A population pharmacokinetics model of balovaptan to support dose selection in adult and pediatric populations

Balovaptan is a brain-penetrating vasopressin receptor 1a antagonist previously investigated for the core symptoms of autism spectrum disorder (ASD). A population pharmacokinetic (PK) model of balovaptan was developed, initially to assist clinical dosing for adult and pediatric ASD studies and subsequently for new clinical indications including malignant cerebral edema (MCE) and post-traumatic stress disorder. The final model incorporates one-compartment disposition and describes time- and dose-dependent non-linear PK through empirical drug binding and a gut extraction component with turnover. An age effect on clearance observed in children was modeled by an asymptotic function that predicts adult-equivalent exposures at 40% of the adult dose for children aged 2-4 years, 70% for 5-9 years, and at the full adult dose for ≥ 10 years. The model was adapted for intravenous (IV) balovaptan dosing and combined with in vitro and ex vivo pharmacodynamic data to simulate brain receptor occupancy as a guide for dosing in a phase II trial of MCE prophylaxis after acute ischemic stroke. A sequence of three stepped-dose daily infusions of 50, 25 and 15 mg over 30 or 60 min was predicted to achieve a target occupancy of ≥ 80% in ≥ 95% of patients over a 3-day period. This model predicts both oral and IV balovaptan exposure across a wide age range and will be a valuable tool to analyze and predict its PK in new indications and target populations, including pediatric patients.

Welfare and management practices of free-ranging yaks (Bos grunniens) in Bhutan

Inaccessibility of veterinary and livestock extension services, and shortages of labour and forage could potentially impact the welfare of yaks ( Bos grunniens) in Bhutan. The objective of this study was to assess practices relating to the welfare and management of free-ranging yaks in Bhutan and explore variations between different yak-farming regions. We interviewed herders and observed the behaviour and health status of their animals, using an adaptation of the Welfare Quality® protocol, in three yak-farming regions (east, central and west) of Bhutan between October 2018 and January 2019. In total, for 567 cows and 549 calves, integumentary condition, body cleanliness, ocular and nasal discharge, diarrhoea, signs of damage, and gait were scored. In addition, we assessed 324 cows and 272 calves for avoidance distance and examined 324 cows for subclinical mastitis. The behaviour of the herds was observed in six consecutive 20-min blocks with each block divided into two stages. The first stage (5 min) consisted of counting the number of animals eating, lying down, standing idle and walking. The second stage (15 min) consisted of counting the number of events of agonistic, allogrooming, flehming, self-licking, rubbing/scratching and playing behaviour. Avoidance distance differed between regions for calves, but not for lactating cows. Integumentary lesions, dirty body areas, nasal discharge, ocular discharge, signs of diarrhoea, subclinical mastitis and lameness were virtually absent. A few instances of agonistic behaviour (6% of all counted behavioural events) and flehming behaviour (5% of all counted behavioural events) were observed. Yaks in the central and western regions exhibited more scratching and rubbing behaviour than those in the eastern region. Herders perform a variety of painful management practices (castration, ear tagging, nasal septum piercing) without analgesia, which is a prominent welfare issue. Furthermore, mortality among yaks is relatively high and water sources often dirty, creating a health risk. Nevertheless, the welfare status of yaks living in various regions of Bhutan was assessed as good at the time of visit.

The integrated GOR-COVID-19 health monitor: quarterly reporting (“short-cycle monitoring”)

Introduction/objective

Given the capricious nature of COVID-19, infections and accompanying restrictive measures to reduce spread of the virus are known to strongly vary over time. The impact of the corona crisis on the mental and physical health of the general population may fluctuate accordingly. The quarterly monitoring research line is aimed to monitor the health impact of the corona crisis over time on a high frequency basis.

Methods

This is achieved through a multi-method approach, combining: a) survey data on perceived impact of corona measures and several health outcomes from two representative panels (∼ 5.000 adolescents/young adults aged 12 and 25 years; ∼ 5.000 adults aged 26+ years), and b) surveillance data of acute health problems from the Nivel Primary Care Database (∼1,6 million patients from 380 general practitioners). Data collection started in September 2021 and continues during the five-year monitoring program. Panel data is collected every quarter; Nivel surveillance data is collected weekly. Our contribution to the EUPHA conference will include data up and until September 2022 (i.e. five rounds of survey and surveillance data).

