Cobalt(III) dibromo-BODIPY-8-hydroxyquinolinate for mitochondria-targeted red light photodynamic therapy

Abstract

The photophysical properties of boron-dipyrromethene (BODIPY) dyes have made them suitable for cellular imaging and photodynamic therapy (PDT). The efficacy of these dyes can be augmented by designing their dibromo/diiodo derivatives. Heteroleptic Co(III) complexes of a tetradentate N,N,N,O-donor polypyridyl phenolate (HL) and bidentate N,O-donor 8-hydroxyquinoline (HL1) and its BODIPY (HL2) or dibromo-BODIPY (HL3) pendants, [CoIII(L)(L1−3)]X (1–3) (where X = ClO4 for 1, 2 and Cl for 3) were synthesized and studied. The dibromo-BODIPY ligand HL3 was structurally characterized. The dibromo-BODIPY complex 3, showing singlet oxygen quantum yield (ϕΔ) value of ∼0.25, displayed remarkable apoptotic photo-cytotoxicity in HeLa cancer cells upon red light (600–720 nm) irradiation giving half-maximal inhibitory concentration (IC50) value of 0.36 μM (photocytotoxicity index: >277). It was less toxic in normal cells. Cellular imaging studies revealed mitochondrial colocalization. This work exemplifies Co(III)–dibromo-BODIPY complex as a new class of metal-based PDT agent with higher efficacy than the dyes alone.