[N,N'-Bis(salicylidene)-1,2-phenylenediamine]iron(III) complexes bearing methoxy substituents at the 3-, 4-, 5-, or 6-positions of the salicylidene moieties (C1 - C4) were previously shown to reach maximum cytotoxic activity within 48 h. This raised the question of cellular processes initiated during shorter incubation times. Therefore, the effects of C1 - C4 were evaluated after 24 h in MDA-MB 231 breast cancer, HL-60 acute myeloid leukemia, and nontumorigenic MCF-10A mammary epithelial cells using cell-based and mitochondria-related assays. All complexes accumulated in MDA-MB 231 and HL-60 cells within 4 h. Despite efficient uptake, the 4-methoxy-substituted complex C2 showed minimal biological activity after 24 h, whereas C1, C3, and C4 induced pronounced, cell type-dependent effects. In MDA-MB 231 cells, these complexes caused mitochondrial membrane depolarization and increased reactive oxygen species (ROS) levels in both mitochondria and cytosol. The effect on oxygen consumption of MDA-MB 231 cells was relatively low. In contrast, C1, C3, and C4 significantly impaired mitochondrial respiration of HL-60 cells. While all three complexes increased cytosolic ROS levels within 4 h, only C4 elevated mitochondrial ROS in HL-60 cells. After 24 h, cell death - induced by both apoptosis and necrosis - was detected in both malignant cell lines. On the contrary, nontumorigenic MCF-10A cells were largely unaffected, with only C1 reducing viability at the highest concentration tested. This study shows that C1, C3, and C4 rapidly induce distinct, cell-specific mitochondrial responses that contribute to early cytotoxic effects, whereas C2 remains largely inactive despite efficient cellular uptake.

In this structure-activity relationship study, chlorido[N,N '-bis(chloro/bromosalicylidene)-1,2-diphenyl-1,2-diaminoethane]iron(III) complexes differing in (i) the configuration of the 1,2-diphenylethane backbone ((RS), (RR/SS), or (SS)) and (ii) the halogen substituents at the salicylidene residue in positions 5 (Cl (1a-c) or Br (2a-c) or 3-Br,5-Cl (3a-c)) were investigated. All complexes were fully characterized and showed high stability with regard to ligand racemization. The antitumor activity was dependent on the configuration and the substitution pattern of the salicylidene moieties. (RS)-Configured complexes were nearly inactive, whereas (RR/SS)- or (SS)-configured complexes displayed almost identical efficacies. 1a-c induced oxidative stress, but only 1b and 1c caused extensive lipid oxidation and ferroptosis as part of the mode of action. Exchange of the 3-Cl substituents for 3-Br only marginally changed the biological effects, whereas the introduction of 3-Br, 5-Cl substituents led to a loss of activity. The differences in effectiveness result from the spatial structure caused by the 1,2-diphenylethane skeleton.

Despite the success of tyrosine kinase inhibitors (TKIs) in treating chronic myeloid leukemia (CML), resistance remains a major challenge due to target mutations and drug efflux. To counter this, chemo-sensitizers - non-cytotoxic agents that restore drug sensitivity - are being explored. A promising approach involves Telmisartan (1)-based cell death modulators, which may help overcome TKI resistance. Modification of the 2-COOH group of Telmisartan to a carboxamide (2-CONH2, Telmiamide (2)) or methyl ester (2-CO2CH3, Telmiester (3)) transformed these derivatives into potent inhibitors of the efflux transporter ABCB1 and the STAT5 protein - two critical mediators of CML persistence during TKI therapy. Both compounds successfully restored Imatinib (Im) sensitivity in TKI-resistant CML cells. The present structure-activity relationship (SAR) analysis demonstrated that substituent modifications at 2-CONH2 and 2-CO2CH3 significantly influenced biological efficacy, stability in cell culture medium, cellular uptake in CML cells, and inhibition of ABCB1 and STAT5. Among the tested compounds, propyl-, butyl-, phenyl-, and 4-phenoxyphenyl-substituted Telmiamides (2a-d) and Telmiesters (3a-d) exhibited strong chemo-sensitizing potential in vitro, with a half-maximal sensitizing concentration (SC50) < 0.5 mu M. Additionally, most derivatives showed improved stability in cell culture, enhancing their suitability for future in vivo studies. When considering cellular uptake in CML cells, these compounds displayed ABCB1 inhibition comparable to the efflux transporter inhibitor Elacridar (E). Notably, their dual mode of action, combining potent ABCB1 and STAT5 inhibition with low cytotoxicity, offers a distinct advantage over Elacridar (E). ADME (absorption, distribution, metabolism, and excretion) studies identified significant limitations in the phenyl carboxamide derivative (2c), revealing low permeability and high metabolism due to the bound phenyl ring. These findings indicate that aromatic residues at the 2-CONH-R group may compromise bioavailability, highlighting a key structural constraint to address in the future optimization of Telmisartan derivatives for therapeutic development. Overall, the study highlights Telmisartan-based derivatives as promising candidates for overcoming TKI resistance in CML and warrants further optimization for clinical translation.

