Cell size reduction induced by inhibition of the mTOR/S6K-signaling pathway protects Jurkat cells from apoptosis

Synergic activity of FGFR2 and MEK inhibitors in the treatment of FGFR2-amplified cancers of unknown primary

Patients with cancer of unknown primary (CUP) carry the double burden of an aggressive disease and reduced access to therapies. Experimental models are pivotal for CUP biology investigation and drug testing. We derived two CUP cell lines (CUP#55 and #96) and corresponding patient-derived xenografts (PDXs), from ascites tumor cells. CUP cell lines and PDXs underwent histological, immune-phenotypical, molecular, and genomic characterization confirming the features of the original tumor. The tissue-of-origin prediction was obtained from the tumor microRNA expression profile and confirmed by single-cell transcriptomics. Genomic testing and fluorescence in situ hybridization analysis identified FGFR2 gene amplification in both models, in the form of homogeneously staining region (HSR) in CUP#55 and double minutes in CUP#96. FGFR2 was recognized as the main oncogenic driver and therapeutic target. FGFR2-targeting drug BGJ398 (infigratinib) in combination with the MEK inhibitor trametinib proved to be synergic and exceptionally active, both in vitro and in vivo. The effects of the combined treatment by single-cell gene expression analysis revealed a remarkable plasticity of tumor cells and the greater sensitivity of cells with epithelial phenotype. This study brings personalized therapy closer to CUP patients and provides the rationale for FGFR2 and MEK targeting in metastatic tumors with FGFR2 pathway activation.

Targeting metabolic adaptive responses induced by glucose starvation inhibits cell proliferation and enhances cell death in osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines

Osimertinib, a tyrosine kinase inhibitor targeting mutant EGFR, has received approval for initial treatment in patients with Non-Small Cell Lung Cancer (NSCLC). While effective in both first- and second-line treatments, patients eventually develop acquired resistance. Metabolic reprogramming represents a strategy through which cancer cells may resist and adapt to the selective pressure exerted by the drug. In the current study, we investigated the metabolic adaptations associated with osimertinib-resistance in NSCLC cells under low glucose culture conditions. We demonstrated that, unlike osimertinib-sensitive cells, osimertinib-resistant cells were able to survive under low glucose conditions by increasing the rate of glucose and glutamine uptake and by shifting towards mitochondrial metabolism. Inhibiting glucose/pyruvate contribution to mitochondrial respiration, glutamine deamination to glutamate, and oxidative phosphorylation decreased the proliferation and survival abilities of osimertinib-resistant cells to glucose starvation. Our findings underscore the remarkable adaptability of osimertinib-resistant NSCLC cells in a low glucose environment and highlight the pivotal role of mitochondrial metabolism in mediating this adaptation. Targeting the metabolic adaptive responses triggered by glucose shortage emerges as a promising strategy, effectively inhibiting cell proliferation and promoting cell death in osimertinib-resistant cells.

Eukaryotic cell size regulation and its implications for cellular function and dysfunction

Depending on cell type, environmental inputs, and disease, the cells in the human body can have widely different sizes. In recent years, it has become clear that cell size is a major regulator of cell function. However, we are only beginning to understand how the optimization of cell function determines a given cell's optimal size. Here, we review currently known size control strategies of eukaryotic cells and the intricate link of cell size to intracellular biomolecular scaling, organelle homeostasis, and cell cycle progression. We detail the cell size-dependent regulation of early development and the impact of cell size on cell differentiation. Given the importance of cell size for normal cellular physiology, cell size control must account for changing environmental conditions. We describe how cells sense environmental stimuli, such as nutrient availability, and accordingly adapt their size by regulating cell growth and cell cycle progression. Moreover, we discuss the correlation of pathological states with misregulation of cell size and how for a long time this was considered a downstream consequence of cellular dysfunction. We review newer studies that reveal a reversed causality, with misregulated cell size leading to pathophysiological phenotypes such as senescence and aging. In summary, we highlight the important roles of cell size in cellular function and dysfunction, which could have major implications for both diagnostics and treatment in the clinic.

Targeting glucosylceramide synthase induces antiproliferative and proapoptotic effects in osimertinib-resistant NSCLC cell models

The EGFR tyrosine kinase inhibitor osimertinib has been approved for the first-line treatment of EGFR-mutated Non-Small Cell Lung Cancer (NSCLC) patients. Despite its efficacy, patients develop resistance. Mechanisms of resistance are heterogeneous and not fully understood, and their characterization is essential to find new strategies to overcome resistance. Ceramides are well-known regulators of apoptosis and are converted into glucosylceramides (GlcCer) by glucosylceramide synthase (GCS). A higher content of GlcCers was observed in lung pleural effusions from NSCLC patients and their role in osimertinib-resistance has not been documented. The aim of this study was to determine the therapeutic potential of inhibiting GCS in NSCLC EGFR-mutant models resistant to osimertinib in vitro and in vivo. Lipidomic analysis showed a significant increase in the intracellular levels of glycosylceramides, including GlcCers in osimertinib resistant clones compared to sensitive cells. In resistant cells, the GCS inhibitor PDMP caused cell cycle arrest, inhibition of 2D and 3D cell proliferation, colony formation and migration capability, and apoptosis induction. The intratumoral injection of PDMP completely suppressed the growth of OR xenograft models. This study demonstrated that dysregulation of ceramide metabolism is involved in osimertinib-resistance and targeting GCS may be a promising therapeutic strategy for patients progressed to osimertinib.

A Photoactive Supramolecular Complex Targeting PD-L1 Reveals a Weak Correlation between Photoactivation Efficiency and Receptor Expression Levels in Non-Small-Cell Lung Cancer Tumor Models

Photo-immunotherapy uses antibodies conjugated to photosensitizers to produce nanostructured constructs endowed with targeting properties and photo-inactivation capabilities towards tumor cells. The superficial receptor density on cancer cells is considered a determining factor for the efficacy of the photodynamic treatment. In this work, we propose the use of a photoactive conjugate that consists of the clinical grade PD-L1-binding monoclonal antibody Atezolizumab, covalently linked to either the well-known photosensitizer eosin or the fluorescent probe Alexa647. Using single-molecule localization microscopy (direct stochastic optical reconstruction microscopy, dSTORM), and an anti-PD-L1 monoclonal antibody labelled with Alexa647, we quantified the density of PD-L1 receptors exposed on the cell surface in two human non-small-cell lung cancer lines (H322 and A549) expressing PD-L1 to a different level. We then investigated if this value correlates with the effectiveness of the photodynamic treatment. The photodynamic treatment of H322 and A549 with the photo-immunoconjugate demonstrated its potential for PDT treatments, but the efficacy did not correlate with the PD-L1 expression levels. Our results provide additional evidence that receptor density does not determine a priori the level of photo-induced cell death.

Intrinsic Resistance to Osimertinib in EGFR Mutated NSCLC Cell Lines Induced by Alteration in Cell-Cycle Regulators

BACKGROUND

Cell-cycle regulators are mutated in approximately 40% of all cancer types and have already been linked to worse outcomes in non-small cell lung cancer adenocarcinomas treated with osimertinib. However, their exact role in osimertinib resistance has not been elucidated.

OBJECTIVE

In this study, we aimed to evaluate how the CDK4/6-Rb axis may affect the sensitivity to osimertinib.

METHODS

We genetically increased the level of CCND1 (Cyclin D1) and reduced the levels of CDKN2A (p16) in two different adenocarcinoma cell lines, PC9 and HCC827. We also retrospectively evaluated the outcome of patients with epidermal growth factor receptor-mutated advanced non-small cell lung cancer depending on their level of Cyclin D1 and p16.

RESULTS

The modified clones showed higher proliferative capacity, modifications in cell-cycle phases, and higher migratory capacity than the parental cells. Cyclin D1-overexpressing clones were highly resistant to acute osimertinib treatment. CDKN2A knockdown conferred intrinsic resistance as well, although a longer time was required for adaption to the drug. In both cases, the resistant phenotype was epidermal growth factor receptor independent and associated with a higher level of Rb phosphorylation, which was unaffected by osimertinib treatment. Blocking the phosphorylation of Rb using abemaciclib, a CDK4/6 inhibitor, exerted an additive effect with osimertinib, increasing sensitivity to this drug and reverting the intrinsic resistant phenotype. In a group of 32 patients with epidermal growth factor receptor-mutated advanced non-small cell lung cancer, assessed for Cyclin D1 and p16 expression, we found that the p16-deleted group presented a lower overall response rate compared with the control group.

