How to design an opioid drug that causes reduced tolerance and dependence
Annals of Neurology , 05/10/2010
Berger AC – Mu opioid receptor (MOR) agonists such as morphine are extremely effective treatments for acute pain. In the setting of chronic pain, however, their long–term utility is limited by the development of tolerance and physical dependence. Drug companies have tried to overcome these problems by simply "dialing up" signal transduction at the receptor, designing more potent and efficacious agonists and more long–lasting formulations. Neither of these strategies has proven to be successful, however, because the net amount of signal transduction, particularly over extended periods of drug use, is a product of much more than the pharmacokinetic properties of potency, efficacy, half–life, and bioavailability, the mainstays of traditional pharmaceutical screening...Here the authors describe recent findings that suggest MOR agonists with diminished propensity to cause tolerance and dependence can be identified by screening drugs for the ability to induce MOR desensitization, endocytosis, and recycling. The authors also discuss preliminary evidence that heteromers of the delta opioid receptor and the MOR are pronociceptive, and that drugs that spare such heteromers may also induce reduced tolerance.