs are administered simultaneously in a "cocktail". This cocktail approach requires efficient analytical methods for the simultaneous quantitation of multiple analytes. We have developed and validated a liquid chromatography-tandem mass spectrometry method for the simultaneous determination of three probe drugs and their metabolites in human plasma. The analytes include omeprazole and its metabolites omeprazole sulfone and 5'-hydroxyomeprazole; buspirone and its metabolite 1-[2-pyrimidyl]-piperazine (1PP); and fexofenadine. These analytes and the internal standard lansoprazole were extracted from plasma using protein precipitation with acetonitrile. Gradient reverse-phase chromatography was performed with 7.5mM ammonium bicarbonate and acetonitrile, and the analytes were quantified in positive ion electrospray mode with multiple reaction monitoring. The method was validated to quantify the concentration ranges of 1.0-1000ng/ml for omeprazole, omeprazole sulfone, 5'-hydroxyomeprazole, and fexofenadine; 0.1-100ng/ml for buspirone, and 1.0-100ng/ml for 1PP. These linear ranges span the plasma concentrations for all of the analytes from probe drug studies. The intra-day precision was between 2.1 and 16.1%, and the accuracy ranged from 86 to 115% for all analytes. Inter-day precision and accuracy ranged from 0.3 to 14% and from 90 to 110%, respectively. The lower limits of quantification were 0.1ng/ml for buspirone and 1ng/ml for all other analytes. This method provides a fast, sensitive, and selective analytical tool for quantification of the six analytes in plasma necessary to support the use of this probe drug cocktail in clinical studies.

Dopamine receptor alterations in female rats with diet-induced decreased brain docosahexaenoic acid (DHA): interactions with reproductive status

Decreased tissue levels of n-3 (omega-3) fatty acids, particularly docosahexaenoic acid (DHA), are implicated in the etiologies of non-puerperal and postpartum depression. This study examined the effects of a diet-induced loss of brain DHA content and concurrent reproductive status on dopaminergic parameters in adult female Long-Evans rats. An alpha-linolenic acid-deficient diet and breeding protocols were used to produce virgin and parous female rats with cortical phospholipid DHA levels 20-22% lower than those fed a control diet containing adequate alpha-linolenic acid. Decreased brain DHA produced a significant main effect of decreased density of ventral striatal D(2)-like receptors. Virgin females with decreased DHA also exhibited higher density of D(1)-like receptors in the caudate nucleus than virgin females with normal DHA. These receptor alterations are similar to those found in several rodent models of depression, and are consistent with the proposed hypodopaminergic basis for anhedonia and motivational deficits in depression.

Abstract 2899: Multiple-dose phase 1 study of 3,3′-diindolylmethane (DIM): Pharmacokinetics and biological effects

We have completed our examination of the safety, tolerability, pharmacokinetics, and effects of twice daily doses of 100 mg and 200 mg of 3, 3’-diindolylmethane (DIM) for four weeks. Healthy adult subjects self-administered an absorption-enhanced formulation of DIM (BR-DIM). Eight subjects received the low dose, and six subjects received the high dose of BR-DIM. Based on medical histories, physical examinations and a battery of blood and urine tests we concluded that BR-DIM in this dosing regimen was very well tolerated, with no significant adverse effects. The pharmacokinetics of DIM were determined at each dose for both the first dose and last dose of BR-DIM in these subjects. The first dose Cmax and AUC values obtained for the two doses were similar to the results of our previous single ascending dose study of BR-DIM. Surprisingly, after four weeks of twice daily dosing, the mean Cmax of DIM fell by 29% and 73% and the mean AUC fell by 46% and 71% in the low and high dose groups, respectively. Multiple daily dosing with BR-DIM clearly altered expression either of specific transporters or of enzymes that biotransform DIM, resulting in a marked decrease in bioavailability. This decreased systemic exposure, however, must be considered in light of the observed induction of CYP1A2, one of our primary biomarkers of effect. Mean CYP1A2 activity increased by 250% at the low dose and by 181% at the high dose, suggesting that effective concentrations of DIM or an active metabolite were achieved in the liver, and that this resulted in induction of hepatic CYP1A2. No effects of BR-DIM were seen on activities of CYPs 2C9, 2D6, or 3A4. The lack of systemic exposure to DIM could result either from induced hepatic metabolism of DIM or from increased biliary secretion of DIM. This proposal for the altered pharmacokinetics of DIM, allowing hepatic effects but not extrahepatic effects, is consistent with the very modest effects of BR-DIM we observed on peripheral blood lymphocyte GST activity, and suggests that the lymphocyte activity may not be an accurate surrogate for hepatic effects of DIM. The lack of significant change in the 2-hydroxyestrone:16α-hydroxyestrone ratio, judged by us to be a key biomarker of efficacy in our previous trial with the DIM precursor indole-3-carbinol, raises the possibility that the change in that ratio is based to a significant extent on extrahepatic hydroxylation of estrone, rather than modulation of hepatic estrogen metabolism. Supported by NCI N01 CN-35008-38 and P20RR021940.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2899.

Design, recruitment, and retention of African-American smokers in a pharmacokinetic study

Background

African-Americans remain underrepresented in clinical research despite experiencing a higher burden of disease compared to all other ethnic groups in the United States. The purpose of this article is to describe the study design and discuss strategies used to recruit and retain African-American smokers in a pharmacokinetic study.

Methods

The parent study was designed to evaluate the differences in the steady-state concentrations of bupropion and its three principal metabolites between African-American menthol and non-menthol cigarette smokers. Study participation consisted of four visits at a General Clinical Research Center (GCRC) over six weeks. After meeting telephone eligibility requirements, phone-eligible participants underwent additional screening during the first two GCRC visits. The last two visits (pharmacokinetic study phase) required repeated blood draws using an intravenous catheter over the course of 12 hours.

Results

Five hundred and fifteen African-American smokers completed telephone screening; 187 were phone-eligible and 92 were scheduled for the first GCRC visit. Of the 81 who attended the first visit, 48 individuals were enrolled in the pharmacokinetic study, and a total of 40 individuals completed the study (83% retention rate).

