Taxane's substituents at C3' affect its regioselective metabolism: different in vitro metabolism of cephalomannine and paclitaxel

Glycyrrhizic Acid Prevents Paclitaxel-Induced Neuropathy via Inhibition of OATP-Mediated Neuronal Uptake

Peripheral neuropathy is a common side effect of cancer treatment with paclitaxel. The mechanisms by which paclitaxel is transported into neurons, which are essential for preventing neuropathy, are not well understood. We studied the uptake mechanisms of paclitaxel into neurons using inhibitors for endocytosis, autophagy, organic anion-transporting polypeptide (OATP) drug transporters, and derivatives of paclitaxel. RT-qPCR was used to investigate the expression levels of OATPs in different neuronal tissues and cell lines. OATP transporters were pharmacologically inhibited or modulated by overexpression and CRISPR/Cas9-knock-out to investigate paclitaxel transport in neurons. Through these experiments, we identified OATP1A1 and OATP1B2 as the primary neuronal transporters for paclitaxel. In vitro inhibition of OATP1A1 and OAT1B2 by glycyrrhizic acid attenuated neurotoxicity, while paclitaxel's antineoplastic effects were sustained in cancer cell lines. In vivo, glycyrrhizic acid prevented paclitaxel-induced toxicity and improved behavioral and electrophysiological measures. This study indicates that a set of OATPs are involved in paclitaxel transport into neurons. The inhibition of OATP1A1 and OATP1B2 holds a promising strategy to prevent paclitaxel-induced peripheral neuropathy.

Herb-drug interaction between Shaoyao-Gancao-Fuzi decoction and tofacitinib via CYP450 enzymes

ETHNOPHARMACOLOGY RELEVANCE

Shaoyao-Gancao-Fuzi decoction (SGFD), a well-known traditional Chinese medicine formula, was originally described in "Treatise on Febrile Diseases" and has been extensively used to dispel wind, eliminate dampness and treat paralysis. It is widely used for the treatment of rheumatoid arthritis in clinic. However, the effect of SGFD on the activity of cytochrome P450 enzymes (CYP450s) and the herb-drug interactions are rarely studied.

OBJECTIVE

The aim of this study was to investigate the effect of SGFD on the activity of CYP450s and evaluate the potential herb-drug interactions between SGFD and tofacitinib, commonly used disease-modifying antirheumatic drug in rheumatoid arthritis.

MATERIALS AND METHODS

The cocktail approach was employed to assess the effect of SGFD on the activity of CYP1A2, 3A4, 2A6, 2E1, and 2C9. The pharmacokinetic profile of oral administration of tofacitinib in rats after two weeks of treatment with SGFD was investigated. RT-qPCR and molecular docking were performed to unveil the underlying mechanism of the herb-drug interaction.

RESULTS

SGFD had no effect on the activities of CYP2E1 and 2C9, had a weak effect on CYP2A6, and had activatory effect on CYP1A2. However, it had a dramatically inhibitory effect on the activity of CYP3A4. Simultaneously, the values of C_max and AUC_0-∞ of tofacitinib were obviously increased after treatment with SGFD for 14 days. The mechanism study manifested that SGFD significantly reduced the gene transcription of CYP3A. Molecular docking work confirmed that the inhibitory activity of glycyrrhetinic acid, glycyrrhizic acid and liquiritin, the main ingredients of SGFD, occurred by occupying the active sites of CYP3A4 and by making favorable interactions with its key residues.

CONCLUSIONS

The system exposure of tofacitinib was increased by SGFD. SGFD could affect the activity and gene expression of the key metabolic enzyme CYP3A. These findings give a clear understanding to predict herb-drug interaction of SGFD for safe clinical use in future.

Cytochrome P450 3A Enzymes Are Key Contributors for Hepatic Metabolism of Bufotalin, a Natural Constitute in Chinese Medicine Chansu

Bufotalin (BFT), one of the naturally occurring bufodienolides, has multiple pharmacological and toxicological effects including antitumor activity and cardiotoxicity. This study aimed to character the metabolic pathway(s) of BFT and to identify the key drug metabolizing enzyme(s) responsible for hepatic metabolism of BFT in human, as well as to explore the related molecular mechanism of enzymatic selectivity. The major metabolite of BFT in human liver microsomes (HLMs) was fully identified as 5β-hydroxylbufotalin by LC-MS/MS and NMR techniques. Reaction phenotyping and chemical inhibition assays showed that CYP3A4 and CYP3A5 were key enzymes responsible for BFT 5β-hydroxylation. Kinetic analyses demonstrated that BFT 5β-hydroxylation in both HLMs and human CYP3A4 followed the biphasic kinetics, while BFT 5β-hydroxylation in CYP3A5 followed substrate inhibition kinetics. Furthermore, molecular docking simulations showed that BFT could bind on two different ligand-binding sites on both CYP3A4 and CYP3A5, which partially explained the different kinetic behaviors of BFT in CYP3A4 and CYP3A5. These findings are very helpful for elucidating the phase I metabolism of BFT in human and for deeper understanding the key interactions between CYP3A enzymes and bufadienolides, as well as for the development of bufadienolide-type drugs with improved pharmacokinetic and safety profiles.

