Development Of A Companion Diagnostic Ihc Assay For The Biomarker-Driven Selection Of C4.4a Positive Patients

C4.4a (LYPD3), a GPI-anchored cell surface protein, has been identified previously as a cancer- and metastasis-associated cell surface protein. It is expressed in a variety of cancer indications and, particularly, in the squamous cell subtype of non-small cell lung cancer (NSCLC) and head and neck cancer. Targeting C4.4a with a specific antibody-drug conjugate showed a potent and selective antitumor activity in various human xenograft models and in patient-derived NSCLC tumor models (Willuda J et al., AACR 2014). Since it has been previously shown in vivo that the expression of C4.4a is required for the response to anti-C4.4a treatment, we initiated the development of an IHC assay that might be used to detect C4.4a expression in patient tumor samples. For the development of this companion diagnostic IHC assay, a novel monoclonal rabbit anti-C4.4a antibody was generated. Since C4.4a is post-transcriptionally modified by shedding, we aimed to identify an antibody that binds to a similar epitope as the therapeutic C4.4a antibody. The immunizations of rabbits with specific peptide sequences of C4.4a and with the full length C4.4a recombinant protein produced several antibody candidates. Those antibody candidates were characterized in regard to their staining characteristics, domain binding, and specificity for C4.4a. Furthermore, the staining pattern of the antibody candidates and the therapeutic C4.4a antibody were compared side by side to ensure that stainings using the newly generated antibodies are predictive for anti-C4.4a treatment. The most promising antibodies were selected to set up and optimize an IHC assay on the Ventana staining platform. In summary, we developed a companion diagnostic IHC assay that might be used to detect C4.4a expression in patient tumor samples. Citation Format: Claudia Schneider, Joseph Couto, Yifei Zhu, Zhiming Liao, Robert Pytela, Alton Hiscox, Sabine Wittemer-Rump, Ulf Forssmann, Lars Linden, Joerg Willuda, Daniel Forler, Matthew Nelson, Ricarda Finnern, Thomas Krahn, Khusru Asadullah. Development of a companion diagnostic IHC assay for the biomarker-driven selection of C4.4a positive patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2836. doi:10.1158/1538-7445.AM2014-2836