Preclinical immunoPET imaging of glioblastoma-infiltrating myeloid cells using Zirconium-89-labeled anti-CD11b antibody

Abstract

Purpose. Glioblastoma is a lethal brain tumor, heavily infiltrated by tumor-associated myeloid cells (TAMCs). TAMCs are emerging as a promising therapeutic target as they suppress antitumor immune responses and promote tumor cell growth. Quantifying TAMCs using non-invasive immunoPET could facilitate patient stratification for TAMC-targeted treatments and monitoring of treatment efficacy. As TAMCs uniformly express the cell surface marker, integrin CD11b, we evaluated a 89 Zr-labeled anti-CD11b antibody for non-invasive imaging of TAMCs in a syngeneic orthotopic mouse glioma model. Procedures.A human/mouse cross-reactive anti-CD11b antibody (clone M1/70) was conjugated to a DFO chelator and radiolabeled with Zr-89. PET/CT and biodistribution with or without a blocking dose of anti-CD11b Ab were performed 72 hours post-injection of 89 Zr-anti-CD11b Ab in mice bearing established orthotopic syngeneic GL261 gliomas. Flow cytometry and immunohistochemistry of dissected GL261 tumors were conducted to confirm the presence of CD11b + TAMCs.Results. Significant uptake of 89 Zr-anti-CD11b Ab was detected at the tumor site (SUVmean = 2.60 ± 0.24) compared with the contralateral hemisphere (SUVmean = 0.6 ± 0.11). Blocking with a 10-fold lower specific activity of 89 Zr-anti-CD11b Ab markedly reduced the SUV in the right brain (SUVmean = 0.11 ± 0.06), demonstrating specificity. Spleen and lymph nodes (myeloid cell rich organs) also showed high uptake of the tracer, and biodistribution analysis correlated with the imaging results. CD11b expression within the tumor was validated using flow cytometry and immunohistochemistry, which showed high CD11b expression primarily in the tumoral hemisphere compared to the contralateral hemisphere.3 Conclusion. These data establish that 89 Zr-anti-CD11b Ab immunoPET targets CD11b + cells (TAMCs) with high specificity in a mouse model of GBM, demonstrating the potential for noninvasive quantification of tumor infiltrating CD11b + immune cells during disease progression and immunotherapy in patients with GBM.

Preclinical ImmunoPET Imaging of Glioblastoma-Infiltrating Myeloid Cells Using Zirconium-89 Labeled Anti-CD11b Antibody

“…TAMCs account for up to 40% of a glioma's cellular mass and play an important role in tumor progression, immunosuppression, and resistance to immunotherapy [4][5][6]. Numerous preclinical studies by us and others have demonstrated that targeting TAMs and MDSCs can prolong survival of mice with gliomas [5,[7][8] and that these cells are associated with poor prognosis in high-grade gliomas [9]. Since TAMCs impede natural and immunotherapy-driven anti-tumor responses, they are a highpriority and promising therapeutic target currently being evaluated in clinical trials [7][8]10] .…”

ImmunoPET: Concept, Design, and Applications

“…773,774 Accumulating evidence has suggested that immunoPET imaging may substantially improve the clinical immunotherapy by dynamically visualizing immune responses across the whole body. 775−777 To achieve this goal, radiotracers have been developed to image interleukins and specific immune cells, including B cells, 778 natural killer cells, 779,780 macrophages, 781−783 myeloid cells, 278,784 and T cells. In this section, we mainly present the most recent evidence of immunoPET strategies in delineating T cells by targeting lineage-associated antigens, immune checkpoint molecules, OX40, and interferon gamma (IFNγ).…”

TIGIT and PD-1 Immune Checkpoint Pathways Are Associated With Patient Outcome and Anti-Tumor Immunity in Glioblastoma

“…Mice were anesthetized by mask inhalation of 1.5% vaporized isoflurane throughout the surgical procedure. GL261 cells (100,000 cells in 2 mL DPBS) were stereotactically implanted into the caudate nucleus using the following coordinates relative to bregma: x = +2.5 mm (lateral), y = +1.5 mm (anterior), and z = 2-3.0 mm (inferior) (33). MRI was performed 7 days post tumor cell implantation to confirm tumor presence, and again at day 40 to measure tumor size growth in control-treated animals and aTIGIT & aPD1 dual blockade-treated animals.…”