Intestinal absorption mechanisms of 2'-deoxy-2'-β-fluoro-4'-azidocytidine, a cytidine analog for AIDS treatment, and its interaction with P-glycoprotein, multidrug resistance-associated protein 2 and breast cancer resistance protein

Separation and quantification of Azvudine in plasma of patients with COVID-19 using LC-MS/MS

Azvudine (FNC) is a new drug conditionally approved in 2022 for the treatment of coronavirus disease 2019 (COVID-19) in China. However, the exposure level of FNC in COVID-19 patients in clinical practice is still obscure, and there is no liquid chromatography-tandem mass spectrometry (LC-MS/MS) or LC method reported for quantifying the FNC. In this study, a simple, fast, and reliable LC-MS/MS method using L-phenylalanine-D5 (Phe-D5) as the internal standard (IS) was developed for the quantification of FNC in plasma from COVID-19 patients. After simple protein precipitation with methanol, the analyte in the supernatant was separated on Waters Atlantis® T3 (2.1 ×100 mm, 3.0 µm) column with the mobile phase consisting of acetonitrile (ACN) - aqueous solution (containing 0.03% heptafluorobutyric acid and 0.2% formic acid). The mobile phase was delivered at 0.3 mL/min in an isocratic elution program (15:85, V: V). The linear relationship of FNC was good within the calibration range of 2.0 - 2000.0 ng/mL, with the recovery of FNC ranging from 81.37% to 103.31% and the matrix effect was 94.77%- 109.83%. The short-term, long-term, and freeze-thaw stability of the FNC assessed in method was acceptable, and all other items met the requirements of validation of the biological analytical method. Finally, the method was applied to detect the exposure level of FNC in plasma samples from patients diagnosed with COVID-19, and the results, which are within the linear range of the method, showed huge inter-individual variation, supporting the significance of therapeutic drug monitoring of FNC.

Pharmacokinetics and absorption mechanism of tandospirone citrate

Tandospirone citrate (TDS) is commonly used for the treatment of patients with generalized anxiety disorder in clinical practice, and several studies are developing new indications for TDS. However, the in vivo processes and absorption properties of TDS have not been systematically investigated. In this work, we conducted a comprehensive investigation using in vivo, in vitro, and ex vivo approaches, involving animal and cellular models, to examine the pharmacokinetic properties and absorption mechanisms of TDS. The results of in vivo studies revealed that the half-life (t 1/2) of TDS was 1.380 ± 0.46 h and 1.224 ± 0.39 h following intragastric (i.g.) and intravenous (i.v.) administration of 20 mg/kg TDS, respectively. This indicates that TDS is rapidly eliminated in rats. The area under the curve (AUC) of TDS after i.g. and i.v. administration was 114.7 ± 40 ng/mL*h and 48,400 ± 19,110 ng/mL*h, respectively, and the absolute bioavailability of TDS was found to be low (0.24%). Furthermore, TDS was extensively metabolized in rats, with the AUC of the major active metabolite [1-[2-pyrimidyl]-piperazine] being approximately 16.38-fold higher than that of TDS after i.g. administration. The results from the in vitro Caco-2 cell model and ex vivo everted gut sac experiment demonstrated that TDS exhibited good permeability, and its transport was influenced by concentration, temperature, and pH. Passive diffusion was identified as the main absorption mechanism. In conclusion, TDS is classified as a Biopharmaceutics Classification System (BCS) class I drug, characterized by high solubility and permeability. The low absolute bioavailability of TDS may be attributed to its rapid metabolism. The pharmacokinetic data and absorption characteristics obtained in this study provide fundamental information for the further development and utilization of TDS.

Efficacy and safety of azvudine in patients with COVID-19: A systematic review and meta-analysis

Introduction

Azivudine has undergone a few randomized controlled trials (RCTs) as of late. This study aimed to assess the COVID-19 treatment with azvudine's efficacy and safety.

Methods

Through January 20, 2023, systematic searches of PubMed, Embase, ClinicalTrials.gov, International Clinical Trials Registry Platform (ICTRP), Cochrane Central Register of Controlled Trials (CENTRAL), and MedRxiv were conducted to find the RCTs. The included studies' bias risk was evaluated using the Cochrane Handbook for Systematic Reviews of Interventions. Meta-analysis was performed using Revman 5.4 (PROSPERO Code: CRD42023395022).