SS-, RR-, SR- and RR/SS-configured 1,3-diethyl-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-ylidenes were introduced as new imidazoline-based N-heterocyclic carbene (NHC) ligands for the design of antitumor-active (NHC)gold(I) complexes (halido(NHC)gold(I) complexes: chlorido (5a-d), bromido (6a-d), iodido (7a-d); SS,SS-, RR,RR-, SR,SR-, and RR,SS-configured [(NHC)2Au(I)]+ complexes: 8a-d). X-ray structures of the SS-configured complexes 5a-7a showed bis-equatorially arranged phenyl rings and disturbed columnar structures with increased Au-Au distances (>5.6 Å). The SR-configuration forced the phenyl ring in a synclinal position above the NHC plane allowing only the formation of separated dimers (5c-7c). In case of the [(NHC)2Au(I)]+ complex 8c, single molecules were observed in the crystals. The steric and dynamic conditions reduced ligand scrambling in solution and thus increased stability. The complexes showed higher growth inhibitory effects in ovarian (A2780wt (wild-type), A2780cis (Cisplatin-resistant)) than in breast cancer cells (MDA-MB-231, MCF-7) and circumvented the Cisplatin resistance in A2780 cells (effects in A2780wt = A2780cis). Chlorido- and bromido(NHC)gold(I) complexes caused comparable effects, because of a fast Br/Cl exchange (6a-d → 5a-d). The iodido(NHC)gold(I) complexes 7a-d were more active, due to a partial degradation to 8a-d. The latter were the most cytotoxic compounds of this study. The configuration of the NHC ligand did not influence the cytotoxicity of the complexes. Enantiomers and diastereomers showed the same antimetabolic effects. On the examples of 5a-d and 8a-d, the cellular uptake was studied. The maximum gold levels in A2780wt and MDA-MB-231 cells were achieved within 30 min of incubation. At concentrations corresponding to the half maximal inhibitory concentration (IC50) values of the antiproliferative effect (5a-d: 20 μM, 8a-d: 5 μM), 5b, 5c, and 5d induced almost the same gold content in A2780wt cells, which was 30-50 % lower than that of 5a. The trend of accumulation for [(NHC)2Au(I)]+ complexes was 8d < 8a < 8b < 8c. Furthermore, 5a-d inhibited the cyclooxygenase-1 (COX-1) and thioredoxin reductase (TrxR) and upregulated the Glutathione (GSH) level in A2780wt cells. Contrarily, 8a-d did not reduce COX-1 and TrxR activity, but led to moderate GSH down-regulation. The GSH level was not lowered in favour of Glutathione disulfide (GSSG), demonstrating that 8a-d influence the formation of GSH. © 2017 Elsevier Inc. All rights reserved.

