Regioselective binding of spermine, N-1,N-12-bismethylspermine, and N-1,N-12-bisethylspermine to tRNA(Phe) as revealed by 750 MHz H-1-NMR and its possible correlation with cell cycling and cytotoxicity

The binding of spermine (SPM). N-1,N-12-bismethylspermine (BMS) and N-1,N-1 2-bisethylspermine (BES) to tRNA(Phe) was studied using H-1-NMR at 750 MHz. The polyamines were enriched in C-13 at the 5-CH2 and 8-CH2 residues and t he nuclear Overhauser enhancement (NOE) cross peaks connecting the H-1-NMR resonances of the C-13-methylenes and several base paired imino protons of tRNA(Phe) were obtained using 1D C-13-half filtered spectra. It was found t hat while SPM and BMS bind to the N(3)-H of base pairs T54-m(1)A58, U50-A64 and U52-A62, BES binds only to T54-m(1)A58 and U50-A64. This regioselectiv ity in the binding of the three polyamines to tRNA was correlated with thei r biological effects on cell growth. Using human melanoma cancer cells (MAL ME-3M), we found that SPM and EMS were without effect and cytostatic, respe ctively, while BES was distinctly cytotoxic. The latter also affected cell cycling and, at variance with SPM and EMS, lead to a distinct G(1)/S cell c ycle arrest.