Comparative Study of Toxicity of Alkoxyamines In Vitro and In Vivo

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Alkylverdazyls as a Source of Alkyl Radicals for Light-Triggered Cancer Cell Death

Two alkylated verdazyl radicals (AlkVZs) were investigated as active compounds for photoinitiated controlled MCF-7 cell death. Observed results unambiguously showed that AlkVZ could be a potential structural moiety for the design of a novel family of photodynamic therapy agents. The main advantage of the proposed substances is an oxygen-independent generation of active radicals, which play a pivotal role in the treatment of oxygen-deficient tumors.

Design of a Targeting and Oxygen-Independent Platform to Improve Photodynamic Therapy: A Proof of Concept

Photodynamic therapy (PDT) is a promising technique to treat different kinds of disease especially cancer. PDT requires three elements: molecular oxygen, a photoactivatable molecule called the photosensitizer (PS), and appropriate light. Under illumination, the PSs generate, in the presence of oxygen, the formation of reactive oxygen species including singlet oxygen, toxic, which then destroys the surrounding tissues. Even if PDT is used with success to treat actinic keratosis or prostate cancer for example, PDT suffers from two major drawbacks: the lack of selectivity of most of the PSs currently used clinically as well as the need for oxygen to be effective. To remedy the lack of selectivity, targeting the tumor neovessels is a promising approach to destroy the vascularization and cause asphyxia of the tumor. KDKPPR peptide affinity for the neuropilin-1 (NRP-1) receptor overexpressed on endothelial cells has already been proven. To compensate for the lack of oxygen, we focused on photoactivatable alkoxyamines (Alks), molecules capable of generating toxic radicals by light activation. In this article, we describe the synthesis of a multifunctional platform combining three units: a PS for an oxygen-dependent PDT, a peptide to target tumor neovessels, and an Alk for an oxygen-independent activity. The synthesis of the compound was successfully carried out, and the study of its photophysical properties showed that the PS retained its capacity to form singlet oxygen and the affinity tests confirmed the affinity of the compound for NRP-1. Thanks to the electron paramagnetic resonance spectroscopy, a technique of choice for radical investigation, the radicals generated by the illumination of the Alk could be detected. The proof of concept was thus successfully established.

An enzymatic acetal/hemiacetal conversion for the physiological temperature activation of the alkoxyamine C–ON bond homolysis

Enzymatic trigger. Upon enzymatic hydrolysis by Subtilisin A, highly stable alkoxyamines are transformed into highly labile alkoxyamines able to homolyze spontaneously in less than 500 seconds, at 37 °C.

Enzymatic triggering of C–ON bond homolysis of alkoxyamines

Alkoxyamine 1 is selectively hydrolyzed by chymotrypsin and substilisin A into alkoxyamine 2H+ for which C–ON bond homolysis occurred with a 4-fold increase in rate constants compared to 1 while non-specific proteases had no effect.

How intramolecular coordination bonding (ICB) controls the homolysis of the C–ON bond in alkoxyamines

Because the C–ON bond homolysis rate constant k_d is an essential parameter of alkoxyamine reactivity, it is especially important to tune k_d without a major alteration of the structure of the molecule. Recently, several approaches have become known, e.g., protonation of functional groups and formation of metal complexes. In this paper, coordination reactions of [Zn(hfac)₂(H₂O)₂] with a series of new SG1-based alkoxyamines affording complexes with different structures are presented. The k_d values of the complexed forms of the alkoxyamines were compared to those of free and protonated ones to reveal the contribution of the electron-withdrawing property and structure stabilization. Together with previously published data, this work provides clues to the design of alkoxyamines that can be effectively activated upon coordination with metal ions. Furthermore, our results provide insight into the mechanism underlying the influence of complexation on the reactivity of alkoxyamines. This led us to describe different types of coordination: intramolecular in nitroxyl fragment, intramolecular in alkyl fragment, intramolecular between alkyl and nitroxyl fragment, and intermolecular one. All of them exhibit different trends which are dramatically altered by changes in conformation.

Because the C–ON bond homolysis rate constant k_d is an essential parameter of alkoxyamine reactivity, it is especially important to tune k_d without a major alteration of the structure of the molecule.