Conclusions

Although recruitment of African-American smokers into a non-treatment, pharmacokinetic study poses challenges, retention is feasible. The results provide valuable information for investigators embarking on non-treatment laboratory-based studies among minority populations.

Single-dose pharmacokinetics and tolerability of absorption-enhanced 3,3'-diindolylmethane in healthy subjects

We have completed a single ascending dose clinical study of the proposed chemopreventive agent 3,3'-diindolylmethane (DIM). The study agent was nutritional-grade, absorption-enhanced BioResponse 3,3'-diindolylmethane (BR-DIM). We determined the safety, tolerability, and pharmacokinetics of single doses of BR-DIM in drug-free, non-smoking, healthy men and women. Groups of four subjects were enrolled for each dose level. After randomization, one subject in each group received placebo whereas three received active BR-DIM. The doses administered were 50, 100, 150, 200, and 300 mg, with the 300-mg dose repeated in an additional group. No BR-DIM-related adverse effects were reported at doses up to 200 mg. At the 300-mg dose, one of six subjects reported mild nausea and headache and one also reported vomiting. Only the latter effect was judged as probably related to the study agent. Analysis of serial plasma samples showed that only one subject at the 50-mg dose had detectable concentrations of DIM. The single 100-mg dose of BR-DIM resulted in a mean maximum plasma concentration (C(max)) of 32 ng/mL and a mean area under the curve (AUC) of 128 h ng/mL, and a single 200-mg dose produced a mean C(max) of 104 ng/mL and a mean AUC of 553 h ng/mL. The single 300-mg dose of BR-DIM resulted in a mean C(max) of 108 ng/mL and a mean AUC of 532 h ng/mL. We conclude that BR-DIM is well tolerated at single doses of up to 200 mg, and that increasing the dose to 300 mg did not result in an increase in C(max).

Decreased brain docosahexaenoic acid content produces neurobiological effects associated with depression: Interactions with reproductive status in female rats

Decreased tissue levels of docosahexaenoic acid (DHA; 22:6n-3) are implicated in the etiologies of non-puerperal and postpartum depression. With the aim of determining neurobiological sequelae of decreased brain DHA content, this study examined the effects of a loss of brain DHA content and concurrent reproductive status in adult female Long-Evans rats. An alpha-linolenic acid-deficient diet and breeding protocols were used to produce virgin and parous female rats with cortical phospholipid DHA levels 23-26% lower than virgin and parous rats fed a control diet containing adequate alpha-linolenic acid. Parous dams were tested/euthanized at weaning (postnatal day 20) of the second litter; virgin females, during diestrus. Decreased brain DHA was associated with decreased hippocampal BDNF gene expression and increased relative corticosterone response to an intense stressor, regardless of reproductive status. In virgin females with decreased brain DHA, serotonin content and turnover in frontal cortex were decreased compared to virgin females with normal brain DHA. In parous dams with decreased brain DHA, the density of 5-HT(1A) receptors in the hippocampus was increased, corticosterone response to an intense stressor was increased, and the latency to immobility in the forced swim test was decreased compared to parous dams with normal DHA. These findings demonstrate neurobiological alterations attributable to decreased brain DHA or an interaction of parous status and brain DHA level. Furthermore, the data are consistent with findings in depressed humans, and thus support a role for DHA as a factor in the etiologies of depressive illnesses, particularly postpartum depression.

Single-Dose and Multiple-Dose Administration of Indole-3-Carbinol to Women: Pharmacokinetics Based on 3,3′-Diindolylmethane

We have completed a phase I trial in women of the proposed chemopreventive natural product indole-3-carbinol (I3C). Women received oral doses of 400, 600, 800, 1,000, and 1,200 mg I3C. Serial plasma samples were analyzed by high-performance liquid chromatography-mass spectrometry for I3C and several of its condensation products. I3C itself was not detectable in plasma. The only detectable I3C-derived product was 3,3'-diindolylmethane (DIM). Mean Cmax for DIM increased from 61 ng/mL at the 400-mg I3C dose to 607 ng/mL following a 1,000-mg dose. No further increase was observed following a 1,200-mg dose. A similar result was obtained for the area under the curve, which increased from 329 h ng/mL at the 400-mg dose to 3,376 h ng/mL after a 1,000-mg dose of I3C. Significant interindividual quantitative variation was seen in plasma DIM values within each dosing group, but the overall profiles were qualitatively similar, with no quantifiable DIM before dosing, tmax at approximately 2 h, and DIM levels near or below 15 ng/mL (the limit of quantitation), by 24 h. Different results were obtained for 14 subjects who received a 400-mg dose of I3C after 8 weeks of twice-daily I3C dosing. Although the predose sampling occurred at least 12 h after the last known ingestion of I3C, 6 of 14 subjects exhibited Cmax for DIM in their predose plasma. Despite this high initial value, plasma DIM for all subjects decreased to near or below the limit of quantitation within the 12-h sampling period. Possible reasons for this disparity between apparent t1/2 of DIM and the high predose values are discussed.

A phase I study of indole-3-carbinol in women: tolerability and effects

We completed a phase I trial of indole-3-carbinol (I3C) in 17 women (1 postmenopausal and 16 premenopausal) from a high-risk breast cancer cohort. After a 4-week placebo run-in period, subjects ingested 400 mg I3C daily for 4 weeks followed by a 4-week period of 800 mg I3C daily. These chronic doses were tolerated well by all subjects. Hormonal variables were measured near the end of the placebo and dosing periods, including determination of the urinary 2-hydroxyestrone/16alpha-hydroxyestrone ratio. Measurements were made during the follicular phase for premenopausal women. Serum estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, and sex hormone binding globulin showed no significant changes in response to I3C. Caffeine was used to probe for cytochrome P450 1A2 (CYP1A2), N-acetyltransferase-2 (NAT-2), and xanthine oxidase. Comparing the results from the placebo and the 800 mg daily dose period, CYP1A2 was elevated by I3C in 94% of the subjects, with a mean increase of 4.1-fold. In subjects with high NAT-2 activities, these were decreased to 11% by I3C administration but not altered if NAT-2 activity was initially low. Xanthine oxidase was not affected. Lymphocyte glutathione S-transferase activity was increased by 69% in response to I3C. The apparent induction of CYP1A2 was mirrored by a 66% increase in the urinary 2-hydroxyestrone/16alpha-hydroxyestrone ratio in response to I3C. The maximal increase was observed with the 400 mg daily dose of I3C, with no further increase found at 800 mg daily. If the ratio of hydroxylated estrone metabolites is a biomarker for chemoprevention, as suggested, then 400 mg I3C daily will elicit a maximal protective effect.

