Novel platinum-based anticancer drug: a complete vibrational study

The introduction of cisplatin to oncology, in the 1970s, marked the onset of the search for novel and improved metal-based anticancer drugs. Polynuclear Pt^II and Pd^II complexes with linear alkylamines as bridging ligands are a class of potential antineoplastic agents that have shown promising cytotoxicity against low-prognosis human cancers, such as metastatic breast adenocarcinoma and osteosarcoma. The present study reports an analysis of [μ-N,N'-bis(3-aminopropyl)butane-1,4-diamine-κ⁴N,N':N'',N''']bis[dichloridoplatinum(II)], [Pt₂Cl₄(C₁₀H₂₆N₄)], denoted Pt₂Spm (Spm is spermine), by vibrational spectroscopy coupled to theoretical calculations. Within the latter, the Density Functional Theory (DFT - mPW1PW/6-31G*) and Effective Core Potential (ECP - LANL2DZ) approaches were used, in order to ensure the most accurate representation of the molecule and achieve a maximum agreement with the experimental data. The solid-state geometry of Pt₂Spm corresponds to C_i symmetry, displaying 132 vibrational modes. A complete assignment of the experimental vibrational profile of the system was attained through the combined application of complementary Raman, FT-IR and Inelastic Neutron Scattering (INS) techniques. INS allowed an unequivocal identification of the CH₂ and NH₂ rocking modes, not clearly detected by the optical techniques, while Raman measurements led to a clear discrimination of the Pt-N stretching frequencies from the two distinct Pt-N moieties within the chelate. The metal-to-metal distances calculated for the molecule under study were found to allow the establishment of effective inter- and intrastrand crosslinks with DNA. These results will hopefully help to clarify the mode of action of the compound, at the molecular level, contributing to the development of improved cisplatin-like chemotherapeutic drugs having a higher efficacy and specificity coupled to lower acquired resistance and deleterious side effects.