Advancing Kir4.2 Channel Ligand Identification through Collision-Induced Affinity Selection Mass Spectrometry.

The inwardly rectifying potassium Kir4.2 channel plays a crucial role in regulating membrane potentials and maintaining potassium homeostasis. Kir4.2 has been implicated in various physiological processes, including insulin secretion, gastric acid regulation, and the pathogenesis of central nervous system diseases. Despite its significance, the number of identified ligands for Kir4.2 remains limited. In this study, we established a method to directly observe ligands avoiding a requirement to observe the high-mass ligand-membrane protein-detergent complexes. This method used collision-induced affinity selection mass spectrometry (CIAS-MS) to identify ligands dissociated from the Kir4.2 channel-detergent complex. The CIAS-MS approach integrated all stages of affinity selection within the mass spectrometer, offering advantages in terms of time efficiency and cost-effectiveness. Additionally, we explored the effect of collisional voltage ramps on the dissociation behavior of the ligand and the ligand at different concentrations, demonstrating dose dependency.

Identification of Ligands for Ion Channels: TRPM2.

Transient receptor potential melastatin 2 (TRPM2) is a calcium-permeable, nonselective cation channel with a widespread distribution throughout the body. It is involved in many pathological and physiological processes, making it a potential therapeutic target for various diseases, including Alzheimer's disease, Parkinson's disease, and cancers. New analytical techniques are beneficial for gaining a deeper understanding of its involvement in disease pathogenesis and for advancing the drug discovery for TRPM2-related diseases. In this work, we present the application of collision-induced affinity selection mass spectrometry (CIAS-MS) for the direct identification of ligands binding to TRPM2. CIAS-MS circumvents the need for high mass detection typically associated with mass spectrometry of large membrane proteins. Instead, it focuses on the detection of small molecules dissociated from the ligand-protein-detergent complexes. This affinity selection approach consolidates all affinity selection steps within the mass spectrometer, resulting in a streamlined process. We showed the direct identification of a known TRPM2 ligand dissociated from the protein-ligand complex. We demonstrated that CIAS-MS can identify binding ligands from complex mixtures of compounds and screened a compound library against TRPM2. We investigated the impact of voltage increments and ligand concentrations on the dissociation behavior of the binding ligand, revealing a dose-dependent relationship.

Drug-Repurposing Screening Identifies a Gallic Acid Binding Site on SARS-CoV-2 Non-structural Protein 7.

SARS-CoV-2 is the agent responsible for acute respiratory disease COVID-19 and the global pandemic initiated in early 2020. While the record-breaking development of vaccines has assisted the control of COVID-19, there is still a pressing global demand for antiviral drugs to halt the destructive impact of this disease. Repurposing clinically approved drugs provides an opportunity to expediate SARS-CoV-2 treatments into the clinic. In an effort to facilitate drug repurposing, an FDA-approved drug library containing 2400 compounds was screened against the SARS-CoV-2 non-structural protein 7 (nsp7) using a native mass spectrometry-based assay. Nsp7 is one of the components of the SARS-CoV-2 replication/transcription complex essential for optimal viral replication, perhaps serving to off-load RNA from nsp8. From this library, gallic acid was identified as a compound that bound tightly to nsp7, with an estimated K d of 15 µM. NMR chemical shift perturbation experiments were used to map the ligand-binding surface of gallic acid on nsp7, indicating that the compound bound to a surface pocket centered on one of the protein's four α-helices (α2). The identification of the gallic acid-binding site on nsp7 may allow development of a SARS-CoV-2 therapeutic via artificial-intelligence-based virtual docking and other strategies.

RGD-Coated Polymer Nanoworms for Enriching Cancer Stem Cells.

Cancer stem cells (CSCs) are primarily responsible for tumour drug resistance and metastasis; thus, targeting CSCs can be a promising approach to stop cancer recurrence. However, CSCs are small in numbers and readily differentiate into matured cancer cells, making the study of their biological features, including therapeutic targets, difficult. The use of three-dimensional (3D) culture systems to enrich CSCs has some limitations, including low sphere forming efficiency, enzymatic digestion that may damage surface proteins, and more importantly no means to sustain the stem properties. A responsive 3D polymer extracellular matrix (ECM) system coated with RGD was used to enrich CSCs, sustain stemness and avoid enzymatic dissociation. RGD was used as a targeting motif and a ligand to bind integrin receptors. We found that the system was able to increase sphere forming efficiency, promote the growth of spheric cells, and maintain stemness-associated properties compared to the current 3D culture. We showed that continuous culture for three generations of colon tumour spheroid led to the stem marker CD24 gradually increasing. Furthermore, the new system could enhance the cancer cell sphere forming ability for the difficult triple negative breast cancer cells, MBA-MD-231. The key stem gene expression for colon cancer also increased with the new system. Further studies indicated that the concentration of RGD, especially at high doses, could inhibit stemness. Taken together, our data demonstrate that our RGD-based ECM system can facilitate the enrichment of CSCs and now allow for the investigation of new therapeutic approaches for colorectal cancer or other cancers.

