Abstract B143: Biomarker imaging of immunogenic cell death in response to cancer therapy.

Abstract

Abstract Objective: Cancer therapy is generally initiated by apoptosis. Immunogenic cell death (ICD) is a type of cell demise that activates an adaptative immune response. In cancer cells, ICD can be induced by radiotherapy or certain anticancer agents. A major characteristic of ICD is the cell surface translocation of calreticulin (CRT), which then acts as an “eat me” signal for dendritic cells. This leads to phagocytosis of the cancer cells followed by priming of tumor specific cytotoxic T cells. In this study, we developed a novel molecular imaging technology using CRT as an imaging biomarker of ICD. The technology was tested on cultured cancer cells and in vivo tumor models for its ability to target cancer cells treated with ICD-inducing agents. Method: For confocal microscopy, fluorescence-activated cell sorting (FACS) analysis, and fluorescent optical imaging, a monoclonal antibody against human CRT (FMC 75) labeled with phycoerythrin was used. For cellular uptake experiments and PET imaging, an anti-CRT antibody was radioiodine labeled using the iodogen method. ICD was induced in CT-26 colon cancer cells by treatment with 20 µM doxorubicin (DX) or a combination of 15 µM mitomycinC plus 150 nM tautomycin (MitoC/TTM). Tumor bearing Balb/C mice prepared by subcutaneous implantation of CT-26 colon cancer cells were treated by intraperitoneal injection with 8 mg/kg DX. Phycoerythrin labeled probes were tail vein injected 4 h later, and optical imaging of fluorescent signals was performed at 8, 16, 24 and 48 h post-injection. Results: Confocal microscopy showed specific binding of phycoerythrin anti-CRT antibodies to the surface of ICD-induced CT-26 cancer cells. FACS analysis with the probe showed a right-shift of fluorescent signals in cells treated with DX. Hence, signal-positive cells were increased from 2.76 ± 0.02 % to 13.81 ± 4.2 % by 4 h of DX treatment. In vivo optical imaging following DX treatment displayed tumor uptake of phycoerythrin anti-CRT antibody probes from 4 h post-injection. Tumor contrast was improved at 16 h, when tumor to background signal ratio in DX treated mice reached 2.2-fold of controls. The antibody probes were radioiodine (125I or 124I) labeled with efficiencies of over 50 %. 124I-labeled CRT antibody binding was increased to 889.6 ± 103.1 % and 386.2 ± 73.6 % of controls in DX and MitoC/TTM treated CT-26 cells, respectively. Conclusion: This study demonstrates that anti-CRT antibody-based probes may be useful for noninvasive monitoring of tumor response to ICD-inducing therapies in living subjects. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B143. Citation Format: Kyung-Ho Jung, Jinwon Park, Jinhee Lee, Quach Cung, Eun Jeong Lee, Kyung-Han Lee. Biomarker imaging of immunogenic cell death in response to cancer therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B143.