A novel class of bis- and tris-chelate diam(m)inebis(dicarboxylato)platinum(IV) complexes as potential anticancer prodrugs

Not the usual suspect - an unexpected organometallic product during the synthesis of cytotoxic platinum(II) complexes

The reaction of (1R,2R)-(cyclohexane-1,2-diamine)dichloridoplatinum(II) with maleic acid unexpectedly resulted in the formation of an organometallic platinum(II) complex featuring a C,O-coordinating ligand. Additionally, a small series of close derivatives with increasing lipophilicity was synthesized. All complexes were fully characterized by multinuclear one- and two-dimensional (1H, 13C, 15N, and 195Pt) NMR spectroscopy, high resolution mass spectrometry, and in one case by X-ray diffraction. The lipophilicity and the impact on the DNA secondary structure as well as the cytotoxic properties in three human cancer cell lines (A549, SW480, and CH1/PA-1) were investigated. Unexpectedly, no clear-cut trend in cytotoxicity was observed with increasing lipophilicity. Also unexpectedly, the complexes showed only a low potential to inhibit cancer cell growth and no sign of interaction with DNA, in sharp contrast to the parent drug oxaliplatin, which seems to be caused by the low reactivity of the investigated compounds.

Combination of Drug Delivery Properties of PAMAM Dendrimers and Cytotoxicity of Platinum(IV) Complexes-A More Selective Anticancer Treatment?

Based on their drug delivery properties and activity against tumors, we combined PAMAM dendrimers with various platinum(IV) complexes in order to provide an improved approach of anticancer treatment. Platinum(IV) complexes were linked to terminal NH₂ moieties of PAMAM dendrimers of generation 2 (G2) and 4 (G4) via amide bonds. Conjugates were characterized by ¹H and ¹⁹⁵Pt NMR spectroscopy, ICP-MS and in representative cases by pseudo-2D diffusion-ordered NMR spectroscopy. Additionally, the reduction behavior of conjugates in comparison to corresponding platinum(IV) complexes was investigated, showing a faster reduction of conjugates. Cytotoxicity was evaluated via the MTT assay in human cell lines (A549, CH1/PA-1, SW480), revealing IC₅₀ values in the low micromolar to high picomolar range. The synergistic combination of PAMAM dendrimers and platinum(IV) complexes resulted in up to 200 times increased cytotoxic activity of conjugates in consideration of the loaded platinum(IV) units compared to their platinum(IV) counterparts. The lowest IC₅₀ value of 780 ± 260 pM in the CH1/PA-1 cancer cell line was detected for an oxaliplatin-based G4 PAMAM dendrimer conjugate. Finally, in vivo experiments of a cisplatin-based G4 PAMAM dendrimer conjugate were performed based on the best toxicological profile. A maximum tumor growth inhibition effect of 65.6% compared to 47.6% for cisplatin was observed as well as a trend of prolonged animal survival.

Platinum(II) 5-substituted-8-hydroxyquinoline coordination compounds induces mitophagy-mediated apoptosis in A549/DDP cancer cells

For the first time, two new mononuclear platinum(II) coordination compounds, [Pt(L1)(DMSO)Cl] (PtL1) and [Pt(L2)(DMSO)Cl] (PtL2) with the 5-(ethoxymethyl)-8-hydroxyquinoline hydrochloride (H-L1) and 5-bromo-8-hydroxyquinoline (H-L2) have been synthesized and characterized. The cytotoxic activity of PtL1 and PtL2 were screened in both healthy HL-7702 cell line and cancer cell lines, human lung adenocarcinoma A549 cancer cells and cisplatin-resistant lung adenocarcinoma A549/DDP cancer cells (A549R), and were compared to that of the H-L1, H-L2, H-L3 ligands and 8-hydroxyquinoline (H-L3) platinum(II) complex [Pt(L3)(DMSO)Cl] (PtL3). MTT results showed that PtL1 bearing one deprotonated L1 ligand against A549R was more potent by 8.8-48.6 fold than that of PtL2 and PtL3 complexes but was more selective toward healthy HL-7702 cells. In addition, PtL1 and PtL3 overcomes tumour drug resistance by significantly inducing mitophagy and causing the change of the related proteins expression, which leads to cell apoptosis. Moreover, the inhibitory effect of PtL1 on A549 xenograft tumour was 68.2%, which was much higher than that of cisplatin (cisPt, ca. 50.0%), without significantly changing nude mice weight in comparison with the untreated group. This study helps to explore the potential of the platinum(II) 5-substituted-8-hydroxyquinoline coordination compounds for the new Pt-resistant cancer therapy.

