RICTOR Amplification Defines a Novel Subset of Patients with Lung Cancer Who May Benefit from Treatment with mTORC1/2 Inhibitors

High sugar diet promotes tumor progression paradoxically through aberrant upregulation of pepck1

High dietary sugar (HDS), a contemporary dietary concern due to excessive intake of added sugars and carbohydrates, escalates the risk of metabolic disorders and concomitant cancers. However, the molecular mechanisms underlying HDS-induced cancer progression are not completely understood. We found that phosphoenolpyruvate carboxykinase 1 (PEPCK1), a pivotal enzyme in gluconeogenesis, is paradoxically upregulated in tumors by HDS, but not by normal dietary sugar (NDS), during tumor progression. Targeted knockdown of pepck1, but not pepck2, specifically in tumor tissue in Drosophila in vivo, not only attenuates HDS-induced tumor growth but also significantly improves the survival of Ras/Src tumor-bearing animals fed HDS. Interestingly, HP1a-mediated heterochromatin interacts directly with the pepck1 gene and downregulates pepck1 gene expression in wild-type Drosophila. Mechanistically, we demonstrated that, under HDS conditions, pepck1 knockdown reduces both wingless and TOR signaling, decreases evasion of apoptosis, reduces genome instability, and suppresses glucose uptake and trehalose levels in tumor cells in vivo. Moreover, rational pharmacological inhibition of PEPCK1, using hydrazinium sulfate, greatly improves the survival of tumor-bearing animals with pepck1 knockdown under HDS. This study is the first to show that elevated levels of dietary sugar induce aberrant upregulation of PEPCK1, which promotes tumor progression through altered cell signaling, evasion of apoptosis, genome instability, and reprogramming of carbohydrate metabolism. These findings contribute to our understanding of the complex relationship between diet and cancer at the molecular, cellular, and organismal levels and reveal PEPCK1 as a potential target for the prevention and treatment of cancers associated with metabolic disorders.

RICTOR amplification is associated with Rictor membrane staining and does not correlate with PD-L1 expression in lung squamous cell carcinoma

RICTOR gene, which encodes the scaffold protein of mTORC2, can be amplified in various tumor types, including squamous cell carcinoma (SCC) of the lung. RICTOR amplification can lead to hyperactivation of mTORC2 and may serve as a targetable genetic alteration, including in lung SCC patients with no PD-L1 expression who are not expected to benefit from immune checkpoint inhibitor therapy. This study aimed to compare RICTOR amplification detected by fluorescence in situ hybridization (FISH) with Rictor and PD-L1 protein expression detected by immunohistochemistry (IHC) in SCC of the lung. The study was complemented by analysis of the publicly available Lung Squamous Cell Carcinoma (TCGA, Firehose legacy) dataset. RICTOR amplification was observed in 20% of our cases and 16% of the lung SCC cases of the TCGA dataset. Rictor and PD-L1 expression was seen in 74% and 44% of the cases, respectively. Rictor IHC showed two staining patterns: membrane staining (16% of the cases) and cytoplasmic staining (58% of the cases). Rictor membrane staining predicted RICTOR amplification as detected by FISH with high specificity (95%) and sensitivity (70%). We did not find any correlation between RICTOR amplification and PD-L1 expression; RICTOR amplification was detected in 18% and 26% of PD-L1 positive and negative cases, respectively. The TCGA dataset analysis showed similar results; RICTOR copy number correlated with Rictor mRNA and protein expression but showed no association with PD-L1 mRNA and protein expression. In conclusion, the correlation between RICTOR amplification and Rictor membrane staining suggests that the latter can potentially be used as a surrogate marker to identify lung SCC cases with RICTOR amplification. Since a significant proportion of PD-L1 negative SCC cases harbor RICTOR amplification, analyzing PD-L1 negative tumors by RICTOR FISH or Rictor IHC can help select patients who may benefit from mTORC2 inhibitor therapy.

Tissue factor overexpression promotes resistance to KRAS-G12C inhibition in non-small cell lung cancer

The recently approved KRASG12C mutation-specific inhibitors sotorasib and adagrasib (KRASG12C-I) represent a promising therapy for KRASG12C-driven non-small cell lung cancer (NSCLC). However, many eligible patients do not benefit due to intrinsic or acquired drug resistance. Tissue factor (TF) is overexpressed in KRAS-mutated (KRASmut) NSCLC and is the target of the FDA-approved ADC Tivdak. Here, we employed HuSC1-39, the parent antibody of a clinical stage TF-ADC (NCT04843709), to investigate the role of TF in KRASmut NSCLC. We found that patients with TF-overexpression had poor survival, elevated P-ERK/P-AKT activity levels and low immune effector cell infiltration in the tumor. In a panel of KRASG12C cell lines, KRASG12C-I response correlated with suppression of TF mRNA, which was not observed in resistant cells. In the drug resistant cells, TF-overexpression relied on an mTORC2-mediated and proteasome-dependent pathway. Combination treatment of HuSC1-39 or mTORC1/2 inhibitor MTI-31 with KRASG12C-I each produced synergistic antitumor efficacy in cell culture and in an orthotopic lung tumor model. TF-depletion in the resistant cells diminished epithelial mesenchymal transition, reduced tumor growth and greatly sensitized KRASG12C-I response. Moreover, employing immunohistochemistry and coculture studies, we demonstrated that HuSC1-39 or MTI-31 reset the tumor microenvironment and restore KRASG12C-I sensitivity by reshaping an M1-like macrophage profile with greatly enhanced phagocytic capacity toward tumor cell killing. Thus, we have identified the TF/mTORC2 axis as a critical new mechanism for triggering immunosuppression and KRASG12C-I resistance. We propose that targeting this axis with HuSC1-39 or MTI-31 will improve KRASG12C-I response in KRAS-driven NSCLC.

Rictor-A Mediator of Progression and Metastasis in Lung Cancer

Lung carcinoma is one of the most common cancer types for both men and women. Despite recent breakthroughs in targeted therapy and immunotherapy, it is characterized by a high metastatic rate, which can significantly affect quality of life and prognosis. Rictor (encoded by the RICTOR gene) is known as a scaffold protein for the multiprotein complex mTORC2. Among its diverse roles in regulating essential cellular functions, mTORC2 also facilitates epithelial-mesenchymal transition and metastasis formation. Amplification of the RICTOR gene and subsequent overexpression of the Rictor protein can result in the activation of mTORC2, which promotes cell survival and migration. Based on recent studies, RICTOR amplification or Rictor overexpression can serve as a marker for mTORC2 activation, which in turn provides a promising druggable target. Although selective inhibitors of Rictor and the Rictor-mTOR association are only in a preclinical phase, they seem to be potent novel approaches to reduce tumor cell migration and metastasis formation. Here, we summarize recent advances that support an important role for Rictor and mTORC2 as potential therapeutic targets in the treatment of lung cancer. This is a traditional (narrative) review based on Pubmed and Google Scholar searches for the following keywords: Rictor, RICTOR amplification, mTORC2, Rictor complexes, lung cancer, metastasis, progression, mTOR inhibitors.

The mTORC2 signaling network: targets and cross-talks

The mechanistic target of rapamycin, mTOR, controls cell metabolism in response to growth signals and stress stimuli. The cellular functions of mTOR are mediated by two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. Rapamycin and its analogs are currently used in the clinic to treat a variety of diseases and have been instrumental in delineating the functions of its direct target, mTORC1. Despite the lack of a specific mTORC2 inhibitor, genetic studies that disrupt mTORC2 expression unravel the functions of this more elusive mTOR complex. Like mTORC1 which responds to growth signals, mTORC2 is also activated by anabolic signals but is additionally triggered by stress. mTORC2 mediates signals from growth factor receptors and G-protein coupled receptors. How stress conditions such as nutrient limitation modulate mTORC2 activation to allow metabolic reprogramming and ensure cell survival remains poorly understood. A variety of downstream effectors of mTORC2 have been identified but the most well-characterized mTORC2 substrates include Akt, PKC, and SGK, which are members of the AGC protein kinase family. Here, we review how mTORC2 is regulated by cellular stimuli including how compartmentalization and modulation of complex components affect mTORC2 signaling. We elaborate on how phosphorylation of its substrates, particularly the AGC kinases, mediates its diverse functions in growth, proliferation, survival, and differentiation. We discuss other signaling and metabolic components that cross-talk with mTORC2 and the cellular output of these signals. Lastly, we consider how to more effectively target the mTORC2 pathway to treat diseases that have deregulated mTOR signaling.

