Nigel J. Sweeney

In-vitro anti-tumor activity studies of bridged and unbridged benzyl-substituted titanocenes

The benzyl-substituted ansa-titanocenes [1,2-di(cyclopentadienyl)-1,2-di-(4-N,N-dimethylaminophenyl)ethanediyl] titanium dichloride (Titanocene X) and [1,2-di(cyclopentadienyl)-1,2-bis(m-dimethoxyphenyl)ethanediyl] titanium dichloride (Titanocene Z), and the benzyl-substituted unbridged titanocene bis-[(p-methoxybenzyl)cyclopentadienyl] titanium(IV) dichloride (Titanocene Y) were tested on the growth of a wide variety of tumor cells in vitro on a panel of 36 human tumor cell lines containing 14 different tumor types investigated in a cellular proliferation assay. Titanocene Y with a mean IC50 value of 65.8×10−6 mol/l over the full panel of 36 cancer cell lines reaches the activity of cisplatin with 14.7×10−6 mol/l within a factor of 4, whereas Titanocene X and Z show significantly less cytotoxic activity. Titanocene Y is most effective on pleura mesothelioma, and uterine and renal cell cancer, where the IC50 values are comparable or significantly better than for cisplatin. In particular, in the case of renal cell cancer and pleura mesothelioma there is an obvious lack of chemotherapeutic reagents, which might be filled by Titanocene Y, where a very promising cytotoxic effect in comparison with cisplatin could be shown.

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.

Novel titanocene anti-cancer drugs and their effect on apoptosis and the apoptotic pathway in prostate cancer cells

Advanced prostate cancer is not curable by current treatment strategies indicating a significant need for new chemotherapeutic options. Highly substituted ansa-titanocene compounds have shown promising cytotoxic activity in a range of cancers. The objectives of this study are to examine the effects of these titanocene compounds on prostate cancer cells.Prostate cell lines were treated with three novel titanocene compounds and compared to titanocene dichloride and cisplatin. Percent apoptosis, viability and cell cycle were assessed using propidium iodide DNA incorporation with flow cytometry. Cytochrome C was assessed by western blotting of mitochondrial and cytoplasmic fractions. Apoptosis Inducing Factor was assessed by confocal microscopy.These novel compounds induced more apoptosis compared to cisplatin in a dose dependent manner. Compound Y had the most significant effect on cell cycle and apoptosis. Despite the release of cytochrome C from the mitochondrial fraction there was no inhibition of apoptosis with the pan caspase inhibitor, ZVAD-FMK. AIF was shown to translocate from the cytosol to the nucleus mediating a caspase independent cell death. Bcl-2 over expressing PC-3 cells, which were resistant to cisplatin induced apoptosis, underwent apoptosis following treatment with all the titanocene compounds.This study demonstrates possible mechanisms by which these novel titanocene compounds can mediate their apoptotic effect in vitro. The fact that they can induce more apoptosis than cisplatin in advanced cancer cell lines would confer an advantage over cisplatin. They represent exciting new agents with future potential for the treatment of advanced prostate cancer.

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.

Activity of [1,2-di(cyclopentadienyl)-1,2-di(p-N,N-dimethylaminophenyl)-ethanediyl] titanium dichloride against tumor colony-forming units

[1,2-di(cyclopentadienyl)-1,2-di(p-N,N-dimethylaminophenyl)-ethanediyl] titanium dichloride is a newly synthesized transition metal-based anti-cancer drug. We studied the anti-tumor activity of this drug (final concentrations: 25, 250 and 2500 μmol/l) against freshly explanted human tumors, using an in vitro soft agar cloning system. A total of eight tumor samples were evaluated using 1-h exposures. Additionally, the breast carcinoma cell line MCF-7 was examined with regard to sensitivity. The tested compound was markedly active against one renal cancer sample, whereas other renal tumors were resistant. Concentration-dependent anti-tumor activity was demonstrated for all samples except for melanoma. At concentrations of 250 μmol/l or less, the compound was less active than cisplatin or equally active at 0.2 μg/ml, whereas at 2500 μmol/l it showed a significant cytotoxic activity against a wide spectrum of tumor types. The highest activity was observed against renal carcinomas (three of three tumor specimens inhibited at 2500 μmol/l). Sensitivity was also highly remarkable in the breast cancer cell line MCF-7 inhibited in a range of 25–2500 μmol/l, whereas melanoma cells seemed to be profoundly resistant. Further clinical development of this drug appears warranted because of the broad cytotoxic activity shown.

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.

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.