Fluorescence-Guided Spatial Drug Screening in 3D Colorectal Cancer Spheroids

The limited recapitulation of critical cancer features in 2D cultures causes poor translatability of preclinical results from in vitro assays to in vivo tumor models. This contributes to slow drug development with a low success rate. 3D cultures better recapitulate the tumor microenvironment, enabling more accurate predictions when screening drug candidates and improving the development of chemotherapeutics. Platinum (Pt) (IV) compounds are promising prodrugs designed to reduce the severe systemic toxicity of widely used Food and Drug Administration (FDA)-approved Pt(II) drugs such as cisplatin. Here, this work presents spatiotemporal evaluations in 3D colorectal cancer (CRC) spheroids of mitochondria-targeting Pt(IV) complexes. CRC spheroids provide a greater pathophysiological recapitulation of in vivo tumors than 2D cultures by a marked upregulation of the ABCG2 chemoresistance marker expression. Furthermore, new 3D-staining protocols are introduced to evaluate the real-time decrease in mitochondria membrane potential (ΔΨ) in CRC spheroids, and a Pt-sensing dye to quantify the Pt mitochondrial accumulation. Finally, this work demonstrates a correlation between in vitro results and the efficacy of the compounds in vivo. Overall, the CRC spheroids represent a fast and cost-effective model to assess the behavior of Pt compounds in vitro and predict their translational potential in CRC treatment.

Recent Advances on Pt-Based Compounds for Theranostic Applications

Since the discovery of cisplatin's antitumoral activity and its approval as an anticancer drug, significant efforts have been made to enhance its physiological stability and anticancer efficacy and to reduce its side effects. With the rapid development of targeted and personalized therapies, and the promising theranostic approach, platinum drugs have found new opportunities in more sophisticated systems. Theranostic agents combine diagnostic and therapeutic moieties in one scaffold, enabling simultaneous disease monitoring, therapy delivery, response tracking, and treatment efficacy evaluation. In these systems, the platinum core serves as the therapeutic agent, while the functionalized ligand provides diagnostic tools using various imaging techniques. This review aims to highlight the significant role of platinum-based complexes in theranostic applications, and, to the best of our knowledge, this is the first focused contribution on this type of platinum compounds. This review presents a brief introduction to the development of platinum chemotherapeutic drugs, their limitations, and resistance mechanisms. It then describes recent advancements in integrating platinum complexes with diagnostic agents for both tumor treatment and monitoring. The main body is organized into three categories based on imaging techniques: fluorescence, positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI). Finally, this review outlines promising strategies and future perspectives in this evolving field.

Electrochemical Detection of a Novel Pt(IV) Prodrug with the Metronidazole Axial Ligand in the Hypoxic Area

We report herein a Pt(IV) prodrug with metronidazole in axial positions Pt-Mnz. The nitroaromatic axial ligand was conjugated with a cisplatin scaffold to irreversibly reduce under hypoxic conditions, thereby retaining the Pt(IV) prodrug in the area of hypoxia. X-ray near-edge adsorption spectroscopy (XANES) on dried drug-preincubated tumor cell samples revealed a gradual release of cisplatin from the Pt-Mnz prodrug instead of rapid intracellular degradation. The ability of the prodrug to penetrate into three-dimensional (3D) spheroid cellular cultures was evaluated by a novel electrochemical assay via a platinum-coated carbon nanoelectrode, capable of single-cell measurements. Using a unique technique of electrochemical measurements in single tumor spheroids, we were able to both detect the real-time response of the axial ligand to hypoxia and establish the depth of penetration of the drug into the tumor model.

Pt(IV) Prodrugs with Non-Steroidal Anti-inflammatory Drugs in the Axial Position

We report herein the design, synthesis, and biological investigation of a series of novel Pt(IV) prodrugs with non-steroidal anti-inflammatory drugs naproxen, diclofenac, and flurbiprofen, as well as these with stearic acid in the axial position. Six Pt(IV) prodrugs 5-10 were designed, which showed superior antiproliferative activity compared to cisplatin as well as an ability to overcome tumor cell line resistance to cisplatin. By tuning the drug lipophilicity via variation of the axial ligands, the most potent Pt(IV) prodrug 7 was obtained, with an enhanced cellular accumulation of up to 153-fold that of cisplatin and nanomolar cytotoxicity both in 2D and 3D cell cultures. Pt²⁺ species were detected at different depths of MCF-7 spheroids after incubation with Pt(IV) prodrugs using a Pt-coated carbon nanoelectrode. Cisplatin accumulation in vivo in the murine mammary EMT6 tumor tissue of BALB/c mice after Pt(IV) prodrug injection was proved electrochemically as well. The drug tolerance study on BALB/c mice showed good tolerance of 7 in doses up to 8 mg/kg.

