Molecular basis for differential recognition of an allosteric inhibitor by receptor tyrosine kinases.

Understanding kinase-inhibitor selectivity continues to be a major objective in kinase drug discovery. We probe the molecular basis of selectivity of an allosteric inhibitor (MSC1609119A-1) of the insulin-like growth factor-I receptor kinase (IGF1RK), which has been shown to be ineffective for the homologous insulin receptor kinase (IRK). Specifically, we investigated the structural and energetic basis of the allosteric binding of this inhibitor to each kinase by combining molecular modeling, molecular dynamics (MD) simulations, and thermodynamic calculations. We predict the inhibitor conformation in the binding pocket of IRK and highlight that the charged residues in the histidine-arginine-aspartic acid (HRD) and aspartic acid-phenylalanine-glycine (DFG) motifs and the nonpolar residues in the binding pocket govern inhibitor interactions in the allosteric pocket of each kinase. We suggest that the conformational changes in the IGF1RK residues M1054 and M1079, movement of the ⍺C-helix, and the conformational stabilization of the DFG motif favor the selectivity of the inhibitor toward IGF1RK. Our thermodynamic calculations reveal that the observed selectivity can be rationalized through differences observed in the electrostatic interaction energy of the inhibitor in each inhibitor/kinase complex and the hydrogen bonding interactions of the inhibitor with the residue V1063 in IGF1RK that are not attained with the corresponding residue V1060 in IRK. Overall, our study provides a rationale for the molecular basis of recognition of this allosteric inhibitor by IGF1RK and IRK, which is potentially useful in developing novel inhibitors with improved affinity and selectivity.

Structural Models for a Series of Allosteric Inhibitors of IGF1R Kinase.

The allosteric inhibition of insulin-like growth factor receptor 1 kinase (IGF1RK) is a potential strategy to overcome selectivity barriers for targeting receptor tyrosine kinases. We constructed structural models of a series of 12 indole-butyl-amine derivatives that have been reported as allosteric inhibitors of IGF1RK. We further studied the dynamics and interactions of each inhibitor in the allosteric pocket via all-atom explicit-solvent molecular dynamics (MD) simulations. We discovered that a bulky carbonyl substitution at the R1 indole ring is structurally unfavorable for inhibitor binding in the IGF1RK allosteric pocket. Moreover, we found that the most potent derivative (termed C11) acquires a distinct conformation: forming an allosteric pocket channel with better shape complementarity and interactions with the receptor. In addition to a hydrogen-bonding interaction with V1063, the cyano derivative C11 forms a stable hydrogen bond with M1156, which is responsible for its unique binding conformation in the allosteric pocket. Our findings show that the positioning of chemical substituents with different pharmacophore features at the R1 indole ring influences molecular interactions and binding conformations of indole-butyl-amine derivatives and, hence, dramatically affects their potencies. Our results provide a structural framework for the design of allosteric inhibitors with improved affinities and specificities against IGF1RK.

Using site-directed mutagenesis to further the understanding of insulin receptor-insulin like growth factor-1 receptor heterodimer structure.

Type 2 diabetes is characterised by the disruption of insulin and insulin-like growth factor (IGF) signalling. The key hubs of these signalling cascades - the Insulin receptor (IR) and Insulin-like growth factor 1 receptor (IGF1R) - are known to form functional IR-IGF1R hybrid receptors which are insulin resistant. However, the mechanisms underpinning IR-IGF1R hybrid formation are not fully understood, hindering the ability to modulate this for future therapies targeting this receptor. To pinpoint suitable sites for intervention, computational hotspot prediction was utilised to identify promising epitopes for targeting with point mutagenesis. Specific IGF1R point mutations F450A, R391A and D555A show reduced affinity of the hybrid receptor in a BRET based donor-saturation assay, confirming hybrid formation could be modulated at this interface. These data provide the basis for rational design of more effective hybrid receptor modulators, supporting the prospect of identifying a small molecule that specifically interacts with this target.

Old hormones of the insulin family as new developmental signals

La insulina fue identificada como una hormona anabólica pancreática,responsable de la homeostasis de la glucosa, y el Factor de Crecimiento similar ala Insulina tipo I (IGF-I) como el mediador de la acción de la Hormona deCrecimiento postnatalmente. Nuevas informaciones moleculares, farmacológicas yembriológicas han ampliado el concepto del papel fisiológico de estas hormonasy sus moléculas relacionadas, particularmente del precursor de la insulina, laproinsulina, en el desarrollo de vertebrados. Los estudios de nuestro laboratoriohan demostrado que la proinsulina está expresada y es funcional antes deque aparezca el páncreas. La expresión de proinsulina en los embriones de polloy ratón muestra regulación transcripcional y post-transcripcional muy fina, conla generación de transcritos específicos embrionarios que se traducen de formasdistintas. El producto de estos mRNAs se mantiene como proinsulina sinprocesar, que protege a las células de la apoptosis excesiva durante la neurulación.En contraste, el IGF-I está expresado más tarde que la proinsulina en el embriónde pollo y comienza en el sistema nervioso. En el embrión de ratón, la generaciónde células madre neurales en cultivo ha permitido estudiar el papel de estasmoléculas en la proliferación y diferenciación de precursores neurales. Laproinsulina y el IGF-I pueden cooperar con los mitógenos (EGF y FGF2) en elcontrol de la proliferación de células madre/precursores mientras que el IGF-I esun factor esencial para la diferenciación neural. Los ratones deficientes en IGF-Ipresentan alteración de la citoarquitectura del bulbo olfatorio con disminución delnúmero de neuronas mitrales y glía radial anormal. Este artículo da una visiónglobal del importante papel de las proteínas de la familia de la insulina en eldesarrollo

Insulin was first identified as an anabolic pancreatic hormone responsible forglucose homeostasis, and Insulin-like Growth Factor (IGF-I) as the mediator of theaction of Growth Hormone on postnatal growth. New molecular, pharmacologicaland embryological information has broadened the scope of the physiological rolesof these hormones and their related molecules, particularly the insulin precursorproinsulin, during vertebrate development. Studies in our laboratory havedemonstrated that proinsulin is expressed and functional before emergence of thepancreas. Proinsulin gene expression in the chick and mouse embryo shows finetranscriptional and postrancriptional regulation with generation of specificembryonic transcripts which are differentially translated. The protein productremains as unprocessed proinsulin that protects the cells from excessive apoptosisduring neurulation. In contrast, IGF-I is expressed later than proinsulin in thechick embryo and it starts in the nervous system. In the mouse embryo, generationof olfactory bulb stem cells in culture has allowed the study of these molecules’role in the proliferation and differentiation of neural precursors. Proinsulin andIGF-I can cooperate with mitogens (EGF and FGF2) in the control of stem/precursor cells proliferation and IGF-I is an essential factor for neuraldifferentiation. Mice deficient in IGF-I present a disruption of olfactory bulbcytoarchitecture, with decreased numbers of mitral cells and abnormal radial glia.This article gives thus an overview of the important role of insulin family proteinsin development