Growth or death? Control of cell destiny by mTOR and autophagy pathways

One of the central regulators of cell growth, proliferation, and metabolism is the mammalian target of rapamycin, mTOR, which exists in two structurally and functionally different complexes: mTORC1 and mTORC2; unlike m TORC2, mTORC1 is activated in response to the sufficiency of nutrients and is inhibited by rapamycin. mTOR complexes have critical roles not only in protein synthesis, gene transcription regulation, proliferation, tumor metabolism, but also in the regulation of the programmed cell death mechanisms such as autophagy and apoptosis. Autophagy is a conserved catabolic mechanism in which damaged molecules are recycled in response to nutrient starvation. Emerging evidence indicates that the mTOR signaling pathway is frequently activated in tumors. In addition, dysregulation of autophagy was associated with the development of a variety of human diseases, such as cancer and aging. Since mTOR can inhibit the induction of the autophagic process from the early stages of autophagosome formation to the late stage of lysosome degradation, the use of mTOR inhibitors to regulate autophagy could be considered a potential therapeutic option. The present review sheds light on the mTOR and autophagy signaling pathways and the mechanisms of regulation of mTOR-autophagy.

Novel RICTOR amplification harbouring entities: FISH validation of RICTOR amplification in tumour tissue after next-generation sequencing

Alterations in mTOR signalling molecules, including RICTOR amplification, have been previously described in many cancers, particularly associated with poor prognosis. In this study, RICTOR copy number variation (CNV) results of diagnostic next-generation sequencing (NGS) were analysed in 420 various human malignant tissues. RICTOR amplification was tested by Droplet Digital PCR (ddPCR) and validated using the "gold standard" fluorescence in situ hybridisation (FISH). Additionally, the consequences of Rictor protein expression were also studied by immunohistochemistry. RICTOR amplification was presumed in 37 cases with CNV ≥ 3 by NGS, among these, 16 cases (16/420; 3.8%) could be validated by FISH, however, ddPCR confirmed only 11 RICTOR-amplified cases with lower sensitivity. Based on these, neither NGS nor ddPCR could replace traditional FISH in proof of RICTOR amplification. However, NGS could be beneficial to highlight potential RICTOR-amplified cases. The obtained results of the 14 different tumour types with FISH-validated RICTOR amplification demonstrate the importance of RICTOR amplification in a broad spectrum of tumours. The newly described RICTOR-amplified entities could initiate further collaborative studies with larger cohorts to analyse the prevalence of RICTOR amplification in rare diseases. Finally, our and further work could help to improve and expand future therapeutic opportunities for mTOR-targeted therapies.

Multifaceted role of mTOR (mammalian target of rapamycin) signaling pathway in human health and disease

The mammalian target of rapamycin (mTOR) is a protein kinase that controls cellular metabolism, catabolism, immune responses, autophagy, survival, proliferation, and migration, to maintain cellular homeostasis. The mTOR signaling cascade consists of two distinct multi-subunit complexes named mTOR complex 1/2 (mTORC1/2). mTOR catalyzes the phosphorylation of several critical proteins like AKT, protein kinase C, insulin growth factor receptor (IGF-1R), 4E binding protein 1 (4E-BP1), ribosomal protein S6 kinase (S6K), transcription factor EB (TFEB), sterol-responsive element-binding proteins (SREBPs), Lipin-1, and Unc-51-like autophagy-activating kinases. mTOR signaling plays a central role in regulating translation, lipid synthesis, nucleotide synthesis, biogenesis of lysosomes, nutrient sensing, and growth factor signaling. The emerging pieces of evidence have revealed that the constitutive activation of the mTOR pathway due to mutations/amplification/deletion in either mTOR and its complexes (mTORC1 and mTORC2) or upstream targets is responsible for aging, neurological diseases, and human malignancies. Here, we provide the detailed structure of mTOR, its complexes, and the comprehensive role of upstream regulators, as well as downstream effectors of mTOR signaling cascades in the metabolism, biogenesis of biomolecules, immune responses, and autophagy. Additionally, we summarize the potential of long noncoding RNAs (lncRNAs) as an important modulator of mTOR signaling. Importantly, we have highlighted the potential of mTOR signaling in aging, neurological disorders, human cancers, cancer stem cells, and drug resistance. Here, we discuss the developments for the therapeutic targeting of mTOR signaling with improved anticancer efficacy for the benefit of cancer patients in clinics.

C5aR1 blockade reshapes immunosuppressive tumor microenvironment and synergizes with immune checkpoint blockade therapy in high-grade serous ovarian cancer

High-grade serous ovarian cancer (HGSC), with a modest response to immune checkpoint blockade (ICB) targeting PD-1/PD-L1 monotherapy, is densely infiltrated by M2-polarized tumor-associated macrophages (TAMs) and regulatory T (Treg) cells. The complement C5a/C5aR1 axis contributes to the programming of the immunosuppressive phenotype of TAMs in solid tumors and represents a promising immunomodulatory target for treating HGSCs. Here, we aimed to identify the relevance of C5aR1 in prognosis, immune microenvironment, and immunotherapy response in HGSCs. The expression and relationship of C5aR1 with tumor-infiltrating immune cells were assessed by immunohistochemistry and flow cytometry in the training cohort (n = 120) and fresh HGSC tissues (n = 36). Transcriptomic analyses of the xenografts delineated the mechanisms driving the immunomodulatory activity of PMX53, an orally bioavailable C5aR1 inhibitor. Therapeutic relevance was confirmed in ex vivo tumor cultures and The Cancer Genome Atlas (TCGA) datasets. C5aR1 expression independently predicted dismal prognosis and was linked to the immunoevasive subtype of HGSC, characterized by increased infiltration of pro-tumor cells (Treg cells, M2-polarized macrophages, and neutrophils) and impaired CD8+T functions. PMX53 antagonized subcutaneous tumor growth, modulated immunosuppressive mechanisms and synergized with aPD-1 in several tumor types. Single-cell RNA-seq analysis revealed predominant C5aR1 expression in TAMs, with an immunosuppressive-related expression signature in C5aR1+TAMs. Furthermore, the combination of C5aR1 and PD-L1 was associated with specific molecular characteristics and matched clinical response annotations. Therefore, the abundance of C5aR1 could predict an inferior prognosis in HGSCs, and incorporating PD-L1 may serve as a novel predictive biomarker to guide therapeutic options.

SFPQ and Its Isoform as Potential Biomarker for Non-Small-Cell Lung Cancer

Cancer markers are measurable molecules in the blood or tissue that are produced by tumor cells or immune cells in response to cancer progression. They play an important role in clinical diagnosis, prognosis, and anti-drug monitoring. Although DNA, RNA, and even physical images have been used, proteins continue to be the most common marker. There are currently no specific markers for lung cancer. Metastatic lung cancer, particularly non-small-cell lung cancer (NSCLC), is one of the most common causes of death. SFPQ, YY1, RTN4, RICTOR, LARP6, and HELLS are expressed at higher levels in cells from NSCLC than in control or cells from inflammatory diseases. SFPQ shows the most difference between the three cell types. Furthermore, the cytoplasmic isoform of SFPQ is only found in advanced cancers. We have developed ELISAs to detect SFPQ and the long and short isoforms. Evidence has shown that the short isoform exists primarily in cancers. Furthermore, immunocytometry studies and IHC analysis have revealed that SFPQ levels are consistent with ELISA results. In addition, enhanced DNA methylation in the SFPQ gene may facilitate the SFPQ expression differences between control and cancer cells. Considering this, elevated SFPQ level and the isoform location could serve as a cancer diagnostic and prognostic marker.

A Systematic Role of Metabolomics, Metabolic Pathways, and Chemical Metabolism in Lung Cancer

Lung cancer (LC) is considered as one of the leading causes of cancer-associated mortalities. Cancer cells' reprogrammed metabolism results in changes in metabolite concentrations, which can be utilized to identify a distinct metabolic pattern or fingerprint for cancer detection or diagnosis. By detecting different metabolic variations in the expression levels of LC patients, this will help and enhance early diagnosis methods as well as new treatment strategies. The majority of patients are identified at advanced stages after undergoing a number of surgical procedures or diagnostic testing, including the invasive procedures. This could be overcome by understanding the mechanism and function of differently regulated metabolites. Significant variations in the metabolites present in the different samples can be analyzed and used as early biomarkers. They could also be used to analyze the specific progression and type as well as stages of cancer type making it easier for the treatment process. The main aim of this review article is to focus on rewired metabolic pathways and the associated metabolite alterations that can be used as diagnostic and therapeutic targets in lung cancer diagnosis as well as treatment strategies.

