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Enhancing the removal of aggregate-prone toxic proteins is a rational therapeutic strategy for a number of neurodegenerative diseases, especially Huntington’s disease and various spinocerebellar ataxias. Ideally, such approaches should preferentially clear the mutant/misfolded species, while having minimal impact on the stability of wild-type/normally-folded proteins. Furthermore, activation of both ubiquitin-proteasome and autophagy-lysosome routes may be advantageous, as this would allow effective clearance of both monomeric and oligomeric species, the latter which are inaccessible to the proteasome. Here we find that compounds that activate the D1 ATPase activity of VCP/p97 fulfill these requirements. Such effects are seen with small molecule VCP activators like SMER28, which activate autophagosome biogenesis by enhancing interactions of PI3K complex components to increase PI(3)P production, and also accelerate VCP-dependent proteasomal clearance of such substrates. Thus, this mode of VCP activation may be a very attractive target for many neurodegenerative diseases. Several neurodegenerative diseases are characterized by the aggregation of cytoplasmic proteins. Here, the authors demonstrate that the small molecule SMER28 activates VCP, which enhances both autophagic and proteasomal clearance of aggregate-prone proteins.

Immunomodulatory imide drugs (IMiDs) like lenalidomide and pomalidomide are effective in treating multiple myeloma (MM) but pose hematotoxicity risks by degrading neosubstrates Ikaros (IKZF1) and Aiolos (IKZF3). When these IMiD scaffolds are integrated into proteolysis targeting chimeras (PROTACs), they can inadvertently lead to the degradation of these neosubstrates alongside the intended protein of interest (POI), raising safety concerns. This study profiles existing PROTACs and reveals instances of undesired degradation of IMiD-associated neosubstrates. We have developed in vitro hematopoietic assays to scrutinize the IMiD effects and describe the mechanistic insights on cell differentiation rewiring towards megakaryocytes together with an activation of the interferon response that is phenocopied by an Ikaros knock-out model. Moreover, we have identified a CRBN ligand that mitigates these safety liabilities and can be effectively incorporated into PROTACs. This advancement provides a promising path toward safer preclinical development of PROTACs, especially as the field expands into chronic disease treatments beyond oncology. IMiD-based PROTACs may degrade IKZF1/3 with hematologic effects. This study profiles these liabilities using hematopoietic assays showing stem cell rewiring and interferon activation and introduces a CRBN ligand that reduces them.