The human neonatal Fc receptor, hFcRn, is a trafficking receptor for human IgG expressed by various cell types such as vascular endothelial cells, antigen presenting cells, and colorectal, mammary, and pulmonary epithelial cells. Binding of FcRn by monomeric IgG occurs in a pH-restricted manner and, depending on the interacting cell type, can lead to IgG recycling or transcytosis. The recycling pathway is predominant in the vascular endothelium and it traffics IgG away from lysosomal degradation; transcytotic IgG transport, on the other hand, has been more commonly observed in intestinal, breast, and lung epithelium. We hypothesize that solid tumors originating from FcRn-expressing epithelia maintain FcRn expression and that functional expression of FcRn in tumors may affect IgG subcellular trafficking, metabolism, and overall tumor disposition. In the investigations presented herein, we provide quantitative evidence of robust FcRn expression by colorectal and breast tumor cell lines as examined by Flow-Assisted Cell Sorting (FACS) and Western Blotting. Furthermore, we show by Fluorescence Microscopy in selected cell lines that FcRn is localized in both early and recycling endosomes and that its localization in recycling endosomes supports its function in these cells, which is also shown by FACS to be predominantly that of a recycling receptor. To evaluate our hypothesis in vivo, we have developed and characterized an hFcRn mouse tumor model in which hFcRn expression is conditional on doxycycline dosing. Briefly, hFcRn-transduced HM7 colorectal tumor cells (HM7-hFcRn+) implanted into athymic nude mice were evaluated as a function of growth kinetics, vascular volume, and hFcRn expression for up to 14 days following cell inoculation. We show by immunohistochemical staining and FACS substantial hFcRn expression in HM7-FcRn+ tumors relative to parental HM7 tumors during the course of study. Tumor growth and tumor vascular volumes were similar to the parental model as shown by caliper measurements and indirect (99m)Tc red blood cell labeling, respectively, suggesting that this model is appropriate for our purpose. These results provide evidence of hFcRn expression in colorectal and breast cancer cell lines commonly used in xenograft studies and suggest that such expression may lead to IgG recycling in these cell types. Furthermore, we have developed a mouse tumor model that will allow us to determine whether the recycling function of hFcRn observed in vitro translates to an in vivo setting and its effect on IgG tumor distribution, metabolism, and ultimately, anti-tumor efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A138.