Near-IR Light-Mediated Cleavage of Antibody-Drug Conjugates Using Cyanine Photocages

A hydrophobic photouncaging reaction to profile the lipid droplet interactome in tissues

Most bioorthogonal photouncaging reactions preferentially occur in polar environments to accommodate biological applications in the aqueous cellular milieu. However, they are not precisely designed to chemically adapt to the diverse microenvironments of the cell. Herein, we report a hydrophobic photouncaging reaction with tailored photolytic kinetics toward solvent polarity. Structural modulations of the aminobenzoquinone-based photocage reveal the impact of cyclic ring size, steric substituent, and electronic substituent on the individual uncaging kinetics (kH2O and kdioxane) and polarity preference (kdioxane/kH2O). Rational incorporation of optimized moieties leads to up to 20.2-fold nonpolar kinetic selectivity (kdioxane/kH2O). Further photochemical spectroscopic characterizations and theoretical calculations together uncover the mechanism underlying the polarity-dependent uncaging kinetics. The uncaged ortho-quinone methide product bears covalent reactivity toward diverse nucleophiles of a protein revealed by tandem mass spectrometry. Finally, we demonstrate the application of such lipophilic photouncaging chemistry toward selective labeling and profiling of proteins in proximity to lipid droplets inside human fatty liver tissues. Together, this work studies the solvent polarity effects of a photouncaging reaction and chemically adapts it toward suborganelle-targeted protein proximity labeling and profiling.

Bioinspired Suction-Driven Strategies with Nanoscale Skin-Controllable Adhesive Architectures for Efficient Liquid Formulated Transdermal Patches

For highly efficient and precise drug release, transdermal drug delivery systems (TDDS) have recently evolved through the combination of intelligent material-based structures with various active components. These strategies are an effort to overcome the significant difficulties in delivering large molecule drugs and nanomaterials due to the physical barrier of the skin, especially the stratum corneum, in traditional TDDS. Interestingly, multiscale suction-driven architectures (SDAs) inspired by bioinspired suction adhesion mechanisms have provided innovative solutions to these challenges. These architectures employ negative pressure to enhance nanoscale skin-controllable skin adhesion, temporarily bypass the skin barrier, and facilitate deep penetration of therapeutic agents, thereby, achieving the goals of increasing drug delivery efficiency and maximizing user convenience as a minimal invasive, needle-free platform. This review provides a comprehensive overview of suction-driven transdermal patches and emphasizes their integration with multifunctional materials to achieve stable adhesion and controlled drug release. Next, we present cost-effective and user-friendly suction-driven drug delivery patch devices through optimization of cupping structures without the incorporation of additional devices. Furthermore, we present cost-effective and user-friendly transdermal drug delivery patch devices that optimize multiscale cupping architectures without the need for additional devices. Potential of bioinspired SDAs in localized and systemic drug delivery through challenging and complex skin, as well as future perspectives, are discussed, along with innovative directions for more efficient and patient-centric transdermal drug delivery solutions.

NIR-II aza-BODIPY Platform for the Development of a Fluorescent Antibody Drug Conjugate

Real-time imaging of antibody-drug conjugates (ADCs) offers valuable insights for assessing tumor targeting specificity, monitoring therapeutic efficacy, and detecting off-target accumulation that may cause adverse effects. To enable precise tracking, we developed a versatile fluorescent platform based on an NIR-II emitting aza-BODIPY dye, which can be site-specifically grafted onto an IgG1 antibody to generate well-defined fluorescent ADCs. As a proof of concept, we synthesized an HER2-targeting trastuzumab immunoconjugate bearing a NIR-II aza-BODIPY fluorophore. The cytotoxic monomethyl auristatin E (MMAE) payload was introduced in the final step, resulting in a trackable and homogeneous ADC suitable for both in vitro and in vivo investigations. The resulting Trastu-azaNIRII-MMAE selectively accumulated in HER2-positive subcutaneous tumors, significantly reducing the tumor growth. Using NIR-II optical imaging, a single injection of the NIR-II-ADC allowed for the detection of the conjugate over a period of more than one month, highlighting its potential for long-term tracking and therapeutic applications.

Seeing in the Future - a Perspective on Combining Light with Chemical Biology Approaches to Treat Retinal Pathologies

New concepts to treat eye diseases have emerged that elegantly combine unnatural light exposure with chemical biology approaches to achieve superior cellular specificity and, as a result, improvement of visual function. Historically, light exposure without further molecular eye treatment has offered limited success including photocoagulation to halt pathological blood vessel growth or low light exposure to stimulate retinal cell viability. To add cellular specificity to such treatments, researchers have introduced various biological or chemical light-sensing molecules and combined those with light exposure. (Pre-)clinical trials describe the use of optogenetics and channelrhodpsins, i. e. light-sensitive ion channels, in patient vision restoration. In the chemical arena, pharmacological agents, rendered light-sensitive by reversible modification with photosensitive protecting compounds ("caging"), have been applied to eyes of living mice to photo-release specific cellular activities. Among these were successful proof-of-principle experiments that were conducted to establish photo-sensitive gene therapies in the eye. For light-mediated treatment in combination with chemical biology, we wish to describe here the current frontiers of research in vision restoration with an eye on differences between biological and chemical light-sensing molecules, patient requirements, and future outlooks.

