Unambiguous Intracellular Localization and Quantification of a Potent Iridium Anticancer Compound by Correlative 3D Cryo X-Ray Imaging, J.J. Conesa (a,b), A.C. Carrasco (c), V. Rodríguez-Fanjul (c), Y. Yang (d), J.L. Carrascosa (b),
P. Cloetens (d), E. Pereiro (a) and A.M. Pizarro (c), Angew. Chem. Int. Ed. 59(3), 1270-1278 (2020); https://doi. org/10.1002/anie.201911510. (a) ALBA Synchrotron Light Source, Barcelona (Spain)
(b) Centro Nacional de Biotecnología/CSIC, Madrid (Spain) (c) IMDEA Nanociencia, Madrid (Spain) (d) ESRF
 A.C. Carrasco et al., J. Med. Chem. 63, 4005-4021 (2020).  J.J. Conesa et al., Sci. Rep. 6, 22354 (2016).
PRINCIPAL PUBLICATION AND AUTHORS
cell cartography obtained by cryo-SXT showed that the metallodrug is accumulated inside mitochondria, associated to mitochondrial inner membranes, while none of the other organelles presented any detectable signal (Figure 70). Together, these results indicate an iridium-driven distortion of the mitochondrial membrane structure and permeability, induced by an opening of non-selective and high-conductance permeability transition pores in the inner
Fig. 70: Intracellular localisation of iridium in MCF7 cells. a) MCF7 cell treated with 1 µM ACC25 for 12 h, overlay of soft X-ray microscopic imaging (grey) and epifluorescence signal (green: mitochondria, red: acidic organelles). b) Ir distribution imaged by 2D XRF on the same cell. c) Overlay of epifluorescence mitochondria signal (green)
with a mask of the Ir signal shown in (b). d) Selected area of the cell in (a), as an overlap of two slices from cryo-SXT and Ir XRF tomography (XRF acquisition area squared in yellow). e) and (f) compare mitochondrion slices from the cryo-SXT and the XRF tomography. g) 3D rendering of the yellow square area in (d) after segmentation of
the organelles. The Ir signal is displayed with the same colour density scale as in (d) and (f). Scale bars: (a)-(d) 5 µm; (e) and (f) 1 µm; (g) 2 µm.
mitochondrial membrane. Complex ACC25, with an overall formal charge of +1 and bearing hydrophobic ligands, behaves as a lipophilic cation. Attracted by the negative membrane potential of the mitochondrial inner membrane, ACC25 accumulates in the mitochondrial matrix against its concentration gradient, thus selectively and efficiently targeting the MCF7 cell mitochondria, ultimately causing cancer cell death.