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.

Arene Variation of Highly Cytotoxic Tridentate Naphthoquinone-Based Ruthenium(II) Complexes and In-Depth In Vitro Studies

The main purpose of this study was to synthesize a new set of naphthoquinone-based ruthenium(II) arene complexes and to develop an understanding of their mode of action. This study systematically reviews the steps of synthesis, aiming to provide a simplified approach using microwave irradiation. The chemical structures and the physicochemical properties of this novel group of compounds were examined by 1H-NMR and 13C-NMR spectroscopy, X-ray diffractometry, HPLC-MS and supporting DFT calculations. Several aspects of the biological activity were investigated in vitro, including short- and long-term cytotoxicity tests, cellular accumulation studies, detection of reactive oxygen species generation, apoptosis induction and NAD(P)H:quinone oxidoreductase 1 (NQO1) activity as well as cell cycle analysis in A549, CH1/PA-1, and SW480 cancer cells. Furthermore, the DNA interaction ability was studied in a cell-free assay. A positive correlation was found between cytotoxicity, lipophilicity and cellular accumulation of the tested complexes, and the results offer some important insights into the effects of the arene. The most obvious finding to emerge from this study is that the usually very chemosensitive CH1/PA-1 teratocarcinoma cells showed resistance to these phthiocol-based organometallics in comparison to the usually less chemosensitive SW480 colon carcinoma cells, which pilot experiments suggest as being related to NQO1 activity.

Novel Salinomycin-Based Paramagnetic Complexes-First Evaluation of Their Potential Theranostic Properties

Combining therapeutic with diagnostic agents (theranostics) can revolutionize the course of malignant diseases. Chemotherapy, hyperthermia, or radiation are used together with diagnostic methods such as magnetic resonance imaging (MRI). In contrast to conventional contrast agents (CAs), which only enable non-specific visualization of tissues and organs, the theranostic probe offers targeted diagnostic imaging and therapy simultaneously.

METHODS

Novel salinomycin (Sal)-based theranostic probes comprising two different paramagnetic metal ions, gadolinium(III) (Gd(III)) or manganese(II) (Mn(II)), as signal emitting motifs for MRI were synthesized and characterized by elemental analysis, infrared spectral analysis (IR), electroparamagnetic resonance (EPR), thermogravimetry (TG) differential scanning calorimetry (DSC) and electrospray ionization mass spectrometry (ESI-MS). To overcome the water insolubility of the two Sal-complexes, they were loaded into empty bacterial ghosts (BGs) cells as transport devices. The potential of the free and BGs-loaded metal complexes as theranostics was evaluated by in vitro relaxivity measurements in a high-field MR scanner and in cell culture studies.

RESULTS

Both the free Sal-complexes (Gd(III) salinomycinate (Sal-Gd(III) and Mn(II) salinomycinate (Sal-Mn(II)) and loaded into BGs demonstrated enhanced cytotoxic efficacy against three human tumor cell lines (A549, SW480, CH1/PA-1) relative to the free salinomycinic acid (Sal-H) and its sodium complex (Sal-Na) applied as controls with IC₅₀ in a submicromolar concentration range. Moreover, Sal-H, Sal-Gd(III), and Sal-Mn(II) were able to induce perturbations in the cell cycle of treated colorectal and breast human cancer cell lines (SW480 and MCF-7, respectively). The relaxivity (r₁) values of both complexes as well as of the loaded BGs, were higher or comparable to the relaxivity values of the clinically applied contrast agents gadopentetate dimeglumine and gadoteridol.

CONCLUSION

This research is the first assessment that demonstrates the potential of Gd(III) and Mn(II) complexes of Sal as theranostic agents for MRI. Due to the remarkable selectivity and mode of action of Sal as part of the compounds, they could revolutionize cancer therapy and allow for early diagnosis and monitoring of therapeutic follow-up.

