Cell fate after mitotic arrest in different tumor cells is determined by the balance between slippage and apoptotic threshold.

Microtubule poisons and other anti-mitotic drugs induce tumor death but the molecular events linking mitotic arrest to cell death are still not fully understood. We have analyzed cell fate after mitotic arrest produced by the microtubule-destabilizing drug vincristine in a panel of human tumor cell lines showing different response to vincristine. In Jurkat, RPMI 8226 and HeLa cells, apoptosis was triggered shortly after vincristine-induced mitotic arrest. However, A549 cells, which express a great amount of Bcl-x(L) and undetectable amounts of Bak, underwent mitotic slippage prior to cell death. However, when Bcl-x(L) gene was silenced in A549 cells, vincristine induced apoptosis during mitotic arrest. Another different behavior was found in MiaPaca2 cells, where vincristine caused death by mitotic catastrophe that switched to apoptosis when cyclin B1 degradation was prevented by proteasome inhibition. Overexpression of Bcl-x(L) or silencing Bax and Bak expression delayed the onset of apoptosis in Jurkat and RPMI 8226 cells, enabling mitotic slippage and endoreduplication. In HeLa cells, overexpression of Bcl-x(L) switched cell death from apoptosis to mitotic catastrophe. Mcl-1 offered limited protection to vincristine-induced cell death and Mcl-1 degradation was not essential for vincristine-induced death. All these results, taken together, indicate that the Bcl-x(L)/Bak ratio and the ability to degrade cyclin B1 determine cell fate after mitotic arrest in the different tumor cell types.

Organometallic Palladium Complexes with a Water-Soluble Iminophosphorane Ligand as Potential Anticancer Agents.

The synthesis and characterization of a new water-soluble iminophosphorane ligand TPA=N-C(O)-2BrC(6)H(4) (C,N-IM; TPA = 1,3,5-triaza-7-phosphaadamantane) 1 is reported. Oxidative addition of 1 to Pd(2)(dba)(3) affords the orthopalladated dimer [Pd(µ-Br){C(6)H(4)(C(O)N=TPA-kC,N)-2}](2) (2) as a mixture of cis and trans isomers (1:1 molar ratio) where the iminophosphorane moeity behaves as a C,N-pincer ligand. By addition of different neutral or monoanionic ligands to 2, the bridging bromide can be cleaved and a variety of hydrophilic or water-soluble mononuclear organometallic palladium(II) complexes of the type [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(L-L)] (L-L = acac (3); S(2)CNMe(2) (4); 4,7-Diphenyl-1,10-phenanthrolinedisulfonic acid disodium salt C(12)H(6)N(2)(C(6)H(4)SO(3)Na)(2) (5)); [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(L)Br] (L = P(mC(6)H(4)SO(3)Na)(3) (6); P(3-Pyridyl)(3) (7)) and, [Pd(C(6)H(4)(C(O)N=TPA)-2}(TPA)(2)Br] (8) are obtained as single isomers. All new complexes were tested as potential anticancer agents and their cytotoxicity properties were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells, normal T-lymphocytes (PBMC) and DU-145 human prostate cancer cells. Compounds [Pd(µ-Br){C(6)H(4)(C(O)N=TPA-kC,N)-2}](2) (2) and [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(acac)] 3 (which has been crystallographically characterized) display the higher cytotoxicity against the above mentioned cancer cell lines while being less toxic to normal T-lymphocytes (peripheral blood mononuclear cells: PBMC). In addition, 3 is very toxic to cisplatin resistant Jurkat shBak indicating a cell death pathway that may be different to that of cisplatin. The interaction of 2 and 3 with plasmid (pBR322) DNA is much weaker than that of cisplatin pointing to an alternative biomolecular target for these cytotoxic compounds. All the compounds show an interaction with human serum albumin (HSA) faster than that of cisplatin.

Cytotoxic hydrophilic iminophosphorane coordination compounds of d8 metals. Studies of their interactions with DNA and HSA.

The synthesis and characterization of a new water-soluble N,N-chelating iminophosphorane ligand TPAN-C(O)-2-NC(5)H(4) (N,N-IM) (1) and its d(8) (Au(III), Pd(II) and Pt(II)) coordination complexes are reported. The structures of cationic [AuCl(2)(N,N-IM)]ClO(4) (2) and neutral [MCl(2)(N,N-IM)] M=Pd (3), Pt(4) complexes were determined by X-ray diffraction studies or by means of density-functional calculations. While the Pd and Pt compounds are stable in mixtures of DMSO/H(2)O over 4 days, the gold derivative (2) decomposes quickly to TPAO and previously reported neutral gold(III) compound [AuCl(2)(N,N-H)] 5 (containing the chelating N,N-fragment HN-C(O)-2-NC(5)H(4)). The cytotoxicities of complexes 2-5 were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells and DU-145 human prostate cancer cells. Pt (4) and Au compounds (2 and 5) are more cytotoxic than cisplatin to these cell lines and to cisplatin-resistant Jurkat sh-Bak cell lines and their cell death mechanism is different from that of cisplatin. All the compounds show higher toxicity against leukemia cells when compared to normal human T-lymphocytes (PBMC). The interaction of the Pd and Pt compounds with calf thymus and plasmid (pBR322) DNA is different from that of cisplatin. All compounds bind to human serum albumin (HSA) faster than cisplatin (measured by fluorescence spectroscopy). Weak and stronger binding interactions were found for the Pd (3) and Pt (4) derivatives by isothermal titration calorimetry. Importantly, for the Pt (4) compounds the binding to HSA was reversed by addition of a chelating agent (citric acid) and by a decrease in pH.