DT2216—a Bcl-xL-specific degrader is highly active against Bcl-xL-dependent T cell lymphomas

Abstract

Background: Patients with advanced T cell lymphomas (TCLs) have limited therapeutic options and poor outcomes in part because their TCLs evade apoptosis through upregulation of anti-apoptotic Bcl-2 proteins. Subsets of TCL cell lines, patientderived xenografts (PDXs), and primary patient samples depend on Bcl-xL for survival. However, small molecule Bcl-xL inhibitors such as ABT263 have failed during clinical development due to on-target and dose-limiting thrombocytopenia. Methods: We have developed DT2216, a proteolysis targeting chimera (PROTAC) targeting Bcl-xL for degradation via Von Hippel-Lindau (VHL) E3 ligase, and shown that it has better anti-tumor activity but is less toxic to platelets compared to ABT263. Here, we examined the therapeutic potential of DT2216 for TCLs via testing its anti-TCL activity in vitro using MTS assay, immunoblotting, and flow cytometry and anti-TCL activity in vivo using TCL cell xenograft and PDX model in mice. Results: The results showed that DT2216 selectively killed various Bcl-xL-dependent TCL cells including MyLa cells in vitro. In vivo, DT2216 alone was highly effective against MyLa TCL xenografts in mice without causing significant thrombocytopenia or other toxicity. Furthermore, DT2216 combined with ABT199 (a selective Bcl-2 inhibitor) synergistically reduced disease burden and improved survival in a TCL PDX mouse model dependent on both Bcl-2 and Bcl-xL. Conclusions: These findings support the clinical testing of DT2216 in patients with Bcl-xL-dependent TCLs, both as a single agent and in rational combinations.

Major advances in targeted protein degradation: PROTACs, LYTACs, and MADTACs

“…Crystal structures of the small molecule bound to VHL provided insight into suitable attachment points to create PROTACs ( 56 ). Indeed, several studies have now shown that this ligand can be incorporated to produce successful PROTACs ( 17 , 24 , 25 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ). In fact, the VHL ligand is one of the most used E3 ligase recruiting elements in the PROTAC field to date.…”

Full Spectrum Flow Cytometry as a Powerful Technology for Cancer Immunotherapy Research

“…This intervention reduced disease progression and increased survival in a TCL PDX mouse model dependent on both Bcl-2 and Bcl-xl. (He et al, 2020;Zhang et al, 2020). The same PROTAC approach has been used to reduce platelet toxicity of navitoclax, a known Bcl-2 and Bcl-xl dual inhibitor (He et al, 2020).…”

“…(He et al, 2020;Zhang et al, 2020). The same PROTAC approach has been used to reduce platelet toxicity of navitoclax, a known Bcl-2 and Bcl-xl dual inhibitor (He et al, 2020). In these studies, FSFC was implemented to evaluate T cells, B cells, myeloid cells, hematopoietic progenitors and hematopoietic stem cells in bone marrow.…”

Proteolysis-targeting chimera against BCL-XL destroys tumor-infiltrating regulatory T cells

“…To avoid the on-target toxicity of BCL-X L inhibitors to platelets, we have recently reported the development of the first-in-class BCL-X L degrader—a proteolysis-targeting chimera (PROTAC) referred to as DT2216—targets BCL-X L to the von Hippel-Lindau (VHL) E3 ligase for ubiquitination and subsequent proteasomal degradation 16 . Because platelets express a low level of VHL E3 ligase, DT2216 has minimal effect on platelets but exhibits an improved cytotoxicity against various cancer cells that are dependent on BCL-X L for survival 16 , 17 . We also developed another similar PROTAC PZ15227 that uses cereblon (CRBN) E3 ligase to induce BCL-X L polyubiquitination and degradation 18 .…”