A Theoretical Study on the Medicinal Properties and Eletronic Structures of Platinum(IV) Anticancer Agents With Cl Substituents

In this paper, we selected Pt(en)Cl4, Pt(dach)Cl4, and Pt(bipy)Cl4 with gradually increasing ligands to explore the ligand effect on the properties of platinum(IV) anticancer drugs. The electronic structures and multiple drug properties of these three complexes were studied at the LSDA/SDD level using the density functional theory (DFT) method. By comparing the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), electron affinity, atomic charge population, and natural bond orbital (NBO), we found that the order of reducibility is Pt(bipy)Cl4 > Pt(en)Cl4 > Pt(dach)Cl4. Our research can provide the theoretical basis for the development of anticancer drugs.

Stereoselective synthesis of oxime containing Pd(II) compounds: Highly effective, selective and stereo-regulated cytotoxicity against carcinogenic PC-3 cells

New palladium compounds [Pd{(1S,4R)-NOH^NH(R)}Cl2] (R = Ph 1a or Bn 1b), [Pd{(1S,4R)-NOH^NH(R)}{(1S,4R)-NO^NH(R)}][Cl] (R = Ph 2a or Bn 2b) and corresponding [Pd{(1R,4S)-NOH^NH(R)}Cl2] (R = Ph 1a’ or Bn 1b’) and...

Tridentate 3-Substituted Naphthoquinone Ruthenium Arene Complexes: Synthesis, Characterization, Aqueous Behavior, and Theoretical and Biological Studies

A series of nine Ru^II arene complexes bearing tridentate naphthoquinone-based N,O,O-ligands was synthesized and characterized. Aqueous stability and their hydrolysis mechanism were investigated via UV/vis photometry, HPLC-MS, and density functional theory calculations. Substituents with a positive inductive effect improved their stability at physiological pH (7.4) intensely, whereas substituents such as halogens accelerated hydrolysis and formation of dimeric pyrazolate and hydroxido bridged dimers. The observed cytotoxic profile is unusual, as complexes exhibited much higher cytotoxicity in SW480 colon cancer cells than in the broadly chemo- (incl. platinum-) sensitive CH1/PA-1 teratocarcinoma cells. This activity pattern as well as reduced or slightly enhanced ROS generation and the lack of DNA interactions indicate a mode of action different from established or previously investigated classes of metallodrugs.

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.

Novel phthiocol-based organometallics with tridentate coordination motif and their unexpected cytotoxic behaviour

Novel phthiocol-based organometallics with in situ formed tridentate N,O,O-coordination motif were established via three-component microwave assisted one-pot reaction. These complexes exhibited enhanced stability in aqueous solution compared to the parental compound KP2048 and showed unexpected cytotoxic behaviour and selectivity in 2D and 3D cell cultures.

Synthesis, characterisation and influence of lipophilicity on cellular accumulation and cytotoxicity of unconventional platinum(iv) prodrugs as potent anticancer agents

Lipophilic platinum(iv) complexes were synthesised of the type [Pt(HL)(AL)(OH)(R)]2+ and [Pt(HL)(AL)(R)2]2+ (HL = 5,6-dimethyl-1,10-phenanthroline or 1,10-phenanthroline; AL = 1S,2S-diaminocyclohexane and R = increasingly lipophilic carboxylate axial ligands (C10-18)) from hydrophilic platinum(ii) precursors that exhibit exceptional anticancer activity. The increased overall lipophilicity of the complexes suggested the formation of spontaneously self-assembled structures in an aqueous environment. The anti-proliferative properties were assessed against one non-cancerous and a panel of cancerous cell lines. Nanomolar levels of activity were observed against several cell lines, with the lowest GI50 of 3.4 nm against the Du145 prostate cancer cell line and over 1100-fold greater activity than cisplatin against HT29 colon carcinoma. RP-HPLC was utilised to establish the relative lipophilicities of each complex. While there seemed to be an increase in cellular accumulation for the lipophilic derivatives in some instances, ICP-MS studies showed no clear correlation between increasing lipophilicity, cellular accumulation and cytotoxicity.

