MRP4/ABCC4 as a new therapeutic target: meta-analysis to determine substrate binding sites as a tool for drug design

AGUSTÍN YANEFF; NICOLÁS DI SIERVI; CARLOS DAVIO; NATALIA GÓMEZ; CARINA SHAYO; ANA SAHORES; ALEJANDRO CAROZZO

Ciudad Autónoma de Buenos Aires

Congreso; Reunión conjunta de sociedades de biociencias; 2017

Sociedad Argentina de investigación clínica

Over the last years, numerous MRP transporters have been suggested as possible pharmacological targets for the treatment of cancer for several reasons: their increased expression in tumor cells, their ability to generate multidrug resistance and transport endogenous substrates that can eventually increase tumor malignancy. Due to the structural complexity of their substrate binding pocket, designing specific pharmacological agents with the ability to selectively modify their affinity to certain substrates represents a challenge in current medicinal chemistry. We have recently established that inhibiting cAMP extrusion by MRP4 could represent a possible effective therapeutic strategy for pancreatic ductal adenocarcinoma treatment. Using available information regarding substrate specificity, homology models and mutagenesis assays, we recapitulate the up-to-date knowledge about MRP structure. We also aligned amino acid sequences to identify the candidate MRP4 residues where cyclic nucleotides may bind. We identified two possible binding sites that are present both in the outward and inward conformation of the transporter. In the first binding site, residues L838 to D842 from transmembrane helix 9 (TM9) are postulated to bind cAMP in the inward conformation, while residues T364, F368, E374 and R375 from TM6 are postulated to bind cAMP in the outward conformation. Residues G779 to R782 from TM8 could bind cAMP in both conformations. Regarding the second binding site, in the inward conformation we postulate that A739 to S743 of extracellular loop 4, together with A982 from TM12 may participate in cAMP binding. In the ourward conformation, the second binding site is composed by C956 and A957 from TM11 and F993 from TM12. Binding site identification may serve as a basis for the future development of inhibitors of MRP4 cAMP specific transport. Also, this meta-analysis could serve to establish structural requirements for any substrate specificity of other MRP transporters.