The dual PI3K/mTOR inhibitor PI-103 promotes immunosuppression, in vivo tumor growth and increases survival of sorafenib-treated melanoma cells

STK11 (LKB1) missense somatic mutant isoforms promote tumor growth, motility and inflammation

Elucidating the contribution of somatic mutations to cancer is essential for personalized medicine. STK11 (LKB1) appears to be inactivated in human cancer. However, somatic missense mutations also occur, and the role/s of these alterations to this disease remain unknown. Here, we investigated the contribution of four missense LKB1 somatic mutations in tumor biology. Three out of the four mutants lost their tumor suppressor capabilities and showed deficient kinase activity. The remaining mutant retained the enzymatic activity of wild type LKB1, but induced increased cell motility. Mechanistically, LKB1 mutants resulted in differential gene expression of genes encoding vesicle trafficking regulating molecules, adhesion molecules and cytokines. The differentially regulated genes correlated with protein networks identified through comparative secretome analysis. Notably, three mutant isoforms promoted tumor growth, and one induced inflammation-like features together with dysregulated levels of cytokines. These findings uncover oncogenic roles of LKB1 somatic mutations, and will aid in further understanding their contributions to cancer development and progression.

Paula Granado-Martínez, Sara Ortega, Elena González-Sánchez et al. report a functional analysis of four cancer-associated mutant isoforms of the gene STK11 using cell-based and animal models. They find the mutant isoforms no longer show tumor suppressor activity, promote tumor growth, and affect the regulation of cytokines and genes involved in vesicle trafficking.

Oxidative Cyclization-Induced Activation of a Phosphoinositide 3-Kinase Inhibitor for Enhanced Selectivity of Cancer Chemotherapeutics

In this work, we designed a prodrug that reacts with cellular oxidative equivalents leading to ether cleavage and cyclization to release an active phosphatidylinositol 3-kinase (PI3K) inhibitor. We show that the compound reduces affinity for PI3KA relative to the PI3K inhibitor, is slow to intercellularly oxidize, and is resistant to liver microsomes. We observed modest activity in untreated acute myeloid leukemia cells and 14-fold selectivity relative to non-cancerous cells. The cellular activity of the compound can be modulated by the addition of antioxidants or oxidants, indicating the compound activity is sensitive to cellular reactive oxygen species (ROS) state. Co-treatment with cytosine arabinoside or doxorubicin was used to activate the compound inside cells. We observed strong synergistic activity specifically in acute myeloid leukemia (AML) cancer cells with an increase in selective anticancer activity of up to 90-fold. Thus, these new self-cyclizing compounds can be used to increase the selectivity of anticancer agents.

Novel chemotherapeutic agent, FND-4b, activates AMPK and inhibits colorectal cancer cell proliferation

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the US with the majority of deaths due to metastatic disease. Current chemotherapeutic regimens involve highly toxic agents, which limits their utility; therefore, more effective and less toxic agents are required to see a reduction in CRC mortality. Novel fluorinated N,N’-diarylureas (FND) were developed and characterized by our group as potent activators of adenosine monophosphate-activated kinase (AMPK) that inhibit cell cycle progression. The purpose of this study was to determine the effect of a lead FND compound, FND-4b, either alone or combined with PI-103 (a dual PI3K/mTOR inhibitor) or SN-38 (active metabolite of irinotecan) on cell cycle arrest and apoptosis of CRC cell lines (both commercially-available and novel lines established from our patient population). Treatment with FND-4b for 24h resulted in a marked induction of phosphorylated AMPK expression and a concomitant reduction in markers of cell proliferation, such as cyclin D1, in all CRC cell lines. Apoptosis was also notably increased in CRC cells treated with FND-4b. Regardless of the genetic profile of the CRC cells, FND-4b treatment alone resulted in decreased cell proliferation. Moreover, the combination of FND-4b with PI-103 resulted in increased cell death in all cell lines, while the combination of FND-4b with SN-38 resulted in increased cell death in select cell lines. Our findings identify FND-4b, which activates AMPK at micromolar concentrations, as a novel and effective inhibitor of CRC growth either alone or in combination with PI-103 and SN-38.

ALDH1A3 is epigenetically regulated during melanocyte transformation and is a target for melanoma treatment

Despite the promising targeted and immune-based interventions in melanoma treatment, long-lasting responses are limited. Melanoma cells present an aberrant redox state that leads to the production of toxic aldehydes that must be converted into less reactive molecules. Targeting the detoxification machinery constitutes a novel therapeutic avenue for melanoma. Here, using 56 cell lines representing nine different tumor types, we demonstrate that melanoma cells exhibit a strong correlation between reactive oxygen species amounts and aldehyde dehydrogenase 1 (ALDH1) activity. We found that ALDH1A3 is upregulated by epigenetic mechanisms in melanoma cells compared with normal melanocytes. Furthermore, it is highly expressed in a large percentage of human nevi and melanomas during melanocyte transformation, which is consistent with the data from the TCGA, CCLE and protein atlas databases. Melanoma treatment with the novel irreversible isoform-specific ALDH1 inhibitor [4-dimethylamino-4-methyl-pent-2-ynthioic acid-S methylester] di-methyl-ampal-thio-ester (DIMATE) or depletion of ALDH1A1 and/or ALDH1A3, promoted the accumulation of apoptogenic aldehydes leading to apoptosis and tumor growth inhibition in immunocompetent, immunosuppressed and patient-derived xenograft mouse models. Interestingly, DIMATE also targeted the slow cycling label-retaining tumor cell population containing the tumorigenic and chemoresistant cells. Our findings suggest that aldehyde detoxification is relevant metabolic mechanism in melanoma cells, which can be used as a novel approach for melanoma treatment.

