Synthesis and aggregation of a porphyrin cored hyperbranched polyglycidol and its application as a macromolecular photosensitizer for photodynamic therapy.

Macromolecules are potentially useful delivery systems for cancer drugs as their size allows them to utilize the enhanced permeability and retention effect (EPR), which facilitates selective delivery to (and retention within) tumors. In addition, macromolecular delivery systems can prolong circulation times as well as protecting and solubilizing toxic and hydrophobic drug moieties. Overall these properties and abilities can result in an enhanced therapeutic effect. Photodynamic therapy (PDT) combines the use of oxygen and a photosensitizer (PS), that become toxic upon light-irradiation. We proposed that a PS encapsulated within a water-soluble macromolecule could exploit the EPR effect and safely and selectively deliver the PS to a tumor. In this paper, we describe the synthesis of a porphyrin cored hyperbranched polymer that aggregated into larger micellar structures. DLS and TEM indicated that these aggregated structures had diameters of 45 nm and 20 nm for the solvated and non-solvated species respectively. The porphyrin cored HBP (PC-HBP), along with the non-encapsulated porphyrin (THPP), were screened against EJ bladder carcinoma cells in the dark and light. Both THPP and PC-HBP displayed good toxicity in the light, with LD50 concentrations of 0.5 μM and 1.7 μM respectively. However, in the dark, the non-incorporated porphyrin (THPP) displayed significant toxicity, generating an LD50 of 4 μM. On the other hand, no dark toxicity was observed for the polymer system (PC-HBP) at concentrations of 100 μM or less. As such, incorporation within the large polymer aggregate serves to eliminate dark toxicity, whilst maintaining excellent toxicity when irradiated.