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In situ albumin-binding and esterase-specifically cleaved BRD4-degrading PROTAC for targeted cancer therapy
Hanhee Cho1, Seong Ik Jeon2, Man Kyu Shim3
1Research Institute of Advanced Materials (RIAM), Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Republic of Korea.
Abstract:
Proteolysis-targeting chimeras (PROTACs) have recently been of great interest in cancer therapy. However, the bioavailability of PROTACs is considerably restricted due to their high hydrophobicity, poor cell permeability, and thereby low tumor targeting ability. Herein, esterase-cleavable maleimide linker (ECMal)-conjugated bromodomain 4 (BRD4)-degrading PROTAC (ECMal-PROTAC) is newly synthesized to exploit plasma albumin as an 'innate drug carrier' that can be accumulated in targeted tumor tissues. The BRD4-degrading ECMal-PROTAC is spontaneously bound to albumins via the thiol-maleimide click chemistry and its esterase-specific cleavage of ECMal-PROTAC is characterized in physiological conditions. The albumin-bound ECMal-PROTACs (Alb-ECMal-PROTACs) have an average size of 6.99 ± 1.38 nm, which is similar to that of free albumins without denaturation or aggregation. When Alb-ECMal-PROTACs are treated to 4T1 tumor cells, they are actively endocytosed and reach their highest intracellular level within 12 h. Furthermore, the maleimide linkers of Alb-ECMal-PROTACs are cleaved by the esterase to release free BRD-4 degrading PROTACs and the cell-internalized PROTACs successfully catalyze the selective degradation of BRD4 proteins, resulting in BRD4 deficiency-related apoptosis. When ECMal-PROTACs are intravenously injected into tumor-bearing mice, they exhibit a 16.3-fold higher tumor accumulation than free BRD4-PROTAC, due to the shuttling effect of albumin for tumor targeting. Finally, ECMal-PROTACs show 5.3-fold enhanced antitumor efficacy compared to free BRD4-PROTAC, without provoking any severe systemic toxicity. The expression of Bcl-2 and c-Myc, the downstream oncogenic proteins of BRD4, are also effectively suppressed. In summary, the in situ albumin binding of ECMal-PROTAC is proven as a promising strategy that effectively modulates its pharmacokinetics and therapeutic performance with high applicability to other types of PROTACs.
Insights
New esterase-cleavable maleimide linker (ECMal)-conjugated PROTACs leverage albumin for enhanced tumor targeting and efficacy in cancer therapy. This strategy improves drug delivery and reduces toxicity, offering a promising approach for PROTAC development.
Area of Science:
- Biochemistry
- Oncology
- Drug Delivery
Background:
- Proteolysis-targeting chimeras (PROTACs) show promise in cancer therapy but suffer from poor bioavailability and tumor targeting.
- High hydrophobicity and low cell permeability limit the effectiveness of conventional PROTACs.
Purpose of the Study:
- To develop a novel PROTAC strategy utilizing plasma albumin as an endogenous drug carrier to enhance tumor accumulation and therapeutic efficacy.
- To synthesize and characterize an esterase-cleavable maleimide linker (ECMal)-conjugated bromodomain 4 (BRD4)-degrading PROTAC (ECMal-PROTAC).
Main Methods:
- ECMal-PROTAC was synthesized and its binding to albumin via thiol-maleimide click chemistry was confirmed.
- Esterase-specific cleavage of the ECMal linker was characterized under physiological conditions.
- In vitro studies assessed cellular uptake and BRD4 degradation in 4T1 tumor cells.
- In vivo studies in tumor-bearing mice evaluated tumor accumulation, antitumor efficacy, and systemic toxicity.
Main Results:
- Albumin-bound ECMal-PROTACs (Alb-ECMal-PROTACs) maintained albumin's structure and were efficiently endocytosed by tumor cells.
- Alb-ECMal-PROTACs demonstrated enhanced tumor accumulation (16.3-fold higher) and superior antitumor efficacy (5.3-fold) compared to free PROTACs.
- The treatment effectively suppressed downstream oncogenic proteins Bcl-2 and c-Myc, leading to apoptosis without significant systemic toxicity.
Conclusions:
- In situ albumin binding of ECMal-PROTAC is a viable strategy to improve PROTAC pharmacokinetics and therapeutic performance.
- This approach offers high applicability for enhancing the delivery and efficacy of other PROTACs in cancer therapy.
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