Iron(III)-salophene catalyzes redox cycles that induce phospholipid peroxidation and deplete cancer cells of ferroptosis-protecting cofactors.

Ferroptosis, a lipid peroxidation-driven cell death program kept in check by glutathione peroxidase 4 and endogenous redox cycles, promises access to novel strategies for treating therapy-resistant cancers. Chlorido [N,N'-disalicylidene-1,2-phenylenediamine]iron (III) complexes (SCs) have potent anti-cancer properties by inducing ferroptosis, apoptosis, or necroptosis through still poorly understood molecular mechanisms. Here, we show that SCs preferentially induce ferroptosis over other cell death programs in triple-negative breast cancer cells (LC50 ≥ 0.07 µM) and are particularly effective against cell lines with acquired invasiveness, chemo- or radioresistance. Redox lipidomics reveals that initiation of cell death is associated with extensive (hydroper)oxidation of arachidonic acid and adrenic acid in membrane phospholipids, specifically phosphatidylethanolamines and phosphatidylinositols, with SCs outperforming established ferroptosis inducers. Mechanistically, SCs effectively catalyze one-electron transfer reactions, likely via a redox cycle involving the reduction of Fe(III) to Fe(II) species and reversible formation of oxo-bridged dimeric complexes, as supported by cyclic voltammetry. As a result, SCs can use hydrogen peroxide to generate organic radicals but not hydroxyl radicals and oxidize membrane phospholipids and (membrane-)protective factors such as NADPH, which is depleted from cells. We conclude that SCs catalyze specific redox reactions that drive membrane peroxidation while interfering with the ability of cells, including therapy-resistant cancer cells, to detoxify phospholipid hydroperoxides.

Development of Cytotoxic GW7604-Zeise's Salt Conjugates as Multitarget Compounds with Selectivity for Estrogen Receptor- Positive Tumor Cells.

(E/Z)-3-(4-((E)-1-(4-Hydroxyphenyl)-2-phenylbut-1-enyl)phenyl)acrylic acid (GW7604) as a carrier was esterified with alkenols of various lengths and coordinated through the ethylene moiety to PtCl3, similar to Zeise's salt (K[PtCl3(C2H4)]). The resulting GW7604-Alk-PtCl3 complexes (Alk = Prop, But, Pent, Hex) degraded in aqueous solution only by exchange of the chlorido ligands. For example, GW7604-Pent-PtCl3 coordinated the amino acid alanine in the cell culture medium, bound the isolated nucleotide 5'-GMP, and interacted with the DNA (empty plasmid pSport1). It accumulated in estrogen receptor (ER)-positive MCF-7 cells primarily via cytosolic vesicles, while it was only marginally taken up in ER-negative SKBr3 cells. Accordingly, GW7604-Pent-PtCl3 and related complexes were inactive in SKBr3 cells. GW7604-Pent-PtCl3 showed high affinity to ERα and ERß without mediating agonistic or ER downregulating properties. GW7604-Alk ligands also increased the cyclooxygenase (COX)-2 inhibitory potency of the complexes. In contrast to Zeise's salt, the GW7604-Alk-PtCl3 complexes inhibited COX-1 and COX-2 to the same extent.

Amino Acids as Chelating Ligands for Platinum: Enhanced Stability in an Aqueous Environment Promoted by Biocompatible Molecules.

Platinum-based chemotherapeutics are a cornerstone in the treatment of many malignancies. However, their dose-limiting side effects have rooted efforts to develop new drug candidates with higher selectivity for tumor tissues and less problematic side effects. Here, we developed a cytotoxic platinum(II) complex based on Zeise's salt, containing the nonsteroidal anti-inflammatory drug acetylsalicylic acid and alanine as ligands (4). The previously developed complex (5) displayed high reactivity against sulfur-containing biomolecules; therefore, we put the focus on the optimization of the structure regarding its stability. Different amino acids were used as biocompatible chelating ligands to achieve this aim. Differences in the coordination sphere caused pronounced changes in the stability of Zeise-type precursors 1-3. Coordination with l-Ala through N in the trans position to ethylene showed the most promising results and was employed to stabilize 5. As a result, complex 4 showed improved stability and cytotoxicity, outperforming both 5 and 1.

