A ubiquitous metal, difficult to track: towards an understanding of the regulation of titanium(iv) in humans

Novel Titanocene Y derivative with albumin affinity exhibits improved anticancer activity against platinum resistant cells

The antitumor activity of Ti(IV)-based compounds put them in the spotlight for cancer treatment in the past, but their lack of stability in vivo due to a high rate of hydrolysis has hindered their development as antitumor drugs. As a possible solution for this problem, we have reported a synthesis strategy through which we combined a titanocene fragment, a tridentate ligand, and a long aliphatic chain. This strategy allowed us to generate a titanium compound (Myr-Ti) capable of interacting with albumin, highly stable in water and with cytotoxic activity in tumor cells[1]. Following a similar strategy, now we report the synthesis of a new compound (Myr-TiY) derived from titanocene Y that shows antitumoral activity in a cisplatin resistant model with a 50% inhibitory concentration (IC50) of 41-76 μM. This new compound shows high stability and a strong interaction with human serum albumin. Myr-TiY has a significant antiproliferative and proapoptotic effect on the tested cancer cells and shows potential tumor selectivity when assayed in non-tumor human epithelial cells being more selective (1.3-3.8 times) for tumor cells than cisplatin. These results lead us to think that the described synthesis strategy could be useful to generate compounds for the treatment of both cisplatin-sensitive and cisplatin-resistant cancers.

An anticancer Ti(IV) complex increases mitochondrial reactive oxygen species levels in relation with hypoxia and endoplasmic-reticulum stress: A distinct non DNA-related mechanism

PhenolaTi is a promising Ti(IV) anticancer complex, with high stability and cytotoxicity, without notable toxic side-effects. Its cellular mechanism was proposed to relate to ER stress. Herein, we investigated the downstream effects of this mode of action in two cancer cell lines: ovarian carcinoma A2780 and cervical adenocarcinoma HeLa. First, although Ti(IV) is a non-redox metal, the formation of mitochondrial reactive oxygen species (ROS) was detected with live-cell imaging. Then, we inspected the effect of the mitochondrial ROS on cytotoxicity, using two methods: (a) addition of compounds that either elevate or reduce the mitochondrial glutathione concentration, thus affecting the oxidative state of the cells; and (b) scavenging mitochondrial ROS. Unlike the results observed for cisplatin, neither method influenced the cytotoxicity of phenolaTi, implying that ROS formation was a mere side effect of its activity. Additionally, live cell imaging displayed the hypoxia induced by phenolaTi, which can be associated with ROS formation. Overall, the results support the notion that ER-stress is the main cellular mechanism of phenolaTi, leading to hypoxia and mitochondrial ROS. The distinct mechanism of phenolaTi, which is different from that of cisplatin, combined with its stability and favorable anticancer properties, altogether make it a strong chemotherapeutic drug candidate.

Sol-Gel-Derived Fibers Based on Amorphous α-Hydroxy-Carboxylate-Modified Titanium(IV) Oxide as a 3-Dimensional Scaffold

The development of novel fibrous biomaterials and further processing of medical devices is still challenging. For instance, titanium(IV) oxide is a well-established biocompatible material, and the synthesis of TiO_x particles and coatings via the sol-gel process has frequently been published. However, synthesis protocols of sol-gel-derived TiO_x fibers are hardly known. In this publication, the authors present a synthesis and fabrication of purely sol-gel-derived TiO_x fiber fleeces starting from the liquid sol-gel precursor titanium ethylate (TEOT). Here, the α-hydroxy-carboxylic acid lactic acid (LA) was used as a chelating ligand to reduce the reactivity towards hydrolysis of TEOT enabling a spinnable sol. The resulting fibers were processed into a non-woven fleece, characterized with FTIR, ¹³C-MAS-NMR, XRD, and screened with regard to their stability in physiological solution. They revealed an unexpected dependency between the LA content and the dissolution behavior. Finally, in vitro cell culture experiments proved their potential suitability as an open-mesh structured scaffold material, even for challenging applications such as therapeutic medicinal products (ATMPs).