The First Anticancer Tris(pyrazolyl)borate Molybdenum(IV) Complexes: Tested in Vitro and in Vivo-A Comparison of O,O-, S,O-, and N,N-Chelate Effects

The synthesis, characterization and biological activity of molybdenum(IV) complexes containing Trofimenko's scorpionato ligand, hydrotris(3-isopropylpyrazolyl)borate (TpiPr ), in addition to varying biologically active as well as other conventional ligands is described. Ligands employed include (O,O-) (S,O-) (N,N-) donors that have been successfully coordinated to the molybdenum center by means of oxygen-atom transfer (OAT) reactions from the known MoVI starting material, TpiPr MoO2 Cl. The synthesized complexes were characterized by standard analytical methods and where possible by X-ray diffraction analysis. The aqueous stability of the compounds was studied by means of UV/Vis spectroscopy and the impact of the attached ligand scaffolds on the oxidation potentials (MoIV to MoV ) was studied by cyclic voltammetry. Utilizing polyvinylpyrrolidone (PVP) as a solubilizing agent, adequate aqueous solubility for biological tests was obtained. Anticancer activity tests and preliminary mode of action studies have been performed in vitro and in vivo.

Fine-Tuning the Activation Mode of an 1,3-Indandione-Based Ruthenium(II)-Cymene Half-Sandwich Complex by Variation of Its Leaving Group

Fine-tuning of the properties of a recently reported 1,3-indandione-based organoruthenium complex is attempted to optimize the stability under physiological conditions. Previous work has shown its capacity of inhibiting topoisomerase IIα; however, fast aquation leads to undesired reactions and ligand cleavage in the blood stream before the tumor tissue is reached. Exchange of the chlorido ligand for six different N-donor ligands resulted in new analogs that were stable at pH 7.4 and 8.5. Only a lowered pH level, as encountered in the extracellular space of the tumor tissue, was capable of aquating the complexes. The 50% inhibitory concentration (IC₅₀) values in three human cancer cell lines differed only slightly, and their dependence on the utilized leaving group was smaller than what would be expected from their differences in cellular accumulation, but in accordance with the very minor variation revealed in measurements of the complexes’ lipophilicity.

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.

Glucose-conjugated platinum(IV) complexes as tumor-targeting agents: design, synthesis and biological evaluation

A new series of glucose-conjugated Pt(IV) complexes that target tumor-specific glucose transporters (GLUTs) was designed, synthesized, and evaluated for their anticancer activities. All six compounds, namely, A1-A6, exhibited increased cytotoxicity that were almost six fold higher than that of oxaliplatin to MCF-7 cells. These Pt(IV) complexes can be reduced to release Pt(II) complexes and cause the death of tumor cells. Simultaneously, the glycosylated Pt(IV) complexes (30.21-91.33 μM) showed lower cytotoxicity that normal LO2 cells compared with cisplatin (5.25 μM) and oxaliplatin (8.34 μM). The intervention of phlorizin as a GLUTs inhibitor increased the IC₅₀ value of the glycosylated Pt(IV) complexes, thereby indicating the potential GLUT transportability. The introduction of glucose moiety to Pt(IV) complexes can effectively enhance the Pt cellular uptake and DNA platination. Results suggested glucose-conjugated Pt(IV) complexes had potential for further study as new anticancer agents.

Water soluble, optically active monofunctional Pd(ii) and Pt(ii) compounds: promising adhesive and antimigratory effects on human prostate PC-3 cancer cells

Water soluble, enantiomerically pure “rule breakers” Pd(ii) and Pt(ii) compounds with promising anticancer potential are reported.

