Title

Characterization of multiple lipophilic binding pockets on the L-cystine/L-glutamate antiporter System xc-

Presentation Type

Poster

Abstract

The system xc- (Sxc-) antiporter is a member of the heteromeric amino acid transporter (HAT) family, which mediates the obligate exchange of extracellular L-cystine for intracellular L-glutamate. Interestingly, both sides of this exchange reaction are important in the function of the central nervous system, as the import of L-cystine is needed for the synthesis of glutathione (GSH) and oxidative protection, while the exported L-glutamate can contribute to neuronal communication, as well as neuropathology. More specifically, excessive system xc- function has been implicated in brain tumor growth and concurrent cell death of surrounding tissue. To study the various roles of Sxc-, our group, in coordination with the Natale and Diaz labs, have been developing small molecules that selectively inhibit the transporter. The inhibitory activity of these analogues was assessed by quantifying their ability to block the uptake of [3H]-L-glutamate into SNB-19 human glioblastoma cells under conditions that were selective for Sxc--mediated uptake. Previous studies carried out by our lab have demonstrated the use of lipophilic isoxazole-hydrazone analogues of AMPA as inhibitors of Sxc-. In the current study we use analogues containing multiple substitutions to further define the interactions of isoxazole-hydrazone derivatives with the Sxc- transporter, especially as relayed to the relative positioning of two distinct lipophilic pockets predicted to be adjacent to the substrate binding site. We also hypothesize that a subset of these compounds may be acting via a mixed inhibition mechanism. The results are important for defining the size and orientation of the lipophilic binding pockets that seem to strongly influence the binding specificity, as well as the kinetics, of Sxc-; therefore allowing more efficient drug design.

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Apr 13th, 3:00 PM Apr 13th, 4:00 PM

Characterization of multiple lipophilic binding pockets on the L-cystine/L-glutamate antiporter System xc-

UC Ballroom

The system xc- (Sxc-) antiporter is a member of the heteromeric amino acid transporter (HAT) family, which mediates the obligate exchange of extracellular L-cystine for intracellular L-glutamate. Interestingly, both sides of this exchange reaction are important in the function of the central nervous system, as the import of L-cystine is needed for the synthesis of glutathione (GSH) and oxidative protection, while the exported L-glutamate can contribute to neuronal communication, as well as neuropathology. More specifically, excessive system xc- function has been implicated in brain tumor growth and concurrent cell death of surrounding tissue. To study the various roles of Sxc-, our group, in coordination with the Natale and Diaz labs, have been developing small molecules that selectively inhibit the transporter. The inhibitory activity of these analogues was assessed by quantifying their ability to block the uptake of [3H]-L-glutamate into SNB-19 human glioblastoma cells under conditions that were selective for Sxc--mediated uptake. Previous studies carried out by our lab have demonstrated the use of lipophilic isoxazole-hydrazone analogues of AMPA as inhibitors of Sxc-. In the current study we use analogues containing multiple substitutions to further define the interactions of isoxazole-hydrazone derivatives with the Sxc- transporter, especially as relayed to the relative positioning of two distinct lipophilic pockets predicted to be adjacent to the substrate binding site. We also hypothesize that a subset of these compounds may be acting via a mixed inhibition mechanism. The results are important for defining the size and orientation of the lipophilic binding pockets that seem to strongly influence the binding specificity, as well as the kinetics, of Sxc-; therefore allowing more efficient drug design.