Assessing ADME properties of CJ-15,208: synthesis of new analogs and examination of P-glycoprotein interactions

Abstract

We are exploring analogs of the macrocyclic tetrapeptide natural product CJ-15,208 (cyclo[Phe-D-Pro-Phe-Trp]) as both potential analgesics and kappa opioid receptor (KOPr) antagonists. KOPr agonists exhibit analgesic activity but do not cause some of the adverse side effects associated with mu opioid agonists. Additionally, both KOPr agonists and antagonists have demonstrated the ability to block reinstatement of cocaine-seeking behavior under different conditions. CJ-15,208 has shown both opioid agonist (antinociceptive) activity and KOPr antagonist activity in vivo, while its D-Trp isomer, [D-Trp]CJ-15,208, has shown predominantly KOPr antagonist activity in vivo. Both compounds penetrate the central nervous system following oral administration and are stable to proteases in plasma and whole blood. However, studies in liver microsomes suggest that these peptides are susceptible to CYP P450 metabolism. Analogs of CJ-15,208 with modification on one of the aromatic residues were synthesized to study and improve pharmacokinetic properties. Additionally, CJ-15,208 and [D-Trp]CJ-15,208 were studied with in vitro biological barrier models using Madin-Darby canine kidney (MDCK) cells, both wild type and a line transfected with the MDR1 gene coding for the efflux protein P-glycoprotein (P-gp). The peptides’ inhibition of P-gp was assessed using rhodamine 123 efflux, and their efflux was assessed by analyzing bidirectional transport across MDCK-MDR1 and MDCK-WT monolayers. Evidence of efflux was observed for CJ-15,208 in the transport studies, but the similar results in the experiments using MDCK-MDR1 and MDCK-WT cells make it unclear which efflux proteins are involved. Preliminary studies suggested that [D-Trp]CJ-15,208 may also be an efflux substrate, but additional studies are need to confirm this. The results of these studies will help guide the design and evaluation of new analogs of these lead peptides.