Development and Validation of Liquid Chromatography-Based Methods to Assess the Lipophilicity of Cytotoxic Platinum(IV) Complexes

Lipophilicity is a crucial parameter for drug discovery, usually determined by the logarithmic partition coefficient (Log P) between octanol and water. However, the available detection methods have restricted the widespread use of the partition coefficient in inorganic medicinal chemistry, and recent investigations have shifted towards chromatographic lipophilicity parameters, frequently without a conversion to derive Log P. As high-performance liquid chromatography (HPLC) instruments are readily available to research groups, a HPLC-based method is presented and validated to derive the partition coefficient of a set of 19 structurally diverse and cytotoxic platinum(IV) complexes exhibiting a dynamic range of at least four orders of magnitude. The chromatographic lipophilicity parameters φ0 and Log kw were experimentally determined for the same set of compounds, and a correlation was obtained that allows interconversion between the two lipophilicity scales, which was applied to an additional set of 34 platinum(IV) drug candidates. Thereby, a φ0 = 58 corresponds to Log P = 0. The same approaches were successfully evaluated to determine the distribution coefficient (Log D) of five ionisable platinum(IV) compounds to sample pH-dependent effects on the lipophilicity. This study provides straight-forward HPLC-based methods to determine the lipophilicity of cytotoxic platinum(IV) complexes in the form of Log P and φ0 that can be interconverted and easily expanded to other metal-based compound classes.

Chlorambucil-conjugated platinum(IV) prodrugs to treat triple-negative breast cancer in vitro and in vivo

Modification of platinum (II) into lipophilic platinum (IV) compounds by introducing biologically active molecules were widely employed to develop new platinum-based prodrugs in the past decade. In this paper, two chlorambucil platinum (IV) complexes, CLB-Pt and CLB-Pt-CLB, were synthesized and displayed very potent antiproliferative activity against all the tested cancer cell lines, such as A549, HeLa and MCF-7, especially to treat the well-known refractory triple-negative breast cancer. CLB-Pt-CLB significantly improved cell-killing effect in triple-negative subtype MDA-MB-231 cells, and showed much stronger cytotoxicity than either monotherapy or combination of cisplatin and chlorambucil. CLB-Pt-CLB prodrug entered cells in dramatically increased amount compared with cisplatin and enhanced DNA damage, inducing cancer cell apoptosis. It exhibited high anticancer activity and no observable toxicity in BALB/c nude mice bearing MDA-MB-231 tumors. The chlorambucil moiety not only greatly assisted the passive diffusion of CLB-Pt-CLB into cells, but also produced the synergism with cisplatin in targeting DNA.

N- and S-donor leaving groups in triazole-based ruthena(ii)cycles: potent anticancer activity, selective activation, and mode of action studies

The functionalization of cycloruthenated triazole arene complexes with N- or S-donors affords pH or redox-activatable complexes with high cytotoxic activities.

Impact of the equatorial coordination sphere on the rate of reduction, lipophilicity and cytotoxic activity of platinum(IV) complexes

The impact of the equatorial coordination sphere on the reduction behavior (i.e. rate of reduction) of platinum(IV) complexes with axial carboxylato ligands was studied. Moreover, the influence of equatorial ligands on the stability, lipophilicity and cytotoxicity of platinum(IV) compounds was evaluated. For this purpose, a series of platinum(IV) complexes featuring axial carboxylato ligands (succinic acid monoesters) was synthesized; anionic carboxylato (OAc^-, oxalate) and halido (Cl^-, Br^-, I^-) ligands served as leaving groups and am(m)ine carrier ligands were provided by monodentately (isopropylamine, ammine+cyclohexaneamine) or bidentately (ethane-1,2-diamine) coordinating am(m)ines. All platinum(IV) products were fully characterized based on elemental analysis, high resolution mass spectrometry and multinuclear (¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt) NMR spectroscopy as well as by X-ray diffraction in some cases. The rate of reduction in the presence of ascorbic acid was determined by NMR spectroscopy and the lipophilicity of the complexes was investigated by analytical reversed phase HPLC measurements. Cytotoxic properties were studied by means of a colorimetric microculture assay in three human cancer cell lines derived from cisplatin sensitive ovarian teratocarcinoma (CH1/PA-1) as well as cisplatin insensitive colon carcinoma (SW480) and non-small cell lung cancer (A549).