Benzyl Ammonium Carbamates Undergo Two-Step Linker Cleavage and Improve the Properties of Antibody Conjugates

Targeted payload delivery strategies, such as antibody-drug conjugates (ADCs), have emerged as important therapeutics. Although considerable efforts have been made in the areas of antibody engineering and labeling methodology, improving the overall physicochemical properties of the linker/payload combination remains an important challenge. Here we report an approach to create an intrinsically hydrophilic linker domain. We find that benzyl α-ammonium carbamates (BACs) undergo tandem 1,6-1,2-elimination to release secondary amines. Using a fluorogenic hemicyanine as a model payload component, we show that a zwitterionic BAC linker improves labeling efficiency and reduces antibody aggregation when compared to a commonly used para-amino benzyl (PAB) linker as well as a cationic BAC. Cellular and in vivo fluorescence imaging studies demonstrate that the model payload is specifically released in antigen-expressing cells and tumors. The therapeutic potential of the BAC linker strategy was assessed using an MMAE payload, a potent microtubule-disrupting agent frequently used for ADC applications. The BAC-MMAE combination enhances labeling efficiency and cellular toxicity when compared to the routinely used PAB-Val-Cit ADC analogue. Broadly, this strategy provides a general approach to mask payload hydrophobicity and improve the properties of targeted agents.

Abraham Patchornik: The Contemporary Relevance of His Work for Chemistry and Biology

Abraham Patchornik was born in 1926 in Ness Ziona, a town in Palestine founded by his great-grandfather Reuben Lehrer in 1883. He started to study chemistry as an undergraduate at the Hebrew University. However, this was interrupted by the war, and he completed his studies in various locations in West Jerusalem. From 1952 to 1956 Patchornik completed his PhD at the (new) Weizmann Institute of Science with Ephraim Katchalski. After a postdoc at the NIH, he returned to the Weizmann in 1958, when he joined the Department of Biophysics. In 1972-1979, he became chairman of the new Department of Organic Chemistry at the Weizmann, and his own research was geared toward applying creative chemistry to solve biological problems. Patchornik passed away in his hometown of Ness Ziona in 2014. Patchornik was a conceptual leader in peptide and polymer chemistry. Given the importance of selective functional group protection for the construction of oligomeric molecules, he became interested in using "nonstandard", orthogonal chemistry for this purpose, i.e. photosensitive protecting groups (PPGs) in place of thermal reactions. It was R.B. Woodward who suggested this strategy to Patchornik in 1965, while Patchornik was on sabbatical leave at Harvard. However, it was not until Patchornik returned to the Weizmann that this idea of a versatile PPG to enable multistep synthesis was realized. Here, we provide an account of the early photosensitive protecting groups that Patchornik and co-workers developed, and the immense impact they have had on various fields. In particular, we survey the use of PPGs in live cell physiology (i.e., caged compounds), and the development of gene chips via light-directed solid-phase synthesis. Further, we highlight recent work applying new PPGs for "photochemical delivery" of drugs, otherwise termed photopharmacology. Finally, we discuss the relationship between caged compounds and how contemporary neuroscience uses genetically encoded chromophores to control cell function.

Light-Activated Anti-Vascular Combination Therapy against Choroidal Neovascularization

Choroidal neovascularization (CNV) underlies the crux of many angiogenic eye disorders. Although medications that target vascular endothelial growth factor (VEGF) are approved for treating CNV, their effectiveness in destroying new blood vessels is limited, and invasive intravitreal administration is required. Additionally, other drugs that destroy established neovessels, such as combretastatin A-4, may have systemic side effects that limit their therapeutic benefits. To overcome these shortcomings, a two-pronged anti-vascular approach is presented for CNV treatment using a photoactivatable nanoparticle system that can release a VEGF receptor inhibitor and a vascular disrupting agent when irradiated with 690 nm light. The nanoparticles can be injected intravenously to enable anti-angiogenic and vascular disrupting combination therapy for CNV through light irradiation to the eyes. This approach can potentiate therapeutic effects while maintaining a favorable biosafety profile for choroidal vascular diseases.

Single-Photon Deep-Red Light-Triggered Direct Release of an Anticancer Drug: An Investigative Tumor Regression Study on a Breast Cancer Spheroidal Tumor Model

Breast adenocarcinoma ranks high among the foremost lethal cancers affecting women globally, with its triple-negative subtype posing the greatest challenge due to its aggressiveness and resistance to treatment. To enhance survivorship and patients' quality of life, exploring advanced therapeutic approaches beyond conventional chemotherapies is imperative. To address this, innovative nanoscale drug delivery systems have been developed, offering precise, localized, and stimuli-triggered release of anticancer agents. Here, we present perylenemonoimide nanoparticle-based vehicles engineered for deep-red light activation, enabling direct chlorambucil release. Synthesized via the reprecipitation technique, these nanoparticles were thoroughly characterized. Light-induced drug release was monitored via spectroscopic and reverse-phase HPLC. The efficacy of the said drug delivery system was evaluated in both two-dimensional and three-dimensional spheroidal cancer models, demonstrating significant tumor regression attributed to apoptotic cell death induced by efficient drug release within cells and spheroids. This approach holds promise for advancing targeted breast cancer therapy, enhancing treatment efficacy and minimizing adverse effects.