Design, Synthesis, Electrochemical, and Biological Evaluation of Fluorescent Chlorido[N,N'-bis(methoxy/hydroxy)salicylidene-1,2-bis(4-methoxyphenyl)ethylenediamine]iron(III) Complexes as Anticancer Agents.

The impact of methoxy and hydroxyl groups at the salicylidene moiety of chlorido[N,N'-bis(methoxy/hydroxy)salicylidene-1,2-bis(4-methoxyphenyl)ethylenediamine]iron(III) complexes was evaluated on human MDA-MB 231 breast cancer and HL-60 leukemia cells. Methoxylated complexes (C1-C3) inhibited proliferation, migration, and metabolic activity in a concentration-dependent manner following the rank order: C2 > C3 > C1. In particular, C2 was highly cytotoxic with an IC50 of 4.2 µM which was 6.6-fold lower than that of cisplatin (IC50 of 27.9 µM). In contrast, hydroxylated complexes C4-C6 were almost inactive up to the highest concentration tested due to lack of cellular uptake. C2 caused a dual mode of cell death, ferroptosis, and necroptosis, whereby at higher concentrations, ferroptosis was the preferred form. Ferroptotic morphology and the presence of ferrous iron and lipid reactive oxygen species proved the involvement of ferroptosis. C2 was identified as a promising lead compound for the design of drug candidates inducing ferroptosis.

Zeta potential shifting nanoemulsions comprising single and gemini tyrosine-based surfactants.

AIM: This study aims to design and evaluate zeta potential shifting nanoemulsions comprising single and gemini type tyrosine-based surfactants for specific cleavage by tyrosine phosphatase. METHODS: Tyrosine-based surfactants, either single 4-(2-amino-3-(dodecylamino)-3-oxopropyl)phenyl dihydrogen phosphate (AF1) or gemini 4-(2-amino-3-((1-(dodecylamino)-3-(4-hydroxyphenyl)-1-oxopropan-2-yl)amino)-3-oxopropyl)phenyl dihydrogen phosphate (AF2) type were synthesized via amide bond formation of tyrosine with dodecylamine followed by phosphorylation. These surfactants were incorporated into nanoemulsions. Nanoemulsions were monitored by incubation with isolated tyrosine phosphatase as well as secreted tyrosine phosphatase of Escherichia coli in terms of phosphate release and zeta potential change. RESULTS: Via isolated tyrosine phosphatase, and mediated by E. coli, phosphate groups of either single or gemini tyrosine-based surfactants could be cleaved by secreted tyrosine phosphatase. Nanoemulsions comprising a single tyrosine-based surfactant resulted in a charge shift from - 13.46 mV to - 4.41 mV employing isolated tyrosine phosphatase whilst nanoemulsions consisting of a gemini tyrosine-based surfactant showed a shift in zeta potential from - 15.92 mV to - 5.86 mV, respectively. CONCLUSION: Nanoemulsions containing tyrosine-based surfactants represent promising zeta potential shifting nanocarrier systems targeting tyrosine phosphatase secreting bacteria.

Reaction Behavior of [1,3-Diethyl-4,5-diphenyl-1H-imidazol-2-ylidene] Containing Gold(I/III) Complexes against Ingredients of the Cell Culture Medium and the Meaning on the Potential Use for Cancer Eradication Therapy.