Introducing the 4-Phenyl-1,2,3-Triazole Moiety as a Versatile Scaffold for the Development of Cytotoxic Ruthenium(II) and Osmium(II) Arene Cyclometalates

Herein we report the synthesis, anticancer potency in vitro, biomolecule interaction, and preliminary mode of action studies of a series of cyclometalated 1,2,3-triazole-derived ruthenium(II) (2a-e) and osmium(II) (3a-e) organometallics of the general form [(η⁶-p-cym)RuCl(κ²-C^N-L)] with varying substituents in postion 1 of the 1,2,3-triazole moiety. These cyclometalates were characterized by standard analytical methods and their structures unambiguously assigned by single crystal X-ray crystallography. The anticancer activity of these novel compounds was tested in the human tumor cell lines A549 (non-small cell lung cancer), SW480 (colon adenocarcinoma), and CH1/PA-1 (ovarian teratocarcinoma), and preliminary structure-activity relationships were derived from the obtained data sets. Various representatives exhibit promising antineoplastic effects with IC₅₀ values down to the low micromolar range. The compounds readily formed stable DMSO adducts after aquation in DMSO-containing solution, but employing DMSO as solubilizer in cytotoxicity assays had no pronounced effect on the cytotoxicity, compared to analogous experiments with DMF for most compounds. We isolated and characterized selected DMSO adducts as triflate salts and found that they show activities in the same range as the parent chlorido metalacycles in MTT assays with the use of DMSO. Osmium(II) cyclometalates exhibited higher antiproliferative activities than their ruthenium(II) counterparts. The IC₅₀ values within each metal series decreased with increasing lipophilicity, which was attributed to higher cellular accumulation. Investigations on their mode of action revealed that the prepared organometallics were unable to inhibit topoisomerase IIα. Still, the most cytotoxic representatives 2b and 3b showed pronounced effects on cell cycle distribution.

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.

Combretastatin A-4 Analogue: A Dual-Targeting and Tubulin Inhibitor Containing Antitumor Pt(IV) Moiety with a Unique Mode of Action

Three new Pt(IV) complexes comprising a combretastatin A-4 analogue were designed and synthesized. The resulting antitumor Pt(IV) complexes could significantly improve the antiproliferative activity and overcome the drug resistance of cisplatin in vitro. Interestingly, these novel compounds not only can carry the DNA binding Pt(II) warhead into the cancer cells but also have a small molecule fragment that can inhibit tubulin polymerization. Among them, complex 13, which was attached to an inhibitor of tubulin at one axial position of Pt(IV) octahedral coordination sphere, could effectively enter cancer cells, arrest the cell cycle in HepG-2 cancer cells at G2/M phases, and induce activation of caspases triggering apoptotic signaling via the mitochondrial-dependent apoptosis pathways. Moreover, complex 13 has the ability to effectively inhibit the tumor growth in the HepG-2 xenograft model without causing significant loss of animal body weight in comparison with cisplatin.

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.

Platinum(II) carboxylato complexes containing 7-azaindoles as N-donor carrier ligands showed cytotoxicity against cancer cell lines

The platinum(II) malonato (Mal) and decanoato (Dec) complexes of the general formulas [Pt(Mal)(naza)₂] (1-3) and cis-[Pt(Dec)₂(naza)₂] (4-7) were prepared, characterized and tested for their in vitro cytotoxicity against cisplatin-sensitive (A2780) and cisplatin-resistant (A2780R) human ovarian carcinoma cell lines and non-cancerous human lung fibroblasts (MRC-5); naza=halogeno-derivatives of 7-azaindole. Complexes 1-7 effectively overcome the acquired resistance of ovarian carcinoma cells to cisplatin. Complexes 2 (IC₅₀=26.6±8.9μM against A2780 and 28.9±6.7μM against A2780R), 4 (IC₅₀=14.5±0.6μM against A2780 and 14.5±3.8μM against A2780R) and 5 (IC₅₀=13.0±1.1μM against A2780 and 13.6±4.9μM against A2780R) indicated decreased toxicity against healthy MRC-5 cells (IC₅₀>50.0μM for 2 and >25.0μM for 4 and 5). The representative complexes 2 and 4 showed mutually different effect on the A2780 cell cycle at IC₅₀ concentrations after 24h exposure. Concretely, the complex 2 caused cell cycle arrest at G₀/G₁ phase, while 4 induced cell death by apoptosis with high population of cells in sub-G₁ cell cycle phase. The hydrolysis and interactions of the selected complexes with biomolecules (glutathione (GSH) and guanosine monophosphate (GMP)) were also studied by means of ¹H NMR and ESI+ mass spectra.