CONCLUSIONS

We conclude that perturbation in cell-cycle regulators leads to intrinsic osimertinib resistance and worse patient outcomes.

Microfluidics engineering towards personalized oncology-a review

Identifying and monitoring the presence of cancer metastasis and highlighting inter-and intratumoral heterogeneity is a central tenet of targeted precision oncology medicine (POM). This process of relocation of cancer cells is often referred to as the missing link between a tumor and metastasis. In recent years, microfluidic technologies have been developed to isolate a plethora of different biomarkers, such as circulating tumor cells (CTCs), tumor-derived vesicles (exosomes), or cell/free nucleic acids and proteins directly from patients' blood samples. With the advent of microfluidic developments, minimally invasive and quantitative assessment of different tumors is becoming a reality. This short review article will touch briefly on how microfluidics at early-stage achievements can be combined or developed with the active vs passive microfluidic technologies, depending on whether they utilize external fields and forces (active) or just microchannel geometry and inherent fluid forces (passive) from the market to precision oncology research and our future prospectives in terms of the emergence of ultralow cost and rapid prototyping of microfluidics in precision oncology.

Neurodevelopmental disorders, like cancer, are connected to impaired chromatin remodelers, PI3K/mTOR, and PAK1-regulated MAPK

Neurodevelopmental disorders (NDDs) and cancer share proteins, pathways, and mutations. Their clinical symptoms are different. However, individuals with NDDs have higher probabilities of eventually developing cancer. Here, we review the literature and ask how the shared features can lead to different medical conditions and why having an NDD first can increase the chances of malignancy. To explore these vital questions, we focus on dysregulated PI3K/mTOR, a major brain cell growth pathway in differentiation, and MAPK, a critical pathway in proliferation, a hallmark of cancer. Differentiation is governed by chromatin organization, making aberrant chromatin remodelers highly likely agents in NDDs. Dysregulated chromatin organization and accessibility influence the lineage of specific cell brain types at specific embryonic development stages. PAK1, with pivotal roles in brain development and in cancer, also regulates MAPK. We review, clarify, and connect dysregulated pathways with dysregulated proliferation and differentiation in cancer and NDDs and highlight PAK1 role in brain development and MAPK regulation. Exactly how PAK1 activation controls brain development, and why specific chromatin remodeler components, e.g., BAF170 encoded by SMARCC2 in autism, await clarification.

CDK4/6 Inhibition Enhances the Efficacy of Standard Chemotherapy Treatment in Malignant Pleural Mesothelioma Cells

BACKGROUND

The loss of the CDKN2A/ARF (cyclin-dependent kinase inhibitor 2A/alternative reading frame) gene is the most common alteration in malignant pleural mesothelioma (MPM), with an incidence of about 70%, thus representing a novel target for mesothelioma treatment. In the present study, we evaluated the antitumor potential of combining the standard chemotherapy regimen used for unresectable MPM with the CDK4/6 (cyclin-dependent kinase 4 or 6) inhibitor abemaciclib.

METHODS

Cell viability, cell death, senescence, and autophagy induction were evaluated in two MPM cell lines and in a primary MPM cell culture.

RESULTS

The simultaneous treatment of abemaciclib with cisplatin and pemetrexed showed a greater antiproliferative effect than chemotherapy alone, both in MPM cell lines and in primary cells. This combined treatment induced cellular senescence or autophagic cell death, depending on the cell type. More in detail, the induction of cellular senescence was related to the increased expression of p21, whereas autophagy induction was due to the impairment of the AKT/mTOR signaling. Notably, the effect of the combination was irreversible and no resumption in tumor cell proliferation was observed after drug withdrawal.

CONCLUSION

Our results demonstrated the therapeutic potential of CDK4/6 inhibitors in combination with chemotherapy for the treatment of MPM and are consistent with the recent positive results in the MiST2 arm in abemaciclib-treated patients.

Metabolic resistance to the inhibition of mitochondrial transcription revealed by CRISPR-Cas9 screen

Cancer cells depend on mitochondria to sustain their increased metabolic need and mitochondria therefore constitute possible targets for cancer treatment. We recently developed small-molecule inhibitors of mitochondrial transcription (IMTs) that selectively impair mitochondrial gene expression. IMTs have potent antitumor properties in vitro and in vivo, without affecting normal tissues. Because therapy-induced resistance is a major constraint to successful cancer therapy, we investigated mechanisms conferring resistance to IMTs. We employed a CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats)-(CRISP-associated protein 9) whole-genome screen to determine pathways conferring resistance to acute IMT1 treatment. Loss of genes belonging to von Hippel-Lindau (VHL) and mammalian target of rapamycin complex 1 (mTORC1) pathways caused resistance to acute IMT1 treatment and the relevance of these pathways was confirmed by chemical modulation. We also generated cells resistant to chronic IMT treatment to understand responses to persistent mitochondrial gene expression impairment. We report that IMT1-acquired resistance occurs through a compensatory increase of mitochondrial DNA (mtDNA) expression and cellular metabolites. We found that mitochondrial transcription factor A (TFAM) downregulation and inhibition of mitochondrial translation impaired survival of resistant cells. The identified susceptibility and resistance mechanisms to IMTs may be relevant for different types of mitochondria-targeted therapies.

Synaptic Release Potentiation at Aging Auditory Ribbon Synapses

Age-related hidden hearing loss is often described as a cochlear synaptopathy that results from a progressive degeneration of the inner hair cell (IHC) ribbon synapses. The functional changes occurring at these synapses during aging are not fully understood. Here, we characterized this aging process in IHCs of C57BL/6J mice, a strain which is known to carry a cadherin-23 mutation and experiences early hearing loss with age. These mice, while displaying a large increase in auditory brainstem thresholds due to 50% loss of IHC synaptic ribbons at middle age (postnatal day 365), paradoxically showed enhanced acoustic startle reflex suggesting a hyperacusis-like response. The auditory defect was associated with a large shrinkage of the IHCs' cell body and a drastic enlargement of their remaining presynaptic ribbons which were facing enlarged postsynaptic AMPAR clusters. Presynaptic Ca²⁺ microdomains and the capacity of IHCs to sustain high rates of exocytosis were largely increased, while on the contrary the expression of the fast-repolarizing BK channels, known to negatively control transmitter release, was decreased. This age-related synaptic plasticity in IHCs suggested a functional potentiation of synaptic transmission at the surviving synapses, a process that could partially compensate the decrease in synapse number and underlie hyperacusis.

Inhibition of Human Malignant Pleural Mesothelioma Growth by Mesenchymal Stromal Cells

BACKGROUND

Malignant Pleural Mesothelioma (MPM) is an aggressive tumor that has a significant incidence related to asbestos exposure with no effective therapy and poor prognosis. The role of mesenchymal stromal cells (MSCs) in cancer is controversial due to their opposite effects on tumor growth and in particular, only a few data are reported on MSCs and MPM.

METHODS

We investigated the in vitro efficacy of adipose tissue-derived MSCs, their lysates and secretome against different MPM cell lines. After large-scale production of MSCs in a bioreactor, their efficacy was also evaluated on a human MPM xenograft in mice.

RESULTS

MSCs, their lysate and secretome inhibited MPM cell proliferation in vitro with S or G0/G1 arrest of the cell cycle, respectively. MSC lysate induced cell death by apoptosis. The efficacy of MSC was confirmed in vivo by a significant inhibition of tumor growth, similar to that produced by systemic administration of paclitaxel. Interestingly, no tumor progression was observed after the last MSC treatment, while tumors started to grow again after stopping chemotherapeutic treatment.

CONCLUSIONS

These data demonstrated for the first time that MSCs, both through paracrine and cell-to-cell interaction mechanisms, induced a significant inhibition of human mesothelioma growth. Since the prognosis for MPM patients is poor and the options of care are limited to chemotherapy, MSCs could provide a potential new therapeutic approach for this malignancy.

Phase II Clinical Trial of Everolimus in a Pan-Cancer Cohort of Patients with mTOR Pathway Alterations

PURPOSE

This was a multicenter, histology-agnostic, single-arm prospective phase II trial of therapeutic activity of everolimus, an oral mTORC1 inhibitor, in patients with advanced solid tumors that harbored TSC1/TSC2 or MTOR mutations.

