Far-red and near-infrared light exhibit lower phototoxicity and deeper penetrance into mammalian tissues, but CPH1-based opto-RTKs also need an external chromophore, such as phycocyanobilin

Far-red and near-infrared light exhibit lower phototoxicity and deeper penetrance into mammalian tissues, but CPH1-based opto-RTKs also need an external chromophore, such as phycocyanobilin.13 Light-controlled homodimerization can be also used to regulate downstream RTK signaling. cell surface receptors activated by diverse ligands and controlling cell fate.1 Excessive RTK activation leads to oncogenesis whereas insufficient RTK signaling is linked to diabetes mellitus, neurodegeneration, growth delay and improper wound healing.2C4 Diseases related to RTK activity impose a heavy burden on health-care systems. Inhibition of RTKs with small-molecule inhibitors and monoclonal antibodies (mAbs) is conventional therapy in various cancers.5 Activation of RTKs with various ligands (replacement therapy), such as insulin and growth factors (GFs), is used to treat diabetes,2 neurodegeneration,6 wound healing and muscle regeneration. 7 While insulin as a hormone acts on multiple organs and tissues,2 the activity of other RTK ligands is usually localized and their use for therapeutic purposes should be Cyclopamine spatio-temporally controlled. Conventional therapies of diseases linked to aberrant RTK signaling usually rely on intravenous infusion of RTK ligands, mAbs or small-molecule inhibitors. Intravenous infusion results in the non-targeted action of injected substances on all organs and tissues, frequently leading to complications that vary in severity. For example, suppression of EGFR signaling with therapeutic anti-EGFR mAbs or inhibitors is used in cancer therapy, but EGFR also plays a central role in skin homeostasis and cardiovascular cell survival. As a result, non-discriminative inhibition of EGFR signaling in a whole organism leads to skin rashes and cardiac toxicity.8 Similarly, activation of TrkA signaling intracerebral infusion of NGF emerged as a potential therapy for Alzheimer’s disease. Clinical trials demonstrated that whereas it slowed disease progression, it also caused back pain due to NGF diffusion into the spinal cord where activation of TrkA leads to secretion of prostaglandins.6 To avoid side effects of conventional therapies and to improve their efficacy, a targeted and Cyclopamine controlled delivery of GFs and mAbs to their sites of Cyclopamine action is required. It can be achieved by engineering of sophisticated delivery vehicles that Cyclopamine are reviewed elsewhere.9 Recently, two novel technologies to control RTK activity and its downstream signaling with light have been developed. In the first one, optogenetic control of RTK signaling relies on genetically encoded chimeric proteins, called opto-RTKs, which are engineered to comprise photoreceptors fused to intracellular RTK domains.10C12 These include dimerizing opto-RTKs based on various photoreceptors10,11,13 and RTK oligomerizing techniques, such as clustering indirectly using cryptochrome 2 (CLICR).14 In the second one, RTK is activated optochemically using semi-genetically encoded RTK chimeras in which dimerization or conformational changes are put under the control of photocaged small molecules.15,16 Other optochemical techniques include photocaging of amino acid residues in the kinase domain17 and photocaging of RTK activators like DNA aptamers,7 RTK inhibition with light-activatable anti-RTK antibodies (photobodies)18,19 and RTK degradation with an opto-PROTAC (proteolysis targeting chimera) technique.20 Here we first describe the principles of design and the major characteristics of modern optogenetic and optochemical tools to optically manipulate RTK functions and RTK downstream signaling. We F2rl1 then discuss how inhibition or destruction of endogenous RTKs with light could be used in cancer therapy and how opto-RTKs and optochemical means of controlling endogenous RTKs could be used to treat insufficient RTK signaling. We next discuss current challenges and possible ways to overcome them for opto-RTK implementation in translational research and therapy. Lastly, we provide an outlook on the future development of optogenetic and optochemical approaches for controlling RTK signaling (DrBphP). Upon action of near-infrared light DrBphP-PCM undergoes conformational changes, leading to RTK activation. (E) Light-induced clustering and CLICR. Top: RTK intracellular domains are fused to Cry2 photoreceptor. Light-induced clustering of Cry2 leads to the activation of opto-RTKs. Bottom: Endogenous RTK activation using CLICR. PLC-SH2-motif is fused to Cry2. Upon action of light SH2-Cry2 fusions cluster and interact with endogenous RTKs. Inactive RTK domains are shown in white while activated RTK domains are shown in orange. Table 1 Optogenetic and optochemical tools controlling RTK activity aureochrome 1 (VfAU1)23 and various derivatives of cryptochrome 2 (Cry2), including its photolyase homology domain (PHR).10 They dimerize upon action of blue light and use available in mammalian tissues flavin mononucleotide as a chromophore. 10 These blue-light controlled opto-RTKs are widely used for and studies of RTK activity.24.