Abstract 4617: Hu177 cryptic epitope: A novel biomarker for the monitoring of treatment of ovarian cancer

Background: Distinct cryptic collagen epitopes are among the protein fragments exposed by collagen type IV remodeling, and recent data indicate that these cryptic epitopes may facilitate tumor migration and angiogenesis. In studies with melanoma patients we tested the hypothesis that melanoma can induce detectable changes in systemic levels of cryptic epitope shedding, specifically the HU177 epitope and were able correlate the levels of HU177 shedding with clinical and pathologic parameters (Ng et al Clin Can Res, 14:6253,2008). In addition in a follow-up study the increased shedding of the Hu177 epitope was shown to correlate with a worse prognosis in primary melanoma (Hamilton et al, J Trans Med8:19,2010). In this study we examined wether the serum levels of these unique cryptic epitopes may be useful to monitor, in a phase II study with ovarian patients, the course of the combination treatment of continuous infusion topotecan with erlotinib over multiple cycles of therapeutic intervention. Methods: We made use of our previously published ELISA serum assay (Ng et al) of which the key components involve the anchoring of the primary Hu177 directed antibody followed by blocking with albumin and then incubation with patient serum. The assay is further developed with a sandwich ELISA consisting of biotinylated anti-collagen IV and an anti-biotin antibody conjugated to horseradish peroxidase, followed by chromagenic color development. A parallel examination of the Hu177 epitope was also conducted with a humanized version of the Hu177 antibody (D93). Serial blood samples were monitored for weekly time periods ranging from 6-20 weeks from 5 patients enrolled in this study. Serum were collected and stored in multiple aliquots at –20oC. Results: All 5 patients demonstrated an eventual lowering of shed epitopes, with the time course for a sustained reduction varying with each patient. Once a nadir in the Hu177 epitope occurred it would last from 4-6 weeks. In one patient (KL) the nadir levels were the most sustained and developed late in the course of treatment who had remarkable decreased changes in CA125 that was previously rapidly increasing. This patient had platinum resistant peritoneal carcinomatosis without any dominant masses. Upon failure of topotecan erlotinib as demonstrated by rising markers and development of ascites and a pleural effusion, the shed epitopes rapidly recurred starting at week 18 of the treatment. Comparable serial data were found with the humanized D93 antibody although the sensitivity was more pronounced with the Hu177 antibody. Conclusions: Our interpretation is that this Hu177 determination may provide an indication of active invasion of extracellular matrix (such as in the peritoneum) and may be a useful indicator of a biological effect. We cannot exclude at this point that erlotinib may be contributing to such effects by changes in the matrix. Supported by a grant from the Chemotherapy Foundation Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4617. doi:1538-7445.AM2012-4617