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Abrocitinib, an oral once-daily Janus kinase 1 selective inhibitor, is under development for the treatment of atopic dermatitis. This phase 1, nonrandomized, open-label, single-dose study (NCT03660241) investigated the effect of renal impairment on the pharmacokinetics, safety, and tolerability of abrocitinib and its metabolites following a 200-mg oral dose. Twenty-three subjects with varying degrees of renal function (normal, moderate, and severe impairment) were enrolled. Active moiety exposures were calculated as the sum of unbound exposures for abrocitinib and its active metabolites. For abrocitinib, the adjusted geometric mean ratios (GMRs; %) for area under the concentration-time curve from time 0 extrapolated to infinite time (AUCinf ) and maximum plasma concentration (Cmax ) were 182.91 (90% CI, 117.09-285.71) and 138.49 (93.74-204.61), respectively, for subjects with moderate renal impairment versus normal renal function; corresponding GMRs were 121.32 (68.32-215.41) and 99.11 (57.30-171.43) for subjects with severe impairment versus normal renal function. Metabolite exposures generally increased in subjects with renal impairment. The GMRs of unbound AUCinf and Cmax of active moiety were 210.20 (154.60-285.80) and 133.87 (102.45-174.92), respectively, for subjects with moderate renal impairment versus normal renal function. Corresponding values were 290.68 (217.39-388.69) and 129.49 (92.86-180.57) for subjects with severe renal impairment versus normal renal function. Abrocitinib was generally safe and well tolerated. Both moderate and severe renal impairment led to higher exposure to abrocitinib active moiety, suggesting that abrocitinib dose should be reduced by half for patients with moderate or severe renal impairment. ClinicalTrials.gov identifier: NCT03660241 This article is protected by copyright. All rights reserved.

Background: Cachexia is common in patients with advanced cancer and has been associated with elevated serum growth/differentiation factor 15 (GDF-15) concentrations. This first-in-patient, phase 1b, study assessed the use of ponsegromab, a monoclonal antibody against GDF-15, in participants with advanced cancer and cachexia. Methods: Adult participants (n = 10) with cachexia, advanced cancer (non-small cell lung, colorectal, or pancreatic), and elevated serum concentrations of GDF-15 received open-label subcutaneous ponsegromab every three weeks (Q3W) for 12 weeks in addition to standard of care anti-cancer treatment. Study endpoints included assessment of ponsegromab safety, tolerability, and pharmacokinetics. Serum GDF-15 concentrations and exploratory measures of efficacy were also assessed. Results: No treatment-related adverse events or injection site reactions were reported. No adverse trends in clinical laboratory tests, vital signs, or electrocardiogram parameters attributable to ponsegromab dosing were evident. Ninety-two adverse events deemed unrelated to treatment were reported; most were mild (Grade 1 = 58.7%) or moderate (Grade 2 = 28.3%) in severity. All participants were negative for anti-drug antibodies at baseline (n = 10) and after receiving 5 doses (Q3W) of ponsegromab (n = 9). Mean unbound ponsegromab Ctrough ranged from 4.041-4383 ng/mL between Days 22-106. An elevated GDF-15 concentration was required for inclusion in the study. Following initiation of study treatment, median unbound GDF-15 concentration was reduced to below the lower limit of quantification (0.0424 ng/mL) on day 1 and remained suppressed until week 15 (3 weeks after final dose). Increases in body weight were observed at all time points during the treatment (weeks 3, 6, 9, and 12) and follow-up (weeks 15, 18, and 24) periods. The mean (SD) body weight at baseline was 70.49 (16.97) kg. An LS mean (SE) increase of 4.63 kg (1.98) was observed at week 12 (end of treatment); representing an increase of approximately 6.5% relative to baseline. Improvements in actigraphy-based assessments of physical activity and in quality of life, including appetite, as assessed by Functional Assessment of Anorexia-Cachexia Therapy (FAACT) total and subscale scores, were also observed during the course of ponsegromab treatment. Conclusions: In participants with advanced cancer, cachexia, and elevated baseline GDF-15, ponsegromab was well tolerated and suppressed serum GDF-15 concentrations to below the median concentration seen in healthy subjects. Preliminary evidence of efficacy, including a mean observed weight gain of approximately 6.5% at 12 weeks, supports continued development of ponsegromab for the treatment of cancer cachexia. Funded by Pfizer. ClinicalTrials.gov: NCT04299048 Citation Format: Jeffrey Crawford, Roberto A. Calle, Susie M. Collins, Yan Weng, Shannon L. Lubaczewski, Clare Buckeridge, Ellen Q. Wang, Magdalena A. Harrington, Anil Tarachandani, Michelle I. Rossulek, James H. Revkin. First-in-patient study of the GDF-15 inhibitor ponsegromab in patients with cancer and cachexia: Safety, tolerability, and exploratory measures of efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT108.

