Comparative in vitro and in vivo pharmacological investigation of platinum(IV) complexes as novel anticancer drug candidates for oral application

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.

Platinum(IV)-Loaded Degraded Glycol Chitosan as Efficient Platinum(IV) Drug Delivery Platform

A new class of anticancer prodrugs was designed by combining the cytotoxicity of platinum(IV) complexes and the drug carrier properties of glycol chitosan polymers: Unsymmetrically carboxylated platinum(IV) analogues of cisplatin, carboplatin and oxaliplatin, namely (OC-6-44)-acetatodiammine(3-carboxypropanoato)dichloridoplatinum(IV), (OC-6-44)-acetaodiammine(3-carboxypropanoato)(cyclobutane-1,1-dicarboxylato)platinum(IV) and (OC-6-44)-acetato(3-carboxypropanoato)(1R,2R-cyclohexane-1,2-diamine)oxalatoplatinum(IV) were synthesised and conjugated via amide bonding to degraded glycol chitosan (dGC) polymers with different chain lengths (5, 10, 18 kDa). The 15 conjugates were investigated with ¹H and ¹⁹⁵Pt NMR spectroscopy, and average amounts of platinum(IV) units per dGC polymer molecule with ICP-MS, revealing a range of 1.3-22.8 platinum(IV) units per dGC molecule. Cytotoxicity was tested with MTT assays in the cancer cell lines A549, CH1/PA-1, SW480 (human) and 4T1 (murine). IC₅₀ values in the low micromolar to nanomolar range were obtained, and higher antiproliferative activity (up to 72 times) was detected with dGC-platinum(IV) conjugates in comparison to platinum(IV) counterparts. The highest cytotoxicity (IC₅₀ of 0.036 ± 0.005 µM) was determined in CH1/PA-1 ovarian teratocarcinoma cells with a cisplatin(IV)-dGC conjugate, which is hence 33 times more potent than the corresponding platinum(IV) complex and twice more potent than cisplatin. Biodistribution studies of an oxaliplatin(IV)-dGC conjugate in non-tumour-bearing Balb/C mice showed an increased accumulation in the lung compared to the unloaded oxaliplatin(IV) analogue, arguing for further activity studies.

Synthesis, Characterization and Photoactivation Studies on the Novel Pt(IV)-Based [Pt(OCOCH3)3(phterpy)] Complex

Photoactivatable Pt(IV) prodrugs represent nowadays an intriguing class of potential metal-based drugs, endowed with more chemical inertness in their oxidized form and better selectivity for the target with respect to the clinically established Pt(II) compounds. In fact, they have the possibility to be reduced by light irradiation directly at the site of interest. For this reason, we synthesized a new Pt(IV) complex, [Pt(OCOCH₃)₃(4'-phenyl-2,2':6',2''-terpyridine)][CF₃SO₃] (1), that is well soluble in aqueous medium and totally unreactive towards selected model biomolecules until its reduction. The highlight of this work is the rapid and efficient photoreduction of 1 with visible light (460 nm), which leads to its reactive Pt(II) analogue. This behavior was made possible by taking advantage of an efficient catalytic system based on flavin and NADH, which is naturally present in the cellular environment. As a comparison, the reduction of 1 was also studied with simple UV irradiation, but both UV-Vis spectrophotometry and ¹H-NMR spectrometry showed that the flavin-catalyzed reduction with visible light was faster. Lastly, the reactivity against two representative biological targets, i.e., human serum albumin and one monofilament oligonucleotide fragment, was evaluated by high-resolution mass spectrometry. The results clearly pointed out that the prodrug 1 did not interact with these targets until its photoreduction to the Pt(II) analogue.

Potent Platinum(IV) Prodrugs That Incorporate a Biotin Moiety to Selectively Target Cancer Cells

Four platinum(IV) prodrugs incorporating a biotin moiety to selectively target cancer cells were synthesised, characterised, and their biological activity assessed. All complexes exhibited exceptional in vitro cytotoxicity against a panel of cancer cell lines, with [Pt(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO₃)₂, (2) exhibiting the lowest GI₅₀ of 4 nM in the prostate Du145 cancer cell line. Each complex displayed significantly enhanced activity compared to cisplatin, with 2 being 1000-fold more active in the HT29 colon cancer cell line. Against the MCF-7 breast cancer cell line, in which high levels of biotin receptors are expressed, 2, [Pt(4,7-dimethoxy-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO₃)₂, (3), and [Pt(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO₃)₂, (4) exhibited enhanced activity compared to their platinum(II) cores, with 4 being 6-fold more active than its platinum(II) precursor. Furthermore, 3 exhibited 3-fold greater selectivity towards MCF-7 breast cancer cells compared to MCF10A breast healthy cells, and this was further confirmed by platinum uptake studies, which showed 3 to have almost 3-fold greater uptake in MCF-7 cells, compared to MCF10A cells. The results show that lipophilicity and selectivity both contributed to the cellular uptake of 1-4; however, this was not always translated to the observed cytotoxicity.