The reactivities of halido[1,3-diethyl-4,5-diphenyl-1H-imidazol-2-ylidene]gold(I) (chlorido (5), bromido (6), iodido (7)), bis[1,3-diethyl-4,5-diphenyl-1H-imidazol-2-ylidene]gold(I) (8), and bis[1,3-diethyl-4,5-diphenyl-1H-imidazol-2-ylidene]dihalidogold(III) (chlorido (9), bromido (10), iodido (11)) complexes against ingredients of the cell culture medium were analyzed by HPLC. The degradation in the RPMI 1640 medium was studied, too. Complex 6 quantitatively reacted with chloride to 5, while 7 showed additionally ligand scrambling to 8. Interactions with non-thiol containing amino acids could not be detected. However, glutathione (GSH) reacted immediately with 5 and 6 yielding the (NHC)gold(I)-GSH complex 12. The most active complex 8 was stable under in vitro conditions and strongly participated on the biological effects of 7. The gold(III) species 9-11 were completely reduced by GSH to 8 and are prodrugs. All complexes were tested for inhibitory effects in Cisplatin-resistant cells, as well as against cancer stem cell-enriched cell lines and showed excellent activity. Such compounds are of utmost interest for the therapy of drug-resistant tumors.

Development of Zeise's Salt Derivatives Bearing Substituted Acetylsalicylic Acid Substructures as Cytotoxic COX Inhibitors.

Zeise's salt derivatives of the potassium trichlorido[η2-((prop-2-en/but-3-en)-1-yl)-2-acetoxybenzoate]platinate(II) type (ASA-Prop-PtCl3/ASA-But-PtCl3 derivatives) were synthesized and characterized regarding their structure, stability, and biological activity. It is proposed that the leads ASA-Prop-PtCl3 and ASA-But-PtCl3 interfere with the arachidonic acid cascade as part of their mode of action to reduce the growth of COX-1/2-expressing tumor cells. With the aim to increase the antiproliferative activity by strengthening the inhibitory potency against COX-2, F, Cl, or CH3 substituents were introduced into the acetylsalicylic acid (ASA) moiety. Each structural modification improved COX-2 inhibition. Especially compounds with F substituents at ASA-But-PtCl3 reached the maximum achievable inhibition of about 70% already at 1 µM. The PGE2 formation in COX-1/2-positive HT-29 cells was suppressed by all F/Cl/CH3 derivatives, indicating COX inhibitory potency in cellular systems. The CH3-bearing complexes showed the highest cytotoxicity in COX-1/2-positive HT-29 cells with IC50 values of 16-27 µM. In COX-negative MCF-7 cells, they were 2-3-fold less active. These data clearly demonstrate that it is possible to increase the cytotoxicity of ASA-Prop-PtCl3 and ASA-But-PtCl3 derivatives by enhancing COX-2 inhibition.

Development of heterodimeric estrogen receptor alpha antagonists to target simultaneously the ligand and coactivator binding site.

One-third of breast cancer patients will develop recurrent cancer within 15 years of endocrine treatment. Notably, tumor growth in a hormone-refractory state still relies on the interaction between estrogen receptor alpha (ERα) and upregulated coactivators. Herein, we suggest that simultaneous targeting of the primary ligand binding site (LBS) and the coactivator binding site (CABS) at ERα represents a promising alternative therapeutic strategy to overcome mutation-driven resistance in breast cancer. We synthesized two series of compounds that connect the LBS-binder (E)-3-{4-[8-fluoro-4-(4-hydroxyphenyl)-2,3-dihydrobenzo[b]oxepin-5-yl]phenyl}acrylic acid 8 with the coactivator binding site inhibitors (CBIs) 4,6-bis(isobutyl(methyl)amino)pyrimidine or 3-(5-methoxy-1H-benzo[d]imidazol-2-yl)propanoic acid via covalent linkage. The most active benzoxepine-pyrimidine conjugate 31 showed strong inhibition of estradiol-induced transactivation (IC50 = 18.2 nM (ERα) and 61.7 nM (ERß)) in a luciferase reporter gene assay as well as high antiproliferative effects in MCF-7 (IC50 = 65.9 nM) and tamoxifen-resistant MCF-7/TamR (IC50 = 88.9 nM) breast cancer cells. All heterodimers exhibited two- to sevenfold higher antagonism at ERα (compared with ERß) and were superior to the acrylic acid precursor 8 in terms of ER antagonism and antiproliferative activity. It was demonstrated on the example of 31 that the compounds did not influence the ERα content in MCF-7 cells and therefore act as pure antiestrogens without downregulating potency. Possible interactions of the CBI at the receptor surface, which enhanced the biological activities, were evaluated using molecular docking studies.

