Label-free streamlined photoacoustic image guidance facilitates NIR-II photoablation in models of melanoma lung metastases

Integrative multiscale imaging bridges the gap between macroscopic organ structures and microscopic cellular processes, enabling holistic visualization of anatomy and function across scales. Photoacoustic imaging (PAI) leverages melanin's potent contrast for label-free melanoma detection, yet its potential in lung imaging, challenged by air-tissue acoustic impedance mismatch, remains unexplored for melanoma lung metastases (MLMs). We used hierarchical multiscale PAI, transitioning from whole-body macroscale to localized mesoscale and single-cell-resolution microscale. PAI also guided photoablation interventions in the first and second near-infrared windows, requiring only 10.4 pg intracellular melanin/cell. Bioinformatic analysis of human MLM tissues revealed perturbed signaling pathways compared with normal skin and lung tissues, accounting for dysfunctional melanogenesis to enable label-free PAI with high sensitivity and specificity. Malignant MLM lesions in living mice, resected mouse lungs, and human lungs were delineated with margins closely conforming to histology. The high sensitivity allowed visualization of low-cellularity microsatellite foci down to a few tens of cell clusters, with sufficient penetration in the lungs of mice and Bama minipigs. The multiscale imaging methodology streamlines a theranostic workflow and specifically identifies MLM burden in a progressive, label-free manner, which may aid real-time tumor ablation in the future.