Research Spotlight

Groppe, J. C. (2019). “Induced degradation of protein kinases by bifunctional small molecules: a next-generation strategy.” Expert Opin Drug Discov Sep 12:1-17. [Epub ahead of print].

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Introduction: Protein kinases are a major target for small-molecule drug development. However, relatively few compounds are free of off-target toxicity and reach the clinic. Because the 500-plus kinases share conserved ATP-binding clefts, the site targeted by competitive inhibitors, generation of specific therapeutics remains a nearly intractable challenge. Areas covered: Inducing degradation, instead of inhibition by occupancy-driven drugs, is an emerging strategy that offers the long-sought specificity, as well as mechanistic benefits. Currently approved inhibitors require steady-state binding and leave proteins intact for interactions in multi-protein complexes. After a general background about induced protein degradation, perspectives on protein kinases are provided. Expert opinion: Induced degradation by state-of-the-art compounds (proteolysis-targeting chimeras, PROTACs) has been shown for protein kinases, albeit in early pre-clinical stages. Further work is required to expand the number of enzymes that could be exploited to direct proteins for degradation by ubiquitylation. In addition, despite the simple modularity of the chimeras, generation of hits will require empirical approaches due to the role of protein-protein interactions and distribution of tagging sites. However, given the advantages of degradation, drug discovery efforts targeting protein kinases should increasingly shift toward generation and screening of inducers of degradation and away from occupancy-based inhibitors of old.

Fritz, K. R., Y. Zhang and L. B. Ruest (2019). “Cdc42 activation by endothelin regulates neural crest cell migration in the cardiac outflow tract.” Dev Dyn 248(9): 795-812.

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BACKGROUND: Congenital cardiovascular malformations are the most common birth defects affecting children. Several of these defects occur in structures developing from neural crest cells. One of the key signaling pathways regulating cardiac neural crest cell (CNCC) development involves the endothelin-A receptor (Ednra). However, the exact function of Ednra signaling in CNCC is unknown. RESULTS: The fate mapping of CNCC in Ednra embryos indicated that the migration of these cells is aberrant in the cardiac outflow tract (OFT), but not in the pharyngeal arches. This premature arrest of CNCC migration occurs independently of CNCC proliferation and apoptosis changes and major gene expression changes. Analysis of the Rho family of small GTPases in the mutant embryos revealed that Cdc42 failed to localize normally in the CNCC migrating in the OFT. The inhibition of Cdc42 activity in cultured embryos recapitulated the migratory phenotype observed in Ednra mice. Further analyses revealed that Cdc42 is part of the signaling pathway activated by endothelin specifically in OFT CNCC to control their migration. CONCLUSIONS: These results indicated that the activation of Cdc42 by endothelin signaling is important for CNCC migration in the OFT but this pathway is not involved in mandibular or pharyngeal arch artery patterning.

Ammoury, M. J., S. Mustapha, P. C. Dechow and J. G. Ghafari (2019). “Two distalization methods compared in a novel patient-specific finite element analysis.” Am J Orthod Dentofacial Orthop 156(3): 326-336.

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INTRODUCTION: Orthodontic mini-implants aid in the correction of distocclusions via direct anchorage (pull from mini-implant to teeth) and indirect anchorage (teeth pulled against other teeth anchored by the mini-implant). The aim of this study was to compare stress levels on the periodontal ligament (PDL) of maxillary buccal teeth in direct and indirect distalization against orthodontic mini-implants and accounting for individual variation in maxillary anatomy and biomechanical characteristics of the compact bone. METHODS: A 3D model of the maxilla containing the different components (teeth, PDL, trabecular and cortical bones) was generated from a computed tomographic scan. Cortical bone was divided into several areas according to previously defined zones. Bone stiffness and thickness data, obtained from 11 and 12 cadavers, respectively, were incorporated into the initial model to simulate the individual cortical bone variation at the different locations. Subsequently, a finite element analysis was used to simulate the distalization modalities. RESULTS: Stresses at the buccal, palatal, mesial, and distal surfaces were significantly different between adjacent teeth under stiffness but not thickness variation. In both distalization modalities, low or no significant correlations were found between stress values and corresponding cortical bone thicknesses. High significant and inverted correlations were observed at the first molar between stress amounts and cortical bone stiffness (direct modality: -0.68 < r < -0.72; indirect modality: -0.80 < r < -0.82; P <0.05). CONCLUSIONS: With the use of a novel finite element approach that integrated human data on variations in bone properties, findings suggested that cortical bone stiffness may influence tooth movement more than bone thickness. Significant clinical implications could be related to these findings.

Logan, S. M., L. B. Ruest, M. D. Benson and K. K. H. Svoboda (2019). “Extracellular Matrix in Secondary Palate Development.” Anat Rec (Hoboken) Sep 12. [Epub ahead of print].

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The secondary palate arises from outgrowths of epithelia-covered embryonic mesenchyme that grow from the maxillary prominence, remodel to meet over the tongue, and meet to fuse at the midline. These events require the coordination of cell proliferation, migration, and gene expression, all of which take place in the context of the extracellular matrix (ECM). Palatal cells generate their ECM, and then stiffen, degrade, or otherwise modify its properties to achieve the required cell movement and organization during palatogenesis. The ECM, in turn, acts on the cells through their matrix receptors to change their gene expression and thus their phenotype. The number of ECM-related gene mutations that cause cleft palate in mice and humans is a testament to the crucial role the matrix plays in palate development and a reminder that understanding that role is vital to our progress in treating palate deformities. This article will review the known ECM constituents at each stage of palatogenesis, the mechanisms of tissue reorganization and cell migration through the palatal ECM, the reciprocal relationship between the ECM and gene expression, and human syndromes with cleft palate that arise from mutation of ECM proteins and their regulators.

Leeper, D. K., A. Noureldin, K. Julien, P. M. Campbell and P. H. Buschang (2019). “Risk assessments in orthodontic patients developing white spot lesions.” J Investig Clin Dent: Sep 22:e12470. [Epub ahead of print].

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AIM: To determine whether caries risk factors, including cariogenic bacterial levels and salivary function, can be used to identify orthodontic patients who develop white spot lesions (WSL). METHODS: This prospective case-control study comprised 50 patients 11-17 years of age, including 25 controls and 25 cases who developed new WSL during treatment. WSL, oral hygiene and fluorosis were evaluated from intraoral photographs. The biofilm was assessed with bacterial cultures and adenosine triphosphate (ATP) bioluminescence. Salivary analyses were performed to determine the pH of saliva and flow rates. A survey was used to assess snacking frequency, oral hygiene and fluoride utilization. RESULTS: There were no between-group pretreatment differences in WSL. Cases reported eating sugary foods significantly more often than the controls. There was a significant decline in oral hygiene during treatment, with no significant between-group difference. There also were no statistically significant between-group differences in the amount of saliva, buffer, ATP bioluminescence and bacterial levels. Both groups showed lower than normal buffer capacity and high bacterial levels. CONCLUSION: Cases had greater sugar intake between meals than controls. ATP bioluminescence, Streptococcus mutans levels with Saliva Check Mutans, and salivary factors do not identify patients who develop WSL.