Bispecific radioimmunoconjugates exploit receptor heterogeneity for positron emission tomography of tumors expressing HER2 and/or EGFR.

HER2 heterogeneity is a challenge for molecular imaging or treating HER2-positive breast cancer (BC). EGFR is coexpressed in some tumors exhibiting HER2 heterogeneity. Bispecific radioimmunoconjugates (bsRICs) that bind HER2 and EGFR were constructed by linking trastuzumab Fab through polyethyleneglycol (PEG) to EGF. We established s.c. tumors in NOD-SCID mice that homogeneously or heterogeneously expressed HER2 and/or EGFR by the inoculation of HER2-positive/EGFR-negative SK-OV-3 cells, EGFR-positive/HER2-negative MDA-MB-468 cells or mixtures of these cells. [Cu]Cu-NOTA-trastuzumab Fab-PEG-EGF were compared to [Cu]Cu-NOTA-trastuzumab Fab or [Cu]Cu-NOTA-EGF for the PET imaging of HER2 and/or EGFR-positive tumors. [Cu]Cu-NOTA-trastuzumab Fab-PEG-EGF bsRICs imaged tumors expressing HER2 or EGFR or heterogeneously expressing these receptors, while monospecific agents only imaged HER2-or EGFR-positive tumors. Our results indicate that bsRICs labeled with Cu are able to exploit receptor heterogeneity for tumor imaging. PET may select patients for radioimmunotherapy with bsRICs complexed to the β-particle emitter, Lu or Auger electron-emitter, In in a theranostic approach.