A general approach for engineering RTKs optically controlled with far-red light

Regulation of receptor tyrosine kinase (RTK) activity is necessary for studying cell signaling pathways in health and disease. We developed a generalized approach for engineering RTKs optically controlled with far-red light. We targeted the bacterial phytochrome DrBphP to the cell surface and allowed its light-induced conformational changes to be transmitted across the plasma membrane via transmembrane helices to intracellular RTK domains. Systematic optimization of these constructs has resulted in optically regulated epidermal growth factor receptor, HER2, TrkA, TrkB, FGFR1, IR1, cKIT and cMet, named eDrRTKs. eDrRTKs induced downstream signaling in mammalian cells in tens of seconds. The ability to activate eDrRTKs with far-red light enabled spectral multiplexing with fluorescent probes operating in a shorter spectral range, allowing for all-optical assays. We validated eDrTrkB performance in mice and found that minimally invasive stimulation in the neocortex with penetrating via skull far-red light-induced neural activity, early immediate gene expression and affected sleep patterns.

Light control of RTK activity: from technology development to translational research

Inhibition of receptor tyrosine kinases (RTKs) by small molecule inhibitors and monoclonal antibodies is used to treat cancer. Conversely, activation of RTKs with their ligands, including growth factors and insulin, is used to treat diabetes and neurodegeneration. However, conventional therapies that rely on injection of RTK inhibitors or activators do not provide spatiotemporal control over RTK signaling, which results in diminished efficiency and side effects. Recently, a number of optogenetic and optochemical approaches have been developed that allow RTK inhibition or activation in cells and in vivo with light. Light irradiation can control RTK signaling non-invasively, in a dosed manner, with high spatio-temporal precision, and without the side effects of conventional treatments. Here we provide an update on the current state of the art of optogenetic and optochemical RTK technologies and the prospects of their use in translational studies and therapy.

Bacterial Phytochrome as a Scaffold for Engineering of Receptor Tyrosine Kinases Controlled with Near-Infrared Light

Optically controlled receptor tyrosine kinases (opto-RTKs) allow regulation of RTK signaling using light. Until recently, the majority of opto-RTKs were activated with blue-green light. Fusing a photosensory core module of Deinococcus radiodurans bacterial phytochrome (DrBphP-PCM) to the kinase domains of neurotrophin receptors resulted in opto-RTKs controlled with light above 650 nm. To expand this engineering approach to RTKs of other families, here we combined the DrBpP-PCM with the cytoplasmic domains of EGFR and FGFR1. The resultant Dr-EGFR and Dr-FGFR1 opto-RTKs are rapidly activated with near-infrared and inactivated with far-red light. The opto-RTKs efficiently trigger ERK1/2, PI3K/Akt, and PLCγ signaling. Absence of spectral crosstalk between the opto-RTKs and green fluorescent protein-based biosensors enables simultaneous Dr-FGFR1 activation and detection of calcium transients. Action mechanism of the DrBphP-PCM-based opto-RTKs is considered using the available RTK structures. DrBphP-PCM represents a versatile scaffold for engineering of opto-RTKs that are reversibly regulated with far-red and near-infrared light.

Fluorescent Biosensors for Neurotransmission and Neuromodulation: Engineering and Applications

Understanding how neuronal activity patterns in the brain correlate with complex behavior is one of the primary goals of modern neuroscience. Chemical transmission is the major way of communication between neurons, however, traditional methods of detection of neurotransmitter and neuromodulator transients in mammalian brain lack spatiotemporal precision. Modern fluorescent biosensors for neurotransmitters and neuromodulators allow monitoring chemical transmission in vivo with millisecond precision and single cell resolution. Changes in the fluorescent biosensor brightness occur upon neurotransmitter binding and can be detected using fiber photometry, stationary microscopy and miniaturized head-mounted microscopes. Biosensors can be expressed in the animal brain using adeno-associated viral vectors, and their cell-specific expression can be achieved with Cre-recombinase expressing animals. Although initially fluorescent biosensors for chemical transmission were represented by glutamate biosensors, nowadays biosensors for GABA, acetylcholine, glycine, norepinephrine, and dopamine are available as well. In this review, we overview functioning principles of existing intensiometric and ratiometric biosensors and provide brief insight into the variety of neurotransmitter-binding proteins from bacteria, plants, and eukaryotes including G-protein coupled receptors, which may serve as neurotransmitter-binding scaffolds. We next describe a workflow for development of neurotransmitter and neuromodulator biosensors. We then discuss advanced setups for functional imaging of neurotransmitter transients in the brain of awake freely moving animals. We conclude by providing application examples of biosensors for the studies of complex behavior with the single-neuron precision.