Predominant 4-hydroxylation of estradiol by constitutive cytochrome P450s in the female ACI rat liver

The ACI rat is extremely sensitive to estrogens as mammary carcinogens, whereas the Sprague-Dawley strain is relatively resistant. Comparison of the disposition and effects of estrogens in these two strains should provide insights into the mechanisms of estrogen carcinogenicity. We have begun this investigation by comparing the metabolism of [(3)H]17beta-estradiol (E2) by liver microsomes prepared from female rats from each strain. Both strains produce estrone (E1) as the major product at E2 concentrations >1 microM, with smaller amounts of 2-hydroxy-E2 formed. As the E2 concentration is decreased, however, aromatic hydroxylation becomes a more dominant pathway for both strains. At starting E2 concentrations as low as 3 nM, Sprague-Dawley liver microsomes produced comparable yields of 2-hydroxy-E2 and E1. In contrast, ACI liver microsomes yielded a profound shift to aromatic hydroxylation as the dominant pathway as E2 concentrations dropped below 1 microM, and this shift reflected the production of 4-hydroxy-E2 as the predominant product. The apparent K(m) for 4-hydroxylation of E2 is <0.8 microM, as opposed to approximately 4 microM for 2-hydroxylation, suggesting that different cytochrome P450s (CYPs) are responsible. Western immunoblotting of the liver microsomal preparations from ACI and Sprague-Dawley rats for CYPs known to catalyze 2- and 4-hydroxylation of E2 revealed that both strains contained comparable amounts of CYP 2B1/2 and 3A1/2, but no detectable amounts of CYP 1B1, the proposed E2 4-hydroxylase. Although this enzyme is not a constitutive CYP in Sprague-Dawley rat liver, its presence in ACI liver could provide a ready explanation for the predominance of 4-hydroxy-E2 as a product. The identity of the estradiol 4-hydroxylase in ACI rat liver and the role of this unique reaction in the heightened sensitivity to E2 carcinogenicity remain to be elucidated.

Metabolic and genotoxic interactions of 2-aminofluorene and 2,4-diaminotoluene

We have reported previously that the rodent carcinogen 2,4-diaminotoluene (2,4-DAT) is not activated as a mutagen to the standard Ames S. typhimurium tester strains when oxidized by prostaglandin H synthase (PHS). 2,4-DAT does, however, enhance the bacterial mutagenicity of the potent mutagen 2-aminofluorene (2-AF) when both compounds are incubated with the PHS activating system. Enhancement of activation of 2-AF would provide a plausible mechanism for the observed co-mutagenicity of 2,4-DAT. Co-incubation with 100 microM 2,4-DAT, however, inhibited the total metabolism of 25 microM 2-AF by 60% in both the PHS/H2O2 system and PHS/arachidonic acid system. The inhibition included a 75% decrease in the formation of water-soluble and protein-bound metabolites and about a 35% decrease in production of the peroxidative metabolites 2-nitrofluorene (NF) and 2-aminodifluorenylamine (ADFA). Azofluorene (AzF) production was the most sensitive to the effects of 2,4-DAT, exhibiting an 80% decrease in both PHS-catalyzed systems. No new 2-AF derived products were observed in the presence of 2,4-DAT. This pronounced inhibition of 2-AF metabolism by 2,4-DAT also was observed in incubations of the aromatic amines with PHS in the presence of S. typhimurium strain TA98. Bacterial N-acetylation of 2-AF did not appear to be an important reaction in any of these incubations. 2,4-DAT not only inhibited 2-AF metabolism by PHS, but also decreased the level of 2-AF covalent binding to the bacterial DNA by as much as 81%. This stands in sharp contrast to the enhancement of the mutagenicity of 2-AF elicited by 2,4-DAT in these same incubations. This clear dissociation between the extent of peroxidative activation, and resultant covalent modification of bacterial DNA, by 2-AF and the subsequent mutagenic response indicates that a metabolic interaction is not involved in the co-mutagenicity of 2,4-DAT.

Efficacy of a novel copper-based footbath preparation for the treatment of ovine footrot during the spread period

OBJECTIVE

To determine the efficacy of a novel copper based footbath preparation (CHF-1020) for treatment of ovine footrot during the spread period.

DESIGN

A series of field trials with treated and control groups run together.

ANIMALS

Mobs of at least 125 sheep on each of six properties in southern New South Wales with equal numbers of controls.

PROCEDURE

Sheep of group A were treated after minimal paring by making them stand in CHF-1020 for 15 minutes. Treatment was undertaken at intervals throughout the period of the trials (14 September to 17 December 1993). Group A sheep were run on the same pasture as those from group B (untreated sheep).

RESULTS

The percentage of sheep exhibiting clinical signs of ovine footrot at the start of the trial ranged from 35 to 88% at score 3 or higher, using a 0 to 5 footscoring system. During the trial, the percentage of infected sheep (greater or equal to score 2) in group B increased and ranged from 40 to 90%. The level of infected sheep in group A on each property was reduced progressively to 1 to 16%. Cure rates of 45 to 94% were achieved, with the lowest rate being on a property with a metal footbath. The next lowest cure rate was 73%. Results indicated that treatment should be undertaken at 2-weekly intervals while spread continues. Treated sheep can be returned to contaminated pastures.

CONCLUSION

CHF-1020 is effective during the spread period and can be used for the progressive eradication of ovine footrot.

