Heterosubstituted Derivatives of PtPFPP for O₂ Sensing and Cell Analysis: Structure-Activity Relationships

Biological applications of phosphorescent probes for sensing molecular oxygen (O₂) and bioimaging have gained popularity, but their choice is rather limited. We describe a family of new heterosubstituted phosphorescent bioprobes based on the Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) dye. The probes are produced by simple click modification of its para-fluorine atoms with thiols, such as 1/2-thio-glucose, thio-poly(ethylene glycol) (PEG), or cysteamine. The probes were designed to have one cell-targeting moiety and three polar moieties forming a hydrophilic shell. Their chemical synthesis and purification were optimized to produce high reaction yields and easy scale-up. The ability to perform as cell-permeable or -impermeable probes was tuned by the polarity and molecular charge of the bioconjugate. The new PtPFPP derivatives were characterized for their spectral properties and cell-penetrating ability in the experiments with mammalian cell cultures, using a time-resolved fluorescence reader and PLIM imaging detection. Structure-activity relationships were established. Thus, the tri- and tetra-PEGylated structures showed low cell internalization allowing their use as extracellular probes, while cysteamine derivatives performed as efficient intracellular probes. No significant cytotoxicity was observed for all of the probes under the experimental conditions used.