Results

A total of five RCTs with 1142 COVID-19 patients, 575 of whom received azvudine, were included. Additionally, seven RCTs are currently being conducted. In terms of clinical improvement and PT-PCR (reverse transcription polymerase chain reaction) negativity, the azvudine group had a greater patient percentage than the usual treatment or placebo group. It also took less time for the PT-PCR to become negative. In comparison to the placebo or standard treatment groups, the frequency of adverse events was reduced in the azvudine group (risk ratio [RR] = 0.89, 95% confidence interval [CI]: 0.80 to 0.99) and major adverse events (RR = 0.63, 95% CI: 0.22 to 1.79) groups.

Conclusions

Without the burden of side effects, azvudine can hasten the clinical symptoms of COVID-19 patients and PT-PCR negative. It will take more extensive research to confirm these conclusions.

Elevated INR in a COVID-19 patient after concomitant administration of azvudine and anticoagulants

Background: Azvudine (FNC) is a promising treatment candidate for managing coronavirus disease 2019 (COVID-19). However, drug interactions with azvudine have been poorly studied, especially with no reported cases of azvudine with anticoagulants such as warfarin and rivaroxaban. Case summary: The patient was diagnosed with lower limb venous thrombosis and took warfarin regularly. The international normalized ratio (INR) was stable (2.0-3.0). However, the INR increased to 7.52 after administering azvudine. The patient had no other factors justifying this change. This increase in INR occurred again with the administration of azvudine in combination with rivaroxaban, and the INR increased to 18.91. After azvudine administration was stopped, the INR did not increase when rivaroxaban was used alone. Conclusion: Azvudine, warfarin, and rivaroxaban might have previously unidentified drug interactions that increased the INR. Therefore, the INR must be closely monitored when they are concomitantly administered in COVID-19 patients.

Neochamaejasmin B extracted from Stellera chamaejasme L. induces apoptosis through caspase-10-dependent way in insect neuronal cells

To explore the toxicity mechanisms of neochamaejasmin B (NCB) extracted from Stellera chamaejasme L., we first evaluated its cytotoxicity in neuronal cells of Helicoverpa zea (AW1 cells). NCB inhibited cell growth and was cytotoxic to AW1 cells in a dose-dependent manner. Further, transmission electron microscopy (TEM) was used to analyze the microstructure, and typical apoptotic characteristics were observed in AW1 cells treated with NCB. Moreover, the NCB-induced apoptosis was dose dependent. Subsequently, we explored the mechanism of apoptosis. A decline in the mitochondrial membrane potential (MMP) was found. Also, the levels of Bax were increased with increases in drug concentration, but there was no statistical difference in Bcl-2 levels at different NCB doses. Caspase-3 and caspase-10 activity was increased. These findings confirmed that NCB induced apoptosis in AW1 cells through a caspase-10-dependent mechanism. The results provide the basic information needed for understanding the toxicity and mechanisms of action of NCB, which could potentially be used to develop NCB as a new insecticide.

Approved HIV reverse transcriptase inhibitors in the past decade

HIV reverse transcriptase (RT) inhibitors are the important components of highly active antiretroviral therapies (HAARTs) for anti-HIV treatment and pre-exposure prophylaxis in clinical practice. Many RT inhibitors and their combination regimens have been approved in the past ten years, but a review on their drug discovery, pharmacology, and clinical efficacy is lacking. Here, we provide a comprehensive review of RT inhibitors (tenofovir alafenamide, rilpivirine, doravirine, dapivirine, azvudine and elsulfavirine) approved in the past decade, regarding their drug discovery, pharmacology, and clinical efficacy in randomized controlled trials. Novel RT inhibitors such as islatravir, MK-8504, MK-8507, MK8583, IQP-0528, and MIV-150 will be also highlighted. Future development may focus on the new generation of novel antiretroviral inhibitors with higher bioavailability, longer elimination half-life, more favorable side-effect profiles, fewer drug-drug interactions, and higher activities against circulating drug-resistant strains.