Enhancement of benzo[a]pyrene diol epoxide mutagenicity by sulfite in a mammalian test system

Sulfur dioxide, a ubiquitous air pollutant, is a co-carcinogen for benzo[a]pyrene (BP). We have demonstrated previously that the interaction between sulfite, the physiological form of sulfur dioxide, and (+/-) -7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), the ultimate carcinogenic form of BP, results in an enhanced mutagenic effect in Salmonella typhimurium strains TA98 and TA100. We report here that this same co-mutagenic effect of sulfite occurs in a mammalian cell line. Treatment of Chinese hamster V79 cells with 50 nM anti-BPDE, a concentration on the linear portion of the dose-response, resulted in a four-fold increase in mutations at the hprt locus relative to the spontaneous rate. When V79 cells were exposed to 1 or 10 mM sulfite immediately prior to the addition of anti-BPDE, the mutation rate increased by 73% and 210%, respectively, over that elicited by anti-BPDE alone. Sulfite itself was moderately cytotoxic, but caused no increase in mutation over the spontaneous rate. Characterization of the dose- and time-dependance of this enhancement of diol epoxide mutagenicity by sulfite closely resembled the effects seen previously in the bacterial system. In particular, enhancement by sulfite was evident when sulfite was added to the cells between 60 min and 1 min prior to the addition of the diol epoxide. Concurrent addition of sulfite and the diol epoxide attenuated the enhancement, and the effect was lost altogether when sulfite was added 10 min after the diol epoxide. The specificity of this effect of sulfite was shown by comparison with sulfate, which at concentrations of either 1 or 10 mM exhibited modest cytotoxicity, but neither was directly mutagenic nor able to enhance the mutagenic effect of anti-BPDE. Binding studies with labeled anti-BPDE showed that the addition of 10 mM sulfite increased binding of anti-BPDE to DNA by over 43%, corresponding to the observed increase in mutant frequency. Interestingly, this difference in level of DNA modification was not apparent after 30 min to 2 h exposures, but only emerged at the 4 h time point. The 4 h point was routinely used for all mutagenicity studies. Binding of anti-BPDE-derived materials to cellular RNA was not altered by 10 mM sulfite. The emergence of increased DNA modification at the latest time point suggests either a more prolonged period of active DNA binding than would occur with diol epoxide, or a difference in the ability to recognize and clear specific DNA adducts. Both possibilities are discussed in regard to the observed formation of 7r,8t,9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a] pyrene-10c-sulfonate (BPT-10-sulfonate) in those incubations. BPT-10-sulfonate is a relatively stable BP derivative which retains the ability to covalently modify DNA. The role of this derivative in the enhancement of diol epoxide mutagenicity by sulfite is strongly suggested by these data.

Effects of sulfite on the uptake and binding of benzo[a]pyrene diol epoxide in cultured murine respiratory epithelial cells

Sulfur dioxide (SO2) may act as a cocarcinogen with benzo[a]pyrene (BaP) in the respiratory tract. We have modeled this effect by examining the interactions of 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) with sulfite, the physiological form of SO2, in a murine respiratory epithelial cell line (C10). We exposed C10 cells to [3H]-anti-BPDE and determined the effects of 1 and 10 mM sulfite on the uptake and subcellular localization of labeled products. Autoradiographic analysis showed that sulfite doubled the nuclear localization of anti-BPDE-derived materials after a 4-hr incubation period. The net nuclear localization of anti-BPDE-derived materials was not affected by sulfite during the first 60 min, but nuclear localization continued to increase in the sulfite-containing incubations throughout the 4-hr incubation period. Little increase in nuclear localization of anti-BPDE-derived material was noted in the incubations without sulfite after 60 min. Subcellular fractionation was performed to determine the amount of label associated with cytosolic and nuclear fractions and to determine covalent binding to protein and DNA. Sulfite produced a modest increase in the amount of [3H]-anti-BPDE-derived products bound to protein; however, binding to nuclear DNA increased by more than 200% with 10 mM sulfite. Analysis of the supernatants from the cytosolic and nuclear fractions of cells exposed to anti-BPDE and sulfite demonstrated the presence of 7r,8t,9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10c-su lfonate (BPT-10-sulfonate). [3H]-BPT-10-sulfonate was unable to enter C10 cells, suggesting that it is formed intracellularly.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of (+/-)-7,8,10-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-9-sulfonate

The genotoxicity of certain benzo[a]pyrene (BP) derivatives is significantly enhanced in strains of Salmonella typhimurium following addition of sulfite to the incubations. The interaction between sulfite and those BP derivatives also results in the formation of isomeric BP sulfonates. As these trihydroxy sulfonates are formed in incubations of BP derivatives and sulfite in which a marked potentiation of bacterial mutagenicity occurs, we have investigated the properties of these novel intermediates. The compound (+/-)-7,8,10-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-9-sulfonate (BPT-9-sulfonate) was isolated and characterized in terms of its chemical and biological activity. This BPT sulfonate isomer is formed by the addition of the sulfite anion radical to the 9,10-double bond of the known promutagen, (+/-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol). Evidence for the free radical character of this addition includes the initiation of the reaction by either peroxidase-catalyzed or chemical one-electron oxidation of sulfite, the inhibition of the reaction by phenolic antioxidants, and the isolation and characterization of the chain termination product, 7,8-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-9,10-disulfonate (BPD-disulfonate). Analysis of incubations of S. typhimurium strain TA98 with BP-7,8-diol and sulfite, which resulted in a 10-fold increase in revertant bacterial colonies above control levels, showed that BPT-9-sulfonate and BPD-disulfonate were the only isolable products derived from BP-7,8-diol. This prompted a further investigation of the chemistry of these products. BPT-9-sulfonate was found to be quite stable in aqueous media, being refractory to acid- or base-catalyzed hydrolysis over a pH range of 3-11.(ABSTRACT TRUNCATED AT 250 WORDS)

An inexpensive system to monitor air flow in isolation units

Isolation units are used extensively for conducting infectious disease research in poultry. By necessity, these units are airtight and receive air only through electrically powered ventilation systems. Therefore, interruptions in electrical service to these units present a serious hazard to the animals they contain. A system was designed to monitor the air flow through isolation units and to alert animal caretakers in the event of any interruption in air flow. The "intelligence" of the system relies on an electronic monitor connected to a telephone line that places alerting telephone calls when it detects loss of air flow to the units. The system is constructed from easily acquired and relatively inexpensive parts and components.