Background Anti-drug antibodies (ADAs) to bococizumab were detected in > 40% of subjects in the SPIRE lipid-lowering trials. The risk of cross-reactivity between anti-bococizumab antibodies and other approved anti-proprotein convertase subtilisin/kexin type-9 (PCSK9) monoclonal antibodies (mAbs) was investigated using a single-assay approach. Methods Bococizumab immunogenicity was assessed in SPIRE-HR, a 52-week study. The highest ADA titer sample from each ADA-positive subject (n = 155) was tested in vitro for cross-reactivity to alirocumab and evolocumab using a novel ADA assay approach. Additional specificity tiers within the bococizumab ADA assay against each drug were validated using recombinant PCSK9 as a surrogate cross-reactive positive control. If the highest ADA titer sample showed cross-reactivity, additional samples from that subject were analyzed. Cross-reactivity was determined by the ability of alirocumab or evolocumab to inhibit the sample signal greater than or equal to the cross-reactivity cut-points. Results ADAs were detected in 44.0% (155/352) of bococizumab-treated subjects, and 27.0% also developed neutralizing antibodies (NAbs). Median ADA and NAb titers ranged from 276 to 526 and 8 to 12 over the course of the study, respectively. From 155 ADA-positive subjects tested for cross-reactivity, one (0.6%) subject showed weak cross-reactivity to both alirocumab and evolocumab. This cross-reactivity signal was transient (from Days 337 to 373) and undetectable at the last ADA-positive timepoint (Day 407). Conclusion A novel, single-assay approach was validated to assess the potential cross-reactivity of anti-bococizumab antibodies to alirocumab and evolocumab. In subjects who developed ADAs to bococizumab, the likelihood of clinically relevant cross-reactivity to marketed anti-PCSK9 mAbs is remote, based on the low frequency of cross-reactivity observed, which was weak in signal inhibition and transient in nature. Clinical Trial Registration The SPIRE-HR study is registered on ClinicalTrials.gov under the identifier NCT01968954.

Abrocitinib, an oral once-daily Janus kinase 1 selective inhibitor, is under development for the treatment of atopic dermatitis. This phase 1, nonrandomized, open-label, single-dose study (NCT03660241) investigated the effect of renal impairment on the pharmacokinetics, safety, and tolerability of abrocitinib and its metabolites following a 200-mg oral dose. Twenty-three subjects with varying degrees of renal function (normal, moderate, and severe impairment) were enrolled. Active moiety exposures were calculated as the sum of unbound exposures for abrocitinib and its active metabolites. For abrocitinib, the adjusted geometric mean ratios (GMRs; %) for area under the concentration-time curve from time 0 extrapolated to infinite time and maximum plasma concentration were 182.91 (90% confidence interval [CI], 117.09-285.71) and 138.49 (90% CI, 93.74-204.61), respectively, for subjects with moderate renal impairment vs normal renal function; corresponding GMRs were 121.32 (90% CI, 68.32-215.41) and 99.11 (90% CI, 57.30-171.43) for subjects with severe impairment vs normal renal function. Metabolite exposures generally increased in subjects with renal impairment. The GMRs of unbound area under the concentration-time curve from time 0 extrapolated to infinite time and maximum plasma concentration of active moiety were 210.20 (90% CI, 154.60-285.80) and 133.87 (90% CI, 102.45-174.92), respectively, for subjects with moderate renal impairment vs normal renal function. Corresponding values were 290.68 (90% CI, 217.39-388.69) and 129.49 (90% CI, 92.86-180.57) for subjects with severe renal impairment vs normal renal function. Abrocitinib was generally safe and well tolerated. Both moderate and severe renal impairment led to higher exposure to abrocitinib active moiety, suggesting that abrocitinib dose should be reduced by half for patients with moderate or severe renal impairment. ClinicalTrials.gov identifier: NCT03660241.