Active control of pharmacokinetics using light-responsive polymer-drug conjugates for boron neutron capture therapy

In boron neutron capture therapy (BNCT), boron drugs should exhibit high intratumoral boron concentrations during neutron irradiation, while being cleared from the blood and normal organs. However, it is usually challenging to achieve such tumor accumulation and quick clearance simultaneously in a temporally controlled manner. Here, we developed a polymer-drug conjugate that can actively control the clearance of the drugs from the blood. This polymer-drug conjugate is based on a biocompatible polymer that passively accumulates in tumors. Its side chains were conjugated with the low-molecular-weight boron drugs, which are immediately excreted by the kidneys, via photolabile linkers. In a murine subcutaneous tumor model, the polymer-drug conjugate could accumulate in the tumor with the high boron concentration ratio of the tumor to the surrounding normal tissue (∼10) after intravenous injection while a considerable amount remained in the bloodstream as well. Photoirradiation to blood vessels through the skin surface cleaved the linker to release the boron drug in the blood, allowing for its rapid clearance from the bloodstream. Meanwhile, the boron concentration in the tumor which was not photoirradiated could be maintained high, permitting strong BNCT effects. In clinical BNCT, the dose of thermal neutrons to solid tumors is determined by the maximum radiation exposure to normal organs. Thus, our polymer-drug conjugate may enable us to increase the therapeutic radiation dose to tumors in such a practical situation.

A Modular Approach for the Synthesis of Diverse Heterobifunctional Cyanine Dyes

Herein, we present a straightforward synthetic route for the design and synthesis of diverse heterobifunctional cyanine 5 dyes. We optimized the workup by harnessing the pH- and functional group-dependent solubility of the asymmetric cyanine 5 dyes. Therefore, purification through chromatography is deferred until the last synthesis step. Demonstrating successful large-scale synthesis, our modular approach prevents functional group degradation by introducing them in the last synthesis step. These modifiable heterobifunctional dyes offer significant utility in advancing biological studies.

Design and validation of a low-cost photomodulator for in vivo photoactivation of a mGluR5 inhibitor

Purpose: Severe side effects prevent the utilization of otherwise promising drugs in treatments. These side effects arise when drugs affect untargeted tissues due to poor target specificity. In photopharmacology, light controls the timing and the location of drug delivery, improving treatment specificity and pharmacokinetic control. Photopharmaceuticals have not seen widespread adoption in part because researchers do not always have access to reliable and reproducible light delivery devices at prices which fit within the larger research budget. Method: In this work, we present a customizable photomodulator for use in both wearable and implantable devices. For experimental validation of the photomodulator, we photolyse JF-NP-26 in rats. Results: We successfully drive in vivo photopharmacology with a tethered photomodulator and demonstrate modifications which enable the photomodulator to operate wirelessly. Conclusion: By documenting our photomodulator development, we hope to introduce researchers to a simple solution which significantly lowers the engineering barriers to photopharmacology research.

Graphical abstract

Researchers present a photomodulator, a device designed to facilitate in vivo photopharmacology. They demonstrate the in vivo capabilities of the photomodulator by photoreleasing raseglurant, an mGluR5 inhibitor, to treat pain in an acute rat model and follow this study by showing how to reconfigure the photomodulator to work wirelessly and interface with other biomedical devices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-023-00334-3.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Rational Design of Hydroxylated Thiazole Orange Photocages for Green Light-Triggered DNA Recombination

The precise control of DNA recombination enables the cell- or time-dependent regulation of gene expression in studies of gene function. Caged estrogen receptor ligands combined with a Cre-ERT2/loxP system are useful tools for light-triggered DNA recombination. However, the photolysis of most caged compounds requires ultraviolet or blue light, which is toxic and displays low tissue penetration. Although a cyanine-based photo-responsive protecting group (PPG) can release estrogen receptor ligands with longer-wavelength light, its low photolytic efficiency requires long illumination times. We developed a caged estrogen receptor ligand with improved green light-responsive PPGs. The rational modification of Hydroxylated Thiazole Orange (HTO) photocages using electron-donating groups (EDGs), such as dimethoxy (DiMeO)-substituted HTO, resulted in high photolytic efficiency (up to ϵΦ ≈320 M-1  cm-1 ). Theoretical calculations demonstrated that the enhanced photolytic efficiencies were derived from the increased intramolecular charge transfer by EDGs upon excitation. The efficient uncaging of estrogen receptor ligands enabled the control of gene recombination in a ligand-dependent Cre-ERT2/loxP system in live cells.

Clickable bisreactive small gold nanoclusters for preparing multifunctionalized nanomaterials: application to photouncaging of an anticancer molecule

In this study, we successfully synthesized a small-sized gold nanocluster (2 nm) coated with homogeneous tripeptides bearing azido and amino groups that enable facile multifunctionalizations. Using sodium phenoxide to reduce tetrachloroauric(iii) acid in the presence of the cysteine-containing tripeptide, we efficiently prepared the gold nanoclusters without damaging the azido group. We then utilized this clickable bisreactive nanocluster as a versatile platform for synthesizing multifunctionalized gold nanomaterials. The resulting nanoclusters were conjugated with an anticancer compound connected to an indolizine moiety for photoinduced uncaging, a photodynamic therapy agent acting as a photosensitizer for uncaging, and a cyclic RGD peptide. The cytotoxicity of the multifunctionalized gold nanoclusters was demonstrated through red light irradiation of human lung cancer-derived A549 cells treated with the synthesized nanomaterials. The significant cytotoxicity exhibited by the cells underscores the potential utility of this method in advanced cancer therapies.

