Localized In Vivo Activation of a Photoactivatable Doxorubicin Prodrug in Deep Tumor Tissue

Sparing sensitive healthy tissue from chemotherapy exposure is a critical challenge in the treatment of cancer. The work described here demonstrates the localized in vivo photoactivation of a new chemotherapy prodrug of doxorubicin (DOX). The DOX prodrug (DOX‐PCB) was 200 times less toxic than DOX and was designed to release pure DOX when exposed to 365 nm light. This wavelength was chosen because it had good tissue penetration through a 1 cm diameter tumor, but had very low skin penetration, due to melanin absorption, preventing uncontrolled activation from outside sources. The light was delivered specifically to the tumor tissue using a specialized fiber‐optic LED system. Pharmacokinetic studies showed that DOX‐PCB had an α circulation half‐life of 10 min which was comparable to that of DOX at 20 min. DOX‐PCB demonstrated resistance to metabolic cleavage ensuring that exposure to 365 nm light was the main mode of in vivo activation. Tissue extractions from tumors exposed to 365 nm light in vivo showed the presence of DOX‐PCB as well as activated DOX. The exposed tumors had six times more DOX concentration than nearby unexposed control tumors. This in vivo proof of concept demonstrates the first preferential activation of a photocleavable prodrug in deep tumor tissue.     

Tumor‐Specific Chemotherapy by Nanomedicine‐Enabled Differential Stress Sensitization

Most of current nanomedicines are administrated intravenously to favour tumor accumulation through enhanced permeability and retention (EPR) effect, which, however, suffers from several drawbacks such as low drug bioavailability and severe side effect. In this work, we have constructed a doxorubicin(Dox)‐based liposomal nanosystem for tumor‐specific chemotherapy, by enabling differential stress sensitization between cancer and normal cells for restricting the chemodrug toxicity exclusively in tumor regions. 2‐Deoxy‐D‐glucose (2DG) was loaded in the nanoliposome to inhibit glycolysis of cancer cells, which works in synergy with the co‐loaded chemodrug Dox to promote mitochondrial depolarization and subsequent apoptosis. In addition, the starvation effect of 2DG can counteract the toxicity of Dox in normal cells and thus mitigates the harmful side effect of chemotherapy. It is expected that such a differential stress sensitization strategy may greatly benefit future nanomedicine design.     

Cathepsin B‐Specific Metabolic Precursor for In Vivo Tumor‐Specific Fluorescence Imaging

Recently, metabolic glycoengineering with bioorthogonal click reactions has focused on improving the tumor targeting efficiency of nanoparticles as delivery vehicles for anticancer drugs or imaging agents. It is the key technique for developing tumor‐specific metabolic precursors that can generate unnatural glycans on the tumor‐cell surface. A cathepsin B‐specific cleavable substrate (KGRR) conjugated with triacetylated N‐azidoacetyl‐d ‐mannosamine (RR‐S‐Ac₃ManNAz) was developed to enable tumor cells to generate unnatural glycans that contain azide groups. The generation of azide groups on the tumor cell surface was exogenously and specifically controlled by the amount of RR‐S‐Ac₃ManNAz that was fed to target tumor cells. Moreover, unnatural glycans on the tumor cell surface were conjugated with near infrared fluorescence (NIRF) dye‐labeled molecules by a bioorthogonal click reaction in cell cultures and in tumor‐bearing mice. Therefore, our RR‐S‐Ac₃ManNAz is promising for research in tumor‐specific imaging or drug delivery.     

Photo‐ and pH‐Responsive Polycarbonate Block Copolymer Prodrug Nanomicelles for Controlled Release of Doxorubicin

Photo/pH dual‐responsive amphiphilic diblock copolymers with alkyne functionalized pendant o‐nitrobenzyl ester group are synthesized using poly(ethylene glycol) as a macroinitiator. The pendant alkynes are functionalized as aldehyde groups by the azide‐alkyne Huisgen cycloaddition. The anticancer drug doxorubicin (DOX) molecules are then covalently conjugated through acid‐sensitive Schiff‐base linkage. The resultant prodrug copolymers self‐assemble into nanomicelles in aqueous solution. The prodrug nanomicelles have a well‐defined morphology with an average size of 20–40 nm. The dual‐stimuli are applied individually or simultaneously to study the release behavior of DOX. Under UV light irradiation, nanomicelles are disassembled due to the ONB ester photocleavage. The light‐controlled DOX release behavior is demonstrated using fluorescence spectroscopy. Due to the pH‐sensitive imine linkage the DOX molecules are released rapidly from the nanomicelles at the acidic pH of 5.0, whereas only minimal amount of DOX molecules is released at the pH of 7.4. The DOX release rate is tunable by applying the dual‐stimuli simultaneously. In vitro studies against colon cancer cells demonstrate that the nanomicelles show the efficient cellular uptake and the intracellular DOX release, indicating that the newly designed copolymers with dual‐stimuli‐response have significant potential applications as a smart nanomedicine against cancer.     

Therapeutic Vesicular Nanoreactors with Tumor‐Specific Activation and Self‐Destruction for Synergistic Tumor Ablation

Polymeric nanoreactors (NRs) have distinct advantages to improve chemical reaction efficiency, but the in vivo applications are limited by lack of tissue‐specificity. Herein, novel glucose oxidase (GOD)‐loaded therapeutic vesicular NRs (thera NR) are constructed based on a diblock copolymer containing poly(ethylene glycol) (PEG) and copolymerized phenylboronic ester or piperidine‐functionalized methacrylate (P(PBEM‐co ‐PEM)). Upon systemic injection, thera NR are inactive in normal tissues. At a tumor site, thera NR are specifically activated by the tumor acidity via improved permeability of the membranes. Hydrogen peroxide (H₂O₂) production by the catalysis of GOD in thera NR increases tumor oxidative stress significantly. Meanwhile, high levels of H₂O₂ induce self‐destruction of thera NR releasing quinone methide (QM) to deplete glutathione and suppress the antioxidant ability of cancer cells. Finally, thera NR efficiently kill cancer cells and ablate tumors via the synergistic effect.     

