Therapy-induced senescent (TIS) cells are cancer cells that become resistant to therapies and enter a dormant stage. These cells can emerge from dormancy and induce tumor resistance and relapse. To provide insight into how TIS cells evolve, it is crucial to develop simple, reproducible methods to study the onset and progression of these cells in human cancer cell cultures. An international team from Johns Hopkins University and Italy’s Politecnico di Milano, Fondazione Istituto Nazionale dei Tumori, and Consiglio Nazionale delle Ricerche developed a noninvasive, multimodal imaging technique to allow early identification of TIS cells. The new technique could improve clinical outcomes by enabling more comprehensive research into treatment resistance in cancer cells. The all-optical, label-free, quantitative microscopy technique combines three complementary microscopy methods: coherent Raman scattering, multiphoton absorption, and optical diffraction tomography, an interferometry technique. Ishan Barman, associate professor of mechanical engineering at Johns Hopkins Whiting School of Engineering. Courtesy of Will Kirk/Johns Hopkins University. Using multimodal vibrational and multiphoton microscopy, coupled with interferometric phase imaging, the researchers were able to observe and characterize the chemical and morphological traits of TIS across early to late stages in human cancer cells. “It’s important to note that we conducted these observations without the use of invasive labels, ensuring that the cells’ natural states were preserved,” said Dario Polli, physics professor at Politecnico di Milano. The researchers observed the cells’ shape, structure, and physical and chemical characteristics throughout their lifecycle. Through quantitative profiling of the cells’ biochemical and morphological features, they obtained a comprehensive description of TIS, including mitochondrial network rearrangement, lipid overproduction, cell flattening, and cell enlargement. Using the multimodal imaging technique, the researchers were able to determine the onset timeline of the hallmarks of TIS, identifying TIS manifestations as early as 24 hours following treatment, followed by the accumulation of lipid vesicles starting at 72 hours. The TIS markers were visible via nonlinear optical microscopy and quantitative phase imaging. The quantitative findings of the team agreed with qualitative senescence markers that were previously identified via standard, slow, invasive techniques. The multimodal imaging technique could offer a rapid, safe, accurate way to detect initial TIS manifestations within human tumoral cultures, advancing research that could lead to new therapies for treatment-resistant cancers. “Our work demonstrates the potential to transform anticancer treatment research,” Johns Hopkins professor Ishan Barman said. “Integrating these microscopy methods could help clinicians make more informed, timely treatment decisions.” The multimodal microscopy technique could also be used in preclinical testing of patient-derived cancer cell cultures. Even with a limited amount of cancer cells from patients, it would be possible to quantitatively assess the efficacy of a proposed treatment using the fast, high-content quantitative microscopy technique directly on nonperturbed samples. The researchers believe that their new, rapid-live screening microscopy technique holds significant promise for the future of cancer studies. “While further research is needed, our results suggest label-free microscopy could become a vital tool to boost treatment efficacy and prevent tumor recurrence by detecting TIS cells early,” Politecnico di Milano researcher Italia Bongarzone said. “This would allow clinicians to adjust therapeutic strategies before drug-induced senescence enables cancer to develop resistance.” The research was published in Science Advances (www.science.org/doi/10.1126/sciadv.adg6231).