Platinum (II) based chemotherapeutics are a cornerstone in the treatment of many malignancies. However, their severe toxicity and dose-limiting side-effects have rooted efforts in the medicinal inorganic community to develop better drug candidates with higher selectivity for tumor tissues and less problematic side effects. In the current study, we developed a cytotoxic platinum (II) complex based on a Zeise’s salt substructure containing the nonsteroidal anti-inflammatory drug (NSAID) acetylsalicylic acid (ASA) as a ligand. Since the original complex displayed high reactivity against sulfur-containing biomolecules, the structure was optimized regarding its stability. Amino acids L-alanine, β-alanine and L-histidine were used as biocompatible chelating ligands to achieve this aim. Differences in the coordination sphere caused pronounced changes in the stability profiles of the Zeise-type precursor complexes 1-3. Of the tested systems, coordination with LAla through N in trans position to ethylene (N-trans) showed the most promising results and was employed to stabilize the previously published complex 5. The stability profiles of all complexes were evaluated by capillary electrophoresis and the biological activity was investigated in vitro in various tumor cell lines. To investigate the effect of the NSAID ligand on the mode-of-action, inhibition of cyclooxygenase enzymes was also tested. Platinum (II) complex 4 containing both the ASA and the Ala ligand showed improved stability and higher cytotoxicity, outperforming both 5 and 1, exhibiting a cytotoxic activity at 25 µM comparable to the reference drug cisplatin.

(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 ER alpha and ER beta 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.

Iron(III) complexes based on N,N´-bis(salicylidene)ethylenediamine (salene) scaffolds have demonstrated promising anticancer features like induction of ferroptosis, an iron dependent cell death. Since poor cellular uptake limits their therapeutical potential, this study aimed to enhance the lipophilic character of chlorido[N,N′-bis(salicylidene)-1,2-bis(3-methoxyphenyl)ethylenediamine]iron(III) complexes by introducing lipophilicity improving ligands such as fluorine (X1), chlorine (X2) and bromine (X3) in 5-position in the salicylidene moieties. After detailed characterization the binding to nucleophiles, logP values and cellular uptake were determined. The complexes were further evaluated regarding their biological activity on MDA-MB 231 mammary carcinoma, the non-tumorous SV-80 fibroblast, HS-5 stroma and MCF-10A mammary gland cell lines. Stability of the complexes in aqueous and biological environments was proven by the lack of interactions with amino acids and glutathione. Cellular uptake was positively correlated with the logP values, indicating that higher lipophilicity enhanced cellular uptake. The complexes induced strong antiproliferative and antimetabolic effects on MDA-MB 231 cells, but were inactive on all non-malignant cells tested. Generation of mitochondrial reactive oxygen species, increase of lipid peroxidation and induction of both ferroptosis and necroptosis were identified as mechanisms of action. In conclusion, halogenation of chlorido[N,N′-bis(salicylidene)-1,2-bis(3-methoxyphenyl)ethylenediamine]iron(III) complexes raises their lipophilic character resulting in improved cellular uptake.

Drug resistance presents a significant challenge in cancer therapy, which has led to intensive research in resistance mechanisms and new therapeutic strategies. In chronic myeloid leukemia (CML), the introduction of Imatinib, the first tyrosine kinase inhibitor (TKI), drastically changed the outcome for patients. However, complete remission still cannot be achieved in a large number of patients in the long term. Therefore, there is a great interest in the design of new drugs to target TKI-resistant cancer cells. A promising approach to enhance the efficacy of Imatinib is the simultaneous application of cell death modulators derived from the Angiotensin II type 1 receptor blocker Telmisartan. The methyl ester (3a) of 4'-((2-propyl-1H-benzo[d]imidazol-1-yl)methyl)-[1,1'-biphenyl]-2-carboxylic acid (LEAD-acid (4)), which is the structural core of Telmisartan, has already been shown to abolish the resistance of Imatinib in TKI-insensitive CML cells at a concentration of 5 μM. As the ester was expected to be unstable in a biological environment, this study attempted to increase the stability through structural modifications. The methyl group was exchanged for longer (3b (ethyl), 3c (propyl), 3d (butyl) and branched (3e (isopropyl), 3f (tert-butyl)) alkyl chains as well as a phenyl (3g) and 4-phenoxyphenyl (3h) group. Furthermore, the esters were bioisosterically replaced with a respective substituted carboxamide (5a-h). The LEAD-amides (5a-h) showed high stability against esterases, while amidases cleaved only the carboxamides with short alkyl chains to a small extent. Esterases hydrolyzed the LEAD-alkylesters (3a-d) dependent on the chain length with τ½ = 55-82 min. Esters with branched alkyl chains were stable and introduction of the aromatic rings mentoined above increased the half-life to τ½ = 280 min and 360 min. In cell culture medium, only 3a-d degraded to 67-78 % after 72 h. However, the uptake studies showed that approximatly 80 % of the esters accumulated in the cell within the first 1-3 h of incubation. Therefore, it can be concluded that the intact LEAD-esters and LEAD-amides caused the biological effects. The compounds were non-cytotoxic and efficiently sensitized KD225 (K562-resistant) CML cells to Imatinib at a half-maximal sensitizing concentration (SC50) of 1.5-2.9 μM (ester derivatives) and 1.3-11.2 μM (amide derivatives).

