Evaluation of [89Zr]Zr-DFO-2Rs15d Nanobody for Imaging of HER2-Positive Breast Cancer

One of the most aggressive forms of breast cancer involvestheoverexpression of human epidermal growth factor receptor 2 (HER2).HER2 is overexpressed in & SIM;25% of all breast cancers and isassociated with increased proliferation, increased rates of metastasis,and poor prognosis. Treatment for HER2-positive breast cancer hasvastly improved since the development of the monoclonal antibody trastuzumab(Herceptin) as well as other biological constructs. However, patientsstill commonly develop resistance, illustrating the need for newertherapies. Nanobodies have become an important focus for potentialdevelopment as HER2-targeting imaging agents and therapeutics. Nanobodieshave many favorable characteristics, including high stability in heatand nonphysiological pH, while maintaining their low-nanomolar affinityfor their designed targets. Specifically, the 2Rs15d nanobody hasbeen developed for targeting HER2 and has been evaluated as a diagnosticimaging agent for single-photon emission computed tomography (SPECT)and positron emission tomography (PET). While a construct of 2Rs15dwith the positron emitter Ga-68 is currently in phase Iclinical trials, the only PET images acquired in preclinical or clinicalresearch have been within 3 h postinjection. We evaluated our in-houseproduced 2Rs15d nanobody, conjugated with the chelator deferoxamine(DFO), and radiolabeled with Zr-89 for PET imaging up to72 h postinjection. [Zr-89]Zr-DFO-2Rs15d demonstrated highstability in both phosphate-buffered saline (PBS) and human serum.Cell binding studies showed high binding and specificity for HER2,as well as prominent internalization. Our in vivo PET imaging confirmedhigh-quality visualization of HER2-positive tumors up to 72 h postinjection,whereas HER2-negative tumors were not visualized. Subsequent biodistributionstudies quantitatively supported the significant HER2-positive tumoruptake compared to the negative control. Our studies fill an importantgap in understanding the imaging and binding properties of the 2Rs15dnanobody at extended time points. As many therapeutic radioisotopeshave single or multiday half-lives, this information will directlybenefit the potential of the radiotherapy development of 2Rs15d forHER2-positive breast cancer patients.