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Hepatocellular carcinoma (HCC) is a type of malignant cancer. Notch signaling is aberrantly expressed in HCC tissues with more evidence showing that this signaling plays a critical role in HCCs. In the present study, we investigate the effects of the anti-convulsant drug valproic acid (VPA) in HCC cells and its involvement in modulating Notch signaling. We found that VPA, acting as a histone deacetylase (HDAC) inhibitor, induced a decrease in HDAC4 and an increase in acetylated histone 4 (AcH4) and suppressed HCC cell growth. VPA also induced down-regulation of Notch signaling via suppressing the expression of Notch1 and its target gene HES1, with an increase of tumor suppressor p21 and p63. Furthermore, Notch1 activation via overexpressing Notch1 active form ICN1 induced HCC cell proliferation and anti-apoptosis, indicating Notch signaling played an oncogenic role in HCC cells. Meanwhile, VPA could reverse Notch1-induced increase of cell proliferation. Interestingly, VPA was also observed to stimulate the expression of G protein-coupled somatostatin receptor type 2 (SSTR2) that has been used in receptor-targeting therapies. This discovery supports a combination therapy of VPA with the SSTR2-targeting agents. Our in vitro assay did show that the combination of VPA and the peptide-drug conjugate camptothecin-somatostatin (CPT-SST) displayed more potent anti-proliferative effects on HCC cells than did each alone. VPA may be a potential drug candidate in the development of anti-HCC drugs via targeting Notch signaling, especially in combination with receptor-targeting cytotoxic agents.

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BACKGROUND AND PURPOSEVoltage-activated Na + channels contain one distinct α-subunit. In the brain NaV1.1, NaV1.2, NaV1.3 and NaV1.6 are the four most abundantly expressed α-subunits. The antiepileptic drugs (AEDs) carbamazepine, phenytoin and lamotrigine have voltage-gated Na + channels as their primary therapeutic targets. This study provides a systematic comparison of the biophysical properties of these four α-subunits and characterizes their interaction with carbamazepine, phenytoin and lamotrigine. EXPERIMENTAL APPROACH Na+ currents were recorded in voltage-clamp mode in HEK293 cells stably expressing one of the four α-subunits. KEY RESULTSNaV1.2 and NaV1.3 subunits have a relatively slow recovery from inactivation, compared with the other subunits and NaV1.1 subunits generate the largest window current. Lamotrigine evokes a larger maximal shift of the steady-state inactivation relationship than carbamazepine or phenytoin. Carbamazepine shows the highest binding rate to the α-subunits. Lamotrigine binding to NaV1.1 subunits is faster than to the other α-subunits. Lamotrigine unbinding from the α-subunits is slower than that of carbamazepine and phenytoin. CONCLUSIONS AND IMPLICATIONSThe four Na + channel α-subunits show subtle differences in their biophysical properties, which, in combination with their (sub)cellular expression patterns in the brain, could contribute to differences in neuronal excitability. We also observed differences in the parameters that characterize AED binding to the Na + channel subunits. Particularly, lamotrigine binding to the four α-subunits suggests a subunit-specific response. Such differences will have consequences for the clinical efficacy of AEDs. Knowledge of the biophysical and binding parameters could be employed to optimize therapeutic strategies and drug development.

Cervical cancer is a second leading cancer death in women world-wide, with most cases in less developed countries. Notch signaling is highly conserved with its involvement in many cancers. In the present study, we established stable cervical cell lines with Notch activation and inactivation and found that Notch activation played a suppressive role in cervical cancer cells. Meanwhile, the transient overexpression of the active intracellular domain of all four Notch receptors (ICN1, 2, 3, and 4) also induced the suppression of cervical cancer Hela cell growth. ICN1 also induced cell cycle arrest at phase G1. Notch1 signaling activation affected the expression of serial genes, especially the genes associated with cAMP signaling, with an increase of genes like THBS1, VCL, p63, c-Myc and SCG2, a decrease of genes like NR4A2, PCK2 and BCL-2. Particularly,The nuclear receptor NR4A2 was observed to induce cell proliferation via MTT assay and reduce cell apoptosis via FACS assay. Furthermore, NR4A2's activation could reverse ICN1-induced suppression of cell growth while erasing ICN1-induced increase of tumor suppressor p63. These findings support that Notch signaling mediates cervical cancer cell growth suppression with the involvement of nuclear receptor NR4A2. Notably, Notch/NR4A2/p63 signaling cascade possibly is a new signling pathway undisclosed.

Summary:Purpose: The transient and the persistent Na + current play a distinct role in neuronal excitability. Several antiepileptic drugs (AEDs) modulate the transient Na + current and block the persistent Na + current; both effects contribute to their antiepileptic properties. The interactions of the AEDs carbamazepine (CBZ) and topiramate (TPM) with the persistent and transient Na + current were investigated. Methods: HEK293 cells stably expressing the α-subunit of the Na + channel Na V 1.3 were used to record Na + currents under voltage-clamp by using the patch-clamp technique in whole-cell configuration and to investigate the effects of CBZ and TPM.Results: The persistent Na + current was present in all cells and constituted 10.3 ± 3.8% of the total current. CBZ partially blocked the persistent Na + current in a concentration-dependent manner [median effective concentration (EC 50 ), 16 ± 4 µM]. CBZ also shifted the steady-state inactivation of the transient Na + current to negative potentials (EC 50 , 14 ± 11 µM). TPM partially blocked the persistent Na + current with a much higher affinity (EC 50 , 61 ± 37 nM) than it affected the steady-state inactivation of the transient Na + current (EC 50 , 3.2 ± 1.8 µM). For the latter effect, TPM was at most half as effective as CBZ.Conclusions: The persistent Na + current flowing through the α-subunit of the Na V 1.3 channel is partially blocked by CBZ at about the same therapeutic concentrations at which it modulates the transient Na + current, adding a distinct aspect to its anticonvulsant profile. The TPM-induced partial block of the persistent Na + current, already effective at low concentrations, could be the dominant action of this drug on the Na + current.

The combination of VPA and a SSTR2-targeting agent provides us a promising approach in treatment of carcinoid tumors.

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