PATIENTS AND METHODS

Patients with tumors with inactivating TSC1/TSC2 or activating MTOR mutations identified in any Clinical Laboratory Improvement Amendments (CLIA)-certified laboratory were eligible. Patients were treated with everolimus 10 mg once daily until disease progression or unacceptable toxicity. The primary endpoint was objective response rate (ORR). Whole-exome sequencing was performed to identify co-occurring genomic alterations.

RESULTS

Between November 2015 and October 2018, 30 patients were enrolled at Dana-Farber Cancer Institute and Memorial Sloan Kettering Cancer Center. Tumors harbored TSC1 (13/30), TSC2 (15/30), concurrent TSC1 and TSC2 (1/30), or MTOR (1/30) mutations. The most common treatment-related adverse event of any grade was mucositis (8/30, 27%); 1 patient had fatal pneumonitis. Partial responses were seen in 2 patients [7%; 95% confidence interval (CI), 1%-22%]. Median progression-free survival was 2.3 months (95% CI, 1.8-3.7 months) and median overall survival (OS) was 7.3 months (95% CI, 4.5-12.7 months). There was no clear association between other genomic alterations and response. Of the 2 patients with objective response, 1 had upper tract urothelial carcinoma with biallelic inactivation of TSC1 and high tumor mutation burden, and the other had uterine carcinoma with biallelic TSC2-inactivating mutations and PEComa-like pathologic features.

CONCLUSIONS

Everolimus therapy had a disappointing ORR (7%) in this pan-cancer, mutation-selected, basket study.See related commentary by Kato and Cohen, p. 3807.

Alt-RPL36 downregulates the PI3K-AKT-mTOR signaling pathway by interacting with TMEM24

Thousands of human small and alternative open reading frames (smORFs and alt-ORFs, respectively) have recently been annotated. Many alt-ORFs are co-encoded with canonical proteins in multicistronic configurations, but few of their functions are known. Here, we report the detection of alt-RPL36, a protein co-encoded with human RPL36. Alt-RPL36 partially localizes to the endoplasmic reticulum, where it interacts with TMEM24, which transports the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) precursor phosphatidylinositol from the endoplasmic reticulum to the plasma membrane. Knock-out of alt-RPL36 increases plasma membrane PI(4,5)P₂ levels, upregulates PI3K-AKT-mTOR signaling, and increases cell size. Alt-RPL36 contains four phosphoserine residues, point mutations of which abolish interaction with TMEM24 and, consequently, alt-RPL36 effects on PI3K signaling and cell size. These results implicate alt-RPL36 as an upstream regulator of PI3K-AKT-mTOR signaling. More broadly, the RPL36 transcript encodes two sequence-independent polypeptides that co-regulate translation via different molecular mechanisms, expanding our knowledge of multicistronic human gene functions.

Many alternative ORFs are co-encoded with characterized proteins, but their function is often not understood. Here, the authors discover that ribosomal protein L36 is co-encoded with alternative protein, which they identify as an upstream regulator of PI3K-AKT-mTOR signaling.

Efficacy of the CDK4/6 Dual Inhibitor Abemaciclib in EGFR-Mutated NSCLC Cell Lines with Different Resistance Mechanisms to Osimertinib

Simple Summary

Osimertinib, a third-generation irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI), has shown marked clinical benefit for non-small cell lung cancer (NSCLC) patients with EGFR activating mutations. However, resistance to osimertinib inevitably develops and heterogeneous mechanisms of acquired resistance have been documented. Therefore, new strategies to bypass resistance are urgently needed. In this study, we investigated the potential activity of abemaciclib as second-line therapeutic approach after osimertinib progression and the effect of combining abemaciclib with osimertinib on the appearance of resistance in osimertinib-sensitive models.

Abstract

Abemaciclib is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6 that inhibits the transition from the G1 to the S phase of the cell cycle by blocking downstream CDK4/6-mediated phosphorylation of Rb. The effects of abemaciclib alone or combined with the third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) osimertinib were examined in a panel of PC9 and HCC827 osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines carrying EGFR-dependent or -independent mechanisms of intrinsic or acquired resistance. Differently from sensitive cells, all the resistant cell lines analyzed maintained p-Rb, which may be considered as a biomarker of osimertinib resistance and a potential target for therapeutic intervention. In these models, abemaciclib inhibited cell growth, spheroid formation, colony formation, and induced senescence, and its efficacy was not enhanced in the presence of osimertinib. Interestingly, in osimertinib sensitive PC9, PC9T790M, and H1975 cells the combination of abemaciclib with osimertinib significantly inhibited the onset of resistance in long-term experiments. Our findings provide a preclinical support for using abemaciclib to treat resistance in EGFR mutated NSCLC patients progressed to osimertinib either as single treatment or combined with osimertinib, and suggest the combination of osimertinib with abemaciclib as a potential approach to prevent or delay osimertinib resistance in first-line treatment.

CX3CR1 positively regulates BCR signaling coupled with cell metabolism via negatively controlling actin remodeling

As an important chemokine receptor, the role of CX3CR1 has been studied extensively on the migration of lymphocytes including T and B cells. Although CX3CR1+ B cells have immune suppressor properties, little is known about its role on the regulation of BCR signaling and B cell differentiation as well as the underlying molecular mechanism. We have used CX3CR1 KO mice to study the effect of CX3CR1 deficiency on BCR signaling and B cell differentiation. Interestingly, we found that proximal BCR signaling, such as the activation of CD19, BTK and SHIP was reduced in CX3CR1 KO B cells upon antigenic stimulation. However, the activation of mTORC signaling was enhanced. Mechanistically, we found that the reduced BCR signaling in CX3CR1 KO B cells was due to reduced BCR clustering, which is caused by the enhanced actin accumulation by the plasma membrane via increased activation of WASP. This caused an increased differentiation of MZ B cells in CX3CR1 KO mice and an enhanced generation of plasma cells (PC) and antibodies. Our study shows that CX3CR1 regulates BCR signaling via actin remodeling and affects B cell differentiation and the humoral immune response.

Acquired BRAF G469A Mutation as a Resistance Mechanism to First-Line Osimertinib Treatment in NSCLC Cell Lines Harboring an EGFR Exon 19 Deletion

BACKGROUND

Osimertinib is a new third-generation, epidermal growth factor receptor-tyrosine kinase inhibitor highly selective for the epidermal growth factor receptor with both activating and T790M mutations. A recent phase III trial showed a statistically significant progression-free survival benefit with osimertinib vs. gefitinib or erlotinib as first-line treatment for EGFR-mutated non-small cell lung cancer, and preliminary data are available on resistance mechanisms to first-line osimertinib therapy.

OBJECTIVE

The objective of this study was to examine potential in vitro mechanisms of acquired resistance to osimertinib in a cell model carrying an EGFR exon 19 deletion.

METHODS

PC9 cells were cultured in the presence of increasing concentrations of osimertinib (ranging from 10 to 500 nM) to generate resistant cells. Three clones resistant to osimertinib (half maximal inhibitory concentration > 1 μM) were isolated, genotyped by next-generation sequencing and tested for drug sensitivity. Cell proliferation and migration, cell death, and signaling transduction pathways were analyzed.

RESULTS

Our study revealed that all the three resistant clones developed acquired resistance via the BRAF G469A mutation maintaining a constitutive activation of the ERK pathway. Stable transfection of PC9 and HCC827 cells with a plasmid containing BRAF G469A rendered the cells resistant to osimertinib. Treatment with selumetinib and trametinib, but not dabrafenib, restored the sensitivity to osimertinib and enhanced cell death in the resistant clones with the BRAF G469A mutation.

CONCLUSIONS

Our in vitro studies revealed the BRAF G469A-activating mutation as a potential mechanism of acquired resistance to first-line osimertinib treatment, and provide a strategy of intervention to overcome this mechanism of resistance.

