title: 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.
authors.affiliation: School of Chemistry, The University of Sydney, New South Wales, 2006, Australia.
authors.forename: Jenny Z
authors.initials: JZ
authors.lastname: Zhang
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Bryce
authors.forename: Antonio
authors.initials: A
authors.lastname: Lanzirotti
authors.forename: Catherine K J
authors.initials: CK
authors.lastname: Chen
authors.forename: David
authors.initials: D
authors.lastname: Paterson
authors.forename: Martin D
authors.initials: MD
authors.lastname: de Jonge
authors.forename: Daryl L
authors.initials: DL
authors.lastname: Howard
authors.forename: Trevor W
authors.initials: TW
authors.lastname: Hambley
mesh_terms: D000880:Anthraquinones; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D004560:Electricity; D005260:Female; D005557:Formaldehyde / Q000737:chemistry; D016591:Histocytological Preparation Techniques / Q000379:methods; D006801:Humans; D042541:Intracellular Space; D009336:Necrosis; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D010984:Platinum / Q000493:pharmacokinetics; D018874:Spheroids, Cellular / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*
chemical_list: D000880:Anthraquinones; D005557:Formaldehyde; D010984:Platinum; D002945:Cisplatin