First unequivocal identification of the critical acyl radicals from the anti-tuberculosis drug isoniazid and its hydrazide analogs by complementary applications of ESR spin-trapping and HPLC/MS methods

Mn(iii)-mediated carbon-centered radicals generate an enhanced immunotherapeutic effect

A strategy for designing cancer therapeutic nanovaccines based on immunogenic cell death (ICD)-inducing therapeutic modalities is particularly attractive for optimal therapeutic efficacy. In this work, a highly effective cancer therapeutic nanovaccine (denoted as MPL@ICC) based on immunogenic photodynamic therapy (PDT) was rationally designed and fabricated. MPL@ICC was composed of a nanovehicle of MnO2 modified with a host-guest complex using amino pillar[6]arene and lactose-pyridine, a prodrug of isoniazid (INH), and chlorine e6 (Ce6). The nanovaccine exhibited excellent biosafety, good targeting ability to hepatoma cells and enrichment at tumor sites. Most importantly, it could modulate the tumor microenvironment (TME) to facilitate the existence of Mn(iii) and Mn(iii)-mediated carbon-centered radical generation with INH released from the prodrug in situ to further strengthen ICD. This is the first report on Mn(iii)-mediated generation of carbon-centered radicals for successful anti-tumor immunotherapy using ICD, which provides a novel strategy for designing highly efficient cancer therapeutic nanovaccines.

Acyl-caged rhodamines: photo-controlled and self-calibrated generation of acetyl radicals for neural function recovery in early AD mice

The biological function of radicals is a broad continuum from signaling to killing. Yet, biomedical exploitation of radicals is largely restricted to the theme of healing-by-killing. To explore their potential in healing-by-signaling, robust radical generation methods are warranted. Acyl radicals are endogenous, exhibit facile chemistry and elicit matrix-dependent biological outcomes. Their implications in health and disease remain untapped, primarily due to the lack of a robust generation method with spatiotemporal specificity. Fusing the Norrish chemistry into the xanthene scaffold, we developed a novel general and modular molecular design strategy for photo-triggered generation of acyl radicals, i.e., acyl-caged rhodamine (ACR). A notable feature of ACR is the simultaneous release of a fluorescent probe for cell redox homeostasis allowing real-time monitoring of the biological outcome of acyl radicals. With a donor of the endogenous acetyl radical (ACR575a), we showcased its capability in precise and continuous modulation of the cell redox homeostasis from signaling to stress, and induction of a local oxidative burst to promote differentiation of neural stem cells (NSCs). Upon intracerebral-injection of ACR575a and subsequent fiber-optical activation, early AD mice exhibited enhanced differentiation of NSCs toward neurons, reduced formation of Aβ plaques, and significantly improved cognitive abilities, including learning and memory.

An unprecedented free radical mechanism for the formation of DNA adducts by the carcinogenic N-sulfonated metabolite of aristolochic acids

The carcinogenicity of aristolochic acids (AAs) has been attributed mainly to the formation of stable DNA-aristolactam (DNA-AL) adducts by its reactive N-sulfonated metabolite N-sulfonatooxyaristolactam (N-OSO3--AL). The most accepted mechanism for such DNA-AL adduct formation is via the postulated but never unequivocally-confirmed aristolactam nitrenium ion. Here we found that both sulfate radical and two ALI-derived radicals (N-centered and C-centered spin isomers) were produced by N-OSO3--ALI, which were detected and unequivocally identified by complementary applications of ESR spin-trapping, HPLC-MS coupled with deuterium-exchange methods. Both the formation of the three radical species and DNA-ALI adducts can be significantly inhibited (up to 90%) by several well-known antioxidants, typical radical scavengers, and spin-trapping agents. Taken together, we propose that N-OSO3--ALI decomposes mainly via a new N-O bond homolysis rather than the previously proposed heterolysis pathway, yielding reactive sulfate and ALI-derived radicals, which are together and in concert responsible for forming DNA-ALI adducts. This study presents strong and direct evidence for the production of free radical intermediates during N-OSO3--ALI decomposition, providing an unprecedented free radical perspective and conceptual breakthrough, which can better explain and understand the molecular mechanism for the formation of DNA-AA adducts, the carcinogenicity of AAs and their potential prevention.

Molecular mechanism for the activation of the potent hepatotoxin acetylhydrazine: Identification of the initial N-centered radical and the secondary C-centered radical intermediates

Acetylhydrazine (AcHZ), a major human metabolite of the widely-used anti-tuberculosis drug isoniazid (INH), was considered to be responsible for its serious hepatotoxicity and potentially fatal liver injury. It has been proposed that reactive radical species produced from further metabolic activation of AcHZ might be responsible for its hepatotoxicity. However, the exact nature of such radical species remains not clear. Through complementary applications of ESR spin-trapping and HPLC/MS methods, here we show that the initial N-centered radical intermediate can be detected and identified from AcHZ activated by transition metal ions (Mn(III)Acetate and Mn(III) pyrophosphate) and myeloperoxidase. The exact location of the radical was found to be at the distal-nitrogen of the hydrazine group by ¹⁵N-isotope-labeling techniques via using ¹⁵N-labeled AcHZ we synthesized. Additionally, the secondary C-centered radical was identified unequivocally as the reactive acetyl radical by complementary applications of ESR spin-trapping and persistent radical TEMPO trapping coupled with HPLC/MS analysis. This study represents the first detection and unequivocal identification of the initial N-centered radical and its exact location, as well as the reactive secondary acetyl radical. These findings should provide new perspectives on the molecular mechanism of AcHZ activation, which may have potential biomedical and toxicological significance for future research on the mechanism of INH-induced hepatotoxicity.

