Study on Novel BCL-XL Degraders Developed Based on BCL-XL/CRBN PROTAC Kits to Enhance BCL-2 Inhibitory Function

Abstract

Evasion of apoptosis is a hallmark of cancer, often involving an imbalance between pro-apoptotic and anti-apoptotic proteins (e.g., BCL-2 family proteins). Upregulation of anti-apoptotic proteins BCL-XL, BCL-2, and MCL-1 promotes tumorigenesis, progression, and therapy resistance. Although small-molecule inhibitors (e.g., ABT-263) have been developed to target these proteins, their high toxicity to platelets limits clinical application. To overcome this limitation, this study designed and synthesized a series of novel proteolysis-targeting chimeras (PROTACs) based on the BCL-XL/CRBN PROTAC kit, focusing on evaluating their ability to degrade BCL-XL and enhance BCL-2 inhibition.

I. Design and Synthesis of PROTAC Molecules

Using ABT-263 as the base structure, novel PROTAC molecules (including pp1–pp8 and a pair of enantiomers, PZ703a/PZ703b) were synthesized by introducing linkers of varying lengths . These molecules aim to achieve selective degradation of BCL-XL by recruiting the CRBN E3 ubiquitin ligase. Preliminary studies focused on pp5, PZ703a, and PZ703b, comparing them with the known degrader DT2216 and inhibitor ABT-263.

II. Evaluation of Cytotoxicity and Protein Degradation Efficacy

In MOLT-4 and RS4;11 cell lines, PZ703b exhibited approximately 2-fold stronger cytotoxicity than its enantiomer PZ703a and the non-enantiomeric mixture pp5. Western blotting analysis revealed that PZ703b effectively induced BCL-XL degradation without significantly affecting BCL-XL levels in platelets, demonstrating ~100-fold higher tumor cell selectivity compared to ABT-263 .

III. Validation of Degradation Mechanism

PZ703b induced rapid and sustained BCL-XL degradation in MOLT-4 cells, a process dependent on VHL and the proteasome pathway. Proteasome inhibitor MG-132 or VHL ligand VHL-032 blocked PZ703b-mediated degradation, confirming its PROTAC functionality. Additionally, PZ703b activated caspase-3-dependent apoptosis, an effect suppressible by the pan-caspase inhibitor QVD .

IV. Ternary Complex Formation Analysis

AlphaLISA and NanoBRET assays evaluated the ability of DT2216, PZ703a, and PZ703b to form ternary complexes with BCL-XL, BCL-2, and VCB (VHL–ElonginB–ElonginC complex). Results showed that PZ703b efficiently promoted {BCL-2:PROTAC:VCB} ternary complex assembly in vitro and in live cells, whereas DT2216 exhibited weaker functionality in cells (Figure 4). Competition assays further demonstrated that PZ703b significantly inhibited BCL-2–Bim interaction, an effect blocked by VHL-032, suggesting enhanced BCL-2 inhibition via ternary complex stabilization.

V. Conclusion

This study successfully developed the novel degrader PZ703b based on the BCL-XL/CRBN PROTAC strategy. PZ703b not only efficiently degrades BCL-XL but also enhances BCL-2 inhibition by promoting {BCL-2:PROTAC:VCB} ternary complex formation, while exhibiting low platelet toxicity. This provides a new approach for targeting BCL-2 family proteins in antitumor drug development.

VI. Which Manufacturers Provide BCL-XL/CRBN PROTAC Kits?

Nanjing UA-Biotech Co., Ltd. (UA-Bio) has independently developed the "Human BCL-XL/CRBN PROTAC Binding Kit", a high-performance in vitro detection platform designed for cutting-edge research on targeting the key apoptosis regulator BCL-XL. This kit enables researchers to dissect the molecular mechanisms of PROTAC-induced "target-PROTAC-E3 ligase" ternary complex formation, offering a precise and efficient starting point for innovative drug development in cancer therapy and overcoming drug resistance.

Nanjing UA-Biotech Co., Ltd. is committed to providing cutting-edge, high-quality reagents and solutions for targeted cancer therapy, apoptosis research, and innovative drug development. For details on the "Human BCL-XL/CRBN PROTAC Binding Kit" (Catalog No.: UA086017), including technical specifications, validation data, or application support, please contact us.