Understanding the Photodynamic Behavior of Red Emitting Re(I)dipyrrinates in Triple-Negative Breast Cancer Cells

The Re-(I)-dipyrrinates complexes having oligo ethylene glycol (OEG) and thioglucose/thiogalactose sugars at the C-8 position are explored for anticancer applications. The X-ray crystal structure of Re-(I)-dipyrrinate having a thiogalactose sugar revealed distorted octrahedral geometry of the central metal. The Re-(I)-dipyrrinates showed red emission (600-900 nm) with noticeably large Stokes shifts (∼5890-6800 cm^-1), a highly desirable property for bioimaging application. The Re-(I)-dipyrrinates were found to be nontoxic in dark conditions on triple negative breast cancer cells (TNBC), whereas Re-(I)-dipyrrinate with OEG group and thioglucose sugar displayed excellent phototoxicity in TNBC with IC₅₀ values of 2.6 and 1.5 μM, respectively. The Re-(I)-dipyrrinate with OEG group displayed preferential colocalization in the lipid droplets and caused lipid peroxidation after light exposure. Additionally, all Re-(I)-dipyrrinates were nontoxic to the normal retinal pigment epithelial cells (RPE-1) both in the dark and under light irradiation, reflecting suitable behavior as the anticancer agents for photodynamic therapy.