NIR Light-Activated Mitochondrial RNA Cross-Linking Strategy for H2S Monitoring and Prolonged Colorectal Tumor Imaging

Molecular diffusion and leakage impede the long-term retention of probes/drugs and may cause potential adverse effects in theranostic fields. Spatiotemporally manipulating the organelle-immobilization behavior of probes/drugs for prolonged tumor retention is indispensable to achieving effective cancer diagnosis and therapy. Herein, we propose a rational strategy that could realize near-infrared light-activated ribonucleic acids (RNAs) cross-linking for prolonged tumor retention and simultaneously endogenous hydrogen sulfide (H2S) monitoring in colorectal tumors. Profiting from efficient singlet oxygen (1O2) generation from Cy796 under 808 nm light irradiation, the 1O2-animated furan moiety in Cy796 could covalently cross-link with cytoplasmic RNAs via a cycloaddition reaction and realize organelle immobilization. Subsequently, specific thiolysis of Cy796 assisted with H2S resulted in homologous product Cy644 with reduced 1O2 generation yields and enhanced absolute fluorescence quantum yields (from 7.42 to 27.70%) with blue-shifted absorption and emission, which avoided the molecular oxidation fluorescence quenching effect mediated by 1O2 and validated fluorescence imaging. Furthermore, studies have demonstrated that our proposed strategy possessed adequate capacity for fluorescence imaging and endogenous H2S detection in HCT116 cells, particularly accumulated at the tumor sites, and retained long-term imaging with excellent biocompatibility. The turn-on fluorescence mode and turn-off 1O2 generation efficiency in our strategy successfully realized a diminished fluorescence cross-talk and oxidation quenching effect. It is adequately envisioned that our proposed strategy for monitoring biomarkers and prolonged tumor retention will contribute tremendous dedication in the clinical, diagnostic, and therapeutic fields.

Bioorthogonal chemistry for prodrug activation in vivo

Prodrugs have emerged as a major strategy for addressing clinical challenges by improving drug pharmacokinetics, reducing toxicity, and enhancing treatment efficacy. The emergence of new bioorthogonal chemistry has greatly facilitated the development of prodrug strategies, enabling their activation through chemical and physical stimuli. This "on-demand" activation using bioorthogonal chemistry has revolutionized the research and development of prodrugs. Consequently, prodrug activation has garnered significant attention and emerged as an exciting field of translational research. This review summarizes the latest advancements in prodrug activation by utilizing bioorthogonal chemistry and mainly focuses on the activation of small-molecule prodrugs and antibody-drug conjugates. In addition, this review also discusses the opportunities and challenges of translating these advancements into clinical practice.

Small molecules and conjugates as theranostic agents

Theranostics, the integration of therapy and diagnostics into a single entity for the purpose of monitoring disease progression and treatment response. Diagnostics involves identifying specific characteristics of a disease, while therapeutics refers to the treatment of the disease based on this identification. Advancements in medicinal chemistry and technology have led to the development of drug modalities that provide targeted therapeutic effects while also providing real-time updates on disease progression and treatment. The inclusion of imaging in therapy has significantly improved the prognosis of devastating diseases such as cancer and neurodegeneration. Currently, theranostic treatment approaches are based on nuclear medicine, while nanomedicine and a wide diversity of macromolecular systems such as gels, polymers, aptamers, and dendrimer-based agents are being developed for the purpose. Theranostic agents have significant roles to play in both early-stage drug development and clinical-stage therapeutic-containing drug candidates. This review will briefly outline the pros and cons of existing and evolving theranostic approaches before comprehensively discussing the role of small molecules and their conjugates.

Stimuli-Responsive Prodrug Chemistries for Cancer Therapy

Prodrugs are pharmacologically inactive, chemically modified derivatives of active drugs, which, following in vivo administration, are converted to the parent drugs through chemical or enzymatic cleavage. The prodrug approach holds tremendous potential to create the enhanced version of an existing pharmacological agent and leverage those improvements to augment the drug molecules' bioavailability, targeting ability, therapeutic efficacy, safety, and marketability. Especially in cancer therapy, prodrug application has received substantial attention. A prodrug can effectively broaden the therapeutic window of its parent drug by enhancing its release at targeted tumor sites while reducing its access to healthy cells. The spatiotemporally controlled release can be achieved by manipulating the chemical, physical, or biological stimuli present at the targeted tumor site. The critical strategy comprises drug-carrier linkages that respond to physiological or biochemical stimuli in the tumor milieu to yield the active drug form. This review will focus on the recent advancements in the development of various fluorophore-drug conjugates that are widely used for real-time monitoring of drug delivery. The use of different stimuli-cleavable linkers and the mechanisms of linker cleavage will be discussed. Finally, the review will conclude with a critical discussion of the prospects and challenges that might impede the future development of such prodrugs.

A BODIPY-picolinium-cation conjugate as a blue-light-responsive caged group

Caged compounds protected with photolabile protecting groups (PPGs) are useful for controlling various biological events with high spatiotemporal resolution. Most of the commonly used PPGs are controlled by ultraviolet light irradiation, but it is desirable to have PPGs controlled by visible light irradiation in order to minimize tissue damage. Here, we describe a boron-dipyrromethene (BODIPY)-picolinium conjugate (BPc group) that functions as a blue-light-controllable PPG. ESR experiments indicate that the photolysis mechanism is based on intramolecular photoinduced electron transfer. We illustrate the applicability of the BPc group to biologically active compounds by employing it firstly to photocontrol release of histamine, and secondly to photocontrol release of a soluble guanylyl cyclase (sGC) activator, GSK2181236A, which induces photovasodilation. The BPc group is expected to be a useful PPG for controlling various biological events with blue light irradiation.

