The potential benefit of simultaneously attacking multiple targets in order to improve therapeutic outcomes has become increasingly clear. This is illustrated in the field of opioid analgesics, where the co- administration of a mu opioid receptor (MOR) agonist with a delta opioid receptor (DOR) antagonist retains the MOR-mediated analgesia but with reduced negative side effects, such as the development of tolerance and dependence, features that limit the clinical use of opioid analgesics. Clinically, it would be preferred to administer a single bifunctional drug containing both opioid receptor actions: MOR agonism to promote analgesia along with DOR antagonism to prevent MOR tolerance and dependence development during chronic administration. We propose to develop such compounds by extending our very promising initial studies that have led to both peptide and non-peptide ligands displaying the desired MOR agonist/DOR antagonist profile and which are active after intraperitoneal administration. We will simultaneously elaborate and improve both peptide and non-peptide series. For the peptide series, our focus will be on increasing potency and MOR efficacy and on improving bioavailability, the latter primarily through glycosylation. For the non-peptide compounds, we will pursue three related peptidomimetic series with the major aims of equalizing MOR and DOR affinity and increasing metabolic stability. A panel of pharmacological and pharmacokinetic assays will be used to evaluate new compounds and to select those best suited for more extensive in vivo analysis. As always, our design of new compounds will be driven by our ligand-receptor structural models which we have successfully demonstrated to be highly valuable for structure-based design.
Opioid drugs such as morphine are the primary treatment for severe pain, however development of tolerance to and dependence on these drugs limits their usefulness. Evidence exists that the desired actions of opioids can be separated from the undesired side effects by simultaneously targeting two different types of opioid receptors. Our goal is to develop single, bifunctional agents that achieve this and thus have potential as safer opioid analgesics.
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