Effective Treatment of Human Breast Carcinoma Xenografts with Single-Dose²¹¹At-Labeled Anti-HER2 Single-Domain Antibody Fragment

Abstract

Single-domain antibody fragments (sdAbs) are attractive for targeted a-particle therapy, particularly with 211 At, because of their rapid accumulation in tumor and clearance from normal tissues. Here, we evaluate the therapeutic potential of this strategy with 5F7 and VHH_1028-2 sdAbs that bind with high affinity to domain IV of human epidermal growth factor receptor type 2 (HER2). Methods: The HER2-specific sdAbs and HER2-irrelevant VHH_2001 were labeled using N-succinimidyl-3-211 At-astato-5-guanidinomethyl benzoate (iso-211 At-SAGMB). The cytotoxicity of iso-211 At-SAGMB-5F7 and iso-211 At-SAGMB-VHH_2001 were compared on HER2-expressing BT474 breast carcinoma cells. Three experiments in mice with subcutaneous BT474 xenografts were performed to evaluate the therapeutic effectiveness of single doses of iso-211 At-SAGMB-5F7 (0.7-3.0 MBq), iso-211 At-SAGMB-VHH_1028 (1.0-3.0 MBq), and iso-211 At-SAGMB-VHH_1028 and iso-211 At-SAGMB-VHH_2001 (1.0 MBq). Results: Clonogenic survival of BT474 cells was reduced after exposure to iso-211 At-SAGMB-5F7 (D 0 5 1.313 kBq/mL) whereas iso-211 At-SAGMB-VHH_ 2001 was ineffective. Dose-dependent tumor growth inhibition was observed with 211 At-labeled HER2-specific 5F7 and VHH_1028 but not with HER2-irrelevant VHH_2001. At the 3.0-MBq dose, complete tumor regression was seen in 3 of 4 mice treated with iso-211 At-SAGMB-5F7 and 8 of 11 mice treated with iso-211 At-SAGMB-VHH_1028; prolongation in median survival was 495% and 414%, respectively. Conclusion: Combining rapidly internalizing, high-affinity HER2-targeted sdAbs with the iso-211 At-SAGMB residualizing prosthetic agent is a promising strategy for targeted a-particle therapy of HER2-expressing cancers.

Alpha‐emitters and targeted alpha therapy in cancer treatment

“…To investigate the effectiveness of the HER2 single-domain antibody, Feng et al designed iso-211 At-SAGMB-5F7 and iso-211 At-SAGMB-VHH_1028. In most treated animals, full tumor regression was seen 200 days following therapy, and the treatments showed good therapeutic efficacy against HER2-positive breast cancer xenografts at a single dose [42]. However, radiolabeling prosthetic groups such as iso-[ 211 At]SAGMB react with multiple lysine residues in the single-domain antibody (sdAb) fragment, resulting in a combination of radioconjugates with a range of properties.…”

“…211 At -Differentiated thyroid cancer [39] 211 At-octreotide SSTR2 Lung cancer [40] 211 At-trastuzumab HER2 Breast cancer [41] iso-211 At-SAGMB-VHH_1028 HER2 Breast cancer [42] iso-[ 211 At]AGMB-PODS-5F7 HER2 Breast cancer [43] 211 At-ATE-MnO 2 -BSA -Breast cancer; colon cancer [44] 225 Ac-FAPI-46 FAP Human pancreatic cancer [45] [ 225 Ac]Ac-DOTA-2Rs15d HER2 HER2pos ovarian cancer [46] 225 Ac-CD45 CD45 Acute myeloid leukemia [47] 213 Bi-h8C3 -Melanoma [48] 213 Bi-DTPA-2Rs15d HER2 Ovarian cancer [49] 213 Bi-DOTATOC SSTR2 Pancreatic tumors [50] 213 Bi-DOTATATE SSTR2 K562-SST2 cell line [51] 212 Pb-sulfur colloid -Ovarian carcinoma [52] [ 212 Pb]Fe(OH) 2 -Ovarian carcinoma [53] 212 Pb-NNV003 CD37 Leukemia [54] 212 Pb-rituximab CD20 Lymphoma [55] 212 Pb-L1-L5 PSMA Prostate cancer [56] 227 Th-PSMA-TTC PSMA Prostate cancer [57] 227 Th-MSLN-TTC MSLN Mesothelioma and ovarian cancer [58] 227 Th-rituximab CD20 Lymphoma [59] 227 Th-trastuzumab HER2 Breast cancer [60] 227 Th-anti-CD22 antibody CD22 Non-Hodgkin lymphoma [61] Abbreviations: FAP, fibroblast activating protein; HER2, human epidermal growth factor type 2; SSTR2, somatostatin receptor subtype 2 .…”

Single-Domain Antibody Theranostics on the Horizon

“…In the HER2-targeted theranostic pair, the therapeutic agent 131 I-GMIB-anti-HER2-VHH1 was developed using 131 I-SGMIB as the prosthetic group, leading to increased stability and lower kidney accumulation of the radiopharmaceutical. The future of nuclear medicine will be continuously shaped by theranostics (62); a-particle2labeled sdAbs are also promising therapeutic components in the sdAb theranostic toolbox (63).…”

Effective Treatment of SSTR2-Positive Small Cell Lung Cancer Using 211At-Containing Targeted α-Particle Therapy Agent Which Promotes Endogenous Antitumor Immune Response

“…The general radiation range is 28−100 μm, equivalent to the diameter of 6−8 eukaryotic cells (10−50 μm), which can significantly increase cell mortality rate per unit absorbed dose, reduce bone marrow toxicity, and limit overexposure to radiation. 22,23 However, unlike conventional drugs and toxins, which kill only directly targeted cells, α-nuclides are unique in their ability to induce radiation-induced bystander effects or crossfire effects. As a result, adjacent tumor cells may be destroyed even if they do not possess the specific tumor-associated receptor, enzyme, or antigen.…”

“…The relative biological effects of α-nuclides are 3–7 times that of β-nuclides, which are shown as irreparable breaks of DNA double strands during mitosis or redistribution. The general radiation range is 28–100 μm, equivalent to the diameter of 6–8 eukaryotic cells (10–50 μm), which can significantly increase cell mortality rate per unit absorbed dose, reduce bone marrow toxicity, and limit overexposure to radiation. , …”