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.

Synthesis and biological evaluation of theranostic Trastuzumab–SN38 conjugate for Near-IR fluorescence imaging and targeted therapy of HER2+ breast cancer

Here, we report on the design, synthesis, and biological evaluation of a new theranostic antibody drug conjugate (ADC), Cy5-Ab-SS-SN38, that consists of the HER2-specific antibody trastuzumab (Ab) connected to the near infrared (NIR) pentamethine cyanine dye Cy5 and SN38, which is a bioactive metabolite of the anticancer drug irinotecan. SN38 is bound to an antibody through a glutathione-responsive self-immolative disulfide carbamate linker. For the first time, we explored this linker in ADC and found that it to reduce the drug release rate, which is important for safe drug delivery. The developed ADC exhibited specific accumulation and nanomolar anti-breast cancer activity on HER2-positive (HER2+) cell lines but no effect on HER2-. Animals treated with this ADC exhibited good tolerance. In vivo studies have shown that the ADC had good targeting ability for HER2+ tumors with much higher anticancer potency than trastuzumab itself or a mixture of trastuzumab with SN38. Side-by-side HER2+/HER2-xenograft at the 10 mg/kg dose exhibited specific accumulation and reduction of HER2+ tumor but not accumulation or growth inhibition of HER2-counterpart. The self-immolative disulfide linker implemented in this study was proven to be successful, broadening its utilization with other antibodies for targeted anticancer therapy in general. We believe that the theranostic ADCs comprising the glutathione-responsive self-immolative disulfide carbamate linker are applicable for the treatment and fluorescent monitoring of malignancies and anticancer drug delivery.

Activatable dual-functional molecular agents for imaging-guided cancer therapy

Theranostics has attracted great attention due to its ability to combine the real-time diagnosis of cancers with efficient treatment modalities. Activatable dual-functional molecular agents could be synthesized by covalently conjugating imaging agents, therapeutic agents, stimuli-responsive linkers and/or targeting molecules together. They could be selectively activated by overexpressed physiological stimuli or external triggers at the tumor sites to release imaging agents and cytotoxic drugs, thus offering many advantages for tumor imaging and therapy, such as a high signal-to-noise ratio, low systemic toxicity, and improved therapeutic effects. This review summarizes the recent advances of dual-functional molecular agents that respond to various physiological or external stimuli for cancer theranostics. The molecular designs, synthetic strategies, activatable mechanisms, and biomedical applications of these molecular agents are elaborated, followed by a brief discussion of the challenges and opportunities in this field.

ESIPT-, AIE-, and AIE + ESIPT-Based Light-Activated Drug Delivery Systems and Bioactive Donors for Targeted Disease Treatment

Targeted release of bioactive molecules for therapeutic purposes is a key area in the biomedical field that is growing quickly, where bioactive molecules are released passively or actively from drug delivery systems (DDSs) or bioactive donors. In the past decade, researchers have identified light as one of the prime stimuli that can implement the efficient spatiotemporally targeted delivery of drugs or gaseous molecules with minimal cytotoxicity and a real-time monitoring ability. This perspective emphasizes recent advances in the photophysical properties of ESIPT- (excited-state intramolecular proton transfer), AIE- (aggregation-induced emission), and AIE + ESIPT-attributed light-activated delivery systems or donors. The three major sections of this perspective describe the distinctive features of DDSs and donors concerning their design, synthesis, photophysical and photochemical properties, and in vitro and in vivo studies demonstrating their relevance as carrier molecules for releasing cancer drugs and gaseous molecules in the biological system.

Reverse Engineering Caged Compounds: Design Principles for their Application in Biology

Light passes through biological tissue, and so it is used for imaging biological processes in situ. Such observation is part of the very essence of science, but mechanistic understanding requires intervention. For more than 50 years a "second function" for light has emerged; namely, that of photochemical control. Caged compounds are biologically inert signaling molecules that are activated by light. These optical probes enable external instruction of biological processes by stimulation of an individual element in complex signaling cascades in its native environment. Cause and effect are linked directly in spatial, temporal, and frequency domains in a quantitative manner by their use. I provide a guide to the basic properties required to make effective caged compounds for the biological sciences.

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.

Design, Development, and Optimisation of Smart Linker Chemistry for Targeted Colonic Delivery-In Vitro Evaluation

Drug targeting is necessary to deliver drugs to a specific site of action at a rate dictated by therapeutic requirements. The pharmacological action of a drug can thereby be optimised while minimising adverse effects. Numerous colonic drug delivery systems have been developed to avoid such undesirable side effects; however, these systems lack site specificity, leaving room for further improvement. The objective of the present study was to explore the potential of amino-alkoxycarbonyloxymethyl (amino-AOCOM) ether prodrugs as a general approach for future colonic delivery. To circumvent inter- and intra-subject variabilities in enzyme activities, these prodrugs do not rely on enzymes but rather are activated via a pH-triggered intramolecular cyclisation−elimination reaction. As proof of concept, model compounds were synthesised and evaluated under various pH conditions, simulating various regions of the gastrointestinal tract (GIT). Probe 15 demonstrated excellent stability under simulated stomach- and duodenum-like conditions and protected 60% of the payload in a small intestine-like environment. Moreover, 15 displayed sustained release at colonic pH, delivering >90% of the payload over 38 h. Mesalamine (Msl) prodrugs 21 and 22 were also synthesised and showed better stability than probe 15 in the simulated upper GIT but relatively slower release at colonic pH (61−68% of Msl over 48 h). For both prodrugs, the extent of release was comparable to that of the commercial product Asacol. This study provides initial proof of concept regarding the use of a cyclisation-activated prodrug for colon delivery and suggests that release characteristics still vary on a case-by-case basis.