Synthesis, Characterization and Host-Guest Complexation of Asplatin: Improved In Vitro Cytotoxicity and Biocompatibility as Compared to Cisplatin

Para-sulfocalix[n]arenes are promising host molecules that can accommodate various chemotherapeutic drugs. Pt(IV)-based complexes, including satraplatin and asplatin, are promising alternatives that overcome the shortcomings of Pt(II) complexes. In this study, asplatin has been synthesized by fusing acetylsalicylic acid (aspirin) and cisplatin. Furthermore, it has been characterized using ¹H NMR, mass spectrometry, elemental analysis, and UHPLC. A host-guest complex of asplatin and p-sulfocalix[4]arene (PSC4) has been developed and characterized using UV, Job’s plot analysis, HPLC, and density functional theory (DFT) calculations. The experimental and computational investigations propose that a 1:1 complex between asplatin and PSC4 is formed. The stability constant of the designed complex has been determined using Job’s plot and UHPLC and computed to be 9.1 × 10⁴ M^–1 and 8.7 × 10⁴ M⁻¹, which corresponds to a free energy of complexation of −6.8 kcal mol^–1, while the calculated value for the inclusion free energy is −13.2 kcal mol⁻¹. Both experimentally and theoretically estimated complexation free energy show that a stable host-guest complex can be formed in solution. The in vitro drug release study displayed the ability of the complex to release its cargo at a cancerous pH (pH of 5.5). Additionally, the asplatin/PSC4 complex is shown to be biocompatible when tested on human skin fibroblast noncancerous cells, demonstrating the highest in vitro cytotoxic activity against (MCF-7), cervical (HeLa), and lung cancer cells (A-549), with IC₅₀ values of 0.75, 2.15, and 3.60 µg/mL, respectively. This is as compared to either cisplatin (IC₅₀ of 5.47, 5.94 and 9.61 µg/mL, respectively) or asplatin (IC₅₀ of 1.54, 5.05 and 3.91 µg/mL, respectively). On the other hand, the free asplatin exhibited higher cytotoxicity on cancerous cells and lower toxicity on noncancerous cells. The outcomes of the present joint theoretical and experimental investigation reinforce the interest in platinum-based anticancer therapeutics when they are protected from undesired interactions and suggest the use of the PSC4 macromolecule as a promising carrier for Pt(IV) anticancer drugs. The formed asplatin/PSC4 inclusion complex may represent an effective chemotherapeutic agent.

Multifunctional Pt(iv) prodrug candidates featuring the carboplatin core and deferoxamine

The synergistic combination of the anticancer drug carboplatin and the iron chelator deferoxamine (DFO) served as a foundation for the development of novel multifunctional prodrugs. Hence, five platinum(iv) complexes, featuring the equatorial coordination sphere of carboplatin, and one or two DFO units incorporated at axial positions, were synthesized and characterized using ESI-HRMS, multinuclear (¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt) NMR spectroscopy and elemental analysis. Analytical studies demonstrated that the chelating properties of the DFO moiety were not compromised after coupling to the platinum(iv) core. The cytotoxic activity of the compounds was evaluated in monolayer (2D) and spheroid (3D) cancer cell models, derived from ovarian teratocarcinoma (CH1/PA-1), colon carcinoma (SW480) and non-small cell lung cancer (A549). The platinum(iv)-DFO prodrugs demonstrated moderate in vitro cytotoxicity (a consequence of their slow activation kinetics) but with less pronounced differences between intrinsically chemoresistant and chemosensitive cell lines as well as between 2D and 3D models than the clinically used platinum(ii) drug carboplatin.

The Protein-Binding Behavior of Platinum Anticancer Drugs in Blood Revealed by Mass Spectrometry

Cisplatin and its analogues are widely used as chemotherapeutic agents in clinical practice. After being intravenously administrated, a substantial amount of platinum will bind with proteins in the blood. This binding is vital for the transport, distribution, and metabolism of drugs; however, toxicity can also occur from the irreversible binding between biologically active proteins and platinum drugs. Therefore, it is very important to study the protein-binding behavior of platinum drugs in blood. This review summarizes mass spectrometry-based strategies to identify and quantitate the proteins binding with platinum anticancer drugs in blood, such as offline high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC–ICP-MS) combined with electrospray ionization mass spectrometry (ESI-MS/MS) and multidimensional LC–ESI-MS/MS. The identification of in vivo targets in blood cannot be accomplished without first studying the protein-binding behavior of platinum drugs in vitro; therefore, relevant studies are also summarized. This knowledge will further our understanding of the pharmacokinetics and toxicity of platinum anticancer drugs, and it will be beneficial for the rational design of metal-based anticancer drugs.

Redox-sensitive polyglutamic acid-platinum(IV) prodrug grafted nanoconjugates for efficient delivery of cisplatin into breast tumor

Targeting cisplatin to the sites of action and decreasing its side effects are still major challenges. Here, we introduced a polyglutamic acid-platinum(IV) prodrug nanoconjugates (γ-PGA-CA-Pt(IV)) constructed by polyglutamic acid and modified platinum(IV) prodrug to reserve the anti-tumor efficacy of cisplatin with decreased side effects. We describe the synthesis, physico-chemical characterization, and redox- and pH-sensitive releasing behavior of the nanoconjugate. In vitro studies revealed that, when incubated with glutathione in advance, the γ-PGA-CA-Pt(IV) nanoconjugate induced significant apoptosis in human breast carcinoma MCF-7 cells. From in vivo antitumor efficacy evaluation, the γ-PGA-CA-Pt(IV) nanoconjugate obviously improved the survival rate of tumor-bearing mice with inhibition of the tumor growth compared with cisplatin. Meanwhile, the nanoconjugates showed remarkable improved safety profile than the free cisplatin.

