Jason Jianxin Guo

Probing the Carboxyester Side Chain in Controlled Deactivation (−)‑Δ8‑Tetrahydrocannabinols

We recently reported on a controlled deactivation/detoxification approach for obtaining cannabinoids with improved druggability. Our design incorporates a metabolically labile ester group at strategic positions within the THC structure. We have now synthesized a series of (−)-Δ8-THC analogues encompassing a carboxyester group within the 3-alkyl chain in an effort to explore this novel cannabinergic chemotype for CB receptor binding affinity, in vitro and in vivo potency and efficacy, as well as controlled deactivation by plasma esterases. We have also probed the chain’s polar characteristics with regard to fast onset and short duration of action. Our lead molecule, namely 2-[(6aR,10aR)-6a,7,10,10a-tetrahydro-1-hydroxy-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-3-yl]-2-methyl-propanoic acid 3-cyano-propyl ester (AM7438), showed picomolar affinity for CB receptors and is deactivated by plasma esterases while the respective acid metabolite is inactive. In further in vitro and in vivo experiments, the compound was found to be a remarkably potent and efficacious CB1 receptor agonist with relatively fast onset/offset of action.

Capturing Unknown Substrates via in Situ Formation of Tightly Bound Bisubstrate Adducts: S-Adenosyl-vinthionine as a Functional Probe for AdoMet-Dependent Methyltransferases

Identifying an enzymes substrates is essential to understand its function, yet it remains challenging. A fundamental impediment is the transient interactions between an enzyme and its substrates. In contrast, tight binding is often observed for multisubstrate-adduct inhibitors due to synergistic interactions. Extending this venerable concept to enzyme-catalyzed in situ adduct formation, unknown substrates were affinity-captured by an S-adenosyl-methionine (AdoMet, SAM)-dependent methyltransferase (MTase). Specifically, the electrophilic methyl sulfonium (alkyl donor) in AdoMet is replaced with a vinyl sulfonium (Michael acceptor) in S-adenosyl-vinthionine (AdoVin). Via an addition reaction, AdoVin and the nucleophilic substrate form a covalent bisubstrate-adduct tightly complexed with thiopurine MTase (2.1.1.67). As such, an unknown substrate was readily identified from crude cell lysates. Moreover, this approach is applicable to other systems, even if the enzyme is unknown.

Hydrogen-Bonded His93 As a Sensitive Probe for Identifying Inhibitors of the Endocannabinoid Transport Protein FABP7

The human brain FABP (FABP7) has been shown to be an intracellular carrier protein that can significantly potentiate the uptake of the endocannabinoid anandamide. For this reason, there is a great interest in the discovery and development of FABP7 inhibitors for treating stress, pain, inflammation, and drug abuse. We found that in the 1H‐NMR spectrum of the protein, a well‐separated downfield resonance arising from the hydrogen‐bonded His93 side chain is very sensitive to ligand binding. Using this characteristic spectral marker together with another well‐resolved upfield resonance from the side chain of Val84, we have identified that an adipocyte FABP (FABP4) inhibitor BMS309403 also binds tightly to FABP7. Our data demonstrated that this unique His93 downfield resonance can be used as a sensitive probe for rapidly and unambiguously identifying novel high‐affinity FABP7 ligands. The findings should help accelerate the discovery of potential drug leads for the modulation of endocannabinoid transport.

Therapeutic Opportunities through the Modulation of Endocannabinoid Transport.

The endocannabinoid system is comprised of cannabinoid receptors (CB1 and CB2), a group of endogenous neuromodulatory lipids (endocannabinoids), and the machinery for their biosynthesis, metabolism, and transit that are involved in a variety of physiological processes including pain, appetite, memory, inflammatory and immune responses. In the brain, endocannabinoids are primarily involved in retrograde signaling, being synthesized and released from postsynaptic neurons to stimulate CB1 receptors located on the presynaptic neurons. Here, we provide an overview of the current research on the transport of endocannabinoids across plasma membranes and their intracellular trafficking with an emphasis on various potential targets for developing therapeutic drugs.