The pharmacokinetics (PK) and pharmacodynamics (PD) of bococizumab, a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor, were compared following a single 150-mg subcutaneous dose administered to healthy subjects (n = 156-158/arm) via: (1) a prefilled syringe (PFS) using drug substance (DS) manufactured by Pfizer, (2) a PFS using DS manufactured by Boehringer Ingelheim Pharma, (3) a prefilled pen using DS manufactured by Pfizer (NCT02458209). Blood samples were collected for 12 weeks postdose. Safety was monitored throughout. Mean maximum plasma concentration (Cmax ) ranged between 11.0 and 11.3 μg/mL, and area under the plasma concentration-time curve (AUCinf ) ranged between 177.6 and 185.0 μg·day/mL across treatments. The 90% confidence intervals for the ratios of adjusted geometric means for Cmax and AUCinf fell within the 80%-125% range for both DS and delivery device comparisons. Comparable low-density lipoprotein cholesterol profiles were observed, with nadir values of 54.3-56.1 mg/dL across treatments. Similar PCSK9 responses were also observed. Safety profiles were similar across treatments, and the majority of adverse events (AEs) were mild. Three subjects reported serious AEs. The most frequently reported AEs were headache, injection-site reaction, and upper respiratory tract infection, with no clear differences across treatments. Comparable PK, PD, and safety were observed following a single bococizumab 150-mg subcutaneous injection regardless of site of DS manufacture or delivery device used.

PURPOSE: To study the comparative short-term safety and efficacy of transcatheter arterial chemoembolization (TACE) with drug-eluting LC Beads loaded with doxorubicin (DEBDOX), doxorubicin-eluting QuadraSpheres (hqTACE), and conventional TACE using ethiodized oil for superselective C-arm computed tomography (CT)-guided treatment of hepatocellular carcinoma (HCC) after the onset of drug shortages. MATERIALS AND METHODS: From March 2010 to March 2011, 166 patients with HCC were treated with 232 superselective TACE procedures using C-arm cone-beam CT at one institution. Patients underwent treatment depending on the availability of materials after the onset of drug shortages. Conventional TACE with doxorubicin, cisplatin, and Ethiodol was performed for 159 procedures, DEBDOX TACE was performed for 47, and hqTACE was performed for 26. Toxicity and objective response were compared at 3 months after treatment. Data were stratified for the high-risk population (Child-Pugh class B, performance status 1, bilobar disease, and/or post-resection recurrence) and initial versus repeat treatment. Kruskal-Wallis H test, Mann-Whitney U test, and Fisher exact test were used to compare the groups, with Bonferroni correction where needed. RESULTS: Whole liver response rates trended higher for conventional TACE (conventional TACE, 65.4%; DEBDOX, 63.8%; hqTACE, 53.8%) (P = .085). Only minor trends for differences in toxicity were observed between the three groups. Low-risk patients had higher whole liver (P = .001) and treated lesion (P = .007) response rates when treated with conventional TACE, but no significant differences were seen for DEBDOX and hqTACE. Treatment-naive patients also had higher whole liver (P = .012) and treated lesion (P = .056) response rates. No advantages for drug-eluting microspheres were found. CONCLUSION: Within statistical power limitations, overall toxicity and efficacy were equivalent in patients treated with LC Beads, QuadraSpheres, or ethiodized oil emulsions, including in high-risk patients, when performed superselectively with cone-beam C-arm CT guidance.

