Fine-tailoring the linker of near-infrared fluorescence probes for nitroreductase imaging in hypoxic tumor cells

Biomimetic Nanoarchitectonics of Hollow Mesoporous Copper Oxide-Based Nanozymes with Cascade Catalytic Reaction for Near Infrared-II Reinforced Photothermal-Catalytic Therapy

Biomimetic nanozyme with natural enzyme-like activities has drawn extensive attention in cancer therapy, while its application was hindered by the limited catalytic efficacy in the complicated tumor microenvironment (TME). Herein, a hybrid biomimetic nanozyme combines polydopamine-decorated CuO with a natural enzyme of glucose oxidase (GOD), among which CuO is endowed with a high loading rate (47.1%) of GOD due to the elaborately designed hollow mesoporous structure that is constructed to maximize the cascade catalytic efficacy. In the TME, CuO could catalyze endogenous H₂O₂ into O₂ for relieving tumor hypoxia and improving the catalytic efficacy of GOD. Whereafter, the amplified glucose oxidation induces starvation therapy, and the generated H₂O₂ and H⁺ enhance the catalytic activity of CuO. Significantly, the tumor-specific chemodynamic therapy (CDT) could be realized when CuO degraded into Cu²⁺ in acidic and reductive TME. Furthermore, the photothermal therapy with high photothermal conversion efficiency (30.2%) is achieved under NIR-II laser (1064 nm) excitation, which could reinforce the generation of reactive oxygen species (•OH and •O₂^-). The TME initiates the biochemical reaction cycle of CuO, O₂, and GOD, which couples with an NIR-II-induced thermal effect to realize O₂-promoted starvation and photothermal-chemodynamic combined therapy. This hybrid biomimetic nanozyme enlightens the further development of nanozymes in multimodal cancer therapy.

Insight into the spatial interaction of D-π-A bridge derived cyanines and nitroreductase for fluorescent cancer hypoxia detection

Nitroreductase (NTR) detection in tumor is critical because NTR level is correlated with hypoxia degree and cancer prognosis. With the feature of high sensitivity and selectivity, fluorescence organic probes for NTR detection exhibited a promising future for tumor hypoxia detection. However, the discovery and design of such probes have been impeded due to the lack of the understanding of spatial match and mismatch of these probes with NTR. Here, we have developed two new nitrophenyl-functionalized trimethincyanine (Cy3) probes with para- or meta- positions of nitro-group in phenyl ring. Para-nitrophenyl substituted Cy3 (pNP-Cy3) exhibited a remarkable response to NTR (20-fold fluorescence enhancement) with good selectivity and sensitivity. Experimental and theoretical analysis verified that the substituent position of nitro group on phenyl ring of dyes altered the spatial arrangement of nitro-substituent group, thereby modulated the spatial match and mismatch between Cy3 dyes and binding domain of NTR, and consequently led to a different fluorescent turn-on response. In tumor-bearing mice model, hypoxia status of A549 xenografted tumor of mice was successfully delineated by using pNP-Cy3. These results may provide a clue for designing new cyanine-derived NTR probe to monitor NTR-overexpressed hypoxia cancer cells.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

Microenvironment-sensitive iridium(iii) complexes for disease theranostics

Microenvironmental parameters, including hypoxia, pH, polarity, viscosity and temperature, play pivotal roles in controlling the biological, physical or chemical behaviors of local molecules. Abnormal changes in these parameters would cause cellular malfunction or become a hallmark of the occurrence of severe diseases. Recently, a number of phosphorescent Ir(iii) complexes have been designed to respond to such parameters due to their attractive properties such as high photostability, long emission lifetimes, and environment-sensitive emission profiles. This review aims to provide a summary of the progress achieved in developing iridium-based probes responding to microenvironmental parameters in biological systems in recent years for diagnosis and treatment of diseases such as cancer and diabetes.