Pharmacokinetics, bioavailability and tissue distribution of chitobiose and chitotriose in rats

Chitooligosaccharides (COSs) have various physiological activities and broad application prospects; however, their pharmacokinetics and tissue distribution remain unclear. In this study, a sensitive and selective ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) method for determining chitobiose (COS 2) and chitotriose (COS 3) in rat serum and tissues was developed. This method was successfully validated based on FDA guidelines in terms of selectivity, calibration curves (lower limit of quantification was 0.002 µg/mL for COS 2 and 0.02 µg/mL for COS 3), precision (intra-day relative standard deviation of 0.04%-3.55% and inter-day relative standard deviation of 1.94%-11.63%), accuracy (intra-day relative error of - 1.81%-11.06% and inter-day relative error of - 9.41%-8.63%), matrix effects, recovery (97.10%-101.29%), stability, dilution integrity, and carry-over effects. Then, the method was successfully applied to the pharmacokinetics and tissue distribution study of COS 2 and COS 3 after intragastric and intravenous administration. After intragastric administration, COS 2 and COS 3 were rapidly absorbed, reached peak concentrations in the serum after approximately 0.45 h, and showed rapid elimination with clearances greater than 18.82 L/h/kg and half-lives lower than 6 h. The absolute oral bioavailability of COS 2 and COS 3 was 0.32%-0.52%. COS 2 and COS 3 were widely distributed in Wistar rat tissues and could penetrated the blood-brain barrier without tissue accumulation.

Design, synthesis and evaluation of 2'-acetylene-7-deaza-adenosine phosphoamidate derivatives as anti-EV71 and anti-EV-D68 agents

A series of phosphoamidate derivatives of nucleoside 2'-acetylene-7-deaza-adenosine (NITD008) were synthesized and evaluated for their in vitro antiviral activities against the enteroviruses EV71 and EV-D68. The phosphoamidate (15f) containing a hexyl ester of l-alanine exhibited the most promising activity against EV71 (IC₅₀ = 0.13 ± 0.08 μM) and was 4-times more potent than NITD008. Meanwhile, the derivative containing a cyclohexyl ester of l-alanine (15l) exhibited the most potent activity with high selectivity index against both EV71 (IC₅₀ = 0.19 ± 0.27 μM, SI = 117.00) and EV-D68 (IC₅₀ = 0.17 ± 0.16 μM, SI = 130.76), which were both higher than that of NITD008. The results indicated that the phosphoamidate 15l was the most promising candidate for further development as antiviral agents for the treatment of both EV71 and EV-D68 infection.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

The Pyrimidine Analog FNC Potently Inhibits the Replication of Multiple Enteroviruses

Human enteroviruses (EVs), including coxsackieviruses, the numbered enteroviruses, and echoviruses, cause a wide range of diseases, such as hand, foot, and mouth disease (HFMD), encephalitis, myocarditis, acute flaccid myelitis (AFM), pneumonia, and bronchiolitis. Therefore, broad-spectrum anti-EV drugs are urgently needed to treat EV infection. Here, we demonstrate that FNC (2'-deoxy-2'-β-fluoro-4'-azidocytidine), a small nucleoside analog inhibitor that has been demonstrated to be a potent inhibitor of HIV and entered into a clinical phase II trial in China, potently inhibits the viral replication of a multitude of EVs, including enterovirus 71 (EV71), coxsackievirus A16 (CA16), CA6, EVD68, and coxsackievirus B3 (CVB3), at the nanomolar level. The antiviral mechanism of FNC involves mainly positive- and negative-strand RNA synthesis inhibition by targeting and competitively inhibiting the activity of EV71 viral RNA-dependent RNA polymerase (3D^pol), as demonstrated through quantitative real-time reverse transcription-PCR (RT-qPCR), in vitro 3D^pol activity, and isothermal titration calorimetry (ITC) experiments. We further demonstrated that FNC treatment every 2 days with 1 mg/kg of body weight in EV71 and CA16 infection neonatal mouse models successfully protected mice from lethal challenge with EV71 and CA16 viruses and reduced the viral load in various tissues. These findings provide important information for the clinical development of FNC as a broad-spectrum inhibitor of human EV pathogens.IMPORTANCE Human enterovirus (EV) pathogens cause various contagious diseases such as hand, foot, and mouth disease, encephalitis, myocarditis, acute flaccid myelitis, pneumonia, and bronchiolitis, which have become serious health threats. However, except for the EV71 vaccine on the market, there are no effective strategies to prevent and treat other EV pathogen infections. Therefore, broad-spectrum anti-EV drugs are urgently needed. In this study, we demonstrated that FNC, a small nucleoside analog inhibitor that has been demonstrated to be a potent inhibitor of HIV and entered into a clinical phase II trial in China, potently inhibits the viral replication of a multitude of EVs at the nanomolar level. Further investigation revealed that FNC inhibits positive- and negative-strand RNA synthesis of EVs by interacting and interfering with the activity of EV71 viral RNA-dependent RNA polymerase (3D^pol). Our findings demonstrate for the first time that FNC is an effective broad-spectrum inhibitor for human EV pathogens.