Chitosan-maleic acid conjugate as potential excipient candidate for oral drug delivery?

Aim: To develop and evaluate chitosan-maleic acid conjugate. Methods: Maleic anhydride was attached to chitosan backbone via amide bond formation resulting in chitosan-maleic acid. After characterization of the product via 1H nuclear magnetic resonance, attenuated total reflectance-Fourier transform IR spectroscopy and 2,4,6-trinitrobenzenesulfonic acid assay, examination of mucoadhesion assessment was carried out. Results: The conjugate presented 44.91% modification and no toxicity could be observed after 1 day of incubation. Mucoadhesive properties exhibited 40.97-fold, 13.31-fold and 9.07-fold increase in elastic modulus, dynamic viscosity and viscous modulus, respectively. Moreover, detachment time was increased in 44.44-fold. Conclusion: Chitosan-maleic acid demonstrated enhanced in mucoadhesive properties resulting in biocompatibility. Therefore, potent candidates as polymeric excipients for oral drug delivery could be developed over corresponding chitosan.

Synthesis and biological evaluation of salophen nickel(II) and cobalt(III) complexes as potential anticancer compounds.

Recent in vitro investigations of N,N'-bis(salicylidene)-1,2-phenylenediamine (SAP) iron(III) complexes substituted with alkyl (ethyl, propyl, butyl) carboxylates at position 4 in tumor and leukemia cells revealed strong cytotoxic activity. In continuation of this study, analogous nickel(II) and cobalt(III) complexes were synthesized and tested in HL-60 leukemia, and cisplatin-sensitive and -resistant A2780 ovarian cancer cell lines. The biological activity depended on the extent of cellular uptake and the formation of reactive oxygen species (ROS). Inactive [(Ni(II)SAP] complexes (1-3) only marginally accumulated in tumor cells and did not induce ROS. The cellular uptake of [Co(III)SAP]Cl complexes (4-6) into the cells depended on the length of the ester alkyl chain (ethyl, 4 < propyl, 5 < butyl, 6). The cytotoxicity correlated with the presence of ROS. The low cytotoxic complex 4 induced only few ROS, while 5 and 6 caused a good to outstanding antiproliferative activity, exerted high ROS generation, and induced cell death after 48 h. Necrostatin-1 prevented the biological effects, proving necroptosis as part of the mode of action. Interestingly, the effects of 5 and 6 were not reversed by Ferrostatin-1, but even enhanced upon simultaneous application to the tumor cells.

Investigations on the Influence of the Axial Ligand in [Salophene]iron(III) Complexes on Biological Activity and Redox Behavior.

The [N,N'-disalicylidene-1,2-phenylenediamine]iron(III) ([salophene]iron(III)) derivatives 1-4 with anionic axial ligands (A = Cl-, NO3-, SCN-, CH3COO-) and complexes 5 and 6 with neutral ligands (A = imidazole, 1-methylimidazole) as well as the µ-oxo dimer 7 inhibited proliferation, reduced metabolic activity, and increased mitochondrial reactive oxygen species. Ferroptosis as part of the mode of action was identified by inhibitor experiments, together with induction of lipid peroxidation and diminished mitochondrial membrane potential. No differences in activity were observed for all compounds except 4, which was slightly less active. Electrochemical analyses revealed for all compounds a fast attachment of the solvent dimethyl sulfoxide and a release of the axial ligand A. In contrast, in dichloromethane and acetonitrile, ligand exchange did not take place, as analyzed by measurements of the standard potential for the iron(III/II) redox reaction.

Structure-activity relationship study to improve cytotoxicity and selectivity of lonafarnib against breast cancer cells.

