In-vitro reactions of a cyanocobalamin-cisplatin conjugate with nucleoside monophosphates.

RATIONALE Cisplatin (CP) is a widely used anticancer drug characterized by toxic side effects that could be alleviated by novel delivery systems including CP prodrugs. The in-vitro incubation of a putative prodrug, obtained by cyanocobalamin (CNCbl) and cis-diamminemonochloroplatinum (II) (mCP), with nucleoside monophosphates (NMPs) was investigated. METHODS The in-vitro reactions between the putative prodrug CNCbl-mCP with the NMPs of adenosine (AMP), guanosine (GMP), cytidine (CMP) and uridine (UMP) were carried out in slightly acid water/methanol solutions at 37 °C for 24 h. Each sample was examined by reversed-phase liquid chromatography coupled with electrospray ionization in positive ion mode and tandem mass spectrometry (RPLC/ESI-MS/MS) by collision induced dissociation (CID) in a linear ion-trap mass spectrometer. RESULTS Seven adducts were recognized as formed by substitution reactions of the chloride ligand in the planar CP. Comparison between observed and theoretical isotopic patterns together with MS/MS fragmentation pathways revealed the presence of single or multiple binding sites depending on the NMP involved. The CNCbl-mCP conjugate was found to interact with N7 or O4 atoms of GMP and UMP, respectively, generating single adducts, while two isomeric adducts were observed for CMP. Finally, AMP gave rise to three isomeric adducts. CONCLUSIONS In agreement with literature data relevant to the interaction between cisplatin and NMPs, the most reactive nucleotides were AMP and GMP. The present LC/ESI-MS/MS approach is very promising to investigate the reactions of CP conjugates with ribonucleotides not only in-vitro but also in-vivo.