Site-Specifically Labeled Immunoconjugates for Molecular Imaging—Part 1: Cysteine Residues and Glycans

Due to their remarkable selectivity and specificity for cancer biomarkers, immunoconjugates have emerged as extremely promising vectors for the delivery of diagnostic radioisotopes and fluorophores to malignant tissues. Paradoxically, however, these tools for precision medicine are synthesized in a remarkably imprecise way. Indeed, the vast majority of immunoconjugates are created via the random conjugation of bifunctional probes (e.g., DOTA-NCS) to amino acids within the antibody (e.g., lysines). Yet antibodies have multiple copies of these residues throughout their macromolecular structure, making control over the location of the conjugation reaction impossible. This lack of site specificity can lead to the formation of poorly defined, heterogeneous immunoconjugates with suboptimal in vivo behavior. Over the past decade, interest in the synthesis and development of site-specifically labeled immunoconjugates—both antibody-drug conjugates as well as constructs for in vivo imaging—has increased dramatically, and a number of reports have suggested that these better defined, more homogeneous constructs exhibit improved performance in vivo compared to their randomly modified cousins. In this two-part review, we seek to provide an overview of the various methods that have been developed to create site-specifically modified immunoconjugates for positron emission tomography, single photon emission computed tomography, and fluorescence imaging. We will begin with an introduction to the structure of antibodies and antibody fragments. This is followed by the core of the work: sections detailing the four different approaches to site-specific modification strategies based on cysteine residues, glycans, peptide tags, and unnatural amino acids. These discussions will be divided into two installments: cysteine residues and glycans will be detailed in Part 1 of the review, while peptide tags and unnatural amino acids will be addressed in Part 2. Ultimately, we sincerely hope that this review fosters interest and enthusiasm for site-specific immunoconjugates within the nuclear medicine and molecular imaging communities

Abstract PD3-08: Modulation of immunity with 2-fluorofucose (2FF) for breast cancer treatment and prevention

Abstract The majority of patients with breast cancer have robust Type II immune responses directed against their tumors with little to no Type I immunity. The dominance of a Type II microenvironment is established early in breast tumorigenesis with a Type II immune signature prevalent even in pre-invasive lesions such as ductal carcinoma in situ. As a result, breast cancer is associated with abundant autoantibodies directed against tumor associated antigens and few infiltrating T-cells in the majority of patients. A recently reported inhibitor of protein and cellular fucosylation, 2-fluorofucose (2FF) has been shown to enhance immune cell function, in part through the generation of fucose-deficient antibodies which result in enhanced antibody dependent cell mediated cytotoxicity, as well as apparent modulation of T-cell dependent activity [Ca Res, Oct 1, 2014 74;2890]. For treatment studies, TgMMTV-neu (MMTVneu; luminal) and C31-Tag (C3T; triple negative) mice were treated orally with vehicle alone and 20mM 2FF when spontaneous tumor volume reached 75-100mm3 until sacrifice (n=20/grp). To assess the ability to prevent breast cancer development, mice were treated orally with vehicle alone, 20 or 50mM 2FF for up to 200 days starting at 6-8 weeks of age (n=20/grp). Tumor kinetics, disease free survival, and overall survival were calculated. Immune responses were evaluated by both DTH and IFN-gamma ELISPOT. To determine immune mechanism of action, NK, B, CD4, or CD8 cells were depleted concurrently with tumor implant. When tumor bearing mice were treated with 2FF, tumor growth was significantly inhibited in both groups over the course of therapy (MMTVneu p&amp;lt;0.0001 and C3T p&amp;lt;0.0001 compared to controls). In addition, survival was significantly prolonged in both models (MMTVneu p&amp;lt;0.0001 and C3T p=0.0014). In the prevention setting, 2FF significantly delayed the average age of tumor onset in both models at both doses with the higher does showing greater efficacy; MMTVneu 20mM, p=0.001, 50mM, p=0.0002. At the time of study termination (300d), 45% of 2FF-treated MMTVneu mice had no evidence of mammary tumors. 2FF also significantly improved the average age of tumor onset in C3T mice when comparing untreated to 20mM (p=0.007), and 50mM (p=0.0007) treated mice. At study termination, 33% of all 2FF-treated C3T animals were disease free. 2FF anti-tumor activity was associated with the induction of tumor antigen specific immunity. After treatment both the MMTVneu (p&amp;lt;0.0001) and C3T (p&amp;lt;0.0001) developed a DTH response to syngeneic tumor lysates. Of note, the DTH response was inversely associated with the rate of tumor growth (p&amp;lt;0.0001). 2FF anti-tumor activity was associated with the induction of tumor antigen specific immunity. Depletion of immune cell subsets using targeting antibodies demonstrated that the anti-tumor response was mediated in large part by CD4 T-cells which are involved in stimulating both humoral and CD8 T-cell responses. 2FF, a novel inhibitor of fucosylation has potent anti-tumor effects in 2 transgenic models of breast cancer; luminal and triple negative mammary tumors. The agent is active in these mouse models in both the treatment and prevention setting and thus may represent a rational therapeutic approach to evaluate in breast cancer patients. Citation Format: Disis ML, Rastetter L, Gad E, Koehnlein M, Senter PD, Gardai S, Okeley NM. Modulation of immunity with 2-fluorofucose (2FF) for breast cancer treatment and prevention. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD3-08.</jats:p