Smart Macrocycles: Cyclodextrin−Porphyrin Photosensitizers for Photodynamic Therapy in Human Bladder Cancer Cells

Urothelial carcinoma of the bladder is one of the most common malignancies of the urinary tract. It remains a therapeutic challenge due to its high recurrence rate and resistance to conventional treatments. Photodynamic therapy (PDT) is an attractive, minimally invasive alternative that enables spatially controlled tumor ablation by activating photosensitizers (PS) with visible light, generating reactive oxygen species (ROS), mainly singlet oxygen (¹O₂), and inducing the targeted death of tumor cancer cells. However, due to poor aqueous solubility and aggregation of porphyrin-based PS, their clinical application is often limited. In this study, we report the biological evaluation of three thiopyridinium porphyrin-cyclodextrin conjugates (Por-CD <b>1a-3a</b>) designed to enhance solubility and cellular delivery while preserving photodynamic activity. In the UM-UC-3 human bladder cancer cell line, we demonstrate that these conjugates exhibit distinct cellular uptake kinetics. PS <b>1a</b> was rapidly internalized, reaching early saturation within 2 h; PS <b>2a</b> displayed a gradual and sustained accumulation up to 4 h; and PS <b>3a</b> demonstrated significant uptake within 30-60 min followed by stabilization. None of the compounds induced significant cytotoxicity in the absence of light at concentrations of 5 or 10 μM, confirming their dark safety profile. After light irradiation, PS <b>1a-3a</b> produced strong PDT effect, with cytotoxicity profiles directly linked to their absorption properties. PS <b>1a</b> showed rapid and stable phototoxicity, PS <b>2a</b> exhibited a slower cytotoxic response, and PS <b>3a</b> caused intense early phototoxicity even after short incubation periods. These findings indicate that Por-CD conjugates possess favorable cellular internalization and strong PDT efficacy. The three derivatives emerge as promising candidates for optimizing PDT strategies targeting bladder cancer cells.