Eric Wehrenberg-Klee MD, Presenter: Nothing to Disclose

Nafize Selcan Turker PhD, Abstract Co-Author: Nothing to Disclose

Pedram Heidari MD, Abstract Co-Author: Nothing to Disclose

Umar Mahmood MD, PhD, Abstract Co-Author: Research Grant, Sabik Medical Inc

Bryan Chang, Abstract Co-Author: Nothing to Disclose

HER3 is a surface receptor tyrosine kinase that plays an important role in pro-oncogenic signaling pathways. The receptor is expressed at low-copy number, which is potentially limiting for PET probe development. We developed an antibody-based PET probe specific for HER3, characterized it in vitro, and successfully image HER3 expressing xenografts. We demonstrate that the ability to image this low-expression surface protein is time-dependent, and is related to internalization of receptor-probe complex

64Cu-DOTA-HER3 F(ab’)2 was prepared from whole HER3 monoclonal antibody with F(ab)’2 fragmentation and chelator conjugation, and its affinity for HER3 assessed using radio-labeled binding studies. HER3 surface-expression on multiple cell lines was confirmed using fluorescent-activated cell sorting (FACS). Probe internalization kinetics were determined by conducting cell uptake studies at both 4°C and 37°C. Results of cell uptake studies were correlated with geometric mean FITC signal obtained from FACS. In vivo PET-CT imaging with 64Cu-DOTA-HER3 F(ab’)2 was conducted using mouse xenografts of MDA-MB 468 and HCC 70 tumors (n=3 for both groups).

The HER3 PET probe demonstrates a HER3 Kd of 6.8 nM. FACS confirmed HER3 expression of approximately 200 receptors per cell across multiple lines. Cell uptake studies demonstrate counts/minute/cell of 0.28, 0.45, 0.82 for MCF-7, HCC-70, and MDA-MB-468 cells, respectively after 1 hour. Time course studies demonstrate linear increase of HER3 probe uptake over time at 37°C but not at 4°C that correlates with findings on FACS. In vivo imaging with the HER3 PET Probe of MDA-MB-468 and HCC70 tumor xenografts demonstrate SUVs of 0.35 and 0.59, with TBRs of 6.0 and 11.4 respectively.

We have developed a HER3 specific PET probe, and demonstrate successful in vivo imaging of HER3 expressing xenografts. We demonstrate that imaging of a low-expression surface protein is possible, and is dependent upon internalization of the receptor-probe complex. These findings have relevance for the development of PET probes for imaging of low-expression receptors of clinical interest.

The developed HER3 PET probe has utility for measuring HER3 expression levels on cancers, which is thought to be a primary mediator of resistance to HER2 inhibition.

Wehrenberg-Klee, E, Turker, N, Heidari, P, Mahmood, U, Chang, B, A Novel PET Probe for Imaging HER3 Receptor Status.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14015897.html