Development and characterization of inhibitors of membrane proteins associated with schizophrenia and pancreatic cancer

The multidrug resistance transporters P-glycoprotein (P-gp) and ABCG2 are highly expressed in the capillary endothelial cells of the blood-brain barrier (BBB). These transporters limit the brain penetration of many drugs, including antipsychotic agents used to treat schizophrenia, by actively effluxing the drugs out of cells and into the blood stream before they can reach their targets. Herein, we describe the synthesis and characterization of novel homodimers of two model antipsychotic drugs and ABC transporter substrates, quetiapine (QT) and paliperidone (Pal). Prodrug homodimers of QT and Pal were synthesized with varying tether lengths and tested for their ability to inhibit substrate transport. Substrate competition assays with crude membranes and inhibition assays in a human BBB cell line, we demonstrated that both QT and Pal dimers are potent inhibitors of either P-gp alone or both transporters respectively. Mutant K-Ras is implicated in about 30% of all cancers and 90% of pancreatic cancers. K-Ras undergoes three post-translational modifications that allow for proper functional localization of Ras to the plasma membrane, making them important targets in the effort to treat cancer. This project focuses on inhibiting hIcmt, the human enzyme responsible for the third step, to cause K-Ras mislocalization and thus reduce biological effects. A collaboration with Prof. Jian Jin at the University of North Carolina has provided us with a library of close to 700 potential hIcmt inhibitors. Based on compounds identified in the library screen, we have developed our current lead inhibitor with an IC50 of 1.5 µM. We have determined our lead compound to be competitive with respect to the methylation substrate and noncompetitive with respect to the methyl donor. In addition to expanding the current library of inhibitors, future work involves characterizing their effects on Ras signaling in human pancreatic cancer cell lines