Mechanism of the Affinity-Enhancing Effect of Isatin on Human Ferrochelatase and Adrenodoxin Reductase Complex Formation: Implication for Protein Interactome Regulation.

Isatin (indole-2, 3-dione) is a non-peptide endogenous bioregulator exhibiting a wide spectrum of biological activity, realized in the cell via interactions with numerous isatin-binding proteins, their complexes, and (sub) interactomes. There is increasing evidence that isatin may be involved in the regulation of complex formations by modulating the affinity of the interacting protein partners. Recently, using Surface Plasmon Resonance (SPR) analysis, we have found that isatin in a concentration dependent manner increased interaction between two human mitochondrial proteins, ferrochelatase (FECH), and adrenodoxine reductase (ADR). In this study, we have investigated the affinity-enhancing effect of isatin on the FECH/ADR interaction. The SPR analysis has shown that FECH forms not only homodimers, but also FECH/ADR heterodimers. The affinity-enhancing effect of isatin on the FECH/ADR interaction was highly specific and was not reproduced by structural analogues of isatin. Bioinformatic analysis performed using three dimensional (3D) models of the interacting proteins and in silico molecular docking revealed the most probable mechanism involving FECH/isatin/ADR ternary complex formation. In this complex, isatin is targeted to the interface of interacting FECH and ADR monomers, forming hydrogen bonds with both FECH and ADR. This is a new regulatory mechanism by which isatin can modulate protein-protein interactions (PPI).

Design, synthesis and biomedical evaluation of mostotrin, a new water soluble tryptanthrin derivative.

Mostotrin (MT), a novel compound, at least five orders of magnitude more soluble in water than its mother substance, was designed and synthesised from tryptanthrin (TR). Its structure was established by nuclear magnetic resonance and mass spectrometry data and confirmed by X­ray analysis, revealing that MT is a pentacyclic product with an additional pseudo­cycle formed with the participation of one intramolecular hydrogen bond. Antimicrobial activity and cytotoxic action against tumour cells in vitro, as well as anti­tumour effects, acute toxicity and anti­inflammatory activities in vivo, were evaluated. Antimicrobial properties of MT against Mycobacterium spp and Bacillus cereus ATCC 10702 appeared to be the same as that of TR, but against the other strains used it was weaker. Furthermore, MT exhibited 5­10 times higher cytotoxic activities against tumour cell lines HCT­116, МСF­7 and K­562 than TR, but was less toxic than TR (LD50 of MT was 375 mg/kg, while LD50 for TR was 75 mg/kg). Additionally, compounds MT and TR were studied in DNA binding tests. The quenching of its fluorescence on addition to DNA solution established MT to be capable of binding to DNA. Its anti­tumour action in vivo on mice with the ascitic form of Ehrlich carcinoma was promising, particularly with joint application of MT and the antitumour drug doxorubicin. In this model, the survival and life span for the doxorubicin and 1 co­treatment group were significantly higher compared to doxorubicin treatment alone. The compound MT showed a lower immunosuppressive effect than TR at the early stages of inflammation induced in mice by LPS from E. Ñoli (MT hardly inhibited the release of IL­1, IL­2, or INF­Î³). These results demonstrated that MT is a perspective hit compound for drug development. In our opinion, further evaluation on the biological effects of MT and its synthetic analogues could lead to safer and more effective anti­tumour and anti­tuberculosis agents than TR itself. MT has also the prospect of application in combination with known anti­tumour drugs for the treatment of oncological diseases.

Low-dose action of tryptanthrin and its derivatives against developing embryos of the sea urchin Strongylocentrotus intermedius.

Nine tryptanthrin derivatives, including tryptanthrin itself, were synthesized using different methods, including oxidation of the corresponding isatins to obtain 1-4, the reaction of tryptanthrin 1 with hydrazine and its derivatives to obtain 5-7, and aldol condensation of 1 with acetone and methylethylketone to obtain 8 and 9. The action of 1-9 in doses corresponding to the IC50 against developing embryos of the sea urchin Strongylocentrotus intermedius and in the sperm test allowed us to estimate to potency of all the compounds and to determine which were cytotoxic. In addition, these studies showed that compounds 3, 4, 8, and 9 had a stimulatory effect at lower doses. In particular, the tryptanthrin derivatives stimulated the larval stages of development in surviving embryos at concentrations lower than the IC50.