Clara Pampillón

Anti-tumor activity of Titanocene Y in xenografted Caki-1 tumors in mice.

The benzyl-substituted unbridged titanocene bis-[(p-methoxybenzyl)cyclopentadienyl] titanium(IV) dichloride (Titanocene Y) was tested in vitro against human renal cancer cells (Caki-1), in which it showed an IC50 value of 36×10–6 mol/l. Titanocene Y was then given in vivo in doses of 10, 20, 30, 40 and 50 mg/kg on 5 consecutive days to Caki-1-bearing mice, and it showed concentration-dependent and statistically significant tumor growth reduction with respect to a solvent-treated control cohort. The maximum tolerable dose of Titanocene Y was determined to be 40 mg/kg and it showed significantly better tumor volume growth reduction than cisplatin given at a dose of 2 mg/kg. This superior activity of Titanocene Y with respect to cisplatin will hopefully lead to clinical tests against metastatic renal cell cancer in the near future.

Substituted titanocenes induce caspase-dependent apoptosis in human epidermoid carcinoma cells in vitro and exhibit antitumour activity in vivo

Titanocene compounds are a novel series of agents that exhibit cytotoxic effects in a variety of human cancer cells in vitro and in vivo. In this study, the antiproliferative activity of two titanocenes (Titanocenes X and Y) was evaluated in human epidermoid cancer cells in vitro. Titanocenes X and Y induce apoptotic cell death in epidermoid cancer cells, with IC50 values that are comparable to cisplatin. Characterisation of the cell death pathway induced by titanocene compounds in A431 cells revealed that apoptosis is preceded by cell cycle arrest and the inhibition of cell proliferation. The induction of apoptosis is dependent on the activation of caspase-3 and -7 but not caspase-8. Furthermore, the antitumour activity of Titanocene Y was tested in an A431 xenograft model of epidermoid cancer. Results indicate that Titanocene Y significantly reduced the growth of A431 xenografts with an antitumour effect similar to cisplatin. These results suggest that titanocenes represent a novel series of promising antitumour agents.

Oxali‐Titanocene Y: A Potent Anticancer Drug

Outside of platinum and ruthenium anticancer drugs, there is significant unexplored space for further metal-based drugs that target cancer, such as titanocene dichloride. One of these promising drug candidates is bis-[(p-methoxybenzyl)cyclopentadienyl]titanium(IV) dichloride (titanocene Y, 1), which is accessible via the hydridolithiation reaction of 6-anisylfulvene and subsequent transmetallation with titanium tetrachloride. Compound 1 exhibits an IC50 value of 21 mm toward the LLC-PK cell line, which has proven to be a good mimic of a kidney carcinoma cell line and a reliable tool for the optimisation of titanocenes against this type of cancer. Additionally, the antiproliferative activity of 1 and other titanocenes has been studied in 36 human tumour cell lines and against explanted human tumours. 6] These in vitro and ex vivo experiments showed that renal cell cancer is the prime target for this novel class of titanocenes, but there is significant activity against ovarian, prostate, cervical, lung, colon, and breast cancers as well. Furthermore, titanocene derivatives give a positive immune response by up-regulating the number of natural killer (NK) cells in mice. These results were underscored by initial mechanistic studies of the effects of these titanocenes on apoptosis and the apoptotic pathway in prostate and cervical cancer cells. Recently, animal studies demonstrated the successful treatment of mice bearing xenografted A431, Caki-1, and MCF-7 tumours with 1. Herein the synthesis and initial cytotoxicity studies of titanocene oxalate and oxali-titanocene Y (2) are presented. The structures and syntheses of 1 and 2 are shown in Scheme 1. A simple anion-exchange reaction in THF employing silver oxalate eliminates insoluble silver chloride and produces 2 or titanocene oxalate. An X-ray crystallographic study established the molecular structure of 2 (Figure 1). Despite the addition of the oxalate bidentate ligand in replacement of the two chlorides on the titanium centre, there is almost no apparent variance in the molecular structures of 1 and 2. The length of the bond between the titanium centre and the carbon atoms of the cyclopentadienide rings are very similar for both 1 and 2. They vary from 2.34 to 2.41 C for 1 and from 2.33 to 2.40 C for 2. Very slight differences can be observed in comparing the titanium centroid distances in 1 (2.06 C) and 2 (2.04 C). The centroid–titanium–centroid angle is 130.78 for 1, whereas the corresponding angle in 2 is 134.88. This widening goes nicely with the more blade-like shape of the oxalate anion, compared with the spherical chloride anions. As expected, the average titanium–chloride bond in 1 is considerably longer (2.37 C) than the average titanium–oxygen bond in 2 (1.99 C). The average carbon–oxygen single and double bonds in 2 are, with 1.30 C and 1.21 C, quite close to those found in free carboxylic acids, showing that there is very little, if any, negative charge located on the oxygen atoms that are not bonded to titanium. In 1 the chloride–titanium–chloride angle is 95.98, which is in the range of other titanocene dichlorides. In 1, however, the oxygen atoms are part of a chelate ring which forces the oxygen–titanium–oxygen angle to 79.08. Despite the addition of the bidentate oxalate ligand. minimal structural change incurred. In tests against LLC-PK cells, which have proven to be a valuable in vitro model for kidney cancer, titanocene oxalate shows an IC50 value of 140 mm, which is a significant improvement (14-fold) relative to titanocene dichloride, with an IC50 value of 2000 mm. Similar behaviour is observed for the p-dimethoxybenzyl-substituted species; 2 is 13-fold more cytotoxic against LLC-PK than 1 and exhibits an IC50 value of 1.6 mm (see Figure 2), which is twice as cytotoxic as cisplatin (3.3 mm). The Scheme 1. Structures and syntheses of titanocene Y (1) and oxali-titanocene Y (2): a) 2LiBEt3H, Et2O, 2BEt3 ; b) TiCl4, THF, 2LiCl(s) ; c) Ag2C2O4, THF, 2AgCl(s).