Lonafarnib is designed as a farnesyltransferase (FTase) inhibitor and displays inhibitory activities against a wide range of tumor cells. However, a major disadvantage is its unselective activity and high cytotoxicity against nonmalignant cells. Therefore, we structurally modified the terminal 4-methylpiperidine-1-carboxamide residue of lonafarnib and evaluated the antiproliferative effects of the resulting derivatives in Michigan Cancer Foundation - 7 (MCF-7) breast cancer cells as well as simian virus 80 (SV-80) fibroblasts. The highest cytotoxicity against both cell lines (IC50 about 2 µM) was shown by the piperidin-4-yl carbamate 15i and the S-(piperidin-4-yl) carbamothioate 15j. Selectivity for tumor cells was realized in the case of the 1-cyclohexyl-1-methylurea derivative 15b. It reduced the growth of MCF-7 cells with an IC50 of 11.4 µM (lonafarnib: IC50 = 10.8 µM) without influence on the growth of SV-80 cells (IC50 > 50 µM; lonafarnib: IC50 = 14.0 µM). Molecular modeling studies were performed to correlate the cytotoxicity with possible FTase interactions. The theoretical investigations, however, documented a comparable attachment of active, less active, and inactive compounds and did not allow an interpretation of the biological results based on these theoretical considerations.

Synthesis, characterization and evaluation of hyaluronic acid-based polymers for nasal delivery.

Epidemiological research has found that between 5 and 12 percent of the population suffers from chronic rhinosinusitis. Patients are dealing with local side effects such as nasal dryness, sporadic sneezing, and nasal pain in addition to the inflammation. The aim of this study was to synthesize a polymer based on hyaluronic acid in order to provide lubrication combined with a ligand leading to a covalent binding on the nasal mucosa. Hyaluronic acid (HA) was modified with L-cysteine ethyl ester hydrochloride (CYS) via amid bond formation. Ellman's assay, together with spectroscopic techniques like IR and 1H NMR, confirmed that HACys had been successfully synthesized. It was demonstrated that HACys is safe for administration on the nasal mucosa. The mucoadhesive potential was determined by 3.26-fold with the rotating cylinder assay and 1.4-fold in terms of bioadhesive examination, respectively. Further, the stability of the modified polymer was improved by 7.6-fold compared to the unmodified polymer. Spraying the formulation on the nasal mucosa, the residence time of a model drug was 1.74-fold prolonged at the site of action compared to unmodified polymer. In light of these findings, modified hyaluronic acid (HACys) displayed compelling properties such as lubricity, targeted application, long-lasting effect, and safety and therefore could be an excellent candidate for nasal application.

Biodegradable arginine based steroid-surfactants: Cationic green agents for hydrophobic ion-pairing.

The aim of this study was to evaluate the safety and efficacy for hydrophobic ion-pairing of surfactants based on arginine (Arg). The prepared Arg-cholesteryl ester (ACE) and Arg-diosgenyl ester (ADE) were characterized regarding solubility, pKa, critical micellar concentration (CMC), biodegradability as well as membrane- and aquatic toxicity using DOTAP as reference. The ability for hydrophobic ion-pairing was evaluated and the lipophilicity of formed complexes was determined. NMR, FT-IR and MS confirmed successful synthesis of Arg-surfactants. The slightly soluble single-charged Arg-surfactants (pH < pKa3 (ACE = 10.42 ± 0.52; ADE = 10.38 ± 0.27)) showed CMCs of 27.17 µM for ACE and 35.67 µM for ADE. CMCs of the sparingly soluble double-charged species (pH < pKa2 (ACE = 5.30 ± 0.20; ADE = 5.55 ± 0.06)) were determined at concentrations of ≥ 250 µM for ACE and ≥ 850 µM for ADE. The enzymatic- and environmental biodegradability was proven by an entire cleavage of Arg-surfactants within 24 h, whereas DOTAP remained stable. Arg-surfactants exhibited lower membrane- (> 2-fold) and aquatic toxicity (> 15-fold) than DOTAP. The complexes formed with Arg-surfactants and insulin showed higher lipophilicity than the DOTAP-complex. According to these results, Arg-surfactants might be a promising safe tool for the delivery of peptide drugs.

