High efficiency of ferricenium salts as radiosensitizers of V79 cells in vitro and the KHT tumor in vivo

Redox-dependent cytotoxicity of ferrocene derivatives and ROS-activated prodrugs based on ferrocenyliminoboronates

Four ferrocene derivatives - ferrocenecarboxylic acid, ferrocenium salt, ferroceneboronic acid, and aminoferrocene - were characterized electrochemically, and their cytotoxicity was probed using cancer cells (line MG-63). We related the observed cytotoxicity with the determined redox potentials of these four ferrocenes - aminoferrocene with its lowest redox potential exhibited the highest cytotoxicity. Thus, we synthesized four derivatives consisting of aminoferrocene and phenylboronic acid residue with the intent to employ them as ROS-activated prodrugs (ROS - reactive oxygen species). We characterized them and studied their time-dependent stability in aqueous environments. Then, we performed electrochemical measurements at oxidative conditions to confirm ROS-responsivity of the synthesized molecules. Finally, the cytotoxicity of the synthesized molecules was tested using cancer MG-63 cells and noncancerous NIH-3T3 cells. The experiments revealed sought behaviour, especially for para-regioisomers of synthesized ferrocenyliminoboronates.

The Cytotoxic Effect of Newly Synthesized Ferrocenes against Cervical Carcinoma Cells Alone and in Combination with Radiotherapy

Cervical cancer is one of the most common types of cancer in women, with approximately 500,000 new cases and 250,000 deaths every year. Radiotherapy combined with chemotherapy represents the treatment of choice for advanced cervical carcinomas. The role of the chemotherapy is to increase the sensitivity of the cancer cells to irradiation. Cisplatin, the most commonly used drug for this purpose, has its limitations. Thus, we used a family of ferrocene derivatives (in addition, one new species was prepared using standard Schlenk techniques) and studied their effects on cervical cancer cells alone and in combination with irradiation. We applied colorimetric assay to determine the cytotoxicity of the compounds; flow cytometry to analyze the production of reactive oxygen species (ROS), cell cycle, and mitochondrial membrane potential (MMP); immunochemistry to study protein expression; and colony forming assay to evaluate changes in radiosensitivity. Treatment with ferrocenes exhibited significant cytotoxicity against cervical cancer cells, associated with increasing ROS production and MMP changes, suggesting the induction of apoptosis. The combined activity of ferrocenes and ionizing radiation highlighted ferrocenes as potential radiosensitizing drugs, while their higher single-agent toxicity in comparison with routinely used cisplatin could also be promising. Our results demonstrate antitumor activity of several tested ferrocenes both alone and in combination with radiotherapy.

Transition metal compounds as cancer radiosensitizers

Combining metallo-drugs with ionising radiation for synergistic cancer cell killing: chemical design principles, mechanisms of action and emerging applications.

Synthesis, antimalarial activities and cytotoxicities of amino-artemisinin-1,2-disubstituted ferrocene hybrids

Artemisinin-ferrocene conjugates incorporating a 1,2-disubstituted ferrocene analogous to that embedded in ferroquine but attached via a piperazine linker to C10 of the artemisinin were prepared from the piperazine artemisinin derivative, and activities were evaluated against asexual blood stages of chloroquine (CQ) sensitive NF54 and CQ resistant K1 and W2 strains of Plasmodium falciparum (Pf). The most active was the morpholino derivative 5 with IC₅₀ of 0.86 nM against Pf K1 and 1.4 nM against Pf W2. The resistance indices were superior to those of current clinical artemisinins. Notably, the compounds were active against Pf NF54 early and late blood stage gametocytes - these exerted >86% inhibition at 1 µM against both stages; they are thus appreciably more active than methylene blue (∼57% inhibition at 1 µM) against late stage gametocytes. The data portends transmission blocking activity. Cytotoxicity was determined against human embryonic kidney cells (Hek293), while human malignant melanoma cells (A375) were used to assess their antitumor activity.

Synthesis and structure-activity relationships of ferrocenyl tamoxifen derivatives with modified side chains

