Pharmacological properties of indolone-N-oxides controlled by a bioreductive transformation in red blood cells?

Abstract

Indolone-N-oxides, long known for their biological activities, possess remarkable anti-infectious properties. With the aim of improving the pharmacological and antimalarial properties of indolone-Noxide derivatives (INODs), 6-(4-chlorophenyl)-7H-[1,3]dioxolo[4,5-f]indol-7-one-5-oxide, compound 1, was selected to study its penetration and biotransformation in red blood cells (RBC) in vitro. Compound 1 accumulated inside RBCs and was rapidly bio-transformed giving a major fluorescent metabolite, the dihydroanalogue, 1-HH, identified after extraction, through LC-MS and NMR analyses. This bioreductive transformation was (i) observed with other INOD derivatives (i: 1-7); (ii) observed in normal, b-thalassemic and Plasmodium falciparum infected RBCs; (iii) temperature and thiol-dependent; (iv) not observed with heat-denatured RBCs, suggesting an enzyme-dependent biotransformation. The dihydro form, 1-HH, has antiplasmodial activity but lower than the parent compound. Since the RBCs represent 99% of the total cellular space of blood in humans, this leads to extensive metabolism of indolone-N-oxide type compounds. Given the redox events occurring in Plasmodium infected RBCs, this bioreductive transformation may be pivotal for parasite redox balance and antiplasmodial activity. However, it may be a drawback when other pharmacological properties of INODs are investigated. These results show the importance of RBCs as an in vitro model to study the biotransformation of drugs, especially antimalarial drugs in the early discovery stages.

1,4-Naphthoquinones and Other NADPH-Dependent Glutathione Reductase- Catalyzed Redox Cyclers as Antimalarial Agents

“…This study implies that the drug activates a redox signaling pathway rather than causing direct oxidative damage. Previous work had indeed shown the importance of redox events occurring in Plasmodium infected red blood cells for the activity of indolone- N -oxides [204]. In these experiments indolone- N -oxides were rapidly bioreduced in the red blood cells to their dihydroanalog in an enzyme-dependent manner.…”

“…(16) were already known in the 19 th century [198] but it is only in 1965 that their ability to be reduced by thiols was described [199]. This finding, and the antiprotozoal activity of some indolone- N -oxide involving a reducing mechanism [200, 201], with the involvement of GSH or another potential reductant, has led to new efforts for the synthesis of potent antimalarial indolone- N -oxides [202–204]. …”

Antibacterial, antifungal and antileishmanial activities of indolone-N-oxide derivatives

“…Interestingly, INOD derivatives were previously reported to interact with thiolcontaining compounds. 7 Therefore, depending on the redox status of the host cell and its metabolic activity, these compounds may be reduced and/or degraded intracellularly even before reaching the parasitic target. This could explain the differential activities on the two stages (axenic and intramacrophagic) and the differential activity between the two macrophage cell lines (peritoneal and RAW).…”

“…This pharmacophore possesses redox properties that create oxidative stress within the infected red blood cell leading to plasmodicidal activities. 7,8 Moreover, INODs show moderate binding affinity toward human serum albumin, 9 which may provide a basis for its rational use in clinical practice and for the development of new antimicrobial archetypes. INODs have the ability to generate radical adducts, 10 which may participate in the observed biological activities.…”

Investigation of a Late‐Stage Derivatiza­tion Approach to Isatogens: Discovery of New Reaction Pathways

“…Indolone N ‐oxides (isatogens) were first prepared by Baeyer1 and constitute an interesting class of stable dipolar compounds that have been shown to display a variety of useful biological properties 2. These compounds are typically generated from 2‐nitrophenylacetylenes in the presence of acid or base,3 or by transition metal catalysis 4.…”