UC San Diego

Activatable cell penetrating peptides (ACPPs) are polycationic cell penetrating peptides (CPPs) whose cellular uptake is minimized by a polyanionic inhibitory domain and then restored upon proteolysis of the peptide linker connecting the polyanionic and polycationic domains. Local activity of proteases able to cut the linker causes amplified retention in tissues and uptake into cells. This ACPP platform has been specifically designed to meet 3 major criteria for contrast and therapeutic agent development. The first criterion was to target a wide spread disease process and mechanism that is inherent to cancer progression, in this case, matrix metalloprotease activity. Secondly, the platform was designed with an amplification mechanism that can deliver multiple molecules per target; in this case the targets are cancer proteases. Thirdly, the ACPP platform is not limited to a single enzyme target, imaging modality, or therapeutic playload. We show the validation of the ACPP concept from tissue culture to systemic administration in tumor bearing mice. ACPPs have enhanced biodistribution compared to the CPP counterpart and they yield MMP dependent contrast in multiple tumors and in metastases. ACPPs can be conjugated to macromolecular weight carriers to further enhance the biodistribution profile by prolonging plasma half-life resulting in enhanced tumor uptake and providing clinically significant contrast as an 111-In radiotracer. The second part of the dissertation focuses on translation from imaging agents into therapeutic agents. We describe the challenges of cell penetration, drug conjugation, stability, and the resulting animal testing using doxorubicin conjugated dendrimers that yielded some promising results. Lastly, we describe the simple attachment of ACPPs to clinically approved therapeutic nanoparticles. This approach has resulted in ACPP based targeted doxorubicin liposomes that have significant anti-tumor activity compared to untargeted liposomes. We conclude that because of preclinical successes, ACPPs have significant potential in the development of a targeting portfolio of imaging and therapeutic agents that could one day be useful in the clinic