Stefin A-functionalized liposomes as a system for cathepsins S and L-targeted drug delivery.

Proteolytic activity in the tumor microenvironment is one of the key elements supporting tumor development and metastasis. One of the key families of proteases that are overexpressed in various types of cancer and implicated in different stages of tumor progression are cysteine cathepsins. Among them, cathepsins S and L can be secreted into the tumor microenvironment by tumor and/or immune cells, making them promising drug delivery targets. Here we present a new system for cathepsin S/L targeting using a liposomal drug carrier system functionalized with the endogenous cysteine cathepsin inhibitor, stefin A. The selective targeting of cathepsins by stefin A-conjugated liposomes was confirmed in vitro and in vivo, demonstrating the potential of this approach for cancer diagnosis and treatment.