Plasma Kallikrein-Activated TGF-β Is Prognostic for Poor Overall Survival in Patients with Pancreatic Ductal Adenocarcinoma and Associates with Increased Fibrogenesis

Pancreatic ductal adenocarcinoma (PDAC) is a hard-to-treat cancer due to the collagen-rich (fibrotic) and immune-suppressed microenvironment. A major driver of this phenomenon is transforming growth factor beta (TGF-β). TGF-β is produced in an inactive complex with a latency-associated protein (LAP) that can be cleaved by plasma kallikrein (PLK), hereby releasing active TGF-β. The aim of this study was to evaluate LAP cleaved by PLK as a non-invasive biomarker for PDAC and tumor fibrosis. An ELISA was developed for the quantification of PLK-cleaved LAP-TGF-β in the serum of 34 patients with PDAC (stage 1−4) and 20 healthy individuals. Biomarker levels were correlated with overall survival (OS) and compared to serum type III collagen (PRO-C3) and type VI collagen (PRO-C6) pro-peptides. PLK-cleaved LAP-TGF-β was higher in patients with PDAC compared to healthy individuals (p < 0.0001). High levels (>median) of PLK-cleaved LAP-TGF-β were associated with poor OS in patients with PDAC independent of age and stage (HR 2.57, 95% CI: 1.22−5.44, p = 0.0135). High levels of PLK-cleaved LAP-TGF-β were associated with high PRO-C3 and PRO-C6, indicating a relationship between the PLK-cleaved LAP-TGF-β fragment, TGF-β activity, and tumor fibrosis. If these preliminary results are validated, circulating PLK-cleaved LAP-TGF-β may be a biomarker for future clinical trials.

Abstract 1568: PLK activated TGF-β functions as a prognostic biomarker for patients with pancreatic ductal adenocarcinoma

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer death with a 5-year survival rate of approximately 7%. Transforming growth factor beta (TGF-β) is highly involved in progression and metastasis in multiple cancers including PDAC. TGF-β is highly involved in tumor fibrosis and immune suppression, and several clinical trials are ongoing to evaluate anti-TGF-β therapies for treating patients diagnosed with cancer and for which biomarkers are key for success. TGF-β is produced in a latent complex with latency-associated protein (LAP), which needs to be cleaved by plasma kallikrein (PLK), releasing TGF-β to enable receptor binding and initiating of signaling. We developed a competitive enzyme-linked immunosorbent assay (ELISA) targeting PLK activated TGF-β and measured it in serum from patients with PDAC.

Methods: An ELISA based on monoclonal antibodies raised against the C-terminal side of the PLK cleavage site of TGF-β at R’58↓ was developed and validated for quantification of PLK activated TGF-β (L59TGF-β) in serum. To confirm that the ELISA was specifically measuring PLK cleaved TGF-β, L59TGF-β was measured in a TGF-β dilution after incubation with and without kallikrein. L59TGF-β was measured in pretreatment serum samples from patients with PDAC (n=39) and healthy controls (n=20). The prognostic value of L59TGF-β levels was examined with Kaplan-Meier analysis and evaluated for association with overall survival (OS) by multivariate cox regression analysis adjusted for age and cancer stage.

Results: L59TGF-β was only detected after incubation with kallikrein, demonstrating that the ELISA specifically detected kallikrein cleaved TGF-β. L59TGF-β was significantly elevated in patients with PDAC compared to healthy controls (p&lt;0.0001). High levels of L59TGF-β (&gt;median) were significantly associated with poor OS (HR: 2.71, 95%CI: 1.23-5.97, p=0.0135) in patients with PDAC, and median OS was 5.5 months (95%CI: 1.50-20.0) compared to 26.3 months (95%CI: 15.3-28.1) for patients with low levels of L59TGF-β. The association between high levels of L59TGF-β and poor OS remained statistically significant after adjusting for age and stage (HR: 2.33, 95%CI: 1.05-5.18, p=0.0372).

Conclusion: Quantification of PLK activated TGF-β (L59TGF-β) in serum predicted poor OS for patients with PDAC. The biomarker value of L59TGF-β should be validated and further investigated in a larger cohort to explore the clinical applicability of the biomarker.

Citation Format: Rasmus S. Pedersen, Neel I. Nissen, Christina Jensen, Jeppe Thorlacius-Ussing, Majken L. Olesen, Lasse Langholm, Tina M. Jensen, Hadi M. Diab, Lars N. Jørgensen, Morten Karsdal, Nicholas Willumsen. PLK activated TGF-β functions as a prognostic biomarker for patients with pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1568.