Selective Cytotoxicity in Chronic Myeloid Leukemia (K-562) Cells Induced by 532 nm LASER Irradiation Without Exogenous Photosensitizers

<b>Background and Objectives:</b> The treatment of Chronic Myeloid Leukemia (CML) faces challenges such as resistance to Tyrosine Kinase Inhibitors (TKIs), necessitating new adjuvant therapies. This study aimed to evaluate the cytotoxic effect of direct, photosensitizer-free irradiation with LASER and LED light on the CML cell line K-562, hypothesizing that LASER light at a specific wavelength would be selectively effective. This work serves as a foundational in vitro study to establish the basis for a potential ex vivo therapeutic strategy. <b>Methods:</b> The human CML cell line K-562 was irradiated with LASER (405, 532, 629 nm) and LED (457, 517, 630 nm) sources at energy doses from 1 to 10 J/cm². Cell viability was assessed 24 h post-irradiation using Trypan Blue exclusion, the MTT assay, and biophysical changes in the cell absorbance spectrum. <b>Results:</b> Irradiation with a 532 nm LASER was the only condition that induced massive, statistically significant, and dose-dependent cytotoxicity, reaching up to 67.8% cell death at 10 J/cm² (<i>p</i> < 0.05). In contrast, other LASER wavelengths and all tested LED wavelengths failed to produce a significant cytotoxic effect. The superiority of the LASER over the LED of a similar wavelength highlights the critical role of the physical properties of light. <b>Conclusions:</b> Direct, photosensitizer-free irradiation with 532 nm LASER light is a potent and selective method for inducing cytotoxicity in K-562 cells in vitro. This effect is critically dependent on both the specific wavelength and the optical properties of the light source. These findings establish a solid foundation for the development of new ex vivo adjuvant therapies, such as extracorporeal photopheresis, for CML, pending further validation of its mechanism and selectivity.