Pre-treatment with the CDK4/6 inhibitor palbociclib improves the efficacy of paclitaxel in TNBC cells

Triple Negative Breast Cancer (TNBC) is a challenging disease due to the lack of druggable targets; therefore, chemotherapy remains the standard of care and the identification of new targets is a high clinical priority. Alterations in the components of the cell cycle machinery have been frequently reported in cancer; given the success obtained with the CDK4/6 inhibitor palbocicib in ER-positive BC, we explored the potential of combining this drug with chemotherapy in Rb-positive TNBC cell models. The simultaneous combination of palbociclib with paclitaxel exerted an antagonistic effect; by contrast, the sequential treatment inhibited cell proliferation and increased cell death more efficaciously than single treatments. By down-regulating the E2F target c-myc, palbociclib reduced HIF-1α and GLUT-1 expression, and hence glucose uptake and consumption both under normoxic and hypoxic conditions. Importantly, these inhibitory effects on glucose metabolism were enhanced by palbociclib/paclitaxel sequential combination; the superior efficacy of such combination was ascribed to the ability of paclitaxel to inhibit palbociclib-mediated induction of AKT and to further down-regulate the Rb/E2F/c-myc signaling. Our results suggest that the efficacy of standard chemotherapy can be significantly improved by a pre-treatment with palbociclib, thus offering a better therapeutic option for Rb-proficient TNBC.

Effects of Neddylation and mTOR Inhibition in Acute Myelogenous Leukemia

Acute myelogenous leukemia (AML) is a heterogeneous disease and often relapses after standard chemotherapy. Recently, the neddylation (NEDD8) and the mammalian target of rapamycin (mTOR) signaling pathways have emerged as promising pharmaceutical targets for AML therapy. However, the interaction of these two pathways remains unclear. Here we evaluated the effects of pevonedistat, an inhibitor of the NEDD8 activating enzyme (NAE), and sapanisertib (TAK-228), an inhibitor of mTORC1 and mTORC2 as single agents or in combination on AML cell lines. We found that inhibition of neddylation with pevonedistat partially inhibited mTOR signaling transduction and vice versa, inhibition of mTOR signaling with sapanisertib partially inhibited neddylation in AML cell lines. Pevonedistat alone was able to induce cytotoxicity in most AML cell lines as well as in primary AML, whereas sapanisertib alone decreased cell metabolic activity, reduced cell size and arrested cells in G0 phase with only minimal induction of cell death. In addition, pevonedistat was able to induce cell differentiation, arrest cells in G2/M cell cycle phases, and induce DNA re-replication and damage. However, co-treatment with sapanisertib suppressed pevonedistat induced apoptosis, differentiation, S/G2/M arrest, and DNA damage. Taken together, our data demonstrate that pevonedistat and sapanisertib exhibit distinct anti-tumor effects on AML cells, i.e. cytotoxic and cytostatic effects, respectively; however, sapanisertib can attenuate pevonedistat-induced cellular responses in AML cells. Understanding mTOR and neddylation pathway interaction could provide therapeutic strategies for treatment of AML and other malignancies.

Long non-coding RNA DLEU1 exerts an oncogenic function in non-small cell lung cancer

OBJECTIVE

To explore the role of long non-coding RNA DLEU1 in the tumorigenesis and progression of non-small cell lung cancer (NSCLC) and the underlying mechanisms.

METHODS

The expression of DLEU1 in NSCLC tumor tissues and adjacent normal tissues was evaluated using bioinformatics analysis and qPCR. The effects of DLEU1 overexpression or deficiency on cell proliferation, apoptosis, migration and invasion were explored experimentally. Additionally, the impact of DLEU1 up-regulation on tumourigenesis was also assessed in vivo.

RESULTS

The expression of DLEU1 was up-regulated in NSCLC tumor tissues. DLEU1 overexpression promoted the proliferation, migration, and invasion, but inhibited the apoptosis of NSCLC cells by upregulating CDK1 expression, binding with SRC and altering the expression of P70(S6K), MMP2 and E-cadherin. Besides, xenograft tumors in nude mice demonstrated that DLEU1 overexpression accelerated tumor growth.

CONCLUSIONS

DLEU1 promoted tumorigenesis and progression of NSCLC, and might be a promising therapeutic target for NSCLC.

Bufadienolides from Venenum Bufonis Inhibit mTOR-Mediated Cyclin D1 and Retinoblastoma Protein Leading to Arrest of Cell Cycle in Cancer Cells

Objective

Bufadienolides, the main components in Venenum Bufonis secreted from toads, have been proved to be with significant anticancer activity aside from the positive inotropic action as cardenolides. Here an underlying anticancer mechanism was further elucidated for an injection made from Venenum Bufonis containing nine bufadienolides.

Methods

One solution reagent and cell cycle analyses were for determining effect of bufadienolides on cancer cells. Western blotting was used for protein expression.

Results

Bufadienolides inhibit cell proliferation and arrest cells in G1 phase. Bufadienolides also inhibit the mammalian target of rapamycin (mTOR) signaling pathway, which is evidenced by the data that bufadienolides inhibit type I insulin-like growth factor- (IGF-1-) activated phosphorylation of mTOR by a concentration- and time-dependent way, as well as phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1). Subsequent results indicated that cyclin D1 expression and phosphorylation of retinoblastoma protein (Rb)—two characterized regulators in cell cycle of G1—are also inhibited and the process is dependent on mTOR pathway.

Conclusion

Bufadienolides inhibit proliferation partially due to arresting cell cycle in G1 phase, which is mediated by inhibiting mTOR-cyclin D1/Rb signal pathway.

The anti-tumor efficacy of CDK4/6 inhibition is enhanced by the combination with PI3K/AKT/mTOR inhibitors through impairment of glucose metabolism in TNBC cells

Background

Cell cycle regulators have gain attention as potential targets for anticancer therapy. Palbociclib is a selective inhibitor of the cyclin-dependent kinases 4 and 6 (CDK4/6), which coordinate the G1-S transition. Palbociclib is currently approved for the treatment of hormone receptor positive, HER2-negative advanced breast cancer (BC) in association with letrozole or fulvestrant. In contrast, its efficacy in triple negative BC (TNBC), either alone or in combined therapies, has not been fully investigated to date.

Methods

Here we evaluated the potential of combining palbociclib with PI3K/mTOR inhibitors in Rb-proficient TNBC cells comparing different schedules of treatment: simultaneous, sequential, or sequential combined treatment (pre-incubation with palbociclib followed by exposure to both palbociclib and PI3K/mTOR inhibitors). We assessed the effects on cell proliferation, cell death, and cell cycle distribution, and looked at the impact of such treatments on glucose metabolism.

Results

Palbociclib exerted cytostatic effects in Rb-positive TNBC cells, inducing a reversible blockade in G0/G1 cell cycle phase associated with down-regulation of CDK6, Rb, and c-myc expression and/or activity. Palbociclib treatment induced AKT signaling, providing a rationale for its combination with PI3K/mTOR inhibitors. The simultaneous or sequential treatment resulted in an additive inhibition of cell proliferation. On the other hand, the sequential combined treatment in which palbociclib was maintained also during exposure to PI3K/mTOR inhibitors gave rise to synergistic anti-proliferative and pro-apoptotic effects, by inhibiting both CDK4/6/Rb/myc and PI3K/mTOR signaling. Interestingly, the inhibition of the Rb/E2F/myc axis mediated by palbociclib resulted in a significant down-regulation of glucose metabolism; most importantly, these inhibitory effects were enhanced by the combination of palbociclib with BYL719 (specific inhibitor of the p110α PI3K-subunit), which promoted a stronger inhibition of GLUT-1 glucose transporter expression, glucose uptake and consumption in comparison with individual treatments, under both normoxic and hypoxic conditions.

Conclusions

Combination of palbociclib with PI3K/mTOR inhibitors may represent a promising therapeutic option for the treatment of Rb-proficient TNBC, with the sequential combined schedule showing a superior efficacy over the other schedules. In addition our results demonstrate that the impairment of glucose metabolism may contribute to the anti-tumor activity of such drug combinations.