Development of an engineered carbamoyl phosphate synthetase with released sensitivity to feedback inhibition by site-directed mutation and casting error-prone PCR

Carbamoyl phosphate synthetase (CPS) is a key enzyme in both pyrimidine and arginine biosynthesis. However, it is inhibited strongly by uridine monophosphate (UMP), which is an intermediate of the de-novo synthesis of pyrimidine nucleoside. In this study, the native carbamoyl phosphate synthetase, from Escherichia coli, was evolved by site-directed mutation and casting error-prone PCR. Compared with the wild-type, the variant N1015 F had released sensitivity to UMP and exhibited 100% of the initial activity in the presence of UMP. Variant K1006A exhibited 0.14-fold improvement in initial activity and kept above 65% of relative activity under the saturated concentration of inhibitor. Structure analysis of variants demonstrated that the reduced sensitivity to inhibitor was largely attributed to the decreased hydrogen bonds, which could reduce the binding affinity with UMP. Also, Phe with large side chain could narrow the binding pocket and generate more steric hindrance. Based on the results in this study, N1015F was an ideal alternative catalyst for the wild-type CPS for pyrimidine biosynthesis.

Absorption Characteristics of Chitobiose and Chitopentaose in the Human Intestinal Cell Line Caco-2 and Everted Gut Sacs

The everted gut sacs and Caco-2 cell models were used to investigate the intestinal absorptive characteristics and subcellular localization of chitobiose and chitopentaose in this study. In everted gut sacs, the absorptive pattern showed no concentration-dependent manner when the concentration was lower than 10 mM. In the presence of phlorizin (100 μM) and phloretin (100 μM), the chitobiose absorption rates decreased by (4.97 ± 0.89)% and (19.2 ± 2.77)%, and they were (10.4 ± 2.43)% and (27.5 ± 1.68)% for chitopentaose. In Caco-2 cells, the concentration showed influences similar to those with the everted gut sacs results. After adding phlorizin and phloretin in the apical side, the P_appAP-BL of chitobiose and chitopentaose significantly decreased. Considering the translocation, they were enriched in endoplasmic reticulum and mitochondrion. This study indicated that concentration and active transporter were capable of mediating the absorption of chitobiose and chitopentaose, and the subcellular localization of them could help to study the mechanisms of their effects.

Interactions Between Emodin and Efflux Transporters on Rat Enterocyte by a Validated Ussing Chamber Technique

Emodin, a major active anthraquinone, frequently interacts with other drugs. As changes of efflux transporters on intestine are one of the essential reasons why the drugs interact with each other, a validated Ussing chamber technique was established to detect the interactions between emodin and efflux transporters, including P-glycoprotein (P-gp), multidrug-resistant associated protein 2 (MRP2), and multidrug-resistant associated protein 3 (MRP3). Digoxin, pravastatin, and teniposide were selected as the test substrates of P-gp, MRP2, and MRP3. Verapamil, MK571, and benzbromarone were their special inhibitors. The results showed that verapamil, MK571, and benzbromarone could increase digoxin, pravastatin, and teniposide absorption, and decrease their E_r values, respectively. Verapamil (220 μM) could significantly increase emodin absorption at 9.25 μM. In the presence of MK571 (186 μM), the P_app values of emodin from M-S were significantly increased and the efflux ratio decreased. With the treatment of emodin (185, 370, and 740 μM), digoxin absorption was significantly decreased while teniposide increased. These results indicated that emodin might be the substrate of P-gp and MRP2. Besides, it might be a P-gp inducer and MRP3 inhibitor on enterocyte, which are reported for the first time. These results will be helpful to explain the drug–drug interaction mechanisms between emodin and other drugs and provide basic data for clinical combination therapy.