Cytotoxicity and structural analyses of 2,2'-Bipyridine-,4,4'-Dimethyl-2,2'-bipyridine- and 2-(2'-Pyridyl)-quinoxalineplatinum(II) complexes

Platinum anticancer complexes incorporating 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (44Me(2)bpy) or 2-(2'-pyridyl) quinoxaline (2pq) as polyaromatic ligands and the S,S or R,R isomer of 1,2-diaminocyclohexane as ancillary ligands in the form [Pt(P-L)(A(L))](2+) have been synthesised and characterised. X-ray diffraction was used to elucidate the structure and stacking behaviour of the complexes, revealing interesting properties that may impact their biological activity. Pulsed gradient spin-echo NMR experiments elucidated the aggregation behaviour of these complexes in solution. The cytotoxicity of each complex was assessed against the L1210 murine leukaemia, HT29 human colon carcinoma and U87 human glioblastoma cell lines and compared to other complexes within this class. The complexes incorporating 44Me(2)bpy were found to be the most potent at inhibiting cell growth with IC50 values for the S,S isomer (0.13-0.5 mu M) less than that for cisplatin (0.36-11 mu M), oxaliplatin (0.9-1.8 mu M) or carboplatin (>50 mu M). Most complexes were found to be very effective against HT29 colon carcinoma cells.