Using proteolysis-targeting chimera technology to reduce navitoclax platelet toxicity and improve its senolytic activity

Abstract

Small molecules that selectively kill senescent cells (SCs), termed senolytics, have the potential to prevent and treat various age-related diseases and extend healthspan. The use of Bcl-xl inhibitors as senolytics is largely limited by their on-target and dose-limiting platelet toxicity. Here, we report the use of proteolysis-targeting chimera (PROTAC) technology to reduce the platelet toxicity of navitoclax (also known as ABT263), a Bcl-2 and Bcl-xl dual inhibitor, by converting it into PZ15227 (PZ), a Bcl-xl PROTAC, which targets Bcl-xl to the cereblon (CRBN) E3 ligase for degradation. Compared to ABT263, PZ is less toxic to platelets, but equally or slightly more potent against SCs because CRBN is poorly expressed in platelets. PZ effectively clears SCs and rejuvenates tissue stem and progenitor cells in naturally aged mice without causing severe thrombocytopenia. With further improvement, Bcl-xl PROTACs have the potential to become safer and more potent senolytic agents than Bcl-xl inhibitors.

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

“…No. SER-PRP-SDS, Zenbio, Research Triangle Park, NC, USA) [14]. Briefly, PRP was transferred into a 50-mL tube containing 5 mL acid citrate buffer (Cat.…”

PROTACs are effective in addressing the platelet toxicity associated with BCL-XL inhibitors

“…Proteomics studies also showed that DT2216 specifically reduced BCL-X L protein levels [21]. The selective degradation for BCL-X L over BCL-2 was also observed with DT2216 analogs in which the VHL-recruiting moiety of DT2216 was replaced by a celebron (CRBN)recruiting moiety [55,56] or inhibitors of apoptosis protein (IAP)-recruiting moiety [57]. It was observed that DT2216 could form stable BCL-2-DT2216-VHL ternary complexes in vitro using AlphaLISA assay [58] but not in live cells, as determined by nanoBRET assay [59].…”

“…Subsequent western blot assays also suggest that the protein levels of selected E3 ligases along with ubiquitin-activating enzyme (E1) and E2 enzymes are also low in human platelets compared to different tumor and senescent cells [21]. Thus, based on these initial observations, several series of BCL-X L -targeting PROTACs have been designed and synthesized by our group [20,21,[55][56][57].…”

“…Chemical structure of PROTAC 1 that recruits IAPs for BCL-X L degradation BCL-X L PROTAC degraders have also been tested in senescent cells and in relevant animal models. PZ15227, a CRBN-recruiting degrader derived from ABT-263 ( Figure 8), selectively induced BCL-X L degradation in senescent cells and non-senescent cells, but not in platelets [56]. Non-senescent cells do not depend on BCL-X L for survival, as a result, PZ15227 selectively induced apoptosis in senescent cells including those derived from WI-38 fibroblasts, IMR90 cells, renal epithelial cells and pre-adipocytes.…”

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes–7

“…This novel modality is expected to extend the boundaries of the druggable genome [22]. He et al have now established an additional benefit of PROTACs: the authors exploit the expression profile of the recruited E3 ligase to inhibit the target in tissues where it is pathogenic, while sparing it in tissues where it is beneficial [23].…”