DNA binding and cytotoxicity of ruthenium(II) and rhenium(I) complexes of 2-amino-4-phenylamino-6-(2-pyridyl)-1,3,5-triazine

[Ru(Bu₂bpy)₂(2-appt)](PF₆)₂ [1·(PF₆)₂, ^tBu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, 2-appt = 2-amino-4-phenylamino- 6-(2-pyridyl)-1,3,5-triazine] and [Re(CO)₃(2-appt)Cl] (2) were prepared and characterized by X-ray crystal analysis. The binding of 1·(PF₆)₂ and 2 to calf thymus DNA (ct DNA) led to increases in the DNA melting temperature (ΔT_m = +12°C), modest hypochromism (29% and 5% of the absorption bands at λ _max = 450 and 376 nm, respectively), and insignificant shifts in the absorption maxima. The binding constants of 1·(PF₆) ₂ and 2 with ct DNA, as determined by absorption titration, are (8.9 ± 0.5) × 10⁴ and (3.6 ± 0.1) × 10 ⁴ dm³ mol^-1, respectively. UV-vis absorption titration, DNA melting studies, and competition dialysis using synthetic oligonucleotides [poly(dA-dT)₂ and poly(dG-dC)₂] revealed that 1·(PF₆)₂ and 2 exhibit a binding preference for AT sequences. A modeling study on the interaction between 1 or 2 and B-DNA revealed that the minor groove is the most favored binding site and an extensive hydrogen-bonding network is formed. As determined by MTT assays, 1·(PF₆)₂ and 2 exhibited moderate cytotoxicities toward several human cancer cell lines (KB-3-1, HepG2, and HeLa), as well as a multi-drug-resistant cancer cell line (KB-V-1). According to confocal microscopic and flow cytometric studies, 1·(PF₆)₂ and 2 induced apoptosis (50-60%) in cancer cells with