Automation of Sample Dispensing Using Pocket Tips for Evaluation of CYP2C9 Isoenzyme Reversible Inhibition in an Evolution Precision Pipetting Platform

Most of the medicinal chemistry compounds received from other Merck Research Laboratories (MRL) for evaluation in our in vitro counterscreenings are in pure DMSO solution. This solvent has shown to be a key interference factor in the radiometric evaluation of cytochrome P-450 (CYP) inhibition. To avoid this problem, we have been using a ternary solvent solution that keeps DMSO concentration to a minimum during the titration of the compounds.

The equipment used at our laboratory to perform the dose—response titration of the compounds in the CYP assays is PerkinElmer Evolution Precision Pipetting Platform (EP3) robots with limited microliter capabilities using disposable tips. The need for a nanoliter dispensing technique that keeps the percentage of DMSO at levels that do not affect the assay, and the need to use pure DMSO solutions at high concentrations to avoid solubility issues of the compounds, moved us to design a new automated sample management process for all compounds that were requested to be tested in these assays.

The PocketTips system (nAscent BioSciences Inc., Wellesley Hills, MA) seemed to be a good option for pipetting very low volumes without acquiring new expensive nanoliter liquid handling equipment. Apparent difficulties with implementation were the unavailability of PocketTips for the 96-tips head of the EP3 (PerkinElmer, Waltham, MA) and the need for testing several CYP isoenzymes (up to four) by using the same rack of tips to save run time and reduce costs.

In this article, we discuss the entire process to introduce and validate a new dispensing process for sampling of compounds with multiple nanoliters dispensing at the assay level, indicating in detail how we implemented the use of recycled PocketTips in our PerkinElmer EP3 workstations.

Androstene-3,5-dienes as ER-β selective SERMs

A series of androstene-3,5-diene derivatives were prepared. Despite lacking the C-3 hydroxyl previously believed necessary for ER activity, some of the analogs retained surprising affinity for ER-beta. For example, diene 4 retained excellent selectivity and potency as an ER-beta agonist and was more selective for ER-beta over the androgen receptor (AR).

Bridged androstenediol analogs as ER-β selective SERMs

A series of bridged androstenediol derivatives was prepared. The bridged compounds exhibited reduced ER-beta selectivity relative to uncyclized analogs.

Estrogen receptor beta-subtype selective tetrahydrofluorenones: use of a fused pyrazole as a phenol bioisostere

Synthesis of a series of fused pyrazole tetrahydrofluorenone analogs which are potent, ERbeta subtype selective ligands is described. Analogs possessing subnanomolar ERbeta binding, greater than 100-fold ERbeta-selectivity, and oral bioavailability are reported.

Androstenediol analogs as ER-beta-selective SERMs

A series of 19-substituted androstenediol derivatives was prepared. Some of the novel analogs were surprisingly potent and selective ligands for ER-beta.

High exogenous homocysteine modifies eye development in early chick embryos

BACKGROUND

Homocysteine is a nonessential aminoacid whose increase is related to the appearance of neural tube defects in humans. In chick embryos, high levels of homocysteine produce neural tube defects and alteration of neural crest cell migration.

METHODS

In our study, 8 microl of L-homocysteine thiolatone (20 micromol) was added to chick embryos of Stages 3-8/10 (Hamburger and Hamilton, 1951), (1238 hr of incubation). Three days later, 50 embryos, externally normal or carrying isolated spinal neural tube defects, were sectioned and stained by hematoxilin-eosin or anti-fibrillin-1 antibody.

RESULTS

The eye showed alterations of the optic cup as microphthalmia, or lens dislocation. In both cases, the incidence of alterations diminished with the age of the homocysteine-increased embryos. Optic cup modifications are probably associated with central nervous system alterations, because most of the affected embryos exhibited isolated spinal neural tube defects and had altered neural crest cells. We have shown for the first time that high exogenous homocysteine during early development could produce a caudally-displaced lens axis before the zonule is formed. Fibrillin-1 is the main component of elastic microfibrils, and in the adult human it is seen as a protein particularly susceptible to homocysteine attack.

CONCLUSIONS

Antibody staining against fibrillin-1 showed no evident morphological differences in distribution between experimental and control embryos in the lens, suggesting that fibrillin-1 was not the cause, and malformations may be attributed to other mechanisms.

TGF-beta(3)-induced chondroitin sulphate proteoglycan mediates palatal shelf adhesion

In mammals, the adhesion and fusion of the palatal shelves are essential mechanisms in the development of the secondary palate. Failure of any of these processes leads to the formation of cleft palate. The mechanisms underlying palatal shelf adhesion are poorly understood, although the presence of filopodia on the apical surfaces of the superficial medial edge epithelial (MEE) cells seems to play an important role in the adhesion of the opposing MEE. We demonstrate here the appearance of chondroitin sulphate proteoglycan (CSPG) on the apical surface of MEE cells only immediately prior to contact between the palatal shelves. This apical CSPG has a functional role in palatal shelf adhesion, as either the alteration of CSPG synthesis by beta-D-Xyloside or its specific digestion by chondroitinase AC strikingly alters the in vitro adhesion of palatal shelves. We also demonstrate the absence of this apical CSPG in the clefted palates of transforming growth factor beta 3 (TGF-beta(3)) null mutant mice, and its induction, together with palatal shelf adhesion, when TGF-beta(3) is added to TGF-beta(3) null mutant palatal shelves in culture. When chick palatal shelves (that do not adherein vivo nor express TGF-beta(3), nor CSPG in the MEE) are cultured in vitro, they do not express CSPG and partially adhere, but when TGF-beta(3) is added to the media, they express CSPG and their adhesion increases strikingly. We therefore conclude that the expression of CSPG on the apical surface of MEE cells is a key factor in palatal shelf adhesion and that this expression is regulated by TGF-beta(3).