Recent progress in targeted therapy for non-small cell lung cancer

The high morbidity and mortality of non-small cell lung cancer (NSCLC) have always been major threats to people's health. With the identification of carcinogenic drivers in non-small cell lung cancer and the clinical application of targeted drugs, the prognosis of non-small cell lung cancer patients has greatly improved. However, in a large number of non-small cell lung cancer cases, the carcinogenic driver is unknown. Identifying genetic alterations is critical for effective individualized therapy in NSCLC. Moreover, targeted drugs are difficult to apply in the clinic. Cancer drug resistance is an unavoidable obstacle limiting the efficacy and application of targeted drugs. This review describes the mechanisms of targeted-drug resistance and newly identified non-small cell lung cancer targets (e.g., KRAS G12C, NGRs, DDRs, CLIP1-LTK, PELP1, STK11/LKB1, NFE2L2/KEAP1, RICTOR, PTEN, RASGRF1, LINE-1, and SphK1). Research into these mechanisms and targets will drive individualized treatment of non-small cell lung cancer to generate better outcomes.

The RNA-binding protein AUF1 facilitates Akt phosphorylation at the membrane

Mammalian target of rapamycin (mTOR), which is part of mTOR complex 1 (mTORC1) and mTORC2, controls cellular metabolism in response to levels of nutrients and other growth signals. A hallmark of mTORC2 activation is the phosphorylation of Akt, which becomes upregulated in cancer. How mTORC2 modulates Akt phosphorylation remains poorly understood. Here, we found that the RNA-binding protein, AUF1 (ARE/poly(U)-binding/degradation factor 1), modulates mTORC2/Akt signaling. We determined that AUF1 is required for phosphorylation of Akt at Thr308, Thr450, and Ser473 and that AUF1 also mediates phosphorylation of the mTORC2-modulated metabolic enzyme glutamine fructose-6-phosphate amidotransferase 1 at Ser243. In addition, AUF1 immunoprecipitation followed by quantitative RT–PCR revealed that the mRNAs of Akt, glutamine fructose-6-phosphate amidotransferase 1, and the mTORC2 component SIN1 associate with AUF1. Furthermore, expression of the p40 and p45, but not the p37 or p42, isoforms of AUF1 specifically mediate Akt phosphorylation. In the absence of AUF1, subcellular fractionation indicated that Akt fails to localize to the membrane. However, ectopic expression of a membrane-targeted allele of Akt is sufficient to allow Akt-Ser473 phosphorylation despite AUF1 depletion. Finally, conditions that enhance mTORC2 signaling, such as acute glutamine withdrawal, augment AUF1 phosphorylation, whereas mTOR inhibition abolishes AUF1 phosphorylation. Our findings unravel a role for AUF1 in promoting membrane localization of Akt to facilitate its phosphorylation on this cellular compartment. Targeting AUF1 could have therapeutic benefit for cancers with upregulated mTORC2/Akt signaling.

mTOR-Mediated Regulation of Immune Responses in Cancer and Tumor Microenvironment

The mechanistic/mammalian target of rapamycin (mTOR) is a downstream mediator in the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways, which plays a pivotal role in regulating numerous cellular functions including cell growth, proliferation, survival, and metabolism by integrating a variety of extracellular and intracellular signals in the tumor microenvironment (TME). Dysregulation of the mTOR pathway is frequently reported in many types of human tumors, and targeting the PI3K/Akt/mTOR signaling pathway has been considered an attractive potential therapeutic target in cancer. The PI3K/Akt/mTOR signaling transduction pathway is important not only in the development and progression of cancers but also for its critical regulatory role in the tumor microenvironment. Immunologically, mTOR is emerging as a key regulator of immune responses. The mTOR signaling pathway plays an essential regulatory role in the differentiation and function of both innate and adaptive immune cells. Considering the central role of mTOR in metabolic and translational reprogramming, it can affect tumor-associated immune cells to undergo phenotypic and functional reprogramming in TME. The mTOR-mediated inflammatory response can also promote the recruitment of immune cells to TME, resulting in exerting the anti-tumor functions or promoting cancer cell growth, progression, and metastasis. Thus, deregulated mTOR signaling in cancer can modulate the TME, thereby affecting the tumor immune microenvironment. Here, we review the current knowledge regarding the crucial role of the PI3K/Akt/mTOR pathway in controlling and shaping the immune responses in TME.

The role of metabolic ecosystem in cancer progression — metabolic plasticity and mTOR hyperactivity in tumor tissues

Despite advancements in cancer management, tumor relapse and metastasis are associated with poor outcomes in many cancers. Over the past decade, oncogene-driven carcinogenesis, dysregulated cellular signaling networks, dynamic changes in the tissue microenvironment, epithelial-mesenchymal transitions, protein expression within regulatory pathways, and their part in tumor progression are described in several studies. However, the complexity of metabolic enzyme expression is considerably under evaluated. Alterations in cellular metabolism determine the individual phenotype and behavior of cells, which is a well-recognized hallmark of cancer progression, especially in the adaptation mechanisms underlying therapy resistance. In metabolic symbiosis, cells compete, communicate, and even feed each other, supervised by tumor cells. Metabolic reprogramming forms a unique fingerprint for each tumor tissue, depending on the cellular content and genetic, epigenetic, and microenvironmental alterations of the developing cancer. Based on its sensing and effector functions, the mechanistic target of rapamycin (mTOR) kinase is considered the master regulator of metabolic adaptation. Moreover, mTOR kinase hyperactivity is associated with poor prognosis in various tumor types. In situ metabolic phenotyping in recent studies highlights the importance of metabolic plasticity, mTOR hyperactivity, and their role in tumor progression. In this review, we update recent developments in metabolic phenotyping of the cancer ecosystem, metabolic symbiosis, and plasticity which could provide new research directions in tumor biology. In addition, we suggest pathomorphological and analytical studies relating to metabolic alterations, mTOR activity, and their associations which are necessary to improve understanding of tumor heterogeneity and expand the therapeutic management of cancer.

Nuclear Transport Factor 2 (NTF2) suppresses WM983B metastatic melanoma by modifying cell migration, metastasis, and gene expression

While changes in nuclear structure and organization are frequently observed in cancer cells, relatively little is known about how nuclear architecture impacts cancer progression and pathology. To begin to address this question, we studied Nuclear Transport Factor 2 (NTF2) because its levels decrease during melanoma progression. We show that increasing NTF2 expression in WM983B metastatic melanoma cells reduces cell proliferation and motility while increasing apoptosis. We also demonstrate that increasing NTF2 expression in these cells significantly inhibits metastasis and prolongs survival of mice. NTF2 levels affect the expression and nuclear positioning of a number of genes associated with cell proliferation and migration, and increasing NTF2 expression leads to changes in nuclear size, nuclear lamin A levels, and chromatin organization. Thus, ectopic expression of NTF2 in WM983B metastatic melanoma abrogates phenotypes associated with advanced stage cancer both in vitro and in vivo, concomitantly altering nuclear and chromatin structure and generating a gene expression profile with characteristics of primary melanoma. We propose that NTF2 is a melanoma tumor suppressor and could be a novel therapeutic target to improve health outcomes of melanoma patients.

DICER activates autophagy and promotes cisplatin resistance in non-small cell lung cancer by binding with let-7i-5p

OBJECTIVE

Drug resistance is the main obstacle in the treatment of non-small cell lung cancer (NSCLC). This study aimed to explore the mechanism of DICER in NSCLC resistance and its downstream signaling pathways.

METHODS

The A549 cisplatin (DDP)-resistant strain A549/DDP was established. A549/DDP cells were transfected with DICER- and let-7i-5p-related vectors, and treated with autophagy activator rapamycin. The cell viability and apoptosis were tested by CCK-8 assay and flow cytometry, respectively. The formation of autophagosomes was observed with a transmission electron microscopy. RT-qPCR and Western blot assay were conducted to detect expression levels of DICER, let-7i-5p, autophagy-related proteins, and the PI3K/AKT/mTOR pathway-related proteins. The dual luciferase reporter gene assay was implemented to confirm the targeted binding of DICER and let-7i-5p.

RESULTS

DICER was highly expressed in DDP-resistant NSCLC tissues and cells, and DICER could target and negatively regulate the expression of let-7i-5p. DDP treatment could inhibit the viability and promote cell apoptosis of A549/DDP cells. Downregulation of DICER in A549/DDP cells exhibited a decrease of cell viability, a decreased ratio of LC3-II/LC3-I and autophagosomes, together with an elevation of cell apoptosis rate and the phosphorylation levels of PI3K/AKT/mTOR. Treatment of rapamycin and let-7i-5p inhibitor reversed the effects of downregulated DICER in cell viability, ratio of LC3-II/LC3-I, autophagosomes, cell apoptosis rate and the phosphorylation levels of PI3K/AKT/mTOR in A549/DDP cells.

