Targeting the C481S Ibrutinib-Resistance Mutation in Bruton’s Tyrosine Kinase Using PROTAC-Mediated Degradation

Abstract

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.

Development of a Potent Protein Degrader against Oncogenic BCR-ABL Protein

“…Accordingly, development of VHL-and CRBN-recruiting PROTACs based on a promiscuous kinase inhibitor ferotinib demonstrated that the degradation profiles of the two PROTACs were not identical, and that there was no correlation between the binding affinity of either PROTAC to the kinases and the extent of PROTAC-induced degradation of the kinases. 44) Thus, the suitable combination of an E3 ligase ligand and a target ligand is critically important to develop a potent degrader. In this point of view, it is important to identify a novel small molecule that recruits another E3 ubiquitin ligase to the target protein appropriately.…”

“…(PROTACs). [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] SNIPERs and PROTACs are chimeric molecules composed of two different ligands connected by a linker; one ligand is for the target protein and the other is for E3 ubiquitin ligases. Accordingly, these molecules are expected to crosslink the target protein and E3 ubiquitin ligases in cells, resulting in ubiquitylation and subsequent degradation of the target protein via the ubiquitin-proteasome system (UPS) ( Fig.…”

PROTACs: great opportunities for academia and industry

“…At almost the same time, the Crews group reported another BTK PROTAC, MT-802, derived from ibrutinib 168 (Fig. 13).…”

Covalent Small Molecules as Enabling Platforms for Drug Discovery

“…Targeted protein degradation induced by small molecules is an emerging strategy in chemical biology and drug discovery . These molecules, often called proteolysis targeting chimeras (PROTACs), have potential therapeutic advantages over typical inhibitors, and the first examples of this technology have recently entered clinical trials . PROTACs are heterobifunctional molecules that bind to a POI and an E3 ligase protein simultaneously (Figure A).…”