Results

Preliminary results from September 2021 through March 2022 indicate that adolescents/young adults reported worse mental and physical health outcomes compared to adults. Moreover, they experienced a more negative impact of corona measures. Accordingly, their mental health related problems, including suicide ideation, spiked between December 2021 and February 2022, a period characterized by highly restrictive COVID-19-measures.

Discussion

The quarterly monitoring research line showcase the relevance and feasibility of integrating multiple data sources in understanding the short- and long-term effect of the corona crisis. The results increase our understanding in the potential adverse effects of corona-related restrictive measures on population health, potentially aiding policy making and health promotion.

A randomized, double-blind, placebo-controlled phase II trial to explore the effects of a GABAA-α5 NAM (basmisanil) on intellectual disability associated with Down syndrome

Background

There are currently no pharmacological therapies to address the intellectual disability associated with Down syndrome. Excitatory/inhibitory imbalance has been hypothesized to contribute to impairments in cognitive functioning in Down syndrome. Negative modulation of the GABA_A-α5 receptor is proposed as a mechanism to attenuate GABAergic function and restore the excitatory/inhibitory balance.

Methods

Basmisanil, a selective GABA_A-α5 negative allosteric modulator, was evaluated at 120 mg or 240 mg BID (80 or 160 mg for 12–13 years) in a 6-month, randomized, double-blind, placebo-controlled phase II trial (Clematis) for efficacy and safety in adolescents and young adults with Down syndrome. The primary endpoint was based on a composite analysis of working memory (Repeatable Battery for the Assessment of Neuropsychological Scale [RBANS]) and independent functioning and adaptive behavior (Vineland Adaptive Behavior Scales [VABS-II] or the Clinical Global Impression-Improvement [CGI-I]). Secondary measures included the Behavior Rating Inventory of Executive Functioning-Preschool (BRIEF-P), Clinical Evaluation of Language Fundamentals (CELF-4), and Pediatric Quality of Life Inventory (Peds-QL). EEG was conducted for safety monitoring and quantitatively analyzed in adolescents.

Results

Basmisanil was safe and well-tolerated; the frequency and nature of adverse events were similar in basmisanil and placebo arms. EEG revealed treatment-related changes in spectral power (increase in low ~ 4-Hz and decrease in high ~ 20-Hz frequencies) providing evidence of functional target engagement. All treatment arms had a similar proportion of participants showing above-threshold improvement on the primary composite endpoint, evaluating concomitant responses in cognition and independent functioning (29% in placebo, 20% in low dose, and 25% in high dose). Further analysis of the individual measures contributing to the primary endpoint revealed no difference between placebo and basmisanil-treated groups in either adolescents or adults. There were also no differences across the secondary endpoints assessing changes in executive function, language, or quality of life.

Conclusions

Basmisanil did not meet the primary efficacy objective of concomitant improvement on cognition and adaptive functioning after 6 months of treatment, despite evidence for target engagement. This study provides key learnings for future clinical trials in Down syndrome.

Trial registration

The study was registered on December 31, 2013, at clinicaltrials.gov as NCT02024789.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11689-022-09418-0.

Bioavailability and pharmacokinetic profile of balovaptan, a selective, brain-penetrant vasopressin 1a receptor antagonist, in healthy volunteers

BACKGROUND

Balovaptan is a potent, selective vasopressin 1a receptor antagonist. The early-phase pharmacokinetics (PK) of balovaptan are reported.

RESEARCH DESIGN AND METHODS

Two Phase 1 studies (overall N = 93) assessed single- and multiple-dose balovaptan PK in healthy adults. One (N = 16) assessed absolute oral bioavailability (10 mg or 50 mg) vs a [¹³C]-balovaptan microdose. The other (N = 77) explored single- (0.5-76 mg) and multiple-dose (14 days; 12-52 mg/day) - randomized 6:2 balovaptan:placebo per dose - PK, dose proportionality, and the effect of food on single-dose (32 mg) C_max and AUC_inf.