The Endocannabinoid System Alleviates Pain in a Murine Model of Cancer-Induced Bone Pain

Metastatic breast cancer is prevalent worldwide, and one of the most common sites of metastasis is long bones. Of patients with disease, the major symptom is pain, yet current medications fail to adequately result in analgesic efficacy and present major undesirable adverse effects. In our study, we investigate the potential of a novel monoacylglycerol lipase (MAGL) inhibitor, MJN110, in a murine model of cancer-induced bone pain. Literature has previously demonstrated that MAGL inhibitors function to increase the endogenous concentrations of 2-arachydonylglycerol, which then activates CB1 and CB2 receptors to inhibit inflammation and pain. We demonstrate that administration of MJN110 significantly and dose dependently alleviates spontaneous pain behavior during acute administration compared with vehicle control. In addition, MJN110 maintains its efficacy in a chronic-dosing paradigm over the course of 7 days without signs of receptor sensitization. In vitro analysis of MJN110 demonstrated a dose-dependent and significant decrease in cell viability and proliferation of 66.1 breast adenocarcinoma cells to a greater extent than KML29, an alternate MAGL inhibitor, or the CB2 agonist JWH015. Chronic administration of the compound did not appear to affect tumor burden, as evidenced by radiograph or histologic analysis. Together, these data support the application for MJN110 as a novel therapeutic for cancer-induced bone pain. SIGNIFICANCE STATEMENT: Current standard of care for metastatic breast cancer pain is opioid-based therapies with adjunctive chemotherapy, which have highly addictive and other deleterious side effects. The need for effective, non-opioid-based therapies is essential, and harnessing the endogenous cannabinoid system is proving to be a new target to treat various types of pain conditions. We present a novel drug targeting the endogenous cannabinoid system that is effective at reducing pain in a mouse model of metastatic breast cancer to bone.

Synthesis and Cytotoxicity of Water-Soluble Dual- and Triple-Action Satraplatin Derivatives: Replacement of Equatorial Chlorides of Satraplatin by Acetates

Pt(II) complexes, such as cisplatin and oxaliplatin, are in widespread use as anticancer drugs. Their use is limited by the toxic side effects and the ability of tumors to develop resistance to the drugs. A popular approach to overcome these drawbacks is to use their kinetically inert octahedral Pt(IV) derivatives that act as prodrugs. The most successful Pt(IV) complex in clinical trials to date is satraplatin, cct-[Pt(NH₃)(c-hexylamine)Cl₂(OAc)₂], that upon cellular reduction releases the cytotoxic cis-[Pt(NH₃)(c-hexylamine)Cl₂]. In an attempt to obtain water-soluble and more effective cytotoxic Pt(IV) complexes, we prepared a series of dual- and triple-action satraplatin analogues, where the equatorial chlorido ligands were replaced with acetates and the axial ligands include innocent and bioactive ligands. Replacement of the chlorides with acetates enhanced the water solubility of the compounds and, with one exception, all of the compounds were very stable in buffer. In general, compounds with one or two axial hydroxido ligands were reduced by ascorbate significantly more quickly than compounds with two axial carboxylates. While replacement of the chlorides with acetates in satraplatin led to a reduction in cytotoxicity, the dual- and triple-action analogues with equatorial acetates had low- to sub-micromolar IC₅₀ values in a panel of eight cancer cells. The triple-action compound cct-[Pt(NH₃)(c-hexylamine)(OAc)₂(PhB)(DCA)] was active in all cell lines, causing DNA damage that induced cell cycle inhibition and apoptosis. Its good activity against CT26 cells in vitro translated into good in vivo efficacy against the CT26 allograft, an in vivo model with intrinsic satraplatin resistance. This indicates that multiaction Pt(IV) derivatives of diamine dicarboxylates are interesting anticancer drug candidates.

Pt(IV) Bifunctional Prodrug Containing 2-(2-Propynyl)octanoato Axial Ligand: Induction of Immunogenic Cell Death on Colon Cancer

The synthesis, characterization, and in vitro activity of a cyclohexane-1 R,2 R-diamine-based Pt(IV) derivative containing the histone deacetylase inhibitor rac-2-(2-propynyl)octanoato, namely, ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV), are reported together with those of its isomers containing enantiomerically enriched axial ligands. These Pt(IV) complexes showed comparable activity, of 2 orders of magnitude higher than reference drug oxaliplatin on three human (HCT 116, SW480, and HT-29) and one mouse (CT26) colon cancer cell lines. In vivo experiments were carried out on immunocompetent BALB/c mice bearing the same syngeneic tumor. The complex ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV) showed higher tumor mass Pt accumulation than oxaliplatin, due to its higher lipophilicity, with negligible nephro- and hepatotoxicities when administered intravenously. A remarkable tumor mass invasion by cytotoxic CD8+ T lymphocytes, following the Pt(IV) treatment, indicated a strong induction of immunogenic cell death.