CONCLUSION

Our research suggests that DICER promotes autophagy and DDP resistance in NSCLC through downregulating let-7i-5p, and inhibits the activation of PI3K/AKT/mTOR pathway.

mTORC2-mediated direct phosphorylation regulates YAP activity promoting glioblastoma growth and invasive characteristics

The Hippo and mTOR signaling cascades are major regulators of cell growth and division. Aberrant regulation of these pathways has been demonstrated to contribute to gliomagenesis and result in enhanced glioblastoma proliferation and invasive characteristics. Several crosstalk mechanisms have been described between these two pathways, although a complete picture of these signaling interactions is lacking and is required for effective therapeutic targeting. Here we report the ability of mTORC2 to directly phosphorylate YAP at serine 436 (Ser436) positively regulating YAP activity. We show that mTORC2 activity enhances YAP transcriptional activity and the induction of YAP-dependent target gene expression while its ablation via genetic or pharmacological means has the opposite affects on YAP function. mTORC2 interacts with YAP via Sin1 and mutational analysis of serine 436 demonstrates that this phosphorylation event affects several properties of YAP leading to enhanced transactivation potential. Moreover, YAP serine 436 mutants display altered glioblastoma growth, migratory capacity and invasiveness both in vitro and in xenograft experiments. We further demonstrate that mTORC2 is able to regulate a Hippo pathway resistant allele of YAP suggesting that mTORC2 can regulate YAP independent of Hippo signaling. Correlative associations between the expression of these components in GBM patient samples also supported the presence of this signaling relationship. These results advance a direct mTORC2/YAP signaling axis driving GBM growth, motility and invasiveness.

The role of mTOR in age-related diseases

The ageing population is becoming a significant socio-economic issue. To address the expanding health gap, it is important to deepen our understanding of the mechanisms underlying ageing in various organisms at the single-cell level. The discovery of the antifungal, immunosuppressive, and anticancer drug rapamycin, which possesses the ability to extend the lifespan of several species, has prompted extensive research in the areas of cell metabolic regulation, development, and senescence. At the centre of this research is the mTOR pathway, with key roles in cell growth, proteosynthesis, ribosomal biogenesis, transcriptional regulation, glucose and lipid metabolism, and autophagy. Recently, it has become obvious that mTOR dysregulation is involved in several age-related diseases, such as cancer, neurodegenerative diseases, and type 2 diabetes mellitus. Additionally, mTOR hyperactivation affects the process of ageing per se. In this review, we provide an overview of recent insights into the mTOR signalling pathway, including its regulation and its influence on various hallmarks of ageing at the cellular level.

Attacking the PI3K/Akt/mTOR signaling pathway for targeted therapeutic treatment in human cancer

Cancer is the second leading cause of human death globally. PI3K/Akt/mTOR signaling is one of the most frequently dysregulated signaling pathways observed in cancer patients that plays crucial roles in promoting tumor initiation, progression and therapy responses. This is largely due to that PI3K/Akt/mTOR signaling is indispensable for many cellular biological processes, including cell growth, metastasis, survival, metabolism, and others. As such, small molecule inhibitors targeting major kinase components of the PI3K/Akt/mTOR signaling pathway have drawn extensive attention and been developed and evaluated in preclinical models and clinical trials. Targeting a single kinase component within this signaling usually causes growth arrest rather than apoptosis associated with toxicity-induced adverse effects in patients. Combination therapies including PI3K/Akt/mTOR inhibitors show improved patient response and clinical outcome, albeit developed resistance has been reported. In this review, we focus on revealing the mechanisms leading to the hyperactivation of PI3K/Akt/mTOR signaling in cancer and summarizing efforts for developing PI3K/Akt/mTOR inhibitors as either mono-therapy or combination therapy in different cancer settings. We hope that this review will facilitate further understanding of the regulatory mechanisms governing dysregulation of PI3K/Akt/mTOR oncogenic signaling in cancer and provide insights into possible future directions for targeted therapeutic regimen for cancer treatment, by developing new agents, drug delivery systems, or combination regimen to target the PI3K/Akt/mTOR signaling pathway. This information will also provide effective patient stratification strategy to improve the patient response and clinical outcome for cancer patients with deregulated PI3K/Akt/mTOR signaling.

mTORC2 regulates ribonucleotide reductase to promote DNA replication and gemcitabine resistance in non-small cell lung cancer

Ribonucleotide reductase (RNR) is the key enzyme that catalyzes the production of deoxyribonucleotides (dNTPs) for DNA replication and it is also essential for cancer cell proliferation. As the RNR inhibitor, Gemcitabine is widely used in cancer therapies, however, resistance limits its therapeutic efficacy and curative potential. Here, we identified that mTORC2 is a main driver of gemcitabine resistance in non-small cell lung cancers (NSCLC). Pharmacological or genetic inhibition of mTORC2 greatly enhanced gemcitabine induced cytotoxicity and DNA damage. Mechanistically, mTORC2 directly interacted and phosphorylated RNR large subunit RRM1 at Ser 631. Ser631 phosphorylation of RRM1 enhanced its interaction with small subunit RRM2 to maintain sufficient RNR enzymatic activity for efficient DNA replication. Targeting mTORC2 retarded DNA replication fork progression and improved therapeutic efficacy of gemcitabine in NSCLC xenograft model in vivo. Thus, these results identified a mechanism through mTORC2 regulating RNR activity and DNA replication, conferring gemcitabine resistance to cancer cells.

Targeting Signaling Pathway Networks in Several Malignant Tumors: Progresses and Challenges

Malignant tumors remain the health problem of highest concern among people worldwide due to its high mortality and recurrence. Lung, gastric, liver, colon, and breast cancers are among the top five malignant tumors in terms of morbidity and mortality. In cancer biology, aberrant signaling pathway regulation is a prevalent theme that drives the generation, metastasis, invasion, and other processes of all malignant tumors. The Wnt/β-catenin, PI3K/AKT/mTOR, Notch and NF-kB pathways are widely concerned and signal crosstalks exist in the five solid tumors. This review provides an innovative summary of the recent progress in research on these signaling pathways, the underlying mechanism of the molecules involved in these pathways, and the important role of some miRNAs in tumor-related signaling pathways. It also presents a brief review of the antitumor molecular drugs that target these signaling pathways. This review may provide a theoretical basis for the study of the molecular biological mechanism of malignant tumors and vital information for the development of new treatment strategies with a focus on efficacy and the reduction of side effects.

The Deubiquitinase USP39 Promotes ESCC Tumorigenesis Through Pre-mRNA Splicing of the mTORC2 Component Rictor

Spliceosomes are large RNA-protein molecular complexes which mediate splicing of pre-mRNA in eukaryotic cells. Their function is frequently altered in cancer, providing opportunities for novel therapeutic approaches. The ubiquitin specific protease 39 (USP39) is a highly conserved deubiquitylation family member that plays an essential role in pre-mRNA splicing where it serves to assemble the mature spliceosome complex. Previous studies have reported that USP39 acts in an oncogenic manner where it contributes to cancer progression and predicts poor prognosis in various human tumor types. Here we report that USP39 is differentially upregulated in human esophageal squamous cell carcinoma (ESCC) and its expression is significantly associated with clinicopathological characteristics including differentiation status and TNM stage. We found the USP39 upregulation was maintained in ESCC cell lines where it functioned to promote cancer cell growth in vitro and in xenografts. RNA-seq analyses identified that mTOR pathway activation was affected by shRNA-mediated silencing of USP39. Subsequent biochemical analyses demonstrated that USP39 regulates the activity of mTORC2 by selectively enhancing the splicing and maturation of Rictor mRNA, although not other key mTORC components. Together, our report proposes USP39 as a biomarker and oncogenic factor in ESCC, with a potential for targeting the USP39/mTOR2/Rictor axis as a therapeutic strategy. Furthermore, our study adds ESCC to the list of cancers where USP39 contributes to tumorigenesis and progression.

Rictor, an essential component of mTOR complex 2, undergoes caspase-mediated cleavage during apoptosis induced by multiple stimuli

Caspase-mediated cleavage of proteins ensures the irreversible commitment of cells to undergo apoptosis, and is thus a hallmark of apoptosis. Rapamycin-insensitive companion of mTOR (rictor) functions primarily as a core and essential component of mTOR complex 2 (mTORC2) to critically regulate cellular homeostasis. However, its role in the regulation of apoptosis is largely unknown. In the current study, we found that rictor was cleaved to generate two small fragments at ~ 50 kD and ~ 130 kD in cells undergoing apoptosis upon treatment with different stimuli such as the death ligand, TRAIL, and the small molecule, AZD9291. This cleavage was abolished when caspases were inhibited and could be reproduced when directly incubating rictor protein and caspase-3 in vitro. Furthermore, the cleavage site of caspase-3 on rictor was mapped at D1244 (VGVD). These findings together robustly demonstrate that rictor is a substrate of caspase-3 and undergoes cleavage during apoptosis. These results add new information for understanding the biology of rictor in the regulation of cell survival and growth.

