Radionuclide Therapy of HER2-Expressing Human Xenografts Using Affibody-Based Peptide Nucleic Acid–Mediated Pretargeting: In Vivo Proof of Principle

Abstract

Affibody molecules are small proteins engineered using a nonantibody scaffold. Radiolabeled Affibody molecules are excellent imaging probes, but their application to radionuclide therapy has been prevented by high renal reabsorption. The aim of this study was to test the hypothesis that Affibody-based peptide nucleic acid (PNA)-mediated pretargeted therapy of human epidermal growth factor receptor 2 (HER2)-expressing cancer extends survival without accompanying renal toxicity. A HER2-targeting Affibody molecule ligated with an AGTCGTGATGTAGTC PNA hybridization probe (Z-SR-HP1) was used as the primary pretargeting agent. A complementary AGTCGTGATGTAGTC PNA conjugated to the chelator DOTA and labeled with the radionuclide Lu (Lu-HP2) was used as the secondary agent. The influence of different factors on pretargeting was investigated. Experimental radionuclide therapy in mice bearing SKOV-3 xenografts was performed in 6 cycles separated by 7 d. Optimal tumor targeting was achieved when 16 MBq/3.5 μg (0.65 nmol) ofLu-HP2 was injected 16 h after injection of 100 μg (7.7 nmol) of Z-SR-HP1. The calculated absorbed dose to tumors was 1,075 mGy/MBq, whereas the absorbed dose to kidneys was 206 mGy/MBq and the absorbed dose to blood (surrogate of bone marrow) was 4 mGy/MBq. Survival of mice was significantly longer ( < 0.05) in the treatment group (66 d) than in the control groups treated with the same amount of Z-SR-HP1 only (37 d), the same amount and activity of Lu-HP2 only (32 d), or phosphate-buffered saline (37 d). The studied pretargeting system can deliver an absorbed dose to tumors appreciably exceeding absorbed doses to critical organs, making Affibody-based PNA-mediated pretargeted radionuclide therapy highly attractive.

Development of Radiotracers for Breast Cancer—The Tumor Microenvironment as an Emerging Target

“…After pretargeted treatment, the absorbed dose in tumors was 5-fold higher than in kidneys. Despite the potential to extend survival of SCOV-3 mice, the renal uptake was still problematic when applying the same dose of [ 177 Lu]Lu-HP2 [ 27 ].…”

On the prevention of kidney uptake of radiolabeled DARPins

“…Low accumulation of the radiolabeled secondary agent in the kidneys is a prerequisite for successful pretargeting. Pretargeting systems based on oligonucleotides [21,22] and bioorthogonal chemistry [23,24] were evaluated in vivo in preclinical studies, while avidin-biotin and bispecific antibody-hapten [25] were translated to clinical trials [26,27].…”

Influence of Several Compounds and Drugs on the Renal Uptake of Radiolabeled Affibody Molecules

“…Pretargeting or multi-step targeting approach has been first applied to overcome the limitations associated with the use of directly radiolabelled mAbs in therapy [13]. We developed a novel pretargeting strategy based on affibody molecules and mediated by peptide nucleic acids (PNA) hybridization [14,15]. Using affibody-based PNA-mediated pretargeting, we obtained a 5-fold higher radioactivity accumulated dose to the tumour than to the kidneys.…”