Quantitative Imaging of Tumor-Associated Macrophages and Their Response to Therapy Using ⁶⁴Cu-Labeled Macrin

Abstract

Tumor associated macrophages (TAMs) are widely implicated in cancer progression, and TAM levels can influence drug responses, particularly to immunotherapy and nanomedicines. However, it has been difficult to quantify total TAM numbers and their dynamic spatiotemporal distribution in a non-invasive and translationally relevant manner. Here, we address this need by developing a pharmacokinetically optimized, 64Cu-labeled polyglucose nanoparticle (Macrin) for quantitative positron emission tomography (PET) imaging of macrophages in tumors. By combining PET with high resolution in vivo confocal microscopy and ex vivo imaging of optically cleared tissue, we found that Macrin was taken up by macrophages with >90% selectivity. Uptake correlated with the content of macrophages in both healthy tissue and tumors (R2 > 0.9), and showed striking heterogeneity in the TAM content of an orthotopic and immunocompetent mouse model of lung carcinoma. In a proof-of-principle application, we imaged Macrin to monitor the macrophage response to neo-adjuvant therapy, using a panel of chemotherapeutic and γ-irradiation regimens. Multiple treatments elicited 180–650% increase in TAMs. Imaging identified especially TAM-rich tumors thought to exhibit enhanced permeability and retention of nanotherapeutics. Indeed, these TAM-rich tumors accumulated >700% higher amounts of a model poly(D,L-lactic-co-glycolic acid)-b-polyethylene glycol (PLGA-PEG) therapeutic nanoparticle compared to TAM-deficient tumors, suggesting that imaging may guide patient selection into nanomedicine trials. In an orthotopic breast cancer model, chemoradiation enhanced TAM and Macrin accumulation in tumors, which corresponded to the improved delivery and efficacy of two model nanotherapies, PEGylated liposomal doxorubicin and a TAM-targeted nanoformulation of the toll-like receptor 7/8 agonist resiquimod (R848). Thus, Macrin imaging offers a selective and translational means to quantify TAMs and inform therapeutic decisions.

Single‐Cell Intravital Microscopy of Trastuzumab Quantifies Heterogeneous in vivo Kinetics

“…c and Supporting Information Fig. S6), where phagocytes including tumor‐associated macrophages are known to reside at high levels, especially in the HT1080 model used here . Indeed, high‐magnification images showed that most Tzm accumulated within phagocytes rather than tumor cells, regardless of HER2 expression (Fig.…”

Multimodal Precision Imaging of Pulmonary Nanoparticle Delivery in Mice: Dynamics of Application, Spatial Distribution, and Dosimetry

“…For instance, a combination of triple imaging techniques (i.e., dark‐field light microscopy, electron microscopy, and nanoscale secondary ion mass spectrometry) was used to study the NP interaction with green algae in the context of NP localization, internalization, and chemical identity . Also, quantitative imaging of co‐localization of tumor associated macrophages with therapeutic 64 Cu‐labeled polyglucose nanoparticle in an orthotopic model of lung adenocarcinoma was accomplished via PET, in vivo confocal microscopy, and tissue‐cleared LSFM . PCXI has already been applied for ex vivo and in vivo studies on mucociliary transport of large microparticles or 5–100 µm fibers in the trachea or upper airways of animal models such as mice and pigs and for monitoring the delivery of liquids to murine lungs via nose or intubated cannula delivery .…”

Understanding the In Vivo Fate of Advanced Materials by Imaging

“…By comparison, imaging extravascular macrophages in solid tumors required a longer circulating NP, thus a 20 nm sized Macrin was developed to maximize tissue penetration and macrophage uptake. [34] Concordantly, these NPs were labeled with Cu 64 (t ½ = 12.7 h). Materials have also been labeled for imaging with other modalities.…”

“…Certain fluorescently tagged NPs, such as the FDA-approved, carboxymethyldextran-coated iron oxide NP ferumoxytol, and a recently developed polyglucose NP Macrin, can be injected to label phagocytes, such as macrophages and neutrophils in the mouse. [34,163,164] On the other hand, cancer cells can be labeled with recently developed telomerase-specific spherical nucleic acid probes. [165] To improve the specificity of labeling, fluorescent antibodies targeting markers expressed on the cell-types of interest can also be used.…”