Mutagenicity of benzo[a]pyrene bay-region sulfonates

The interaction between the sulfite anion and specific benzo[a]pyrene (B[a]P) derivatives produces a novel class of benzo[a]pyrene sulfonates. (+/-)-7,8,9-Trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10-sulfonate (B[a]PT-10-sulfonate) is formed in high yields in incubations containing (+/-)-7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyre ne (anti-BPDE) and sulfite, and sulfite strongly enhances the mutagenicity of the diolepoxide toward Salmonella typhimurium under those conditions. Although B[a]PT-10-sulfonate itself shows little direct mutagenicity over a 1-20 microM concentration range, this reactive bay-region intermediate does enhance the mutagenicity of anti-BPDE in strains TA98 and TA100 by up to 280%. No significant enhancement was seen when up to 20 microM B[a]PT-10-sulfonate was used in concert with another direct-acting mutagen, N-acetoxy-acetylaminofluorene (N-AcO-AAF). The isomeric product derived from sulfite and (+/-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-diol) is (+/-)-7,8,10-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-9-sulfonate (B[a]PT-9-sulfonate). Like B[a]PT-10-sulfonate, B[a]PT-9-sulfonate is not mutagenic to strains TA97, TA98 and TA100. This sulfonate exhibited little enhancing activity with anti-BPDE over a 1-20 microM concentration range, but did enhance the mutagenic response of strain TA98 to 0.2 microM N-Aco-AAF by up to 128%. Sulfite, anti-BPDE and B[a]PT-sulfonates were also examined for the ability to induce a forward mutation at the hgprt locus (8-azaguanine resistance) in strains of S.typhimurium. Sulfite caused a marked enhancement of forward mutation due to anti-BPDE in both TA98 and TA100. Surprisingly, concurrent administration of B[a]PT-10-sulfonate with anti-BPDE did not increase the number of mutant colonies. The extensive conversion of anti-BPDE to B[a]PT-10-sulfonate under conditions where sulfite enhances diolepoxide mutagenicity, when coupled with this enhancement of diolepoxide mutagenicity by B[a]PT-10-sulfonate in the reverse mutation assay, supports this novel B[a]P derivative as a mediator of the sulfite-dependent enhancement of B[a]P genotoxicity. Determining why this enhancing effect was not seen when selecting for mutation at the hgprt locus of S.typhimurium will require further study.

Peroxyl radical-dependent epoxidation of cyclopenteno[c,d]pyrene

We have reported previously that cyclopenteno[c,d]pyrene (CPP), an environmentally prevalent polycyclic aromatic hydrocarbon, is activated as a bacterial mutagen by several model systems which generate peroxyl radicals. In this report we present our findings on the chemical fate of CPP in these activating systems. The peroxyl radical systems employed are microsomal prostaglandin H synthase and arachidonic acid, the hematin-catalyzed decomposition of a lipid hydroperoxide, and the autoxidation of the sulfite anion. Reverse-phase HPLC analysis of stable products of CPP metabolism yielded qualitatively identical profiles from the first two systems. The three major products from these systems were analyzed by UV/visible and fluorescence spectroscopy, and a mass spectrum was obtained for the most abundant product. Based on these spectral analyses and on chromatographic behavior, the three products were identified as the cis- and trans-isomers of 3,4-dihydroxy-3,4-dihydro-CPP and 4-keto-(3H)-CPP. The identities of these products and their quantitative distributions relative to the epoxide hydrolase activities present in the microsomal system and the hematin system clearly establish 3,4-epoxy-CPP as the key intermediate and probable active mutagen generated in the peroxyl radical-dependent metabolism of CPP. This epoxidation of the activated aliphatic double bond of CPP extends the known range of peroxyl radical-dependent oxygenations by demonstrating the direct, one-step activation of a carcinogenic, environmentally relevant hydrocarbon. Strikingly different results are obtained in the sulfite-dependent system. The epoxide-derived metabolites seen with the peroxyl radical systems are very minor products. Instead, two product peaks elute near the solvent fron on reverse-phase HPLC. These are apparently monohydroxy-CPP sulfonates. Such products may form either by the direct addition of the sulfite anion radical to the activated double bond of CPP or by peroxyl radical-dependent epoxidation of CPP followed by nucleophilic addition of sulfite. Precedent for both of these reactions has been reported with analogous benzo[a]pyrene derivatives. The occurrence of these radical-dependent transformations in intact mammalian systems has not been investigated, but the ability of all three model systems employed to convert CPP to potent bacterial mutagens implies that these pathways should be studied further.

Sulfite enhancement of diolepoxide mutagenicity: the role of altered glutathione metabolism

Sulfur dioxide is a cocarcinogen for benzo[a]pyrene in the respiratory tract of rats and hamsters. Sulfur dioxide exists under physiological conditions as the sulfite ion. Sulfite enhances the mutagenic potency of (+-)-7r,8t-dihydroxy-9t,-10t- epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) and 7r,8t-dihydroxy-9c10c-epoxy-7,8,9,10-tetrahydrobenzo[a]py ren e (syn-BPDE) in Salmonella typhimurium strains TA98 and TA100. This enhancement of diolepoxide mutagenicity is observed with sulfite concentrations between 1 and 20 mM, and the concentration dependence is identical for the two diolepoxides. Half-maximal enhancement of mutagenicity occurs at approximately 5 mM sulfite. Sulfite is neither toxic nor mutagenic to the bacteria under these conditions. The enhancement of diolepoxide mutagenicity requires that the bacteria be exposed to sulfite prior to the addition of the diolepoxide. Simultaneous addition of sulfite and diolepoxide significantly decreases the enhancing effect, and addition 15 min after the diolepoxide virtually abolishes the effect. This is consistent with sulfite serving to increase the efficiency of processes leading to DNA modification by the diolepoxides, rather than some effect subsequent to DNA adduct formation. Direct evidence for this hypothesis was provided by determining the effect of sulfite on mutagenicity and DNA binding in TA98 using [3H]anti-BPDE. Exposure of the bacteria to 10 mM sulfite for 5 min prior to the addition of the labeled mutagen led to as much as 170% increase in DNA binding levels relative to parallel incubations without sulfite. Corresponding increases in mutagenicity were seen as well. As sulfite can affect the glutathione/glutathione-S-transferase systems, the primary cellular defense against BPDE, the effect of sulfite on these pathways in Salmonella was determined. When strain TA98 was treated with N-acetoxy-2-acetamidofluorene, a direct-acting mutagen not scavenged by glutathione, prior addition of 10 mM sulfite to the bacteria had no effect on resultant viability or mutagenicity. Assessment of the bacterial glutathione levels revealed that 10 mM sulfite treatment results in an 82% decrease in the concentration of the cosubstrate. We were, however, unable to detect diolepoxide-glutathione conjugates in any of our incubations. Moreover, the presence of sulfite leads to significant trapping of the diolepoxide in the form of sulfonate derivatives. Based on these data, we conclude that the depletion of glutathione does indeed play a role in the enhancement of diolepoxide mutagenicity in S. typhimurium.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzo[a]pyrene bay-region sulfonates, a novel class of reactive intermediates