Bococizumab is a humanized monoclonal antibody binding proprotein convertase subtilisin/kexin type 9, which may be a potential therapeutic option for reducing low-density lipoprotein cholesterol (LDL-C) levels in patients with hypercholesterolemia. In this 24-week, multicenter, double-blind, placebo-controlled, dose-ranging study (NCT01592240), subjects with LDL-C levels ≥80 mg/dl on stable statin therapy were randomized to Q14 days subcutaneous placebo or bococizumab 50, 100, or 150 mg or Q28 days subcutaneous placebo or bococizumab 200 or 300 mg. Doses of bococizumab were reduced if LDL-C levels persistently decreased to ≤25 mg/dl. The primary end point was the absolute change in LDL-C levels from baseline to week 12 after placebo or bococizumab administration. Continuation of bococizumab administration through to week 24 enabled the collection of safety data over an extended period. Of the 354 subjects randomized, 351 received treatment (placebo [n = 100] or bococizumab [n = 251]). The most efficacious bococizumab doses were 150 mg Q14 days and 300 mg Q28 days. Compared with placebo, bococizumab 150 mg Q14 days reduced LDL-C at week 12 by 53.4 mg/dl and bococizumab 300 mg Q28 days reduced LDL-C by 44.9 mg/dl; this was despite dose reductions in 32.5% and 34.2% of subjects at week 10 or 8, respectively. Pharmacokinetic/pharmacodynamic model-based simulation assuming no dose reductions predicted that bococizumab would lower LDL-C levels by 72.2 and 55.4 mg/dl, respectively. Adverse events were similar across placebo and bococizumab groups. Few subjects (n = 7; 2%) discontinued treatment because of treatment-related adverse events. In conclusion, bococizumab significantly reduced LDL-C across all doses despite dose reductions in many subjects. Model-based simulations predicted greater LDL-C reduction in the absence of bococizumab dose reduction. The Q14 days regimen is being evaluated in phase 3 clinical trials.

Norepinephrine reuptake inhibitors (NRIs) acutely increase norepinephrine (NE) levels, but therapeutic antidepressant activity is only observed after weeks of treatment because central NE levels progressively increase during continued drug exposure. Similarly, while NRIs acutely increase blood pressure (BP) and heart rate (HR) due to enhanced sympathetic neurotransmission, chronic treatment changes the responsiveness of the central noradrenergic system and suppresses these effects via autonomic regulation. To better understand the relationship between NE increases and cardiovascular safety, we investigated acute and chronic effects of the NRI reboxetine on central NE release and on BP and HR and electrical alternans, a measure of arrhythmia liability, in guinea pigs. NE release was assessed by microdialysis in medial prefrontal cortex (mPFC) and hypothalamic paraventricular nucleus (PVN); BP and HR were measured by telemetry. Animals were treated for 28 days with 15 mg/kg/day of reboxetine or vehicle via an osmotic minipump and then challenged with acute intravenous doses of reboxetine. Animals chronically treated with reboxetine had 2-fold higher extracellular basal NE levels in mPFC and PVN compared to basal levels after chronic vehicle treatment BP was significantly increased after the first day of treatment, and gradually returned to vehicle levels by day 21. These data indicate that chronic NRI treatment may lead to an increase in central NE levels and a concomitant reduction in BP based on exposure-response curves compared to vehicle treatment, suggesting a larger separation between preclinical estimates of efficacy vs. safety compared to acute NRI treatment. (c) 2012 Elsevier Inc. All rights reserved.

Objective To determine the pharmacokinetics, safety and tolerability of fesoterodine, and assess the utility of 3-day bladder diaries (exploratory objective) in pediatric subjects with neurogenic detrusor overactivity or idiopathic overactive bladder (OAB). Methods In this 8-week open-label study, subjects (8–17 years, >25 kg) received fesoterodine 4 mg for 4 weeks, then 8 mg for 4 weeks. Blood samples were obtained at weeks 4 and 8. Results Of 21 subjects enrolled, 11 had neurogenic detrusor overactivity and 10 had idiopathic OAB; 1 discontinued (personal reasons). Mean age and weight were 13.2 years and 54.0 kg for boys (n = 12) and 13.1 years and 49.2 kg for girls (n = 9). 5-Hydroxy-methyltolterodine plasma concentrations did not differ by diagnosis and were consistent with predictions based on adult data. Treatment-related adverse events (all mild or moderate) included 1 event each of dry mouth, constipation, dry eyes and blurred vision, and 2 events each of nausea and increased post-void residual volume. Three-day bladder diaries proved feasible. Conclusions Oral administration of fesoterodine in pediatric subjects (>25 kg) with idiopathic OAB or neurogenic detrusor overactivity produced steady-state plasma 5-hydroxy-methyltolterodine exposures similar to those in adults. The doses given were well tolerated.

