PET imaging of glioblastoma multiforme EGFR expression for therapeutic decision guidance.

Abstract

After initial therapy and total resection of glioblastoma multiforme (GBM), 80-90% of recurrences occur at the surgical margins. Insufficient sensitivity and specificity of current imaging techniques based on non-specific vascular imaging agents lead to delay in diagnosis of residual and/or recurrent disease. A tumor-specific imaging agent for GBM may improve detection of small residual disease in the post-operative period, and improve ability to distinguish tumor recurrence from its imaging mimics that can delay diagnosis. To this end, we developed an EGFR-targeted PET probe and assessed its ability to image EGFR WT (U87) and EGFRvIII (Gli36vIII) expressing GBMs in both murine intra-cranial xenografts and in a surgical-resection model. The developed imaging probe, (64)Cu-DOTAcetuximab-F(ab´)2, binds with a Kd of 11.2 nM to EGFR expressing GBM. (64)Cu-DOTA-cetuximab-F(ab´)2 specifically localized to intra-cranial tumor with a significant difference in SUVmean between tumor and contralateral brain for both Gli36vIII and U87 tumors (P<0.01 for both comparisons), with mean TBR of 22.5±0.7 for Gli36vIII tumors and 28.9±2.1 for U87 tumors (TBR±SEM). Tracer uptake by tumor was significantly inhibited by pre-injection with cetuximab (P<0.01 for both), with SUVmean reduced by 68% and 58% for Gli36vIII and U87 tumors, respectively. Surgical resection model PET-CT imaging demonstrates residual tumor and low nonspecific uptake in the resection site. We conclude that (64)Cu-DOTA-cetuximab-F(ab´)2 binds specifically to intracranial EGFR WT and EGFRvIII expressing GBM, demonstrates excellent TBR, and specifically images small residual tumor in a surgical model, suggesting future clinical utility in identifying true tumor recurrence.