1. Orally bioavailable BTK PROTAC active against wild-type and C481 mutant BTKs in human lymphoma CDX mouse models
Ye Seul Lim, Sun-Mi Yoo, Vineet Patil, Han Wool Kim, Hyun-Hwi Kim, Beomseon Suh, Ji Youn Park, Na-Rae Jeong, Chi Hoon Park, Je Ho Ryu, Byung-Hoon Lee, Pilho Kim, Song Hee Lee Blood Adv. 2023 Jan 10;7(1):92-105.doi: 10.1182/bloodadvances.2022008121.
Bruton tyrosine kinase (BTK) is an important signaling hub that activates the B-cell receptor (BCR) signaling cascade. BCR activation can contribute to the growth and survival of B-cell lymphoma or leukemia. The inhibition of the BCR signaling pathway is critical for blocking downstream events and treating B-cell lymphomas. Herein, we report potent and orally available proteolysis-targeting chimeras (PROTACs) that target BTK to inactivate BCR signaling. Of the PROTACs tested, UBX-382 showed superior degradation activity for wild-type (WT) and mutant BTK proteins in a single-digit nanomolar range of half-maximal degradation concentration in diffuse large B-cell lymphoma cell line. UBX-382 was effective on 7 out of 8 known BTK mutants in in vitro experiments and was highly effective in inhibiting tumor growth in murine xenograft models harboring WT or C481S mutant BTK-expressing TMD-8 cells over ibrutinib, ARQ-531, and MT-802. Remarkably, oral dosing of UBX-382 for <2 weeks led to complete tumor regression in 3 and 10 mg/kg groups in murine xenograft models. UBX-382 also provoked the cell type-dependent and selective degradation of cereblon neosubstrates in various hematological cancer cells. These results suggest that UBX-382 treatment is a promising therapeutic strategy for B-cell-related blood cancers with improved efficacy and diverse applicability.
2. Targeting the C481S Ibrutinib-Resistance Mutation in Bruton's Tyrosine Kinase Using PROTAC-Mediated Degradation
Alexandru D Buhimschi, Haley A Armstrong, Momar Toure, Saul Jaime-Figueroa, Timothy L Chen, Amy M Lehman, Jennifer A Woyach, Amy J Johnson, John C Byrd, Craig M Crews Biochemistry. 2018 Jul 3;57(26):3564-3575.doi: 10.1021/acs.biochem.8b00391.Epub 2018 Jun 14.
Inhibition of Bruton's tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has emerged as a transformative treatment option for patients with chronic lymphocytic leukemia (CLL) and other B-cell malignancies, yet >80% of CLL patients develop resistance due to a cysteine to serine mutation at the site covalently bound by ibrutinib (C481S). Currently, an effective treatment option for C481S patients exhibiting relapse to ibrutinib does not exist, and these patients have poor outcomes. To address this, we have developed a PROteolysis TArgeting Chimera (PROTAC) that induces degradation of both wild-type and C481S mutant BTK. We selected a lead PROTAC, MT-802, from several candidates on the basis of its potency to induce BTK knockdown. MT-802 recruits BTK to the cereblon E3 ubiquitin ligase complex to trigger BTK ubiquitination and degradation via the proteasome. MT-802 binds fewer off-target kinases than ibrutinib does and retains an equivalent potency (>99% degradation at nanomolar concentrations) against wild-type and C481S BTK. In cells isolated from CLL patients with the C481S mutation, MT-802 is able to reduce the pool of active, phosphorylated BTK whereas ibrutinib cannot. Collectively, these data provide a basis for further preclinical study of BTK PROTACs as a novel strategy for treatment of C481S mutant CLL.