Synthesis and characterization of cyclohexane-1R,2R-diamine-based Pt(iv) dicarboxylato anticancer prodrugs: their selective activity against human colon cancer cell lines

Three pairs of asymmetric dicarboxylato derivatives based on the cisplatin and oxaliplatin-like skeletons have been synthesized de novo or re-synthesized. The axial ligands consist of one medium-chain fatty acid (MCFA), namely clofibrate (i.e. 2-(p-chlorophenoxy)-2-methylpropionic acid, CA), heptanoate (HA) or octanoate (OA), respectively, and an inactive acetato ligand that imparts acceptable water solubility to such conjugates. Stability tests provided evidence for the partial formation of two hydrolyzed products, corresponding to two monoaqua diastereomers derived from the substitution of an equatorial chlorido ligand with a water molecule. The complexes have been tested on three different colon cancer cell lines having different histological history, and also on the cisplatin-sensitive A2780 ovarian cancer cell line for comparison. This allowed the evaluation not only of the increase in activity on passing from Pt(ii) to Pt(iv) derivatives, but also the selectivity towards colon cancer cells brought about by the cyclohexane-1R,2R-diamine carrier ligand.

Synthesis, characterization and nucleic acid binding studies of mononuclear copper(II) complexes derived from azo containing O, O donor ligands

Azo linked salicyldehyde and a new 2-hydroxy acetophenone based ligands (HL¹ and HL²) with their copper(II) complexes [Cu(L¹)₂] (1) and [Cu(L²)₂] (2) were synthesized and characterized by spectroscopic methods such as ¹H, 13C NMR, UV-Vis spectroscopy and elemental analyses. Calculation based on Density Functional Theory (DFT), have been performed to obtain optimized structures. Binding studies of these copper (II) complexes with calf thymus DNA (ct-DNA) and torula yeast RNA (t-RNA) were analyzed by absorption spectra, emission spectra and Viscosity studies and Molecular Docking techniques. The absorption spectral study indicated that the copper(II) complexes of 1 and 2 had intrinsic binding constants with DNA or RNA in the range of 7.6 ± 0.2 × 10³ M^-1 or 6.5 ± 0.3 × 10³M^-1 and 5.7 ± 0.4 × 10⁴ M^-1 or 1.8 ± 0.5 × 10³ M^-1 respectively. The synthesized compounds and nucleic acids were simulated by molecular docking to explore more details mode of interaction of the complexes and their orientations in the active site of the receptor.

Synthesis of monofunctional platinum(iv) carboxylate precursors for use in Pt(iv)-peptide bioconjugates

Herein we present platinum(iv) bioconjugates with polyarginine peptides as prospective prodrug delivery systems. Asymmetrical platinum(iv) complexes 3 were obtained via oxidation of parent platinum(ii) complexes 2 with N-bromosuccinimide (NBS) in the presence of succinic anhydride. The combination of these two oxidation reagents furnishes the platinum(iv) environment with two different axial ligands, one of which bears a free carboxylic acid. All platinum(ii) and (iv) compounds were characterized by FT-IR, ESI-MS, HPLC, ¹H-, ¹³C- and ¹⁹⁵Pt-NMR. Standard solid-phase peptide chemistry was used for the synthesis of polyarginine (R₉) peptides. Coupling of the platinum complexes with peptides N-terminally afforded peptide monoconjugates, which were purified by semi-preparative HPLC and characterized by analytical HPLC and ESI-MS. Platinum(iv)-peptide bioconjugates as well as platinum(ii) and platinum(iv) complexes were tested as cytotoxic agents against two different human cancer cell lines (MCF-7, HepG2) and normal human fibroblasts cell lines (GM5657T). Preliminary in vitro data showed that all platinum(iv) complexes exhibit lower activity than their platinum(ii) precursors towards most cell lines. Interestingly, in the case of HepG2 cells, the Pt(iv)-(R)₉-G-A-L bioconjugate (4a) showed even higher activity compared to the non-targeting platinum(iv) parent compound.

Mechanism of hydrolysis of a platinum(IV) complex discovered by atomic telemetry

Herein we report on the hydrolysis mechanism of [Pt{N(p-HC₆F₄)CH₂}₂(NC₅H₅)₂(OH)₂], a platinum(IV) complex that exhibits anti-cancer properties. Atomic telemetry, an in situ technique based on electron structure sensitive X-ray spectroscopy, revealed that hydrolysis preceded any reduction of the metal center. The obtained results are complemented with ¹⁹F NMR measurements and theoretical calculations and support the observation that this Pt^IV complex does not reduce spontaneously to Pt^II in HEPES buffer solution at pH 7.4 and after 24 h incubation. These results are of importance for the design of novel Pt-based coordination complexes as well as understanding their behavior under physiological conditions.

Silver nanoparticles: Their role as antibacterial agent against Aeromonas salmonicida subsp. salmonicida in rainbow trout (Oncorhynchus mykiss)

The rise of bacterial resistance to antibiotics is one of the great challenges of our age. One of the strategies to limit the development of antibiotics resistance is the investigation of alternative antimicrobials. As silver nanoparticles demonstrated a potent bactericidal activity in vitro, the aim of this study was to evaluate the in vivo antibacterial activity of silver nanoparticles against Aeromonas salmonicida subsp. salmonicida. Rainbow trout (n = 120) were divided into four groups of 30 fish each. First group was challenged with A. salmonicida (Positive control), the second group was challenged with A. salmonicida and exposed to silver nanoparticles by immersion for three hours (100 μg/L), the third group was challenged with A. salmonicida and intraperitoneally injected with silver nanoparticles (17 μg/mL) and the fourth group was sham-treated and served as a negative control group. At the 7th day post challenge, histopathology of the positive control group revealed the presence of bacterial aggregates in tissues with degenerative and necrotic changes, while at the 35th day post challenge, only liver necrosis persisted. Silver nanoparticles-treated and negative control groups did not show any clinical signs, mortalities or histopathological alterations and they were tested negative for A. salmonicida. The immersion in silver nanoparticles did not result in detectable residues of silver in the muscles 35 days after treatment. These findings demonstrate the antibacterial properties of silver nanoparticles against A. salmonicida infection. Therefore, they could be used for development of antibacterial agents in aquaculture.

