Comparison of methods for in vivo and ex vivo quantification of iron in murine brain tumors.

BACKGROUND: Iron is a redox-active biological trace element with concentration-dependent effects on human health and disease. This study evaluated multiple methods to quantify iron oxide nanoparticles for potential theragnostic applications in brain cancer. METHODS: Iron quantification protocols were developed for magnetic resonance imaging (MRI), x-ray fluorescence spectroscopy (XRF), UV-visible spectroscopy (UV-Vis), and inductively coupled plasma mass spectrometry (ICP-MS). The techniques were evaluated in cell culture models and murine brain tumors treated with the iron oxide nanoparticle ferumoxytol. All methods were assessed for correlation between administered ferumoxytol dose and iron measurement as well as agreement with the ICP-MS gold standard. RESULTS: In vivo MRI T2* and XRF iron measurements correlated with administered ferumoxytol dose (T2*: ρ = -0.64, p = 0.0034; XRF: ρ = 0.97, p = 2 x 10-15) and ex vivo ICP-MS results (T2*: ρ = -0.69, p = 0.012; XRF: ρ = 0.91, p < 2.2 x 10-16) with stronger, more significant correlations emerging for XRF than MRI T2*. However, unlike MRI, XRF cannot identify the spatial distribution of iron deposits. The developed UV-Vis protocol quantified iron in cell culture samples but failed in ex vivo brain tumor tissue. CONCLUSION: The successful in vivo and ex vivo quantification of tumor iron accumulation indicates that these methods are relevant in preclinical and clinical settings involving diagnosis and treatment of various human diseases. This work establishes a clear framework for choosing the ideal method based on iron concentration, equipment, budget, and sample identity.