Imaging tumor-associated macrophages in head and neck squamous cell carcinoma using fluorine-19 MRI

In this project, we aim to translate a fluorine-19 (19F) MRI technology to visualize the tumor associated macrophage (TAM) burden in patients with recurrent head and neck squamous cell carcinoma (HNSCC). HNSCC is the sixth most common cancer worldwide. TAMs often comprise a significant volume fraction of tumor

mass, and a high TAM burden in the tumor microenvironment is associated with poor therapeutic prognosis. In HNSCC patients developing locoregionally recurrent or metastatic disease, anti-PD-1 antibody checkpoint inhibitor therapy is currently the standard of care, however, the response rates remain poor (~20%). TAMs have

been associated with immunosuppression and T-cell exclusion, which are associated with a low response rate to checkpoint inhibitors. Thus, there is an urgent need for biomarker probes that can non-invasively monitor TAMs in clinical trials to help stratify patients and rationally optimize therapeutic strategies. Towards this goal,

we propose translating a fast-clearing perfluorocarbon (PFC) nanoemulsion as a 19F MRI tracer to assay TAMs in vivo. Following intravenous injection, the size and morphology of nonbiologic PFC nanoemulsion droplets make them susceptible to endocytosis by phagocytic immune cells, particularly macrophages. The in situ labeled

cells accumulate at inflammatory lesions, and the resulting 19F MRI hot-spots can be quantified, where the signal is linearly proportional to the macrophage burden. In situ PFC macrophage labeling has been used in a multitude of preclinical inflammation models, including in the context of TAMs. However, no injectable, clinical PFC

nanoemulsion imaging agent product exists despite the proven specificity and safety of these compositions. Building on this work, the proposal has three Specific Aims: Aim 1. Perfluorocarbon NE formulation. This aim will identify a lead formulation and collaborate with a contract manufacturing organization to produce a novel

nanoemulsion composition (“TAM-Sense”) at liter scale suitable for a Phase 1 trial. Aim 2. Safety, pharmacokinetics, biodistribution and genotoxicity studies. We will perform in vivo GLP studies of TAM-Sense in two animal species to evaluate pharmacotoxicology and clearance profiles following intravenous injection, as

well as in vitro genotoxicity assays. Aim 3. Clinical studies. We will conduct a pilot clinical trial (N=12 total) to image TAMs in recurrent HNSCC patients at UC San Diego prior to treatment with anti-PD-1 antibodies. The endpoints will include (i) safety and (ii) assessment of apparent ‘TAM burden’ biomarker (i.e., F-atoms/tumor

volume) via 19F MRI hot-spot quantitation at tumor mass. We will explore the predictive strength of the 19F MRI findings versus PD-L1 and CD68 (macrophage) immunostaining of biopsies in the same patients. Moreover, we will perform exploratory analyses correlating TAM burden to clinical outcomes, including 6-month progression-

free survival (PFS) and objective response rate (ORR). This pilot study will generate important safety and proof- of-concept biomarker data needed to support and adequately power a more definitive future trial.