RESULTS

Absolute balovaptan bioavailability was high (103-116%). Steady-state (Day 14) balovaptan PK was approximately dose proportional with a half-life of 45-47 hours, but single-dose C_max increased more than dose proportionally and half-life was inversely dose-proportional - a discordance partially attributable to a dose-and-time-dependent volume of distribution. Accumulation (Day 1-Day 14) was inversely dose-proportional (~3.5 [12 mg] to ~1.8 [52 mg]). There was no relevant effect of a high-fat meal on single-dose balovaptan exposure. There were no safety signals: 2/93 subjects discontinued for adverse events.

CONCLUSIONS

Balovaptan was well tolerated at single (≤76 mg) and multiple (≤52 mg/day) doses, with a PK profile supportive of once-daily administration without food restrictions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03764449; NCT01418963.

A phase 2 clinical trial of a vasopressin V1a receptor antagonist shows improved adaptive behaviors in men with autism spectrum disorder

There are no approved pharmacological therapies to address the core symptoms of autism spectrum disorder (ASD), namely, persistent deficits in social communication and social interaction and the presence of restricted, repetitive patterns of behaviors, interests, or activities. The neuropeptide vasopressin has been implicated in the regulation of social behaviors, and its modulation has emerged as a therapeutic target for ASD. The phase 2 VANILLA clinical trial reported here evaluated balovaptan, an orally administered selective vasopressin V1a receptor antagonist, in 223 men with ASD and intelligence quotient ≥70. The drug was administered daily for 12 weeks and was compared with placebo. Participants were randomized to placebo (n = 75) or one of three balovaptan dose arms (1.5 mg, n = 32; 4 mg, n = 77; 10 mg, n = 39). Balovaptan treatment was not associated with a change from baseline compared with placebo at 12 weeks in the primary efficacy endpoint (Social Responsiveness Scale, 2nd Edition). However, dose-dependent and clinically meaningful improvements on the Vineland-II Adaptive Behavior Scales composite score were observed for participants treated with balovaptan 4 or 10 mg compared with placebo. This was driven principally by improvements in the Vineland-II socialization and communication scores. Balovaptan was well tolerated across all doses, and no drug-related safety concerns were identified. These results support further study of balovaptan as a potential treatment for the socialization and communication deficits in ASD.

Population Pharmacokinetic and Exposure-dizziness Modeling for a Metabotropic Glutamate Receptor Subtype 5 Negative Allosteric Modulator in Major Depressive Disorder Patients

Dizziness, the most frequently observed adverse event in patients with major depressive disorder, was observed with basimglurant, a selective, orally active metabotropic glutamate receptor subtype 5 negative allosteric modulator. The potential relationship between dizziness and basimglurant exposure was explored. The pharmacokinetics of basimglurant was characterized with nonlinear mixed effects modeling using data from 288 trial participants enrolled in five clinical trials. The pharmacokinetics of basimglurant after daily oral administration of a modified release formulation was best described by a two-compartment disposition model with a transit compartment, lag time for the absorption, and first-order elimination. The largest covariate effects were the effect of smoking and male gender on apparent clearance followed by the effect of body weight on distribution volumes. Clearance was twofold higher in smokers and 40% higher in males. A logistic regression model showed a statistically significant correlation between basimglurant C_max and incidence of dizziness. An increased risk of dizziness is predicted with increasing doses.

Results and evaluation of a first-in-human study of RG7342, an mGlu5 positive allosteric modulator, utilizing Bayesian adaptive methods

AIM

The objectives of this first-in-human study were to evaluate the safety and tolerability, pharmacokinetics and pharmacodynamics, and maximum tolerated dose (MTD) of single ascending oral doses of RG7342, a positive allosteric modulator (PAM) of the metabotropic glutamate receptor 5 (mGlu5) for the treatment of schizophrenia, in healthy male subjects.

METHODS

This was a single-centre, randomized, double-blind, adaptive study of 37 subjects receiving single ascending oral doses of RG7342 (ranging from 0.06-1.2 mg, n = 27) or placebo (n = 10). A modified continual reassessment method, with control for the probability of overdosing based on the occurrence of dose-limiting events (DLEs), was applied to inform the subsequent dose decisions for RG7342.