Exploring Titanium(IV) Complexes as Potential Antimicrobial Compounds

Due to the rapid mutation of pathogenic microorganisms, drug-resistant superbugs have evolved. Antimicrobial-resistant germs may share their resistance genes with other germs, making them untreatable. The search for more combative antibiotic compounds has led researchers to explore metal-based strategies centered on perturbing the bioavailability of essential metals in microbes and examining the therapeutic potential of metal complexes. Given the limited knowledge on the application of titanium(IV), in this work, eight Ti(IV) complexes and some of their corresponding ligands were screened by the Community for Open Antimicrobial Drug Discovery for antimicrobial activity. The compounds were selected for evaluation because of their low cytotoxic/antiproliferative behavior against a human non-cancer cell line. At pH 7.4, these compounds vary in terms of their solution stability and ligand exchange lability; therefore, an assessment of their solution behavior provides some insight regarding the importance of the identity of the metal compound to the antimicrobial therapeutic potential. Only one compound, Ti(deferasirox)₂, exhibited promising inhibitory activity against the Gram-positive bacteria methicillin-resistant Staphylococcus aureus and minimal toxicity against human cells. The ability of this compound to undergo transmetalation with labile Fe(III) sources and, as a consequence, inhibit Fe bioavailability and ribonucleotide reductase is evaluated as a possible mechanism for its antibiotic effect.

Iron Chelator Transmetalative Approach to Inhibit Human Ribonucleotide Reductase

Efforts directed at curtailing the bioavailability of intracellular iron could lead to the development of broad-spectrum anticancer drugs given the metal's role in cancer proliferation and metastasis. Human ribonucleotide reductase (RNR), the key enzyme responsible for synthesizing the building blocks of DNA replication and repair, depends on Fe binding at its R2 subunit to activate the catalytic R1 subunit. This work explores an intracellular iron chelator transmetalative approach to inhibit RNR using the titanium(IV) chemical transferrin mimetic (cTfm) compounds Ti(HBED) and Ti(Deferasirox)2. Whole-cell EPR studies reveal that the compounds can effectively attenuate RNR activity though seemingly causing different changes to the labile iron pool that may account for differences in their potency against cells. Studies of Ti(IV) interactions with the adenosine nucleotide family at pH 7.4 reveal strong metal binding and extensive phosphate hydrolysis, which suggest the capacity of the metal to disturb the nucleotide substrate pool of the RNR enzyme. By decreasing intracellular Fe bioavailability and altering the nucleotide substrate pool, the Ti cTfm compounds could inhibit the activity of the R1 and R2 subunits of RNR. The compounds arrest the cell cycle in the S phase, indicating suppressed DNA replication, and induce apoptotic cell death. Cotreatment cell viability studies with cisplatin and Ti(Deferasirox)2 reveal a promising synergism between the compounds that is likely owed to their distinct but complementary effect on DNA replication.

Synthesis of asymmetrical diaminobis(alkoxo)-bisphenol compounds and their C1-symmetrical mono-ligated titanium(iv) complexes as highly stable highly active antitumor compounds

Asymmetrical 2,2'-((ethane-1,2-diylbis((2-hydroxyethyl)azanediyl))bis(methylene))diphenol substituted compounds and their C1-symmetrical diaminobis(phenolato)-bis(alkoxo) titanium(iv) complexes were synthesized, with one symmetrical analogue. X-ray crystallography corroborated tight ligand binding. Different substitutions on the two aromatic rings enabled fine-tuning of the complex properties, giving enhanced solubility, high anticancer activity (IC50 < 4 μM), and significant hydrolytic stability.