The impact of whole human blood on the kinetic inertness of platinum(iv) prodrugs - an HPLC-ICP-MS study

The potential advantage of platinum(iv) complexes as alternatives to classical platinum(ii)-based drugs relies on their kinetic stability in the body before reaching the tumor site and on their activation by reduction inside cancer cells. In this study, an analytical workflow has been developed to investigate the reductive biotransformation and kinetic inertness of platinum(iv) prodrugs comprising different ligand coordination spheres (respectively, lipophilicity and redox behavior) in whole human blood. The distribution of platinum(iv) complexes in blood pellets and plasma was determined by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave digestion. An analytical approach based on reversed-phase (RP)-ICP-MS was used to monitor the parent compound and the formation of metabolites using two different extraction procedures. The ligand coordination sphere of the platinum(iv) complexes had a significant impact on their accumulation in red blood cells and on their degree of kinetic inertness in whole human blood. The most lipophilic platinum(iv) compound featuring equatorial chlorido ligands showed a pronounced penetration into blood cells and a rapid reductive biotransformation. In contrast, the more hydrophilic platinum(iv) complexes with a carboplatin- and oxaliplatin-core exerted kinetic inertness on a pharmacologically relevant time scale with notable amounts of the compound accumulated in the plasma fraction.

Dual-acting antitumor Pt(iv) prodrugs of kiteplatin with dichloroacetate axial ligands

DNA and mitochondria of tumor cells are the targets of Pt(iv) complexes of kiteplatin with biologically active dichloroacetate as axial ligands.

NEAT1 upregulates EGCG-induced CTR1 to enhance cisplatin sensitivity in lung cancer cells

Platinum-based drugs are the firstline of treatment for non-small cell lung cancer (NSCLC), but resistance to these drugs is a major obstacle to effective chemotherapy. Our previous study revealed that the green tea polyphenol, EGCG, induced cisplatin transporter CTR1 (copper transporter 1) and enhanced cisplatin sensitivity in ovarian cancer. In this study, we found that EGCG upregulated CTR1 and increased platinum accumulation in NSCLC (A549, H460 and H1299) cells, cDDP-resistant A549 cells and a nude mouse xenograft model. Cisplatin-induced inhibition of cell growth was enhanced by EGCG treatment in vitro and in vivo. MicroRNA hsa-mir-98-5p appears to suppress CTR1 gene expression, while long non-coding RNA (lncRNA) nuclear enriched abundant transcript 1 (NEAT1) appears to enhance it. Bioinformatics analysis showed that hsa-mir-98-5p has specific complementary binding sites for NEAT1. In addition, hsa-mir-98-5p was predicted to be a putative CTR1 target. NEAT1 may act as a competing endogenous lncRNA to upregulate EGCG-induced CTR1 by sponging hsa-mir-98-5p in NSCLC. Our findings reveal a novel mechanism how NEAT1 upregulates EGCG-induced CTR1 and enhances cisplatin sensitivity in vitro and in vivo, and suggest EGCG could serve as an effective adjuvant chemotherapeutic in lung cancer treatment.

In vitro assessment of the antimicrobial activity of silver and zinc oxide nanoparticles against fish pathogens

BACKGROUND

Antibiotic resistance is a global issue that threatens public health. The excessive use of antibiotics contributes to this problem as the genes of antibiotic resistance can be transferred between the bacteria in humans, animals and aquatic organisms. Metallic nanoparticles could serve as future substitutes for some conventional antibiotics because of their antimicrobial activity. The aim of this study was to evaluate the antimicrobial effects of silver and zinc oxide nanoparticles against major fish pathogens and assess their safety in vitro. Silver nanoparticles were synthesized by chemical reduction and characterized with UV-Vis spectroscopy, transmission electron microscopy and zeta sizer. The concentrations of silver and zinc oxide nanoparticles were measured using inductively coupled plasma-mass spectrometry. Subsequently, silver and zinc oxide nanoparticles were tested for their antimicrobial activity against Aeromonas hydrophila, Aeromonas salmonicida subsp. salmonicida, Edwardsiella ictaluri, Edwardsiella tarda, Francisella noatunensis subsp. orientalis, Yersinia ruckeri and Aphanomyces invadans and the minimum inhibitory concentrations were determined. MTT assay was performed on eel kidney cell line (EK-1) to determine the cell viability after incubation with nanoparticles. The interaction between silver nanoparticles and A. salmonicida was investigated by transmission electron microscopy.

RESULTS

The tested nanoparticles exhibited marked antimicrobial activity. Silver nanoparticles inhibited the growth of both A. salmonicida and A. invadans at a concentration of 17 µg/mL. Zinc oxide nanoparticles inhibited the growth of A. salmonicida, Y. ruckeri and A. invadans at concentrations of 15.75, 31.5 and 3.15 µg/mL respectively. Silver nanoparticles showed higher cell viability when compared to zinc oxide nanoparticles in the MTT assay. Transmission electron microscopy showed the attachment of silver nanoparticles to the bacterial membrane and disruption of its integrity.

