A new titanocenyl amide containing flavone as pendant group has been synthesized by reaction of titanocenyl carboxylic acid chloride and 7-Aminoflavone and structurally characterized by spectroscopic methods. This species and eight previously synthesized titanocenyl amide complexes have been tested in breast adenocarcinoma cancer cell line, MCF-7. The functionalization of titanocene dichloride with amides enhances the cytotoxic activity in MCF-7. Two sets of titanocenyl amides can be identified, with
The development of efficient metal-based anticancer drugs currently still is a scientific challenge. The design of such species requires careful selection of the metal center and ligands surrounding their coordination sphere in order to achieve the desired biological activity but, keeping in mind that it is also desirable to maintain low-toxic side effects. In 1979, Köpf and Köpf-Maier opened a new chapter in the medicinal chemistry with the discovery of the first metallocene-based organometallic anticancer agent, titanocene dichloride, Cp2TiCl2. The fact that it possesses antitumor properties in cancer cell lines that are insensitive to cisplatin as well as lower toxic effects than cisplatin, has motivated the scientific community to continue investigating this species [
The structure modification of titanocene dichloride to enhance its anticancer properties requires a careful selection of the functional group to be appended to the cyclopentadienyl ring or replacement of the ancillary ligands for more active ones. Recently, we published the synthesis, structure, and biological activity of titanocenyl amide complexes in colon cancer cell line HT-29 [
All reactions were run under an atmosphere of dry nitrogen using Schlenk glassware or a glovebox, unless otherwise stated. Reaction vessels were flame-dried under a stream of nitrogen, and anhydrous solvents were transferred by oven-dried syringes or cannula. Tetrahydrofuran was dried and deoxygenated by distillation over K-benzophenone under nitrogen. Infrared spectra were obtained in dried KBr pellets. The NMR spectra were obtained on a DRX-500 MHz Bruker spectrometer. For the samples prepared on CDCl3, chemical shifts were reference relative to C
The breast adenocarcinoma cell line MCF7 was purchased from American Type Culture Collection and was kept at 37°C and 95% Air/5% CO2. Growth medium for MCF7 was Eagle’s Minimum Essential Media supplemented with 10% (v/v) fetal bovine serum, 1% (v/v) antibiotic/antimycotic, nonessential aminoacids, and 0.01 mg/mL bovine insulin. MTT and Triton X-100 used for the cytotoxic assay were obtained from Sigma. All MTT manipulations were performed in a dark room.
Titaniumcarboxylate (0.25 mmoL, 77.4 mg) was dissolved in SOCl2 (1.0 mL), and stirred for 2 h at rt. Excess SOCl2 was removed under high-vacuum and dried for 24 h. The precipitate was dissolved in CH2Cl2 (2.0 mL), added dropwise to a mixture of the NaH (0.75 mmoL, 18 mg) and the 7-Aminoflavone (0.25 mmoL, 59.4 mg) in CH2Cl2 (6.0 mL) and stirred for another 20 h. After filtration through celite, the solvent was washed with a mixture of 1N HCl and NaCl (1.0 g each 10 mL) (
Biological activity was determined using the MTT assay originally described by Mossman [
The syntheses of eight of the nine titanocenyl amide complexes presented have been reported previously by our group [
The cytotoxicities of the titanocenyl complexes on breast adenocarcinoma cancer MCF-7 cell line were measured using a slightly modified MTT assay at 72 hours [
The objective of this study is to investigate the role of the substituents on the phenyl ring with different polarities, steric and electrodonating capabilities and the resulting anticancer properties on breast cancer. Figure
Cytotoxicities of titanocenyl amides studied on MCF-7 breast cancer cell line at 72 h, as determined by MTT assay. IC values are the average of four independent measurements with their standard deviations ( ).
Complex | IC50 | Structure |
---|---|---|
Cp2TiCl2 |
Dose-response curves for selected Amide-Functionalized Titanocenyls complexes against MCF-7 breast cancer cells at 72 hours of drug exposure. Legend: complex-
Upon analysis of Table
To put in perspective these titanocenyl amides, we should compare them with other functionalized titanocenes. Recently, other amide-functionlized titanocenes have been reported with anticancer properties with cytotoxicities in the 10-5 M range in six cancer cell lines: BJAB (lymphoma), MelHo and A375 (melanoma), MCF-7 (breast carcinoma), and Nalm-6 and Jurkat (leukemia) [
Other types of functionalized titanocenes have been reported with enhanced cytotoxic properties and IC50 values in the micromolar range [
Beckhove and co-workers have reported anticancer properties of bis-[p-methoxybenzyl)cyclopentadienyl] titanium dichloride (Titanocene Y). This is active against a wide variety of cancer cell lines. Moreover, Titanocene Y has been tested in explanted human breast tumor cells and in xenografted MCF-7 tumors in mice with promising results in terms of doses, low toxicity, and reduction of tumor volume [
The functionalization of titanocene dichloride with amides (phenyl amides) increases the cytotoxic activity of the resulting titanocenyl amide complexes. One possible explanation could be the Ti-O(amide) bond which provides stability in aqueous environment and makes the complex more resistant to hydrolysis. Although this is highly speculative, based on the structural features of these titanocenyl amides and the hypothesis that albumin is the carrier protein of titanocene into the target place inside the cell [
Enrique Meléndez acknowledges the NIH-MBRS SCORE Grant no. S06 GM008103-36 at University of Puerto Rico-Mayagüez and NSF-MRI Program for providing funds for the purchase of the 500 MHz NMR instrument.