Two-Photon Sensitive Coumarinyl Photoremovable Protecting Groups with Rigid Electron-Rich Cycles Obtained by Domino Reactions Initiated by a 5-exo-Dig Cyclocarbopalladation

Triplet-Triplet Annihilation Upconversion-Based Photolysis: Applications in Photopharmacology

The emerging field of photopharmacology is a promising chemobiological methodology for optical control of drug activities that could ultimately solve the off-target toxicity outside the disease location of many drugs for the treatment of a given pathology. The use of photolytic reactions looks very attractive for a light-activated drug release but requires to develop photolytic reactions sensitive to red or near-infrared light excitation for better tissue penetration. This review will present the concepts of triplet-triplet annihilation upconversion-based photolysis and their recent in vivo applications for light-induced drug delivery using photoactivatable nanoparticles.

Towards a Light-mediated Gene Therapy for the Eye using Caged Ethinylestradiol and the Inducible Cre/lox System

Increasingly, retinal pathologies are being treated with virus-mediated gene therapies. To be able to target viral transgene expression specifically to the pathological regions of the retina with light, we established an in vivo photoactivated gene expression paradigm for retinal tissue. Based on the inducible Cre/lox system, we discovered that ethinylestradiol is a suitable alternative to Tamoxifen as ethinylestradiol is more amenable to modification with photosensitive protecting compounds, i.e., "caging." Identification of ethinylestradiol as a ligand for the mutated human estradiol receptor was supported by in silico binding studies showing the reduced binding of caged ethinylestradiol. Caged ethinylestradiol was injected into the eyes of double transgenic GFAP-CreERT2 mice with a Cre-dependent tdTomato reporter transgene followed by irradiation with light of 450 nm. Photoactivation significantly increased retinal tdTomato expression compared to controls. We thus demonstrated a first step towards the development of a targeted, light-mediated gene therapy for the eyes.

Record release of tetramethylguanidine using a green light activated photocage for rapid synthesis of soft materials

Photocages have enabled spatiotemporally governed organic materials synthesis with applications ranging from tissue engineering to soft robotics. However, the reliance on high energy UV light to drive an often inefficient uncaging process limits their utility. These hurdles are particularly evident for more reactive cargo, such as strong organobases, despite their attractive potential to catalyze a range of chemical transformations. Herein, two metal-free boron dipyrromethene (BODIPY) photocages bearing tetramethylguanidine (TMG) cargo are shown to induce rapid and efficient polymerizations upon exposure to a low intensity green LED. A suite of spectroscopic characterization tools were employed to identify the underlying uncaging and polymerization mechanisms, while also determining reaction quantum efficiencies. The results are directly compared to state-of-the-art TMG-bearing ortho-nitrobenzyl and coumainylmethyl photocages, finding that the present BODIPY derivatives enable step-growth polymerizations that are >10× faster than the next best performing photocage. As a final demonstration, the inherent multifunctionality of the present BODIPY platform in releasing radicals from one half of the molecule and TMG from the other is leveraged to prepare polymers with starkly disparate physical properties. The present findings are anticipated to enable new applications of photocages in both small-molecule photochemistry for medicine and advanced manufacturing of next generation soft materials.

Photoactivatable Liposomes for Blue to Deep Red Light-Activated Surface Drug Release: Application to Controlled Delivery of the Antitumoral Drug Melphalan

Liposome-based nanoparticles able to release, via a photolytic reaction, a payload anchored at the surface of the phospholipid bilayer were prepared. The liposome formulation strategy uses an original drug-conjugated blue light-sensitive photoactivatable coumarinyl linker. This is based on an efficient blue light-sensitive photolabile protecting group modified by a lipid anchor, which enables its incorporation into liposomes, leading to blue to green light-sensitive nanoparticles. In addition, the formulated liposomes were doped with triplet-triplet annihilation upconverting organic chromophores (red to blue light) in order to prepare red light sensitive liposomes able to release a payload, by upconversion-assisted photolysis. Those light-activatable liposomes were used to demonstrate that direct blue or green light photolysis or red light TTA-UC-assisted drug photolysis can effectively photorelease a drug payload (Melphalan) and kill tumor cells in vitro after photoactivation.

Self-Immolative Photosensitizers for Self-Reported Cancer Phototheranostics

Photosensitizers to precise target and change fluorescence upon light illumination could accurately self-report where and when the photosensitizers work, enabling us to visualize the therapeutic process and precisely regulate treatment outcomes, which is the unremitting pursuit of precision and personalized medicine. Here, we report self-immolative photosensitizers by adopting a strategy of light-manipulated oxidative cleavage of C═C bonds that can generate a burst of reactive oxygen species, to cleave to release self-reported red-emitting products and trigger nonapoptotic cell oncosis. Strong electron-withdrawing groups are found to effectively suppress the C═C bond cleavage and phototoxicity via studying the structure-activity relationship, allowing us to elaborate NG1-NG5 that could temporarily inactivate the photosensitizer and quench the fluorescence by different glutathione (GSH)-responsive groups. Thereinto, NG2 with 2-cyano-4-nitrobenzene-1-sulfonyl group displays excellent GSH responsiveness than the other four. Surprisingly, NG2 shows better reactivity with GSH in weakly acidic condition, which inspires the application in weakly acidic tumor microenvironment where GSH elevates. To this end, we further synthesize NG-cRGD by anchoring integrin α_vβ₃ binding cyclic pentapeptide (cRGD) for tumor targeting. In A549 xenografted tumor mice, NG-cRGD successfully deprotects to restore near-infrared fluorescence because of elevated GSH in tumor site, which is subsequently cleaved upon light irradiation releasing red-emitting products to report photosensitizer working, while effectively ablating tumors via triggered oncosis. The advanced self-immolative organic photosensitizer may accelerate the development of self-reported phototheranostics in future precision oncology.

