HER3 PET Imaging: 68Ga-Labeled Affibody Molecules Provide Superior HER3 Contrast to 89Zr-Labeled Antibody and Antibody-Fragment-Based Tracers

Abstract

HER3 (human epidermal growth factor receptor type 3) is a challenging target for diagnostic radionuclide molecular imaging due to the relatively modest overexpression in tumors and substantial expression in healthy organs. In this study, we compared four HER3-targeting PET tracers based on different types of targeting molecules in a preclinical model: the 89Zr-labeled therapeutic antibody seribantumab, a seribantumab-derived F(ab)2-fragment labeled with 89Zr and 68Ga, and the 68Ga-labeled affibody molecule [68Ga]Ga-ZHER3. The novel conjugates were radiolabeled and characterized in vitro using HER3-expressing BxPC-3 and DU145 human cancer cells. Biodistribution was studied using Balb/c nu/nu mice bearing BxPC-3 xenografts. HER3-negative RAMOS xenografts were used to demonstrate binding specificity in vivo. Autoradiography was conducted on the excised tumors. nanoPET/CT imaging was performed. New conjugates specifically bound to HER3 in vitro and in vivo. [68Ga]Ga-DFO-seribantumab-F(ab’)2 was considered unsuitable for imaging due to the low stability and high uptake in normal organs. The highest tumor-to-non-tumor contrast with [89Zr]Zr-DFO-seribantumab and [89Zr]Zr-DFO-seribantumab-F(ab’)2 was achieved at 96 h and 48 h pi, respectively. Despite lower tumor uptake, [68Ga]Ga-ZHER3 provided the best imaging contrast due to the fastest clearance from blood and normal organs. The results of our study suggest that affibody-based tracers are more suitable for PET imaging of HER3 expression than antibody- and antibody-fragment-based tracers.

Targeting Tumor Cells Overexpressing the Human Epidermal Growth Factor Receptor 3 with Potent Drug Conjugates Based on Affibody Molecules

“…Internalization of [ 99m Tc]Tc-Z HER3 -ABD-mcDM1 was studied in BxPC-3 and DU145 cells using the ‘acid wash’ method [ 24 ]. In brief, the cells were incubated with 0.1 nM [ 99m Tc]Tc-Z HER3 -ABD-mcDM1 at 37 °C for 1, 2, 4, and 8 h. At each time point a set of dishes was removed from the incubator and cells were incubated with 0.2 M glycine buffer (with 0.15 M NaCl, 4 M Urea, pH 2.0) for 5 min on ice.…”

“…Affibody molecules, specifically interacting with HER3 have been described [ 21 , 22 ]. These binders have been radiolabeled and investigated as radionuclide molecular imaging agents in pre-clinical mouse models, where they were able to visualize HER3-expressing tumors and to discriminate between high and low receptor expression [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. The most promising variant for molecular imaging was Z HER3:08698 with specific and strong interaction with HER3 (equilibrium dissociation constant, K D 50 pM) [ 22 ].…”

Molecular imaging of pancreatic ductal adenocarcinoma

“…Seribantumab is another fully human anti-HER3 monoclonal antibody, and in a preclinical study, [ 89 Zr]Zr-DFO-seribantumab and [ 89 Zr]Zr-DFO-seribantumab-F(ab') 2 had the highest tumor-to-background ratio at 96 and 48 h after injection, respectively. 42 Despite lower tumor uptake, the best imaging contrast with gallium-68 ( 68 Ga, T 1/2 = 1.1 h)labeled affibody molecule [ 68 Ga]Ga-Z HER3 was observed because of the fastest clearance of blood and normal organs. However, it is noteworthy that HER3 is relatively mild overexpression in tumors and is highly expressed in healthy organs, making HER3 still a challenging molecular imaging target.…”

“…In recent years, several other HER3 targeting vectors, including HER3‐specific antibody fragments and affibody, have been developed and used as PET imaging probes. Seribantumab is another fully human anti‐HER3 monoclonal antibody, and in a preclinical study, [ 89 Zr]Zr‐DFO‐seribantumab and [ 89 Zr]Zr‐DFO‐seribantumab‐F(ab') 2 had the highest tumor‐to‐background ratio at 96 and 48 h after injection, respectively 42 . Despite lower tumor uptake, the best imaging contrast with gallium‐68 ( 68 Ga, T 1/2 = 1.1 h)‐labeled affibody molecule [ 68 Ga]Ga‐Z HER3 was observed because of the fastest clearance of blood and normal organs.…”

Radionuclides in Diagnostics and Therapy of Malignant Tumors: New Development

“…Due to their high refolding capacity, labeling of ESPs can be performed in harsh conditions (e.g., heating, acidic or basic pH), which gives more freedom to select an appropriate labeling methodology. Rinne and co-workers [ 8 ] evaluated the use of a 68Ga-labeled ESP, affibody molecule [ 68 Ga]Ga-(HE) 3 -ZHER3:08698-NODAGA, for the PET imaging of xenografts expressing human epidermal growth factor type 3 (HER3). [ 68 Ga]Ga-(HE) 3 -ZHER3:08698-NODAGA was compared with the 89Zr-labeled antibody seribantumab and its fragment, seribantumab-F(ab’)2.…”