Abstract 399: A new rabbit monoclonal antibody to FOXM1 for immuohistochemical assessment

Purpose and Background: Forkhead box protein M1 (FOXM1) is a major oncogenic transcription factor regulating genes involved in G1-S and G2-M cell cycle transitions. FOXM1 has been implicated in tumorigenesis, facilitating tumor proliferation, angiogenesis and migration. Genome wide microarray studies consistently demonstrated FOXM1 upregulation in many solid malignancies. FOXM1 overexpression is associated with poor patient prognosis through blocking cytostatic and cytotoxic activity in taxane, platinum-based, and anthracycline anti-cancer drugs thereby increasing chemotherapeutic resistance. FOXM1 is broadly distributed during embryonic development, but restricted to progenitor and proliferating cells in mature tissues. However, broad tissue immunohistochemistry (IHC) based distribution studies are currently lacking. Furthermore, commercially available FOXM1 IHC antibodies are limited to rabbit polyclonals which are susceptible to batch inconsistencies. The need for a consistent monoclonal antibody validated in IHC is currently unmet. Herein, we report on FOXM1 distribution on a wide ranging collection of normal and tumor tissues using a newly developed rabbit monoclonal antibody (RabMAb), Clone EP372. Design: Rabbits were immunized with a recombinant N-terminal FOXM1 protein fragment, allowing detection of the three isoforms: FOXM1A, FOXM1B, and FOXM1C. Sera collected from immunized rabbits were screened by ELISA, Western Blot (WB) and IHC. After fusion, antibody from final hybridoma cells were characterized by ELISA and WB. This antibody, designated as Clone EP372 was further characterized through IHC testing using formalin-fixed, paraffin embedded (FFPE) human normal and tumor tissue microarrays (TMA). Results: A single band at approximately 100 kDa was detected by WB in Hela cell lysates. IHC analysis on 31 cases of human normal TMA comprising 15 different tissue types showed that FOXM1 only labeled cells in regenerative tissues, with nuclear expression in germinal center cells in the tonsil, proliferating colonic crypt cells, stromal cells in the endometrium, spleen and testis. Fifteen of 30 tumor cases were FOXM1 positive, expressed in astrocytoma, melanoma, and carcinomas of the bladder, thyroid, endometrium, ovarian, colon, hepatocellular, lung, cervical, stomach, and breast. Conclusion: The RabMAb FOXM1 antibody, Clone EP372 specifically labels proliferating cells in regenerative tissues and in a broad spectrum of human tumors. This expression pattern is concordant with results from the literature. To our knowledge, this is the first report that systematically evaluated FOXM1 expression across a broad number of normal human tissues and a variety of human tumors via IHC. Additional research in the role of FOXM1 in tumorigenesis and drug resistance across tissue types will help bolster the prognostic and therapeutic significance of this key oncogenic regulator. Citation Format: Jackie K. Chan, Aihua Li, Jason K. Law, Asish V. Nand, Taiying Chen. A new rabbit monoclonal antibody to FOXM1 for immuohistochemical assessment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 399.