Identification and characterization of in vitro and in vivo metabolites of steroidal alkaloid veratramine

Veratramine, a steroidal alkaloid originating from Veratrum nigrum L., has demonstrated distinct anti-tumor and anti-hypertension effects, however, its metabolism has rarely been explored. The objective of the current study was to provide a comprehensive investigation of its metabolic pathways. The in vitro metabolic profiles of veratramine were evaluated by incubating it with liver microsomes and cytosols. The in vivo metabolic profiles in plasma, bile, urine and feces were monitored by UPLC-MS/MS after oral (20 mg/kg) and i.v. (50 µg/kg) administration in rats. Meanwhile, related P450s inhibitors and recombinant P450s and SULTs were used to identify the isozymes responsible for its metabolism. Eleven metabolites of veratramine, including seven hydroxylated, two sulfated and two glucuronidated metabolites, were characterized. Unlike most alkaloids, the major reactive sites of veratramine were on ring A and B instead of on the amine moiety. CYP2D6 was the major isozyme mediating hydroxylation, and substrate inhibition was observed with a Vmax , Ki and Clint of 2.05 ± 0.53 nmol/min/mg, 33.08 ± 10.13 µ m and 13.58 ± 1.27 µL/min/mg. SULT2A1, with Km , Vmax and Clint values of 19.37 ± 0.87 µ m, 1.51 ± 0.02 nmol/min/mg and 78.19 ± 8.57 µL/min/mg, was identified as the major isozyme contributing to its sulfation. In conclusion, CYP2D6 and SULT2A1 mediating hydroxylation and sulfation were identified as the major biotransformation for veratramine.

Characterization of in vitro metabolites of TM-2, a potential antitumor drug, in rat, dog and human liver microsomes using liquid chromatography/tandem mass spectrometry

RATIONALE

TM-2 (13-(N-Boc-3-i-butylisoserinoyl-4,10-β-diacetoxy-2-α-benzoyloxy-5-β,20-epoxy-1,13-α-dihydroxy-9-oxo-19-norcyclopropa[g]tax-11-ene) is a novel semi-synthetic taxane derivative. Our previous study demonstrated that it is a promising taxane derivative. The in vitro comparative metabolic profile of a drug between animals and humans is a key issue that should be investigated at early stages of drug development to better select drug candidates. In this study, the in vitro metabolic pathways of TM-2 in rat, dog and human liver microsomes were established and compared.

METHODS

TM-2 was incubated with liver microsomes in the presence of NADPH. Two different types of mass spectrometers - a hybrid linear trap quadrupole orbitrap (LC/LTQ-Orbitrap) mass spectrometer and a triple-quadrupole tandem mass spectrometer (LC/QqQ) were employed to acquire structural information of TM-2 metabolites. Accurate mass measurement using LC/LTQ-Orbitrap was used to determine the accurate mass data and elemental compositions of metabolites thereby confirming the proposed structures of the metabolites. For the chemical inhibition study, selective P450 inhibitors were added to incubations to initially characterize the cytochrome P450 (CYP) enzymes involved in the metabolism of TM-2.

RESULTS

A total of 12 components (M1-M12) were detected and identified as the metabolites of TM-2 in vitro. M1-M5 were formed by hydroxylation of the taxane ring or the lateral chain. Hydroxylated products can be further oxidized to the dihydroxylated metabolites M6-M10. M11 was a trihydroxylated metabolite. M12 was tentatively identified as a carboxylic acid derivative. The metabolism of TM-2 is much the same in all three species with some differences. The chemical inhibition study initially demonstrated that the formation of M2, the major metabolite of TM-2, is mainly mediated by CYP3A4.

CONCLUSIONS

Hydroxylation is the major biotransformation of the TM-2 pathway in vitro. CYP3A4 may play a dominant role in the formation of M2 in liver microsomes. The knowledge of the metabolic pathways of TM-2 is important to support further research of TM-2.

Quantitative assignment of reaction directionality in a multicompartmental human metabolic reconstruction

Reaction directionality is a key constraint in the modeling of genome-scale metabolic networks. We thermodynamically constrained reaction directionality in a multicompartmental genome-scale model of human metabolism, Recon 1, by calculating, in vivo, standard transformed reaction Gibbs energy as a function of compartment-specific pH, electrical potential, and ionic strength. We show that compartmental pH is an important determinant of thermodynamically determined reaction directionality. The effects of pH on transport reaction thermodynamics are only seen to their full extent when metabolites are represented as pseudoisomer groups of multiple protonated species. We accurately predict the irreversibility of 387 reactions, with detailed propagation of uncertainty in input data, and manually curate the literature to resolve conflicting directionality assignments. In at least half of all cases, a prediction of a reversible reaction directionality is due to the paucity of compartment-specific quantitative metabolomic data, with remaining cases due to uncertainty in estimation of standard reaction Gibbs energy. This study points to the pressing need for 1), quantitative metabolomic data, and 2), experimental measurement of thermochemical properties for human metabolites.

Quantitative structure-retention relationship studies for taxanes including epimers and isomeric metabolites in ultra fast liquid chromatography

Seven pairs of epimers and one pair of isomeric metabolites of taxanes, each pair of which have similar structures but different retention behaviors, together with additional 13 taxanes with different substitutions were chosen to investigate the quantitative structure-retention relationship (QSRR) of taxanes in ultra fast liquid chromatography (UFLC). Monte Carlo variable selection (MCVS) method was adopted to choose descriptors. The selected four descriptors were used to build QSRR model with multi-linear regression (MLR) and artificial neural network (ANN) modeling techniques. Both linear and nonlinear models show good predictive ability, of which ANN model was better with the determination coefficient R(2) for training, validation and test set being 0.9892, 0.9747 and 0.9840, respectively. The results of 100 times' leave-12-out cross validation showed the robustness of this model. All the isomers can be correctly differentiated by this model. According to the selected descriptors, the three dimensional structural information was critical for recognition of epimers. Hydrophobic interaction was the uppermost factor for retention in UFLC. Molecules' polarizability and polarity properties were also closely correlated with retention behaviors. This QSRR model will be useful for separation and identification of taxanes including epimers and metabolites from botanical or biological samples.