CONCLUSIONS

This is the first study on inhibitory effects of silver and zinc oxide nanoparticles towards A. salmonicida and A. invadans. Moreover, zinc oxide nanoparticles inhibited the growth of Y. ruckeri. In low concentrations, silver nanoparticles were less cytotoxic than zinc oxide nanoparticles and represent an alternative antimicrobial compound against A. hydrophila, A. salmonicida and A. invadans.

Epigenetic and antitumor effects of platinum(IV)-octanoato conjugates

We present the anticancer properties of cis, cis, trans-[Pt(IV)(NH₃)₂Cl₂(OA)₂] [Pt(IV)diOA] (OA = octanoato), Pt(IV) derivative of cisplatin containing two OA units appended to the axial positions of a six-coordinate Pt(IV) center. Our results demonstrate that Pt(IV)diOA is a potent cytotoxic agent against many cancer cell lines (the IC₅₀ values are approximately two orders of magnitude lower than those of clinically used cisplatin or Pt(IV) derivatives with biologically inactive axial ligands). Importantly, Pt(IV)diOA overcomes resistance to cisplatin, is significantly more potent than its branched Pt(IV) valproato isomer and exhibits promising in vivo antitumor activity. The potency of Pt(IV)diOA is a consequence of several factors including enhanced cellular accumulation correlating with enhanced DNA platination and cytotoxicity. Pt(IV)diOA induces DNA hypermethylation and reduces mitochondrial membrane potential in cancer cells at levels markedly lower than the IC₅₀ value of free OA suggesting the synergistic action of platinum and OA moieties. Collectively, the remarkable antitumor effects of Pt(IV)diOA are a consequence of the enhanced cellular uptake which makes it possible to simultaneously accumulate high levels of both cisplatin and OA in cells. The simultaneous dual action of cisplatin and OA by different mechanisms in tumor cells may result in a markedly enhanced and unique antitumor effects of Pt(IV) prodrugs.

Platinum, palladium, gold and ruthenium complexes as anticancer agents: Current clinical uses, cytotoxicity studies and future perspectives

Metallodrugs offer potential for unique mechanism of drug action based on the choice of the metal, its oxidation state, the types and number of coordinated ligands and the coordination geometry. This review illustrates notable recent progress in the field of medicinal bioinorganic chemistry as many new approaches to the design of innovative metal-based anticancer drugs are emerging. Current research addressing the problems associated with platinum drugs has focused on other metal-based therapeutics that have different modes of action and on prodrug and targeting strategies in an effort to diminish the side-effects of cisplatin chemotherapy. Examples of metal compounds and chelating agents currently in clinical use, clinical trials or preclinical development are highlighted.

An albumin-based tumor-targeted oxaliplatin prodrug with distinctly improved anticancer activity in vivo

An oxaliplatin-based platinum(iv) drug which specifically binds to albumin after i.v. application led to several complete responses in tumor-bearing mice.

The design of targeted platinum(iv) prodrugs is a very promising approach to enhance the low selectivity of platinum(ii) drugs towards cancerous tissue in order to reduce the impact on healthy tissue and, consequently, the often severe side-effects. Herein, we report a set of mono-functionalized cis- and oxaliplatin-based platinum(iv) complexes bearing a maleimide moiety, which allows selective binding to serum albumin in the bloodstream. This leads not only to a prolonged plasma half-life by avoidance of fast renal clearance, but also to preferential accumulation of the drug in the tumor tissue due to the EPR-effect. Additionally, analogous succinimide-functionalized derivatives were prepared to verify the influence of the maleimide moiety. First experiments showed that all the maleimide compounds are stable and also possess good albumin-binding properties in whole serum. Further analytical studies on in vivo samples proved the highly increased plasma half-life, as well as tumor accumulation of the maleimide-functionalized substances. In vivo antitumor experiments with CT-26-bearing mice showed that, in contrast to the cisplatin derivatives, the oxaliplatin-based complexes had exceptionally better activity than the free drug resulting in the cure of the majority of treated mice. Subsequent analysis suggested that a distinctly faster reduction as well as reduced tumor accumulation of the cisplatin derivative might explain the worse performance compared to the oxaliplatin(iv) complexes. Taken together, a novel lead platinum(iv) complex with outstanding antitumor activity is presented, which will now be further developed towards clinical phase I trials.

Oral delivery of a platinum anticancer drug using lipid assisted polymeric nanoparticles

Self-assembled cholesterol-asplatin-incorporated nanoparticles (SCANs) were prepared for oral delivery of a Pt(IV) prodrug. SCANs exhibit high gastrointestinal stability, sustained drug release and enhanced cell uptake. The oral bioavailability of SCANs was 4.32-fold higher than that of free Pt(IV) prodrugs. The oral administration of SCANs efficaciously inhibits tumor growth with negligible toxicity.