Genomic Evolution in a Patient With Lung Adenocarcinoma With a Germline EGFR T790M Mutation

INTRODUCTION

A subset of lung adenocarcinomas (ADs) has been found to have somatic activating mutations in the tyrosine kinase domain of the EGFR gene, associated with response to EGFR tyrosine kinase inhibitor therapy. Rare germline mutations within this domain, including EGFR T790M, have been associated with genetic susceptibility to lung ADs. Using high-throughput sequencing, we elucidate the genomic evolution in tissues from a patient with lung AD carrying a germline EGFR T790M mutation.

METHODS

We performed microdissection, targeted panel, and whole-exome sequencing to molecularly characterize multiple foci of atypical adenomatous hyperplasia (AAH), in situ and invasive components of AD, normal lung tissue, and whole blood from the patient. Normal lung tissue was analyzed for potential acquired somatic genome alterations ("field effect").

RESULTS

All lesions harbored a secondary somatic EGFR mutation, either L858R or L861Q, in addition to the germline T790M mutation. Clear overlap was observed between the somatic profiles of in situ and invasive AD components, confirming clonal relatedness. AAH lesions shared few to no somatic alterations with the AD, suggesting clonal independence. No robust evidence of field effect was identified in the normal lung tissue.

CONCLUSIONS

Somatic EGFR mutations are early events in the pathogenesis of lung ADs arising in the context of germline EGFR T790M. Synchronous AAH lesions seem to be independent. Stepwise genomic evolution is observed in association with invasiveness of the neoplastic cell population.

Regulation and metabolic functions of mTORC1 and mTORC2

Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves cross talk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin, and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge of their cellular, tissue, as well as systemic functions in metabolism. Nevertheless, our knowledge of the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging, and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review discusses the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders, and aging.

Combating TKI resistance in CML by inhibiting the PI3K/Akt/mTOR pathway in combination with TKIs: a review

Chronic myeloid leukemia (CML), a myeloproliferative hematopoietic cancer, is caused by a genetic translocation between chromosomes 9 and 22. This translocation produces a small Philadelphia chromosome, which contains the Bcr-Abl oncogene. The Bcr-Abl oncogene encodes the BCR-ABL protein, upregulates various signaling pathways (JAK-STAT, MAPK/ERK, and PI3K/Akt/mTOR), and out of which the specifically highly active pathway is the PI3K/Akt/mTOR pathway. Among early treatments for CML, tyrosine kinase inhibitors (TKIs) were found to be the most effective, but drug resistance against kinase inhibitors led to the discovery of novel alternative therapies. At this point, the PI3K/Akt/mTOR pathway components became new targets due to stimulation of this pathway in TKIs-resistant CML patients. The current review article deals with reviewing the scientific literature on the PI3K/Akt/mTOR pathway inhibitors listed in the National Cancer Institute (NCI) drug dictionary and proved effective against multiple cancers. And out of those enlisted inhibitors, the US FDA has also approved some PI3K inhibitors (Idelalisib, Copanlisib, and Duvelisib) and mTOR inhibitors (Everolimus, Sirolimus, and Temsirolimus) for cancer therapy. So far, several inhibitors have been tested, and further investigations are still ongoing. Even in Imatinib, Nilotinib, and Ponatinib-resistant CML cells, a dual PI3K/mTOR inhibitor, BEZ235, showed antiproliferative activity. Therefore, by considering the literature data of these reviews and further examining some of the reported inhibitors, which proved effective against the PI3K/Akt/mTOR signaling pathway in multiple cancers, may improve the therapeutic approaches towards TKI-resistant CML cells where the respective signaling pathway gets upregulated.

RICTOR Amplification Promotes NSCLC Cell Proliferation through Formation and Activation of mTORC2 at the Expense of mTORC1

Non-small cell lung cancer (NSCLC) is characterized by genomic alterations, yet a targetable mutation has not been discovered in nearly half of all patients. Recent studies have identified amplification of RICTOR, an mTORC2-specific cofactor, as a novel actionable target in NSCLC. mTORC2 is one of two distinct mTOR complexes to sense environmental cues and regulate a variety of cellular processes, including cell growth, proliferation, and metabolism, all of which promote tumorigenesis when aberrantly regulated. Interestingly, other components of mTORC2 are not coamplified with RICTOR in human lung cancer, raising the question as to whether RICTOR amplification-induced changes are dependent on mTORC2 function. To model RICTOR amplification, we overexpressed Rictor using the Cas9 Synergistic Activation Mediator system. Overexpression of Rictor increased mTORC2 integrity and signaling, but at the expense of mTORC1, suggesting that overexpressed Rictor recruits common components away from mTORC1. Additionally, Rictor overexpression increases the proliferation and growth of NSCLC 3D cultures and tumors in vivo. Conversely, knockout of RICTOR leads to decreased mTORC2 formation and activity, but increased mTORC1 function. Because Rictor has mTOR-dependent and -independent functions, we also knocked out mLST8, a shared mTOR cofactor but is specifically required for mTORC2 function. Inducible loss of mLST8 in RICTOR-amplified NSCLC cells inhibited mTORC2 integrity and signaling, tumor cell proliferation, and tumor growth. Collectively, these data identify a mechanism for Rictor-driven tumor progression and provide further rationale for the development of an mTORC2-specific inhibitor. IMPLICATIONS: RICTOR amplification drives NSCLC proliferation through formation of mTORC2, suggesting mTORC2-specific inhibition could be a beneficial therapeutic option.

Developing the novel bioinformatics algorithms to systematically investigate the connections among survival time, key genes and proteins for Glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is one of the most common malignant brain tumors and its average survival time is less than 1 year after diagnosis.

RESULTS

Firstly, this study aims to develop the novel survival analysis algorithms to explore the key genes and proteins related to GBM. Then, we explore the significant correlation between AEBP1 upregulation and increased EGFR expression in primary glioma, and employ a glioma cell line LN229 to identify relevant proteins and molecular pathways through protein network analysis. Finally, we identify that AEBP1 exerts its tumor-promoting effects by mainly activating mTOR pathway in Glioma.

CONCLUSIONS

We summarize the whole process of the experiment and discuss how to expand our experiment in the future.

New Entrants into Clinical Trials for Targeted Therapy of Breast Cancer: An Insight

Breast cancer is too complex with various different molecular alterations involved in its pathogenesis and progression. Over the decade, we have seen a surge in the development of drugs for bimolecular targets and for the signal transduction pathways involved in the treatment line of breast cancer. These drugs, either alone or in combination with conventional treatments like chemotherapy, hormone therapy and radiotherapy, will help oncologists to get a better insight and do the needful treatment. These novel therapies bring various challenges along with them, which include the dosage selection, patient selection, schedule of treatment and weighing of clinical benefits over side effects. In this review, we highlight the recently studied target molecules that have received indications in breast carcinoma, both in the localized and in an advanced state and about their inhibitors which are in clinical development which can give the immense potential to clinical care in the near future.

Biomarker-driven phase 2 umbrella trial study for patients with recurrent small cell lung cancer failing platinum-based chemotherapy

BACKGROUND

A high percentage of small cell lung cancer (SCLC) cases harbor cell cycle-related gene mutations and RICTOR amplification. Based on underlying somatic mutations, the authors have conducted a phase 2 biomarker-driven, multiarm umbrella study.

METHODS

The SCLC Umbrella Korea StudiES (SUKSES) is an adaptive platform trial that undergoes continual modification according to the observed outcomes. This study included 286 patients with SCLC who failed platinum therapy and who had known genomic profiles based on a predesigned screening trial. Patients with MYC amplification or CDKN2A and TP53 co-alterations were allocated to adavosertib (SUKSES protocol C [SUKSES-C]; 7 patients) and those with RICTOR amplification were allocated to vistusertib (SUKSES-D; 4 patients). Alternatively, patients who were without any predefined biomarkers were assigned to a non-biomarker-selected arm: adavosertib (SUKSES-N1; 21 patients) or AZD2811NP (SUKSES-N3; 15 patients).

RESULTS

Patients in the SUKSES-C and SUKSES-N1 arms demonstrated no objective response. Three patients presented with stable disease (SD) in SUKSES-C and 6 patients in SUKSES-N1. The median progression-free survival (PFS) was 1.3 months (95% confidence interval, 0.9 months to not available) for SUKSES-C and 1.2 months (95% CI, 1.1-1.4 months) for SUKSES-N1. Patients in the SUKSES-D arm demonstrated no objective response and no SD, with a PFS of 1.2 months (95% CI, 1.0 months to not available). The SUKSES-N3 arm had 5 patients with SD and a PFS of 1.6 months (95% CI, 0.9-1.7 months), without an objective response. Grade≥3 adverse events (graded according to National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.03]) were observed as follows: 3.2% in the SUKSES-C and SUKSES-N1 arms and 50.0% in the SUKSES-D arm. Target-related neutropenia (grade≥3) was observed in approximately 60.0% of patients in the AZD2811NP arm using the current dosing schedule.

