ABSTRACT
Light of different wavelengths can be used to obtain a more profitable outcome of photodynamic therapy (PDT), according to the absorption bands of the photosensitizer (PS). Low-grade cervical intraepithelial neoplasias (CINs) are superficial lesions that can be treated with light of shorter wavelength than red because a large light penetration depth in tissue is not necessary. We report a comparative investigation performed to evaluate the efficacy of light-emitting diodes (LEDs) of different wavelengths in the photodynamic treatment applied to both 2D and 3D HeLa cell spheroid cultures. The spheroids are utilized as a PDT dosage model, and cell viability is evaluated at different sections of the spheroids by confocal microscopy. Cells incubated with m-tetrahydroxyphenyl chlorin are illuminated with LED systems working in the low fluence range, emitting in the violet (390-415 nm), blue (440-470 nm), red (620-645 nm) and deep red (640-670 nm) regions of the light spectrum at various exposures times (t I) comprised between 0.5 and 30 min. PDT experiments performed on both 2D and 3D cell cultures indicate that the PDT treatment outcome is more efficient with violet light followed by red light. Dynamic data from the front displacement velocity of large 2D-quasi-radial colonies generated from cell spheroids adhered to the Petri dish bottom as well as the evolution of the 3D growth give further insight about the effect of PDT at each condition. Results from 3D cultures indicate that the penetration of the violet light is appropriate to kill HeLa cells several layers below, showing cell damage and death not only in the outer rim of the illuminated spheroids, where a PS accumulation exists, but also in the more internal region. Results indicate that violet LED light could be useful to treat CINs involving superficial dysplasia.