Advances in oral delivery of anti-cancer prodrugs

INTRODUCTION

Most anticancer drugs have poor aqueous solubility and low permeability across the gastrointestinal tract. Furthermore, extensive efflux by P-glycoproteins (P-gp) in the small intestine also limits the efficient delivery of anticancer drugs via oral route. Area covered: This review explores the prodrug strategy for oral delivery of anticancer drugs. Different categories of oral anticancer prodrugs along with recent clinical studies have been comprehensively reviewed here. Furthermore, novel anticancer prodrugs such as polymer-prodrugs and lipid-prodrugs have been discussed in detail. Finally, various nanocarrier-based approaches employed for oral delivery of anticancer prodrugs have also been discussed. Expert opinion: Premature degradation of anticancer prodrugs in the gastrointestinal tract could lead to variable pharmacokinetics and undesired toxicity. Despite their increased aqueous solubility, the oral bioavailability of several anticancer prodrugs are limited by their poor permeability across the gastrointestinal tract. These limitations can be overcome by the use of functional excipients (polymers, lipids, amino acids/dipeptides), which are specifically absorbed via transporters and receptor-mediated endocytosis. Oral delivery of anticancer prodrugs using nanocarrier-based drug delivery system is a recent development; however it should be justified based on the comparative advantages of encapsulating prodrug in a nanocarrier versus the use of anticancer prodrug molecule itself.

The role of the equatorial ligands for the redox behavior, mode of cellular accumulation and cytotoxicity of platinum(IV) prodrugs

The current study aims to elucidate the possible reasons for the significantly different pharmacological behavior of platinum(IV) complexes with cisplatin-, carboplatin- or nedaplatin-like cores and how this difference can be related to their main physicochemical properties. Chlorido-containing complexes are reduced fast (within hours) by ascorbate and are able to unwind plasmid DNA in the presence of ascorbate, while their tri- and tetracarboxylato analogs are generally inert under the same conditions. Comparison of the lipophilicity, cellular accumulation and cytotoxicity of the investigated platinum compounds revealed the necessity to define new structure-property/activity relationships (SPRs and SARs). The higher activity and improved accumulation of platinum(IV) complexes bearing Cl(-) in equatorial position cannot only be attributed to passive diffusion facilitated by their lipophilicity. Therefore, further platinum accumulation experiments under conditions where active/facilitated transport mechanisms are suppressed were performed. Under hypothermic conditions (4°C), accumulation of dichloridoplatinum(IV) complexes is reduced down to 10% of the amount determined at 37°C. These findings suggest the involvement of active and/or facilitated transport in cellular uptake of platinum(IV) complexes with a cisplatin-like core. Studies with ATP depletion mediated by oligomycin and low glucose partially confirmed these observations, but their feasibility was severely limited in the adherent cell culture setting.

Multi-scale imaging of anticancer platinum(iv) compounds in murine tumor and kidney

Nano-scale secondary ion mass spectrometry (NanoSIMS) enables trace element and isotope analyses with high spatial resolution. This unique capability has recently been exploited in several studies analyzing the subcellular distribution of Au and Pt anticancer compounds. However, these studies were restricted to cell culture systems. To explore the applicability to the in vivo setting, we developed a combined imaging approach consisting of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), NanoSIMS and transmission electron microscopy (TEM) suitable for multi-scale detection of the platinum distribution in tissues. Applying this approach to kidney and tumor samples upon administration of selected platinum(iv) anticancer prodrugs revealed uneven platinum distributions on both the organ and subcellular scales. Spatial platinum accumulation patterns were quantitatively assessed by LA-ICP-MS in histologically heterogeneous organs (e.g., higher platinum accumulation in kidney cortex than in medulla) and used to select regions of interest for subcellular-scale imaging with NanoSIMS. These analyses revealed cytoplasmic sulfur-rich organelles accumulating platinum in both kidney and malignant cells. Those in the tumor were subsequently identified as organelles of lysosomal origin, demonstrating the potential of the combinatorial approach for investigating therapeutically relevant drug concentrations on a submicrometer scale.

Prediction of logP for Pt(II) and Pt(IV) complexes: Comparison of statistical and quantum-chemistry based approaches

The octanol/water partition coefficient, logP, is one of the most important physico-chemical parameters for the development of new metal-based anticancer drugs with improved pharmacokinetic properties. This study addresses an issue with the absence of publicly available models to predict logP of Pt(IV) complexes. Following data collection and subsequent development of models based on 187 complexes from literature, we validate new and previously published models on a new set of 11 Pt(II) and 35 Pt(IV) complexes, which were kept blind during the model development step. The error of the consensus model, 0.65 for Pt(IV) and 0.37 for Pt(II) complexes, indicates its good accuracy of predictions. The lower accuracy for Pt(IV) complexes was attributed to experimental difficulties with logP measurements for some poorly-soluble compounds. This model was developed using general-purpose descriptors such as extended functional groups, molecular fragments and E-state indices. Surprisingly, models based on quantum-chemistry calculations provided lower prediction accuracy. We also found that all the developed models strongly overestimate logP values for the three complexes measured in the presence of DMSO. Considering that DMSO is frequently used as a solvent to store chemicals, its effect should not be overlooked when logP measurements by means of the shake flask method are performed. The final models are freely available at http://ochem.eu/article/76903.