Pharmacokinetic–pharmacodynamic (PK–PD) modeling greatly enables quantitative implementation of the “learn and confirm” paradigm across different stages of drug discovery and development. This work describes the successful prospective application of this concept in the discovery and early development of a novel κ-opioid receptor (KOR) antagonist, PF-04455242, where PK–PD understanding from preclinical biomarker responses enabled successful prediction of the clinical response in a proof of mechanism study. Preclinical data obtained in rats included time course measures of the KOR antagonist (PF-04455242), a KOR agonist (spiradoline), and a KOR-mediated biomarker response (prolactin secretion) in plasma. Clinical data included time course measures of PF-04455242 and prolactin in 24 healthy volunteers following a spiradoline challenge and single oral doses of PF-04455242 (18 and 30 mg). In both species, PF-04455242 successfully reversed spiradoline-induced prolactin response. A competitive antagonism model was developed and implemented within NONMEM to describe the effect of PF-04455242 on spiradoline-induced prolactin elevation in rats and humans. The PK–PD model-based estimate of K i for PF-04455242 in rats was 414 ng/mL. Accounting for species differences in unbound fraction, in vitro K i and brain penetration provided a predicted human K i of 44.4 ng/mL. This prediction was in good agreement with that estimated via the application of the proposed PK–PD model to the clinical data (i.e., 39.2 ng/mL). These results illustrate the utility of the proposed PK–PD model in supporting the quantitative translation of preclinical studies into an accurate clinical expectation. As such, the proposed PK–PD model is useful for supporting the design, selection, and early development of novel KOR antagonists.

High-throughput sequencing promises to accelerate the discovery of sequence variants, but distinguishing oncogenic mutations from irrelevant “passenger” mutations remains a major challenge. Here we present an analysis of two sequence variants of the MET receptor (hepatocyte growth factor receptor) R970C and T992I (also designated R988C and T1010I). Previous reports indicated that these sequence variants are transforming and contribute to oncogenesis. We screened patients with chronic lymphocytic leukemia (CLL), acute myeloid leukemia (AML), chronic myelomonocytic leukemia (CMML), colorectal cancer, endometrial cancer, thyroid cancer, or melanoma, as well as individuals without cancer, and found these variants at low frequencies in most cohorts, including normal individuals. No evidence of increased phosphorylation or transformative capacity by either sequence variant was found. Because small-molecule inhibitors for MET are currently in development, it will be important to distinguish between oncogenic sequence variants and rare single-nucleotide polymorphisms to avoid the use of unnecessary, and potentially toxic, cancer therapy agents. Cancer Res; 70(15); 6233–7. ©2010 AACR.

We examined the effects of dose and dosing protocol on the pharmacodynamics of in vivo nitroglycerin (NTG) tolerance in conscious rats. Mechanism-based pharmcokinetic/pharmacodynamic (PK/PD) models were tested for their ability to describe the observed data.Rats were infused with 1, 3, or 10 microg/min of NTG or vehicle for 10 h. Peak mean arterial pressure (MAP) response to an hourly 30 microg i.v. NTG challenge dose (CD) was measured before, during, and at 12 and 24 h after infusion. In separate experiments, the MAP effects of repeated bolus doses of NTG were compared to those after a continuous infusion, both at a total dose of 510 microg NTG.NTG tolerance was indicated by a decrease in peak MAP response to the CD, relative to the preinfusion peak MAP response. Tolerance toward the MAP effects of bolus CD was observed within 1 h of 10 microg/min of NTG infusion (26.8 +/- 2.8% vs. 10.6 +/- 0.4% for 0 and 1 h, respectively, p0.001), and the rate and extent of tolerance development increased with the infusion dose. No apparent MAP tolerance was observed when NTG was given as multiple bolus doses whereas significant MAP tolerance was observed when this dose was infused continuously. PK/PD modeling indicated that a cofactor/enzyme depletion mechanism could adequately describe the composite data.Our data showed that in vivo nitrate tolerance was dose- and dosing protocol-dependent. The pharmacodynamics of tolerance development are consistent with depletion of either critical enzymes or cofactors that are necessary to induce vasodilation.

