Abstract 5836: Non-invasive quantification of fibroblast activation protein (FAP) cleaved type III collagen in serum reflects FAP activity and has biomarker potential in non-small cell lung cancer
Authors: Pedersen Rasmus Sund , Thorlacius-Ussing Jeppe , Willumsen Nicholas , Karsdal Morten A. 
Published: April 2023

Abstract
Introduction: Fibroblast activation protein (FAP) is an established cancer associated fibroblast (CAF) marker. FAP is highly expressed in the cancer stroma and is a predictor of poor survival for patients with non-small cell lung cancer (NSCLC). For this reason, it is being explored as a potential drug target. FAP has broad proteolytic activity and can directly promote multiple aspects of tumor progression. The aim of this study was to develop a tool to non-invasively measure FAP activity and validate its potential as a non-invasive biomarker in NSCLC.
Methods: An ELISA, named C3F, was developed to reflect proteolytic activity of FAP by quantifying FAP-mediated cleavage of type III collagen in serum. To confirm that C3F reflects proteolytic activity of FAP, type III collagen was assayed after incubation with and without FAP. C3F was measured in serum samples from healthy controls (n = 26) and patients with NSCLC: adenocarcinoma (AD) (n = 26) and squamous cell carcinoma (SCC) (n = 14). An ELISA quantifying matrix metalloprotease degraded type III collagen (C3M) was used for measuring the same serum samples and compared to C3F using spearman correlation test and area under receiver operating characteristic curves (AUROCs).
Results: A C3F signal only appeared after FAP cleavage of type III collagen, supporting that C3F reflects FAP proteolytic activity. Compared to healthy controls, C3F was significantly elevated in serum from patients with SCC (p = 0.0004, AUROC = 0.86), but not AD (p = 0.21, AUROC = 0.66). C3F was also significantly elevated in SCC compared to AD (p = 0.030, AUROC = 0.77). In comparison, C3M was significantly elevated in serum from both SCC and AD compared to healthy controls (p &lt; 0.0001, AUROC = 0.93 and p &lt; 0.0001, AUROC = 0.92, respectively), but no difference was seen between SSC and AD (p &gt; 0.99, AUROC = 0.56). Only a moderate correlation was seen between C3M and C3F (r = 0.58, p &lt; 0.0001).
Conclusion: FAP activity can be non-invasively quantified in serum by assaying FAP cleaved type III collagen (C3F). C3F shows promise as a cancer biomarker in NSCLC with potential for discriminating between NSCLC subtypes. As C3F reflects FAP activity, it is potentially a more suitable (or complementary) biomarker for anti-FAP drug development and prediction of anti-FAP treatment response compared to methods that asses the presence of FAP.
Citation Format: Rasmus Sund Pedersen, Jeppe Thorlacius-Ussing, Nicholas Willumsen, Morten A. Karsdal. Non-invasive quantification of fibroblast activation protein (FAP) cleaved type III collagen in serum reflects FAP activity and has biomarker potential in non-small cell lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5836.