Antitumor activity of Titanocene Y in xenografted PC3 tumors in mice

Chemotherapeutic options for androgen-independent prostate cancer are extremely limited with minimum survival advantage. The benzyl-substituted unbridged titanocene bis-[(p-methoxybenzyl) cyclopentadienyl] titanium(IV) dichloride (Titanocene Y) was tested in vitro against the human prostate cancer androgen-independent cell, PC-3, which demonstrated an IC50 value of 56 x 10(-6) mol/L compared to 5.6 x 10(-6) mol/L for cisplatin. Then Titanocene Y was given at the maximum tolerable dose of 40 mg/kg/d on five consecutive days to one cohort of eight PC3 tumor-bearing male NMRI: nu/nu mice, while a second cohort was treated similarly with 3 mg/kg/d of cisplatin. Both of these mouse cohorts showed a statistically significant tumor growth reduction with respect to the third solvent-treated control group, which led to T/C values of 42% for cisplatin and 52% for Titanocene Y at the end of the experiment. This encouraging activity of Titanocene Y against prostate tumors in vivo, which is almost comparable with respect to cisplatin hopefully leads to further development of Titanocene Y in the future.

Effects of titanocene dichloride derivatives on prostate cancer cells, specifically DNA damage-induced apoptosis.

While locally advanced prostate cancer is initially treatable with androgen ablation, eventually cells develop a castrate‐resistant phenotype. Currently, there are no effective treatments for this form of the disease with Docetaxel only providing a small survival advantage. In this study, the effects of novel derivatives of titanocene dichloride on prostate cancer cell lines has been investigated.

Synthesis and Cytotoxicity Studies of New Morpholino-Functionalised and N-Heteroaryl-Substituted Titanocene Anticancer Drugs

From the carbolithiation of 6-morpholino fulvene (3) and different lithiated nitrogen containing heterocycles (2-N-methylimidazolyl, 2-N-(N,N-dimethylamino)methyl-imidazolyl, and 2-N-methylindolyl), the corresponding lithium cyclopentadienide intermediate (4a-c) was formed. These three lithiated intermediates underwent a transmetallation reaction with TiCl(4) resulting in morpholino-functionalised titanocenes 5a-c. When these titanocenes were tested against LLC-PK cells, the IC(50) values obtained were of 24, 36, and 41 microM respectively. The most cytotoxic titanocene in this paper (5a) with an IC(50) value of 24 microM is found to be almost ten times less cytotoxic than cis-platin, which showed an IC(50) value of 3.3 microM when tested on the epithelial pig kidney LLC-PK cell line, and approximately 2 times less cytotoxic than its dimethylamino-functionalised analogue. Encouragingly however, the IC(50) value obtained for titanocene 5a is approximately 100 times better than titanocene dichloride itself.

Structures of 6-(substituted-phenyl)fulvenes

The syntheses and crystal structures of a series of 6-(substituted-phenyl) fulvenes are reported. In three instances the molecular structures determined by X-Ray crystallography were compared to the results of DFT calculations. In these cases only minor differences were found between the optimised DFT calculation and the molecule found in the crystal structure. This is of particular interest in the case of 6-(p-[N-acetyl]aminophenyl)fulvene which shows intermolecular hydrogen bonding.