Benefit of Later-Time-Point PET Imaging of HER3 Expression Using Optimized Radiocobalt-Labeled Affibody Molecules

Abstract

HER3-binding affibody molecules are a promising format for visualization of HER3 expression. Cobalt-55, a positron-emitting isotope, with a half-life of 17.5 h, allows for next-day imaging. We investigated the influence of the charge of the radiocobalt–chelator complex on the biodistribution of anti-HER3 affibody molecule (HE)3-ZHER3 and compared the best radiocobalt-labeled variant with a recently optimized gallium-labeled variant. Affibody conjugates (HE)3-ZHER3-X (X = NOTA, NODAGA, DOTA, DOTAGA) were labeled with [57Co]Co (surrogate for 55Co). Affinity measurements, binding specificity and cellular processing were studied in two HER3-expressing cancer cell lines. Biodistribution was studied 3 and 24 h post-injection (pi) in mice with HER3-expressing BxPC-3 xenografts and compared to [68Ga]Ga-(HE)3-ZHER3-NODAGA. Micro-single-photon emission tomography/computed tomography (microSPECT/CT) and micro-positron emission tomography/computed tomography (microPET/CT) imaging was performed 3 and 24 h pi. Stably labeled conjugates bound to HER3 with subnanomolar affinity. [57Co]Co-(HE)3-ZHER3-DOTA had the best tumor retention and a significantly lower concentration in blood than other conjugates, leading to superior tumor-to-blood and tumor-to-liver ratios 24 h pi. Compared to [68Ga]Ga-(HE)3-ZHER3-NODAGA 3 h pi, [57Co]Co-(HE)3-ZHER3-DOTA provided superior imaging contrast in liver 24 h pi. Concluding, the composition and charge of the [57Co]Co–chelator complex influenced the uptake in tumors and normal tissue. [57Co]Co-(HE)3-ZHER3-DOTA provided the best imaging properties among the cobalt-labeled conjugates. Delayed imaging of HER3 expression with [57Co]Co-(HE)3-ZHER3-DOTA improved imaging contrast compared to early-time-point imaging with [68Ga]Ga-(HE)3-ZHER3-NODAGA.

66Ga-PET-imaging of GRPR-expression in prostate cancer: production and characterization of [66Ga]Ga-NOTA-PEG2-RM26

“…However, the low level of internalized activity resembled the behavior of radiocobalt-labeled NOTA-PEG 2 -RM26 22,39 , and was considerably lower than the level of internalization of its [ 111 In]In-labeled analog 21 . Similar to [ 55/57 Co]Co-PEG 2 -RM26, the radiocobalt label also led to lower amounts of internalized activity with affibody molecules, and it is hypothesized that the radiocobalt label leaks from or is transported out of the cell by specific cobalt-efflux mechanisms 22,[39][40][41] . It could be speculated that similar mechanisms are in place for gallium.…”

PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology

“…[ 18 F]AlF-Z HER3:08698 showed that clear visualization of HER3 expressing xenografts is possible, as early as 1 h pi [ 266 ]. However, later time points generally provided improved imaging contrast [ 261 , 264 , 265 ]. Although no complete dose finding study was reported, injected doses between 1–3 µg have been used for imaging purposes and an injected mass of 70 µg resulted in a significant decrease in uptake in xenografts and even in the liver [ 256 , 258 ].…”

“…It was further demonstrated that different labels influence the imaging properties of Z HER3 in different ways. Several studies have focused on reducing hepatic uptake of anti-HER3 affibody molecules by investigating the influence of molecular design and a radiolabeling approach [ 89 , 265 , 268 ]. For example, an increased negative charge of the radiometal-chelator complex reduced the hepatic uptake by 2-fold, significantly increasing the tumor-to-liver ratio [ 89 ].…”

“…Implementation of this molecular design in combination with a NOGADA chelator at C-terminus significantly improved the tumor-to-liver ratio [ 268 ]. Among the radiometal labels, radiocobalt labeled (HE) 3 -Z HER3:08698 -DOTA has shown to be the most promising variant, for the first time exceeding a tumor-to-liver ratio of one, a prerequisite for the detection of HER3 expressing metastases in liver [ 265 ]. The use of non-residualizing iodine labeled further increased this ratio to 2.4 (4 h pi), a similar ratio to what was achieved by co-injection of the affibody trimer [ 107 , 267 ].…”

“… Imaging of HER3 expression (white arrows) in xenografted mice using 89 Zr-labeled mAb [ 252 ], biparatopic dimer of sdAb [ 259 ], and 57 Co-labeled affibody molecule ( 57 Co-Z) [ 265 ]. Yellow arrows point to the uptake in the liver and red arrows in the kidneys.…”