From medium to endoplasmic reticulum: Tracing anticancer phenolato titanium(IV) complex by 19F NMR detection

Titanium(IV) complexes of diaminobis(phenolato)-bis(alkoxo) ligands are promising anticancer drugs, showing marked in-vivo efficacy with no toxic side-effects in mice, hence, it is of interest to elucidate their mechanism of action. Herein, we employed a fluoro-substituted derivative, FenolaTi, for mechanistic analysis of the active species and its cellular target by quantitative ¹⁹F NMR detection to reveal its biodistribution and reactivity in extracellular and intracellular matrices. Upon administration to the serum-containing medium, FenolaTi interacted with bovine serum albumin. 20 h post administration, the cellular accumulation of FenolaTi derivatives was estimated as 37% of the administered compound, in a concentration three orders-of-magnitude higher than the administered dose, implying that active membrane transportation facilitates cellular penetration. An additional 19% of the administered dose that was detected in the extracellular environment had originated from post-apoptotic cells. In the cell, interaction with cellular proteins was detected. Although some intact Ti(IV) complex localized in the nucleus, no signals for isolated DNA fractions were detected and no reactivity with nuclear proteins was observed. Interestingly, higher accumulation of FenolaTi-derived compounds in the endoplasmic reticulum (ER) and interaction with proteins therein were detected, supporting the role of the ER as a possible target for cytotoxic bis(phenolato)-bis(alkoxo) Ti(IV) complexes.

Using X-ray Diffraction Techniques for Biomimetic Drug Development, Formulation, and Polymorphic Characterization

Drug development is a decades-long, multibillion dollar investment that often limits itself. To decrease the time to drug approval, efforts are focused on drug targets and drug formulation for optimal biocompatibility and efficacy. X-ray structural characterization approaches have catalyzed the drug discovery and design process. Single crystal X-ray diffraction (SCXRD) reveals important structural details and molecular interactions for the manifestation of a disease or for therapeutic effect. Powder X-ray diffraction (PXRD) has provided a method to determine the different phases, purity, and stability of biological drug compounds that possess crystallinity. Recently, synchrotron sources have enabled wider access to the study of noncrystalline or amorphous solids. One valuable technique employed to determine atomic arrangements and local atom ordering of amorphous materials is the pair distribution function (PDF). PDF has been used in the study of amorphous solid dispersions (ASDs). ASDs are made up of an active pharmaceutical ingredient (API) within a drug dispersed at the molecular level in an amorphous polymeric carrier. This information is vital for appropriate formulation of a drug for stability, administration, and efficacy purposes. Natural or biomimetic products are often used as the API or the formulation agent. This review profiles the deep insights that X-ray structural techniques and associated analytical methods can offer in the development of a drug.

Exploring Serum Transferrin Regulation of Nonferric Metal Therapeutic Function and Toxicity

Serum transferrin (sTf) plays a pivotal role in regulating iron biodistribution and homeostasis within the body. The molecular details of sTf Fe(III) binding blood transport, and cellular delivery through transferrin receptor-mediated endocytosis are generally well-understood. Emerging interest exists in exploring sTf complexation of nonferric metals as it facilitates the therapeutic potential and toxicity of several of them. This review explores recent X-ray structural and physiologically relevant metal speciation studies to understand how sTf partakes in the bioactivity of key non-redox active hard Lewis acidic metals. It challenges preconceived notions of sTf structure function correlations that were based exclusively on the Fe(III) model by revealing distinct coordination modalities that nonferric metal ions can adopt and different modes of binding to metal-free and Fe(III)-bound sTf that can directly influence how they enter into cells and, ultimately, how they may impact human health. This knowledge informs on biomedical strategies to engineer sTf as a delivery vehicle for metal-based diagnostic and therapeutic agents in the cancer field. It is the intention of this work to open new avenues for characterizing the functionality and medical utility of nonferric-bound sTf and to expand the significance of this protein in the context of bioinorganic chemistry.

