Loss of S6K1 But Not S6K2 in the Tumor Microenvironment Suppresses Tumor Growth by Attenuating Tumor Angiogenesis

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

The mechanistic target of rapamycin kinase (MTOR) is pivotal for cell growth, metabolism, and survival. It functions through two distinct complexes, mechanistic TORC1 and mechanistic TORC2 (mTORC1 and mTORC2). These complexes function in the development and progression of cancer by regulating different cellular processes, such as protein synthesis, lipid metabolism, and glucose homeostasis. The mTORC1 complex senses nutrients and initiates proliferative signals, and mTORC2 is crucial for cell survival and cytoskeletal rearrangements. mTORC1 and mTORC2 have therefore emerged as potential targets for cancer treatment. Several mTOR inhibitors, including rapamycin and its analogs (rapalogs), primarily target mTORC1 and are effective for specific cancer types. However, these inhibitors often lead to resistance and limited long-term advantages due to the activation of survival pathways through feedback mechanisms. Researchers have created next-generation inhibitors targeting mTORC1 and mTORC2 and dual PI3K/mTOR inhibitors to address these difficulties. These inhibitors demonstrate enhanced anti-tumor effects by simultaneously disrupting multiple signaling pathways and show promise for improved and long-lasting therapies. However, development of resistance and adverse side effects remain a significant obstacle. Recent additions known as RapaLinks have emerged as a boon to counter drug-resistant cancer cells, as they are more potent and provide a more comprehensive blockade of mTOR signaling pathways. This Review combines current research findings and clinical insights to enhance our understanding of the crucial role of mTOR signaling in cancer biology and highlights the evolution of mTOR inhibitors as promising therapeutic approaches.

Exploring the therapeutic mechanisms of Coptidis Rhizoma in gastric precancerous lesions: a network pharmacology approach

BACKGROUND

Gastric precancerous lesions are a critical stage in the development of gastric cancer or gastric adenocarcinoma, and their outcome plays an important role in the malignant progression of gastric cancer. Coptidis Rhizoma has a good effect on Gastric precancerous lesions. However, the specific mechanisms of its action remain incompletely elucidated.

METHODS

Network pharmacology and molecular docking techniques were used to explore the active ingredients and molecular mechanism of Coptidis Rhizoma in treating gastric precancerous lesions. The active compounds of Coptidis Rhizoma and their potential gastric precancerous lesions related targets were obtained from TCMSP, GeneCards, and OMIM databases. An interaction network based on protein-protein interactions (PPIs) was constructed to visualize the interactions between hub genes. Analysis of GO enrichment and KEGG pathway were conducted using the DAVID database. An investigation of interactions between active compounds and potential targets was carried out by molecular docking. Finally, animal experiments were conducted to verify the effect and mechanism of Coptidis Rhizoma in treating precancerous lesions of gastric cancer.

RESULTS

A total of 11 active compounds and 95 anti-gastric precancerous lesions targets of Coptidis Rhizoma were screened for analysis. GO enrichment analysis showed that the mechanism of Coptidis Rhizoma acting on gastric precancerous lesions involves gene expression regulation and apoptosis regulation. KEGG pathway enrichment analysis showed that Coptidis Rhizoma against gastric precancerous lesions involving the AKT /HIF-1α/VEGF signalling pathway. Molecular docking simulations indicated potential interactions between these compounds and core targets involved in anti-gastric precancerous lesions activity. In addition, it was confirmed in vivo that Berberine and Coptidis Rhizoma may reverse atrophy and potential intestinal metaplasia by inhibiting the expression of p-AKT, HIFA, and VEGF.

CONCLUSION

Bioactive compounds in Coptidis Rhizoma have the potential to prevent atrophy and intestinal metaplasia. These compounds function by regulating the proteins implicated in AKT /HIF-1α/VEGF signalling pathways that are crucial in gastric epithelial cell differentiation, proliferation and maturation.