RESULTS

DLEs consisted of dizziness, nausea and vomiting, and the incidence and severity of these adverse events increased in a concentration-dependent manner. RG7342 doses of 1.2 mg under fasting conditions, which reached a mean maximum plasma concentration (C_max ) of 10.2 ng ml^-1 , were not tolerated (four out of six subjects experienced DLEs). RG7342 showed dose-proportional pharmacokinetics, with rapid absorption and a biphasic decline, and a mean terminal half-life estimated to be >1000 h.

CONCLUSIONS

Single oral doses of RG7342 were generally tolerated up to 0.6 mg under fasting and 0.9 mg under fed conditions in healthy subjects. Bayesian adaptive methods describing the probability of DLEs were applied effectively to support dose escalation. MTDs (fasting, fed) were associated with a C_max of 6.5 ng ml^-1 . The development of RG7342 was discontinued owing to the potential challenges associated with a long half-life in context of the observed adverse events.

Lymphatic drainage pathways from the cervix uteri: implications for radical hysterectomy?

OBJECTIVE

Radical hysterectomy with pelvic lymphadenectomy is the treatment of choice for early-stage cervical cancer. Wertheim's original technique has been often modified, mainly in the extent of parametrectomy. Okabayashi's technique is considered as the most radical variant regarding removal of the ventral parametrium and paracolpal tissues. Surgical outcome concerning recurrence and survival is good, but morbidity is high due to autonomic nerve damage. While the autonomic network has been studied extensively, the lymphatic system is less understood. This study describes the lymphatic drainage pathways of the cervix uteri and specifically the presence of lymphatics in the vesico-uterine ligament (VUL).

METHODS

A developmental series of 10 human female fetal pelves was studied. Paraffin embedded blocks were sliced in transverse sections of 8 or 10 μm. Analysis was performed by staining with antibodies against LYVE-1 (lymphatic endothelium), S100 (Schwann cells), alpha-Smooth Muscle Actin (smooth muscle cells) and CD68 (macrophages). The results were three-dimensionally represented.

RESULTS

Two major pathways drained the cervix uteri: a supra-ureteral pathway, running in the cardinal ligament superior to the ureter, and a dorsal pathway, running in the utero-sacral ligament towards the rectal pillars. No lymph vessels draining the cervix uteri were detected in the VUL. In the paracolpal parametrium lymph vessels draining the upper vagina fused with those from the bladder.

CONCLUSIONS

The VUL does not contain lymphatics from the cervix uteri. Hence, the favorable survival outcomes of the Okabayashi technique cannot be explained by radical removal of lymphatic pathways in the ventrocaudal parametrium.

Safety, tolerability and pharmacokinetics of dalcetrapib following single and multiple ascending doses in healthy subjects: a randomized, double-blind, placebo-controlled, phase I study

BACKGROUND

Dalcetrapib is a modulator of cholesteryl ester transfer protein (CETP) activity developed to raise levels of high-density lipoprotein cholesterol (HDL-C) with the goal of further reduction of cardiovascular events additive to standard of care alone. In clinical studies, dalcetrapib has been shown to effectively increase levels of HDL-C with no significant safety concerns.

OBJECTIVE

The primary objective was to investigate the safety of single ascending and multiple ascending doses of dalcetrapib at doses markedly greater than that intended therapeutically (600 mg/day). Secondary objectives were to investigate the pharmacokinetics/pharmacodynamics and dose proportionality of dalcetrapib.

STUDY DESIGN

Randomized, double-blind, placebo-controlled, combined single and multiple ascending dose phase I study. Healthy males (age 18-65 years, body mass index 18-32 kg/m2) were randomized to four of five dalcetrapib doses (2100, 2700, 3300, 3900 or 4500 mg) or placebo, with ≥10 days washout between doses (n = 15, single ascending doses) or to dalcetrapib (1800, 2100, 3000 or 3900 mg once daily) or placebo for 7 days (four cohorts, each n = 10, randomization 8 : 2, multiple ascending doses).

MAIN OUTCOME MEASURE

Tolerability and safety were assessed by monitoring adverse events (AEs), laboratory parameters, vital signs and 12-lead ECG recordings. Primary pharmacokinetic assessments were area under the plasma concentration-time curve (AUC) from time zero to infinity (AUC(∞)) and maximum observed plasma concentration (C(max)) [single doses] and AUC from time zero to 24 hours (AUC(24)) and C(max) (multiple doses). Pharmacodynamic assessments included CETP activity and lipids (multiple dosing only).

