Abstract
Brain cancers include primary tumours, such as Glioblastoma, and secondary tumours, known as brain metastases. Glioblastoma is the most common primary brain cancer. While around 10% of cancer patients are diagnosed with brain metastases during illness, autopsy studies suggest the incidence may reach 40-75%, underscoring substantial underdiagnosis. The incidence of both glioblastoma and brain metastases continues to rise.
Current treatments include surgical resection when feasible, followed by radiotherapy and chemotherapy, but prognosis remains poor, with these treatments being largely non-curative. Imaging is crucial for diagnosis and management, with gadolinium-based contrast agents considered the clinical standard for magnetic resonance imaging (MRI). However, gadolinium is contraindicated in patients with renal impairment or allergy, prompting interest in alternatives. Ferumoxytol, an ultrasmall superparamagnetic iron oxide nanoparticle originally developed for iron-deficiency anaemia, has emerged as a promising substitute. Ferumoxytol is phagocytosed by macrophages, crosses the blood-brain barrier, and provides high-resolution contrast, making it well-suited for brain tumour imaging. It is currently being trialled at Dunedin Hospital as an alternative to gadolinium and may better identify tumours with high tumour-associated macrophage (TAM) content. A pilot clinical trial suggested improved survival in patients with high-TAM tumours who received ferumoxytol.
This project sought to determine if ferumoxytol retention in tissue correlates with TAMs and to optimise immunostaining for proteins associated with iron metabolism and macrophage content, for future development of an assay to investigate iron-related markers in brain tumours. Twenty-one ferumoxytol-administered brain tumour samples from the main clinical trial were assessed. Ferumoxytol was detected using Perl’s Prussian blue stain, and macrophages were identified with a CD163 antibody. Additional antibodies targeting transferrin receptor (TFRC), glutathione peroxidase 4 (GPX4), and toll-like receptor 4 (TLR4) were applied. Ferumoxytol was identified in some tumours, with CD163 staining correlating with higher iron deposition in most cases. Immunohistochemistry was optimised for TFRC, GPX4, and TLR4, showing positive and heterogeneous staining. Attempts to establish a multiplex immunofluorescence panel were unsuccessful and remain a future goal.
These findings suggest a link between ferumoxytol-iron accumulation and macrophage infiltration and show that iron-related proteins differ across tumours. Ongoing work will develop an iron-related protein immunostaining assay to assess protein distribution across brain tumours for correlation with ferumoxytol uptake, TAM content, and patient survival. Additional work is investigating if iron metabolism, TAM biology, and oncogene expression affect brain tumours following ferumoxytol administration, highlighting its potential not only as an imaging agent but as a candidate therapeutic adjunct.