A novel, integrated in vitro carcinogenicity test to identify genotoxic and non-genotoxic carcinogens using human lymphoblastoid cells

Human exposure to carcinogens occurs via a plethora of environmental sources, with 70-90% of cancers caused by extrinsic factors. Aberrant phenotypes induced by such carcinogenic agents may provide universal biomarkers for cancer causation. Both current in vitro genotoxicity tests and the animal-testing paradigm in human cancer risk assessment fail to accurately represent and predict whether a chemical causes human carcinogenesis. The study aimed to establish whether the integrated analysis of multiple cellular endpoints related to the Hallmarks of Cancer could advance in vitro carcinogenicity assessment. Human lymphoblastoid cells (TK6, MCL-5) were treated for either 4 or 23 h with 8 known in vivo carcinogens, with doses up to 50% Relative Population Doubling (maximum 66.6 mM). The adverse effects of carcinogens on wide-ranging aspects of cellular health were quantified using several approaches; these included chromosome damage, cell signalling, cell morphology, cell-cycle dynamics and bioenergetic perturbations. Cell morphology and gene expression alterations proved particularly sensitive for environmental carcinogen identification. Composite scores for the carcinogens' adverse effects revealed that this approach could identify both DNA-reactive and non-DNA reactive carcinogens in vitro. The richer datasets generated proved that the holistic evaluation of integrated phenotypic alterations is valuable for effective in vitro risk assessment, while also supporting animal test replacement. Crucially, the study offers valuable insights into the mechanisms of human carcinogenesis resulting from exposure to chemicals that humans are likely to encounter in their environment. Such an understanding of cancer induction via environmental agents is essential for cancer prevention.

Modulation of sestrin confers protection to Cr(VI) induced neuronal cell death in Drosophila melanogaster

Increased oxidative stress is one of the major causes of hexavalent chromium [Cr(VI)], a heavy metal with diverse applications and environmental presence, induced neuronal adversities in exposed organism including Drosophila. Sestrin (sesn), an oxidative stress responsive gene, emerges as a novel player in the management of oxidative stress response. It is reported to be regulated by Target of rapamycin (TOR) and the former regulates autophagy and plays an important role in the prevention of neurodegeneration. Due to limited information regarding the role of sesn in chemical induced cellular adversities, it was hypothesized that modulation of sesn may improve the Cr(VI) induced neuronal adversities in Drosophila. Upon exposure of Cr(VI) (5.0-20.0 μg/ml) to D. melanogaster larvae (w¹¹¹⁸; background control), neuronal cell death was observed at 20.0 μg/ml of Cr(VI) concentration which was found to be reversed by targeted sesn overexpression (Elav-GAL4>UAS-sesn) in those cells of exposed organism by the induction of autophagy concomitant with decreased reactive oxygen species (ROS) level, p-Foxo-, p-JNK- and p-Akt-levels with decreased apoptosis. Conversely, after sesn knockdown (Elav-GAL4>UAS-sesn^RNAi) in neuronal cells, they become more vulnerable to oxidative stress and apoptosis. Furthermore, knockdown of sesn in neuronal cells of exposed organism resulted in decreased autophagy with increased TOR and p-S6k levels while overexpression of sesn led to their decreased levels suggestive of decreased anabolic and increased catabolic activity in neuronal cells shifting energy towards the augmentation of cellular repair. Taken together, the study suggests therapeutic implications of sesn against chemical induced neuronal adversities in an organism.

Combined Inhibition of CDK4/6 and PI3K/AKT/mTOR Pathways Induces a Synergistic Anti-Tumor Effect in Malignant Pleural Mesothelioma Cells

Malignant pleural mesothelioma (MPM) is a progressive malignancy associated to the exposure of asbestos fibers. The most frequently inactivated tumor suppressor gene in MPM is CDKN2A/ARF, encoding for the cell cycle inhibitors p16^INK4a and p14^ARF, deleted in about 70% of MPM cases. Considering the high frequency of alterations of this gene, we tested in MPM cells the efficacy of palbociclib (PD-0332991), a highly selective inhibitor of cyclin-dependent kinase (CDK) 4/6. The analyses were performed on a panel of MPM cell lines and on two primary culture cells from pleural effusion of patients with MPM. All the MPM cell lines, as well as the primary cultures, were sensitive to palbociclib with a significant blockade in G0/G1 phase of the cell cycle and with the acquisition of a senescent phenotype. Palbociclib reduced the phosphorylation levels of CDK6 and Rb, the expression of myc with a concomitant increased phosphorylation of AKT. Based on these results, we tested the efficacy of the combination of palbociclib with the PI3K inhibitors NVP-BEZ235 or NVP-BYL719. After palbociclib treatment, the sequential association with PI3K inhibitors synergistically hampered cell proliferation and strongly increased the percentage of senescent cells. In addition, AKT activation was repressed while p53 and p21 were up-regulated. Interestingly, two cycles of sequential drug administration produced irreversible growth arrest and senescent phenotype that were maintained even after drug withdrawal. These findings suggest that the sequential association of palbociclib with PI3K inhibitors may represent a valuable therapeutic option for the treatment of MPM.

Cannabidiol Reduces Leukemic Cell Size - But Is It Important?

The anti-cancer effect of the plant-derived cannabinoid, cannabidiol, has been widely demonstrated both in vivo and in vitro. However, this body of preclinical work has not been translated into clinical use. Key issues around this failure can be related to narrow dose effects, the cell model used and incomplete efficacy. A model of acute lymphoblastic disease, the Jurkat T cell line, has been used extensively to study the cannabinoid system in the immune system and cannabinoid-induced apoptosis. Using these cells, this study sought to investigate the outcome of those remaining viable cells post-treatment with cannabidiol, both in terms of cell size and tracking any subsequent recovery. The phosphorylation status of the mammalian Target of Rapamycin (mTOR) signaling pathway and the downstream target ribosomal protein S6, were measured. The ability of cannabidiol to exert its effect on cell viability was also evaluated in physiological oxygen conditions. Cannabidiol reduced cell viability incompletely, and slowed the cell cycle with fewer cells in the G2/M phase of the cell cycle. Cannabidiol reduced phosphorylation of mTOR, PKB and S6 pathways related to survival and cell size. The remaining population of viable cells that were cultured in nutrient rich conditions post-treatment were able to proliferate, but did not recover to control cell numbers. However, the proportion of viable cells that were gated as small, increased in response to cannabidiol and normally sized cells decreased. This proportion of small cells persisted in the recovery period and did not return to basal levels. Finally, cells grown in 12% oxygen (physiological normoxia) were more resistant to cannabidiol. In conclusion, these results indicate that cannabidiol causes a reduction in cell size, which persists post-treatment. However, resistance to cannabidiol under physiological normoxia for these cells would imply that cannabidiol may not be useful in the clinic as an anti-leukemic agent.

Modified STAP conditions facilitate bivalent fate decision between pluripotency and apoptosis in Jurkat T-lymphocytes

Low extracellular pH (pHe) is not only the result of cancer metabolism, but a factor of anti-cancer drug efficacy and cancer immunity. In this study, the consequences of acidic stress were evaluated by applying STAP protocol on Jurkat T-lymphocytes (2.0 × 10(6) cells/ml, 25 min in 37 °C). We detected apoptotic process exclusively in pH 3.3 treated cells within 8 h with western blotting (WB). This programmed cell death led to significant drop of cell viability in 72 h measured by MTT assay resulting PI positive population on flow cytometry (FCM) at day 7. Quantified RT-PCR (qRT-PCR) data indicated that all of above mentioned responses are irrelevant to expression of OCT4 gene variants. Interestingly enough, pluripotent cells represented by positive alkaline phosphatase (AP) staining survived acidic stress and consequently proportion of AP positive cells was significantly increased after pH 3.3 treatment (day 7). In general, acidic treatment led to an apoptotic condition for Jurkat T-lymphocytes, which occurred independent of OCT4 induction.

Loss of GSK-3 Causes Abnormal Astrogenesis and Behavior in Mice

Altered activity of glycogen synthase kinase-3 (GSK-3) is associated with psychiatric diseases and neurodegenerative diseases. GSK-3 is a key regulator in multiple aspects of neuronal differentiation in the brain. However, little is known about the role of GSK-3 in astrocyte development. To examine the role of GSK-3 in astrocytes, we generated a conditional knockout mouse using a glial fibrillary acidic protein (GFAP)-cre driver, in which the GSK-3 alpha and beta genes are deleted in astrocytes. We found that GFAP-cre-mediated GSK-3 deletion led to a larger brain. The number and size of astrocytes were increased in GSK-3 mutant brains. The levels of GFAP and phospho-STAT3, indicators of astrogenesis, were elevated in GSK-3 mutants. Furthermore, we found upregulation of astrocyte regulatory molecules such as phospho-AKT, phospho-S6, and cyclin D in GSK-3 mutant brains. Finally, GSK-3 mutant mice exhibited aberrant anxiety and social behavior. Our results suggest that GSK-3 plays a significant role in astrocyte development and behavioral control in mice.

