Comparative breast tumor imaging to identify the expression of type I IGF receptor (IGF1R) by anti-IGF1R antibody-conjugated small molecule fluorophore or quantum dots in vivo.

Abstract

Abstract Abstract #6001 The type I insulin-like growth factor (IGF) receptor (IGF1R) is a transmembrane receptor tyrosine kinase involved in breast cancer proliferation, survival, and metastasis. Several antibodies against IGF1R, including some in clinical trials, downregulate the level of IGF1R both in cell line studies and in in vivo animal experiments. Thus, this downregulation is a biodynamic marker of antibody delivery to the tumor. To date, identification of IGF1R expression and its downregulation in vivo in a non-invasive way is still challenging. In this study, we sort to use two different fluorescent technologies, small molecule fluorophores, or quantum dots (QDs), to detect receptor expression and its downregulation by antibodies in vivo. Alexa 680 is a small molecule fluorophore that can be excited with a peak emission at 705 nm. QDs are nanocrystals that emit fluorescence upon excitation, and QDs with a peak emission at 705 nm was used in this study. Both Alexa 680 and QDs were conjugated with AVE-1642, a humanized anti-IGF1R antibody developed by sanofi-aventis. After conjugation, they both were able to detect the expression of IGF1R and its downregulation in in vitro cell line studies. We used mouse xenograft tumor models to examine their efficacies in vivo. AVE-1642 conjugated Alexa 680 or QDs (705 nm) was intravenously delivered to mice bearing mammary xenograft tumors that express IGF1R. After 24 hours of circulation, Alexa 680 fluorescence was shown to solely localize to the xenograft tumor, with little non-specific targeting to other tissue or organs in mice. In addition, Alexa 680 fluorescence was diminished in tumors that had downregulated IGF1R by antibody pretreatment. In contrast, conjugated QDs fluorescence was mainly localized to liver, spleen, bone marrow and lymph nodes, with very small amount of QDs in the xenograft tumors. The QDs fluorescence in xenograft tumors remained unchanged even when IGF1R was downregulated by antibody pretreatment. Furthermore, we identified that QDs were mainly localized to the hepatic sinusoids, and subsequently engulfed by Kupffer cells. Taken together, our data suggest that small molecule fluorophores, such as Alexa 680, are useful agents to detect the expression and downregulation of IGF1R in vivo. Our data provide valuable insight not only into the clinical development of anti-IGF1R antibodies, but also to other targeted therapy as well. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6001.