First evidence for N7-Platinated Guanosine derivatives cell uptake mediated by plasma membrane transport processes.

Nucleos(t)ide analogues (NA) belong to a family of compounds widely used in anticancer/antiviral treatments. They generally exhibit a cell toxicity limited by cellular uptake levels and the resulting nucleos(t)ides metabolism modifications, interfering with the cell machinery for nucleic acids synthesis. We previously synthesized purine nucleos(t)ide analogues N7-coordinated to a platinum centre with unaltered sugar moieties of the type: [Pt(dien)(N7-dGuo)]2+ (1; dien = diethylenetriamine; dGuo = 2'-deoxy-guanosine), [Pt(dien)(N7-dGMP)] (2; dGMP = 5'-(2'-deoxy)-guanosine monophosphate), and [Pt(dien)(N7-dGTP)]2- (3; dGTP = 5'-(2'-deoxy)-guanosine triphosphate), where the indicated electric charge is calculated at physiological pH (7.4). In this work, we specifically investigated the uptake of these complexes (1-3) at the plasma membrane level. Specific experiments on HeLa cervical cancer cells indicated a relevant cellular uptake of the model platinated deoxynucleos(t)ide 1 and 3 while complex 2 appeared unable to cross the cell plasma membrane. Obtained data buttress an uptake mechanism involving Na+-dependent concentrative transporters localized at the plasma membrane level. Consistently, 1 and 3 showed higher cytotoxicity with respect to complex 2 also suggesting selective possible applications as antiviral/antitumor drugs among the used model compounds.

Transport of platinum bonded nucleotides into proteoliposomes, mediated by Drosophila melanogaster thiamine pyrophosphate carrier protein (DmTpc1).

The results of the present study suggest that DmTpc1 is actively implicated in the specific uptake of free cytoplasmic Pt bonded nucleotides, and therefore could be linked to the mechanism of action of some platinum-based antitumor drugs. Although DmTpc1 has a low affinity for model [Pt(dien)(N7-5'-dGTP)] and cis-[Pt(NH3)2(py)(N7-5'-dGTP)] compared to dATP it's well known that DNA platination level of few metal atoms per double-stranded molecule may account for the pharmacological activity of platinum based antitumor drugs. This is the first investigation where it has been demonstrated that a mitochondrial carrier is directly involved in the transport of metalated purines related with the cisplatin mechanism of action. Moreover it is shown as a lower hindrance of nucleotide bonded platinum complexes could strongly enhance mitochondrial uptake. Furthermore, a new application of ICP-AES addressed to measure the transport of metalated nucleobases, by using a recombinant protein reconstituted into liposomes, has been here, for the first time, developed and compared with a standard technique such as the liquid scintillation counting.