PET imaging of HER1-expressing xenografts in mice with 86Y-CHX-A″-DTPA-cetuximab

Abstract

Cetuximab is a recombinant, human/mouse chimeric IgG1, monoclonal antibody (mAb) that binds to the epidermal growth factor receptor (EGFR/HER1). Cetuximab is approved for the treatment of patients with HER1-expressing metastatic colorectal cancer. Limitations in currently reported radiolabeled cetuximab for PET applications prompted the development of 86Y-CHX-A”-DTPA-cetuximab as an alternative for imaging HER1-expressing cancer. 86Y-CHX-A”-DTPA-cetuximab can also serve as a surrogate marker for 90Y therapy. Methods Bifunctional chelate, CHX-A”-DTPA was conjugated to cetuximab and radiolabeled with 86Y. In vitro immunoreactivity was assessed in HER1-expressing A431 cells. In vivo biodistribution, PET imaging and non-compartmental pharmacokinetics were performed on mice bearing HER1-expressing human colorectal (LS-174T and HT29), prostate (PC-3 and DU145), ovarian (SKOV3) and pancreatic (SHAW) tumor xenografts. Receptor blockage was demonstrated by co-injection of either 0.1 or 0.2 mg cetuximab. Results 86Y-CHX-A”-DTPA-cetuximab was routinely prepared with a specific activity of 1.5– 2 GBq/mg and in vitro immunoreactivity ranging from 65–75 %. Biodistribution and PET imaging studies demonstrated high HER1-specific tumor uptake of the radiotracer and clearance from non-specific organs. In LS-174T tumor bearing mice injected with the 86Y-CHX-A”-DTPA-cetuximab alone, 86Y-CHX-A”-DTPA-cetuximab plus 0.1 mg cetuximab or 0.2 mg cetuximab, the tumor uptake values at 3 d were 29.3 ± 4.2, 10.4 ± 0.5 and 6.4 ± 0.3 % ID/g, respectively, demonstrating dose-dependent blockage of the target. Tumors were clearly visualized 1 d after injecting 3.8–4.0 MBq 86Y-CHX-A”-DTPA-cetuximab. Quantitative PET revealed highest tumor uptake in LS-174T (29.55 ± 2.67 % ID/cc) and lowest tumor uptake in PC-3 (15.92 ± 1.55 % ID/cc) xenografts at 3 d after injection. Tumor uptake values quantified by PET were closely correlated (r2= 0.9, n=18) to values determined by biodistribution studies. Conclusion This study demonstrates the feasibility in preparation of high specific activity 86Y-CHX-A”-DTPA-cetuximab and its application for quantitative non-invasive PET imaging of HER1-expressing tumors. 86Y-CHX-A”-DTPA-cetuximab offers an attractive alternative to previously labeled cetuximab for PET and warrants further investigation for clinical translation.

Evaluation of cetuximab as a candidate for targeted α-particle radiation therapy of HER1-positive disseminated intraperitoneal disease

“…The usefulness of cetuximab was also confirmed in a study in which cetuximab labeled with 86 Y was studied for positron-emission tomography (PET) imaging. 24,25 The studies described herein are both exploratory and confirmatory to the above hypothesis, evaluating the potential of cetuximab for a-targeted therapy of disseminated intraperitoneal disease. Consistent with previous studies from this laboratory, this investigation also includes studies combining chemotherapeutics (gemcitabine and carboplatin) with RIT to assess potential therapeutic efficacy enhancement of HER1 targeting a-emitting high-LET 212 Pb-labeled cetuximab.…”

“…[21][22][23][24]26,[35][36][37][38] Cetuximab has been the focus of several imaging studies with the objective of assessing the value of this mAb for disease monitoring, HER1 expression and distribution, patient selection and for performing dosimetric calculations. [23][24][25][26] The preclinical studies from this laboratory demonstrated excellent targeting of s.c. tumor by 111 In-cetuximab given intravenously. 23 Targeting was obtained in 5 tumor models (2 colorectal, 1 prostate, 1 pancreatic and 1 ovarian), determined by direct quantitation of tissues and by planar g-scintigraphy.…”

“…[23][24][25] These studies were performed with mice bearing subcutaneous (s.c.) tumor xenografts and the radiolabeled cetuximab given by an intravenous (i.v.) route.…”

“…Several imaging investigations have explored the practicality of using cetuximab for monitoring disease, assaying EGFR expression, determining patient selection as well as for performing dosimetric calculations for RIT. [21][22][23][24][25][26] The possibility that cetuximab might be appropriate for RIT applications was demonstrated in a set of studies published by this laboratory. 23 Tumor targeting of 111 In-cetuximab was validated in 5 tumor models by direct quantitation of tumor tissue and with g-scintigraphy.…”

Imaging agents for in vivo molecular profiling of disseminated prostate cancer - targeting EGFR receptors in prostate cancer: Comparison of cellular processing of [111In]-labeled affibody molecule ZEGFR:2377 and cetuximab

“…The use of natural ligands is limited by their physiological activity that can provoke adverse reactions: nausea, vomiting, diarrhea, hypotension, fever and chills (17). Intact mAbs demonstrated their capacity to image EGFR-expressing tumors (18)(19)(20) but the sensitivity of such tracers can be limited by the long biodistribution times, slow tumor penetration, and slow blood clearance of the tracers, which reduces target or non-target contrast. The affibody molecules, a new class of imaging agents combine small size of natural ligands, absence of physiological action, and high affinity to target and can be used for radioimmuno-diagnostic.…”