Category: Preclinical Development
Purpose: Acute Myeloid Leukemia (AML) is an aggressive blood malignancy with abysmal clinical outcomes. Here, we describe the novel mechanism of action of a class of small molecules, dimers of melampomagnolide B (MMB), that can potently and selectively induce apoptosis in primary AML relative to healthy hematopoietic stem and progenitor cells (HSPCs). Because these compounds do not share the known mechanisms of the parent compound, parthenolide, we sought to characterize their AML-selective mechanism through chemoproteomic target identification.
Methods: By applying a "clickable" alkyne tag to our small molecule of interest, we were able add a biotin tag to protein targets in situ after treating primary leukemia and normal blood samples with our tagged molecule. Following the click reaction, biotin-tagged proteins were isolated via streptavidin purification and subjected to proteomic mass spectrometry to compare protein targets in AML, normal peripheral blood, and HSPCs.
Results: From this analysis, we find that MMB dimer targets show very little overlap between AML, normal blood cells and HSPCs. Exclusively in the AML setting, they exhibit a mechanism of action based on induced proteasomal degradation of multiple cancer-specific protein targets through direct ligation to ribosomal ubiquitin. Additionally, a quantitative analysis of the differential protein targets evidences that one of the major targets of this induced degradation is DNA-dependent protein kinase (DNA-PK), a key driver of the overactive non-homologous end joining observed in leukemia.
Conclusion: Induced proteasomal degradation of cancer targets is a powerful mechanism of action for small molecules. This work supports the development of MMB dimers as proteolysis-targeting dimers, a novel subclass of molecules with dramatic clinical potential.
Venumadhav Janganati– University of Arkansas for Medical Sciences, Little Rock, Arkansas
Bommagani Shobanbabu– University of Arkansas for Medical Sciences, Little Rock, Arkansas
Peter Crooks– University of Arkansas for Medical Sciences, Little Rock, Arkansas
Craig Jordan– University of Colorado Denver, Aurora, Colorado