Targeted photoimmunotherapy based on photosensitizer-antibody conjugates for multiple myeloma treatment.

Despite the high in vitro efficacy of photodynamic therapeutics, lack of tumor targeting significantly reduces their in vivo efficacy and thus limits their clinical use. Photoimmunotherapy (PIT) is a new synthetic strategy to target and treat cancer by photodynamic therapy (PDT). In this study, we describe design and synthesis of a third-generation photosensitizer comprising a PEGylated-phthalocyanine star-polymer photosensitizer that covalently bound to a myeloma tumor-selective antibody (MAb) via the carbodiimide chemistry. The free photosensitizer demonstrated a minimum dark toxicity when tested in mammalian myeloma cell line (SP2/OR); and a moderate phototoxicity after irradiation with non thermal laser red light as a result of light-induced production of cytotoxic singlet oxygen species. Covalent attachment of the photosensitizer (Pc) to the MAb resulted in a significantly enhanced phototoxicity. This is mainly ascribed to the fact that internalization enhances phototoxicity of Pc-MAb bioconjugates. The radioactivated photoimmuno-conjugates 131I(PcMAb) demonstrated the highest phototoxicity to myeloma cells. The suggested bioconjugates are promising candidates as multiple therapeutic models for in vivo treatment of myeloma.