Photoinduced charge-separated molecular probe for ultrasensitive spectrum analysis and rapid colorimetric detection of platinum ions

Increased utilization of platinum ions in chemicals and drugs escalates environmental pollution and toxicity associated with Pt ions. However, current analysis and detection strategies of Pt ions display limited sensitivity due to the similar inert metal nature of platinum to gold. Herein, a photoinduced charge-separated molecule (MTPA)₂Ab was synthesized as a probe for enhanced sensitive selection of Pt ions. Long-lived charge-separated states generated upon exposure to 365 nm light lead to a stable complex between (MTPA)₂Ab and PtCl₂/PtCl₄ with highly-selectivity via sequential photoinduced electron transfers. Owing to the linear relationship of complex characteristic absorption and fluorescence emission intensities to Pt²⁺/Pt⁴⁺ concentrations, ultrasensitive spectrum analysis of Pt ions is achieved with a detection limit of 14.2 nM (2.8 ppb) for Pt²⁺ and 12.6 nM (2.5 ppb) for Pt⁴⁺ by an absorption spectrometer and 9.8 nM (1.9 ppb) for Pt ions (Pt²⁺/Pt⁴⁺) by a fluorescence spectrometer, far less than the reported values. Furthermore, a portable test box is developed based on (MTPA)₂Ab test strips due to distinguishable color change with Pt²⁺/Pt⁴⁺ concentrations for rapid colorimetric detection of Pt ions. The results highlight the promise of photoinduced charge-separated molecular probe in ultrasensitive and rapid detection of Pt ions to overcome current limitations of detection strategies.

A Versatile Fluorescent Sensor Array for Platinum Anticancer Drug Detection in Biological Fluids

Platinum complexes remain frontline anticancer therapies, even after 50 years of usage in clinical applications. However, there is still a lack of methodology to robustly detect and quantify these complexes in biological fluids. We report here a fluorescent sensor array comprising six sensors that demonstrates progress toward the detection of platinum levels in chemotherapy patients. Linear discriminant analysis was performed to examine each multidimensional data set, and the array was able to discriminate platinum from other biologically relevant metals and heavy metals and separately able to differentiate and identify platinum complexes with different coordination environments with 100% accuracy. Finally, the array showed sensitivity to various cisplatin and oxaliplatin concentrations in human plasma and was able to discriminate between a cohort of 27 cancer patients at different stages of platinum treatment. We envisage that our array system could lead to a better understanding of blood platinum concentrations of chemotherapy patients and could inform the modification of dosage regimes to minimize dose-limiting side effects.

Using a High Quantum Yield Fluorescent Probe with Two-Photon Excitation to Detect Cisplatin in Biological Systems

A direct detection protocol for the anticancer drug of cisplatin is highly desirable for studying its actions and side effects. In this work, a high quantum yield fluorescent probe with two-photon excitation to detect cisplatin was designed. The probe (RD640-TC) was based on the rhodamine 640 (Rh640) fluorophore, responding to cisplatin with red fluorescence. It showed an excellent linear correlation between the fluorescence response and the concentration of cisplatin over the range of 2-50 μM, suggesting a feasible tool for convenient detection of cisplatin. RD640-TC had high fluorescence quantum yield (Φ = 0.68) and two-photon absorption properties, which made it more favorable to probe cisplatin in biological systems. We exemplified RD640-TC for the detection of cisplatin in cells and zebrafish, providing an accessible tool for in vivo tracking of cisplatin, which has great potential value for studying how cisplatin is processed at cellular level and further for facilitating the investigation into the origin of cisplatin's toxicity.

A BODIPY-based fluorescent sensor for the detection of Pt2+ and Pt drugs

A novel BODIPY-based fluorescent sensor PS was designed for imaging Pt2+, cisplatin and nedaplatin in aqueous medium and biological environments, providing great potential for studying the Pt-drug metabolism and the development of new platinum drugs.

