A Novel Engineered Anti-CD20 Tracer Enables Early Time PET Imaging in a Humanized Transgenic Mouse Model of B-cell Non-Hodgkins Lymphoma

Abstract

Purpose: The aim of this article was to evaluate the use of a novel engineered anti-CD20 protein based on the 10 kDa human fibronectin type 3 domain (FN3) and subsequently compare with 64 Cu-rituximab for positron emission tomography (PET) imaging of CD20. Results: In vitro assay demonstrated FN3 binds CD20 with 20 nmol/L affinity on CD20-expressing cells. 64 Cu-FN3 CD20 showed clear, high-contrast visualization of huCD20-expressing B cells in the spleen of transgenic mice as early as 1 hour postinjection [38 AE 3% injected dose (ID)/g] and exhibited a spleen-toblood ratio of 13 by 4 hours. This is higher uptake (P ¼ 0.04) and 10-fold greater signal-to-background (P ¼ 0.04) than the 64 Cu-rituximab antibody radiotracer. Tumor uptake (16.8 AE 1.6 vs. 5.6 AE 1.4%ID/g) and tumor:background ratios were superior for FN3 CD20 relative to rituximab in xenograft studies as well. Conclusions:The 64 Cu-Do-FN3 CD20 radiotracer represents a novel small, high-affinity binder for imaging human CD20, which may be well suited for B-cell non-Hodgkin's lymphoma imaging in patients at early time points.

Theranostic Radiolabeled Anti-CD20 sdAb for Targeted Radionuclide Therapy of Non-Hodgkin Lymphoma

“…After labeling with 64 Cu via DOTA, they evaluated it as a PET radiotracer for B-cell NHL. In a similar animal model as used in our study, tumor uptake was high, 16.8% AE 1.6% ID/g after 4 hours, decreasing to about 6% after 24 hours, with a T/B ratio of 4.1 (41). Even though a higher background signal was observed early after administration, 64 Cu-FN3 CD20 measured higher tumor uptake compared with our lead sdAb, resulting in a high tumor-to-background tissue ratio.…”

Targeted PET imaging strategy to differentiate malignant from inflamed lymph nodes in diffuse large B-cell lymphoma

“…In addition, the DLBCL mice in this study exhibited loss of body weight, splenomegaly, lymphadenopathy, low blood hemoglobin levels, elevated white blood cell counts, and decreased blood platelet counts, all of which accurately mimic the pathophysiological symptoms of human DLBCL (24). Many previous lymphoma PET imaging studies used xenograft lymphoma tumors in immunocompromised mice (39)(40)(41)(42). Our study conducted in this elaborate DLBCL mouse model more accurately simulates the clinical scenario than those studies.…”

Same-Day Imaging Using Small Proteins: Clinical Experience and Translational Prospects in Oncology

“…A small anti-CD20 receptor protein based on the 10-kDa human FN3 has been generated for PET imaging of B-cell lymphomas (37). 64 Cu-DOTA-FN3 CD20 was evaluated in human CD20-transgenic mice and showed a high specific accumulation in the spleen and other CD20-expressing organs as soon as 1 h after injection.…”

“…64 Cu-DOTA-FN3 CD20 was evaluated in human CD20-transgenic mice and showed a high specific accumulation in the spleen and other CD20-expressing organs as soon as 1 h after injection. In nontransgenic mice bearing human CD20 tumors, 64 Cu-FN3 CD20 showed specific tumor targeting with low healthy-tissue uptake as soon as 4 h after injection (37). Recently, synthesis of a human and cynomolgus crossreactive anti-PD-L1 FN3 scaffold was described.…”