Intracellular localization of an osmocenyl‐tamoxifen derivative in breast cancer cells revealed by synchrotron radiation X‐ray fluorescence nanoimaging

We have recently developed a series of tamoxifen‐like metallocifens of the group‐8 metals (Fe, Ru and Os) with strong antiproliferative activity on the triple negative breast cancer cells (MDA‐MB‐231). This property, not observed for the organic analog 4‐hydroxytamoxifen, has been associated with the unique redox behavior of metallocenic moieties, readily affording reactive quinone methides in cancer cells. To shed light on the mechanism of action of these molecules, synchrotron radiation X‐ray fluorescence (SR‐XRF) nanoimaging studies were performed on cells exposed to osmocenyl‐tamoxifen (Oc‐OH‐Tam) to disclose its intracellular distribution using osmium as an intrinsic reporter. High resolution mapping of the lipophilic Oc‐OH‐Tam in cells, revealed its preferential accumulation in the endomembrane system encompassing endoplasmic reticulum, nuclear envelope and vesicular structures. This is consistent with the ability of the amino nitrogen chain of the compounds to be protonated at physiological pH and responsible for electrostatic interactions between Oc‐OH‐Tam and membranes. We propose a comprehensive scenario that provides new insight into the cellular behavior and activation of Oc‐OH‐Tam and advances the understanding of its mechanism of action.

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