TY - JOUR T1 - An <sup>89</sup>Zr-HDL PET Tracer Monitors Response to a CSF1R Inhibitor JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 433 LP - 436 DO - 10.2967/jnumed.119.230466 VL - 61 IS - 3 AU - Christian A. Mason AU - Susanne Kossatz AU - Lukas M. Carter AU - Giacomo Pirovano AU - Christian Brand AU - Navjot Guru AU - Carlos Pérez-Medina AU - Jason S. Lewis AU - Willem J.M. Mulder AU - Thomas Reiner Y1 - 2020/03/01 UR - http://jnm.snmjournals.org/content/61/3/433.abstract N2 - The immune function within the tumor microenvironment has become a prominent therapeutic target, with tumor-associated macrophages (TAMs) playing a critical role in immune suppression. We propose an 89Zr-labeled high-density lipoprotein (89Zr-HDL) nanotracer as a means of monitoring response to immunotherapy. Methods: Female MMTV-PyMT mice were treated with pexidartinib, a colony-stimulating factor 1 receptor (CSF1R) inhibitor, to reduce TAM density. The accumulation of 89Zr-HDL within the tumor was assessed using PET/CT imaging and autoradiography, whereas TAM burden was determined using immunofluorescence. Results: A significant reduction in 89Zr-HDL accumulation was observed in PET/CT images, with 2.9% ± 0.3% and 3.7% ± 0.2% injected dose/g for the pexidartinib- and vehicle-treated mice, respectively. This reduction was corroborated ex vivo and correlated with decreased TAM density. Conclusion: These results support the potential use of 89Zr-HDL nanoparticles as a PET tracer to quickly monitor the response to CSF1R inhibitors and other therapeutic strategies targeting TAMs. ER -