A nitroreductase-activatable near-infrared theranostic photosensitizer for photodynamic therapy under mild hypoxia

In this study, a near-infrared (NIR) theranostic photosensitizer was developed based on a heptamethine aminocyanine dye with a long-lived triplet state. This theranostic molecule can be activated by nitroreductase under mild hypoxia to be used in fluorescence imaging and highly efficient photodynamic therapy (PDT) both in 2D and 3D (spheroids) HeLa cell culture models.

Hypoxia-activated NIR photosensitizer anchoring in the mitochondria for photodynamic therapy

Photodynamic therapy is considered as a promising treatment for cancer, but still faces several challenges. The hypoxic environment in solid tumors, imprecise tumor recognition and the lack of selectivity between normal and cancer cells extremely hinder the applications of photodynamic therapy in clinics. Moreover, the "always on" property of photosensitizers also increases the toxicity to normal tissues when exposed to light irradiation. In this study, a hypoxia-activated NIR photosensitizer ICy-N was synthesized and successfully applied for in vivo cancer treatment. ICy-N is in the inactivated state with low fluorescence whereas its NIR emission (λ em = 716 nm) was induced via reduction caused by nitroreductase at the tumor site. In addition, the reduced product ICy-OH was specially located in the mitochondria and demonstrated a high singlet oxygen production under 660 nm light irradiation, which efficiently induced cell apoptosis (IC50 = 0.63 μM). The in vivo studies carried out in Balb/c mice indicated that ICy-N was suitable for precise tumor hypoxia imaging and can work as an efficient photosensitizer for restraining tumor growth through the PDT process.

Nitroreductase-Activatable Theranostic Molecules with High PDT Efficiency under Mild Hypoxia Based on a TADF Fluorescein Derivative

High specificity detection and site-specific therapy are still the main challenges for theranostic anticancer prodrugs. In this work, we reported two smart activatable theranostic molecules based on a thermally activated delayed fluorescence fluorescein derivative. Nitroreductase induced by a mild hypoxia microenvironment of a solid tumor was used to activate the fluorescence and photodynamic therapy (PDT) efficiency by employing the intramolecular photoinduced electron transfer mechanism. A high PDT efficiency under 10% oxygen concentration was achieved, which is better than that of porphyrin (PpIX), a traditional photosensitizer. Such an excellent PDT efficiency can be attributed to lysosome disruption because the theranostic molecule can specifically enter the lysosomes of cells. Importantly, the strategy of targeting the mild hypoxic cells in the edge of tumor tissue could heal the "Achilles' heel" of traditional PDT. We believe that this theranostic molecule has a high potential to be applied in clinical investigation as a theranostic anticancer prodrug.

A Fluorescent Cocktail Strategy for Differentiating Tumor, Inflammation, and Normal Cells by Detecting mRNA and H2O2

Accurately distinguishing tumors from noncancerous inflammation and normal tissues is hugely significent for tumor diagnosis and therapy. However, tumor and inflammatory tissues have similar pathologic characteristics in their microenvironment, making differentiation very difficult. Here, a fluorescent cocktail nanoparticle capable of simultaneously detecting intracellular mRNA and H₂O₂ was designed to differentiate tumors from nontumor cells. To detect targeted mRNA in living cells, a DNA probe was generated using the fluorescence resonance energy transfer (FRET) principle. A pH-responsive amphiphilic polymer was synthesized to realize the transportation of the DNA probe. In addition, the polymer was conjugated with a coumarin-boronic acid ester (Cou-BE) H₂O₂ probe. According to the change in the fluorescence of Cou-BE, tumor and inflammatory cells could be distinguished from normal cells owing to their high concentration of H₂O₂. Because of the different concentrations of tumor-related mRNA in tumor and nontumor cells, the fluorescence intensity of the DNA probe-loaded nanoparticles inside tumor cells was different from that inside inflammatory cells. Therefore, our fluorescent cocktail strategy could discriminate simultaneously tumor, inflammation, and normal cells through the cooperative detection of intracellular mRNA and H₂O₂, which demonstrated potential application value in biomedical research and clinical diagnosis.