RESULTS

Exposure increased with dose but was less than proportional to increasing dose after single dosing, although deviation from dose proportionality could not be demonstrated for C(max). Dose proportionality was consistent following multiple doses. Steady state was modelled to have been reached by approximately 4 days, with little to no accumulation. CETP activity reduction was dose dependent (maximum -55% after 3900 mg; placebo -2.6%) at 6 hours post-dose on day 1, while HDL-C increased by 12-19% (placebo -13%) on day 8 following treatment with 1800-3900 mg/day for 7 days. All AEs were mild or moderate in intensity and there were no serious AEs, deaths or withdrawals due to AEs. No clinically relevant effects on laboratory parameters, cardiac parameters or vital signs were noted.

CONCLUSION

Single-dose dalcetrapib up to 4500 mg and multiple doses up to 3900 mg were generally safe and well tolerated.

Lack of clinically relevant drug-drug interactions when dalcetrapib is co-administered with ezetimibe

AIMS

Dalcetrapib, which targets cholesteryl ester transfer protein activity, is in development for prevention of cardiovascular events. Because dalcetrapib will likely be prescribed with other lipid-modifying therapies such as ezetimibe, a study was performed to investigate potential pharmacokinetic interactions between dalcetrapib and ezetimibe. Lipids changes and tolerability were secondary endpoints.

METHODS

Co-administration of dalcetrapib 900 mg (higher than the phase III dose) with ezetimibe was investigated in a three period, three treatment crossover study in healthy males: 7 days of dalcetrapib, 7 days of dalcetrapib plus ezetimibe, 7 days of ezetimibe alone. A full pharmacokinetic profile was performed on day 7 of each treatment.

RESULTS

Co-administration of dalcetrapib with ezetimibe was associated with minimal changes in dalcetrapib exposure compared with dalcetrapib alone. Least squares mean ratio (LSMR) (90% confidence interval) was 93.6 (87.1, 100.7) for AUC(0,24 h) and 99.0 (85.2, 115.0) for C(max) . Ezetimibe exposure was reduced with co-administration of ezetimibe with dalcetrapib compared with ezetimibe alone: LSMR 80.3 (74.6, 86.4) for AUC(0,24 h) and 88.9 (80.9, 99.9) for C(max) for total ezetimibe. High-density lipoprotein cholesterol increases associated with co-administration of dalcetrapib with ezetimibe (+29.8%) were comparable with those with dalcetrapib alone (+25.6%), while the reduction in low-density lipoprotein cholesterol with co-administration (-35.9%) was greater than with ezetimibe alone (-20.9%). Dalcetrapib was generally well tolerated when administered alone and when co-administered with ezetimibe.

CONCLUSION

Co-administration of dalcetrapib with ezetimibe was not associated with clinically significant changes in pharmacokinetic parameters or tolerability and did not diminish the lipid effects of either drug.

No clinically relevant drug-drug interactions when dalcetrapib is co-administered with atorvastatin

OBJECTIVES

Dalcetrapib, which targets cholesteryl ester transfer protein, is in clinical development for prevention of cardiovascular events and is likely to be used concomitantly with statins. Two studies investigated co-administration of dalcetrapib with atorvastatin and any effects of the timing of atorvastatin on the pharmacokinetics of dalcetrapib.

RESEARCH DESIGN AND METHODS

Two crossover studies were performed in healthy subjects: a two-period study of dalcetrapib 900 mg concurrently with atorvastatin (concurrent dosing study) and a three-period study of dalcetrapib 600 mg (dose chosen for Phase III) with atorvastatin concurrently or serially 4 h after dalcetrapib (interval dosing study).

MAIN OUTCOME MEASURES

The primary pharmacokinetic end points were AUC(0 - 24) and C(max); lipid effects and tolerability were secondary end points.

RESULTS

In the concurrent study (n = 26), co-administration reduced dalcetrapib AUC(0 - 24) and C(max) and caused small changes in AUC(0 - 24) and C(max) of atorvastatin and its active metabolites. In the interval study (n = 52), serial and concurrent co-administration of atorvastatin resulted in similar reductions in dalcetrapib exposure that were comparable to those observed in the concurrent dosing study. Co-administration did not decrease the efficacy of dalcetrapib or atorvastatin and was generally well tolerated.