Entirely S-protected thiolated hydroxyethylcellulose: Design of a dual cross-linking approach for hydrogels.

AIM: The aim of this study was the synthesis and evaluation of entirely S-protected thiolated hydroxyethylcellulose (HEC) with low and high viscosity, as well as thiolated poly-L-lysine (poly-L-Lys) used as dual-acting ionic as well as thiol-disulfide exchange mediated cross-linking hydrogel. METHODS: Bis(mercaptosuccinic acid) was covalently attached to low and high viscous HECs via Fisher esterification, obtaining S-protected polymers. Poly-L-Lys-cysteine was synthesized via amidation of poly-L-Lys-HBr with cysteine (Cys). Thiolated polymers were examined in terms of cytotoxicity and rheological behavior of hydrogels containing these thiomers was evaluated with a cone-plate rheometer. RESULTS: Thiomers showed less cytotoxicity compared to the corresponding unmodified polymers. Rheological studies showed that cross-linking occurred between the two polymers via thiol-disulfide exchange reactions facilitated by the complementary charges. Employing poly-L-Lys-Cys in a concentration of either 0.5 or 5% (m/v) resulted in a 34.5-fold or 17.3-fold as well as a 53.6-fold or 29.6-fold improvement in dynamic viscosity within 5 min at 37 °C on S-protected thiolated low and high viscous HEC, compared to the corresponding unmodified HECs, respectively. CONCLUSION: By the combination of anionic S-protected thiolated polymers with a cationic thiolated polymer, dual-acting hydrogels exhibiting a time dependent increase in viscosity can be designed.

Charge converting nanostructured lipid carriers containing a cell-penetrating peptide for enhanced cellular uptake.

HYPOTHESIS: The aim of this study was the development of nanostructured lipid carriers (NLCs) decorated with a polycationic cell-penetrating peptide (CPP). A coating with polyphosphates (PP) enables charge conversion at target cells being triggered by the membrane bound enzyme intestinal alkaline phosphatase (IAP). EXPERIMENTS: The CPP, stearyl-nona-L-arginine (R9SA) was obtained by solid phase synthesis. Formed nanocarriers were characterized regarding size, polydispersity index, zeta potential and charge conversion in the presence of IAP and on Caco-2 cells. The BCS class IV drug saquinavir (SQV) was loaded into NLCs in different concentrations. Mucus diffusion ability of the NLCs was evaluated by the rotating tube method. Furthermore, cellular uptake was evaluated on Caco-2 cells and endosomal escape properties were investigated using erythrocytes. FINDINGS: All NLCs were obtained in a size range between 146 nm and 152 nm and a polydispersity index of 0.2. Incubation of PP coated PP-R9SA-NLCs with IAP led to a charge conversion from -41.8 mV to 6.4 mV (Δ48.2 mV). After four hours of incubation with IAP, phosphate release reached a plateau, indicating a faster polyphosphate cleavage than on Caco-2. Drug load and encapsulation efficiency of SQV was obtained up to 80.6% and 46.5 µg/mg. Mucus diffusion was increasing in the following rank order: R9SA-NLCs < blank NLCs < PP-R9SA-NLCs. R9SA-NLCs and PP-R9SA-NLCs increased the cellular uptake 15.6- and 13.2-fold, respectively, compared to the control NLCs. Erythrocytes interaction study revealed enhanced endosomal escape properties for R9SA-NLCs and PP-R9SA-NLCs when incubated with IAP.

Recent development of gold(I) and gold(III) complexes as therapeutic agents for cancer diseases.