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.

The present structure-activity relationship study investigates the development of novel chemosensitizers targeting therapy-resistant cancer stem cells (CSCs). We used 4 '-((2-propyl-1H-benzo[d]imidazole-1-yl)methyl)-[1,1 '-biphenyl]-2-carboxylic acid, derived from the angiotensin II type 1 receptor blocker telmisartan, as a lead structure, demonstrating that the biphenyl moiety is essential for chemosensitizing activity. Introducing a methyl carboxylate or carboxamide instead of the COOH-group significantly enhanced this effect, leading to the development of highly potent compounds. These novel, noncytotoxic chemosensitizers effectively target CSCs and overcome drug resistance by interfering with CSC persistence mechanisms-hyperactivated STAT5 signaling and increased drug transporter activity-with demonstrated efficacy in leukemia, ovarian, and prostate cancers. The carboxamide of telmisartan (telmi-amide, 7c) significantly reduced tumor growth in an imatinib-resistant leukemia xenograft model, both as monotherapy and combined with imatinib, showing promising oral bioavailability and tolerability. In summary, telmisartan derivatives act as effective chemosensitizers and offer an innovative strategy for targeting CSCs in various malignant diseases.

Fluorinated chlorido[salophene]iron(III) complexes (salophene = N,N '-bis(salicylidene)-1,2-phenylenediamine) are promising anticancer agents. Apoptosis and necrosis induction have already been described as part of their mode of action. However, the involvement of ferroptosis in cell death induction, as confirmed for other chlorido[salophene]iron(III) complexes, has not yet been investigated. Furthermore, the mechanism of cellular uptake of these compounds is unknown. Therefore, the biological activity of the fluorescent chlorido[salophene]iron(III) complexes with a fluorine substituent at positions 3, 4, 5, or 6 at the salicylidene moieties (C1-C4) was evaluated in malignant and nonmalignant cell lines with focus on the involvement of the transferrin receptor-1 (TfR-1) in cellular uptake, the influence of the complexes on mitochondrial function, and the analysis of the molecular mechanism of cell death. All complexes significantly decreased the metabolic activity in the tested ovarian cancer (A2780, A2780cis), breast cancer (MDA-MB 231), and leukemia (HL-60) cell lines, while the nonmalignant human stroma cell line HS-5 at a concentration of 0.5 mu M, which represents the IC50 of the complexes in most of the used tumorigenic cell lines, was not affected. The mitochondrial function was impaired, as evidenced by a reduced mitochondrial membrane potential Delta Psi m and decreased mitochondrial activity. Besides apoptosis and necroptosis, ferroptosis was identified as part of the mode of action. It was further demonstrated for the first time that fluorinated chlorido[salophene]iron(III) complexes downregulate TfR-1 expression, comparable to ferristatin II, an iron transport inhibitor that acts via TfR-1 degradation. FerroOrange staining further indicated that the complexes strongly increased the intracellular iron(II) level as a driving force to induce ferroptosis. In conclusion, these fluorinated chlorido[salophene]iron(III) complexes are potent, tumor cell-specific chemotherapeutic agents, with the potential to treat various types of cancers.

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.

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.

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.

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.

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.

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.

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.

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.