The mutagenicity of 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) toward Salmonella typhimurium strain TA98 is enhanced by over 1.5-fold by the addition of 1-10 mM sulfite to the incubations. Sulfite itself is neither mutagenic nor toxic to the bacteria under these conditions. Analysis of anti-BPDE-derived products from these bacterial incubations demonstrates that, in addition to the expected hydrolysis products of the epoxide, novel more polar metabolites are produced. These same more polar compounds are produced by the addition of anti-BPDE to buffered aqueous solutions of sulfite. The major product of this reaction has been characterized by UV/visible and fluorescence spectroscopy, NI-FAB mass spectrometry, and proton NMR spectroscopy and is identified as 7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10-sulfonate (BPT-10-sulfonate). This derivative is formed by the nucleophilic addition of sulfite to the 9,10-oxirane ring of anti-BPDE. This product is easily differentiated both spectrally and chromatographically from the isomeric 7,8,10-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-9-sulfonate reported from the attack of the sulfite anion radical on the activated aliphatic double bond of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) [Curtis et al. (1988) Carcinogenesis 9, 2015]. The nucleophilic trapping of diol epoxides by water or thiols is assumed to represent a detoxication of this class of mutagen. In contrast, the extensive conversion of anti-BPDE to BPT-10-sulfonate in the bacterial incubations correlates with a marked enhancement of resultant mutagenicity. Further support for a key role of BPT-10 sulfonate in the enhancement of anti-BPDE mutagenicity is provided by our findings on the reactivity of this compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Redox cycling of resorufin catalyzed by rat liver microsomal NADPH-cytochrome P450 reductase

The O-dealkylation of 7-alkoxyresorufins to the highly fluorescent compound, resorufin (7-hydroxyphenoxazone), provides a rapid, sensitive, and convenient assay of certain forms of liver microsomal cytochrome P450. The results of this study indicate that NADPH-cytochrome P450 reductase catalyzes the reduction of resorufin (and the 7-alkoxyresorufins) to a colorless, nonfluorescent compound(s). The reduction of resorufin by NADPH-cytochrome P450 reductase was supported by NADPH but not NADH, and was not inhibited by dicumarol, which established that the reaction was not catalyzed by contaminating DT-diaphorase (NAD[P]H-quinone oxidoreductase). In addition to the rate of reduction, the extent of reduction of resorufin was dependent on the concentration of NADPH-cytochrome P450 reductase. The maintenance of steady-state levels of reduced resorufin required the continuous oxidation of NADPH, during which molecular O2 was consumed. When NADPH was completely consumed, the spectroscopic and fluorescent properties of resorufin were fully restored. These results indicate that the reduction of resorufin by NADPH-cytochrome P450 reductase initiates a redox cycling reaction. Stoichiometric measurements revealed of 1:1:1 relationship between the amount of NADPH and O2 consumed and the amount of H2O2 formed (measured fluorometrically). The amount of O2 consumed during the redox cycling of resorufin decreased approximately 50% in the presence of catalase, whereas the rate of O2 consumption decreased in the presence of superoxide dismutase. These results suggest that, during the reoxidation of reduced resorufin, O2 is converted to H2O2 via superoxide anion. Experiments with acetylated cytochrome c further implicated superoxide anion as an intermediate in the reduction of O2 to H2O2. However, the ability of reduced resorufin to reduce acetylated cytochrome c directly (i.e., without first reducing O2 to superoxide anion) precluded quantitative measurements of superoxide anion formation. Superoxide dismutase, but not catalase, increased the steady-state level of reduced resorufin and considerably delayed its reoxidation. This indicates that superoxide anion is not only capable of reoxidizing reduced resorufin, but is considerably more effective than molecular O2 in this regard. Overall, these results suggest that NADPH-cytochrome P450 reductase catalyzes the one-electron reduction of resorufin (probably to the corresponding semiquinoneimine radical) which can either undergo a second, one-electron reduction (presumably to the corresponding dihydroquinoneimine) or a one-electron oxidation by reducing molecular O2 to superoxide anion.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic activation of cyclopenteno[c,d]pyrene by peroxyl radicals

The conversion of cyclopento[c,d]pyrene (CPP) to forms which are mutagenic to Salmonella typhimurium strain TA98 has been demonstrated in systems which generate peroxyl radicals. The systems examined included prostaglandin H synthase (PHS) and arachidonic acid, 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) and hematin, and the autoxidation of the sulfite ion. In all cases concentration-dependent activation of CPP was observed at hydrocarbon concentrations between 10 and 100 microM. Neither CPP nor the peroxyl radical systems alone were mutagenic or toxic to the tester strain. The use of hydroxygen peroxide with PHS, a peroxidative system which does not yield peroxyl radicals, does not activate CPP. The involvement of a CPP epoxide was examined using 1,1,1-trichloropropene-2,3-oxide. Addition of this epoxide hydrolase inhibitor to incubations of CPP with the PHS/arachidonic acid system resulted in a 210% increase in induced revertants relative to the system in the absence of the inhibitor. The addition of pure rat liver microsomal epoxide hydrolase to incubations of CPP with the 15-HPETE/hematin system resulted in a concentration-dependent loss of mutagenicity, further supporting the intermediacy of an epoxide. The site of metabolism of CPP is the cyclopenteno double bond based on the formation of products which display distinct pyrene-type fluorescence spectra. The involvement of the cyclopenteno double bond also is shown by the inability of the 15-HPETE/hematin system to activate 3,4-dihydrocyclopenteno[c,d]pyrene as a mutagen. CPP is the first environmentally-relevant carcinogenic hydrocarbon found to be activated directly by peroxyl radical systems without prior biotransformation to a diol derivative by the cytochrome P-450 system. These findings expand the range of potentially toxic substrates to be considered for activation by peroxyl radical pathways.

