Novel Isatin Thiosemicarbazone Derivatives as Potent Inhibitors of β-Amyloid Peptide Aggregation and Toxicity

Inhibition of β-amyloid peptide (Αβ) aggregation in Alzheimer's disease (AD) is among the therapeutic approaches against AD which still attracts scientific research interest. In the search for compounds that interact with Aβ and disrupt its typical aggregation course toward oligomeric or polymeric toxic assemblies, small organic molecules of natural origin, combining low molecular weight (necessary blood-brain barrier penetration) and low toxicity (necessary for pharmacological application), are greatly sought after. Isatin (1H-indoline-2,3-dione), a natural endogenous indole, and many of its derivatives exhibit a wide spectrum of neuropharmacological and chemotherapeutic properties. The synthesis and biological evaluation of four new isatins as inhibitors of Aβ aggregation is presented herein. In these derivatives, the N-phenyl thiosemicarbazide moiety is joined at the 3-oxo position of isatin through Schiff base formation, and substitutions are present at the indole nitrogen and position 5 of the isatin core. Biophysical studies employing circular dichroism, thioflavin T fluorescence assay, and transmission electron microscopy reveal the potential of the isatin thiosemicarbazones (ITSCs) to alter the course of Αβ aggregation, with two of the derivatives exhibiting outstanding inhibition of the aggregation process, preventing completely the formation of amyloid fibrils. Furthermore, in in vitro studies in primary neuronal cell cultures, the ITSCs were found to inhibit the Aβ-induced neurotoxicity and reactive oxygen species production at concentrations as low as 1 μM. Taken all together, the novel ITSCs can be considered as privileged structures for further development as potential AD therapeutics.

Nickel(II) bis(isatin thiosemicarbazone) complexes induced apoptosis through mitochondrial signaling pathway and G0/G1 cell cycle arrest in IM-9 cells

Three novel complexes (1, 3 and 4) ligating N-substituted isatin thiosemicarbazone derivatives have been synthesized and their structural and biological characteristics have been compared with those of the known analogs (2, 5-7 and 8). In addition, the structure of the representative ligands (L1, L3 and L4) and complex (4) was confirmed by single crystal X-ray diffraction method. All the complexes (1-8) were assessed for their cytotoxic property against a panel of four human cancer cells such as HepG-2 (liver), MOLM-14 (acute monocytic leukemia), U937 (histiocytic lymphoma). and IM-9 (myeloma). Complex 4 exhibited prominent cytotoxic property against MOLM-14, U937 and IM-9 cell lines. Moreover, the results were compared with the well-known anticancer drugs like doxorubicin, cisplatin and daunorubicin. Besides, complex 4 enhanced the apoptotic cell death in IM-9 cell line and induced cell cycle arrest at G1 phase. Western blot analysis revealed the down-regulation of Bcl-2 (b-cell lymphoma-2), up-regulation of Bax (bcl-2 associated X protein), release of cytochrome c and activation of caspases-3 in IM-9 cells by complex 4. Importantly, complex 4 was not toxic to the normal Vero cell line (IC₅₀ > 300 μM). In addition, complex 4 showed the concentration dependent cleavage of supercoiled (SC) DNA to its nicked circular (NC) form.