Molecular modelling to tailor glicodendrimers as drug delivery systems for anticancer nucleoside analogues targeting haematological malignancies

Nowadays the application of nanotechnology in the field of biomedicine is rapidly rising and nanotechnology-based chemotherapy is widely apply to treat many type of cancers, such as hematological malignancies. This family of cancers includes various malignant neoplasms that affect blood or lymph systems. The interest of our study is focused on the drugs used to treat leukemia, which is an acute or chronic disease characterized by an abnormal increase in the number of white blood cells in the tissues and often also in the blood. To treat leukemia, many type of treatments are suggested and the most used technique is chemotherapy. Among the various drugs, the nucleotide analogues (NAs) are one of the most efficient antimetabolites used to treat leukemia. Fludarabine and clofarabine are the two NAs taken into account in our study, and their cytotoxic effect strongly depends on the entrance and on their activation inside the cell. Due to their hydrophilic nature, NAs cannot passively cross the cellular membrane and they must be phosphorylated to their active triphosphate form once inside the cell. To overcome the various NAs problems, the use of dendrimer as drug delivery system has been suggested. The poly(propyleneimine) dendrimers of fourth generation (PPI G4) partially modified with maltose (PPI-Mal OS G4) has been suggested to be superior among the other NAs carriers. In this study we present computational approaches, based on Molecular Dynamics simulations, to elucidate the molecular reasons behind clofarabine and fludarabine different displacement/interaction with the dendrimers. The compound-dendrimer complexes were protonated to simulate their behavior at neutral or acid environment condition. Our results confirmed what seen with in vivo experiments. Interestingly, both the drug nucleoside forms do not interact with the PPI G4 dendrimer, neither with PPI-Mal OS G4 one. Furthermore, in compound-dendrimer complexes, it was evident that the dendrimer protonation affects the interaction mode in term of drug orientation. Indeed clofarabine triphosphate completelly change its orientation in presence of PPI-Mal OS G4 dendrimer in acid environment. It was characterize by the phosphate part turned to the center of the dendrimer, which interacted with the inner parts of the dendrimer, and its acid nucleic base stay exposed to the solvent. On the other hand, the fludarabine nucleotide was able to interact with the dendrimer surface and to settled in different positions. Therefore these compound displacements suggest that the fludarabine triphosphate had a more flexible structure compared to the clofarabine triphosphate. Most likely, the PPI-Mal OS G4 dendrimer can efficiently deliver the fludarabine nucleotide inside the cell and the compound can easily detach from the dendrimer surface. Contrariwise, the clofarabine nucleotide orientation do not allow an easy released of the drug inside the cell, and the use of PPI G4 dendrimer as carrier do not extol its cytotoxicity. Furthermore, investigation of electrostatic potential of compound-dendrimer complex highlighted that clofarabine was able to neutralize the dendrimer surface charge, while the fludarabine-dendrimer complex remained positively charged. Surprisingly, the clofarabine behavior may limit the ability of compound-dendrimer complex to enter the cell, since positively charged nanoparticles have much greater tendency to penetrate cell membranes than neutral or negatively charged ones.