Effective Oral Administration of an Antitumorigenic Nanoformulated Titanium Complex

Orally administered anticancer drugs facilitate treatment, but the acidic conditions in the stomach often challenge their availability. PhenolaTi is a Ti^IV -based nontoxic anticancer drug with marked in-vivo efficacy. We report that nanoformulation protects phenolaTi from decomposition in stomach-like conditions. This is evidenced by similar NMR characteristics and similar in-vitro cytotoxicity toward murine (CT-26) and human (HT-29) colon cancer cells before and after incubation of nanoformulated phenolaTi (phenolaTi-F) at pH 2, unlike results with the unformulated form of the complex. Furthermore, administration of phenolaTi-F in animal drinking water revealed a notable inhibition of tumor growth in Balb/c and immune-deficient (Nude) mice inoculated with CT-26 and HT-29 cells, respectively. In-vivo efficacy was at least similar to that of the corresponding intraperitoneal treatment with phenolaTi-F and the clinically employed oral drug, capecitabine. No body weight loss or clinical signs of toxicity were evident in the phenolaTi-F-treated animals. These findings demonstrate a new convenient mode of cancer treatment through oral administration by safe titanium-based drugs.

Titanium Tackles the Endoplasmic Reticulum: A First Genomic Study on a Titanium Anticancer Metallodrug

PhenolaTi is an advanced non-toxic anticancer chemotherapy; this inert bis(phenolato)bis(alkoxo) Ti(IV) complex demonstrates the intriguing combination of high and wide efficacy with no detected toxicity in animals. Here we unravel the cellular pathways involved in its mechanism of action by a first genome study on Ti(IV)-treated cells, using an attuned RNA sequencing-based available technology. First, phenolaTi induced apoptosis and cell-cycle arrest at the G2/M phase in MCF7 cells. Second, the transcriptome of the treated cells was analyzed, identifying alterations in pathways relating to protein translation, DNA damage, and mitochondrial eruption. Unlike for common metallodrugs, electrophoresis assay showed no inhibition of DNA polymerase activity. Reduced in vitro cytotoxicity with added endoplasmic reticulum (ER) stress inhibitor supported the ER as a putative cellular target. Altogether, this paper reveals a distinct ER-related mechanism by the Ti(IV) anticancer coordination complex, paving the way for wider applicability of related techniques in mechanistic analyses of metallodrugs.

Fueling a Hot Debate on the Application of TiO2 Nanoparticles in Sunscreen

Titanium is one of the most abundant elements in the earth's crust and while there are many examples of its bioactive properties and use by living organisms, there are few studies that have probed its biochemical reactivity in physiological environments. In the cosmetic industry, TiO2 nanoparticles are widely used. They are often incorporated in sunscreens as inorganic physical sun blockers, taking advantage of their semiconducting property, which facilitates absorbing ultraviolet (UV) radiation. Sunscreens are formulated to protect human skin from the redox activity of the TiO2 nanoparticles (NPs) and are mass-marketed as safe for people and the environment. By closely examining the biological use of TiO2 and the influence of biomolecules on its stability and solubility, we reassess the reactivity of the material in the presence and absence of UV energy. We also consider the alarming impact that TiO2 NP seepage into bodies of water can cause to the environment and aquatic life, and the effect that it can have on human skin and health, in general, especially if it penetrates into the human body and the bloodstream.

Challenges and Chances in the Preclinical to Clinical Translation of Anticancer Metallodrugs

Despite being “sentenced to death” for quite some time, anticancer platinum compounds are still the most frequently prescribed cancer therapies in the oncological routine and recent exciting news from late-stage clinical studies on combinations of metallodrugs with immunotherapies suggest that this situation will not change soon. It is perhaps surprising that relatively simple molecules like cisplatin, discovered over 50 years ago, are still widely used clinically, while none of the highly sophisticated metal compounds developed over the last decade, including complexes with targeting ligands and multifunctional (nano)formulations, have managed to obtain clinical approval. In this book chapter, we summarize the current status of ongoing clinical trials for anticancer metal compounds and discuss the reasons for previous failures, as well as new opportunities for the clinical translation of metal complexes.

