Tetrathiomolybdate
Excess dietary molybdenum has been found to result in copper deficiency in grazing animals (
ruminants). In the digestive tract of ruminants, the formation of compounds containing sulfur and molybdenum, known as thiomolybdates, prevents the absorption of copper and can cause fatal copper-dependent disorders
(10). Tetrathiomolybdate (TM) is a molecule that can form high-affinity complexes with copper, controlling free copper (copper that is not bound to
ceruloplasmin), and inhibiting copper
chaperones and copper-containing
enzymes (11, 12). TM's ability to lower free copper levels is exploited in the treatment of Wilson's disease, a genetic disorder characterized by copper accumulation in tissues responsible for
hepatic and
neurologic disorders. Neurologic worsening has been linked with toxic levels of free copper in the
serum of neurologically presenting patients. TM therapy seems able to stabilize neurologic status and prevent neurologic deterioration in these patients, as opposed to the standard initial treatment of choice
(13).
Copper is also a required
cofactor for enzymes involved in
inflammation and
angiogenesis, known to accelerate
cancer progression and
metastasis. Copper depletion studies employing TM have been initiated in patients with advanced
malignancies with the aim of preventing disease progression or relapse. These pilot trials showed promising results in individuals with metastatic kidney cancer
(14), metastatic colorectal cancer
(15), and breast cancer with high risk of relapse
(16). TM was relatively well-tolerated and stabilized disease or prevented relapse in correlation with copper depletion. TM's efficacy is also investigated in animal models of inflammatory and immune-related diseases
(17, 18) and, at this point, clinical studies are needed to evaluate whether copper depletion could stabilize diseases and improve survival in humans, as suggested by a trial of TM therapy with patients with
biliary cirrhosis (19).