Development of a Photoswitchable Lithium-Sensitive Probe to Analyze Nonselective Cation Channel Activity in Migrating Cancer Cells

Abstract

This is the first work to use a newly designed Li 1-selective photoswitchable probe Sabrina Heng Lithium (SHL) in living colon cancer cells to noninvasively monitor cation channel activity in real time by the appearance of lithium hot spots detected by confocal microscopy. Punctate Li 1 hot spots are clustered in the lamellipodial leading edges of HT29 human colon cancer cells and are colocalized with aquaporin-1 (AQP1) channels. AQP1 is a dual water and cyclic-nucleotidegated cation channel located in lamellipodia and is essential for rapid cell migration in a subset of aggressive cancers. Both the Li 1 hot spots and cell migration are blocked in HT29 cells by the AQP1 ion channel antagonist AqB011. In contrast, Li 1 hot spots are not evident in a poorly migrating colon cancer cell line, SW620, which lacks comparable membrane expression of AQP1. Knockdown of AQP1 by RNA interference in HT29 cells significantly impairs Li 1 hot spot activity. The SHL probe loaded in living cells shows signature chemical properties of ionic selectivity and reversibility. Dynamic properties of the Li 1 hot spots, turning on and off, are confirmed by time-lapse imaging. SHL is a powerful tool for evaluating cation channel function in living cells in real time, with particular promise for studies of motile cells or interlinked networks not easily analyzed by electrophysiological methods. The ability to reset SHL by photoswitching allows monitoring of dynamic signals over time. Future applications of the Li 1 probe could include high-throughput optical screening for discovering new classes of channels, or finding new pharmacological modulators for nonselective cation channels.

Combined pharmacological administration of AQP1 ion channel blocker AqB011 and water channel blocker Bacopaside II amplifies inhibition of colon cancer cell migration

“…The experiment was performed using a similar method as previously published 79 . Prior to transfection, HT29 cells were grown to 30% confluence in DMEM medium with 10% FBS.…”

Molecular Targets for Combined Therapeutic Strategies to Limit Glioblastoma Cell Migration and Invasion

“…The expression of AQP1 in the leading edges of migrating cells has been linked to enhanced motility, as documented in neural crest (McLennan et al, 2020) and various types of cancer cells including colon cancer, gliomas, breast cancer, and endothelial cells involved in angiogenic responses (McCoy and Sontheimer, 2007;Pei et al, 2016a;Nakhjavani et al, 2019;Tomita et al, 2019). AQP1 is a dual water and ion channel (Anthony et al, 2000;Yu et al, 2006;Campbell et al, 2012;Kourghi et al, 2018), which has been suggested to accelerate cell migration by enabling parallel water and cation entry (Yool et al, 2009;Pei et al, 2019), promoting the cellular lamellipodial and filopodial extensions needed for forward movement. Inhibition of either the AQP1 water pores (in each subunit) or the ion channel (thought to reside in the central pore of the tetramer) slows migration in AQP1-expressing cancer cell lines (Kourghi et al, 2016;Pei et al, 2016b), and the inhibition of both shows an enhanced blocking effect on motility .…”

DNAzyme-Based Lithium-Selective Imaging Reveals Higher Lithium Accumulation in Bipolar Disorder Patient-Derived Neurons

“…Despite demonstrated success in using fluorescent sensors to detect divalent metal ions such as Ca 2+ , Zn 2+ , and Cu 2+ , , effective sensors for detecting monovalent metal ions, especially Li + , is quite limited. − Among the fluorescent Li + sensors, sensors based on organic crown, such as chiral diaza-9-crown-3 derivatives, [2.1.1]-cryptates, KLI-1 and KLI-2, methyl-1-aza-12-crown-4, and 1-(9-anthryl)-4-ferrocenyl-2-aza-1,3-butadiene, have received the most attention. − However, they have limited selectivity over other competing monovalent ions, such as Na + and K + , which are present in biological systems in much higher concentrations than that of Li + , and most of them have limited solubility in water and thus do not work well under physiological conditions. To our knowledge, Sabrina Heng lithium (SHL), based on merocyanine and spiropyran isomers changing upon Li + binding, was the first and is the only intracellular Li + optical sensor reported . However, its cellular detection range (137 mM Li + without Na + ) is beyond the window of physiological relevant concentrations.…”