AN Ir-PNA BIOCONJUGATE FOR 1O2 PRODUCTION IN PDT: TOWARD A POTENTIAL DUAL THERAPEUTIC AGENT

A novel PNA-Ir(III) complex bioconjugate was prepared by linking covalently a Peptide Nucleic Acid (PNA) sequence with a luminescent Ir(III) cyclometalled complex, aiming to obtain a potential dual therapeutic agent that could exploit the 1O2 generated by the Ir complex in Photodynamic Therapy (PDT), and the antisense strategy promoted by a specific PNA chain due to its potentiality as a carrier to deliver PNA inside the cells and to overcome the issues of PNA alone. In this first work, we focused on the preparation of the conjugate and its use as a photosensitizer for PDT. Type II PDT consists of the production of the highly reactive and toxic 1O2 through an energy transfer between molecular oxygen and a photosensitizing molecule when the system is irradiated with a proper light source. The conjugation was carried out following two strategies, one of which involved the formation of a novel Ir complex bearing a terminal carboxylic group (Ir-COOH). The Ir-PNA conjugate presented only slight differences in the photophysical properties compared to the Ir-COOH complex. The 1O2 production by both Ir-COOH and Ir-PNA was first measured in cuvette, showing a higher efficiency when the PNA chain is present (Φ=0.54). A consequent in vitro viability experiment on Hela cells revealed the photocytotoxicity of Ir-PNA, nontoxic in the dark, when irradiated with UV light (EC50 = 18 μM), while for Ir-COOH a certain toxicity is measured also in the dark (Figure 1). Lastly, the uptake of the two compounds by Hela cells was followed with two-photons absorption (TPA) microscopy, showing that Ir-PNA aggregates in both the cytoplasm and the nucleus and presents a higher uptake than Ir-COOH alone, also opening the possibility in further studies to exploit TPA for PDT to avoid the issues linked to the use of UV light.