Unveiling the Role of Mechanistic Target of Rapamycin Kinase (MTOR) Signaling in Cancer Progression and the Emergence of MTOR Inhibitors as Therapeutic Strategies

mTOR inhibitors in targeting autophagy and autophagy-associated signaling for cancer cell death and therapy

The mechanistic target of rapamycin (mTOR) is a protein kinase that plays a central regulatory switch to control multifaceted cellular processes, including autophagy. As a nutrient sensor, mTOR inhibits autophagy by phosphorylating and inactivating key regulators, including ULK1, Beclin-1, UVRAG, and TFEB, preventing autophagy initiation and lysosomal biogenesis. It also suppresses autophagy-related protein expression, prioritizing growth over cellular recycling. Under nutrient deprivation, mTORC1 activity decreases, allowing autophagy to restore cellular homeostasis. Hyperautophagic activities lead to autophagic cell death; sometime after the point of no return, the cell goes for non-apoptotic, non-necrotic cell death i.e., Autosis. In cancer, the crosstalk between autophagy and mTOR is context-dependent, driving either cell survival or autophagy-dependent cell death. Using mTOR inhibitors, autophagic cell death can be induced to regulate cell growth, and proliferation is a potential therapeutic option for cancer treatment. mTOR inhibitors are broadly categorized into two types, i.e., natural and synthetic mTOR inhibitors. Although several studies in preclinical and clinical trials of various synthetic mTOR inhibitors are now in focus for cancer therapies, limited work has been done to explore autophagic cell death-inducing mTOR inhibitors. In addition, many natural mTOR inhibitors display better efficacy over synthetic mTOR inhibitors due to their lower toxicity, biocompatibility, and potential to overcome drug resistance in inducing autophagic cell death for cancer treatment.

Study on drug-mediated protein-protein interaction in single living cells by fluorescence cross-correlation spectroscopy

Drug-mediated protein-protein interaction and drug-protein interaction form the basis of drug development and pharmacological research. How to obtain the information of drug-protein or protein-protein interaction in living cells is still a big challenge. In this work, we reported a new method for studying drug-mediated protein-protein interaction in living cells by using fluorescence cross-correlation spectroscopy (FCCS). We used the mammalian target of rapamycin (mTOR) as a model and studied drug-mediated FRB protein-FKBP12 protein interaction in living cells. The FRB protein covers amino acid residues of mTOR from 2015 to 2114 and FKBP12 is a receptor-binding protein. First, FRB was fused with the green fluorescent protein EGFP (FRB-EGFP), and FKBP12 was fused with the red fluorescent protein mCherry (FKBP12-mCherry) using genetic engineering technology. Then, FCCS was used to obtain information on drug-mediated FRB protein-FKBP12 protein interaction in living cells. According to the autocorrelation curves and cross-correlation curves, we can obtain cross-correlation (CC) values of the interaction between two proteins. The CC value was positively correlated with the interaction between two proteins. Furthermore, we developed a method for measuring IC50 for evaluating drug efficacy in living cells based on CC values. Compared with the current methods, our method can be used to study drug-mediated protein-protein interaction and evaluate effects of drugs on protein-protein interaction in living cells, and may become a useful tool for drug development and pharmacological research.

An in- vitro measurement for the toxicity of peptides inhibit hexokinase II in breast cancer cell lines

The role of the enzyme hexokinase 2 in many cancers has been identified through increased glycolysis or binding to the pro-apoptotic channel located in the outer mitochondrial membrane, (VDCA1) and protein kinase (MTOR). To prevent the cancer-causing pathways of this enzyme, it is possible to disrupt the interaction of hexokinase subunits. Peptides can be utilized to interfere with the interaction of subunits by binding to amino acids that contribute to enzyme dimerization. Nowadays, peptides have become a suitable option for the treatment of various diseases, especially cancer, due to their small size, ease of synthesis, and ability to penetrate the tumor. This study examined the toxic effect of peptides that inhibit enzyme interaction on tumorigenic MCF-7 and MDA-MB-231 and non-tumorigenic MCF10A cell lines through MTT analysis and flow cytometry to determine cell apoptosis. The MCF-7 line experienced a significant decrease in cell proliferation with both peptides. The RYALFSS peptide caused a decrease in the number of MDA-MB-231 cells, but the EKGLGATTHPTAAVKML peptide caused a significant increase. There was no significant increase or decrease in the MCF10A cell line. The study's finding indicate that peptides can serve as a tool to prevent the proliferation of carcinogenic cells.

IL-11 promotes Ang II-induced autophagy inhibition and mitochondrial dysfunction in atrial fibroblasts

This study aimed to investigate potential targets for the pathogenesis of atrial fibrillation to facilitate the development of effective treatments. Atrial fibroblasts were isolated and stimulated with 1 μM angiotensin-II (Ang-II) for 24 h. To increase interleukin 11 (IL-11) expression, overexpression plasmids were transfected into atrial fibroblasts. The role and the underlying mechanism of IL-11 in atrial fibrillation were examined by immunofluorescence, measurements of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP), and western blotting assays. Results demonstrated that IL-11 was upregulated in Ang-II-elicited atrial fibroblasts. Ang-II treatment increases alpha-smooth muscle actin (α-SMA), ROS and MMP levels, and p62 expression but decreases microtubule-associated protein light chain 3 II/I (LC3 II/I) and Beclin-1 expressions in atrial fibroblasts. These effects were further amplified by IL-11 overexpression. Mechanistically, the mammalian target of rapamycin (mTOR) pathway expression was enhanced in Ang-II-induced atrial fibroblasts, which was further elevated by IL-11 upregulation. IL-11 facilitates Ang II-induced differentiation of atrial fibroblasts into myofibroblasts by promoting oxidative stress, mitochondrial dysfunction, and autophagy inhibition through the mTOR pathway.