Unambiguous Intracellular Localization and Quantification of a Potent Iridium Anticancer Compound by Correlative 3D Cryo X‐Ray Imaging

Abstract

The iridium half‐sandwich complex [Ir(η5:κ1‐C5Me4CH2py)(2‐phenylpyridine)]PF6 is highly cytotoxic: 15–250× more potent than clinically used cisplatin in several cancer cell lines. We have developed a correlative 3D cryo X‐ray imaging approach to specifically localize and quantify iridium within the whole hydrated cell at nanometer resolution. By means of cryo soft X‐ray tomography (cryo‐SXT), which provides the cellular ultrastructure at 50 nm resolution, and cryo hard X‐ray fluorescence tomography (cryo‐XRF), which provides the elemental sensitivity with a 70 nm step size, we have located the iridium anticancer agent exclusively in the mitochondria. Our methodology provides unique information on the intracellular fate of the metallodrug, without chemical fixation, labeling, or mechanical manipulation of the cells. This cryo‐3D correlative imaging method can be applied to a number of biochemical processes for specific elemental localization within the native cellular landscape.

Dose-efficient multimodal microscopy of human tissue at a hard X-ray nanoprobe beamline

“…We expect to extend this multimodal approach to 3D applications by combining the experimental setup presented with a high-precision rotation stage, suited for tomography experiments (Kalbfleisch et al, 2022). Such experiments require longer measuring times and entail higher absorbed doses, so the flexible optimization of experimental parameters is crucial for their success, possibly along with the implementation of cryogenic sample cooling (Deng et al, 2018;Conesa et al, 2020;Gramaccioni et al, 2020). Should radiation damage prevent the reliable collection of high-dose XRF tomography data, lower dose phase-contrast tomography could still be used to produce or validate quantitative results from 2D XRF scans on samples of variable thickness (Bardelli et al, 2021).…”

“…It is applied for the chemical investigation of samples from a wide range of research fields. In biology and medicine it proved useful within studies on both non-human (Duc ˇic ´et al, 2011;Victor et al, 2018;Deng et al, 2018;Silva Barreto et al, 2020) and human (Fus et al, 2019;Pascolo et al, 2019;Carmona et al, 2019;Conesa et al, 2020) cells and tissues. The main benefit of performing XRF experiments at synchrotron radiation facilities is the high spatial resolution enabled by increasingly tight X-ray focal spot sizes, along with the high throughput enabled by the high photon flux.…”

Gallium (III) Complexes in Cancer Chemotherapy

“…For example, a mitochondrion‐target rhenium complex ( 12 ) conjugated with iron chelates can destroy cellular iron homeostasis, leading to tumor cell death; [22] a tri‐Mn complex ( 13 ) as a catalase can scavenge hydrogen peroxide accumulated in inflammation sites, which was applied in stroke treatment [23] . An iridium half‐sandwich complex ACC25 ( 14 ), a lipophilic cation, is highly restricted to mitochondria and distorts the mitochondrial membrane, resulting in a net influx of calcium ions into the mitochondrion matrix [24] . Therefore, tremendous progress made in recent years provides us important information on the correlation between the nature of metal coordination and the biological contexts such as cellular events, biochemistry, and the carcinogenic process, and facilitates the discovery and characterization of new metal drugs.…”

3D-surface reconstruction of cellular cryo-soft X-ray microscopy tomograms using semi-supervised deep learning

“…the organization of cellular organelles with statistically relevant amounts of data in 3D volumes as in the yeast cell cycle 14 , nanoparticle uptake 1 and parasite infection 15 . Moreover, the compatibility of cryo-SXT with cryo-fluorescence microscopy or cryo-hard x-ray fluorescence microscopy allows the identification and visualization of specific cellular structures and processes 16,17 .…”