Sulfite-dependent mutagenicity of benzo[a]pyrene derivatives

Benzo[a]pyrene (BP) and sulfur dioxide (SO2) are ubiquitous air pollutants and are also components of tobacco smoke. Although SO2 itself is not carcinogenic, concurrent administration with BP results in enhancement of respiratory tract tumorigenesis. In biological systems, SO2 exists as its hydrated form, sulfite (SO3(2-) ). Sulfite readily undergoes autoxidation, generating potent oxidant species. When 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) is included in sulfite autoxidation mixtures it is converted to more polar products, most notably 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (BP tetraols). This implies the intermediacy of 7,8-dihydroxy-9,10-epoxy- 7,8,9,10-tetrahydro-benzo[a]pyrenes (BPDE). We report here the sulfite-dependent conversion of BP-7,8-diol to forms highly mutagenic to Salmonella typhimurium strain TA 98. This activation is observed at BP-7,8-diol concentrations of from 2 to 40 microM and at sulfite concentrations of from 0.5 to 10 mM. In the presence of 10 microM BP-7,8-diol, half-maximal activation is observed at 1.6 mM sulfite. Sulfite itself is neither toxic nor mutagenic to the bacteria under these conditions. The time course of the activation of BP-7,8-diol and its sensitivity to inhibition by antioxidants indicate a requirement for sulfite autoxidation. These data further support the sulfite-dependent epoxidation of BP-7,8-diol. Not only does sulfite convert this promutagen to its active mutagenic form, sulfite also enhances the mutagenic activity of BP diolepoxides toward the tester strain. The reversion frequency in response to 0.1-0.5 microM anti-BPDE is increased by up to 33% in the presence of 1 mM sulfite, and by up to 270% with 10 mM sulfite. The mechanism of this enhancement of anti-BPDE activity is not known, but could be related to inhibition of the glutathione-S-transferase system which has been previously reported for sulfite. These results are discussed in regard to the noted cocarcinogenicity of sulfur dioxide for BP.

Co-oxidation of xenobiotics: lipid peroxyl derivatives as mediators of metabolism

Systems which carry out peroxyl-dependent oxidations can serve as activation systems for carcinogenic compounds. Some function via classical peroxidase reactions in which an enzyme-derived oxidant performs the electron abstraction from or oxygen donation to the oxidizable substrate. This mechanism applies to the peroxidative activation of aromatic amines and of the phenolic compound diethylstilbestrol. These classical peroxidase reactions may be initiated by hydrogen peroxide or by organic peroxides, including lipid hydroperoxides. A different mechanism is involved in the oxygenation of polycyclic aromatic hydrocarbons and of aflatoxin B1. In these cases the oxidant is a peroxyl radical, and the reaction occurs by the direct, non-enzymatic interaction of the peroxyl radical and the oxidizable substrate. Most peroxyl radicals in biological systems are lipid-derived. The key reaction which distinguishes the peroxyl radical-dependent oxidations from the classical peroxidase reactions is the ability of the former to epoxidize activated carbon-carbon double bonds. The epoxidation of benzo[a]pyrene derivatives has been studied extensively in subcellular and whole cell and tissue systems, and is discussed as a model for this class of reaction. Determining the generality of this activation path and its role in vivo present the major questions to be answered in regard to the importance of these reactions in chemical carcinogenesis.

Epoxidation of (+/-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene during (bi)sulfite autoxidation: activation of a procarcinogen by a cocarcinogen

The (bi)sulfite ion undergoes extensive autoxidation in neutral aqueous media with the formation of sulfur trioxide radical anion that is detected by ESR. The radical anion subsequently reacts with molecular oxygen to form a peroxyl radical. We find that when (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) is included in this autoxidation system, BP-7,8-diol is converted to diolepoxides, ultimate carcinogenic derivatives of benzo[a]pyrene. This epoxidation occurs with a stereoselectivity consistent with either a peroxyl radical or a peracid as the epoxidizing agent. The epoxidation is dependent on the concentration of both (bi)sulfite and oxygen. In the presence of 10 microM butylated hydroxyanisole, which abolishes (bi)sulfite autoxidation, no (bi)sulfite-dependent epoxidation occurs. These results are discussed in regard to the mechanism of (bi)sulfite autoxidation, and in relationship to the cocarcinogenicity of sulfur dioxide [anhydrous (bi)sulfite] for benzo[a]pyrene-induced pulmonary neoplasia.

Metabolism of arachidonic acid by hamster trachea lack of stimulation by A23187

The metabolism of arachidonic acid has been studied using hamster trachea in short-term organ culture. To study endogenous substrate utilization, tissue lipids were labeled with [3H]-arachidonic acid, whereas exogenous substrate turnover was assessed by the addition of 100 microM [14C]-arachidonic acid to the medium. Both exogenous and endogenous arachidonate were converted primarily to 6-keto-PGF1 alpha and PGE2, with varying amounts of an unidentified non-polar product noted. Production of the prostanoids increased steadily with time up to 24 hours. No significant generation of lipoxygenase products was found. Release of incorporated labeled arachidonic acid was nearly linear with time, resulting in the transfer of about 10% of the total label into the medium after 24 hours. About 3% of the total label was converted to prostaglandins. In the presence of 10 microM A23187, release of label was increased by only 25 to 60% relative to the control. Analysis of labeled compounds in the medium showed that this increase resulted from increased release of unchanged arachidonic acid, and that the yield of oxygenated products was the same as from the control incubations.

