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Gliomas are malignant tumors that originate in the central nervous system (CNS). Any tumor that forms in glial cells, or in supporting tissue of the brain is called a glioma. Glioblastoma (GBM) is a subtype of glioma that tends to grow rapidly, spread to other tissues, and has a poor prognosis. GBM is the most aggressive and the most common adult primary intracranial neoplasm (Delgado-Martín & Medina, 2020; Louis et al., 2016). GBM is more common in people ages 50 to 70 and is more prevalent in men than women (Louis et al., 2016). The symptoms or signs of the presence of this type of tumor are: increased pressure on the brain, headaches, seizures, memory loss, and behavioral changes (Sizoo et al., 2010). GBM was previously known as glioblastoma multiforme and the term "multiform" refers to the tumor heterogeneity (Sturm et al., 2014). GBMs may have originated from different kinds of cells, such as astrocytes and oligodendrocytes. The histological features that distinguish GBM from all the other gliomas are the presence of necrosis (dead cells) and the increase in blood vessels around the tumor (D'Alessio et al., 2019). The World Health

Current studies in photodynamic therapy (PDT) against cancer are focused on the development of new photosensitizers (PSs), with higher phototoxic action. The aim of this study was to compare the therapeutic efficiency of tri-cationic meso-substituted porphyrin derivatives (Tri-Py + -Me-PF, Tri-Py + -Me-Ph, Tri-Py + -Me-CO 2 Me and Tri-Py + -Me-CO 2 H) with the well-known tetra-cationic T 4 PM. The phototoxic action of these derivatives was assessed in human colon adenocarcinoma cells by cell viability, intracellular localization and nuclear morphology analysis. In the experimental conditions used we determined that after light activation -PF, -Ph and -CO 2 Me cause a more significant decline of cell viability compared to -CO 2 H and T 4 PM. These results suggest that the nature of the peripheral substituent influences the extent of cell photodamage. Moreover, we have demonstrated that PS concentration, physicochemical properties and further light activation determine the PDT response. All porphyrins were clearly localized as a punctuated pattern in the cytoplasm of the cells, and the PDT scheme resulted in apoptotic cell death after 3 h post-PDT. The tri-cationic porphyrin derivatives Tri-Py + -Me-PF, Tri-Py + -Me-Ph and Tri-Py + -Me-CO 2 Me showed a promising ability, making them good photosensitizer candidates for oncological PDT.

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