We report here the synthesis and cell-proliferation properties of derivatives of the breast cancer drug tamoxifen, in which the -O(CH(2))(2)N(CH(3))(2) side chain, responsible for the drug's antiestrogenic properties, has been modified by a ferrocenyl moiety. We recently reported the diphenol compound 5, in which this amino chain had been replaced with an acyl-ferrocenyl (-O(CH(2))(2)C(O)[(eta(5)-C(5)H(4))FeCp]) group, and which showed antiproliferative effects against both the hormone-dependent MCF-7 and -independent MDA-MB-231 breast cancer cell lines. We now report the results of a structure-activity relationship (SAR) study, in which the lateral chain length has been varied, the ketone group has been omitted, and the number of phenol groups has been varied. Compounds 1-4, with a side chain lacking the carbonyl function (-O(CH(2))(n)[(eta(5)-C(5)H(4))FeCp], n = 1-4) and which show a decreasing affinity for ERalpha (ER = estrogen receptor) with increasing chain length, act as estrogens on MCF-7 cells, and mild cytotoxics on PC-3 prostate cancer cells, with IC(50) values around 10 microM. The two monophenolic derivatives of 2, 2 a and 2 b, which show a reduced affinity for ERalpha compared to 2, are also estrogenic, but are only slightly cytotoxic. Finally, we have reexamined compound 5 and discovered that its antiproliferative effect against the MCF-7 cell line does not arise from antiestrogenicity as we had originally suspected, but by means of a cytotoxic pathway. This compound is also sensitive to the number of phenol groups as cell death is diminished when one of the hydroxyl groups is omitted (5 a and 5 b). Molecular modeling studies of the ligand-ERalpha binding stability are broadly consistent with the experimental binding affinity results for compounds 2, 2 a, 2 b, 5, 5 a, and 5 b. Electrochemical experiments show that 1-4, 2 a, and 2 b are stable to oxidation on the electrochemical timescale, unlike 5, 5 a, and 5 b, and that cytotoxicity is related to less positive phenol oxidation potentials. The SAR study shows that the presence of a ketone group and two phenol groups is necessary for strong receptor binding and cytotoxic effects, and that all compounds are estrogenic, despite the presence of a bulky side chain.

Nanoparticles loaded with ferrocenyl tamoxifen derivatives for breast cancer treatment

For the first time, two organometallic triphenylethylene compounds (Fc-diOH and DFO), with strong antiproliferative activity in breast cancer cells, but insoluble in biological fluids, were incorporated in two types of stealth nanoparticles (NP): PEG/PLA nanospheres (NS) and nanocapsules (NC). Their physicochemical parameters were measured (size, zeta potential, encapsulation and loading efficiency), and their biological activity was assessed. In vitro drug release after high dilution of loaded NPs was measured by estradiol binding competition in MELN cells. The influence of the encapsulated drugs on the cell cycle and apoptosis was studied by flow cytometry analyses. Notwithstanding potential drug adsorption at the NP surface, Fc-diOH and DFO were incorporated efficiently in NC and NS, which slowly released both compounds. They arrested the cell cycle in the S-phase and induced apoptosis, whose activity is increased by loaded NS. A decrease in their antiproliferative activity by the antioxidant alpha-tocopherol indicated that reactive oxygen species (ROS) may be involved. Therefore, nanosystems, containing for the first time a high load of anticancer organometallic triphenylethylenes, have been developed. Their small size and delayed drug release, combined with their enhanced apoptotic potential, are compatible with an increased persistence in the blood and a promising antitumour activity.

Non platinum metal complexes as anti-cancer drugs

The development of metal complexes with platinum central atoms such as cisplatin or carboplatin had an enormous impact on current cancer chemotherapy. However, the spectrum of cancers that can be treated with platinum agents is narrow and treatment efficacy suffers from side effects and resistance phenomena. These unresolved problems in platinum-based anti-cancer therapy have stimulated increased research efforts in the search for novel non platinum-containing metal species as cytostatic agents. Preclinical and clinical investigations showed that the development of new metal agents with modes of action different from cisplatin is possible. Thus, complexes with iron, cobalt, or gold central atoms have shown promising results in preclinical studies and compounds with titanium, ruthenium, or gallium central atoms have already been evaluated in phase I and phase II trials. This review covers some relevant examples of preclinical and clinical research on novel non platinum metal complexes.

Metal complex SERMs (selective oestrogen receptor modulators). The influence of different metal units on breast cancer cell antiproliferative effects

The selective oestrogen receptor modulator tamoxifen is a leading agent in the adjuvant treatment of breast cancer. Several organometallic moieties have been vectorised with tamoxifen, in order to improve on the latter's antiproliferative properties by the addition of a potentially cytotoxic moiety, and have been evaluated versus both oestrogen receptor positive (MCF7) and oestrogen receptor negative (MDA-MB231) breast cancer cells. For tamoxifen analogues with ((R,R)-trans-1,2-diaminocyclohexane)platinum(II), cyclopentadienyl rhenium tricarbonyl, and ruthenocene tethers, there was no enhancement of the antiproliferative effect on oestrogen receptor positive cells, nor any cytotoxic effect on oestrogen receptor negative cells, while those containing cyclopentadienyl titanium dichloride showed an oestrogenic effect. However, compounds where ferrocene replaces tamoxifen's phenyl ring were strongly cytotoxic against both cell lines. The synthesis and biological results of these compounds is reviewed and placed in the historic context of inorganic compounds in therapy.