Cell Penetrating Peptide Uptake by Human Tissue

Abstract

Objective 1) Assess activatable cell penetrating peptide (ACPP) uptake by human tissue. 2) Compare ACPP uptake in normal and cancer tissue. Methods ACPPs are peptides that become activated for cellular uptake by cleavage in the presence of specific proteases. Fluorescently tagging ACPPs and designing a cleavage site recognized by proteases abundant in cancer allows for selective uptake and imaging. Cleavable ACPPs consist of L-amino acids linkers, while uncleavable linkers consist of corresponding D-isomers. To assess ACPP uptake by human tissue, we imaged freshly ressected surgical specimens following incubation with ACPP. Uptake was analyzed by measuring average fluorescent intensities (AFI) for histologically identified areas of cancer and normal tissue. Standardized uptake value (SUV) measurements, which represents fluorescence uptake per given tissue weight, and zymography were also performed. Results Average cancer-to-normal AFI ratio when treated with cleavable ACPP was 2.6±0.6 (p=0.003) and with uncleavable control was 1.4±0.5 (p=0.5). Considering cancer tissue alone, average AFI was 22.5 ±2.2 when treated with cleavable and 11.4 ±1.2 when treated with uncleavable ACPP (p=0.004). Tissue SUV when treated with cleavable ACPP was 2.5±0.8mg-1, whereas tissue treated with control ACPP was 1.7±1.0mg-1 (p=0.24). Zymography results show that inactive protease is ubiquitous in cancer and normal tissue while active form is more abundant in cancer. Conclusions In freshly resected human cancer tissue, uptake of cleavable ACPP is ∼2-fold greater than that of uncleavable ACPP. Furthermore, cleavable ACPP uptake is ∼2.5-fold greater in cancer compared to normal tissue. This differential uptake can potentially be used for in vivo imaging of cancer to guide surgical resection.