Differential inhibition of rat α3* and α7 nicotinic acetylcholine receptors by tetrandrine and closely related bis-benzylisoquinoline derivatives

Inhibitory Effect of Hernandezine on the Proliferation of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) causes 830000 deaths every year and is becoming the third malignant tumor worldwide. One of the primary reasons is the lack of effective drugs. Hernandezine (HER), a bisbenzylisoquinoline alkaloid of Thalictrum simplex, has been confirmed to have antitumor activity. But there are few reports about its effect on HCC and the underlying mechanisms still remain unclear. Therefore, the antitumor effects and mechanisms of HER on HCC were evaluated in HepG2 and Hep3B cells. The in vitro experiments demonstrated that HER significantly induced G0/G1 phase arrest, inhibited the proliferation and promoted cell apoptosis in liver cancer cell lines. In the mechanisms, the antitumor effects of HER on liver cancer cells were mediated by phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT) pathway and reactive oxygen species (ROS), simultaneously. In one way, HER inhibited the activities of PI3K-AKT pathway, which interrupt the dimer formation of cyclin-dependent kinase 4 (CDK4) and cyclin D1 (CCND1) and result to G0/G1 phase arrest. In another way, after HER treatment, ROS accumulated in liver cancer cells and caused mitochondria injury which further influenced the expression of apoptosis-related proteins and eventually resulted to HepG2 and Hep3B cell apoptosis. In addition, HER showed a tumor restrain function in HepG2 and Hep3B bearing nude mice. Overall, these findings indicated that HER is a promising antitumor drug, which may provide a new direction for clinical HCC treatment.

Hernandezine induces autophagic cell death in human pancreatic cancer cells via activation of the ROS/AMPK signaling pathway

Hernandezine (Her) is a bisbenzylisoquinoline alkaloid extracted from the traditional Chinese herbal medicine Thalictrum glandulosissimum. Evidence shows that Her is a natural agonist of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and induces apoptosis and autophagy in tumor cells. In this study, we investigated the role of autophagy in Her-induced cell death in human pancreatic cancer cell lines. We showed that Her dose-dependently suppressed cell proliferation, promoted autophagy and induced autophagic death in pancreatic ductal adenocarcinoma (PDAC) cell lines Capan-1 and SW1990. The IC50 values of Her in inhibition of Capan-1 and SW1990 cells were 47.7 μM and 40.1 μM, respectively. Immunoblotting showed that Her (1−40 μM) promoted the conversion of LC3-I to LC3-II, and Her exerted concentration-dependent and time-dependent effects on autophagy activation in PDAC cells. In transmission electron microscopy and fluorescence image analysis, we found that autophagic vacuoles were significantly increased in Her-treated cells. Knockdown of ATG5, a key gene in the autophagy pathway, alleviated the activation of autophagy by Her. These results demonstrated that Her induced autophagy in PDAC cells. Intensely activated autophagy could promote cell death. The autophagy inhibitors, BafA1 and HCQ significantly inhibited Her-induced cell death, implying that Her induced autophagic cell death in PDAC cells. Moreover, we showed that Her activated autophagy by increasing the phosphorylation of AMPK and decreasing the phosphorylation of mTOR/p70S6K. Knockdown of AMPKα relieves the autophagic cell death induced by Her. Furthermore, Her concentration-dependently enhanced reactive oxygen species (ROS) generation in PDAC cells. Antioxidants could reduce the phosphorylation of AMPK and suppress autophagic cell death induced by Her. Our study provides evidence for the development of Her as a therapeutic agent for the treatment of pancreatic cancer.

Interaction Effects between Doxorubicin and Hernandezine on the Pharmacokinetics by Liquid Chromatography Coupled with Mass Spectrometry

Doxorubicin (DOX) is an effective anti-tumor drug widely used in clinics. Hernandezine (HER), isolated from a Chinese medicinal herb, has a selective inhibitory effect on DOX multidrug resistance, making DOX more effective in treating cancer. The aim of this study was to investigate the effect of the interaction of HER and DOX on pharmacokinetics. Male Sparague-Dawley rats were randomly divided into three groups: a single DOX group, a single HER group, and a combination group. Plasma concentrations of DOX and HER were determined by the LC-MS/MS method at specified time points after administration, and the main pharmacokinetic parameters were estimated. The results showed that there were significant differences in the C_max and AUC_0-∞ of DOX in the single drug group and combined drug group, indicating that HER could improve the absorption of DOX. However, DOX in combination, in turn, reduced the free drug concentration of HER, possibly because DOX enhanced the HER drug-protein binding effect. The results could be used as clinical guidance for DOX and HER to avoid adverse reactions.

