New aryl and acylsulfonamides as state-dependent inhibitors of Nav1.3 voltage-gated sodium channel.

Voltage-gated sodium channels (Navs) play an essential role in neurotransmission, and their dysfunction is often a cause of various neurological disorders. The Nav1.3 isoform is found in the CNS and upregulated after injury in the periphery, but its role in human physiology has not yet been fully elucidated. Reports suggest that selective Nav1.3 inhibitors could be used as novel therapeutics to treat pain or neurodevelopmental disorders. Few selective inhibitors of this channel are known in the literature. In this work, we report the discovery of a new series of aryl and acylsulfonamides as state-dependent inhibitors of Nav1.3 channels. Using a ligand-based 3D similarity search and subsequent hit optimization, we identified and prepared a series of 47 novel compounds and tested them on Nav1.3, Nav1.5, and a selected subset also on Nav1.7 channels in a QPatch patch-clamp electrophysiology assay. Eight compounds had an IC50 value of less than 1 µM against the Nav1.3 channel inactivated state, with one compound displaying an IC50 value of 20 nM, whereas activity against the inactivated state of the Nav1.5 channel and Nav1.7 channel was approximately 20-fold weaker. None of the compounds showed use-dependent inhibition of the cardiac isoform Nav1.5 at a concentration of 30 µM. Further selectivity testing of the most promising hits was measured using the two-electrode voltage-clamp method against the closed state of the Nav1.1-Nav1.8 channels, and compound 15b displayed small, yet selective, effects against the Nav1.3 channel, with no activity against the other isoforms. Additional selectivity testing of promising hits against the inactivated state of the Nav1.3, Nav1.7, and Nav1.8 channels revealed several compounds with robust and selective activity against the inactivated state of the Nav1.3 channel among the three isoforms tested. Moreover, the compounds were not cytotoxic at a concentration of 50 µM, as demonstrated by the assay in human HepG2 cells (hepatocellular carcinoma cells). The novel state-dependent inhibitors of Nav1.3 discovered in this work provide a valuable tool to better evaluate this channel as a potential drug target.

Subcellular dynamics and functional activity of the cleaved intracellular domain of the Na+ channel ß1 subunit.

The voltage-gated Na+ channel ß1 subunit, encoded by SCN1B, regulates cell surface expression and gating of α subunits and participates in cell adhesion. ß1 is cleaved by α/ß and γ-secretases, releasing an extracellular domain and intracellular domain (ICD), respectively. Abnormal SCN1B expression/function is linked to pathologies including epilepsy, cardiac arrhythmia, and cancer. In this study, we sought to determine the effect of secretase cleavage on ß1 function in breast cancer cells. Using a series of GFP-tagged ß1 constructs, we show that ß1-GFP is mainly retained intracellularly, particularly in the endoplasmic reticulum and endolysosomal pathway, and accumulates in the nucleus. Reduction in endosomal ß1-GFP levels occurred following γ-secretase inhibition, implicating endosomes and/or the preceding plasma membrane as important sites for secretase processing. Using live-cell imaging, we also report ß1ICD-GFP accumulation in the nucleus. Furthermore, ß1-GFP and ß1ICD-GFP both increased Na+ current, whereas ß1STOP-GFP, which lacks the ICD, did not, thus highlighting that the ß1-ICD is necessary and sufficient to increase Na+ current measured at the plasma membrane. Importantly, although the endogenous Na+ current expressed in MDA-MB-231 cells is tetrodotoxin (TTX)-resistant (carried by Nav1.5), the Na+ current increased by ß1-GFP or ß1ICD-GFP was TTX-sensitive. Finally, we found ß1-GFP increased mRNA levels of the TTX-sensitive α subunits SCN1A/Nav1.1 and SCN9A/Nav1.7. Taken together, this work suggests that the ß1-ICD is a critical regulator of α subunit function in cancer cells. Our data further highlight that γ-secretase may play a key role in regulating ß1 function in breast cancer.

Emerging roles for multifunctional ion channel auxiliary subunits in cancer.

Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavß, Cavγ) and downregulated (e.g. Kvß) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navß1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.

Life-threatening Petersen's hernia following open Beger's procedure.

Petersen's hernia (an internal hernia between the transverse mesocolon and Roux limb following Roux-en-Y reconstruction) is well described following laparoscopic gastric bypass surgery. We describe a Petersen-type hernia in a patient who had undergone complex open upper gastrointestinal surgery for chronic pancreatitis.