Metal complexes have demonstrated significant antitumor activities and platinum complexes are well established in the clinical application of cancer chemotherapy. However, the platinum-based treatment of different types of cancers is massively hampered by severe side effects and resistance development. Consequently, the development of novel metal-based drugs with different mechanism of action and pharmaceutical profile attracts modern medicinal chemists to design and synthesize novel metal-based agents. Among non-platinum anticancer drugs, gold complexes have gained considerable attention due to their significant antiproliferative potency and efficacy. In most situations, the gold complexes exhibit anticancer activities by targeting thioredoxin reductase (TrxR) or other thiol-rich proteins and enzymes and trigger cell death via reactive oxygen species (ROS). Interestingly, gold complexes were recently reported to elicit biochemical hallmarks of immunogenic cell death (ICD) as an ICD inducer. In this review, the recent progress of gold(I) and gold(III) complexes is comprehensively summarized, and their activities and mechanism of action are documented.

Investigations of the reactivity, stability and biological activity of halido (NHC)gold(I) complexes.

The significance of the halido ligand (Cl-, Br-, I-) in halido[3-ethyl-4-phenyl-5-(2-methoxypyridin-5-yl)-1-propyl-1,3-dihydro-2H-imidazol-2-ylidene]gold(I) complexes (2-4) in terms of ligand exchange reactions, including the ligand scrambling to the bis[3-ethyl-4-phenyl-5-(2-methoxypyridin-5-yl)-1-propyl-1,3-dihydro-2H-imidazol-2-ylidene]gold(I) complex (5), was evaluated by HPLC in acetonitrile/water = 50:50 (v/v) mixtures. In the presence of 0.9% NaCl, the bromido (NHC)gold(I) complex 3 was immediately transformed into the chlorido (NHC)gold(I) complex 2. The iodido (NHC)gold(I) complex 4 converted under the same conditions during 0.5 h of incubation by 52.83% to 2 and by 8.77% to 5. This proportion remained nearly constant for 72 h. The halido (NHC)gold(I) complexes also reacted very rapidly with 1 eq. of model nucleophiles, e.g., iodide or selenocysteine (Sec). For instance, Sec transformed 3 in the proportion 73.03% to the (NHC)Au(I)Sec complex during 5 min of incubation. This high reactivity against this amino acid, present in the active site of the thioredoxin reductase (TrxR), correlates with the complete inhibition of the isolated TrxR enzyme at 1 µM. Interestingly, in cellular systems (A2780cis cells), even at a 5-fold higher concentration, no increased ROS levels were detected. The concentration required for ROS generation was about 20 µM. Superficially considered, the antiproliferative and antimetabolic activities of the halido (NHC)Au(I) complexes correlate with the reactivity of the Au(I)-X bond (2 < 3 < 4). However, it is very likely that degradation products formed during the incubation in cell culture medium participated in the biological activity. In particular, the high-cytotoxic [(NHC)2Au(I)]+ complex (5) distorts the results.

Development of methylated cobalt-alkyne complexes with selective cytotoxicity against COX-positive cancer cell lines.

Derivatives of the cytotoxic cyclooxygenase (COX) inhibitor [(prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS) with a methyl group in the 3, 4, 5, or 6 position of the acetylsalicylic acid (ASS) scaffold were synthesized with the aim to achieve enhanced selectivity for COX-2. From this modification, a higher specificity for COX-2-expressing tumors is expected, preventing COX-1-mediated side effects. The cobalt-alkyne complexes were tested for their COX-inhibitory and antiproliferative properties as well as their cellular uptake. Methylation reduced the effects at the isolated COX-1, whereas those at the isolated COX-2 remained nearly constant compared to Co-ASS. In cellular systems, the new compounds showed superior cytotoxicity toward the COX-positive HT-29 colon carcinoma cells than cisplatin. The reduced growth-inhibitory potency in T-24 cells, which express distinctly fewer COX enzymes (COX-1/COX-2 = 50/1) than HT-29 cells (COX-1/COX-2 = 50/50), and the only marginal activity in COX-negative MCF-7 breast cancer cells point to an interference in the arachidonic acid cascade through COX-2 inhibition as part of the mode of action, especially as the cellular uptake was even higher in MCF-7 cells than in T-24 cells. These findings clearly demonstrate that the methylated cobalt-alkyne complexes possess promising potential for further development as reasonable alternatives to the limited platinum-based antitumor agents.