Octa-O-bis-(R,R)-Tartarate Ditellurane (SAS) - a novel bioactive organotellurium(IV) compound: synthesis, characterization, and protease inhibitory activity.

Octa-O-bis-(R,R)-Tartarate Ditellurane (SAS) is a new Te(IV) compound, comprised of two tellurium atoms, each liganded by four oxygen atoms from two carboxylates and two alkoxides of two tartaric acids. Unlike many other Te(IV) compounds, SAS was highly stable in aqueous solution. It interacted with thiols to form an unstable Te(SR)(4) product. The product of the interaction of SAS with cysteine was isolated and characterized by mass spectroscopy and elemental analysis. SAS selectively inactivated cysteine proteases, but it did not inactivate other families of proteolytic enzymes. It displayed selectivity towards the cysteine protease cathepsin B, a human enzyme of pharmaceutical interest, with a second order rate constant k(i)/K(i)=5900 M(-1) s(-1).

The synthetic tellurium compound, AS101, is a novel inhibitor of IL-1beta converting enzyme.

The organotellurium compound, trichloro(dioxoethylene-O,O') tellurate (AS101) has been shown previously to exert diverse biologic activities both in vitro and in vivo. This compound was recently found to react with thiols and to catalyze their oxidation. This property of AS101 raises the possibility that it may serve as a cysteine protease inhibitor. In the present study, using a substrate-specific enzymatic assay, we show that treatment of caspase-1 (interleukin-1beta [IL-1beta] converting enzyme [ICE]) with AS101 inhibits its enzymatic activity in a dose-dependent manner. Moreover, the results show that AS101 treatment causes a significant reduction in the active form of IL-18 and IL-1beta in peripheral blood mononuclear cells (PBMC) and in human HaCat keratinocytes. We further demonstrate that the inhibitory effect of AS101 does not involve nitric oxide (NO) or interferon-gamma (IFN-gamma), two possible regulators of IL-18 production, and does not occur at the mRNA level, suggesting a posttranscriptional mechanism of action. More importantly, AS101 downregulates IL-18 and IL-1beta serum levels in a mouse model of lipopolysaccharide (LPS)-induced sepsis, resulting in increased survival. Recent studies emphasize the pathophysiologic role of IL-18 and IL-1beta in a variety of inflammatory diseases. Thus, their blockage by the nontoxic compound, AS101, currently used in clinical studies, may provide clinical advantage in the treatment of these diseases.

Multifunctional tellurium molecule protects and restores dopaminergic neurons in Parkinson's disease models.

In Parkinson's disease (PD) dopaminergic neurons in the substantia nigra (SN) become dysfunctional and many ultimately die. We report that the tellurium immunomodulating compound ammonium trichloro(dioxoethylene-O,O'-)tellurate (AS101) protects dopaminergic neurons and improves motor function in animal models of PD. It is effective when administered systemically or by direct infusion into the brain. Multifunctional activities of AS101 were identified in this study. These were mainly due to the peculiar Tellur(IV)-thiol chemistry of the compound, which enabled the compound to interact with cysteine residues on both inflammatory and apoptotic caspases, resulting in their inactivation. Conversely, its interaction with a key cysteine residue on p21(ras), led to its activation, an obligatory activity for AS101-induced neuronal differentiation. Furthermore, AS101 inhibited IL-10, resulting in up-regulation of GDNF in the SN. This was associated with activation of the neuroprotective kinases Akt and mitogen-activated protein kinases, and up-regulation of the antiapoptotic protein Bcl-2. Inhibition of caspase-1 and caspase-3 activities were associated with decreased neuronal death and inhibition of IL-1beta. We suggest that, because multiple mechanisms are involved in the dysfunction and death of neurons in PD, use of a multifunctional compound, exerting antiapoptotic, anti-inflammatory, and neurotrophic-inducing capabilities may be potentially efficacious for the treatment of PD.