Investigating In\nVivo Tumor Biomolecular Changes Following\nRadiation Therapy Using Raman Spectroscopy

Treatment resistance is a major bottleneck in the success\nof cancer\ntherapy. Early identification of the treatment response or lack thereof\nin patients can enable an earlier switch to alternative treatment\nstrategies that can enhance response rates. Here, Raman spectroscopy\nwas applied to monitor early tumor biomolecular changes in sensitive\n(UM-SCC-22B) and resistant (UM-SCC-47) head and neck tumor xenografts\nfor the first time in in vivo murine tumor models in response to radiation\ntherapy. We used a validated multivariate curve resolution-alternating\nleast-squares (MCR-ALS) model to resolve complex multicomponent Raman\nspectra into individual pure spectra and their respective contributions.\nWe observed a significant radiation-induced increase in the contributions\nof lipid-like species (<i>p</i> = 0.0291) in the radiation-sensitive\nUM-SCC-22B tumors at 48 h following radiation compared to the nonradiated\nbaseline (prior to commencing treatment). We also observed an increase\nin the contribution of collagen-like species in the radiation-resistant\nUM-SCC-47 tumors at 24 h following radiation compared to the nonradiated\nbaseline (<i>p</i> = 0.0125). In addition to the in vivo\nanalysis, we performed ex vivo confocal Raman microscopic imaging\nof frozen sections derived from the same tumors. A comparison of all\ncontrol and treated tumors revealed similar trends in the contributions\nof lipid-like and collagen-like species in both in vivo and ex vivo\nmeasurements; however, when evaluated as a function of time, longitudinal\ntrends in the scores of collagen-like and lipid-like components were\nnot consistent between the two data sets, likely due to sample numbers\nand differences in sampling depth at which information is obtained.\nNevertheless, this study demonstrates the potential of fiber-based\nRaman spectroscopy for identifying early tumor microenvironmental\nchanges in response to clinical doses of radiation therapy.