Nature 552, 194–199 (2017) https://doi.org/10.1038/nature25016

Credit: NATURE

Disulfiram (DSF) is a drug used for treatment of alcohol dependency through inhibition of liver aldehyde dehydrogenase, but it also shows activity against a broad spectrum of malignancies. The antitumor activity of DSF is enhanced by its chelation of copper. To determine the direct molecular target responsible for the anticancer effect of DSF, Skrott et al. first developed an in vivo HPLC–MS approach, through which they found that mouse tumors preferentially accumulate a complex between the DSF metabolite DTC and copper (CuET), with high toxicity against targeted cells. Although CuET induces phenotypes similar to those seen with proteasome inhibitors, including accumulation of polyubiquitylated (polyUb) proteins, it did not inhibit 20S proteasome-dependent protein turnover or 26S proteasome activity. Instead, CuET inhibited processing of polyUb proteins by p97, which acts upstream of the proteasome and has protease and segregase activities. Experiments with p97 inhibitors using fluorescence recovery after photobleaching (FRAP) indicated that CuET inhibits the p97 segregase activity that extracts polyUb proteins from cellular structures. More specifically, CuET inhibits the NPL4 component of the segregase, inducing its clustering in the nucleus of treated cells, which is dependent on a putative zinc finger within the protein. These results support a model wherein CuET binding to NPL4 induces its immobilization and disruption of activity, ultimately leading to cell death, and provide a therapeutic option for tumors that are dependent on p97.