Gefitinib inhibits invasive phenotype and epithelial-mesenchymal transition in drug-resistant NSCLC cells with MET amplification

Despite the initial response, all patients with epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) eventually develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs). The EGFR-T790M secondary mutation is responsible for half of acquired resistance cases, while MET amplification has been associated with acquired resistance in about 5-15% of NSCLCs. Clinical findings indicate the retained addiction of resistant tumors on EGFR signaling. Therefore, we evaluated the molecular mechanisms supporting the therapeutic potential of gefitinib maintenance in the HCC827 GR5 NSCLC cell line harbouring MET amplification as acquired resistance mechanism. We demonstrated that resistant cells can proliferate and survive regardless of the presence of gefitinib, whereas the absence of the drug significantly enhanced cell migration and invasion. Moreover, the continuous exposure to gefitinib prevented the epithelial-mesenchymal transition (EMT) with increased E-cadherin expression and down-regulation of vimentin and N-cadherin. Importantly, the inhibition of cellular migration was correlated with the suppression of EGFR-dependent Src, STAT5 and p38 signaling as assessed by a specific kinase array, western blot analysis and silencing functional studies. On the contrary, the lack of effect of gefitinib on EGFR phosphorylation in the H1975 cells (EGFR-T790M) correlated with the absence of effects on cell migration and invasion. In conclusion, our findings suggest that certain EGFR-mutated patients may still benefit from a second-line therapy including gefitinib based on the specific mechanism underlying tumor cell resistance.

Effects of sorafenib on energy metabolism in breast cancer cells: role of AMPK-mTORC1 signaling

In this study, we investigated the effects and the underlying molecular mechanisms of the multi-kinase inhibitor sorafenib in a panel of breast cancer cell lines. Sorafenib inhibited cell proliferation and induced apoptosis through the mitochondrial pathway. These effects were neither correlated with modulation of MAPK and AKT pathways nor dependent on the ERα status. Sorafenib promoted an early perturbation of mitochondrial function, inducing a deep depolarization of mitochondrial membrane, associated with drop of intracellular ATP levels and increase of ROS generation. As a response to this stress condition, the energy sensor AMPK was rapidly activated in all the cell lines analyzed. In MCF-7 and SKBR3 cells, AMPK enhanced glucose uptake by up-regulating the expression of GLUT-1 glucose transporter, as also demonstrated by AMPKα1 RNA interference, and stimulated aerobic glycolysis thus increasing lactate production. Moreover, the GLUT-1 inhibitor fasentin blocked sorafenib-induced glucose uptake and potentiated its cytotoxic activity in SKBR3 cells. Persistent activation of AMPK by sorafenib finally led to the impairment of glucose metabolism both in MCF-7 and SKBR3 cells as well as in the highly glycolytic MDA-MB-231 cells, resulting in cell death. This previously unrecognized long-term effect of sorafenib was mediated by AMPK-dependent inhibition of the mTORC1 pathway. Suppression of mTORC1 activity was sufficient for sorafenib to hinder glucose utilization in breast cancer cells, as demonstrated by the observation that the mTORC1 inhibitor rapamycin induced a comparable down-regulation of GLUT-1 expression and glucose uptake. The key role of AMPK-dependent inhibition of mTORC1 in sorafenib mechanisms of action was confirmed by AMPKα1 silencing, which restored mTORC1 activity conferring a significant protection from cell death. This study provides insights into the molecular mechanisms driving sorafenib anti-tumoral activity in breast cancer, and supports the need for going on with clinical trials aimed at proving the efficacy of sorafenib for breast cancer treatment.

Everolimus and mTOR inhibition in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors are rare and the majority of patients present in the advanced stage. Over the past few decades, treatment for patients with metastatic well- or moderately differentiated pancreatic neuroendocrine tumors have not significantly impeded tumor progression nor improved survival. However, recent mapping of intracellular signaling pathways promoting tumor proliferation, growth, and angiogenesis has presented mammalian target of rapamycin (mTOR) as a potential target within the phosphatidylinositol 3-kinase-Akt pathway. With the development of the new-generation mTOR inhibitor everolimus, a series of clinical trials over the last 5 years have demonstrated significant benefit in delaying tumor progression. This review focuses on the mechanism of mTOR inhibition and traces the development of clinical evidence for the use of mTOR inhibitors in well- to moderately differentiated advanced pancreatic neuroendocrine tumors.

Regulation of the glutamate transporter EAAT3 by mammalian target of rapamycin mTOR

The serine/threonine kinase mammalian target of rapamycin (mTOR) is stimulated by insulin, growth factors and nutrients and confers survival of several cell types. The kinase has previously been shown to stimulate amino acid uptake. In neurons, the cellular uptake of glutamate by the excitatory amino-acid transporters (EAATs) decreases excitation and thus confers protection against excitotoxicity. In epithelia, EAAT3 accomplishes transepithelial glutamate and aspartate transport. The present study explored, whether mTOR regulates EAAT3 (SLC1A1). To this end, cRNA encoding EAAT3 was injected into Xenopus oocytes with or without cRNA encoding mTOR and the glutamate induced current (I(glu)), a measure of glutamate transport, determined by dual electrode voltage clamp. Moreover, EAAT3 protein abundance was determined utilizing chemiluminescence. As a result, I(glu) was observed in Xenopus oocytes expressing EAAT3 but not in water injected oocytes. Coexpression of mTOR significantly increased I(glu), an effect reversed by rapamycin (100 nM). mTOR coexpression increased EAAT3 protein abundance in the cell membrane. The decay of I(glu) following inhibition of carrier insertion with brefeldin A in oocytes coexpressing EAAT3 with mTOR was similar in the presence and absence of rapamycin (100 nM). In conclusion, mTOR is a novel powerful regulator of EAAT3 and may thus contribute to protection against neuroexcitotoxicity.

TOR signaling regulates planarian stem cells and controls localized and organismal growth

Target of Rapamycin (TOR) controls an evolutionarily conserved signaling pathway that modulates cellular growth and division by sensing levels of nutrients, energy and stress. As such, TOR signaling is a crucial component of tissues and organs that translates systemic signals into cellular behavior. The ubiquitous nature of TOR signaling, together with the difficulty of analyzing tissue during cellular turnover and repair, have limited our understanding of how this kinase operates throughout the body. Here, we use the planarian model system to address TOR regulation at the organismal level. The planarian TOR homolog (Smed-TOR) is ubiquitously expressed, including stem cells (neoblasts) and differentiated tissues. Inhibition of TOR with RNA interference severely restricts cell proliferation, allowing the study of neoblasts with restricted proliferative capacity during regeneration and systemic cell turnover. Strikingly, TOR signaling is required for neoblast response to amputation and localized growth (blastema). However, in the absence of TOR signaling, regeneration takes place only within differentiated tissues. In addition, TOR is essential for maintaining the balance between cell division and cell death, and its dysfunction leads to tissue degeneration and lack of organismal growth in the presence of nutrients. Finally, TOR function is likely to be mediated through TOR Complex 1 as its disruption recapitulates signs of the TOR phenotype. Our data reveal novel roles for TOR signaling in controlling adult stem cells at a systemic level and suggest a new paradigm for studying TOR function during physiological turnover and regeneration.

Understanding PLZF: two transcriptional targets, REDD1 and smooth muscle α-actin, define new questions in growth control, senescence, self-renewal and tumor suppression

PLZF can function as a transcriptional activator or as a transcriptional repressor. Recent studies have identified two direct transcriptional targets of PLZF, REDD1 and smooth muscle α-actin. REDD1 is activated by PLZF. It mediates the PLZF-dependent downregulation of TORC1 and is responsible for the maintenance of pluripotency in cultures of spermatogonial progenitor cells. This activity may extend to other stem-like cell types. The effect of REDD1 on TORC1 also raises the possibility that REDD1 controls cell growth, tumorigenicity and senescence. The regulatory loop extending from PLZF via REDD1 to TORC1 identifies REDD1 as a critical determinant of TOR activity. The transcription of smooth muscle α-actin is repressed by PLZF. In fibroblasts, this downregulation is accompanied by a change of cell shape and a dramatic reorganization of the cytoskeleton. It is also correlated with the acquisition of cellular resistance to oncogenic transformation. The resistance is selective, it works against some oncoproteins but not against others. The molecular mechanisms underlying the changes in the cytoskeleton and in the susceptibility to oncogenic transformation are unknown. However these changes are dependent on the activity of RAS and thus probably involve the RAC/RHO family of proteins.