Characterization of radicals in polysorbate 80 using electron paramagnetic resonance (EPR) spectroscopy and spin trapping

Polysorbates are an important class of nonionic surfactants that are widely used to stabilize biopharmaceuticals. The degradation of polysorbate 20 and 80 and the related particle formation in biologics are heavily discussed in the pharmaceutical community. Although a lot of experimental effort was spent in the detailed study of potential degradation pathways, the underlying mechanisms are only sparsely understood. Besides enzymatic hydrolysis, another proposed mechanism is associated with radical-induced (auto)oxidation of polysorbates. To characterize the types and the origin of the involved radicals and their propagation in bulk material as well as in diluted polysorbate 80 solutions, we applied electron paramagnetic resonance (EPR) spectroscopy using a spin trapping approach. The prerequisite for a meaningful experiment using spin traps is an understanding of the trapping rate, which is an interplay of (i) the presence of the spin trap at the scene of action, (ii) the specific reactivity of the selected spin trap with a certain radical as well as (iii) the stability of the formed spin adducts (a slow decay rate). We discuss whether and to which extent these criteria are fulfilled regarding the identification of different radical classes that might be involved in polysorbate oxidative degradation processes. The ratio of different radicals for different scenarios was determined for various polysorbate 80 quality grades in bulk material and in aqueous solution, showing differences in the ratio of present radicals. Possible correlations between the radical content and product parameters such as the quality grade, the manufacturing date, the manufacturer, the initial peroxide content according to the certificate of analysis of polysorbate 80 are discussed.

Mineralization of cyanides via a novel Electro-Fenton system generating •OH and •O2. WATER RESEARCH 2022;209:117890. [PMID: 34856430 DOI: 10.1016/j.watres.2021.117890]

Traditional methods of cyanides' (CN-) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO-) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2-. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2- were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO- intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN- was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2- via nucleophilic addition to quickly form NO3-, preventing the formation of CNO- and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.

Measurement methods of single cell drug response

In the last decades, a wide multitude of research activity has been focused on the development of new drugs, and devoted to overcome the challenges of high cost and low efficiency in drug evaluation. The measurement of drug response at the single cell level is a quicker, more direct and more accurate way to reflect drug efficacy, which can shorten the drug development period and reduce research costs. Therefore, the single cell drug response (SCDR) measurement technology has aroused extensive attention from researchers, and has become a hot topic in the fields of drug research and cell biology. Recent years have seen the emergence of various SCDR measurement technologies that feature different working principles and different levels of measurement performance. To better examine, compare and summarize the characteristics and functions of these technologies, we select signal-to-noise ratio, throughput, content, invasion, and device complexity as the criteria to evaluate them from the drug efficacy perspective. This review aims to highlight sixteen kinds of SCDR measurement technologies, including patch-clamp technique, live-cell interferometry, capillary electrophoresis, secondary ion mass spectrometry, and more, and report widespread representative examples of SCDR measurement the recent approaches for over the past forty years. Based on their reaction principles, these technologies are classified into four categories: electrical, optical, electrochemical, and mass spectrometry, and a detailed comparison is made between them. After in-depth understanding of these technologies, it is expected to improve or integrate these technologies to propose better SCDR measurement strategies, and explore methods in new drug development and screening, as well as disease diagnosis and treatment.

Proton-assisted electron transfer and hydrogen-atom diffusion in a model system for photocatalytic hydrogen production

Solar energy can be converted into chemical energy by photocatalytic water splitting to produce molecular hydrogen. Details of the photo-induced reaction mechanism occurring on the surface of a semiconductor are not fully understood, however. Herein, we employ a model photocatalytic system consisting of single atoms deposited on quantum dots that are anchored on to a primary photocatalyst to explore fundamental aspects of photolytic hydrogen generation. Single platinum atoms (Pt₁) are anchored onto carbon nitride quantum dots (CNQDs), which are loaded onto graphitic carbon nitride nanosheets (CNS), forming a Pt₁@CNQDs/CNS composite. Pt₁@CNQDs/CNS provides a well-defined photocatalytic system in which the electron and proton transfer processes that lead to the formation of hydrogen gas can be investigated. Results suggest that hydrogen bonding between hydrophilic surface groups of the CNQDs and interfacial water molecules facilitates both proton-assisted electron transfer and sorption/desorption pathways. Surface bound hydrogen atoms appear to diffuse from CNQDs surface sites to the deposited Pt₁ catalytic sites leading to higher hydrogen-atom fugacity surrounding each isolated Pt₁ site. We identify a pathway that allows for hydrogen-atom recombination into molecular hydrogen and eventually to hydrogen bubble evolution.