Vascular nitrate tolerance is often accompanied by changes in the activity and/or expression of a number of proteins. However, it is not known whether these changes are associated with the vasodilatory properties of nitrates, or with their tolerance mechanisms. We examined the hemodynamic effects and vascular gene expressions of 2 nitric oxide (NO) donors: nitroglycerin (NTG) and S-nitroso-N-acetylpenicillamine (SNAP). Rats received 10 μg/min NTG, SNAP, or vehicle infusion for 8 hours. Hemodynamic tolerance was monitored by the maximal mean arterial pressure (MAP) response to a 30-μg NTG or SNAP bolus challenge dose (CD) at various times during infusion. Gene expression in rat aorta after NTG or SNAP treatment was determined using cDNA microarrays, and the relative differences in expression after drug treatment were evaluated using several statistical techniques. MAP response of the NTG CD was attenuated from the first hour of NTG infusion (P .05, ANOVA) or control infusion (P> .05, ANOVA). Student t-statistics revealed that 447 rat genes in the aorta were significantly altered by NTG treatment (P

We examined the direct involvement of endothelial nitric oxide (eNOS) in nitrate tolerance using eNOS knockout (eNOS (−/−)) and wild-type (eNOS (+/+)) mice. Animals were treated with either nitroglycerin (NTG, 20 mg kg−1s.c. 3×daily for 3 days) or vehicle (5% dextrose, D5W), and nitrate tolerance was assessed ex vivo in isolated aorta by vascular relaxation studies and cyclic GMP accumulation. Western blot was performed to determine NOS expression after NTG treatment. In both the eNOS (−/−) and (+/+) mice, the EC50 from NTG concentration-response curve was increased by ∼3 fold, and vascular cyclic GMP accumulation was similarly decreased after NTG pretreatment. Vascular tolerance did not lead to changes in eNOS protein expression in eNOS (+/+) mice. These results indicate that vascular nitrate tolerance was similarly induced in eNOS (−/−) and (+/+) mice, suggesting that eNOS may not be critically involved in nitrate tolerance development in mice. British Journal of Pharmacology (2002) 135, 299–302; doi:10.1038/sj.bjp.0704532

SummaryAim To characterize the single-dose pharmacokinetics (PK) and pharmacodynamics (PD) of bococizumab, a monoclonal antibody inhibiting proprotein convertase subtilisin/kexin type 9 (PCSK9), administered subcutaneously (s.c.) to the abdomen, thigh, or upper arm (NCT02043301). Methods Seventy-five adults with low-density lipoprotein cholesterol (LDL-C) ≥130 mg/dL and not on background lipid-lowering therapy were randomized (1:1:1) to a single 150-mg s.c. dose of bococizumab administered to the abdomen, thigh, or upper arm. Blood samples for bococizumab and lipids were collected for 12 weeks post-dose. Results: Plasma bococizumab concentration-time profiles and PK parameters were generally similar across injection sites. Mean maximum observed concentration (Cmax) ranged from 8.14 to 11.9 μg/mL and area under the concentration-time curve (AUCinf) ranged from 160.3 to 198.9 μg•day/mL. The median time to Cmax (Tmax) ranged from 4.25 to 6.93 days. Similar LDL-C concentration-time profiles were observed across injection sites, with mean (% coefficient of variation) maximum reductions in LDL-C of –57.5% (15.8), –57.0% (25.9), and –55.0% (24.1) for the abdomen, thigh, and upper arm, respectively. Adverse events (AEs) were mostly mild and generally similar across injection sites. Commonly reported AEs were upper respiratory tract infection (9.3%), headache (6.7%), and injection-site reaction (6.7%). One serious AE was reported (ischemic colitis), which was not considered related to study drug. Conclusions Similar PK profiles and robust LDL-C reductions were observed following single 150-mg s.c. injections of bococizumab administered to the abdomen, thigh, or upper arm in untreated subjects with LDL-C ≥130 mg/dL. Bococizumab was generally well-tolerated following a single 150-mg s.c. administration in this subject population. ClinicalTrials. gov identifier: NCT02043301

