molecules of the month

The Merck LMP7 inhibitor, M3258, is an orally available, selective, and reversible inhibitor of the immunoproteasome proteolytic subunit, LMP7. In contrast to the constitutive proteasome, the immunoproteasome is predominantly expressed in hematolymphoid cells such as in multiple myeloma cells. Pan-proteasome inhibitors (pan-PIs) such as bortezomib, carfilzomib, and ixazomib are standard treatments for multiple myeloma, but cause a range of toxicities likely due to constitutive proteasome inhibition. This selective immunoproteasome inhibitor may lead to similar activity in MM patients but with better tolerability. Non-clinical safety studies in rat and dog identified a smaller spectrum of target organs for M3258 than pan-PIs, supporting this hypothesis. Additionally, while pan-PIs is cytotoxic to immune cells and other cells, M3258 only inhibits proliferation in human B…