Bis- and Tetrakis(carboxylato)platinum(IV) complexes with mixed axial ligands - synthesis, characterization, and cytotoxicity

A series of twelve novel diamminetetrakis(carboxylato)platinum(IV) and 18 novel bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) complexes with mixed axial carboxylato ligands was synthesized and characterized by multinuclear (1) H-, (13) C-, (15) N-, and (195) Pt-NMR spectroscopy. Their cytotoxic potential was evaluated (by MTT assay) against three human cancer cell lines derived from ovarian teratocarcinoma (CH1/PA-1), lung (A549), and colon carcinoma (SW480). In the cisplatin-sensitive CH1/PA-1 cancer cell line, diamminetetrakis(carboxylato)platinum(IV) complexes showed IC50 values in the low micromolar range, whereas, for the most lipophilic compounds of the bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) series, IC50 values in the nanomolar range were found.

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.

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.

Hydrogen bonding and anticancer properties of water-soluble chiral p-cymene Ru(II) compounds with amino-oxime ligands

The investigation of the hydrogen-bonding effect on the aggregation tendency of ruthenium compounds [(η⁶-p-cymene)Ru(κNHR,κNOH)Cl]Cl (R = Ph (1a), Bn (1b)) and [(η⁶-p-cymene)Ru(κ²NH(2-pic),κNOH)][PF₆]₂ (1c), [(η⁶-p-cymene)Ru(κNHBn,κNO)Cl] (2b) and [(η⁶-p-cymene)Ru(κNBn,κ²NO)] (3b), has been performed by means of concentration dependence ¹H NMR chemical shifts and DOSY experiments. The synthesis and full characterization of new compounds 1c, [(η⁶-p-cymene)Ru(κNPh,κ²NO)] (3a) and 3b are also reported. The effect of the water soluble ruthenium complexes 1a-1c on cytotoxicity, cell adhesion and cell migration of the androgen-independent prostate cancer PC3 cells have been assessed by MTT, adhesion to type-I-collagen and recovery of monolayer wounds assays, respectively. Interactions of 1a-1c with DNA and human serum albumin have also been studied. Altogether, the properties reported herein suggest that ruthenium compounds 1a-1c have considerable potential as anticancer agents against advanced prostate cancer.

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

Platinum(IV) complexes are promising candidates as prodrugs for oral application in anticancer chemotherapy. However, only a few Pt(IV) compounds entered (pre)clinical trials, e.g. satraplatin, while most of the others were only tested in vitro. Aim of the study was investigation of the in vivo pharmacological behavior as well as the anticancer activity of two novel platinum(IV) complexes vs. satraplatin. The drugs were selected due to significantly different in vitro cytotoxicity while sharing some physicochemical properties (e.g. lipophilicity). Initial experiments indicated that the highly in vitro cytotoxic compound 1 ((OC-6-33)-dichloridobis((4-ethoxy)-4-oxobutanoato)-bis(ethylamine)platinum(IV)) was also characterized by high drug absorption and tissue platinum levels after oral application. Interestingly, analysis of serum samples using SEC-ICP-MS revealed that the administered drugs have completely been metabolized and/or bound to proteins in serum within 2 h after treatment. With regard to the activity in vivo, the outcomes were rather unexpected: although potent anticancer effect of 1 was observed in cell culture, the effects in vivo were rather minor. Nevertheless, 1 was superior to 2 ((OC-6-33)-diammine(cyclobutane-1,1-dicarboxylato)-bis((4-cyclopentylamino)-4-oxobutanoato)platinum(IV)) after i.p. administration, which was, at least to some extent, in accordance to the cell culture experiments. After oral gavage, both compounds exhibited comparable activity. This is remarkable considering the distinctly lower activity of 2 in cell culture as well as the low platinum levels detected both in serum and tissues after oral application. Consequently, our data indicate that the prediction of in vivo anticancer activity by cell culture experiments is not trivial, especially for orally applied drugs.