292 (PB072) - Development of selective MCL-1 heterobifunctional degraders

Abstract

Background: MCL1 is a member of the Bcl-2 family that plays a key role in cellular homeostasis through the regulation of apoptosis as well as other less characterized functions. The growing recognition of MCL-1 role in cancer cell survival and its association with the development of anticancer drug resistance makes it an attractive target for cancer therapy. Several inhibitors have been developed during the past decade and some of them have entered clinical trials, but no drugs have been approved for clinical use so far. Targeted protein degradation using heterobifunctional degraders has emerged as a novel therapeutic modality in drug discovery. This technology has many potential advantages over traditional inhibitors, e.g. reduced side effects and drug resistance, extended duration of action, elevated selectivity, and the opportunity to target “undruggable” proteins. In this study, we report the development of the first-in-class MCL-1 bifunctional degraders with in vivo PD effect. Material and Methods: Compounds’ affinity to CRBN (Cereblon), an E3 ligase, and to MCL-1 was determined by FP and SPR, respectively. AlphaLISA and HTRF were utilized to confirm ternary complex formation. Cell viability was assessed by CellTiter-Glo Assay. Apoptosis induction and changes in mitochondrial membrane potential were assessed by flow cytometry using Annexin/PI and TMRE staining, respectively. Targeted protein degradation in cells treated with compounds in the absence or presence of apoptosis inhibitor was assessed by WB. The mechanism of action of the compounds was confirmed in cancer cells pre-treated with proteasome or NEDD8-Activating Enzyme inhibitors, or CRBN-targeting siRNA, and then treated with the compounds. MCL-1 abundance and expression of apoptosis markers were confirmed by WB. PK studies were conducted in CD1 mice and Sprague Dawley rats, and PD studies in CB-17 SCID mice xenografted with MV4–11 cells. Results: Synthesized compounds bind CRBN and MCL-1 with high affinity, form a ternary complex in vitro and induce the degradation of MCL-1 in cells, which is caspase- and proteasome-dependent and leads to apoptosis induction. These series of compounds showed a nM range cytotoxic activity in haematological cancer cell lines with the best compounds having an IC50 <100 nM. Moreover, MCL-1 degradation in vivo can be achieved by IP administration leading to the initiation of the programmed cell death. Conclusions: Our compounds have a broad cytotoxic activity toward cultured human cancer cells and a promising in vivo pharmacokinetic profile. Our data indicate that targeting MCL-1 by employing bifunctional degraders represents a potentially new and effective strategy for cancer treatment. No conflict of interest.