meso-Substituted AB3-type phenothiazinyl porphyrins and their indium and zinc complexes photosensitising properties, cytotoxicity and phototoxicity on ovarian cancer cells

Abstract

New meso-substituted AB₃-type phenothiazinyl porphyrins and ferrocenylvinyl phenothiazinyl porphyrin were synthesised by Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions, respectively. The free porphyrins were further used in the synthesis of new indium(III) or zinc(II) porphyrin complexes. All porphyrins exhibit red fluorescence emission in solution, a property that remains unimpaired following internalisation in ovarian A2780 cancer cells, as evidenced by fluorescence microscopy images. The In(III) phenothiazinyl porphyrin complexes show a higher quantum yield of fluorescence emission (2aΦ_F = 30%, 4aΦ_F = 29%, 5aΦ_F = 28%) compared to the free base porphyrin precursors, or Zn(II) complex 4b (Φ_F = 10%). The potential of novel phenothiazinyl porphyrins to act as photosensitisers was evaluated using two distinct approaches. The first was through the measurement of the singlet oxygen quantum yield Φ_Δ(¹O₂), while the second employed in vitro measurements of metabolic activity, oxidative stress, nuclear factor-erythroid 2 related factor 2 (Nrf-2) activation and tumour necrosis factor-alpha (TNF-α) under both dark and light irradiation conditions. As reflected by the IC₅₀ values, the most potent cytotoxicity of the phenothiazinyl porphyrins against the A2780 cells was observed for In(III) ferrocenylvinyl phenothiazinyl porphyrin 4a (36.38 μM), the remaining compounds are less cytotoxic. The reduction in metabolic activity was observed in A2780 ovarian tumour cells treated with 4a and 6a and exposed to light compared to treatment in the absence of light. The oxidative stress, TNF-α and Nrf-2 transcription factor were particularly notable when A2780 cells were treated with 4a and subsequently photoirradiated, the oxidative stress was linked to the highest value of Φ_Δ(¹O₂) recorded for 4a (60%).