Affibody-DyLight Conjugates for In Vivo Assessment of HER2 Expression by Near-Infrared Optical Imaging

Purpose: Amplification of the HER2/neu gene and/or overexpression of the corresponding protein have been identified in approximately 20 % of invasive breast carcinomas. Assessment of HER2 expression in vivo would advance development of new HER2-targeted therapeutic agents and, potentially, facilitate choice of the proper treatment strategy offered to the individual patient. We present novel HER2-specific probes for in vivo evaluation of the receptor status by near-infrared (NIR) optical imaging. Experimental Design: Affibody molecules were expressed, purified, and labeled with NIR-fluorescent dyes. The binding affinity and specificity of the obtained probe were tested in vitro. For in vivo validation, the relationship of the measured NIR signal and HER2 expression was characterized in four breast cancer xenograft models, expressing different levels of HER2. Accumulation of Affibody molecules in tumor tissue was further confirmed by ex vivo analysis. Results: Affibody-DyLight conjugates showed high affinity to HER2 (KD = 3.6660.26). No acute toxicity resulted from injection of the probes (up to 0.5 mg/kg) into mice. Pharmacokinetic studies revealed a relatively short (37.5362.8 min