CONCLUSIONS

To the best of the authors' knowledge, the current study is the first biomarker-driven umbrella study conducted in patients with recurrent SCLC. Although the current study demonstrated the limited clinical efficacy of monotherapy, novel biomarker approaches using other cell cycle inhibitor(s) or combinations warrant further investigation.

RICTOR/mTORC2 affects tumorigenesis and therapeutic efficacy of mTOR inhibitors in esophageal squamous cell carcinoma

Dysregulation of mTORC1/mTORC2 pathway is observed in many cancers and mTORC1 inhibitors have been used clinically in many tumor types; however, the mechanism of mTORC2 in tumorigenesis is still obscure. Here, we mainly explored the potential role of mTORC2 in esophageal squamous cell carcinoma (ESCC) and its effects on the sensitivity of cells to mTOR inhibitors. We demonstrated that RICTOR, the key factor of mTORC2, and p-AKT (Ser473) were excessively activated in ESCC and their overexpression is related to lymph node metastasis and the tumor-node-metastasis (TNM) phase of ESCC patients. Furthermore, we found that mTORC1/ mTORC2 inhibitor PP242 exhibited more efficacious anti-proliferative effect on ESCC cells than mTORC1 inhibitor RAD001 due to RAD001-triggered feedback activation of AKT signal. Another, we demonstrated that down-regulating expression of RICTOR in ECa109 and EC9706 cells inhibited proliferation and migration as well as induced cell cycle arrest and apoptosis. Noteworthy, knocking-down stably RICTOR significantly suppresses RAD001-induced feedback activation of AKT/PRAS40 signaling, and enhances inhibition efficacy of PP242 on the phosphorylation of AKT and PRAS40, thus potentiates the antitumor effect of RAD001 and PP242 both in vitro and in vivo. Our findings highlight that selective targeting mTORC2 could be a promising therapeutic strategy for future treatment of ESCC.

Long-term survival with targeted therapy in an advanced non-small cell lung cancer patient based on genetic profiling

Non-small cell lung cancer (NSCLC) is a profoundly devastating disease that is the leading cause of cancer-related death worldwide. With the rapid development of next-generation sequencing (NGS), which has supplied the ability to decode tumors at the DNA level, so that targeted therapy plays a crucial role in improving NSCLC survival. We first reported a 32-year-old Chinese female patient received the ninth-line treatment, who was initially diagnosed with advanced NSCLC with EGFR 19 deletion. The patient had a satisfactory clinical response to initial gefitinib treatment. Subsequently, an EGFR T790M mutation was detected from plasma-derived circulating tumor DNA (ctDNA) by ddPCR after disease progression, while NGS did not. Osimertinib was still tried but had no therapeutic effect. Then the disease even progressed on the administration of chemotherapy and gefitinib in succession. Rebiopsy for NGS detection was performed, and gefitinib plus anlotinib/vemurafenib were tried. And then, gefitinib plus crizotinib were administrated for MET amplification after the third biopsy. Furthermore, chemotherapy combined with immunotherapy was performed due to the PD-L1 positive expression. Up to now, osimertinib treatment was undertaken to base on an EGFR exon 20 T790M mutation using NGS-based genotyping in cerebrospinal fluid (CSF) ctDNA. Tumor genome dynamic monitoring can identify tumor driving genes and drug resistance mechanisms to guide tumor treatment. This study found that the total survival time of advanced NSCLC patients was more than four years after chemoradiotherapy and targeted therapy, indicating the significance of dynamic monitoring of gene alterations for cancer treatment.

The role of RICTOR amplification in targeted therapy and drug resistance

The emergence of tyrosine kinase inhibitors (TKIs) has changed the current treatment paradigm and achieved good results in recent decades. However, an increasing number of studies have indicated that the complex network of receptor tyrosine kinase (RTK) co-activation could influence the characteristic phenotypes of cancer and the tumor response to targeted treatments. One of strategies to blocking RTK co-activation is targeting the downstream factors of RTK, such as PI3K-AKT-mTOR pathway. RICTOR, a core component of mTORC2, acts as a key effector molecule of the PI3K-AKT pathway; its amplification is often associated with poor clinical outcomes and resistance to TKIs. Here, we discuss the biology of RICTOR in tumor and the prospects of targeting RICTOR as a complementary therapy to inhibit RTK co-activation.

mTOR in Lung Neoplasms

With the discovery of rapamycin 45 years ago, studies in the mechanistic target of rapamycin (mTOR) field started 2 decades before the identification of the mTOR kinase. Over the years, studies revealed that the mTOR signaling is a master regulator of homeostasis and integrates a variety of environmental signals to regulate cell growth, proliferation, and metabolism. Deregulation of mTOR signaling, particularly hyperactivation, frequently occurs in human tumors. Recent advances in molecular profiling have identified mutations or amplification of certain genes coding proteins involved in the mTOR pathway (eg, PIK3CA, PTEN, STK11, and RICTOR) as the most common reasons contributing to mTOR hyperactivation. These genetic alterations of the mTOR pathway are frequently observed in lung neoplasms and may serve as a target for personalized therapy. mTOR inhibitor monotherapy has met limited clinical success so far; however, rational drug combinations are promising to improve efficacy and overcome acquired resistance. A better understanding of mTOR signaling may have the potential to help translation of mTOR pathway inhibitors into the clinical setting.

KPT-9274, an Inhibitor of PAK4 and NAMPT, Leads to Downregulation of mTORC2 in Triple Negative Breast Cancer Cells

Triple negative breast cancer (TNBC) is difficult to treat due to lack of druggable targets. We have found that treatment with the small molecule inhibitor KPT-9274 inhibits growth of TNBC cells and eventually leads to cell death. KPT-9274 is a dual specific inhibitor of PAK4 and Nicotinamide Phosphoribosyltransferase (NAMPT). The PAK4 protein kinase is often highly expressed in TNBC cells and has important roles in cell growth, survival, and migration. Previously we have found that inhibition of PAK4 leads to growth inhibition of TNBC cells both in vitro and in vivo. Likewise, NAMPT has been shown to be dysregulated in cancer due to its role in cell metabolism. In order to understand better how treating cells with KPT-9274 abrogates TNBC cell growth, we carried out an RNA sequencing of TNBC cells treated with KPT-9274. As a result, we identified Rictor as an important target that is inhibited in the KPT-9274 treated cells. Conversely, we found that Rictor is predicted to be activated when PAK4 is overexpressed in cells, which suggests a role for PAK4 in the regulation of Rictor. Rictor is a component of mTORC2, one of the complexes formed by the serine/threonine kinase mTOR. mTOR is important for the control of cell growth and metabolism. Our results suggest a new mechanism by which the KPT-9274 compound may block the growth of breast cancer cells, which is via inhibition of mTORC2 signaling. Consistent with this, sequencing analysis of PAK4 overexpressing cells indicates that PAK4 has a role in activation of the mTOR pathway.

Targeting mTOR and Metabolism in Cancer: Lessons and Innovations

Cancer cells support their growth and proliferation by reprogramming their metabolism in order to gain access to nutrients. Despite the heterogeneity in genetic mutations that lead to tumorigenesis, a common alteration in tumors occurs in pathways that upregulate nutrient acquisition. A central signaling pathway that controls metabolic processes is the mTOR pathway. The elucidation of the regulation and functions of mTOR can be traced to the discovery of the natural compound, rapamycin. Studies using rapamycin have unraveled the role of mTOR in the control of cell growth and metabolism. By sensing the intracellular nutrient status, mTOR orchestrates metabolic reprogramming by controlling nutrient uptake and flux through various metabolic pathways. The central role of mTOR in metabolic rewiring makes it a promising target for cancer therapy. Numerous clinical trials are ongoing to evaluate the efficacy of mTOR inhibition for cancer treatment. Rapamycin analogs have been approved to treat specific types of cancer. Since rapamycin does not fully inhibit mTOR activity, new compounds have been engineered to inhibit the catalytic activity of mTOR to more potently block its functions. Despite highly promising pre-clinical studies, early clinical trial results of these second generation mTOR inhibitors revealed increased toxicity and modest antitumor activity. The plasticity of metabolic processes and seemingly enormous capacity of malignant cells to salvage nutrients through various mechanisms make cancer therapy extremely challenging. Therefore, identifying metabolic vulnerabilities in different types of tumors would present opportunities for rational therapeutic strategies. Understanding how the different sources of nutrients are metabolized not just by the growing tumor but also by other cells from the microenvironment, in particular, immune cells, will also facilitate the design of more sophisticated and effective therapeutic regimen. In this review, we discuss the functions of mTOR in cancer metabolism that have been illuminated from pre-clinical studies. We then review key findings from clinical trials that target mTOR and the lessons we have learned from both pre-clinical and clinical studies that could provide insights on innovative therapeutic strategies, including immunotherapy to target mTOR signaling and the metabolic network in cancer.