Perifosine and CCI 779 co-operate to induce cell death and decrease proliferation in PTEN-intact and PTEN-deficient PDGF-driven murine glioblastoma

Background

Platelet derived growth factor receptor (PDGFR) activity is deregulated in human GBM due to amplification and rearrangement of the PDGFR-alpha gene locus or overexpression of the PDGF ligand, resulting in the activation of downstream kinases such as phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR). Aberrant PDGFR signaling is observed in approximately 25-30% of human GBMs, which are frequently molecularly classified as the proneural subclass. It would be valuable to understand how PDGFR driven GBMs respond to Akt and mTOR inhibition.

Methodology/Principal Findings

Using genetically engineered PTEN-intact and PTEN-deficient PDGF-driven mouse models of GBM that closely mimic the histology and genetics of the human PDGF subgroup, we investigated the effect of inhibiting Akt and mTOR alone or in combination in vitro and in vivo. We used perifosine and CCI-779 to inhibit Akt and mTOR, respectively. Here, we show in vitro data demonstrating that the most effective inhibition of Akt and mTOR activity in both PTEN-intact and PTEN-null primary glioma cell cultures is obtained when using both inhibitors in combination. We next investigated if the effects we observed in culture could be duplicated in vivo by treating mice with gliomas for 5 days. The in vivo treatments with the combination of CCI-779 and perifosine resulted in decreased Akt and mTOR signaling, which correlated to decreased proliferation and increased cell death independent of PTEN status, as monitored by immunoblot analysis, histology and MRI.

Conclusions/Significance

These findings underline the importance of simultaneously targeting Akt and mTOR to achieve significant down-regulation of the PI3K pathway and support the rationale for testing the perifosine and CCI-779 combination in the human PDGF-subgroup of GBM.

Inhibition of voltage-gated K+ channels in dendritic cells by rapamycin

Rapamycin, an inhibitor of the serine/threonine kinase mammalian target of rapamycin (mTOR), is a widely used immunosuppressive drug. Rapamycin affects the function of dendritic cells (DCs), antigen-presenting cells participating in the initiation of primary immune responses and the establishment of immunological memory. Voltage-gated K(+) (Kv) channels are expressed in and impact on the function of DCs. The present study explored whether rapamycin influences Kv channels in DCs. To this end, DCs were isolated from murine bone marrow and ion channel activity was determined by whole cell patch clamp. To more directly analyze an effect of mTOR on Kv channel activity, Kv1.3 and Kv1.5 were expressed in Xenopus oocytes with or without the additional expression of mTOR and voltage-gated currents were determined by dual-electrode voltage clamp. As a result, preincubation with rapamycin (0-50 nM) led to a gradual decline of Kv currents in DCs, reaching statistical significance within 6 h and 50 nM of rapamycin. Rapamycin accelerated Kv channel inactivation. Coexpression of mTOR upregulated Kv1.3 and Kv1.5 currents in Xenopus oocytes. Furthermore, mTOR accelerated Kv1.3 channel activation and slowed down Kv1.3 channel inactivation. In conclusion, mTOR stimulates Kv channels, an effect contributing to the immunomodulating properties of rapamycin in DCs.

Enhanced production and isotope enrichment of recombinant glycoproteins produced in cultured mammalian cells

NMR studies of post-translationally modified proteins are complicated by the lack of an efficient method to produce isotope enriched recombinant proteins in cultured mammalian cells. We show that reducing the glucose concentration and substituting glutamate for glutamine in serum-free medium increased cell viability while simultaneously increasing recombinant protein yield and the enrichment of non-essential amino acids compared to culture in unmodified, serum-free medium. Adding dichloroacetate, a pyruvate dehydrogenase kinase inhibitor, further improves cell viability, recombinant protein yield, and isotope enrichment. We demonstrate the method by producing partially enriched recombinant Thy1 glycoprotein from Lec1 Chinese hamster ovary (CHO) cells using U-¹³C-glucose and ¹⁵N-glutamate as labeled precursors. This study suggests that uniformly ¹⁵N,¹³C-labeled recombinant proteins may be produced in cultured mammalian cells starting from a mixture of labeled essential amino acids, glucose, and glutamate.

Hypoxia-inducible factors--regulation, role and comparative aspects in tumourigenesis

Hypoxia-inducible factors (HIFs) play a key role in the cellular response experienced in hypoxic tumours, mediating adaptive responses that allow hypoxic cells to survive in the hostile environment. Identification and understanding of tumour hypoxia and the influence on cellular processes carries important prognostic information and may help identify potential hypoxia circumventing and targeting strategies. This review summarizes current knowledge on HIF regulation and function in tumour cells and discusses the aspects of using companion animals as comparative spontaneous cancer models. Spontaneous tumours in companion animals hold a great research potential for the evaluation and understanding of tumour hypoxia and in the development of hypoxia-targeting therapeutics.

Low dietary inorganic phosphate stimulates lung tumorigenesis through altering protein translation and cell cycle in K-ras(LA1) mice

Recent surveys indicate that Pi intake has increased steadily as Pi-containing foods have increased. Our previous study demonstrated that high dietary Pi strongly stimulated lung tumorigeneis. In order to answer the issue whether low Pi may be chemopreventive, we examined the effects of low Pi on lung cancer. Eighteen 5-wk-old male K-ras(LA1) lung cancer model mice were randomly allocated to 2 groups. One group was fed a normal diet (0.5% Pi) and other group was fed low Pi (0.1% Pi) diet for 4 wk. Lung cancer development was evaluated by histopathological examination, Western blot, kinase assay, and immunohistochemistry. Low Pi increased the expression of sodium-dependent phosphate co-transporter 2b, and activated Akt signal with decreased PTEN expression in the lungs of K-ras(LA1) mice. Low Pi increased the Akt/mTOR-mediated protein translation through upregulating the phosphorylation of p70S6K and 4E-BP1. In addition, low Pi stimulated cell cycling as evidenced by altered cell cycle regulators such as cyclin D1 and D3. Finally, low Pi increased lung tumorigenesis in K-ras(LA1) mice compared to the normal diet group. Our results clearly demonstrated that low Pi also promoted lung tumorigenesis, thus suggesting that an appropriate intake of dietary Pi may be critical for lung cancer prevention as well as treatment.

The BH3-mimetic ABT-737 targets the apoptotic machinery in cholangiocarcinoma cell lines resulting in synergistic interactions with zoledronic acid

PURPOSE

In TFK-1 and EGI-1 cholangiocarcinoma cell lines, zoledronic acid (ZOL) determines an S-phase block without apoptosis. Here, we investigated the occurrence of apoptosis stigmata when ZOL is associated to the BH3-mimetic ABT-737.

METHODS

In EGI-1 and TFK-1 cholangiocarcinoma cell lines untreated or treated with ABT-737 alone or in combination with ZOL, the pro-survival protein's pattern (BCL-2, BCL-XL, MCL-1, HSP72, HSP27) was investigated by biochemical criteria along with the occurrence of mitochondrial damage evaluated by cytofluorimetric analysis using a cationic dye.

RESULTS

ABT-737 induced growth inhibition and significantly affected the colony-forming ability of both EGI-1 and TFK-1 cells. However, activated PARP-1 or/and caspase-3 cleavage (apoptosis markers) were detected only at the highest ABT-737 concentrations used. Combined treatment showed synergistic effect by converting the predominant cytostatic effect of ZOL into a cytotoxic one as shown by striking increment of mitochondrial harmed cells along with PARP-1 activation and caspase-3 cleavage.

CONCLUSION

The lack of apoptosis following ZOL treatment in these cholangiocarcinoma cell lines appears to be multifactorial and could be ascribed to the large constitutive expression of pro-survival proteins. The efficacy of ZOL treatment requires a concomitant unleashing of apoptosis using a selective BH3-mimetic as ABT-737. The rational targeting of specific components of the apoptotic pathway may appear a useful approach to improve the treatment of refractory or relapsed cholangiocarcinoma. Combined treatment could be further explored in in vivo tumor model of cholangiocarcinoma.