Computer-assisted discovery and evaluation of potential ribosomal protein S6 kinase beta 2 inhibitors

S6K2 is an important protein in mTOR signaling pathway and cancer. To identify potential S6K2 inhibitors for mTOR pathway treatment, a virtual screening of 1,575,957 active molecules was performed using PLANET, AutoDock GPU, and AutoDock Vina, with their classification abilities compared. The MM/PB(GB)SA method was used to identify four compounds with the strongest binding energies. These compounds were further investigated using molecular dynamics (MD) simulations to understand the properties of the S6K2/ligand complex. Due to a lack of available 3D structures of S6K2, OmegaFold served as a reliable 3D predictive model with higher evaluation scores in SAVES v6.0 than AlphaFold, AlphaFold2, and RoseTTAFold2. The 150 ns MD simulation revealed that the S6K2 structure in aqueous solvation experienced compression during conformational relaxation and encountered potential energy traps of about 19.6 kJ mol-1. The virtual screening results indicated that Lys75 and Lys99 in S6K2 are key binding sites in the binding cavity. Additionally, MD simulations revealed that the ligands remained attached to the activation cavity of S6K2. Among the compounds, compound 1 induced restrictive dissociation of S6K2 in the presence of a flexible region, compound 8 achieved strong stability through hydrogen bonding with Lys99, compound 9 caused S6K2 tightening, and the binding of compound 16 was heavily influenced by hydrophobic interactions. This study suggests that these four potential inhibitors with different mechanisms of action could provide potential therapeutic options.

S6K1 deficiency in tumor stroma impairs lung metastasis of melanoma in mice

Accumulating data suggest that ribosomal protein S6 kinase 1 (S6K1), an effector in the mammalian target of rapamycin (mTOR) pathway, plays pleiotropic roles in tumor progression. However, to date, while the tumorigenic function of S6K1 in tumor cells has been well elucidated, its role in the tumor stroma remains poorly understood. We recently showed that S6K1 mediates vascular endothelial growth factor A (VEGF-A) production in macrophages, thereby supporting tumor angiogenesis and growth. As macrophage-derived VEGF-A is crucial for both tumor cell intravasation and extravasation across the vascular endothelium, our previous findings suggest that stromal S6K1 signaling is required for tumor metastatic spread. Therefore, we aimed to determine the impact of host S6K1 depletion on tumor metastasis using a murine model of pulmonary metastasis (S6k1-/- mice implanted with B16F10 melanoma). The ablation of S6K1 in the host microenvironment significantly reduced the metastasized B16F10 melanoma cells on the lung surface in both spontaneous and intravenous lung metastasis mouse models without affecting the incidence of metastasis to distant lymph nodes. In addition, stromal S6K1 loss decreased the number of tumor cells circulating in the peripheral blood of mice bearing B16F10 xenografts without affecting the vascular leakage induced by VEGF-A in vivo. These observations demonstrate that S6K1 signaling in host cells other than endothelial cells is required to modulate the host microenvironment to facilitate the metastatic spread of tumors via blood circulation, thus revealing its novel role in the tumor stroma during tumor progression.

Aging - what it is and how to measure it

The current understanding of the biology of aging is largely based on research aimed at identifying factors that influence lifespan. However, lifespan as a sole proxy measure of aging has limitations because it can be influenced by specific pathologies (not generalized physiological deterioration in old age). Hence, there is a great need to discuss and design experimental approaches that are well-suited for studies targeting the biology of aging, rather than the biology of specific pathologies that restrict the lifespan of a given species. For this purpose, we here review various perspectives on aging, discuss agreement and disagreement among researchers on the definition of aging, and show that while slightly different aspects are emphasized, a widely accepted feature, shared across many definitions, is that aging is accompanied by phenotypic changes that occur in a population over the course of an average lifespan. We then discuss experimental approaches that are in line with these considerations, including multidimensional analytical frameworks as well as designs that facilitate the proper assessment of intervention effects on aging rate. The proposed framework can guide discovery approaches to aging mechanisms in all key model organisms (e.g., mouse, fish models, D. melanogaster, C. elegans) as well as in humans.

Targeting the "hallmarks of aging" to slow aging and treat age-related disease: fact or fiction?

Aging is a major risk factor for a number of chronic diseases, including neurodegenerative and cerebrovascular disorders. Aging processes have therefore been discussed as potential targets for the development of novel and broadly effective preventatives or therapeutics for age-related diseases, including those affecting the brain. Mechanisms thought to contribute to aging have been summarized under the term the "hallmarks of aging" and include a loss of proteostasis, mitochondrial dysfunction, altered nutrient sensing, telomere attrition, genomic instability, cellular senescence, stem cell exhaustion, epigenetic alterations and altered intercellular communication. We here examine key claims about the "hallmarks of aging". Our analysis reveals important weaknesses that preclude strong and definitive conclusions concerning a possible role of these processes in shaping organismal aging rate. Significant ambiguity arises from the overreliance on lifespan as a proxy marker for aging, the use of models with unclear relevance for organismal aging, and the use of study designs that do not allow to properly estimate intervention effects on aging rate. We also discuss future research directions that should be taken to clarify if and to what extent putative aging regulators do in fact interact with aging. These include multidimensional analytical frameworks as well as designs that facilitate the proper assessment of intervention effects on aging rate.

