Evaluation of photothermal therapy and optical clearing agents in the treatment of cutaneous melanoma - murine study

• Ano de defesa: 2024
• Autor(a) principal: Martinelli, Letícia Palombo
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Agentes clareadores ópticos; Melanoma; Optical clearing agents; Photothermal therapy; Terapia fototérmica
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/76/76133/tde-25112024-091218/

Melanoma is the most aggressive type of skin cancer and constitutes a significant public health concern due to its increasing incidence and the limited response to currently available therapeutic options. Despite its low incidence, melanoma exhibits high mortality rates. The standard treatment remains surgical resection. Radiotherapy, chemotherapy, and immunotherapy are employed predominantly as palliative treatments. Therefore, there is an urgent need to develop new therapeutic approaches. Photothermal therapy (PTT) has emerged as a promising technique based on the use of a compound known as a photosensitizer (PS) and the application of light at an appropriate wavelength for its activation. Upon absorbing energy from light, the PS transitions to an excited state and, upon returning to the ground state, releases heat. In the case of cutaneous melanoma, the high concentration of melaninone of the primary biological absorbersconstitutes a significant barrier, as therapies utilizing light in the visible spectrum exhibit limited responses due to poor light penetration into the tumor. Optical clearing agents (OCAs) have been employed to minimize light attenuation in tissues. Our strategy involves establishing an effective protocol for treating cutaneous melanoma in an animal model by utilizing PTT in conjunction with optical clearing. Through Optical Coherence Tomography (OCT), it was possible to determine the attenuation coefficient of melanoma after the application of OCAs and in normal skin, observing a reduction of up to 43% in the tumor. This indicates that the clearing agents enhance light penetration in pigmented tumors. Optical properties were also analyzed using diffuse reflectance, revealing high heterogeneity in the tumors and intense tissue vascularization. Overall, a decrease in reflectance between 450 and 600 nm was observed. In the in vivo experiments, the most effective protocol for PTT was identified as an irradiance of 0.5 W/cm2, 10 minutes of irradiation with an 808 nm laser, and a Nano-dICG concentration of 200 M for intratumoral administration. Additional tests were conducted on both more and less pigmented tumors, with and without the application of OCAs. The experimental group that exhibited the highest survival rate consisted of the more pigmented cells without OCA application, achieving complete lesion treatment in 30% of the cases within this group. Unexpectedly, the group that received OCAs prior to the administration of the nanoemulsion showed a greater temperature increase, but the treatment was less effective. In the group where OCA was applied after Nano-dICG, the temperature variation was significantly lower. This led to photostability tests, which demonstrated that OCAs react with the nanoemulsion, increasing its size, rendering it unstable, and causing its disaggregation, thereby reducing its photothermal effect. Finally, utilizing photoacoustic and bioluminescence techniques, PTT was performed with intravenous application of Nano-dICG in both immunodeficient and immunocompetent animals. In the former, a 75% survival rate was observed in mice over 30 days, while in the latter, a 100% survival rate was achieved one hour after intravenous injection of the molecule. B16F10 cells were injected into the caudal vein of immunocompetent animals with treated primary lesions to assess the development of metastasis, and no metastasis was observed in any of the cases.