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 P _ow 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.