Design of novel peptide ligands which have opioid agonist activity and CCK antagonist activity for the treatment of pain.

Disease states such as neuropathic pain offer special challenges in drug design due to the system changes which accompany these diseases. In this manuscript we provide an example of a new approach to drug design in which we have modified a potent and selective peptide ligand for the CCK-2 receptor to a peptide which has potent agonist binding affinity and bioactivity at delta and mu opioid receptors, and simultaneous antagonist activity at CCK receptors. De novo design based on the concept of overlapping pharmacophores was a central hypothesis of this design, and led to compounds such as H-Tyr-DPhe-Gly-DTrp-NMeNle-Asp-Phe-NH(2) (i.e., RSA 601) which have the designed properties.

Conformation-activity relationships of opioid peptides with selective activities at opioid receptors.

The discovery of endogenous opioid peptides 25 years ago opened up a new chapter in efforts to understand the origins and control of pain, its relationships to other biological functions, including inflammatory and other immune responses, and the relationships of opioid peptides and their receptors to a variety of undesirable or toxic side effects often associated with the nonpeptide opiates such as morphine including addiction, constipation, a variety of neural toxicities, tolerance, and respiratory depression. For these investigations the need for potent and highly receptor selective agonists and antagonists has been crucial since they in principle allow one to distinguish unequivocally the roles of the different opioid receptors (mu, delta, and kappa) in the various biological and pathological roles of the opioid peptides and their receptors. Conformational and topographical constraint of the linear natural endogenous opioid peptides has played a major role in developing peptide ligands with high selectivity for mu, delta, and kappa receptors, and in understanding the conformational, topographical, and stereoelectronic structural requirements of the opioid peptides for their interactions with opioid receptors. In turn, this had led to insights into the three-dimensional pharmacophore for opioid receptors. In this article we review and discuss some of the developments that have led to potent, selective, and stable peptide and peptidomimetic ligands that are highly potent and selective, and that have delta agonist, mu antagonist, and kappa agonist biological activities (other authors in this issue will discuss the development of other types of activities and selectivities). These have led to ligands that provide unique insight into opioid pharmacophores and the critical roles opioid ligands and receptor scan play in pain, addiction, and other human maladies.

Differential modulation of antipredator defensive behavior in Swiss-Webster mice following acute or chronic administration of imipramine and fluoxetine.

The Mouse Defense Test Battery (MDTB) has been designed to assess defensive reactions in Swiss-Webster mice to situations associated with a natural predator, the rat. Primary measures taken before, during and after predator confrontation comprise escape attempts, predator assessment, defensive attack and flight. Previous reports from this laboratory have shown that the panic-promoting drug yohimbine potentiated flight behavior, while long-term treatment with the panicolytic agent alprazolam reduced this response. In order to evaluate further the possibility that the MDTB may represent an effective animal model of panic attacks, the present study investigated the behavioral effect of imipramine and fluoxetine, two serotonin reuptake inhibitors (SRIs) known to alleviate panic symptoms when given on a repeated basis. Both drugs were administered acutely and chronically (one daily IP injection for 21 days) at 5, 10 and 15 mg/kg. Our results showed that a single dose of imipramine or fluoxetine strongly potentiated flight reactions in response to an approaching predator and increased defensive attack toward the rat. This was in contrast to chronic treatment with each drug which dramatically decreased flight responses and defensive attack behaviors. In addition, long-term administration with both SRIs produced a reliable attenuation of predator assessment activities. Taken together, these findings suggest an acute anxiogenic-like effect of imipramine and fluoxetine followed by a fear/anxiety reducing effect after repeated administrations. These results support clinical observations revealing an acute anxiogenic effect of SRIs followed by an anxiolytic and/or panicolytic effect after chronic use, and support previous results suggesting that the MDTB may be useful for the investigation of panic-modulating agents.