Spectroscopic Insights into the Localization and Photodynamic Efficacy of Aluminum Tetrasulfonated Phthalocyanine for Colorectal Cancer Therapy

This article explores the potential of aluminum tetrasulfonated phthalocyanine (AlPcS₄) as a photosensitizer for photodynamic therapy (PDT) in colorectal cancer (CRC), utilizing Raman imaging, steady-state absorption and fluorescence spectroscopy in UV-Vis spectral region, and transient absorption spectroscopy. Our study demonstrates that in human colon cancer cells, the administered photosensitizer preferentially localizes to the endoplasmic reticulum and lipid droplets, mirroring its distribution in normal cells. Furthermore, the addition of DTAC significantly enhances the permeability of cell membranes to AlPcS₄, leading to an increased intracellular concentration of the photosensitizer, as evidenced by the elevated fluorescence intensity around 679 nm, even after just 30 min of incubation. Photochemical property assessments of AlPcS₄ in both cellular and cell-free environments indicate only minimal interaction with cells. The differences observed in absorption and fluorescence spectra, as well as in the singlet excited state lifetime of AlPcS₄ in the presence of cells, are negligible compared to those measured in a neat buffer solution. However, the extended triplet-state lifetime observed with both Caco-2 and CCD-18Co cells (460 μs) versus buffer alone (407 μs) provides clear evidence of interaction between AlPcS₄ and the cells.