Purpose or Case Report: The incidence of head and neck malignancies among children has increased substantially in the last five decades. The immunosuppressive tumor micro-environment (TME) represents a major roadblock in the treatment of head and neck tumors. We have demonstrated previously that an elevated level of myeloid derived suppressor cells (MDSC) in the tumor correlates directly with a poor prognosis, and that MDSC levels can be reduced using inhibitors of inducible nitric oxide synthase (iNOS). In this pre-clinical study, we utilized non-contrast magnetic resonance imaging (MRI) and nanoparticle contrast-enhanced computed tomography (CECT) to monitor tumor responses to TME-directed combinatorial therapies that included iNOS inhibition, immunomodulation, checkpoint inhibition, and radiation.
Methods & Materials: In vivo studies were performed in syngeneic mouse models of HPV- and HPV+ squamous cell carcinoma. Animals were treated with CRT (cyclophosphamide + fractionated radiation), an immune checkpoint inhibitor (anti-PD1), and TME modulating nitric oxide synthase (NOS) inhibitors. Non-contrast T2-weighted (T2w) MRI was performed for longitudinal monitoring of disease progression. High-resolution CT angiography and delayed CECT was performed using a blood-pool nanoparticle contrast agent to image tumor vasculature, vessel leakiness, tumor vessel cooption and distant metastatic spread. Treatment response was evaluated using RECIST criteria.
Results: Non-contrast MRI enabled quantitative 3D analysis of changes in primary tumor volume. Nanoparticle delivery of the broad spectrum NOS inhibitor L-NAME resulted in the best treatment outcome [29% complete response (CR), 57% partial response (PR), 0% stable disease (SD) and 14% progressive disease (PD)] compared to control treatments [0% CR, 64% PR, 7% SD and 29% PD] in HPV+ tumors. HPV+ tumors demonstrated better treatment outcomes compared to HPV- tumors. Whole-body multi-modal imaging (MRI and CECT) enabled spatio-temporal quantitative analysis of metastatic disease progression to draining and distant lymph nodes. Metastatic spread to lungs and abdominal region was also observed.
Conclusions: Our work highlights the utility of advanced imaging for in vivo whole-body longitudinal monitoring of treatment response to multimodal TME-directed therapies in pre-clinical testing. Nanoparticle delivered broad-spectrum NOS inhibition provides the best TME modulation treatment on a background of CRT + anti-PD1.