Exploring the Biological Mechanism of Mammalian Phosphatidylinositol-3-Kinase/Protein Kinase B/Target of Rapamycin (PI3K/Akt/mTOR) Signaling in the Treatment of Triple-Negative Breast Cancer (TNBC)

We aimed to study the biological effect of PI3K/Akt/mTOR signal pathway on the treatment of TNBC, along with the efficiency of PI3K inhibitor BKM120, mTOR inhibitor PF-4708671 and dual inhibitor GDC-0980 on treating breast cancer in terms of proliferation and apoptosis utilizing MDA-MB-213 cell line, as well as on the expression of S6K1. The expressions of PI3K, mTOR and Akt in TNBC and paired adjacent tissues were detected by PCR. After treatment with BKM120, PF-4708671 and GDC-0980 for 24, 48, 72 and 96 hours, CCK-8 method was employed to assess the proliferation and apoptosis curves of the MDA-MB-231 cell line, the expression of S6K1 was detected by Western Blot. Expressions of PI3K, mTOR and Akt in TNBC tissues were significantly increased than those in normal specimens (P = 0.000); Compared with control group, cell proliferation treated with three inhibitors was significantly impeded, of which the inhibitory effect of PF-5708671 was slightly stronger than BKM120, while the strongest inhibitory effect was observed for GDC-0980 treatment. After 48 hours treatment, the expression intensity of p-mTOR, p-PI3K and S6K1 in MDA-MB-213 cells treated with BKM120, PF-4708671 and GDC-0980 was decreased, of which the suppression of p-mTOR, p-PI3K and S6K1 by GDC-0980 was stronger than other groups. The inclined expression of PI3K, mTOR and Akt was observed in TNBC tissues. The antagonists targeting the PI3K/Akt/mTOR signaling could inhibit the proliferation of triple-negative breast cancer cell line, of which the dual inhibitor exerted the strongest inhibition effect, and could decreased the expression of S6K1 and activity. The antagonists targeting the PI3K/Akt/mTOR signal transduction showed a promising prospect in the treatment of TNBC.

Beyond controlling cell size: functional analyses of S6K in tumorigenesis

As a substrate and major effector of the mammalian target of rapamycin complex 1 (mTORC1), the biological functions of ribosomal protein S6 kinase (S6K) have been canonically assigned for cell size control by facilitating mRNA transcription, splicing, and protein synthesis. However, accumulating evidence implies that diverse stimuli and upstream regulators modulate S6K kinase activity, leading to the activation of a plethora of downstream substrates for distinct pathobiological functions. Beyond controlling cell size, S6K simultaneously plays crucial roles in directing cell apoptosis, metabolism, and feedback regulation of its upstream signals. Thus, we comprehensively summarize the emerging upstream regulators, downstream substrates, mouse models, clinical relevance, and candidate inhibitors for S6K and shed light on S6K as a potential therapeutic target for cancers.

p70 S6 kinase as a therapeutic target in cancers: More than just an mTOR effector

p70 S6 kinase (p70^S6K) is best-known for its regulatory roles in protein synthesis and cell growth by phosphorylating its primary substrate, ribosomal protein S6, upon mitogen stimulation. The enhanced expression/activation of p70^S6K has been correlated with poor prognosis in some cancer types, suggesting that it may serve as a biomarker for disease monitoring. p70^S6K is a critical downstream effector of the oncogenic PI3K/Akt/mTOR pathway and its activation is tightly regulated by an ordered cascade of Ser/Thr phosphorylation events. Nonetheless, it should be noted that other upstream mechanisms regulating p70^S6K at both the post-translational and post-transcriptional levels also exist. Activated p70^S6K could promote various aspects of cancer progression such as epithelial-mesenchymal transition, cancer stemness and drug resistance. Importantly, novel evidence showing that p70^S6K may also regulate different cellular components in the tumor microenvironment will be discussed. Therapeutic targeting of p70^S6K alone or in combination with traditional chemotherapies or other microenvironmental-based drugs such as immunotherapy may represent promising approaches against cancers with aberrant p70^S6K signaling. Currently, the only clinically available p70^S6K inhibitors are rapamycin analogs (rapalogs) which target mTOR. However, there are emerging p70^S6K-selective drugs which are going through active preclinical or clinical trial phases. Moreover, various screening strategies have been used for the discovery of novel p70^S6K inhibitors, hence bringing new insights for p70^S6K-targeted therapy.