Gold(III) Complexes & HeLa Cells

Gold(III)-Dithiocarbamato Complexes

• Gold(III)-dithiocarbamato complexes can induce cancer cell death via thioredoxin redox system inhibition and activation of the ERK pathway.
• These complexes exhibit enhanced stability due to the presence of chelating dithiocarbamato ligands.
• Cancer cell death occurs through apoptotic and nonapoptotic mechanisms.
• The complexes inhibit thioredoxin reductase activity.
• The complexes generate free radicals and modify mitochondrial functions.
• ERK1/2 phosphorylation is increased as a result of exposure to the complexes.
• Deregulation of the thioredoxin reductase/thioredoxin redox system is a major mechanism involved cancer-fighting activity.

Gold(III) Complexes as Anticancer Agents

• Gold(I) compounds possess anti-inflammatory and immunosuppressive properties.
• Gold(I) compounds used for treatment of rheumatoid arthritis were considered for anticancer activity.
• Gold(I) compounds, such as auranofin, were found to exert significant antitumor activity in vitro and in vivo.
• Development of gold(III) complexes as antitumor agents has been hampered by their poor stability under physiological conditions.
• Selected gold(III) complexes can exert outstanding cytotoxic activity toward various tumor cell lines.
• The molecular components involved in the cascade of events that trigger cell death requires identification.
• Gold(I) and gold(III) complexes interact with cellular components other than DNA.
• Downregulation of the antiapoptotic Bcl-2 molecule and an upregulation of the proapoptotic Bax protein are achieved.
• Proteasome, in vitro and in vivo is a possible target of gold(III)-dithiocarbamato derivatives.
• Inhibition of proteasomal chymotrypsin-like activity leads to accumulation of ubiquinated proteins.
• Mitochondrial thioredoxin reductase appears to be a very specific target.

Effects of Gold(III) Complexes on Cancer Cells

• Derivatives trigger cell death by activating apoptotic and nonapoptotic pathways.
• Derivatives change some mitochondrial functions such as membrane potential and permeability.
• Derivatives stimulate ROS generation.
• Derivatives are particularly effective in inhibiting the activity of selenoenzyme thioredoxin reductase with similar or even higher efficiency.
• Complexes induce phosphorylation of ERK.
• ERK activation can be completely blocked by the antioxidant N-acetyl-L-cysteine (NAC).

X-Ray Crystallography of Gold(III) Complexes

• Complexes [Au(DMDT)X2] and [Au(ESDT)X2] have been designed to closely reproduce the main features of cisplatin.
• Coordination of both DMDT and ESDT ligands occurs in a near square-planar geometry.
• The NCSS moiety coordinates the metal center in a bidentate symmetrical mode through the sulfur-donating atoms.
• Coordination positions occupied by two cis-gold(III)-halogen atoms may undergo hydrolysis.

Apoptotic Activity of Gold(III) Complexes

• Complexes induce cell death in a dose-dependent way.
• No substantial differences were observed among chloro- and bromo-derivatives containing the same dithiocarbamato ligand.
• Compounds trigger cell death by activating not only apoptotic pathways but also other death mechanisms (i.e., necrosis).
• Cells treated with cisplatin induced a complete PARP cleavage, confirming that the reference drug leads to cell death only through an apoptotic pathway.

Mitochondrial Function Effects

• Tested complexes can alter some mitochondrial functions such as membrane potential and permeability conditions, and stimulate ROS generation.
• The respiratory control ratio (RCR) measured in whole mitochondria is scarcely affected.
• Uncoupled respiration shows a limited inhibition, indicating that the electron flow along the respiratory chain is not significantly affected.
• Complexes 1 and 2 caused a marked drop of membrane potential.
• Tested derivatives exhibit a marked effect when permeability transition, measured in terms of mitochondrial swelling, was taken into account
• Complexes 1-4 able to induce formation of hydrogen peroxide.

Molecular Targets at Mitochondrial and Cytosolic Levels

• Thioredoxin reductase (TrxR) appears to be a very specific intracellular target
• Both gold(I) and gold(III) complexes are highly specific inhibitors of mitochondrial thioredoxin reductase.
• Gold compounds preferentially interact with this site since selenol displays a greater affinity toward heavy metals.

Analysis of ERK Phosphorylation

• Thioredoxin reductase is a key enzyme for maintenance of intracellular reduced environment.
• Impairment of TrxR will lead to increased levels of oxidized Trx.
• Oxidized Trx results in dissociation and consequent activation of the MAPK pathway.
• Apoptotic stimuli are transmitted to caspases through the activation of MAPKKK.
• Complexes increase the levels of phosphorylated ERK1/2 in HeLa cells.
• It's hypothesized that a persistent ERK1/2 activation triggered at first by accumulation of hydrogen peroxide and then by activation of ASK-1 may be responsible for cell death.