Abstract

Recently, anticancer treatments were discovered to induce cell senescence other than death, a critical phenotype driving tumor recurrence. This calls for the development of safe, precise, and rapid tools to reveal critical therapy-induced senescence (TIS). Here, we present label-free multimodal nonlinear optical (NLO) microscopy as a powerful technique to spot early TIS. We home-built a microscope including different NLO modalities: Stimulated Raman Scattering (SRS), forward and epi-detected Coherent Anti-Stokes Raman Scattering (CARS and E-CARS), and Two-Photon Excited Fluorescence (TPEF). The infrared laser source outputs synchronized narrowband 780 nm pump pulses and 950-1050 nm tunable Stokes pulses, so to match the CH-stretching region of the Raman spectrum. Thanks to the co-registration of these NLO signals from label-free TIS cells and controls, we unveiled quantitative all-optical traits of early-stage TIS, monitored over 72 hours of treatment. TPEF from metabolic coenzymes combined with E-CARS from cardiolipin and cytochrome C indicated an shrinking of mitochondrial networks. CARS and SRS revealed lipid vesicles accumulation in cytoplasms. Nuclei enlarged irregularly, visualized via subtraction of SRS signals of proteins and lipids, and CARS from deoxyribose. We believe our results will strongly influence anticancer pre-clinical studies and translated clinical applications, constituting a quick, non-invasive, and accurate aid to expose TIS manifestation in tumors.

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