CONCLUSIONS

These results indicate no clinically relevant interactions for co-administration of dalcetrapib with atorvastatin.

A single-center, open-label, one-sequence study of dalcetrapib coadministered with ketoconazole, and an in vitro study of the S-methyl metabolite of dalcetrapib

BACKGROUND

Dalcetrapib (RO4607381/JTT-705) is currently under clinical investigation for the prevention of cardiovascular events. It inhibits the activity of cholesteryl ester transfer protein and has been reported to increase levels of high-density lipoprotein cholesterol.

OBJECTIVE

Because dalcetrapib is likely to be coadministered with agents that inhibit the cytochrome P450 (CYP) 3A4 isozyme, this study aimed to determine the effect of ketoconazole, a strong CYP3A4 inhibitor, on the pharmacokinetics of dalcetrapib.

METHODS

An open-label, 1-sequence study was conducted in 2 cohorts of healthy, nonsmoking male volunteers aged 18 through 65 years, with a body mass index of 18 to 32 kg/m(2). The first cohort received dalcetrapib 600 mg on days 1 and 7 and ketoconazole 400 mg on days 2 through 7, and, based on the results of a planned interim analysis, the second cohort received dalcetrapib 900 mg alone on days 1 and 7 and ketoconazole on days 2 through 7. Pharmacokinetic and safety parameters were assessed at specific times throughout the study. To confirm CYP involvement in the metabolism of the inactive metabolite dalcetrapib-S-methyl, in vitro studies were performed using human liver microsomes and recombinantly expressed CYP isoforms.

RESULTS

Of the 26 participants, 96% were white, with a mean age of 38.1 years and a mean weight of 78.6 kg. In the in vivo portion of the study, coadministration of ketoconazole with dalcetrapib 600 mg had no significant effect on any pharmacokinetic parameter of dalcetrapib. Coadministration of ketoconazole with dalcetrapib 900 mg was associated with significant decreases in the dalcetrapib C(max) (-23%; P = 0.002) and AUC(0-infinity) (-18%; P = 0.001) and a significant increase in oral clearance (22%; P = 0.001). Significant increases in the C(max) (P = 0.001) and AUC(0-infinity) (P < 0.001) of dalcetrapib-S-methyl were observed with coadministration of ketoconazole. The combination was generally well tolerated, with 32 of 35 adverse events (91.4%) being mild in intensity. The most frequent adverse events were headache (6/26 [23.1%] in the ketoconazole group; 4/18 [22.2%] in the group receiving dalcetrapib 900 mg plus ketoconazole) and diarrhea (4/26 [15.4%] in the ketoconazole group; 2/18 [11.1%] in the group receiving dalcetrapib 900 mg plus ketoconazole). The in vitro studies confirmed the involvement of CYP3A in the metabolism of dalcetrapib-S-methyl.

CONCLUSIONS

In this clinical study in healthy male volunteers, coadministration of dalcetrapib 600 mg with the CYP3A4 inhibitor ketoconazole was not associated with any significant changes in the pharmacokinetic parameters of the parent compound. Coadministration of dalcetrapib 900 mg with ketoconazole was associated with significant decreases in the dalcetrapib C(max) and AUC, contrary to the increases that would be expected if dalcetrapib were a substrate for CYP3A4. The combination of dalcetrapib and ketoconazole was generally well tolerated.

In vitro and in vivo assessment of the effect of dalcetrapib on a panel of CYP substrates

OBJECTIVE

The primary objective of this study was to investigate the drug-drug interaction potential of dalcetrapib on drugs metabolized via major cytochrome P450 (CYP) isoforms using both in vitro and clinical approaches. A secondary objective was to investigate the safety and tolerability of dalcetrapib alone or co-administered either with a combination of five probe drugs or with rosiglitazone.

RESEARCH DESIGN AND METHODS

Human liver microsomes and a panel of substrates for CYP enzymes were used to determine IC(50) for inhibition of CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. In addition, two drug-drug interaction studies were conducted in healthy males: dalcetrapib 900 mg plus the Cooperstown 5 + 1 drug cocktail, which includes substrates for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, and dalcetrapib 900 mg plus rosiglitazone, a substrate for CYP2C8. Pharmacokinetic and safety parameters were assessed.

