Multiple myeloma (MM) is a cancer of plasma cells, that is incurable, and the second most common form of blood cancer. Proteasome inhibitors (PIs) are considered a mainstay in the treatment of MM and mantle cell lymphoma (MCL). Current drugs, based on PIs however, target the chymotrypsin-like activity of the 20S proteasome, and inhibit the activities of both the 20S and 26S proteasomes. Thus, it is possible that selective drug intervention specifically inhibiting only the 20S proteasomes will improve the rates of cancer cell toxicity, and minimize the deleterious side effects of the current therapeutic regimens.
Our preliminary work revealed a family of 20S proteasome inhibitors, which we termed Catalytic Core Regulators (CCRs) that selectively target the 20S proteasome rather than the 26S complex. Based on sequence motif and structural elements of the CCRs we have designed an artificial protein that is capable of inhibiting the 20S proteasome. We anticipate that these findings will lead to the design of synthetic proteins, peptides or peptidomimetic compounds targeting cancer cells more specifically. This specificity will pose the compounds in an attractive light for using them in various therapeutic applications. What is exciting from the commercialization perspective, is that pharmaceutical research has switched to revisit the use of peptides as therapeutics. Pharmaceutical companies have seen the development of peptides as a promising direction to lower their risk position. Overall, peptide therapeutics have a 20% chance of receiving regulatory approval, a probability that is 50% higher than that for the approval of small molecules, which form the basis of so called traditional drugs.
In the course of this project, we demonstrated that an artificial small protein, named CPloop, physically binds the 20S proteasome and not the 26S proteasome. We determined the site of binding within the protein and mapped the 20S proteasome interactions site. We also demonstrated that the cellular levels of CPloop stabilized the cellular levels of 20S proteasome substrates. Overall, our results demonstrate that possibility of specific inhibition of the 20S proteasome by an artificially designed small protein. These findings highlights the potential of the designed CPloop as a novel therapeutic agent.