Rapamycin-induced phosphaturia

BACKGROUND

The mammalian target of rapamycin (mTOR) is known to stimulate a variety of transport mechanisms including the intestinal phosphate transporter NaPi-IIb. The present study was performed to elucidate whether mTOR similarly regulates the major renal tubular phosphate transporter NaPi-IIa.

METHODS

To this end, NaPi-IIa was expressed in Xenopus oocytes with or without mTOR and phosphate transport estimated from phosphate-induced (1 mM) current (I(pi)).

RESULTS

As a result, I(pi) was observed in NaPi-IIa-expressing but not in H(2)O-injected Xenopus oocytes. Co-expression of mTOR significantly enhanced I(pi) in NaPi-IIa-expressing Xenopus oocytes, an effect abrogated by treatment with rapamycin (50 nM for the last 24 h of incubation). In a second series of experiments, the effect of rapamycin was analysed in mice. The in vivo administration of rapamycin (3 microg/g body weight/day) for 3 days resulted in phosphaturia in mice despite a tendency of plasma phosphate concentration to decrease.

CONCLUSIONS

mTOR contributes to the regulation of renal phosphate transport, and rapamycin thus influences phosphate balance.

Inhibition of mTORC1 activity by REDD1 induction in myeloma cells resistant to bortezomib cytotoxicity

The combination of bortezomib and dexamethasone is becoming the reference induction treatment for multiple myeloma patients younger than 65 years. Despite its advantage over vincristin adryamicin dexamethasone induction treatment, bortezomib does not benefit all patients. We hypothesize that heterogeneity of the response experienced by myeloma patients is, at least in part, due to genomic variations in the malignant plasma cells. To test this hypothesis we used gene expression profiling to identify early responsive genes induced by bortezomib in resistant myeloma cells. Our study revealed: (i) a dramatic induction of REDD1, a negative regulator of mammalian target of rapamycin kinase complex 1 (mTORC1) activity, in these cells; (ii) a transient cell size decrease associated with REDD1 overexpression; and (iii) partial restoration of bortezomib sensitivity in REDD1 knockdown bortezomib-resistant myeloma cells. Together, these results identify a possible novel mechanism of bortezomib resistance in myeloma patients mediated by REDD1 overexpression involving inhibition of mTORC1 activity and suggest that the use of mammalian target of rapamycin inhibitors in myeloma patients could be deleterious.

Synergistic activity of letrozole and sorafenib on breast cancer cells

Estrogens induce breast tumor cell proliferation by directly regulating gene expression via the estrogen receptor (ER) transcriptional activity and by affecting growth factor signaling pathways such as mitogen-activated protein kinase (MAPK) and AKT/mammalian target of rapamycin Complex1 (mTORC1) cascades. In this study we demonstrated the preclinical therapeutic efficacy of combining the aromatase inhibitor letrozole with the multi-kinase inhibitor sorafenib in aromatase-expressing breast cancer cell lines. Treatment with letrozole reduced testosterone-driven cell proliferation, by inhibiting the synthesis of estrogens. Sorafenib inhibited cell proliferation in a concentration-dependent manner; this effect was not dependent on sorafenib-mediated inhibition of Raf1, but involved the down-regulation of mTORC1 and its targets p70S6K and 4E-binding protein 1 (4E-BP1). At concentrations of 5-10 μM the growth-inhibitory effect of sorafenib was associated with the induction of apoptosis, as indicated by release of cytochrome c and Apoptosis-Inducing Factor into the cytosol, activation of caspase-9 and caspase-7, and PARP-1 cleavage. Combination of letrozole and sorafenib produced a synergistic inhibition of cell proliferation associated with an enhanced accumulation of cells in the G(0)/G(1) phase of the cell cycle and with a down-regulation of the cell cycle regulatory proteins c-myc, cyclin D1, and phospho-Rb. In addition, longer experiments (12 weeks) demonstrated that sorafenib may be effective in preventing the acquisition of resistance towards letrozole. Together, these results indicate that combination of letrozole and sorafenib might constitute a promising approach to the treatment of hormone-dependent breast cancer.

Pulse mTOR inhibitor treatment effectively controls cyst growth but leads to severe parenchymal and glomerular hypertrophy in rat polycystic kidney disease

The efficacy of mammalian target of rapamycin (mTOR) inhibitors is currently tested in patients affected by autosomal dominant polycystic kidney disease. Treatment with mTOR inhibitors has been associated with numerous side effects. However, the renal-specific effect of mTOR inhibitor treatment cessation in polycystic kidney disease is currently unknown. Therefore, we compared pulse and continuous everolimus treatment in Han:SPRD rats. Four-week-old male heterozygous polycystic and wild-type rats were administered everolimus or vehicle by gavage feeding for 5 wk, followed by 7 wk without treatment, or continuously for 12 wk. Cessation of everolimus did not result in the appearance of renal cysts up to 7 wk postwithdrawal despite the reemergence of S6 kinase activity coupled with an overall increase in cell proliferation. Pulse everolimus treatment resulted in striking noncystic renal parenchymal enlargement and glomerular hypertrophy that was not associated with compromised kidney function. Both treatment regimens ameliorated kidney function, preserved the glomerular-tubular connection, and reduced proteinuria. Pulse treatment at an early age delays cyst development but leads to striking glomerular and parenchymal hypertrophy. Our data might have an impact when long-term treatment using mTOR inhibitors in patients with autosomal dominant polycystic kidney disease is being considered.

Pharmacological retention of oral mucosa progenitor/stem cells

Oral mucosa progenitor/stem cells reside as a small-sized cell population that eventually differentiates concurrently with an increase in cell size. Activation of the mammalian target of rapamycin (mTOR) leads to an increase in cell size. We hypothesized that rapamycin, a specific inhibitor of mTOR, will maintain primary human oral keratinocytes as a small-sized, undifferentiated cell population capable of retaining their proliferative capacity. Primary, rapamycin-treated (2 nM, 20 nM) oral keratinocytes showed a diminished cell size that correlated with a higher clonogenicity, a longer-term proliferative potential, and a slower cycling cell population concurrent with decreased expression of a differentiation marker when compared with untreated cells. Only the 2-nM rapamycin-treated oral keratinocytes maintained their ability to regenerate oral mucosa in vitro after 15 weeks of culture. Rapamycin, a Food and Drug Administration-approved drug, may have applicability for use in creating a highly proliferative cell population for use in regenerative medicine.

Rapamycin protects against rotenone-induced apoptosis through autophagy induction

Ubiquitin proteasome system (UPS) and autophagy lysosome pathway (ALP) are the two most important routes for degradation of aggregated/misfolded proteins. Additionally, ALP is so far the only known route to clear entire organelles, such as mitochondria. We proposed that enhancement of ALP may be beneficial for some neurodegenerative disorders, such as Parkinson's disease (PD), in which the accumulation of aggregated/misfolded proteins and the dysfunction of mitochondria are the two major pathogenesis. Mitochondrial complex I inhibitor rotenone, which causes dysfunction mitochondria and UPS, has been considered as one of the neurotoxins related to PD. In this study, rotenone-exposed human neuronal SH-SY5Y cells were used as an in vitro model for us to determine whether autophagy enhancer rapamycin could protect against rotenone-induced injury and its underlying mechanisms. The observed results showed that rapamycin alleviated rotenone-induced apoptosis, whose effects were partially blocked when autophagy related gene 5 (Atg5) was suppressed by Atg5 small interference RNA (siRNA) transfection. Additionally, the results showed that rapamycin pretreatment diminished rotenone-induced accumulation of high molecular weight ubiquitinated bands, and reduced rotenone-induced increase of cytochrome c in cytosolic fraction and decreased mitochondrial marker cytochrome oxidase subunit IV (COX IV) in mitochondrial fraction. The changes in cytochrome c and COX IV indicated that the decreased translocation of cytochrome c from mitochondria to cytosol was probably due to the turn over of entire injured mitochondria. The results that lysosome and mitochondria were colocolized within the cells pretreated with rapamycin and that the mitochondria could be found within autophagy double membrane structures further supported that the damaged mitochondria might be cleared through autophagy, which process has been termed as "mitophagy." Our studies suggested that autophagy enhancer rapamycin is neuroprotective against rotenone-induced apoptosis through autophagy enhancement. We concluded that pharmacologically induction of autophagy by rapamycin may represent a useful therapeutic strategy as disease-modifiers in PD.