Calcium Uncaging with Visible Light

Ru(ii) polypyridyl complexes as photocages for bioactive compounds containing nitriles and aromatic heterocycles

Photocaging allows for precise spatiotemporal control over the release of biologically active compounds with light. Most photocaged molecules employ organic photolabile protecting groups; however, biologically active compounds often contain functionalities such as nitriles and aromatic heterocycles that cannot be caged with organic groups. Despite their prevalence, only a few studies have reported successful caging of nitriles and aromatic heterocycles. Recently, Ru(ii)-based photocaging has emerged as a powerful method for the release of bioactive molecules containing these functional groups, in many cases providing high levels of spatial and temporal control over biological activity. This Feature Article discusses recent developments in applying Ru(ii)-based photocaging towards biological problems. Our groups designed and synthesized Ru(ii)-based platforms for the photoinduced delivery of cysteine protease and cytochrome P450 inhibitors in order to achieve selective control over enzyme inhibition. We also reported Ru(ii) photocaging groups derived from higher-denticity ancillary ligands that possess photophysical and photochemical properties distinct from more traditional Ru(ii)-based caging groups. In addition, for the first time, we are able to rapidly synthesize and screen Ru(ii) polypyridyl complexes that elicit desired properties by solid-phase synthesis. Finally, our work also defined steric and orbital mixing effects that are important factors in controlling photoinduced ligand exchange.

Photo-cleavable analog of BAPTA for the fast and efficient release of Ca2

A new photocleavable analog of BAPTA chelating ligand has a high affinity towards Ca2+ ions (K = 2.5 × 106 M-1). The use of photolabile 3-(hydroxymethyl)-2-naphthol core in the design of photo-BAPTA allows for the efficient (Φ = 0. 63) and very fast (τ < 12 μs) release of Ca2+ ions upon 300 or 350 nm irradiation.

Smart Nanostructures for Cargo Delivery: Uncaging and Activating by Light

Nanotechnology has begun to play a remarkable role in various fields of science and technology. In biomedical applications, nanoparticles have opened new horizons, especially for biosensing, targeted delivery of therapeutics, and so forth. Among drug delivery systems (DDSs), smart nanocarriers that respond to specific stimuli in their environment represent a growing field. Nanoplatforms that can be activated by an external application of light can be used for a wide variety of photoactivated therapies, especially light-triggered DDSs, relying on photoisomerization, photo-cross-linking/un-cross-linking, photoreduction, and so forth. In addition, light activation has potential in photodynamic therapy, photothermal therapy, radiotherapy, protected delivery of bioactive moieties, anticancer drug delivery systems, and theranostics (i.e., real-time monitoring and tracking combined with a therapeutic action to different diseases sites and organs). Combinations of these approaches can lead to enhanced and synergistic therapies, employing light as a trigger or for activation. Nonlinear light absorption mechanisms such as two-photon absorption and photon upconversion have been employed in the design of light-responsive DDSs. The integration of a light stimulus into dual/multiresponsive nanocarriers can provide spatiotemporal controlled delivery and release of therapeutic agents, targeted and controlled nanosystems, combined delivery of two or more agents, their on-demand release under specific conditions, and so forth. Overall, light-activated nanomedicines and DDSs are expected to provide more effective therapies against serious diseases such as cancers, inflammation, infections, and cardiovascular disease with reduced side effects and will open new doors toward the treatment of patients worldwide.

Cloaked Caged Compounds: Chemical Probes for Two-Photon Optoneurobiology

Caged neurotransmitters, in combination with focused light beams, enable precise interrogation of neuronal function, even at the level of single synapses. However, most caged transmitters are, surprisingly, severe antagonists of ionotropic gamma-aminobutyric acid (GABA) receptors. By conjugation of a large, neutral dendrimer to a caged GABA probe we introduce a "cloaking" technology that effectively reduces such antagonism to very low levels. Such cloaked caged compounds will enable the study of the signaling of the inhibitory neurotransmitter GABA in its natural state using two-photon uncaging microscopy for the first time.

A Green Light-Triggerable RGD Peptide for Photocontrolled Targeted Drug Delivery: Synthesis and Photolysis Studies

We describe for the first time the synthesis and photochemical properties of a coumarin-caged cyclic RGD peptide and demonstrate that uncaging can be efficiently performed with biologically compatible green light. This was accomplished by using a new dicyanocoumarin derivative (DEAdcCE) for the protection of the carboxyl function at the side chain of the aspartic acid residue, which was selected on the basis of Fmoc-tBu SPPS compatibility and photolysis efficiency. The shielding effect of a methyl group incorporated in the coumarin derivative near the ester bond linking both moieties in combination with the use of acidic additives such as HOBt or Oxyma during the basic Fmoc-removal treatment were found to be very effective for minimizing aspartimide-related side reactions. In addition, a conjugate between the dicyanocoumarin-caged cyclic RGD peptide and ruthenocene, which was selected as a metallodrug model cargo, has been synthesized and characterized. The fact that green-light triggered photoactivation can be efficiently performed both with the caged peptide and with its ruthenocenoyl bioconjugate reveals great potential for DEAdcCE-caged peptide sequences as selective drug carriers in the context of photocontrolled targeted anticancer strategies.

Design and Synthesis of a 4-Nitrobromobenzene Derivative Bearing an Ethylene Glycol Tetraacetic Acid Unit for a New Generation of Caged Calcium Compounds with Two-Photon Absorption Properties in the Near-IR Region and Their Application in Vivo

Among biologically active compounds, calcium ions (Ca2+) are one of the most important species in cell physiological functions. Development of new calcium chelators with two-photon absorption (TPA) properties is a state-of-the-art challenge for chemists. In this study, we report the first and efficient synthesis of 5-bromo-2-nitrobenzyl-substituted ethylene glycol tetraacetic acid (EGTA) as a platform for a new generation of calcium chelators with TPA properties in the near-infrared region. New calcium chelators with high TPA properties, that is, a two-photon (TP) fragmentation efficiency of δu = 20.7 GM at 740 nm for 2-(4-nitrophenyl)benzofuran (NPBF)-substituted EGTA (NPBF-EGTA, K d = 272 nM) and δu = 7.8 GM at 800 nm for 4-amino-4'-nitro-1,1'-biphenyl (BP)-substituted EGTA (BP-EGTA, K d = 440 nM) derivatives, were synthesized using Suzuki-Miyaura coupling reactions of the bromide with benzofuran-2-boronic acid and 4-(dimethylamino)phenyl boronic acid, respectively. The corresponding acetoxymethyl (AM) esters were prepared and successfully applied to the Ca2+-uncaging reaction triggered by TP photolysis in vivo.

Cooperative Veratryle and Nitroindoline Cages for Two-Photon Uncaging in the NIR

Tandem uncaging systems in which a two-photon absorbing module and a cage moiety, linked via a phosphorous clip, that act together by Förster resonance energy transfer (FRET) have been developed. A library of these compounds, using different linkers and cages (7-nitroindolinyl or nitroveratryl) has been synthesized. The investigation of their uncaging and two-photon absorption properties demonstrates the scope and versatility of the engineering strategy towards efficient two-photon cages and reveals surprising cooperative and topological effects. The interactions between the 2PA module and the caging moiety are found to promote cooperative effects on the 2PA response while additional processes that enhance the uncaging efficiency are operative in well-oriented nitroindoline-derived dyads. These synergic effects combine to lead to record two-photon uncaging cross-section values (i.e., up to 20 GM) for uncaging of carboxylic acids.