Evaluation of a radiocobalt-labelled affibody molecule for imaging of human epidermal growth factor receptor 3 expression

Abstract

The human epidermal growth factor receptor 3 (HER3) is involved in the development of cancer resistance towards tyrosine kinase-targeted therapies. Several HER3‑targeting therapeutics are currently under clinical evaluation. Non-invasive imaging of HER3 expression could improve patient management. Affibody molecules are small engineered scaffold proteins demonstrating superior properties as targeting probes for molecular imaging compared with monoclonal antibodies. Feasibility of in vivo HER3 imaging using affibody molecules has been previously demonstrated. Preclinical studies have shown that the contrast when imaging using anti-HER3 affibody molecules can be improved over time. We aim to develop an agent for PET imaging of HER3 expression using the long-lived positron-emitting radionuclide cobalt-55 (55Co) (T1/2=17.5 h). A long-lived cobalt isotope 57Co was used as a surrogate for 55Co in this study. The anti-HER3 affibody molecule HEHEHE-ZHER3-NOTA was labelled with radiocobalt with high yield, purity and stability. Biodistribution of 57Co-HEHEHE-ZHER3-NOTA was measured in mice bearing DU145 (prostate carcinoma) and LS174T (colorectal carcinoma) xenografts at 3 and 24 h post injection (p.i.). Tumour-to-blood ratios significantly increased between 3 and 24 h p.i. (p<0.05). At 24 h p.i., tumour-to-blood ratios were 6 for DU145 and 8 for LS174T xenografts, respectively. HER3‑expressing xenografts were clearly visualized in a preclinical imaging setting already 3 h p.i., and contrast further improved at 24 h p.i. In conclusion, the radiocobalt-labelled anti-HER3 affibody molecule, HEHEHE-ZHER3-NOTA, is a promising tracer for imaging of HER3 expression in tumours.

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

“…Cobalt participates in radiolabeling in a divalent state, thus decreasing the charge of the metal-chelator complex by 1 compared to similar complexes with trivalent metals, such as gallium-68 or indium-111. It was hypothesized that an increased negative charge can reduce unspecific hepatic uptake and, therefore, enhance the tumorto-liver contrast [27]. This hypothesis was further supported by comparing the effect of differently charged radiometal-chelator complexes on the biodistribution of ZHER3 labeled with 68 Ga and 111 In and HER2-targeting affibody molecules [26,31,36].…”

“…Cobalt-55 is a somewhat more unconventional PET isotope, with a half-life of 17.5 h. It can be produced with a medical cyclotron; preclinical evaluation of cobalt-55-labeled tracers targeting PSMA and GRPR, as well as clinical application of cobalt-55 to study brain injuries has been reported [33][34][35]. An initial study of a radiocobalt-labeled affibody ZHER3-NOTA showed promising results, reporting for the first time a tumor-to-liver ratio above 1 [27]. Cobalt participates in radiolabeling in a divalent state, thus decreasing the charge of the metal-chelator complex by 1 compared to similar complexes with trivalent metals, such as gallium-68 or indium-111.…”

“…[ 68 Ga]Ga-(HE) 3 -Z HER3 -NODAGA was labeled with high radiochemical yield (89 ± 1%, determined by ITLC) and radiochemical purity exceeding 98% (ITLC) after purification with size-exclusion chromatography. 3 -Z HER3 -NOTA were previously published by [27]. Purity of [ 57 Co]Co-(HE) 3 -Z HER3 -NOTA was >99% after purification with NAP5 size-exclusion chromatography [27].…”

“…Compared to HER2, the level of HER3 overexpression in cancer cells is low [25] and uptake in normal tissue complicates image interpretation. However, it was previously observed that uptake of HER3 affibody molecules in normal organs decreases over time, while tumor-associated activity cleared more slowly [26,27]. Therefore, HER3 imaging contrast could potentially benefit from delayed imaging (up to 24 h pi), which was previously observed for indium-111-labeled anti-HER3 affibody molecules [26] and for radiolabeled anti-HER1 (EGFR) affibody molecules [28][29][30].…”

“…An initial study of a radiocobalt-labeled affibody Z HER3 -NOTA showed promising results, reporting for the first time a tumor-to-liver ratio above 1 [27]. Cobalt participates in radiolabeling in a divalent state, thus decreasing the charge of the metal-chelator complex by 1 compared to similar complexes with trivalent metals, such as gallium-68 or indium-111.…”