Matrix Metalloprotease Generated Fragments of Type VI Collagen Have Serum Biomarker Potential in Cancer - A Proof of Concept Study

Abstract

Background: Type VI collagen (COL6) is associated with several pro-tumorigenic events. COL6 is primarily composed of three alpha-chains (a1-a3) forming a specialized microfibrillar network to support tissue architecture. COL6 homeostasis is lost in the tumor due to increased COL6 synthesis by activated fibroblast and altered proteolytic degradation by matrix metalloproteases (MMPs). Consequently, pathology-specific COL6 fragments are released to the circulation. This study evaluates four COL6 fragments measured in serum as potential biomarkers for cancer.

Methods: C6Ma1 (MMP-generated neo-epitope on the a1 chain), C6Ma3 (MMP-generated neo-epitope on the a3 chain), PRO-C6 (C-terminal of the a3 chain) and IC-6 (internal epitope on the a1 chain) were measured by ELISA in serum from patients with various stage 1-4 cancer indications (n = 4-11 per indication, total n = 65) and healthy controls (n = 13).

Results: C6Ma1 and C6Ma3 were significantly elevated in most cancer types compared to controls; PRO-C6 and IC6 were not. No significant differences were seen according to age, gender and TNM stage. Comparing cancer patients to controls, the AUROC was 0.90 (P < .0001), 0.87 (P < .0001), 0.59 (P = .311) and 0.53 (P = .747) for C6Ma1, C6Ma3, PRO-C6 and IC-6, respectively. Only C6M and C6Ma3 correlated significantly (Spearman, r = 0.74, P < .0001).

Conclusions: MMP-generated COL6 fragments (C6Ma1, C6Ma3) were elevated in serum from cancer patients compared to controls and had promising diagnostic accuracy. This supports that MMP-mediated COL6 remodeling is important in tumorigenesis and indicate cancer biomarker potential of quantifying COL-6 fragments in serum. Future studies should determine biological and clinical applicability of the COL-6 serum biomarkers in relation to cancer.

Figure 1

Schematic illustration of s type VI collagen (COL6) tetramer consisting of a1, a2, and a3 heterotrimers and with illustrations of the COL6 biomarker targets (C6Ma1, C6Ma3, IC-6 and PRO-C6) measured in serum. Details of the biomarkers can be found in Table 1.

Figure 2

Serum levels (ng/ml) of the four different type VI collagen (COL6) fragments (see Table 1 for details) in healthy controls and in patients with various solid tumor types. Biomarker levels from controls were compared to individual patient groups by a Kruskal-Wallis test adjusted for multiple comparisons with Dunn's test. *P < .05, **P < .01, ***P < .001, ****P < .0001. SCLC: small cell lung cancer; NSCLC: non-small cell lung cancer.

Figure 3

Serum levels (ng/ml) of four different type VI collagen (COL6) fragments measured in patients with various solid tumor types according to early (1 + 2) vs late (3 + 4) stage of disease as well as three patients with unknown stage. Each tumor indication has been given its own symbol. Biomarker levels were compared by the Mann–Whitney test. No significant differences could be detected. SCLC: small cell lung cancer; NSCLC: non-small cell lung cancer.

Figure 4

Diagnostic power evaluated by receiver operating characteristics (ROC) curve analysis for the ability of the four serum COL-6 fragments to separate healthy controls from patients with cancer. AUROC, area under the ROC curve.

Figure 5

Diagnostic power evaluated by receiver operating characteristics (ROC) curve analysis for the ability of the four serum COL-6 fragments combined to separate healthy controls from patients with cancer. AUROC, area under the ROC curve.