Excited‐State Dynamics of a Two‐Photon‐Activatable Ruthenium Prodrug

We present a new approach to investigate how the photodynamics of an octahedral ruthenium(II) complex activated through two‐photon absorption (TPA) differ from the equivalent complex activated through one‐photon absorption (OPA). We photoactivated a Ru^II polypyridyl complex containing bioactive monodentate ligands in the photodynamic therapy window (620–1000 nm) by using TPA and used transient UV/Vis absorption spectroscopy to elucidate its reaction pathways. Density functional calculations allowed us to identify the nature of the initially populated states and kinetic analysis recovers a photoactivation lifetime of approximately 100 ps. The dynamics displayed following TPA or OPA are identical, showing that TPA prodrug design may use knowledge gathered from the more numerous and easily conducted OPA studies.     

Synthesis of a Far‐Red Photoactivatable Silicon‐Containing Rhodamine for Super‐Resolution Microscopy

The rhodamine system is a flexible framework for building small‐molecule fluorescent probes. Changing N‐substitution patterns and replacing the xanthene oxygen with a dimethylsilicon moiety can shift the absorption and fluorescence emission maxima of rhodamine dyes to longer wavelengths. Acylation of the rhodamine nitrogen atoms forces the molecule to adopt a nonfluorescent lactone form, providing a convenient method to make fluorogenic compounds. Herein, we take advantage of all of these structural manipulations and describe a novel photoactivatable fluorophore based on a Si‐containing analogue of Q‐rhodamine. This probe is the first example of a “caged” Si‐rhodamine, exhibits higher photon counts compared to established localization microscopy dyes, and is sufficiently red‐shifted to allow multicolor imaging. The dye is a useful label for super‐resolution imaging and constitutes a new scaffold for far‐red fluorogenic molecules.     

Far‐Red and Near‐IR AIE‐Active Fluorescent Organic Nanoprobes with Enhanced Tumor‐Targeting Efficacy: Shape‐Specific Effects

The rational design of high‐performance fluorescent materials for cancer targeting in vivo is still challenging. A unique molecular design strategy is presented that involves tailoring aggregation‐induced emission (AIE)‐active organic molecules to realize preferable far‐red and NIR fluorescence, well‐controlled morphology (from rod‐like to spherical), and also tumor‐targeted bioimaging. The shape‐tailored organic quinoline–malononitrile (QM) nanoprobes are biocompatible and highly desirable for cell‐tracking applications. Impressively, the spherical shape of QM‐5 nanoaggregates exhibits excellent tumor‐targeted bioimaging performance after intravenously injection into mice, but not the rod‐like aggregates of QM‐2.     

Development of a Photoactivatable Phosphine Probe for Induction of Intracellular Reductive Stress with Single‐Cell Precision

Photoactivatable phosphines that induce intracellular reductive stress are reported. The design of these probes takes advantage of the conjugate addition of trialkylphosphines to carbocyanine dyes, which can be reverted photochemically to produce the trialkylphosphine and a fluorescent reporter. The photochemical release depends on the efficiency of photoinduced electron transfer from the indolenine arm of the probe to the coumarin acceptor. These probes readily permeate the mammalian plasma membrane and can be photoactivated in live cells. Upon irradiation of the probe, the released trialkylphosphine induces intracellular reductive stress, which ultimately leads to formation of thioflavin‐positive intracellular protein aggregates. These effects could be induced in individual cells within a monolayer, with minimal disturbance of neighboring cells.     

Tumor‐Targeting of EGFR Inhibitors by Hypoxia‐Mediated Activation

The development of receptor tyrosine‐kinase inhibitors (TKIs) was a major step forward in cancer treatment. However, the therapy with TKIs is limited by strong side effects and drug resistance. The aim of this study was the design of novel epidermal growth factor receptor (EGFR) inhibitors that are specifically activated in malignant tissue. Thus, a Co^III‐based prodrug strategy for the targeted release of an EGFR inhibitor triggered by hypoxia in the solid tumor was used. New inhibitors with chelating moieties were prepared and tested for their EGFR‐inhibitory potential. The most promising candidate was coupled to Co^III and the biological activity tested in cell culture. Indeed, hypoxic activation and subsequent EGFR inhibition was proven. Finally, the compound was tested in vivo, also revealing potent anticancer activity.     

Organic Semiconducting Pro‐nanostimulants for Near‐Infrared Photoactivatable Cancer Immunotherapy

In this study, an organic semiconducting pro‐nanostimulant (OSPS) with a near‐infrared (NIR) photoactivatable immunotherapeutic action for synergetic cancer therapy is presented. OSPS comprises a semiconducting polymer nanoparticle (SPN) core and an immunostimulant conjugated through a singlet oxygen (¹O₂) cleavable linkers. Upon NIR laser irradiation, OSPS generates both heat and ¹O₂ to exert combinational phototherapy not only to ablate tumors but also to produce tumor‐associated antigens. More importantly, NIR irradiation triggers the cleavage of ¹O₂‐cleavable linkers, triggering the remote release of the immunostimulants from OSPS to modulate the immunosuppressive tumor microenvironment. Thus, the released tumor‐associated antigens in conjunction with activated immunostimulants induce a synergistic antitumor immune response after OSPS‐mediated phototherapy, resulting in the inhibited growth of both primary/distant tumors and lung metastasis in a mouse xenograft model, which is not observed for sole phototherapy.