TGF-beta3 is required for the adhesion and intercalation of medial edge epithelial cells during palate fusion

Transforming growth factor-beta3 (TGF-beta3) plays a critical role during palate development, since mutations of the TGF-beta3 gene give rise to cleft palate in both humans and mice. Striking alterations have been reported in the behaviour and differentiation of medial edge epithelial (MEE) cells in TGF-beta3 knockout mouse palates. In the present paper, we provide evidence of alterations in MEE intercellular adhesion in TGF-beta3 -/- mouse palates using immunohistochemistry with monoclonal antibodies to a panel of cell adhesion and cytoskeletal molecules including E-cadherin, alpha and beta catenin, beta actin, vinculin and beta2 integrin. In vitro labeling of opposing MEE with two different lipophilic markers and subsequent analysis by confocal microscopy revealed that wild type MEE cells intercalate as soon as the midline epithelial seam forms. This finding indicates that the palate may elongate in a dorso-ventral direction by means of convergent extension, as occurs in other embryonic developmental processes. In contrast, this intercalation does not occur in the TGF-beta3 -/- MEE but it can be rescued by the exogenous addition of TGF-beta3. Thus, the substantial alteration of MEE intercellular adhesion observed in TGF-beta3 -/- palates may account for the defect in palatal shelf adhesion and the formation of cleft palate.

Medial edge epithelial cell fate during palatal fusion

To explain the disappearance of medial edge epithelial (MEE) cells during palatal fusion, programmed cell death, epithelial-mesenchymal transformation, and migration of these cells to the oral and nasal epithelia have been proposed. However, MEE cell death has not always been accepted as a mechanism involved in midline epithelial seam disappearance. Similarly, labeling of MEE cells with vital lipophilic markers has not led to a clear conclusion as to whether MEE cells migrate, transform into mesenchyme, or both. To clarify these controversies, we first utilized TUNEL techniques to detect apoptosis in mouse palates at the fusion stage and concomitantly analyzed the presence of macrophages by immunochemistry and confocal microscopy. Second, we in vitro infected the MEE with the replication-defective helper-free retroviral vector CXL, which carries the Escherichia coli lacZ gene, and analyzed beta-galactosidase activity in cells after fusion to follow their fate. Our results demonstrate that MEE cells die and transform into mesenchyme during palatal fusion and that dead cells are phagocytosed by macrophages. In addition, we have investigated the effects of the absence of transforming growth factor beta(3) (TGF-beta(3)) during palatal fusion. Using environmental scanning electron microscopy and TUNEL labeling we compared the MEE of the clefted TGF-beta(3) null and wild-type mice. We show that MEE cell death in TGF-beta(3) null palates is greatly reduced at the time of fusion, revealing that TGF-beta(3) has an important role as an inducer of apoptosis during palatal fusion. Likewise, the bulging cells observed on the MEE surface of wild-type mice prior to palatal shelf contact are very rare in the TGF-beta(3) null mutants. We hypothesize that these protruding cells are critical for palatal adhesion, being morphological evidence of increased cell motility/migration.

Bulging medial edge epithelial cells and palatal fusion

The surface of the medial edge epithelium of embryonic day 12, 13 and 14 mouse palatal shelves was observed utilising Environmental Scanning Electron Microscopy (ESEM). This technique offers the advantage of visualisation of biological samples after short fixation times in their natural hydrated state. Bulging epithelial cells were observed consistently on the medial edge epithelium prior to palatal shelf fusion. Additionally, we have used ESEM to compare the morphology and surface features of palatal shelves from embryonic day 13 to 16 mouse embryos that are homozygous null (TGF-beta3 -/-), heterozygous (TGF-beta3 +/-) or homozygous normal (TGF-beta3 +/+) for transforming growth factor beta-3 (TGF-beta3). At embryonic day 15 and 16 most TGF-beta3 +/- and +/+ embryos showed total palatal fusion, whilst all TGF-beta3 null mutants had cleft palate: the middle third of the palatal shelves had adhered, leaving an anterior and posterior cleft. From embryonic day 14 to 16 abundant cells were observed bulging on the medial edge epithelial surface of palates from the TGF-beta3 +/- and +/+ embryos. However, they were never seen in the TGF-beta3 null embryos, suggesting that these surface bulges might be important in palatal fusion and that their normal differentiation is induced by TGF-beta3. The expression pattern of E-Cadherin, beta-catenin, chondroitin sulphate proteoglycan, beta-Actin and vinculin as assayed by immunocytochemistry in these cells shows specific variations that suggest their importance in palatal shelf adhesion.