A red fluorescent BODIPY probe for iridium (III) ion and its application in living cells

A new red fluorescent probe 1 based on BODIPY skeleton has been successfully synthesized through introduction of 2-(thiophen-2-yl) quinoline moiety at meso- and 3-position, which exhibits excellent optical performance, including high fluorescence quantum yield, large pseudo Stokes' shift as well as high selectivity and sensitivity towards iridium (III) ion in aqueous solution and in living cells.

A Ratiometric Fluorescent Probe for Cisplatin: Investigating the Intracellular Reduction of Platinum(IV) Prodrug Complexes

The Pt^IV prodrug strategy has emerged as an excellent alternative to tackle the problems associated with conventional Pt^II drug therapy. However, there is a lack of tools to study how this new class of Pt^IV drugs are processed at the cellular level. Herein, we report the first ratiometric probe for cisplatin detection and use it to investigate Pt^IV anticancer complexes in biological systems. The probe was able to distinguish between cisplatin and its Pt^IV derivatives, allowing us to probe the intracellular reduction of Pt^IV prodrug complexes. The correlation between the amount of active Pt^II species available after intracellular reduction of Pt^IV complexes and their cytotoxicity and the role glutathione plays in the reduction of Pt^IV complexes were investigated.

A sequential enzyme-activated and light-triggered pro-prodrug nanosystem for cancer detection and therapy

A sequential enzyme-activated and light-triggered pro-prodrug has been developed for cancer biomarker detection and on-demand therapy.

A two-photon-activated prodrug for therapy and drug release monitoring

A two-photon-activated prodrug has been developed for drug release monitoring and photo-controllable therapy.

On the outside looking in: redefining the role of analytical chemistry in the biosciences

Analytical chemistry has much to offer to an improved understanding of biological systems.

Azide vs Alkyne Functionalization in Pt(II) Complexes for Post-treatment Click Modification: Solid-State Structure, Fluorescent Labeling, and Cellular Fate

Tracking of Pt(II) complexes is of crucial importance toward understanding Pt interactions with cellular biomolecules. Post-treatment fluorescent labeling of functionalized Pt(II)-based agents using the bioorthogonal Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has recently been reported as a promising approach. Here we describe an azide-functionalized Pt(II) complex, cis-[Pt(2-azidobutyl)amido-1,3-propanediamine)Cl2] (1), containing the cis geometry and difunctional reactivity of cisplatin, and present a comparative study with its previously described alkyne-functionalized congener. Single-crystal X-ray diffraction reveals a dramatic change in the solid-state arrangement with exchange of the alkyne for an azide moiety wherein 1 is dominated by a pseudo-chain of Pt-Pt dimers and antiparallel alignment of the azide substituents, in comparison with a circular arrangement supported by CH/π(C≡C) interactions in the alkyne version. In vitro studies indicate similar DNA binding and click reactivity of both congeners observed by fluorescent labeling. Interestingly, complex 1 shows in vitro enhanced click reactivity in comparison to a previously reported azide-appended Pt(II) complex. Despite their similar behavior in vitro, preliminary in cellulo HeLa studies indicate a superior imaging potential of azide-functionalized 1. Post-treatment fluorescent labeling of 1 observed by confocal fluorescence microscopy shows nuclear and intense nucleolar localization. These results demonstrate the potential of 1 in different cell line localization studies and for future isolation and purification of Pt-bound targets.

Evaluation of fluorophore-tethered platinum complexes to monitor the fate of cisplatin analogs

The platinum drugs cisplatin, carboplatin, and oxaliplatin are highly utilized in the clinic and as a consequence have been extensively studied in the laboratory setting, sometimes by generating fluorophore-tagged analogs. Here, we synthesized two Pt(II) complexes containing ethane-1,2-diamine ligands linked to a BODIPY fluorophore, and compared their biological activity with previously reported Pt(II) complexes conjugated to carboxyfluorescein and carboxyfluorescein diacetate. The cytotoxicity and DNA damage capacity of Pt-fluorophore complexes was compared to cisplatin, and the Pt-BODIPY complexes were found to be more cytotoxic with reduced cytotoxicity in cisplatin-resistant cells. Microscopy revealed a predominately cytosolic localization, with nuclear distribution at higher concentrations. Spheroids grown from parent and resistant cells revealed penetration of Pt-BODIPY into spheroids, and retention of the cisplatin-resistant spheroid phenotype. While most activity profiles were retained for the Pt-BODIPY complexes, accumulation in resistant cells was only slightly affected, suggesting that some aspects of Pt-fluorophore cellular pharmacology deviate from cisplatin.