RB-101 is a prodrug which acts by splitting at the disulfide bond once inside the brain, to form two selective enzyme inhibitors and blocking both types of the zinc-metallopeptidase enkephalinase enzymes. This inhibits the breakdown of the endogenous opioid peptides known as enkephalins. These two enzymes, aminopeptidase N (APN) and neutral endopeptidase 24.11 (NEP), are responsible for the breakdown of both kinds of enkephalin naturally found in the body, and so RB-101 causes a buildup of both Met-enkephalin and Leu-enkephalin.
Unlike the more commonly used enkephalinase inhibitor racecadotril, which only acts peripherally and has antidiarrheal effects, RB-101 is able to enter the brain, and thus produces a range of effects, acting as an analgesic, anxiolytic and antidepressant. The antidepressant and anxiolytic actions are thought to be mediated through the delta opioid receptor, while the analgesic effects most likely result from a mix of mu and delta activity. Animal studies suggest that RB-101 is also likely to be useful in relieving the symptoms of acute opioid withdrawal and in the management of opioid dependence.
A significant advantage of inhibiting the breakdown of endogenous opioid peptides rather than stimulating opioid receptors with exogenous drugs is that the levels of opioid peptides are only increased slightly from natural levels, thus avoiding overstimulation and upregulation of the opioid receptors. This means that even when RB-101 is used in high doses for extended periods of time, there is no development of dependence on the drug or tolerance to its analgesic effects. Consequently, even though RB-101 is able to produce potent analgesic effects via the opioid system, it is unlikely to be addictive.
Unlike conventional opioid agonists, RB-101 also failed to produce respiratory depression, which suggests it might be a much safer drug than traditional opioid painkillers. RB-101 also powerfully potentiated the effects of traditional analgesics such as ibuprofen and morphine, suggesting that it could be used to boost the action of a low dose of normal opioids which would otherwise be ineffective.
RB-101 itself is not orally active and so has not been developed for medical use in humans, however modification of the drug has led to newer orally acting compounds such as RB-120 and RB-3007, which may be more likely to be adopted for medical use if clinical trials are successful.
^Roques BP (April 1992). "Peptidomimetics as receptors agonists or peptidase inhibitors: A structural approach in the field of enkephalins, ANP and CCK". Biopolymers. 32 (4): 407–10. doi:10.1002/bip.360320417. PMID1320419.
^Noble F, Soleilhac JM, Soroca-Lucas E, Turcaud S, Fournie-Zaluski MC, Roques BP (April 1992). "Inhibition of the enkephalin-metabolizing enzymes by the first systemically active mixed inhibitor prodrug RB 101 induces potent analgesic responses in mice and rats". The Journal of Pharmacology and Experimental Therapeutics. 261 (1): 181–90. PMID1560364.
^Fournié-Zaluski MC, Coric P, Turcaud S, Lucas E, Noble F, Maldonado R, Roques BP (Jun 1992). "Mixed inhibitor-prodrug" as a new approach toward systemically active inhibitors of enkephalin-degrading enzymes". Journal of Medicinal Chemistry. 35 (13): 2473–81. doi:10.1021/jm00091a016. PMID1352352.
^Noble F, Smadja C, Roques BP (December 1994). "Role of endogenous cholecystokinin in the facilitation of mu-mediated antinociception by delta-opioid agonists". The Journal of Pharmacology and Experimental Therapeutics. 271 (3): 1127–34. PMID7996417.
^Valverde O, Maldonado R, Fournie-Zaluski MC, Roques BP (July 1994). "Cholecystokinin B antagonists strongly potentiate antinociception mediated by endogenous enkephalins". The Journal of Pharmacology and Experimental Therapeutics. 270 (1): 77–88. PMID8035345.
^Honore P, Buritova J, Fournié-Zaluski MC, Roques BP, Besson JM (April 1997). "Antinociceptive effects of RB101, a complete inhibitor of enkephalin-catabolizing enzymes, are enhanced by a cholecystokinin type B receptor antagonist, as revealed by noxiously evoked spinal c-Fos expression in rats". The Journal of Pharmacology and Experimental Therapeutics. 281 (1): 208–17. PMID9103499.
