At present, mitotane (MTT) represents the first-line pharmacological approach for the treatment of advanced adrenocortical carcinoma (ACC). Despite clear evidence that the drug can reduce the clinical signs of steroid excess in secreting ACC, the mechanism mediating the possible toxic effect of MTT on tumor cells still remains obscure. This study investigated the intracellular events underlying the toxic effect of MTT by studying qualitative and quantitative alterations in mitochondrial morphology and functions in human adrenocortical cancer cell lines, H295R and SW13. Increasing concentrations of MTT resulted in rapid intracellular accumulation and conversion of the drug. Cytostatic and cytotoxic effects were evident at doses corresponding to the therapeutic window (30-50 mM) through an apoptotic mechanism involving caspase 3/7. Electron microscopic analysis of cell mitochondria displayed MTT-induced dose-and time-dependent alterations in the morphology of the organelle. These alterations were characterized by a marked swelling and a decrease in the number of respiratory cristae, accompanied by a significant depolarization of the mitochondrial membrane potential, finally leading to the disruption of the organelle. A drastic reduction of oxygen consumption was observed due to mitochondrial membrane damage, which was accompanied by a decrease in the levels of VDAC1 integral membrane channel. These findings contribute to better understand the intracellular mechanism of action of MTT in ACC cells, showing that its cytotoxic effect seems to be mainly mediated by an apoptotic process activated by the disruption of mitochondria.

The embodiment of 4-aminoproline residues (Amp) into the arginine-glycine-aspartate (RGD) sequence led to the discovery of a novel class of high-affinity alpha Vbeta 3/alpha Vbeta 5 integrin binders [IC 50 h (alpha Vbeta 3) 0.03-5.12 nM; IC 50 h (alpha Vbeta 5) 0.88-154 nM]. A total of eight cyclopeptides of type cyclo-[-Arg-Gly-Asp-Amp-], 5- 12, were assembled by a standard solid-phase peptide synthesis protocol that involved the C2-carboxyl and C4-amino functionalities of the proline scaffolds, leaving the N (alpha)-nuclear site untouched. Functionalization of this vacant proline site with either alkyl or acyl substituents proved feasible, with significant benefit to the integrin binding capabilities of the ligands. Notably, six out of eight cyclopeptide inhibitors, 5- 7 and 9- 11, showed moderate yet significant selectivity toward the alpha Vbeta 3 receptor. The three-dimensional structure in water was determined by NMR techniques and molecular dynamics calculations. Docking studies to the X-ray crystal structure of the extracellular segment of integrin alpha Vbeta 3 complexed with reference compound 1 were also performed on selected analogues to highlight the structural features required for potent ligand binding affinity.

A click chemistry approach was applied for the discovery of triazole-based arginine-glycine-aspartate (RGD) mimetics by Cu(I)-catalyzed 1,3-dipolar alkyne-azide coupling reaction, which showed binding affinity properties toward α(v)β(3)/α(v)β(5) integrins. Biological assays showed compound 18 capable of binding α(v)β(3) integrin with nanomolar affinity according to a two-sites model, and molecular modeling studies revealed a peculiar π-stacking interaction between the triazole ring and Tyr178 side chain. Accordingly, compound 18 inhibited the adhesion of integrin-expressing human melanoma cells to RGD-containing proteins of the extracellular matrix, such as vitronectin, fibronectin, and osteopontin, and also angiogenesis in in vitro and in vivo experimental models. The relevant biological effects exerted by compound 18 suggest its potential application as an antiangiogenic agent in the diagnosis and therapy of tumors where α(v)β(3) integrin expression is up-regulated.