Cancer stemness contributes to cluster formation of colon cancer cells and high metastatic potentials.

The ability of cancer cells to form clusters is a characteristic feature in the development of metastatic tumours with drug resistance. Several studies demonstrated that clusters of circulating tumour cells (CTCs) have a greater metastatic potential to establish new tumours at secondary sites than single CTCs. However, the mechanism of cluster formation is not well understood. In this study, we investigated whether cancer stemness would contribute to cluster formation. We used a tumour sphere culture method to enrich cancer stem cells (CSCs) from colon cancer cells and found that during the second generation of sphere culture, clusters (between 3 and 5 cells) formed within the first 24 hours, whereas the rest remained as single cells. The clusters were analysed for stemness and metastatic potential, including gene expressions for cancer stemness (CD133 and Lgr5), epithelial-mesenchymal transition (E-cadherin and TGF-ß 1-3) and hypoxia-induced factors (HIF-1α and HIF-2α). The results showed that the clusters expressed higher levels of these genes and colon CSC surface markers (including CD24, CD44 and CD133) than the single cells. Among these markers, CD24 seemed the major contributor linking the cells into the clusters. These clusters also showed a stronger ability to both form colonies and migrate. Our data collectively suggest that colon cancer stemness contributes to cluster formation and that clustered cells exhibit a great metastatic potential. Our study thus provides a method to study the CTC clusters and derive insight into oncogenesis and metastasis.

Insluin and epithelial growth factor (EGF) promote programmed death ligand 1(PD-L1) production and transport in colon cancer stem cells.

BACKGROUND: Programmed cell death ligand 1 (PD-L1) is an important immune-inhibitory protein expressed on cancer cells to mediate cancer escape through interaction with PD-1 expressed on activated T lymphocytes (T cells). Previously, we reported that colon and breast cancer stem cells (CSCs) expressed much higher levels of PD-L1 than their parental cells, suggesting they will be more resistant to immune attack. METHODS: We investigated the underlining mechanism of PD-L1 increase in colon CSCs, with a special focus on the effect of insulin and epithelial growth factor (EGF), the two fundamental components to sustain the metabolism and stemness in the culture of CSCs. RESULTS: We found that insulin increased the total and surface PD-L1 levels through PI3K/Akt/mTOR pathway as the increase could be inhibited by the dual inhibitor of the pathway, BEZ235. EGF didn't affect the total PD-L1 levels of CSCs but increased the cell surface protein levels by flow cytometry analysis, indicating EGF promotes the transport of PD-L1 to the cell surface. Blocking cell surface PD-L1 with a specific antibody resulted in a significant reduction of tumour sphere formation but didn't interfere with the sphere growth, suggesting that cell surface PD-L1 may act as an adhering molecule for CSCs. CONCLUSIONS: Apart from the essential roles in metabolism and stemness, insulin and EGF involve in up-regulation of PD-L1 expression in colon CSCs, therefore the inhibition of insulin and EGF/EGFR pathways can be considered for cancer immunotherapy or combined with PD-1/PD-L1 antibody-based cancer immunotherapy to eliminate CSCs.

Biodistribution of PNIPAM-Coated Nanostructures Synthesized by the TDMT Method.

Targeting the spleen with nanoparticles could increase the efficacy of vaccines and cancer immunotherapy, and have the potential to treat intracellular infections including leishmaniasis, trypanosome, splenic TB, AIDS, malaria, and hematological disorders. Although, nanoparticle capture in both the liver and spleen has been well documented, there are only a few examples of specific capture in the spleen alone. It is proposed that the larger the nanoparticle size (>400 nm) the greater the specificity and capture within the spleen. Here, we synthesized five nanostructures with different shapes (ranging from spheres, worms, rods, nanorattles, and toroids) and poly( N-isopropylacrylamide), PNIPAM, surface coating using the temperature-directed morphology transformation (TDMT) method. Globular PNIPAM (i.e., water insoluble) surface coatings have been shown to significantly increase cell uptake and enhanced enzyme activity. We incorporated a globular component of PNIPAM on the nanostructure surface and examined the in vivo biodistribution of these nanostructures and accumulation in various tissues and organs in a mouse model. The in vivo biodistribution as a function of time was influenced by the shape and PNIPAM surface composition, in which organ capture and retention was the highest in the spleen. The rods (∼150 nm in length and 15 nm in width) showed the highest capture and retention of greater than 35% to the initial injection amount compared to all other nanostructures. It was found that the rods specifically targeted the cells in the red pulp region of the spleen due to the shape and PNIPAM coating of the rod. This remarkable accumulation and selectively into the spleen represents new nanoparticle design parameters to develop new splenotropic effects for vaccines and other therapeutics.