2D and 3D anticancer activity of diiron bis-cyclopentadienyl complexes incorporating flurbiprofen and chlorambucil

The new diiron complex [Fe2Cp2(CO){Ph2P(4-C6H4CO2H)}(μ-CO){μ-CNMe(Cy)}]CF3SO3, [2]CF3SO3 (Cp = η5-C5H5, Cy = C6H11), was synthesized with a 92% yield from a tricarbonyl precursor and 4-(diphenylphosphanyl)benzoic acid. The carboxylic acid group in [2]+ was exploited for bio-conjugation with flurbiprofen and chlorambucil through esterification procedures, affording complexes [3-4]CF3SO3 (36-55% yields). Comprehensive characterization of the products was achieved using IR, multinuclear NMR spectroscopy and mass spectrometry. The log Pow values and the stability under physiologically relevant conditions were determined, revealing a considerable fraction of [3-4]+ still detectable in water/methanol solution after 72 hours and in DMEM culture medium/methanol solution after 24 hours. The antiproliferative activity was assessed in 2D across a panel of nine cancer cell lines, where [3,4]+ displayed IC50 values in the low-micromolar range and revealed the ability to overcome oxaliplatin resistance mechanisms. When tested in 3D cultures of human colon cancer and melanoma cells, [3,4]+ exhibited cytotoxic activity comparable to that of cisplatin. Targeted assays revealed that both [3]+ and [4]+ substantially preserved the COX inhibitory effect of flurbiprofen and the DNA damaging efficacy of chlorambucil, respectively.