^Roques BP, Noble F (November 1996). "Association of enkephalin catabolism inhibitors and CCK-B antagonists: a potential use in the management of pain and opioid addiction". Neurochemical Research. 21 (11): 1397–410. doi:10.1007/bf02532381. PMID8947930.
^Cordonnier L, Sanchez M, Roques BP, Noble F. Blockade of morphine-induced behavioral sensitization by a combination of amisulpride and RB101, comparison with classical opioid maintenance treatments. British Journal of Pharmacology. 2007 May;151(1):94-102. PMID17351659
^Noble F, Turcaud S, Fournié-Zaluski MC, Roques BP (November 1992). "Repeated systemic administration of the mixed inhibitor of enkephalin-degrading enzymes, RB101, does not induce either antinociceptive tolerance or cross-tolerance with morphine". European Journal of Pharmacology. 223 (1): 83–9. doi:10.1016/0014-2999(92)90821-K. PMID1478260.
^Noble F, Coric P, Turcaud S, Fournié-Zaluski MC, Roques BP (March 1994). "Assessment of physical dependence after continuous perfusion into the rat jugular vein of the mixed inhibitor of enkephalin-degrading enzymes, RB 101". European Journal of Pharmacology. 253 (3): 283–7. doi:10.1016/0014-2999(94)90203-8. PMID8200422.
^Noble F, Fournié-Zaluski MC, Roques BP (January 1993). "Unlike morphine the endogenous enkephalins protected by RB101 are unable to establish a conditioned place preference in mice". European Journal of Pharmacology. 230 (2): 139–49. doi:10.1016/0014-2999(93)90796-K. PMID8422896.
^Stein, edited by Christoph (1999). Opioids in pain control : basic and clinical aspects. Cambridge, UK: Cambridge University Press. ISBN978-0521622691.CS1 maint: extra text: authors list (link)
^Boudinot E, Morin-Surun M, Foutz AS, Fournié-Zaluski M, Roques BP, Denavit-Saubié M (February 2001). "Effects of the potent analgesic enkephalin-catabolizing enzyme inhibitors RB101 and kelatorphan on respiration". Pain. 90 (1–2): 7–13. doi:10.1016/S0304-3959(00)00382-1. PMID11166965.
^Nieto MM, Wilson J, Walker J, et al. (September 2001). "Facilitation of enkephalins catabolism inhibitor-induced antinociception by drugs classically used in pain management". Neuropharmacology. 41 (4): 496–506. doi:10.1016/S0028-3908(01)00077-6. PMID11543770.
^Noble F, Smadja C, Valverde O, et al. (December 1997). "Pain-suppressive effects on various nociceptive stimuli (thermal, chemical, electrical and inflammatory) of the first orally active enkephalin-metabolizing enzyme inhibitor RB 120". Pain. 73 (3): 383–91. doi:10.1016/S0304-3959(97)00125-5. PMID9469529.
^Le Guen S, Mas Nieto M, Canestrelli C, et al. (July 2003). "Pain management by a new series of dual inhibitors of enkephalin degrading enzymes: long lasting antinociceptive properties and potentiation by CCK2 antagonist or methadone". Pain. 104 (1–2): 139–48. doi:10.1016/S0304-3959(02)00486-4. PMID12855323.
^Le Guen S, Mas Nieto M, Canestrelli C, Chen H, Fournié-Zaluski MC, Cupo A, Maldonado R, Roques BP, Noble F (July 2003). "Pain management by a new series of dual inhibitors of enkephalin degrading enzymes: long lasting antinociceptive properties and potentiation by CCK2 antagonist or methadone". Pain. 104 (1–2): 139–48. doi:10.1016/S0304-3959(02)00486-4. PMID12855323.
^Noble F, Roques BP (February 2007). "Protection of endogenous enkephalin catabolism as natural approach to novel analgesic and antidepressant drugs". Expert Opinion on Therapeutic Targets. 11 (2): 145–59. doi:10.1517/1472822.214.171.124. PMID17227231.