Interaction of Novel 3TC-Prodrugs with the Efflux Protein P-GP.

GUALDESI, MARÍA S., BRIÑÓN, MARGARITA C., QUEVEDO, MARIO A.

Congreso; 2° Reunión Internacional de Ciencias Farmacéuticas (RICiFa).; 2012

Lamivudine (3TC) is an antiviral drug with widely demonstrated clinical efficacy. However, the emergence of resistant viral strains has limited its effect, and so several strategies have been envisioned to optimize its pharmacotherapeutic properties. The design of prodrugs is a recognized approach to reach this goal. In line with this, we have previously reported results concerning the intestinal permeability of 3TC-Etha and 3TC-Buta, two novel 3TC prodrugs, in which 3TC-Etha was subjected to P-glycoprotein (P-gp) mediated efflux in the intestine, while 3TC-Buta was not. Based on these reports, the objective of this work is to identify the structural basis of this selective recognition by applying molecular modeling methods. Molecular structures were constructed with Gabedit software. Conformational and energetic analyses were performed using Gaussian03. The complexes between the ligands and crystallographic P-gp (pdb: 3G60) were predicted by molecular docking, using software packages designed by Open Eye Inc (FRED, OMEGA)1,2. Molecular dynamics simulations were performed with Amber12, with the structures visualized using VMD and Ligplot softwares. The binding of known P-gp substrates (rhodamine-123, zidovudine and abacavir) was determined and compared to that of 3TC, 3TC-Etha and 3TC-Buta. All the substrates oriented their hydrophobic moieties within the main hydrophobic cavity of the binding pocket, establishing Van der Waals interactions. Regarding 3TC, it bound in a similar pattern than P-gp substrates. Considering that our experimental studies determined that 3TC was not substrate of P-gp, we propose that it may be unable to reach the transmembrane binding site due to its low hydrophobicity When the binding of 3TC-Etha was studied, it was deeply buried into the hydrophobic cavity of the binding pocket, establishing Van der Waals interactions with aromatic residues. From the docking of 3TC-Buta, a completely different binding mode was found, suggesting that this compound may not be a P-gp substrate. Further comparisons between the binding of 3TC-Etha and 3TC-Buta were performed by molecular dynamics simulations. The binding of both compounds was stabilized by hydrophobic forces, and for 3TC-Etha additional stabilization was gained through electrostatic contacts. 3TC-Buta did not exhibit this property, suggesting that a electrostatic repulsion is present. Energetic residue decomposition analyses confirmed the presence of electrostatic repulsion for 3TC-Buta but not for 3TC-Etha, supporting our previous experimental finding that 3TC-Etha is a P-gp substrate but 3TC-Buta is not. It was possible to correlate experimental findings regarding the affinity of 3TC-Etha and 3TC-Butha for P-gp, by means of molecular modeling methods, which might be applied in the further design of new 3TC prodrugs with improved bioavailability.