Getting to the core of platinum drug bio-distributions: the penetration of anti-cancer platinum complexes into spheroid tumour models

Abstract

Elemental mapping and fluorescence imaging techniques are frequently employed to probe the distribution of platinum-based chemotherapeutics within biological systems. Although useful, these techniques have unique limitations: elemental mapping methods, such as those that use particle beams, typically require rigorous sample preparation that can alter chemical distributions, whilst in situ visible fluorescence studies require fluorescent-tagging of the platinum component and may be confounded by factors such as ligand loss. The present study aimed to establish reliable methods for accurately probing the bio-distribution of platinum compounds within the model tumour micro-environment of the well characterised DLD-1 colorectal cancer cell spheroids. 3D X-ray fluorescence computed micro-tomography (XRF-CT) was performed on intact untreated spheroids to determine the effect of physical sectioning and chemical fixation on elemental distributions. It was revealed for the first time that cisplatin can readily penetrate through DLD-1 spheroids and accumulate in the central hypoxic and necrotic regions of the spheroids. Furthermore, formalin fixing was shown to cause significant changes to the distributions and concentrations of the elements, particularly in the cases of platinum and zinc. This effect was not observed in the cryo-fixed and cryo-sectioned samples. X-ray fluorescence microscopy (XFM) was used to re-examine the fate of platinum in the previously reported fluorescence distribution studies of platinum(ii) complexes tagged with fluorescent anthraquinone moieties. In contrast to the fluorescence distributions, in which fluorescence was observed predominantly around the periphery of the spheroids, the XFM revealed a high level of platinum in the spheroid centre, indicating that ligand exchange occurred within the peripheral cell layers. Both the platinum maps and the fluorescence images exhibit similar diffusion trends, supporting the conclusion that charge on the compound can slow cellular uptake can enhance tumour penetration.

Coordination compounds in cancer: Past, present and perspectives

“…Exposition of such foci to cytotoxic concentrations of cytostatics can eliminate quiescent or stem cell populations (Zhang et al, 2012). Moreover, information provided by integrative global approaches, including NGS, pharmacokinetic analysis and metallomics, can even serve as a biomarker tool predicting a cancer relapse (Araujo et al, 2014).…”

Comparison Between Polypyridyl and Cyclometalated Ruthenium(II) Complexes: Anticancer Activities Against 2D and 3D Cancer Models

“…Moreover, MCTSs can mimic therapeutic problems associated with the metabolic and proliferative gradients found in solid tumors, such as the altered responsiveness of chronically hypoxic tumor cells, as well as multidrug resistance to apoptosis-inducing agents. [43,44] In this respect, MCTSs serve as a useful tool for negative anticancer drug selection and reduce the need for animal testing. Several methods have been designed to generate tumor spheroids, among which agarose-coated liquid-overlay 96-well plate culture provides an easy-to-handle protocol for generating single MCTSs.…”

Analysis of Platinum and Trace Metals in Treated Glioma Rat Cells by X-Ray Fluorescence Emission

“…Methods using chemical fixation must be avoided [19,20]. Cryofixation is strongly suggested as Roudeau et al reviews [18].…”

“…However, in some cases, the sample preparation has involved steps of immunolabeling protocol that could modify the elemental distribution and contents in the cells. It is well-known that the sample preparation is a critical step to avoid any contamination [18][19][20]. Therefore, in order to retain the cell structure as well as the distribution of endogenous elements, different samples such as a control case, an exposed to cisplatin, and an exposed to liposomal cisplatin were studied.…”