Mitochondrion-targeting and in situ photocontrolled protein delivery via photocages

Defects in mitochondrial proteostasis contribute to many disorders, including cancer, neurodegeneration, and metabolic and genetic diseases. A strategy aimed at restoring the damaged mitochondrial proteostasis is the mitochondrion-targeting and carrier-free delivery of exogenous functional proteins that can replace the endogenous dysfunctional proteins. The modification of a protein with a photolabile protecting group (PPG, i.e., photocage group) can be activated in situ by response to illumination, leading to release of the protein from its photocage. Here, the Cys and peptide photocages with coumarin were first prepared and characterized for proof of concept. Then, we designed a pair of photocage groups PPG-RhB and PPG-TPP using coumarin and mitochondrion-targeting Rhodamine B (RhB) and triphenylphosphine (TPP), and another pair of organelle-nontarget photocage groups Br-PPG and NO2-PPG for comparison. The proteins modified with these two pairs of photocage groups undergo photolysis in solutions, and can penetrate cell membrane toward their destinations in the carrier-free fashions. The intracellular protein photocages are in situ activated by illumination at 405 nm, and the proteins are released from their photocages in mitochondria and cytoplasm, respectively. This strategy of light-responsive and carrier-free cellular delivery enables mitochondrial and cytoplasmic accumulation of exogenous proteins.

Spatiotemporal Control of Biology: Synthetic Photochemistry Toolbox with Far-Red and Near-Infrared Light

The complex network of naturally occurring biological pathways motivates the development of new synthetic molecules to perturb and/or detect these processes for fundamental research and clinical applications. In this context, photochemical tools have emerged as an approach to control the activity of drug or probe molecules at high temporal and spatial resolutions. Traditional photochemical tools, particularly photolabile protecting groups (photocages) and photoswitches, rely on high-energy UV light that is only applicable to cells or transparent model animals. More recently, such designs have evolved into the visible and near-infrared regions with deeper tissue penetration, enabling photocontrol to study biology in tissue and model animal contexts. This Review highlights recent developments in synthetic far-red and near-infrared photocages and photoswitches and their current and potential applications at the interface of chemistry and biology.

Recent advances in combretastatin A-4 codrugs for cancer therapy

CA4 is a potent microtubule polymerization inhibitor and vascular disrupting agent. However, the in vivo efficiency of CA4 is limited owing to its poor pharmacokinetics resulting from its high lipophilicity and low water solubility. To improve the water solubility, CA4 phosphate (CA4P) has been developed and shows potent antivascular and antitumor effects. CA4P had been evaluated as a vascular disrupting agent in previousc linical trials. However, it had been discontinued due to the lack of a meaningful improvement in progression-free survival and unfavorable partial response data. Codrug is a drug design approach to chemically bind two or more drugs to improve therapeutic efficiency or decrease adverse effects. This review describes the progress made over the last twenty years in developing CA4-based codrugs to improve the therapeutic profile and achieve targeted delivery to cancer tissues. It also discusses the existing problems and the developmental prospects of CA4 codrugs.

The Potential of Topoisomerase Inhibitor-Based Antibody–Drug Conjugates

DNA topoisomerases are essential enzymes that stabilize DNA supercoiling and resolve entanglements. Topoisomerase inhibitors have been widely used as anti-cancer drugs for the past 20 years. Due to their selectivity as topoisomerase I (TOP1) inhibitors that trap TOP1 cleavage complexes, camptothecin and its derivatives are promising anti-cancer drugs. To increase accumulation of TOP1 inhibitors in cancer cells through the targeting of tumors, TOP1 inhibitor antibody–drug conjugates (TOP1-ADC) have been developed and marketed. Some TOP1-ADCs have shown enhanced therapeutic efficacy compared to prototypical anti-cancer ADCs, such as T-DM1. Here, we review various types of camptothecin-based TOP1 inhibitors and recent developments in TOP1-ADCs. We then propose key points for the design and construction of TOP1-ADCs. Finally, we discuss promising combinatorial strategies, including newly developed approaches to maximizing the therapeutic potential of TOP1-ADCs.

Photouncaging of Carboxylic Acids from Cyanine Dyes with Near-Infrared Light

Near-infrared light (NIR; 650-900 nm) offers unparalleled advantages as a biocompatible stimulus. The development of photocages that operate in this region represents a fundamental challenge due to the low energy of the excitation light. Herein, we repurpose cyanine dyes into photocages that are available on a multigram scale in three steps and efficiently release carboxylic acids in aqueous media upon irradiation with NIR light up to 820 nm. The photouncaging process is examined using several techniques, providing evidence that it proceeds via photooxidative pathway. We demonstrate the practical utility in live HeLa cells by delivery and release of the carboxylic acid cargo, that was otherwise not uptaken by cells in its free form. In combination with modularity of the cyanine scaffold, the realization of these accessible photocages will fully unleash the potential of the emerging field of NIR-photoactivation and facilitate its widespread adoption outside the photochemistry community.