Correlation between RICTOR overexpression and amplification in advanced solid tumors

Rapamycin-insensitive companion of mTOR (RICTOR) is a key component of mammalian target of rapamycin (mTOR) complex 2 (mTORC2), and promotes cellular proliferation and survival through the activation of downstream AGC kinase family members. The amplification of RICTOR has been proposed as a therapeutically relevant genomic alteration. However, other than next-generation sequencing, precise diagnostic methods to detect RICTOR amplification in advanced solid cancers have not been fully explored. We performed immunohistochemistry (IHC) analysis on solid tumor tissues from 435 cancer patients. Overexpression of RICTOR was found in 213 cases (49.0 %: 1+, 29.4 %; 2+, 15.2 %; 3+, 4.4 %) consisting of 111 colorectal cancers, 42 gastric cancers, 16 renal cell carcinomas, 8 soft tissue sarcomas, 6 hepatocellular carcinomas, 6 cholangiocarcinomas, 4 lung cancers, and 37 other tumors. RICTOR overexpression was heterogeneous (stained < 50 % of the tumor volume) in 32.4 % (12/37) of IHC-positive cases. We performed fluorescence in situ hybridization (FISH) in 37 RICTOR-overexpressed IHC-positive cases (1+, 12; 2+, 11; 3+, 14) and 13 IHC-negative solid tumors. FISH enabled us to detect RICTOR amplification in 7/12 (58.3 %) IHC 1+, 10/11 (90.9 %) IHC 2+, and 11/14 (78.6 %) IHC 3+ cases. In total, there was amplification in 75.7 % (n = 28) of the RICTOR-overexpressed cases, according to FISH. There was RICTOR amplification in only 7.7 % of the RICTOR IHC-negative cases. RICTOR amplification was significantly more common in IHC-positive cases than in IHC-negative cases (p < 0.0001). The IHC results correlated well with those of FISH (r = 0.60). RICTOR overexpression is more common in solid tumors than previously reported in cases detected by next-generation sequencing. This discrepancy may be caused by intratumoral heterogeneity. In conclusion, heterogeneous RICTOR overexpression is common in solid tumors and RICTOR IHC can be used as a screening tool to detect RICTOR amplification.

Unmasking the impact of Rictor in cancer: novel insights of mTORC2 complex

Genomic alterations affecting components of the mechanistic target of rapamycin (mTOR) pathway are found rather frequently in cancers, suggesting that aberrant pathway activity is implicated in oncogenesis of different tumor types. mTOR functions as the core catalytic kinase of two distinct complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), which control numerous vital cellular processes. There is growing evidence indicating that Rictor, an essential subunit of the mTORC2 complex, is inappropriately overexpressed across numerous cancer types and this is associated with poor survival. To date, the candidate mechanisms responsible for aberrant Rictor expression described in cancer are two: (i) gene amplification and (ii) epigenetic regulation, mainly by microRNAs. Moreover, different mTOR-independent Rictor-containing complexes with oncogenic role have been documented, revealing alternative routes of Rictor-driven tumorigenesis, but simultaneously, paving the way for identifying novel biomarkers and therapeutic targets. Here, we review the main preclinical and clinical data regarding the role of Rictor in carcinogenesis and metastatic behavior as well as the potentiality of its alteration as a target.

TKI-resistant ALK-rearranged lung adenocarcinoma with secondary CTNNB1 p.S45V and tertiary ALK p.I1171N mutations

Anaplastic lymphoma kinase (ALK)-rearranged non-small cell lung cancer (NSCLC) is an important molecular subgroup of tumors that are typically sensitive to tyrosine kinase inhibitors (TKIs). Although a substantial portion of patients benefit from TKIs, this approach is complicated by intrinsic and acquired resistance. We report a patient with ALK-rearranged NSCLC who showed an initial response to targeted therapy, but developed resistance to multiple TKIs. Serial comprehensive genomic profiling (CGP) was performed at four independent points during the clinical course. We review the pathology and clonal progression of the tumor, with CGP identifying a secondary CTNNB1 p.S45V mutation after the initiation of targeted therapy, followed by tertiary ALK p.I1171N. The presence of an alteration in a second oncogenic driver gene suggests a possible mechanism for resistance, and a secondary therapeutic target. Due to the involvement of Wnt signaling in the pathogenesis of many tumors and its association with immune evasion, a variety of therapeutic strategies are being developed to target this pathway. This case exemplifies the challenges of targeted therapeutics in the face of tumor progression, as well as the increasing role of genomics in understanding tumor biology.

Next generation sequencing of lung adenocarcinoma subtypes with intestinal differentiation reveals distinct molecular signatures associated with histomorphology and therapeutic options

OBJECTIVES

We aim to provide a better understanding of the molecular landscape of primary lung adenocarcinomas with intestinal differentiation.

MATERIAL AND METHODS

Five invasive mucinous adenocarcinomas (IMA) and seven pulmonary enteric adenocarcinomas (PEAD) were included in this study. Furthermore, we analyzed six pulmonary colloid adenocarcinomas (CAD), including one primary tumor, one metastasis, and two sample pairs consisting of the primary colloid lung tumor and a matching metastasis and an acinar component, respectively. All samples were characterized using immunohistochemistry (TTF-1, CK7, CK20, CDX2, Ki-67, ALK and PD-L1) and a next generation sequencing panel covering 404 cancer-related genes (FoundationOne® gene panel).

RESULTS AND CONCLUSION

While Ki-67 expression was comparably low in IMA (range: 8-15%) and in primary CAD (range: 5-8%), we observed considerably higher proliferation rates in the non-colloid tumor compartment (16%) and metastases (72%) from CAD, as well as in the PEAD-group (36-71%). The overall tumor mutational burden was lowest in IMA (2.5 mutations per megabase), intermediate in CAD (5.8 mutations per megabase) and highest in PEAD (16.8 mutations per megabase). KRAS mutations were frequent in all three tumor subtypes, but TP53 mutations were mostly limited to PEAD. While chromosomal alterations were rare in IMA, we discovered MYC amplifications in three of four CAD. Comparing primary and metastatic CAD, we observed the acquisition of multiple mutations and chromosomal alterations. PEAD had a variety of chromosomal alterations, including two cases with RICTOR amplification. PD-L1 expression (20%, 50% and 80% of tumor cells) was limited to three PEAD samples, only. In conclusion, we provide a detailed insight into the molecular alterations across and within the different subtypes of pulmonary adenocarcinomas with intestinal differentiation. From a clinical perspective, we provide data on potential treatment strategies for patients with PEAD, including immunotherapy.

Disruption of the RICTOR/mTORC2 complex enhances the response of head and neck squamous cell carcinoma cells to PI3K inhibition

Phosphoinositide 3-kinase (PI3K) is aberrantly activated in head and neck squamous cell carcinomas (HNSCC) and plays a pivotal role in tumorigenesis by driving Akt signaling, leading to cell survival and proliferation. Phosphorylation of Akt Thr308 by PI3K-PDK1 and Akt Ser473 by mammalian target of rapamycin complex 2 (mTORC2) activates Akt. Targeted inhibition of PI3K is a major area of preclinical and clinical investigation as it reduces Akt Thr308 phosphorylation, suppressing downstream mTORC1 activity. However, inhibition of mTORC1 releases feedback inhibition of mTORC2, resulting in a resurgence of Akt activation mediated by mTORC2. While the role of PI3K-activated Akt signaling is well established in HNSCC, the significance of mTORC2-driven Akt signaling has not been thoroughly examined. Here we explore the expression and function of mTORC2 and its obligate subunit RICTOR in HNSCC primary tumors and cell lines. We find RICTOR to be overexpressed in a subset of HNSCC tumors, including those with PIK3CA or EGFR gene amplifications. Whereas overexpression of RICTOR reduced susceptibility of HNSCC tumor cells to PI3K inhibition, genetic ablation of RICTOR using CRISPR/Cas9 sensitized cells to PI3K inhibition, as well as to EGFR inhibition and cisplatin treatment. Further, mTORC2 disruption led to reduced viability and colony forming abilities of HNSCC cells relative to their parental lines and induced loss of both activating Akt phosphorylation modifications (Thr308 and Ser473). Taken together, our findings establish RICTOR/mTORC2 as a critical oncogenic complex in HNSCC and rationalize the development of an mTORC2-specific inhibitor for use in HNSCC, either combined with agents already under investigation, or as an independent therapy.