Substance-Based Bibliometrics: Identifying Research Gaps by Counting and Analyzing Substances

Identifying research gaps and generating research questions are often a first step in developing ideas for writing a research paper or grant proposal. The concept of substance-based bibliometrics uses the counts of substances in the scientific literature to better understand, assess, and clarify the state and impact of information in the chemical sciences. Connecting substances indexed to specific bioactivity or target indicators can lead to assessing the biochemical, biological, and medicinal relevance of substances as well as developing ideas for expanding drug design and discovery through identifying and modifying the structural features of molecules. This study uses Chemical Abstracts through the SciFinder database to count for the occurrence of substances in the scientific literature. The study sets out search strategies for discovering potential research gaps and new ideas through visualization of chemical structures with known bioactivity and target indicators. The author recommends that subject librarians integrate research gap training in their bibliographic instruction classes, particularly to upper-level undergraduate and graduate chemistry students.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

In Vivo Anticancer Activity of a Nontoxic Inert Phenolato Titanium Complex: High Efficacy on Solid Tumors Alone and Combined with Platinum Drugs

Due to the toxicity of platinum compounds used in the clinic as anticancer chemotherapies, titanium serves as a safe and attractive alternative. Lately, we introduced a new family of Ti complexes based on readily available phenolato ligands, demonstrating incredibly high hydrolytic stability, with the lead compound phenolaTi demonstrating wide cytotoxic activity toward the NCI‐60 panel of human cancer cell lines, with an average GI₅₀ value of 4.7±2 μm. Herein, we evaluated in vivo: a) the safety, and b) the growth inhibitory capacity (efficacy) of this compound. PhenolaTi was found to be effective in vivo against colon (CT‐26) and lung (LLC‐1) murine cell lines in syngeneic hosts and toward a human colon cancer (HT‐29) cell line in immune‐deficient (Nude) mice, with an efficacy similar to that of known chemotherapy. Notably, no clinical signs of toxicity were observed in the treated mice, namely, no effect on body weight, spleen weight or kidney function, unlike the effects observed with the positive control Pt drugs. Studies of combinations of phenolaTi and Pt drugs provided evidence that similar efficacy with decreased toxicity may be achieved, which is highly valuable for medicinal applications.

Synthesis of Pure Enantiomers of Titanium(IV) Complexes with Chiral Diaminobis(phenolato) Ligands and Their Biological Reactivity

Racemic and enantiomerically pure titanium(IV) complexes with ortho-brominated or para-nitrated chiral diaminobis(phenolato) ligands were prepared with NH and NMe cyclohexyldiamino bridges through ligand to metal chiral induction. The hydrolytic behavior of the complexes was evaluated, identifying the N-methylated complex as the most stable. A representative NH complex hydrolyzed to first give a dimeric structure in solution as deduced by NMR diffusion measurements, followed by formation of clusters with higher nuclearity, as was supported by X-ray characterization of a tetranuclear cluster obtained in trace amounts following 30 days in water solutions. The cytotoxicity of the enantiomerically pure and racemic complexes was measured on HT-29 human colon cancer cell line based on the MTT assay; all stereochemical configurations of the N-methylated complex were inactive, whereas for the NH complexes, the racemic mixtures were mostly inactive but the pure enantiomers exhibited similarly high cytotoxicity, supporting a polynuclear active species. Analysis of the two enantiomers of the most active brominated complex for their cytotoxicity on human ovarian A2780, cisplatin resistant A2780cp and multi-drug-resistant A2780adr cell lines as well as for their apoptosis induction on the A2780 line revealed similar reactivity, supporting a similar mechanism for the two enantiomers.

Exploring titanium(IV) chemical proximity to iron(III) to elucidate a function for Ti(IV) in the human body