Computational Design, Synthesis, and Photochemistry of Cy7-PPG, an Efficient NIR-Activated Photolabile Protecting Group for Therapeutic Applications

Photolabile Protecting Groups (PPGs) are molecular tools used, for example, in photopharmacology for the activation of drugs with light, enabling spatiotemporal control over their potency. Yet, red-shifting of PPG activation wavelengths into the NIR range, which penetrates the deepest in tissue, has often yielded inefficient or insoluble molecules, hindering the use of PPGs in the clinic. To solve this problem, we report herein a novel concept in PPG design, by transforming clinically-applied NIR-dyes with suitable molecular orbital configurations into new NIR-PPGs using computational approaches. Using this method, we demonstrate how Cy7, a class of NIR dyes possessing ideal properties (NIR-absorption, high molecular absorptivity, excellent aqueous solubility) can be successfully converted into Cy7-PPG. We report a facile synthesis towards Cy7-PPG from accessible precursors and confirm its excellent properties as the most redshifted oxygen-independent NIR-PPG to date (λmax =746 nm).

Light-Controllable Binary Switch Activation of CAR T Cells

Major challenges to chimeric antigen receptor (CAR) T cell therapies include uncontrolled immune activity, off-tumor toxicities and tumor heterogeneity. To overcome these challenges, we engineered CARs directed against small molecules. By conjugating the same small molecule to distinct tumor-targeting antibodies, we show that small molecule specific-CAR T cells can be redirected to different tumor antigens. Such binary switches allow control over the degree of CAR T cell activity and enables simultaneous targeting of multiple tumor-associated antigens. We also demonstrate that ultraviolet light-sensitive caging of small molecules blocks CAR T cell activation. Exposure to ultraviolet light, uncaged small molecules and restored CAR T cell-mediated killing. Together, our data demonstrate that a light-sensitive caging system enables an additional level of control over tumor cell killing, which could improve the therapeutic index of CAR T cell therapies.

Development of Photoremovable Linkers as a Novel Strategy to Improve the Pharmacokinetics of Drug Conjugates and Their Potential Application in Antibody-Drug Conjugates for Cancer Therapy

Although there have been extensive research and progress on the discovery of anticancer drug over the years, the application of these drugs as stand-alone therapy has been limited by their off-target toxicities, poor pharmacokinetic properties, and low therapeutic index. Targeted drug delivery, especially drug conjugate, has been recognized as a technology that can bring forth a new generation of therapeutics with improved efficacy and reduced side effects for cancer treatment. The linker in a drug conjugate is of essential importance because it impacts the circulation time of the conjugate and the release of the drug for full activity at the target site. Recently, the light-triggered linker has attracted a lot of attention due to its spatiotemporal controllability and attractive prospects of improving the overall pharmacokinetics of the conjugate. In this paper, the latest developments of UV- and IR-triggered linkers and their application and potential in drug conjugate development are reviewed. Some of the most-well-researched photoresponsive structural moieties, such as UV-triggered coumarin, ortho-nitrobenzyl group (ONB), thioacetal ortho-nitrobenzaldehyde (TNB), photocaged C40-oxidized abasic site (PC4AP), and IR-triggered cyanine and BODIPY, are included for discussion. These photoremovable linkers show better physical and chemical stabilities and can undergo rapid cleavage upon irradiation. Very importantly, the drug conjugates containing these linkers exhibit reduced off-target toxicity and overall better pharmacokinetic properties. The progress on photoactive antibody-drug conjugates, such as antibody-drug conjugates (ADC) and antibody-photoabsorber conjugate (APC), as precision medicine in clinical cancer treatment is highlighted.

NIR Light-Triggered Quantitative Pulsed Drug Release

Quantitative drug release is important for improving therapeutic efficiency and avoiding side effects. While using long-term delivery system for repeated therapies, it is indispensable but challenging to accurately control the drug dosing. Here, a photocleavable prodrug loaded hydrogel is proposed for near infrared (NIR) light-triggered quantitative pulsed drug release. IR783, a commercially available NIR fluorescent dye, is conjugated with methyl honokiol (mHNK) to give a photocleavable IR783-mHNK prodrug. Injectable glycol chitosan (GC) hydrogel is chosen as a reservoir, in which IR783-mHNK can be efficiently loaded via electrostatic and hydrophobic interactions. Upon 680 nm light-emitting diode (LED) light irradiation, IR783-mHNK cleaves and mHNK is released. Notably, it is found that IR783-mHNK presents synchronous photocleavage-fluorescence bleaching phenomenon. The released amount of mHNK is visible by measuring the residual fluorescent intensity of hydrogel. Quantitative drug release is achieved by controlling irradiation duration and the drug release process is visible by fluorescence imaging. The prodrug-loaded hydrogel shows good stability, minimum leakage and efficient light responsibility both in vitro and in vivo. After light triggering, monitorable quantitative mHNK release and on-demand sleep-promotiing effect are verified in mice without toxicities.