Hernandezine, a Bisbenzylisoquinoline Alkaloid with Selective Inhibitory Activity against Multidrug-Resistance-Linked ATP-Binding Cassette Drug Transporter ABCB1

The overexpression of ATP-binding cassette (ABC) drug transporter ABCB1 (P-glycoprotein, MDR1) is the most studied mechanism of multidrug resistance (MDR), which remains a major obstacle in clinical cancer chemotherapy. Consequently, resensitizing MDR cancer cells by inhibiting the efflux function of ABCB1 has been considered as a potential strategy to overcome ABCB1-mediated MDR in cancer patients. However, the task of developing a suitable modulator of ABCB1 has been hindered mostly by the lack of selectivity and high intrinsic toxicity of candidate compounds. Considering the wide range of diversity and relatively nontoxic nature of natural products, developing a potential modulator of ABCB1 from natural sources is particularly valuable. Through screening of a large collection of purified bioactive natural products, hernandezine was identified as a potent and selective reversing agent for ABCB1-mediated MDR in cancer cells. Experimental data demonstrated that the bisbenzylisoquinoline alkaloid hernandezine is selective for ABCB1, effectively inhibits the transport function of ABCB1, and enhances drug-induced apoptosis in cancer cells. More importantly, hernandezine significantly resensitizes ABCB1-overexpressing cancer cells to multiple chemotherapeutic drugs at nontoxic, nanomolar concentrations. Collectively, these findings reveal that hernandezine has great potential to be further developed into a novel reversal agent for combination therapy in MDR cancer patients.

In vitro screening strategies for nicotinic receptor ligands

A common historical strategy to the discovery of nicotinic receptor ligands has involved the use of radioligand-binding assays for ligand identification in combination with two-electrode voltage clamp in Xenopus oocytes for electrophysiological characterization. More recently, higher-throughput methodologies have replaced these approaches to accommodate screening of large compound libraries and to provide increased capacity for electrophysiological profiling in mammalian cell lines. We, and others, have implemented cell-based screening assays using the fluorometric imaging plate reader (FLIPR) for primary and lead optimization screening of nicotinic receptor agonists and positive allosteric modulators (PAMs). Using GH4C1 cells expressing the rat alpha7 nicotinic receptor, both acetylcholine and nicotine produced concentration-dependent elevations of intracellular calcium with EC(50) values of 5.5 and 1.6 microM, respectively. PAM activity was robustly detected using the FLIPR assay; for example, the known alpha7 receptor PAM 5-hydroxyindole failed to directly activate the receptor but produced a leftward shift of the nicotine concentration-response curve in combination with a potentiation of the maximum evoked response to nicotine. Electrophysiological confirmation of agonist activity was achieved using the Dynaflow rapid perfusion system and patch clamp in the same GH4C1 cell expression system. Estimated EC(50) values for acetylcholine-evoked currents in GH4C1/alpha7 cells were 55 and 576 microM for area-under-the-curve (AUC) and maximum peak height calculations, respectively. Similarly, PAM activity was confirmed using electrophysiological recordings while also allowing for the mechanistic discrimination of compounds, not possible using the FLIPR assay. Specifically, PAMs capable of slowing the rapid desensitization of alpha7 receptors to different extents were discernable in these studies. Further improvements in the capacity to screen compounds using electrophysiology has been achieved by implementation of high-throughput gigaohm quality recording systems such as the QPatch and PatchXpress where agonist EC(50) values are highly comparable to those obtained using conventional manual patch clamp.

A novel method for patch-clamp automation

An increasing demand of the pharmaceutical industry for automated electrophysiological stations for ion channel drug discovery has recently resulted in the development of several commercial platforms for secondary and safety screening of ion channel modulators. These commercial systems have demonstrated an enhanced throughput, however, often at the expense of some quality-sensitive aspects of traditional patch-clamp recordings. To improve data quality and content, we have developed a patch-clamp robot that fully automates manual patch-clamp recordings, including patch pipette handling, gigaseal formation, obtaining whole-cell or perforated-cell configuration, drug application, and data acquisition. Utilization of glass micropipettes results in high-quality electrophysiological recordings with an overall success rate of about 30% in perforated-cell mode. A fast drug application system with low volume requirements (1-1.5 ml) allows the study of ligand-gated ion channels on a millisecond scale. As proof-of-concept, we present two assays developed for voltage-gated human ether-a-go-go-related and ligand-gated alpha(7) nicotinic receptor ion channels. The system throughput was a single concentration-response curve every 30-40 min or 12-17 6-point concentration-response curves daily, representing a significant improvement of typical manual patch-clamp throughput. This system represents an efficient method for patch-clamp automation without the need for a complex and expensive electrophysiological set-up for cell visualization.