1. Recent studies indicate that nitroglycerin (NTG) can produce beneficial clinical effects in healing anal fissures through the relaxation of the internal anal sphincter. The in vivo relaxation effects of NTG on the anorectal smooth muscle have not been studied and it is not known whether this tissue may also exhibit pharmacological tolerance toward NTG. 2. We have developed an in vivo procedure in the anaesthetized rat that permits continual monitoring of anorectal pressure after intravenous (i.v.) and intra-rectal application of NTG. The relaxant effects of NTG were quantified via the area-under-the-contraction-waveforms vs time curve (AUEC). 3. AUEC decreased significantly after intra-rectal bolus doses of NTG (5 - 25 microg), in a dose- and time-dependent manner. Sustained relaxation effects on anorectal pressure were also observed after continuous intra-rectal infusions of NTG. 4. Two-hours of i.v. NTG infusion led to a significant reduction in the mean arterial blood pressure (MAP) response toward a i.v. NTG (30 microg) bolus challenge. In contrast, relaxation of the anorectal pressure toward the challenge dose was not altered after NTG infusion. 5. In isolated tissues, cyclic GMP accumulation was significantly decreased after NTG pre-incubation in the rat aorta but not in the rat anorectal smooth muscle and anal sphincter. 6. These results indicate that the relaxation response toward NTG was not diminished in the anorectum under conditions that produced vascular tolerance. Thus, NTG causes significant and sustained in vivo relaxation of anorectal smooth muscle in the anaesthetized rat without evidence of tolerance development.

Thirty-two structurally diverse drugs used for the treatment of various conditions of the central nervous system (CNS), along with two active metabolites, and eight non-CNS drugs were measured in brain, plasma, and cerebrospinal fluid in the P-glycoprotein (P-gp) knockout mouse model after subcutaneous administration, and the data were compared with corresponding data obtained in wild-type mice. Total brain-to-plasma (B/P) ratios for the CNS agents ranged from 0.060 to 24. Of the 34 CNS-active agents, only 7 demonstrated B/P area under the plasma concentration curve ratios between P-gp knockout and wild-type mice that did not differ significantly from unity. Most of the remaining drugs demonstrated 1.1- to 2.6-fold greater B/P ratios in P-gp knockout mice versus wild-type mice. Three, risperidone, its active metabolite 9-hydroxyrisperidone, and metoclopramide, showed marked differences in B/P ratios between knockout and wild-type mice (6.6- to 17-fold). Differences in B/P ratios and cerebrospinal fluid/plasma ratios between wild-type and knockout animals were correlated. Through the use of this model, it appears that most CNS-active agents demonstrate at least some P-gp-mediated transport that can affect brain concentrations. However, the impact for the majority of agents is probably minor. The example of risperidone illustrates that even good P-gp substrates can still be clinically useful CNS-active agents. However, for such agents, unbound plasma concentrations may need to be greater than values projected using receptor affinity data to achieve adequate receptor occupancy for effect.

