New Iron(III)-Containing Composite of Salinomycinic Acid with Antitumor Activity—Synthesis and Characterization

In this study we demonstrated for the first time synthetic procedures for composites of salinomycin (SalH) and two-line ferrihydrite. The products were characterized by various methods such as elemental analysis, attenuated total reflectance–Fourier-transform spectroscopy (ATR-FTIR), electron paramagnetic resonance spectroscopy (EPR), powder X-ray diffraction analysis (XRD), electrospray-ionization mass spectrometry (ESI-MS), thermogravimetric analysis with differential thermal analysis (DTA) and mass spectrometry (TG-DTA/MS). The EPR spectra of the isolated compounds consisted of signals associated with both isolated Fe3+ ions and magnetically coupled Fe3+ ions. Powder XRD analyses of the isolated products showed two intense and broad peaks at 9° and 15° 2Θ, corresponding to salinomycinic acid. Broad peaks with very low intensity around 35°, assigned to two-line ferrihydrite, were also registered. Based on the experimental results, we concluded that salinomycin sodium reacted with Fe(III) chloride to form composites consisting of two-line ferrihydrite and salinomycinic acid. One of the composites exerted pronounced antitumor activity in the sub-micromolar concentration range against human cervical cancer (HeLa), non-small-cell lung cancer (A549), colon cancer (SW480), and ovarian teratocarcinoma (CH1/PA1) cells.