Prodrug strategies for targeted therapy triggered by reactive oxygen species

2',7'-dichlorofluorescin-based analysis of Fenton chemistry reveals auto-amplification of probe fluorescence and albumin as catalyst for the detection of hydrogen peroxide

Fluorophore 2',7'-dichlorofluorescin (DCF) is the most frequently used probe for measuring oxidative stress in cells, but many aspects of DCF remain to be revealed. Here, DCF was used to study the Fenton reaction in detail, which confirmed that in a cell-free system, the hydroxyl radical was easily measured by DCF, accompanied by the consumption of H2O2 and the conversion of ferrous iron into ferric iron. DCF fluorescence was more specific for hydroxyl radicals than the measurement of thiobarbituric acid (TBA)-reactive 2-deoxy-D-ribose degradation products, which also detected H2O2. As expected, hydroxyl radical-induced DCF fluorescence was inhibited by iron chelation, anti-oxidants, and hydroxyl radical scavengers and enhanced by low concentrations of ascorbate. Remarkably, due to DCF fluorescence auto-amplification, Fenton reaction-induced DCF fluorescence steadily increased in time even when all ferrous iron was oxidized. Surprisingly, the addition of bovine serum albumin rendered DCF sensitive to H2O2 as well. Within cells, DCF appeared not to react directly with H2O2 but indirect via the formation of hydroxyl radicals, since H2O2-induced cellular DCF fluorescence was fully abolished by iron chelation and hydroxyl radical scavenging. Iron chelation in H2O2-stimulated cells in which DCF fluorescence was already increasing did not abrogate further increases in fluorescence, suggesting DCF fluorescence auto-amplification in cells. Collectively, these data demonstrate that DCF is a very useful probe to detect hydroxyl radicals and hydrogen peroxide and to study Fenton chemistry, both in test tubes as well as in intact cells, and that fluorescence auto-amplification is an intrinsic property of DCF.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

Metal- and Reagent-Free Electrochemical Synthesis of Alkyl Arylsulfonates in a Multi-Component Reaction

This work presents the first electrochemical preparation of alkyl arylsulfonates by direct anodic oxidation of electron-rich arenes. The reaction mechanism features a multi-component reaction consisting of electron-rich arenes, an alcohol of choice and excess SO2 in an acetonitrile-HFIP reaction mixture. In-situ formed monoalkyl sulfites are considered as key intermediates with bifunctional purpose. Firstly, this species functions as nucleophile and secondly, excellent conductivity is provided. Several primary and secondary alcohols and electron-rich arenes are implemented in this reaction to form the alkyl arylsulfonates in yields up to 73 % with exquisite selectivity. Boron-doped diamond electrodes (BDD) are employed in divided cells, separated by a simple commercially available glass frit.

NIR light-triggered nanomaterials-based prodrug activation towards cancer therapy

Nanomaterials-based prodrug activation systems have been widely explored in cancer therapy, aiming at overcoming limited dosage formulation, systemic toxicity, and insufficient pharmacokinetic performance of parent drugs. For better delivery control, various stimuli systems, especially nanomaterials-based ones, have come to the forefront. Among them, near-infrared (NIR) light takes advantage of on-demand/site-specific regulation and non-invasiveness. In this review, we will address the developments of nanomaterials-based prodrug over the last decade, the activation mechanisms, and bioapplications under NIR light triggering. The advantages and limitations of NIR-triggered prodrug activation strategies and the perspectives of the next-generation prodrug nanomedicine will also be summarized. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Reactive Oxygen Species (ROS)-Sensitive Prodrugs of the Tyrosine Kinase Inhibitor Crizotinib

Tyrosine kinase inhibitors revolutionized cancer therapy but still evoke strong adverse effects that can dramatically reduce patients' quality of life. One possibility to enhance drug safety is the exploitation of prodrug strategies to selectively activate a drug inside the tumor tissue. In this study, we designed a prodrug strategy for the approved c-MET, ALK, and ROS1 tyrosine kinase inhibitor crizotinib. Therefore, a boronic-acid trigger moiety was attached to the 2-aminopyridine group of crizotinib, which is a crucial position for target kinase binding. The influence of the modifications on the c-MET- and ALK-binding ability was investigated by docking studies, and the strongly reduced interactions could be confirmed by cell-free kinase inhibition assay. Furthermore, the newly synthesized compounds were tested for their activation behavior with H₂O₂ and their stability in cell culture medium and serum. Finally, the biological activity of the prodrugs was investigated in three cancer cell lines and revealed a good correlation between activity and intrinsic H₂O₂ levels of the cells for prodrug A. Furthermore, the activity of this prodrug was distinctly reduced in a non-malignant, c-MET expressing human lung fibroblast (HLF) cell line.

Development of Prodrugs for PDT-Based Combination Therapy Using a Singlet-Oxygen-Sensitive Linker and Quantitative Systems Pharmacology

Photodynamic therapy (PDT) has become an effective treatment for certain types of solid tumors. The combination of PDT with other therapies has been extensively investigated in recent years to improve its effectiveness and expand its applications. This focused review summarizes the development of a prodrug system in which anticancer drugs are activated locally at tumor sites during PDT treatment. The development of a singlet-oxygen-sensitive linker that can be conveniently conjugated to various drugs and efficiently cleaved to release intact drugs is recapitulated. The initial design of prodrugs, preliminary efficacy evaluation, pharmacokinetics study, and optimization using quantitative systems pharmacology is discussed. Current treatment optimization in animal models using physiologically based a pharmacokinetic (PBPK) modeling approach is also explored.

Oxidative Cyclization-Induced Activation of a Phosphoinositide 3-Kinase Inhibitor for Enhanced Selectivity of Cancer Chemotherapeutics

In this work, we designed a prodrug that reacts with cellular oxidative equivalents leading to ether cleavage and cyclization to release an active phosphatidylinositol 3-kinase (PI3K) inhibitor. We show that the compound reduces affinity for PI3KA relative to the PI3K inhibitor, is slow to intercellularly oxidize, and is resistant to liver microsomes. We observed modest activity in untreated acute myeloid leukemia cells and 14-fold selectivity relative to non-cancerous cells. The cellular activity of the compound can be modulated by the addition of antioxidants or oxidants, indicating the compound activity is sensitive to cellular reactive oxygen species (ROS) state. Co-treatment with cytosine arabinoside or doxorubicin was used to activate the compound inside cells. We observed strong synergistic activity specifically in acute myeloid leukemia (AML) cancer cells with an increase in selective anticancer activity of up to 90-fold. Thus, these new self-cyclizing compounds can be used to increase the selectivity of anticancer agents.