AS101: An overview on a leading tellurium-based prodrug

• AS101 is a potent Te(IV) immunomodulator prodrug that entered clinical trials. • A useful overview of its chemical and biological features is provided. • The state of the art for AS101 medicinal applications is provided. • Perspectives for the design of novel metalloid-based drugs are delineated. Inorganic chemistry holds a central role in the management of several diseases both from the diagnostic as well as from the therapeutic point of view. Various platinum drugs are approved at the global or local level for cancer treatment while other transition metals are used for different therapeutic applications or diagnosis. However, even semimetals i.e., the elements which lie on the diagonal connecting boron to polonium are being used in medicine where some compounds with therapeutic properties have been approved by the Food and drugs Administration (FDA) and the European Medicinal Agency (EMA). In the last decades growing attention has been devoted towards tellurium for the preparation of pharmacologically active agents. In this context, Ammonium trichloro(dioxoethylene-O,O′)tellurate (AS101) emerged as a reference tellurium-based compound. This Te(IV) compound is well tolerated in animal models and its peculiar reactivity towards thiol residues of enzymes such as cysteine proteases is at the heart of its pharmacological effects. Actually, AS101 entered several clinical trials due to its good tolerability. In this mini-review the main chemical and biological aspects of this promising metalloid-based drug are briefly summarized and the outcomes as well as future perspectives for the design of improved Te-based compounds are discussed.