Despite its natural abundance and widespread use as food, paint additive, and in bone implants, no specific biological function of titanium is known in the human body. High concentrations of Ti(IV) could result in cellular toxicity, however, the absence of Ti toxicity in the blood of patients with titanium bone implants indicates the presence of one or more biological mechanisms to mitigate toxicity. Similar to Fe(III), Ti(IV) in blood binds to the iron transport protein serum transferrin (sTf), which gives credence to the possibility of its cellular uptake mechanism by transferrin-directed endocytosis. However, once inside the cell, how sTf bound Ti(IV) is released into the cytoplasm, utilized, or stored remain largely unknown. To explain the molecular mechanisms involved in Ti use in cells we have drawn parallels with those for Fe(III). Based on its chemical similarities with Fe(III), we compare the biological coordination chemistry of Fe(III) and Ti(IV) and hypothesize that Ti(IV) can bind to similar intracellular biomolecules. The comparable ligand affinity profiles suggest that at high Ti(IV) concentrations, Ti(IV) could compete with Fe(III) to bind to biomolecules and would inhibit Fe bioavailability. At the typical Ti concentrations in the body, Ti might exist as a labile pool of Ti(IV) in cells, similar to Fe. Ti could exhibit different types of properties that would determine its cellular functions. We predict some of these functions to mimic those of Fe in the cell and others to be specific to Ti. Bone and cellular speciation and localization studies hint toward various intracellular targets of Ti like phosphoproteins, DNA, ribonucleotide reductase, and ferritin. However, to decipher the exact mechanisms of how Ti might mediate these roles, development of innovative and more sensitive methods are required to track this difficult to trace metal in vivo.

The role of citrate, lactate and transferrin in determining titanium release from surgical devices into human serum

The presence of ionic titanium in the serum of patients with titanium implants is currently unexplained. This is presumed due to corrosion, and yet the serum titanium concentration measured in patients is far greater than that predicted by its solubility. The binding of titanium ion as Ti(IV) to human transferrin (hTF) in serum indicates that Ti(IV) ions interact with human physiology. This is an intriguing finding since there is currently no known role for titanium ions in human physiology. Thus, understanding the factors that determine in vivo titanium ion release is relevant to further understanding this metal's interactions with human biochemistry. The present study sought to determine the extent of titanium ion release of into human serum in vitro, and the role of citrate, lactate and hTF in this process. It was found that, when surgical devices of commercially pure titanium were placed into human serum, citrate and lactate concentrations were the prime determinants of titanium release. Crystallography revealed Ti(IV) bound to hTF in the presence of citrate alone, signalling that citrate can act as an independent ligand for Ti(IV) binding to hTF. Based on these findings, a two-stage process of titanium ion release into human serum that is dependent upon both citrate and hTF is proposed to explain the ongoing presence of titanium ion in human subjects with implanted titanium devices.

Are cucurbiturils better drug carriers for bent metallocenes? Insights from theory

Bent metallocenes (BM) have anti-tumor properties but they face a serious drug efficacy problem due to poor aqueous solubility and rapid hydrolysis under physiological conditions. These two problems can be fixed by encapsulating them in host molecules such as cyclodextrin (CD), cucurbituril (CB) etc. Experimentally, CD-BM, CB-BM host-guest complexes have been investigated to check the efficiency of the drug delivery and efficiency of the encapsulated drug. CB has been reported to be a better host than CD but the reasons for this has not been figured out. This can be done by finding out the mechanism of binding and the nature of the binding forces in both the inclusion complexes. This is exactly done here by performing a DFT study at BP86/TZP level on CB-BM host-guest systems. For comparison CD-BM with β-cyclodextrin as host have been studied. Four BMs (Cp₂MCl₂, M=Ti, V, Nb, Mo) and their corresponding cations (Cp₂MCl⁺, Cp₂M²⁺) are chosen as guests and they are encapsulated into cucurbit-[6]-uril (CB[6]) and cucurbit-[7]-uril(CB[7]) host systems. Computations reveal that CB[7] accommodates well the BMs over CB[6] due to their larger cavity size and also CB[7] is found to be a better host than β-cyclodextrin. BMs enter vertically rather than horizontally into the CB cavity. The reversible binding of BMs within CB[7] is controlled by various non-bonding interactions and mainly by hydrogen bonding between the portal oxygen atoms and Cp protons as revealed by QTAIM analysis. On the other hand, the interaction between the wall nitrogen atoms in CB[7] and chlorine atoms attached to the metal in BM strengthens the M-Cl bonds that prevents rapid hydrolysis of M-Cl and M-Cp bonds saving the drug. Comparatively, BMs experience less electrostatic attraction and more Pauli repulsion within β-cyclodextrin cavity and this affects the drug binding with CD. This makes β-cyclodextrin a less suitable drug carrier for BMs than CBs. Among the four BMs, niobocene binds strongly and titanocene binds weakly with CBs. EDA clearly shows that all the interactions between the guest and host are non-covalent in nature and electrostatic interactions outperform high-repulsion resulting in stable complexes. Cations form stronger complexes than neutral BMs. FMO analysis reveals that neutral BMs are less reactive compared to their cations and complexes are more reactive in CB[6] environment due to excess strain. QTAIM analysis helps to bring out the newer insights in these types of host-guest systems.

