Photodynamic Molecular Beacon Triggered by Fibroblast Activation Protein on Cancer-Associated Fibroblasts for Diagnosis and Treatment of Epithelial Cancers

Abstract

Fibroblast activation protein (FAP) is a cell-surface serine protease highly expressed on cancer-associated fibroblasts of human epithelial carcinomas but not on normal fibroblasts, normal tissues, and cancer cells. We report herein a novel FAP-triggered photodynamic molecular beacon (FAP-PPB) comprising of a fluorescent photosensitizer and a black hole quencher 3 linked by a peptide sequence (TSGPNQEQK) specific to FAP. FAP-PPB was effectively cleaved by both human FAP and murine FAP. Using the HEK293 transfected cells (HEK-mFAP, FAP+; HEK-Vector, FAP−), systematic in vitro and in vivo experiments validated the FAP-specific activation of FAP-PPB in cancer cells and mouse xenografts, respectively. FAP-PPB was cleaved by FAP, allowing fluorescence restoration in FAP-expressing cells, while leaving non-expressing FAP cells undetectable. Moreover, FAP-PPB showed FAP-specific photocytotoxicity toward HEK-mFAP cells whereas it was non-cytotoxic toward HEK-Vector cells. This study suggests that the FAP-PPB is a potentially useful tool for epithelial cancer detection and treatment.

Activatable Photosensitizers: Agents for Selective Photodynamic Therapy

“…Among these systems, which consist of a disease-targeted linker, a PS and a quencher, the "photodynamic molecular beacons" (PMB) developed by Zheng and co-workers are noteworthy. [51][52][53][54][55][56][57][58][59][60][61] The excited state of the PS in this aPS is efficiently quenched via Förster Resonance Energy Transfer (FRET) to a quencher that is closely positioned through a linker. When the linker is cleaved by a cancer-specific stimulus, such as an enzyme, the quencher separates from the PS associated with regeneration of its photoactivity.…”

Photodynamic therapy of cancer — Challenges of multidrug resistance

“…Lo et al developed a novel FAP-triggered PDT beacon which could induce signi¯cant photocytotoxicity in FAP-expressing cells and be activated in FAP-expressing stromal¯broblasts in vivo. 82 Although many PS-conjugates are unsuitable for systemic administration for many reasons (e.g., systemic toxicity, high cost), they may be an ideal candidate for intratumoral delivery.…”

Fibroblast activation protein

“…In vitro and in vivo experiments have validated the FAP-specific activation of FAP-PPB in cancer cells and mouse xenografts. 62 In addition, Huang et al 63 conjugated Doxorubicin (Dox) with a FAP-specific dipeptide to develop a FAP-targeting prodrug of Dox (FTPD). They demonstrated that FAP-cleaved FTPD exhibited significantly higher cytotoxicity against 4T1 cells in vitro than the uncatalyzed prodrug.…”