Neurotrophin receptor tyrosine kinases regulated with near-infrared light

Optical control over the activity of receptor tyrosine kinases (RTKs) provides an efficient way to reversibly and non-invasively map their functions. We combined catalytic domains of Trk (tropomyosin receptor kinase) family of RTKs, naturally activated by neurotrophins, with photosensory core module of DrBphP bacterial phytochrome to develop opto-kinases, termed Dr-TrkA and Dr-TrkB, reversibly switchable on and off with near-infrared and far-red light. We validated Dr-Trk ability to reversibly light-control several RTK pathways, calcium level, and demonstrated that their activation triggers canonical Trk signaling. Dr-TrkA induced apoptosis in neuroblastoma and glioblastoma, but not in other cell types. Absence of spectral crosstalk between Dr-Trks and blue-light-activatable LOV-domain-based translocation system enabled intracellular targeting of Dr-TrkA independently of its activation, additionally modulating Trk signaling. Dr-Trks have several superior characteristics that make them the opto-kinases of choice for regulation of RTK signaling: high activation range, fast and reversible photoswitching, and multiplexing with visible-light-controllable optogenetic tools.

Optogenetically controlled protein kinases for regulation of cellular signaling

Protein kinases are involved in the regulation of many cellular processes including cell differentiation, survival, migration, axon guidance and neuronal plasticity. A growing set of optogenetic tools, termed opto-kinases, allows activation and inhibition of different protein kinases with light. The optogenetic regulation enables fast, reversible and non-invasive manipulation of protein kinase activities, complementing traditional methods, such as treatment with growth factors, protein kinase inhibitors or chemical dimerizers. In this review, we summarize the properties of the existing optogenetic tools for controlling tyrosine kinases and serine-threonine kinases. We discuss how the opto-kinases can be applied for studies of spatial and temporal aspects of protein kinase signaling in cells and organisms. We compare approaches for chemical and optogenetic regulation of protein kinase activity and present guidelines for selection of opto-kinases and equipment to control them with light. We also describe strategies to engineer novel opto-kinases on the basis of various photoreceptors.

[Monoclonal antibodies in high-grade gliomas]

The review is devoted to a relatively young direction in therapy of malignant gliomas, which is based on applying monoclonal antibodies against tumour-associated antigens. The current data on efficacy of main therapeutic agents in clinical practice or clinical trials concerning high-grade gliomas, especially glioblastoma multiforme, is summarized. Of particular interest is bevacizumab, a humanized monoclonal antibody against vascular endothelial growth factor (anti-VEGF), which is widely used in glioblastoma. Major clinical trials devoted to bevacizumab monotherapy and combinations of bevacizumab with other therapeutic modalities in primary and recurrent glioblastoma conducted since 2006 till now are reviewed. The results ofexperimental and clinical application ofmonoclonal antibodies against epidermal growth factor receptor (EGFR) and its mutant variant EGFRvIII are analyzed, showing the most significant clinical effectiveness of nimotuzumab--a humanized monoclonal antibody. Significant part of the review is devoted to discussion of experimental and clinical data concerning efficacy of antibodies against VEGF receptor 2, platelet-derived growth factor receptor α, hepatocyte growth factor and its receptor c-Met. Unbiassed analysis of clinical trials on monoclonal antibodies does not allow us to conclude that passive immunotherapy directed against antigens listed above can significantly improve the overall survival of patients suffering from glioblastoma multiforme. This finding has encouraged us to mention several alternative approaches to passive immunotherapy and to list several prospective antigens for developing monoclonal antibodies.

Expression of a recombinant extracellular fragment of human vascular endothelial growth factor receptor VEGFR1 in E. coli

Human vascular endothelium growth factor receptor VEGFR1 is a type III fms-like tyrosine kinase with weakly pronounced tyrosine kinase function. The second and third IgG-like domains of the extracellular part of VEGFR1 act as "traps" for VEGF and are prospective candidates for antiangiogenic therapy of VEGF-dependent tumors. cDNA encoding extracellular Ig-like domains 2, 3, 4 of VEGFR1 was cloned in expressing vectors pET28a, pET32a, and pQE60. The recombinant protein was expressed in E. coli cells and purified by metal affinity chromatography. An expressing construction and a superproducer strain were created, allowing the production of high amounts of recombinant VEGFR1 extracellular fragment, needed for experimental in vivo antiangiogenic therapy.