A fibroblast activation protein targeted optical tracer for identifying primary and metastatic sarcoma during resection

Feredun Azari; Gregory T Kennedy; Ian Folkert; Gregory Jones; Ashley Chang; Andrew Conner; Elizabeth Bernstein; Bilal Nadeem; Neil T Sullivan; Evgeniy Eruslanov; Steven Albelda; Philip Low; Sunil Singhal

doi:10.1186/s13550-025-01289-5

A fibroblast activation protein targeted optical tracer for identifying primary and metastatic sarcoma during resection

EJNMMI Res. 2025 Jul 29;15(1):94. doi: 10.1186/s13550-025-01289-5.

Authors

Feredun Azari^{1

2

3}, Gregory T Kennedy⁴, Ian Folkert⁵, Gregory Jones⁶, Ashley Chang⁴, Andrew Conner⁶, Elizabeth Bernstein⁷, Bilal Nadeem⁴, Neil T Sullivan⁴, Evgeniy Eruslanov^{4

5}, Steven Albelda⁸, Philip Low⁹, Sunil Singhal⁴

Affiliations

¹ Department of Thoracic Surgery, University of Pennsylvania, Philadelphia, PA, USA. azarif@ccf.org.
² Heart, Vascular, and Thoracic Institute, Cleveland Clinic Foundation, Cleveland, OH, USA. azarif@ccf.org.
³ Department of Thoracic Surgery, Hospital of the University of Pennsylvania, 3400 Spruce Street, 6 White Building, Philadelphia, PA, 19104, USA. azarif@ccf.org.
⁴ Department of Thoracic Surgery, University of Pennsylvania, Philadelphia, PA, USA.
⁵ Department of Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA, USA.
⁶ Heart, Vascular, and Thoracic Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.
⁷ Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
⁸ Department of Pulmonary Medicine, Perelman School of Medicine, Philadelphia, PA, USA.
⁹ Department of Chemistry, Purdue University, West Lafayette, IN, USA.

Abstract

Background: Sarcomas represent a heterogeneous group of mesenchymal tumors that, despite accounting for only 1% of cancers worldwide, rank among the top five causes of cancer-related deaths in patients under 20 years old. Surgical resection remains the primary treatment for these malignancies, as effective systemic therapies are limited, particularly for high-grade disease. However, surgical outcomes are often compromised by incomplete resection, leading to high local and distal recurrence rates. Intraoperative molecular imaging has emerged as a promising approach to improve surgical outcomes but has been hindered by the lack of tumor-specific targeting agents. Fibroblast activation protein (FAP), selectively expressed by mesenchymal tumors and absent in healthy tissues, presents a promising target for fluorescence-guided cancer resections.

Results: We demonstrate that 41% of human sarcomas express FAP, with expression correlating with higher histologic grade. The FAP-S0456 optical tracer specifically bound to FAP-expressing sarcomas with minimal binding to normal tissues, exhibiting excellent tumor-to-background ratios (3.8 ± 0.43). In vitro studies confirmed FAP-S0456's specificity for human FAP with a dissociation constant of approximately 10 nM. In murine xenograft models, the tracer accurately identified both primary tumors and pulmonary metastases of FAP-expressing sarcomas. Importantly, using needle confocal laser endomicroscopy, we demonstrated that FAP-S0456 enables real-time, single-cell visualization of metastatic tumor cells during surgery, including micrometastases not detected by conventional imaging.

Conclusions: FAP-S0456 represents a promising molecular imaging agent for the detection and surgical removal of primary and metastatic sarcomas. Its high specificity for FAP-expressing tumor cells, favorable biodistribution profile, and ability to detect microscopic disease offer potential to improve complete surgical resection. These findings support the development of FAP-targeted fluorescence-guided surgery for sarcoma patients, which may lead to improved oncologic outcomes, particularly for those with pulmonary metastases where complete surgical clearance is critical for survival.

Keywords: FAP expressing primary; Fibroblast activation protein; Micro metastatic tumors; Targeted optical tracer identifies.