Hybrid Lipid Polymer Nanoparticles for Combined Chemo- and Photodynamic Therapy

Retinoblastoma is a malignant tumor of the retina in infants. Conventional therapies are associated to severe side effects and some of them induce secondary tumors. Photodynamic therapy (PDT) thus appears as a promising alternative as it is nonmutagenic and generates minimal side effects. The effectiveness of PDT requires the accumulation of a photosensitizer (PS) in the tumor. However, most porphyrins are hydrophobic and aggregate in aqueous medium. Their incorporation into a nanocarrier may improve their delivery to the cell cytoplasm. In this work, we designed biodegradable liponanoparticles (LNPs) consisting of a poly(d,l)-lactide (PDLLA) nanoparticle coated with a phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-3-trimethylammonium-propane) bilayer. An anticancer drug, beta-lapachone (β-Lap) and a PS, m-THPC, were co-encapsulated for combined chemo- and PDT because it has been suggested that they may have a synergistic effect based on the activation of β-Lap by PDT-induced over-expression of the enzyme NQO1. Using dynamic light scattering measurements, cryogenic transmission electron microscopy, and fluorescence confocal microscopy, we selected the appropriate conditions for the encapsulation of the compounds. LNPs were internalized in retinoblastoma cells within few hours. No obvious synergistic effect related to the activation of β-Lap by PDT was observed. Conversely, the LNPs were cytotoxic at lower doses of the two encapsulated compounds as compared to the single therapies. Analysis of the combinatorial treatment showed that PDT and chemotherapy had an additive effect on the viability of retinoblastoma cells.