Deubiquitinases: A Backdoor into Undruggable Targets?

Molecular model of the yeast proteasome.

Molecular model of the yeast proteasome.

Ubiquitin modification of a protein directs events such as targeting for proteasomal degradation. Targeting a protein for degradation through ubiquitin modification is one way to regulate the amount of time a signaling protein, such as a kinase or other enzyme, is available to participate in cell signaling events. Deubiquitinases (DUBs) are enzymes that cleave the ubiquitin tags from proteins, and they have been implicated in several diseases, including cancer.

With their roles in the stabilization of proteins involved in cell cycle progression and other critical processes, DUBs are promising targets for small molecule inhibitors, particularly since they may provide a “back door” for targeting otherwise intractable, undruggable proteins by modulating their half lives. However, finding small molecule inhibitors of the ubiquitin proteases to date has not been trivial. Here we highlight two papers describing the identification and characterization of small molecule inhibitors against the DUB USP7. Continue reading

Review: Validation of a high throughput cell-based assay to screen compounds for mitochondrial toxicity

mitotox_covertipDrug-induced mitochondrial toxicity is a concern for pharmaceuticals that was, until recently, limited by the availability of a cell-based assay that is amenable to rapid high-throughput screening. Incorporating high-throughput assay chemistry that can detect mitochondrial dysfunction early in drug discovery programs provides the opportunity to identify potential mitotoxicants before they reach clinical trials or the market population.

In the paper reviewed here (1) Swiss and colleagues have validated the use of a commercially available Mitochondrial ToxGlo™ Asssay (2) to replace traditional methods that not only require expensive reagents and/or equipment but also do not lend themselves easily to high-throughput screening formats. Continue reading

The 64 billion dollar question: Is my compound or treatment toxic?

CellTox™ Green Dye is excluded from viable cells, but it binds to DNA from cells with compromised membrane integrity.

CellTox™ Green Dye is excluded from viable cells, but it binds to DNA from cells with compromised membrane integrity.

Determining the exact cause/effect relationship between a treatment and a cellular outcome is not a simple matter, but is critical for really understanding how therapeutic treatments affect target cells or exercise any off-target effects.

Four key factors are critical for determining whether or not a particular treatment or compound is toxic.

  1. Dosage (usually addressed by a dilution series)
  2. Exposure time
  3. Mechanism of Action
  4. Cell Type

In a recent Promega Webinar, A Cytotoxicity Assay That Fits Your Timeline, Promega scientist Dr. Andrew Niles presented the CellTox™ Green Cytotoxicity Assay—a new tool that gives researchers more power to answer the question “Is my compound or treatment toxic?” Continue reading