Correlation between immunohistochemistry and RICTOR fluorescence in situ hybridization amplification in small cell lung carcinoma

Small cell lung carcinoma (SCLC) accounts for approximately 15% of all lung cancers and remains a challenging disease, with no significant improvement in the field of targeted therapies. The RICTOR gene (rapamycin-insensitive companion of mTOR [mammalian target of rapamycin]), which encodes a key structural (scaffold) protein of mTOR complex 2), has recently been identified as one of the most frequently amplified genes and a potential therapeutic target in SCLC. The aim of this study was to compare immunohistochemical (IHC) expression of Rictor and phospho-Akt (a downstream target of mTOR complex 2) with RICTOR amplification as detected by fluorescence in situ hybridization (FISH) in SCLC. RICTOR FISH and Rictor and phospho-Akt IHC staining were performed on 100 formalin-fixed, paraffin-embedded SCLC samples. RICTOR amplification was detected in 15 samples (15%). IHC positivity for Rictor and phospho-Akt was observed in 37 (37%) and 42 (42%) samples, respectively. Considering FISH as the diagnostic standard, the sensitivity and specificity of Rictor IHC were 93% and 73%, whereas the sensitivity and specificity of phospho-Akt IHC were 80% and 65%, respectively. Rictor expression was higher in distant metastases than in primary tumor samples and lymph node metastases. There was no association between RICTOR amplification and clinical outcome. However, high expression of either Rictor or phospho-Akt was associated with significantly decreased overall survival. In conclusion, IHC expression of Rictor correlates highly with RICTOR amplification. Therefore, Rictor IHC can be used as a cost-effective method to select patients for RICTOR FISH and, potentially, for mTORC1/2 inhibitor therapy.

Disruption of the Scaffolding Function of mLST8 Selectively Inhibits mTORC2 Assembly and Function and Suppresses mTORC2-Dependent Tumor Growth In Vivo

mTOR is a serine/threonine kinase that acts in two distinct complexes, mTORC1 and mTORC2, and is dysregulated in many diseases including cancer. mLST8 is a shared component of both mTORC1 and mTORC2, yet little is known regarding how mLST8 contributes to assembly and activity of the mTOR complexes. Here we assessed mLST8 loss in a panel of normal and cancer cells and observed little to no impact on assembly or activity of mTORC1. However, mLST8 loss blocked mTOR association with mTORC2 cofactors RICTOR and SIN1, thus abrogating mTORC2 activity. Similarly, a single pair of mutations on mLST8 with a corresponding mutation on mTOR interfered with mTORC2 assembly and activity without affecting mTORC1. We also discovered a direct interaction between mLST8 and the NH₂-terminal domain of the mTORC2 cofactor SIN1. In PTEN-null prostate cancer xenografts, mLST8 mutations disrupting the mTOR interaction motif inhibited AKT S473 phosphorylation and decreased tumor cell proliferation and tumor growth in vivo. Together, these data suggest that the scaffolding function of mLST8 is critical for assembly and activity of mTORC2, but not mTORC1, an observation that could enable therapeutic mTORC2-selective inhibition as a therapeutic strategy. SIGNIFICANCE: These findings show that mLST8 functions as a scaffold to maintain mTORC2 integrity and kinase activity, unveiling a new avenue for development of mTORC2-specific inhibitors.

A Novel mTORC1/2 Inhibitor (MTI-31) Inhibits Tumor Growth, Epithelial-Mesenchymal Transition, Metastases, and Improves Antitumor Immunity in Preclinical Models of Lung Cancer

PURPOSE

We aimed to investigate efficacy and mechanism of MTI-31 (LXI-15029), a novel mTORC1/mTORC2 inhibitor currently in human trial (NCT03125746), in non-small cell lung cancer (NSCLC) models of multiple driver mutations and tyrosine kinase inhibitor (TKI)-resistance.

EXPERIMENTAL DESIGN

Gene depletion, inhibitor treatment, immunological, flow cytometry, cellular, and animal studies were performed to determine in vitro and in vivo efficacy in NSCLC models of driver mutations and elucidate roles by mTOR complexes in regulating migration, epithelial-mesenchymal transition (EMT), metastasis, intracranial tumor growth, and immune-escape.

RESULTS

MTI-31 potently inhibited cell proliferation (IC₅₀ <1 μmol/L) and in vivo tumor growth in multiple NSCLC models of EGFR/T790M, EML4-ALK, c-Met, or KRAS (MED <10 mg/kg). In EGFR-mutant and/or EML4-ALK-driven NSCLC, MTI-31 or disruption of mTORC2 reduced cell migration, hematogenous metastasis to the lung, and abrogated morphological and functional traits of EMT. Disruption of mTORC2 inhibited EGFR/T790M-positive tumor growth in mouse brain and prolonged animal survival correlating a diminished tumor angiogenesis and recruitment of IBA1+ microglia/macrophages in tumor microenvironment. MTI-31 also suppressed programmed death ligand 1 (PD-L1) in EGFR- and ALK-driven NSCLC, mediated in part by mTORC2/AKT/GSK3β-dependent proteasomal degradation. Depletion of mTOR protein or disruption of mTOR complexes profoundly downregulated PD-L1 and alleviated apoptosis in Jurkat T and primary human T cells in a tumor-T cell coculture system.

CONCLUSIONS

Our results highlight mTOR as a multifaceted regulator of tumor growth, metastasis, and immune-escape in EGFR/ALK-mutant and TKI-resistant NSCLC cells. The newly characterized mechanisms mediated by the rapamycin-resistant mTORC2 warrant clinical investigation of mTORC1/mTORC2 inhibitors in patients with lung cancer.

mTOR Signaling in Cancer and mTOR Inhibitors in Solid Tumor Targeting Therapy

The mammalian or mechanistic target of rapamycin (mTOR) pathway plays a crucial role in regulation of cell survival, metabolism, growth and protein synthesis in response to upstream signals in both normal physiological and pathological conditions, especially in cancer. Aberrant mTOR signaling resulting from genetic alterations from different levels of the signal cascade is commonly observed in various types of cancers. Upon hyperactivation, mTOR signaling promotes cell proliferation and metabolism that contribute to tumor initiation and progression. In addition, mTOR also negatively regulates autophagy via different ways. We discuss mTOR signaling and its key upstream and downstream factors, the specific genetic changes in the mTOR pathway and the inhibitors of mTOR applied as therapeutic strategies in eight solid tumors. Although monotherapy and combination therapy with mTOR inhibitors have been extensively applied in preclinical and clinical trials in various cancer types, innovative therapies with better efficacy and less drug resistance are still in great need, and new biomarkers and deep sequencing technologies will facilitate these mTOR targeting drugs benefit the cancer patients in personalized therapy.

Mammals and Dictyostelium rictor mutations swapping reveals two essential Gly residues for mTORC2 activity and integrity

mTORC2 regulates a variety of vital cellular processes, and its aberrant functioning is often associated with various diseases. Rictor is a peculiar and distinguishing mTORC2 component playing a pivotal role in controlling its assembly and activity. Among living organisms Rictor is conserved from unicellular eukaryotes to metazoan. We replaced two distinct, but conserved, glycines in both the Dictyostelium piaA gene and its human ortholog, rictor. The two conserved residues are spaced by approximately 50 aminoacids and both are embedded within a conserved region falling in between the Ras-GEFN2 and Rictor_V domains. The effects of point mutations on the mTORC2 activity and integrity were assessed by biochemical and functional assays.In both cases, the reciprocal exchange between mammals and Dictyostelium rictor and piaA gene point mutations impaired mTORC2 activity and integrity.Our data indicate that the two Gly residues are essential for the maintenance of mTORC2 activity and integrity in organisms that appear to be distantly related, suggesting a primeval role in the assembly and proper TOR complex 2 functioning.

Concomitant targeting of the mTOR/MAPK pathways: novel therapeutic strategy in subsets of RICTOR/KRAS-altered non-small cell lung cancer

Despite a therapeutic paradigm shift into targeted-driven medicinal approaches, resistance to therapy remains a hallmark of lung cancer, driven by biological and molecular diversity. Using genomic and expression data from advanced non-small cell lung cancer (NSCLC) patients enrolled in the BATTLE-2 clinical trial, we identified RICTOR alterations in a subset of lung adenocarcinomas and found RICTOR expression to carry worse overall survival. RICTOR-altered cohort was significantly enriched in KRAS/MAPK axis mutations, suggesting a co-oncogenic driver role in these molecular settings. Using NSCLC cell lines, we showed that, distinctly in KRAS mutant backgrounds, RICTOR blockade impairs malignant properties and generates a compensatory enhanced activation of the MAPK pathway, exposing a unique therapeutic vulnerability. In vitro and in vivo concomitant pharmacologic inhibition of mTORC1/2 and MEK1/2 resulted in synergistic responses of anti-tumor effects. Our study provides evidence of a distinctive therapeutic opportunity in a subset of NSCLC carrying concomitant RICTOR/KRAS alterations.