Peroxidative oxidation of bilirubin during prostaglandin biosynthesis

The peroxidative oxidation of bilirubin has been characterized in the ram seminal vesicle microsomal system. The oxidation was monitored by following the loss in absorbance of bilirubin at 440 nm. Bilirubin behaves as a peroxidase substrate for prostaglandin H synthase. The oxidation may be initiated by the addition of arachidonic acid or peroxides to incubations containing ram seminal vesicle microsomes and bilirubin, and is sensitive to inhibition by reduced glutathione. The arachidonate-dependent oxidation, but not the peroxide-initiated case, is inhibited by indomethacin. Similar results were obtained using microsomal preparations from mouse, rat, and pig lungs. Spectral and chromatographic examination of the products of bilirubin oxidation in the ram seminal vesicle system demonstrate that biliverdin is produced in this system by the dehydrogenation of bilirubin, but that this product accounts for only about 15% of the bilirubin consumed. Biliverdin itself is not oxidized in this system. At least three highly polar, fluorescent products also are formed from bilirubin. Though not identified, these polar products differ markedly in chromatographic behavior from the major fluorescent products obtained following the singlet oxygen oxidation or the autoxidation of bilirubin.

Inactivation of prostaglandin H synthase and prostacyclin synthase by phenylbutazone. Requirement for peroxidative metabolism

Phenylbutazone (PB), a nonsteroidal anti-inflammatory drug, is an efficient reducing cofactor for the peroxidase activity of prostaglandin H synthase (PHS). Most reducing cofactors for the peroxidase protect PHS and prostacyclin synthase from inactivation by hydroperoxides. PB, however, does not protect these enzymes, but rather augments their hydroperoxide-dependent inactivation. Using ram seminal vesicle microsomes as a source of PHS and prostacyclin synthase, we have examined the interaction of PB and exogenous hydroperoxides. Chromatographic analysis of the metabolism of 14C-labeled arachidonic acid in this system revealed that PB-dependent inactivation of PHS is markedly increased in the presence of 100 microM H2O2. This inactivation is a linear function of PB concentration between 10 and 250 microM, with a half-maximal effect in this range at about 100 microM PB. Prostacyclin synthase is even more sensitive to inactivation by the combined PB and H2O2 treatment, with a corresponding half-maximal effect at PB concentrations near 25 microM. This PB- and H2O2-dependent inactivation is demonstrable whether PGH2 is generated in situ from arachidonic acid or is added exogenously, supporting a direct effect of the treatment on prostacyclin synthase. As PB undergoes peroxide-dependent co-oxygenation catalyzed by PHS, we propose that it is an oxygenated derivative of PB, rather than the parent compound, which is responsible for the inactivation of PHS and prostacyclin synthase. Nafazatrom, a competitive inhibitor of PB co-oxygenation, blocks the effects of the PB and H2O2 treatment, supporting our proposal.

Prostaglandin H synthase-dependent co-oxygenation of (+/-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene in hamster trachea and human bronchus explants

The role of prostaglandin H synthase (PHS) in the metabolism of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) has been examined in short-term explant cultures of hamster and human tracheobronchial tissues. Labeled BP-7,8-diol was incubated with the explants in the presence and absence of the PHS substrate arachidonic acid (20:4) and the PHS inhibitor indomethacin. The addition of 10 microM to 200 microM 20:4 to incubations of hamster trachea with 5 microM BP-7,8-diol caused significant increases in the formation of 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[ a]pyrene (anti-BPDE). These increases were not seen when 1 microM or 20 microM BP-7,8-diol was employed. The stimulation of anti-BPDE formation was observed after incubations of from 1 to 48 h. This stimulation was inhibited to the basal level by 20 microM indomethacin, supporting the role of PHS in the response. No effect of 20:4 was seen on the uptake of BP-7,8-diol by the tracheas or on the formation of water-soluble metabolites. Significant increases in covalent binding of BP-7,8-diol metabolites to DNA of the tracheal epithelium were also elicited by the addition of 20:4, however these increases were not well correlated quantitatively with the increases in anti-BPDE formation. H.p.l.c. profiles of deoxynucleoside adducts from basal and 20:4-stimulated incubations were qualitatively identical. Far greater variability of metabolism was seen in human bronchus explants, but 20:4-dependent increases in anti-BPDE formation could be demonstrated in those tissues as well. Inhibition of this stimulation by indomethacin was either absent or incomplete. This variation in the effect of indomethacin was explained by the examination of the products of 20:4 metabolism by the two tissues. Hamster trachea produced almost exclusively PHS metabolites whereas human bronchus yielded predominantly products of lipoxygenases, enzymes insensitive to indomethacin. In conclusion, this study indicates that co-oxygenation of chemical carcinogens can occur in hamster and human tracheobronchial tissues. The concentration-dependence observed with BP-7,8-diol, however, suggests that this pathway is of minor importance in the activation of BP in these tissues.

Phenylbutazone-dependent epoxidation of 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene. A new mechanism for prostaglandin H synthase-catalyzed oxidations

The nonsteroidal anti-inflammatory drug phenylbutazone markedly enhances the hydroperoxide-dependent epoxidation of 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene catalyzed by microsomal and Tween-20 solubilized preparations of prostaglandin H synthase. Furthermore, phenylbutazone radically alters the hydroperoxide specificity of 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene epoxidation. In the absence of phenylbutazone, only allylic hydroperoxides are effective in initiating epoxidation, whereas in the presence of phenylbutazone the reaction can be initiated by t-butyl hydroperoxide, cumene hydroperoxide, and hydrogen peroxide. All effects are dependent on the concentration of phenylbutazone present. The primary event is the oxidation of phenylbutazone by prostaglandin H synthase. This pathway yields a peroxy radical of phenylbutazone which appears to be the epoxidizing agent. This activation of a primary substrate by a peroxidase resulting in metabolism of a secondary substrate is analogous to the halogenation reactions catalyzed by chloroperoxidase. This represents a new class of oxidation reactions catalyzed by prostaglandin H synthase.