The ideal pain medication would be devoid of the serious side effects associated with the currently used opioids (respiratory depression, constipation, dependence, addiction). Mitragynine is a corynanthe-type indole alkaloid isolated as the major alkaloid component of the leaves of the plant Mitragyna speciosa; a ?legal high? sold over the internet as kratom, and is currently unregulated. Mitragynine-related natural products possess affinity for mu opioid receptors and exhibit analgesia in rodent models when given systemically. Mitragynine pseudoindoxyl (MP), is a semi-synthetic analog related to mitragynine, which is more potent of an analgesic compared to mitragynine. This scaffold also behaves as delta antagonist, and as a biased mu agonist towards G-protein transduction systems. MP shows reduced respiratory depression, tolerance and dependence, and no rewarding behavior in mice. Thus, this template represents an excellent starting point for developing analgesics with a superior side effect profile to all clinically used mu opioid analgesics. We will also to create a library of derivatives of MP by using total and semi-synthetic approaches. Detailed pharmacological characterization of these analogs will lead to a substantially better understanding of SAR of MP-type compounds. Our final goal is to characterize the compounds pharmacologically in vitro and in vivo. Analogs will be evaluated for potency and an advantageous side-effect profile (i.e. absent or reduced tolerance, dependence, respiratory depression, constipation, reward and aversion). Physicochemical properties like solubility, stability, permeation and CNS penetration, also will be studied. The long-term objective of this proposal is to understand if G-biased MOR agonism in combination with DOR antagonism can lead to reduced tolerance/physical dependence in multiple rodent pain models (thermal, inflammatory, neuropathic) and also lead to synthesis of non-addicting and non-abusable analgesics. The central hypothesis is to diversify the MP template using our total synthetic/semi-synthetic approaches and prepare compounds with a MOR-DOR mixed agonist-antagonist profile with increased metabolic stability. These goals will be accomplished through an interdisciplinary team with significant experience in medicinal chemistry, synthetic chemistry, pharmacology, neuroscience, drug metabolism and pharmacokinetics.

Public Health Relevance

Morphine, the most commonly prescribed drug for sufferers of chronic pain, has many dangerous side effects. Mitragynine is a naturally occurring alkaloid that is found in kratom leaves, which grow in parts of Southeast Asia, and shows promise in the treatment of pain. Our group will develop a method that will allow us to make mitragynine derived mitragynine pseudoindoxyl based derivatives, with the aim of developing analgesics without the abuse potential of morphine and derivatives that may be useful in treating pain without developing addiction.

National Institute of Health (NIH)
National Institute on Drug Abuse (NIDA)
Exploratory/Developmental Grants (R21)
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Special Emphasis Panel (ZRG1)
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Rapaka, Rao
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St. Louis College of Pharmacy
Schools of Pharmacy
Saint Louis
United States
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