Sympathetic activation has been suggested as a mechanism of acute nitrate tolerance, but the available literature is not definitive. We investigated the effects of prazosin, an alpha1-adrenoceptor antagonist, on acute nitroglycerin (NTG) hemodynamics and tolerance development in normal conscious rats. The effect of prazosin bolus injection (300 microg/kg) on NTG hemodynamics was first determined after acute dosing. The extent of maximal mean arterial pressure (MAP) response and the duration of drug-induced hypotension to NTG bolus doses (5, 15, and 30 microg) were measured before and after prazosin. In separate studies, the effects of prazosin on NTG tolerance development were examined. Rats received either 10 microg/min NTG or vehicle infusion for 5 hours after predosing with prazosin (300 microg/kg). Maximal MAP response to the hourly 30-microg NTG i.v. bolus challenge dose (CD) was determined before and after prazosin, and during NTG or vehicle infusion. Our results showed that bolus doses of NTG (at 5, 15, and 30 microg) dose-dependently decreased maximal MAP by 20.8 +/- 5.8, 26.1 +/- 5.0, and 30.6 +/- 5.7 mm Hg, respectively. Prazosin caused an average of 16 mm Hg depression in MAP, and it only slightly potentiated the hypotensive effects of bolus doses of NTG both after acute dosing and during continuous infusion. Prazosin treatment prolonged the duration of NTG-induced MAP response by about 4-fold for all NTG doses examined (P0.01 versus corresponding dose before prazosin, ANOVA). In both prazosin-treated and untreated groups, NTG infusion significantly attenuated the MAP response of the NTG CD starting from 1 hour of infusion (P0.001 versus 0 hour response, ANOVA), confirming tolerance development. In the presence of NTG tolerance development, prazosin no longer enhanced the apparent duration of NTG action. The hypotensive effect produced by the 30-microg NTG CD lasted for 7 +/- 2 and 10 +/- 2 seconds for prazosin-treated and untreated groups, respectively (P0.05, ANOVA). Our results showed that, in both NTG-tolerant and control animals, prazosin only slightly potentiated the maximum hypotensive effects of a challenge NTG dose, but did not significantly alter the pharmacodynamics of NTG-induced hemodynamic tolerance. Thus, in our animal model, sympathetic blockade by prazosin neither prevented nor attenuated in vivo tolerance induced by NTG.

Literature reports have suggested that hemodynamic response toward organic nitrates may be reduced in obese patients, but this effect has not been studied. We compared the mean arterial pressure (MAP) responses toward single doses of nitroglycerin (NTG, 0.5-50 micro g) in conscious Zucker obese (ZOB), Zucker lean (ZL), and Sprague-Dawley (SD) rats. NTG tolerance development in these animal groups was separately examined. Rats received 1 and 10 micro g/min of NTG or vehicle infusion, and the maximal MAP response to an hourly 30 micro g NTG IVchallenge dose (CD) was measured. Steady-state NTG plasma concentrations were measured during 10 micro g/min NTG infusion. The Emax and ED50 values obtained were 33.9 +/- 3.6 and 3.5 +/- 1.7 micro g for SD rats, 33.2 +/- 4.1 and 3.0 +/- 1.4 micro g for ZL rats, and 34.8 +/- 3.9 and 5.3 +/- 2.8 micro g for ZOB rats, respectively. No difference was found in the dose-response curves among these 3 groups (P.05, 2-way ANOVA). Neither the dynamics of NTG tolerance development, nor the steady-state NTG plasma concentrations, were found to differ among these 3 animal groups. These results showed that ZOB rats are not more resistant to the hemodynamic effects of organic nitrates compared with their lean controls. Thus, the acute and chronic hemodynamic effects induced by NTG are not sensitively affected by the presence of obesity in a conscious animal model of genetic obesity.

Vascular nitrate tolerance is often accompanied by changes in the activity and/or expression of a number of proteins. However, it is not known whether these changes are associated with the vasodilatory properties of nitrates, or with their tolerance mechanisms. We examined the hemodynamic effects and vascular gene expressions of 2 nitric oxide (NO) donors: nitroglycerin (NTG) and S-nitroso-N-acetylpenicillamine (SNAP). Rats received 10 microg/min NTG, SNAP, or vehicle infusion for 8 hours. Hemodynamic tolerance was monitored by the maximal mean arterial pressure (MAP) response to a 30-microg NTG or SNAP bolus challenge dose (CD) at various times during infusion. Gene expression in rat aorta after NTG or SNAP treatment was determined using cDNA microarrays, and the relative differences in expression after drug treatment were evaluated using several statistical techniques. MAP response of the NTG CD was attenuated from the first hour of NTG infusion (P.001, analysis of variance [ANOVA]), but not after SNAP (P.05, ANOVA) or control infusion (P.05, ANOVA). Student t-statistics revealed that 447 rat genes in the aorta were significantly altered by NTG treatment (P.05). An adjusted t-statistic approach using resampling techniques identified a subset of 290 genes that remained significantly different between NTG treatment vs control. In contrast, SNAP treatment resulted in the up-regulation of only 7 genes and the down-regulation of 34 genes. These results indicate that continuous NTG infusion induced widespread changes in vascular gene expression, many of which are consistent with the multifactorial and complex mechanisms reported for nitrate tolerance.