Design and synthesis of aptamer-cyclometalated iridium(III) complex conjugate targeting cancer cells

Targeted therapy showed broad application prospects in the treatment of various types of cancer. Through carriers such as aptamers, antibodies, proteins and peptides, targeted therapy can selectively deliver drugs into tumor cells. Compared with traditional treatment methods such as chemo- and radiotherapy, targeted drug delivery systems can reduce the toxic effects of drugs on normal cells and avoid adverse reactions. Herein, an aptamer-cyclometalated iridium(III) complex conjugate (ApIrC) has been designed and developed as a targeted anticancer agent. Owing to the targeting ability of aptamers, ApIrC specifically bound to nucleolin over-expressed on the surface of cancer cells and showed strong fluorescence signal for tumor imaging and diagnosis. ApIrC had more substantial cellular uptake in cancer cells than the iridium complex alone and exhibited favorable low toxicity to normal cells. After uptake by cells through endocytosis, ApIrC can selectively accumulated in mitochondria and induced caspase-3/7-dependent cell death. Remarkably, ApIrC can also specifically target 3D multicellular spheroids (MCSs) and show excellent tumor permeability. So, it can effectively reach the interior of MCSs and cause cell damage. To our knowledge, this is the first report of the aptamer-cyclometalated iridium(III) complex conjugate which studied for cancer targeted therapy. The developed conjugate has great potential to be developed as novel therapeutics for effective and low-toxic cancer treatment.

Human Serum Albumin Dimerization Enhances the S2 Emission of Bound Cyanine IR806

Cyanine molecules are important phototheranostic compounds given their high fluorescence yield in the near-infrared region of the spectrum. We report on the frequency and time-resolved spectroscopy of the S₂ state of IR806, which demonstrates enhanced emission upon binding to the hydrophobic pocket of human serum albumin (HSA). From excitation-emission matrix spectra and electronic structure calculations, we identify the emission as one associated with a state having the polymethine chain twisted out of plane by 103°. In addition, we find that this configuration is significantly stabilized as the concentration of HSA increases. Spectroscopic changes associated with the S₁ and S₂ states of IR806 as a function of HSA concentration, as well as anisotropy measurements, confirm the formation of HSA dimers at concentrations greater than 10 μM. These findings imply that the longer-lived S₂ state configuration can lead to more efficient phototherapy agents, and cyanine S₂ spectroscopy may be a useful tool to determine the oligomerization state of HSA.

Synthesis of sialic acid conjugates of the clinical near-infrared dye as next-generation theranostics for cancer phototherapy

Cancer is a multifaceted global health problem that requires continuous action to develop next-generation cancer theranostics. Inspired by the emerging use of indocyanine green (ICG), the only clinically approved near-infrared (NIR) dye for cancer phototherapy, here we synthesized two ICG conjugate theranostics by coupling ICG to sialic acid (Sia) through the C2 and C9 positions of Sia, respectively, referred to as Sia-C2-ICG and Sia-C9-ICG. Encouragingly, Sia-C2/C9-ICGs show superior in vitro properties, including enhanced stability, reduced non-specific binding to serum proteins, and improved blood compatibility, highlighting the benefits of Sia coupling. Notably, in vivo NIR imaging shows that Sia-C9-ICG significantly promotes tumor targeting and effectively prolongs the circulation time in the body, while Sia-C2-ICG is superior to ICG but inferior to Sia-C9-ICG in targeting tumors. Furthermore, Sia-C9-ICG combined with NIR laser irradiation can lead to excellent photothermal and photodynamic therapies for cancer cells, resulting in superior solid tumor ablation. To our knowledge, this is the first report of Sia-NIR conjugates achieving significant tumor reduction in vivo. Together, these advances render Sia-C9-ICG an attractive lead as next-generation cancer theranostics that can be translated clinically to treat human patients.

A red-light activatable and mitochondrion-targeting PtIV complex to overcome drug resistance

The therapeutic effects of platinum anticancer drugs are commonly whittled away by drug resistance, which is associated with drug efflux and the nucleotide excision repair (NER) pathway. Activation of drugs...

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

Efficient Visible/NIR Light-driven Uncaging of Hydroxylated Thiazole Orange-based Caged Compounds in Aqueous Media

In photoactivation strategies with bioactive molecules, one-photon visible or two-photon near-infrared light-sensitive caged compounds are desirable tools for biological applications because they offer reduced phototoxicity and deep tissue penetration. However, visible-light-sensitive photoremovable protecting groups (PPGs) reported so far have displayed high hydrophobicity and low uncaging cross sections (εΦ < 50) in aqueous media, which can obstruct the control of bioactivity with high spatial and temporal precision. In this study, we developed hydroxylated thiazole orange (HTO) derivatives as visible-light-sensitive PPGs with high uncaging cross sections (εΦ ≈ 370) in aqueous solution. In addition, 2PE photolysis reactions of HTO-caged glutamate were achieved using a NIR laser (940 nm). Moreover, HTO-caged glutamate can activate N-methyl-d-aspartic acid receptors in Xenopus oocytes and mammalian cells with green-light illumination, thus allowing optical control of biological functions.

A hydroxylated thiazole orange (HTO)-caged glutamate efficiently releases a glutamate for temporal activation of ion channels under visible-to-NIR light in aqueous media.

Antibody-drug conjugates: Recent advances in linker chemistry

Antibody–drug conjugates (ADCs) are gradually revolutionizing clinical cancer therapy. The antibody–drug conjugate linker molecule determines both the efficacy and the adverse effects, and so has a major influence on the fate of ADCs. An ideal linker should be stable in the circulatory system and release the cytotoxic payload specifically in the tumor. However, existing linkers often release payloads nonspecifically and inevitably lead to off-target toxicity. This defect is becoming an increasingly important factor that restricts the development of ADCs. The pursuit of ADCs with optimal therapeutic windows has resulted in remarkable progress in the discovery and development of novel linkers. The present review summarizes the advance of the chemical trigger, linker‒antibody attachment and linker‒payload attachment over the last 5 years, and describes the ADMET properties of ADCs. This work also helps clarify future developmental directions for the linkers.