Turning Red without Feeling Embarrassed─Xanthenium-Based Photocages for Red-Light-Activated Phototherapeutics

Herein, we present high-yielding, concise access to a set of xanthenium-derived, water-soluble, low-molecular-weight photocages allowing light-controlled cargo release in the green to red region. Very importantly, these new photocages allow installation of various payloads through ester, carbamate, or carbonate linkages even at the last stage of the synthesis. Payloads were uncaged with high efficiency upon green, orange, or red light irradiation, leading to the release of carboxylic acids, phenols, and amines. The near-ideal properties of a carboxanthenium derivative were further evaluated in the context of light-controlled drug release using a camptothecin-derived chemotherapeutic drug, SN38. Notably, the caged drug showed orders of magnitude lower efficiency in cellulo, which was reinstated after red light irradiation. The presented photocages offer properties that facilitate the translation of photoactivated chemotherapy toward clinical applications.

Wavelength-Dependent, Orthogonal Photoregulation of DNA Liberation for Logic Operations

In this study, we synthesized two phosphoramidites based on 2,7-bis-{4-nitro-8-[3-(2-propyl)-styryl]}-9,9-bis-[1-(3,6-dioxaheptyl)]-fluorene (BNSF) and 4,4'-bis-{8-[4-nitro-3-(2-propyl)-styryl]}-3,3'-di-methoxybiphenyl (BNSMB) structures as visible light-cleavable linkers for oligonucleotide conjugation. In addition to the commercial ultraviolet (UV) photocleavable (PC) linker, the BNSMB linker was further applied as a building component to construct photoregulated DNA devices as duplex structures, which are functionalized with fluorophores and quenchers. Selective cleavage of PC and BNSMB is achieved in response to ultraviolet (UV) and visible light irradiations as two inputs, respectively. This leads to controllable dissociation of pieces of DNA fragments, which is followed by changes of fluorescence emission as signal outputs of the system. By tuning the number and position of the photocleavable molecules, fluorophores, and quenchers, various DNA devices were developed, which mimic the functions of Boolean logic gates and achieve logic operations in AND, OR, NOR, and NAND gates in response to two different wavelengths of light inputs. By sequence design, the photolysis products can be precisely programmed in DNA devices and triggered to release in a selective and/or sequential manner. Thus, this photoregulated DNA device shows potential as a wavelength-dependent drug delivery system for selective control over the release of multiple individual therapeutic oligonucleotide-based drugs. We believe that our work not only enriches the library of photocleavable phosphoramidites available for bioconjugation but also paves the way for developing spatiotemporal-controlled, orthogonal-regulated DNA-based logic devices for a range of applications in materials science, polymers, chemistry, and biology.

Red Light-Responsive Upconverting Nanoparticles for Quantitative and Controlled Release of a Coumarin-Based Prodrug

Photolytic reactions allow the optical control of the liberation of biological effectors by photolabile protecting groups. The development of versatile technologies enabling the use of deep-red or NIR light excitation still represents a challenging issue, in particular for light-induced drug release (e.g., light-induced prodrug activation). Here, light-sensitive biocompatible lipid nanocapsules able to liberate an antitumoral drug through photolysis are presented. It is demonstrated that original photon upconverting nanoparticles (LNC-UCs) chemically conjugated to a coumarin-based photocleavable linker can quantitatively and efficiently release a drug by upconversion luminescence-assisted photolysis using a deep-red excitation wavelength. In addition, it is also able to demonstrate that such nanoparticles are stable in the dark, without any drug leakage in the absence of light. These findings open new avenues to specifically liberate diverse drugs using deep-red or NIR excitations for future therapeutic applications in nanomedicine.

Strategy for Engineering High Photolysis Efficiency of Photocleavable Protecting Groups through Cation Stabilization

Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and application of PPGs in recent years have particularly focused on the development of molecules with high molar absorptivity at long irradiation wavelengths. However, a crucial parameter, which is pivotal to the efficiency of uncaging and which has until now proven highly challenging to improve, is the photolysis quantum yield (QY). Here, we describe a novel and general approach to greatly increase the photolysis QY of heterolytic PPGs through stabilization of an intermediate chromophore cation. When applied to coumarin PPGs, our strategy resulted in systems possessing an up to a 35-fold increase in QY and a convenient fluorescent readout during their uncaging, all while requiring the same number of synthetic steps for their preparation as the usual coumarin systems. We demonstrate that the same QY engineering strategy applies to different photolysis payloads and even different classes of PPGs. Furthermore, analysis of the DFT-calculated energy barriers in the first singlet excited state reveals valuable insights into the important factors that determine photolysis efficiency. The strategy reported herein will enable the development of efficient PPGs tailored for many applications.