Boel Löfberg

Etretinate (Tegison^®, Tigason^®), a retinoid used for the treatment of skin disorders such as psoriasis, was shown to be teratogenic in the human. Because of the long terminal half-life of this drug ( 100 days), considerable plasma levels of etretinate and its main metabolite, etretin (acitretin), were observed for up to 2 years following discontinuation of therapy. We have therefore investigated, in a newly developed animal model, the potential teratogenic risk of such persisting levels of these aromatic retinoids.Etretinate was administered by intragastric infusion throughout organogenesis in the mouse (day 8-15) via subcutaneously implanted osmotic minipumps connected to external reservoirs containing oily solutions of the drug. Dose-dependent developmental effects were found, the fetal weight decreased and the resorption rate and incidence of major malformation increased. A dose of 0.84 mg/kg/day resulted in retinoid-specific defects, in particular shortening of the limbs and cleft palate. This low dose infused resulted in mean etretinate concentrations of 6.5 ng/ml maternal plasma and 12.5 ng/g embryo (measured on days 10 and 12 of gestation). The corresponding concentrations of the metabolite etretin were 38 ng/ml plasma and 95 ng/g embryo. Our results emphasize the high teratogenic risk of relatively low, persisting concentrations of etretinate and etretin such as those observed after discontinuation of human therapy, because the area of the concentration-time curve is likely to be the decisive parameter in regard to teratogenesis.

The objectives were to estimate and compare, in silico and in vivo, the effects of a strong and a moderate CYP3A4 inhibitor on AZD1305 pharmacokinetics. In silico, simulations were performed with the computer software Simcyp, and the predicted outcome was compared with the results observed in healthy male subjects. In silico, the geometric mean plasma exposure of AZD1305 + ketoconazole showed a 7.1‐fold higher AUC and a 4.4‐fold higher C_max compared with AZD1305 alone. Coadministration with verapamil gave a 1.9‐fold higher AUC and a 1.7‐fold higher C_max compared with AZD1305 alone. In vivo, the plasma exposure of AZD1305 + ketoconazole showed a 7.7‐fold higher AUC and a 4.8 ‐fold higher C_max compared with AZD1305 alone. Coadministration with verapamil gave a 2.2‐fold higher AUC and a 2.0‐fold higher C_max compared with AZD1305 alone. The mean maximum QT_cF increase from baseline was 407, 487, and 437 milliseconds for AZD1305, alone and in combination with verapamil or ketoconazole, respectively. Simcyp predicted the effects of ketoconazole and verapamil on the sensitive CYP3A4 substrate AZD1305 pharmacokinetics well. Both the in vivo study and the Simcyp predictions suggest a contraindication for strong CYP3A4 inhibitors and AZD1305 when given in combination.

The in vitro metabolic stability assays are indispensable for screening the metabolic liability of new chemical entities (NCEs) in drug discovery. Intrinsic clearance (CLint) values from liver microsomes and/or hepatocytes are frequently used to assess metabolic stability as well as to quantitatively predict in vivo hepatic plasma clearance (CLH). An often used approximation is the so called wellstirred model which has gained widespread use. The applications of the well-stirred model are typically dependent on several measured parameters and hence with potential for error-propagation. Despite widespread use, it was recently suggested that the well-stirred model in some circumstances has been misused for in vitro in vivo extrapolation (IVIVE). In this work, we follow up that discussion and present a retrospective analysis of IVIVE for hepatic clearance prediction from in vitro metabolic stability data. We focus on the impact of input parameters on the well stirred model; in particular comparing “reference model” (with all experimentally determined values as input parameters) versus simplified models (with incomplete input parameters in the models). Based on a systematic comparative analysis and model comparison using datasets of diverse drug-like compounds and NCEs from rat and human, we conclude that simplified models, disregarding binding data, may be sufficiently good for IVIVE evaluation and compound ranking at early stage for cost-effective screening. Factors that can influence prediction accuracy are discussed, including in vitro intrinsic clearance (CLint) and in vivo CLint scaling factor used, non-specific binding to microsomes (fum), blood to plasma ratio (CB/CP) and in particular fraction unbound in plasma (fu). In particular, the fu discrepancies between literature data and in-house values and between two different compound concentrations 1 and 10 μM are exemplified and its potential impact on prediction performance is demonstrated using a simulation example.

In the Western world, over 350,000 deaths and $30 billion in medical costs are attributed annually to stroke. Head and spinal cord trauma cause an estimated 250,000 deaths annually and result in medical costs of $15 billion. Although stroke and head/spinal cord trauma are leading causes of disability and death in humans, no adequate neuroprotective treatment is available. Glutamate antagonists derived from the quinoxa-linedione scaffold are as drug candidates for neuroprotection in stroke and trauma. Quinoxalinedione derivatives such as 2,3-dihydroxy-6- nitro-7-sulfamoylbenzo(f)quinoxaline and 6-(1H-imidazol-1-yl)-7-nitro-2,3-(1H,4H)-quinoxalinedione failed clinical trials because of insolu-bility and resulting nephrotoxicity. Introduction of a phosphonate group into the quinoxalinedione skeleton improves solubility and leaves potency for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor unchanged. Phosphonate quinoxalinedione derivatives ZK202000 and ZK200775 protected rodent brain against sequelae of permanent occlusion of the middle cerebral artery and head trauma. No major deleterious effects on motor coordination, cardiovascular, or respiratory systems were detected in doses required for neuroprotection. No psychotomimetic and no neurotoxic side effects, typical for N-methyl-D-aspartate antagonists, were observed following treatment with phosphonate quinoxalinediones.

NMRI mice were treated on day 11 (day 0 = plug day) of gestation with a single oral dose of 100 mg/kg of either all‐trans‐etretin (acitretin) or 13‐cis‐etretin. For teratology studies mice were sacrificed on day 18 of gestation, and the fetuses were examined for malformations. For pharmacokinetic studies, groups of 5 mice were sacrificed after 5, 10, and 30 min and 1, 2, 4, and 8 h. The concentrations of retinoids in maternal plasma and in embryos were determined by a newly developed HPLC gradient method. All‐transetretin induced malformations in 94% of the fetuses, mainly in fore and hind limbs and cleft palate. 13‐cis‐etretin did not show any teratogenic or embryolethal effects at the dose level used. These findings could be explained by a transplacental pharmacokinetic study. The maximum peak level and also the AUC (area under the concentration‐time curve) values of all‐trans‐etretin in the embryos was 7–8 times higher than corresponding values for 13‐cis‐etretin, probably due to extensive transport of the trans‐isomer and limited transport of the cis‐isomer from maternal plasma to the embryos. The concentration quotient between embryo and the maternal plasma was between 0.43 and 1.10 for all‐trans‐etretin, and only 0.16–0.31 for 13‐cis‐etretin over the time period studied. An in vivo isomerization of the compounds was also observed which was more extensive for 13‐cis‐etretin than for all‐trans‐etretin. Our results indicate that the low teratogenic potency of 13‐cis‐etretin is due to a limited placental transfer of this compound; on the other hand, the potent teratogen all‐transetretin is rapidly and extensively transferred to the embryo.