A Protein-Capsid-Based System for Cell Delivery of Selenocysteine

Area of Science:

• Biotechnology and Nanomedicine
• Drug Delivery Systems
• Cancer Therapeutics

Background:

• Selenocysteine (Sec) shows potential as an anticancer drug but has limited therapeutic use due to broad cytotoxicity.
• Targeted drug delivery is crucial to enhance the efficacy and safety of Sec.
• Engineered protein capsids offer a promising platform for nanocarrier development.

Purpose of the Study:

• To engineer a nanocarrier for targeted delivery of selenocysteine (Sec).
• To evaluate the efficacy of an engineered Aquifex aeolicus lumazine synthase (AaLS) capsid for Sec delivery.
• To assess the cellular uptake and cytotoxic response of Sec delivered via the AaLS-based nanocarrier.

Main Methods:

• Modification of an engineered AaLS variant (AaLS-IC) with the diselenide dimer of Sec (Sec2) to form a selenenylsulfide conjugate (AaLS-IC-Sec).
• Investigation of the structural context's role in capsid loading efficiency.
• Assessment of Sec release from the nanocarrier using reducing agents (glutathione, dithiothreitol).
• Evaluation of AaLS-IC-Sec cellular penetration and cytotoxicity across six cell lines.

Main Results:

• Successful generation of a selenocysteine-loaded nanocarrier (AaLS-IC-Sec) using an engineered AaLS capsid.
• Demonstration that the structural context of the cysteine residue is critical for efficient Sec loading.
• Quantitative release of Sec from the nanocarrier mediated by reducing agents.
• Correlation between cellular uptake, intracellular trafficking, and cytotoxic sensitivity of AaLS-IC-Sec across different cell lines.

Conclusions:

• The engineered AaLS-IC capsid serves as an effective nanocarrier for selenocysteine.
• The nanocarrier facilitates targeted delivery and release of Sec into cells.
• AaLS-IC-Sec demonstrates potential for targeted cancer therapy by exhibiting cell-specific cytotoxicity.