Synthesis, Characterization, and Biological Evaluation of Red-Absorbing Fe(II) Polypyridine Complexes

Abstract

Cancer is known to be one of the major causes of death nowadays. Among others, chemotherapy with cisplatin is a commonly used treatment. Although widely employed, cisplatin is known to cause severe side effects, such as nerve and kidney damage, nausea, vomiting, and bone marrow suppression. Most importantly, a number of cancer tumors are acquiring resistance to cisplatin, limiting its clinical use. There is therefore a need for the discovery of novel anticancer agents. Complementary to chemotherapy, Photodynamic Therapy (PDT) has expanded the range of treatment opportunities of numerous kinds of cancer. Nonetheless, the currently approved PDT photosensitizers (PSs) suffer from major drawbacks, which include poor water solubility or photobleaching, in addition to a slow clearance from the body that causes photosensitivity. Due to these limitations, there is a need for the development of new PDT PSs. To overcome these problems, a lot of research groups around the world are currently focusing their attention towards the development of new metal complexes as PDT PSs. However, most synthesized compounds reported so far show limited use due to their poor absorption in the phototherapeutic window. Herein, we report on the preparation and characterization of three Fe(II) polypyridine complexes (4-6) and evaluate their potential as both anticancer agents and PDT PSs. Very importantly, these compounds are stable in human plasma, photostable upon continuous LED irradiation, and absorb in the red region of the spectrum. We could demonstrate that through additional sulfonic acid groups on the polypyridine ligand being used (bphen: 4,7-diphenyl-1,10-phenanthroline), the water solubility of the complexes could be highly improved, whereas the photophysical properties did not significantly change. One of these complexes (4) shows interesting toxicity, with IC 50 values in the low micromolar range in the dark as well as some phototoxicity upon irradiation at 480 and 540 nm against RPE-1 and HeLa cells.

A Ru(II) polypyridyl complex bearing aldehyde functions as a versatile synthetic precursor for long-wavelength absorbing photodynamic therapy photosensitizers

“…. The 1 O2 quantum yields were determined by two methods, as previously published by our group:[50,51] 1) direct method by measurement of the luminescence of 1 O2 at 1270 nm, 2) indirect method by measurement of the variation in absorbance of the reporter molecule imidazole (in CH3CN) or histidine (in PBS). The obtained values were compared with a O2)Ru(bipy)3Cl2=0.22) in a aqueous solution [47].…”

Evaluation of the Potential of Cobalamin Derivatives Bearing Ru(II) Polypyridyl Complexes as Photosensitizers for Photodynamic Therapy

“…For this purpose, two different methods have been used: 1) direct by measurement of the phosphorescence of 1 O 2 , 2) indirect by measurement of the change in absorbance of a reporter molecule. [39] Worthy of note, only singlet oxygen quantum yields over 20 % can be detected via the direct method with our apparatus. The results shown in Table 2 demonstrate that compounds 1 and 2 are producing 1 O 2 only poorly.…”

Systematic investigation of the antiproliferative activity of a series of ruthenium terpyridine complexes

“…For this purpose, we determined the distribution coefficient (logP values) of the complexes between an aqueous PBS phase and a lipophilic octanol phase by the "shake-flask" method, as previously performed by our group with other metal complexes. [70,71] All compounds were mostly found in the aqueous phase, which we assume, is due to the positive charge of the metal complexes.…”