In vitro combinations of inert phenolato Ti(iv) complexes with clinically employed anticancer chemotherapy: synergy with oxaliplatin on colon cells

Advanced anticancer phenolato titanium(iv) complexes were combined with known chemotherapeutic anticancer drugs applied in the clinic and were analyzed in vitro on cell lines most sensitive to the Ti(iv) complex and relevant to the clinical application of the known drugs. Combination of the Ti(iv) complex with cisplatin on ovarian cells showed mostly an additive behavior, also on a line resistant to cisplatin. Combination of the Ti(iv) complex with fluorouracil on colon cells gave near additive behavior, and that with oxaliplatin gave a synergistic behavior at a wide range of Ti : Pt ratios, but only when the drugs were administered together. Increasing the time intervals between the administration of Ti and of Pt turned the behavior to antagonistic, suggesting some deactivation of Pt by the Ti agent. For combinations where the drugs were applied together, the behavior depended on the effect level, and higher effects gave greater synergism, implying that technical aspects such as solubility are influential. Nevertheless, more complex patterns recorded for combinations where the drugs had been applied separately suggested multiple mechanisms with different concentration dependence. Overall the results point to high medicinal potential for the tested compounds for anticancer combination treatments.

Fluorescent antitumor titanium(iv) salen complexes for cell imaging

First live cell imaging using florescent salen Ti(iv) complexes, which are cytotoxic and inactive, both entering the cell but with different subcellular accumulations.

Expanding the Therapeutic Potential of the Iron Chelator Deferasirox in the Development of Aqueous Stable Ti(IV) Anticancer Complexes

The recent X-ray structure of titanium(IV)-bound human serum transferrin (STf) exhibiting citrate as a synergistic anion reveals a difference in Ti(IV) coordination versus iron(III), the metal endogenously delivered by the protein to cells. This finding enriches our bioinspired drug design strategy for Ti(IV)-based anticancer therapeutics, which applies a family of Fe(III) chelators termed chemical transferrin mimetic (cTfm) ligands to inhibit Fe bioavailability in cancer cells. Deferasirox, a drug used for iron overload disease, is a cTfm ligand that models STf coordination to Fe(III), favoring Fe(III) binding versus Ti(IV). This metal affinity preference drives deferasirox to facilitate the release of cytotoxic Ti(IV) intracellularly in exchange for Fe(III). An aqueous speciation study performed by potentiometric titration from pH 4 to 8 with micromolar levels of Ti(IV) deferasirox at a 1:2 ratio reveals exclusively Ti(deferasirox)2 in solution. The predominant complex at pH 7.4, [Ti(deferasirox)2]2-, exhibits the one of the highest aqueous stabilities observed for a potent cytotoxic Ti(IV) species, demonstrating little dissociation even after 1 month in cell culture media. UV-vis and 1H NMR studies show that the stability is unaffected by the presence of biomolecular Ti(IV) binders such as citrate, STf, and albumin, which have been shown to induce dissociation or regulate cellular uptake and can alter the activity of other antiproliferative Ti(IV) complexes. Kinetic studies on [Ti(deferasirox)2]2- transmetalation with Fe(III) show that a labile Fe(III) source is required to induce this process. The initial step of this process occurs on the time scale of minutes, and equilibrium for the complete transmetalation is reached on a time scale of hours to a day. This work reveals a mechanism to deliver Ti(IV) compounds into cells and trigger Ti(IV) release by a labile Fe(III) species. Cellular studies including other cTfm ligands confirm the Fe(III) depletion mechanism of these compounds and show their ability to induce early and late apoptosis.