RESULTS

In vitro, dalcetrapib was inhibitory to all CYP enzymes tested. IC(50) values ranged from 1.5 +/- 0.1 microM for CYP2C8 to 82 +/- 4 microM for CYP2D6. Co-administration of dalcetrapib plus drug cocktail showed no clinically relevant effect of 900 mg dalcetrapib on activity of CYP1A2, CYP2C19, CYP2D6, CYP2C9, or CYP3A4 following repeated administration. Co-administration of dalcetrapib plus rosiglitazone showed no clinically relevant effect of dalcetrapib 900 mg on activity of CYP2C8. Dalcetrapib was generally well tolerated.

CONCLUSIONS

Although in vitro studies indicated that dalcetrapib inhibits CYP activity, two clinical studies showed no clinically relevant effect on any of the major CYP isoforms at a 900 mg dose, which is higher than the 600 mg dose being explored in phase III studies. Dalcetrapib was generally well tolerated in these studies. However, these studies were limited to a small number of healthy males; additional, larger studies are necessary to study its safety.

Identification and characterization of DdPDE3, a cGMP-selective phosphodiesterase from Dictyostelium

In Dictyostelium cAMP and cGMP have important functions as first and second messengers in chemotaxis and development. Two cyclic-nucleotide phosphodiesterases (DdPDE 1 and 2) have been identified previously, an extracellular dual-specificity enzyme and an intracellular cAMP-specific enzyme (encoded by the psdA and regA genes respectively). Biochemical data suggest the presence of at least one cGMP-specific phosphodiesterase (PDE) that is activated by cGMP. Using bioinformatics we identified a partial sequence in the Dictyostelium expressed sequence tag database that shows a high degree of amino acid sequence identity with mammalian PDE catalytic domains (DdPDE3). The deduced amino acid sequence of a full-length DdPDE3 cDNA isolated in this study predicts a 60 kDa protein with a 300-residue C-terminal PDE catalytic domain, which is preceded by approx. 200 residues rich in asparagine and glutamine residues. Expression of the DdPDE3 catalytic domain in Escherichia coli shows that the enzyme has Michaelis-Menten kinetics and a higher affinity for cGMP (K(m)=0.22 microM) than for cAMP (K(m)=145 microM); cGMP does not stimulate enzyme activity. The enzyme requires bivalent cations for activity; Mn(2+) is preferred to Mg(2+), whereas Ca(2+) yields no activity. DdPDE3 is inhibited by 3-isobutyl-1-methylxanthine with an IC(50) of approx. 60 microM. Overexpression of the DdPDE3 catalytic domain in Dictyostelium confirms these kinetic properties without indications of its activation by cGMP. The properties of DdPDE3 resemble those of mammalian PDE9, which also shows the highest sequence similarity within the catalytic domains. DdPDE3 is the first cGMP-selective PDE identified in lower eukaryotes.

Intrathecal production of HIV antibodies in suspected AIDS encephalopathy

Thirty-one serum and CSF samples from 21 HIV-antibody-positive patients with neurological deficits were examined to prove or exclude intrathecal production of HIV antibodies. By dilution, sera were adjusted to the IgG concentration of the corresponding CSF samples. Both samples were then serially diluted in log2 steps down to the detection limit and were tested in an anti-HIV ELISA. From the dilution obtained at the cut-off level, a quotient QHIV was derived as an indicator of intrathecal production of HIV antibodies. Six of a total of eight samples with a QHIV value of greater than or equal to 2 were correlated which the clinical diagnosis of AIDS-related dementia complex (ARDC). However, a QHIV less than 1 did not exclude the development of ARDC, as was shown during follow-up in one case. Different methods are compared for the determination of intrathecal production of IgG and anti-HIV. A quotient QHIV greater than or equal to 2 is suggested to be highly indicative of intrathecal production of anti-HIV as well as of the development of ARDC.

Construction and function of a new hydraulic cuff occluder

The construction of a new type of vascular cuff occluder for use in conscious animals is described. This occluder has the following features: 1. Safe complete vessel occlusion. 2. Occlusion at a definite cuff pressure with extrathoracally pressure control behind the cuff. 3. Long term implantability. 4. Possibility of multiple usage and sterilization.