X-Band Electron Paramagnetic Resonance For Monitoring Of Melanin-Associated Radical Changes In Zebrafish Melanoma Xenografts In Vivo.

This protocol presents a novel in vivo application of X-band (9.5 GHz) electron paramagnetic resonance spectroscopy for monitoring melanin-associated radical dynamics in zebrafish (Danio rerio) melanoma xenograft models. The goal of this method is to enable direct, label-free, and quantitative assessment of melanin-associated redox changes during embryonic development, and tumor-host interactions in a physiologically relevant vertebrate model. By leveraging the intrinsic paramagnetic properties of melanin, this approach provides complementary biochemical information that cannot be obtained using conventional fluorescence-based imaging alone. Importantly, the detected electron paramagnetic resonance signal reflects the redox-active fraction of the melanin polymer and therefore serves as a redox-sensitive readout rather than a direct measure of total pigment abundance. Method performance was validated through selective detection of melanin-associated radicals in pigmented wild-type embryos, absence of signal in albino controls, statistically significant developmental changes in normalized electron paramagnetic resonance signal across independent biological replicates, and comparable results obtained using alternative sample holders and frozen samples. By combining X-band electron paramagnetic resonance spectroscopy with zebrafish xenograft models, this protocol provides a scalable, ethically favorable, and transferable platform for preclinical melanoma research, redox biology studies, and evaluation of melanogenesis-modulating interventions.