1152: A Novel Serological Biomarker Measuring a Fragment of Cartilage Intermediate Layer Protein 1 Is Highly Upregulated in Rheumatic Diseases

Helena Port¹, Walter P Maksymowych², Morten Karsdal³, Anne-Christine Bay-Jensen³ and Signe Holm Nielsen³, ¹University of Copenhagen, Copenhagen, Denmark, ²Department of Medicine, University of Alberta, Edmonton, AB, Canada, ³Nordic Bioscience, Herlev, Denmark

Background/Purpose: A hallmark of rheumatic joint diseases is altered cartilage protein turnover and protein composition. During cartilage erosions, the cartilage intermediate layer protein-1 (CILP-1), is secreted from articular chondrocytes and then deposited into the cartilage extracellular matrix. CILP-1 is cleaved by proteases, generating neo-epitope fragments, which are released into circulation and may reflect disease activity. We developed an immunoassay targeting an ADAMTS5- and MMP-generated neo-epitope of CILP-1, named CILP-AM. We aimed to explore the relevance of CILP-AM in joint-related diseases in two exploratory patient studies and investigated the prognostic potential of CILP-AM in anti-TNF-α treatment.

Methods: A novel direct immunoassay CILP-AM was developed and technically validated. The biomarker was measured in two independent studies (discovery and validation study). The discovery study included serum samples from 13 healthy donors (mean age 35.8, 50% female), 18 patients with rheumatoid arthritis (RA) (mean 35.6, 50% female),14 patients with ankylosing spondylitis (AS) (mean age 36.6, 47% female) and 8 patients with osteoarthritis (OA) (mean age 69.9, 50% female), from Proteogenex, CA, USA. The validation study included serum samples from 86 patients with AS (mean age 45.33, 22.7% female) and 23 patients with RA (mean age 57.8, 21.7% female) from the University of Alberta, Canada, and 105 healthy donors (mean age 41.2, 48% female). Study samples were collected after informed consent and approved by the local ethical committee in compliance with the Helsinki declaration of 1997. One-way ANOVA analyses were performed for both studies at baseline. The area under the receiver operating characteristic curve (AUROC) analysis was performed to investigate the discrimination accuracy of CILP-AM between patients with AS or RA and healthy controls at baseline. Both analyses were adjusted for age and gender. A logistic regression model was used to predict response to anti-TNF-α treatment in patients with AS based on a 50% reduction of BASDAI index after 3 months of treatment in the validation study (patients were biologically naïve before treatment).

Results: A technically robust and specific assay was developed prior to the measurement of the discovery and validation studies. In the discovery study, patients with RA, AS and OA had significantly higher levels of CILP-AM compared to healthy donors (p< 0.01, p< 0.001, p< 0.05, Fig 1. A). In the validation study, patients with AS and RA presented significantly higher levels of CILP-AM compared to healthy controls (p< 0.001, Fig. 1 B), and CILP-AM was able to separate patients with AS or RA from healthy controls with an AUC of 0.99 (specificity 100%, sensitivity 98%, p< 0.001). The likelihood of responding to anti-TNF-α treatment showed a tendency to be higher for a unit increase of CILP-AM at baseline (OR=3.28, 95% CI = [0.85;12.64] p-value= 0.07, Fig. 1 C).

Conclusion: The novel blood-biomarker CILP-AM was significantly elevated in patients with AS and RA compared to healthy controls in both the discovery and validation studies. CILP-AM may provide useful understanding regarding the cartilage degradation processes in joint-related diseases.
Fig 1. Levels of CILP-AM in healthy donors and patients with joint-related diseases in the discovery and validation study. All analyses were adjusted for age and gender. Data is shown as Tukey plots. A) Differences between healthy donors and joint-related diseases in the discovery study. B) Differences between healthy donors and joint-related diseases in the validation study. C) Differences between responders and non-responders to anti-TNF-α treatment in patients with AS from the validation study.
Disclosures: H. Port, None; W. Maksymowych, AbbVie, Boehringer-Ingelheim, Celgene, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, UCB, CARE Arthritis Limited; M. Karsdal, Nordic Bioscience; A. Bay-Jensen, Nordic Bioscience; S. Holm Nielsen, Nordic Bioscience.