LA-ICP-MS imaging in multicellular tumor spheroids - a novel tool in the preclinical development of metal-based anticancer drugs

A novel application of advanced elemental imaging offers cutting edge in vitro assays with more predictive power on the efficacy of anticancer drugs in preclinical development compared to two dimensional cell culture models. We propose LA-ICP-MS analysis of multicellular spheroids, which are increasingly being used as three dimensional (3D) models of tumors, for improving the in vitro evaluation of anticancer metallodrugs. The presented strategy is very well suited for screening drug-tumor penetration, a key issue for drug efficacy. A major advantage of tumor spheroid models is that they enable us to create a tissue-like structure and function. With respect to 2D culture on the one hand and in vivo models on the other, multicellular spheroids thus show intermediate complexity, still allowing high repeatability and adequate through-put for drug research. This strongly argues for the use of spheroids as bridging models in preclinical anticancer drug development. Probing the lateral platinum distribution within these tumor models allows visualizing the penetration depth and targeting of platinum-based complexes. In the present study, we show for the first time that spatially-resolved metal accumulation in tumor spheroids upon treatment with platinum compounds can be appropriately assessed. The optimized LA-ICP-MS setup allowed discerning the platinum localization in different regions of the tumor spheroids upon compound treatment at biologically relevant (low micromolar) concentrations. Predominant platinum accumulation was observed at the periphery as well as in the center of the spheroids. This corresponds to the proliferating outermost layers of cells and the necrotic core, respectively, indicating enhanced platinum sequestration in these regions.

Electrochemical Detection of Platinum(IV) Prodrug Satraplatin in Serum

We report the design and fabrication of a reagentless and reusable electrochemical sensor for detection of satraplatin (SAT), a platinum(IV) prodrug. The detection strategy is based on the electrocatalytic reaction between the Pt(IV) center of SAT and surface-immobilized methylene blue. We systematically evaluated the effect of passivating diluent chain length on the overall sensor performance. Our results show that the use of a shorter diluent like 2-mercaptoethanol is more advantageous than using a longer and more passivating diluent such as 6-mercapto-1-hexanol. Independent of the use of cyclic voltammetry or chronoamperometry as the sensor interrogation technique, all three sensors, each passivated with a different alkanethiol diluent, have been demonstrated to be sensitive; the limit of detection is in the range of 1-10 μM. They are also highly specific and do not respond to Pt(II) drugs such as cisplatin and carboplatin. More importantly, they are selective enough to be employed directly in 50% serum. This sensing strategy has potential applications in clinical pharmacokinetics studies.

Recent Advances in Platinum (IV) Complex-Based Delivery Systems to Improve Platinum (II) Anticancer Therapy

Cisplatin and its platinum (Pt) (II) derivatives play a key role in the fight against various human cancers such as testicular, ovarian, head and neck, lung tumors. However, their application in clinic is limited due to dose- dependent toxicities and acquired drug resistances, which have prompted extensive research effort toward the development of more effective Pt (II) delivery strategies. The synthesis of Pt (IV) complex is one such an area of intense research fields, which involves their in vivo conversion into active Pt (II) molecules under the reducing intracellular environment, and has demonstrated encouraging preclinical and clinical outcomes. Compared with Pt (II) complexes, Pt (IV) complexes not only exhibit an increased stability and reduced side effects, but also facilitate the intravenous-to-oral switch in cancer chemotherapy. The overview briefly analyzes statuses of Pt (II) complex that are in clinical use, and then focuses on the development of Pt (IV) complexes. Finally, recent advances in Pt (IV) complexes in combination with nanocarriers are highlighted, addressing the shortcomings of Pt (IV) complexes, such as their instability in blood and irreversibly binding to plasma proteins and nonspecific distribution, and taking advantage of passive and active targeting effect to improve Pt (II) anticancer therapy.

Tumor microenvironment in focus: LA-ICP-MS bioimaging of a preclinical tumor model upon treatment with platinum(IV)-based anticancer agents

The selection of drug candidates for entering clinical development relies on in vivo testing in (solid) tumor animal models. However, the heterogeneity of tumor tissue (e.g. in terms of drug uptake or tissue composition) is rarely considered when testing novel drug candidates. Therefore, we used the murine colon cancer CT-26 tumor model to study the spatially-resolved drug distribution in tumor tissue upon repetitive treatment of animals over two weeks with three investigational platinum(IV)-based anticancer agents, oxaliplatin or satraplatin. A quantitative laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging method revealed a heterogeneous platinum distribution, which correlated well with the histologic features of the tumor and surrounding tissue at the microscopic level. In most of the cases, higher amounts of intratumoral platinum were found in the surrounding tissue than in the malignant parts of the sample. This indicates that determination of average platinum amounts (e.g. by microwave-assisted digestion of the sample followed by analysis with ICP-MS) might overestimate the drug uptake in tumor tissue causing misleading conclusions. In addition, we studied the platinum distribution in the kidneys of treated animals to probe if accumulation in the cortex and medulla predict potential nephrotoxicity. A 10-fold increase of platinum in the cortex of the kidney over the medulla was observed for oxaliplatin and satraplatin. Although these findings are similar to those in the platinum distribution of the nephrotoxic anticancer drug cisplatin, treatment with the compounds of our study did not show signs of nephrotoxicity in clinical use or clinical trials (oxaliplatin, satraplatin) and did not result in the alteration of renal structures. Thus, predicting the side effects based on bioimaging data by LA-ICP-MS should be considered with caution. To the best of our knowledge, this is the first LA-ICP-MS study on spatially-resolved platinum accumulation in tissues after repetitive platinum-based anticancer drug treatment of mice bearing a preclinical tumor model.