The use of novel selectivity metrics in kinase research

Background

Compound selectivity is an important issue when developing a new drug. In many instances, a lack of selectivity can translate to increased toxicity. Protein kinases are particularly concerned with this issue because they share high sequence and structural similarity. However, selectivity may be assessed early on using data generated from protein kinase profiling panels.

Results

To guide lead optimization in drug discovery projects, we propose herein two new selectivity metrics, namely window score (WS) and ranking score (RS). These metrics can be applied to standard in vitro data–including intrinsic enzyme activity/affinity (Ki, IC₅₀ or percentage of inhibition), cell-based potency (percentage of effect, EC₅₀) or even kinetics data (Kd, Kon and Koff). They are both easy to compute and offer different viewpoints from which to consider compound selectivity.

Conclusions

We performed a comparative analysis of their respective performance on several data sets against already published selectivity metrics and analyzed how they might influence compound selection. Our results showed that the two new metrics bring additional information to prioritize compound selection.

Graphical Abstract

Two novel metrics were developed to better estimate selectivity of compounds screened on multiple proteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-1413-y) contains supplementary material, which is available to authorized users.

Therapeutic interventions to disrupt the protein synthetic machinery in melanoma

Control of the protein synthetic machinery is deregulated in many cancers, including melanoma, to increase the protein production. Tumor suppressors and oncogenes play key roles in protein synthesis from the transcription of rRNA and ribosome biogenesis to mRNA translation initiation and protein synthesis. Major signaling pathways are altered in melanoma to modulate the protein synthetic machinery, thereby promoting tumor development. However, despite the importance of this process in melanoma development, involvement of the protein synthetic machinery in this cancer type is an underdeveloped area of study. Here, we review the coupling of melanoma development to deregulation of the protein synthetic machinery. We examine existing knowledge regarding RNA polymerase I inhibition and mRNA translation focusing on their inhibition for therapeutic applications in melanoma. Furthermore, the contribution of amino acid biosynthesis and involvement of ribosomal proteins are also reviewed as future therapeutic strategies to target deregulated protein production in melanoma.

PI3K pathway inhibitors: potential prospects as adjuncts to vaccine immunotherapy for glioblastoma

Constitutive activation of the PI3K pathway has been implicated in glioblastoma (GBM) pathogenesis. Pharmacologic inhibition can both inhibit tumor survival and downregulate expression of programmed death ligand-1, a protein highly expressed on glioma cells that strongly contributes to cancer immunosuppression. In that manner, PI3K pathway inhibitors can help optimize GBM vaccine immunotherapy. In this review, we describe and assess the potential integration of various classes of PI3K pathway inhibitors into GBM immunotherapy. While early-generation inhibitors have a wide range of immunosuppressive effects that could negate their antitumor potency, further work should better characterize how contemporary inhibitors affect the immune response. This will help determine if these inhibitors are truly a therapeutic avenue with a strong future in GBM immunotherapy.

Therapeutic targeting of the mTOR-signalling pathway in cancer: benefits and limitations

The mammalian target of rapamycin (mTOR) plays an important role in the regulation of protein translation, cell growth and metabolism. The mTOR protein forms two distinct multi-subunit complexes: mTORC1 and mTORC2. The mTORC1 complex is activated by diverse stimuli, such as growth factors, nutrients, energy and stress signals; and essential signalling pathways, such as PI3K and MAPK, in order to control cell growth, proliferation and survival. mTORC1 also activates S6K1 and 4EBP1, which are involved in mRNA translation. The mTORC2 complex is resistant to rapamycin inhibitory activity and is generally insensitive to nutrient- and energy-dependent signals. It activates PKC-α and Akt and regulates the actin cytoskeleton. Deregulation of the mTOR-signalling pathway (PI3K amplification/mutation, PTEN loss of function, Akt overexpression, and S6K1, 4EBP1 and eIF4E overexpression) is common in cancer, and alterations in components of the mTOR pathway have a major role in tumour progression. Therefore, mTOR is an appealing therapeutic target in many tumours. Here we summarize the upstream regulators and downstream effectors of the mTORC1 and mTORC2 pathways, the role of mTOR in cancer, and the potential therapeutic values and issues related to the novel agents targeting the mTOR-signalling pathway.

Sorafenib inhibits intracellular signaling pathways and induces cell cycle arrest and cell death in thyroid carcinoma cells irrespective of histological origin or BRAF mutational status

BACKGROUND

Patients with dedifferentiated or anaplastic thyroid carcinomas currently lack appropriate treatment options. Kinase inhibitors are among the most promising new agents as alternative strategies. The BRAF- and multi-kinase inhibitor, sorafenib, has already shown antitumor effects in thyroid carcinoma patients in a phase III clinical trial. In this study we aim to better characterize molecular effects and efficacy of sorafenib against thyroid carcinoma cells with various histological origins and different BRAF mutational status. Analysis of different signaling pathways affected by sorafenib may contribute to assist a more specific therapy choice with fewer side effects. Twelve thyroid carcinoma cell lines derived from anaplastic, follicular and papillary thyroid carcinomas with wildtype or mutationally activated BRAF were treated with sorafenib. Growth inhibition, cell cycle arrest, cell death induction and inhibition of intracellular signaling pathways were then comprehensively analyzed.

METHODS

Cell viability was analyzed by MTT assay, and the cell cycle was assessed by flow cytometry after propidium iodide staining. Cell death was assessed by lactate dehydrogenase liberation assays, caspase activity assays and subG1 peak determinations. Inhibition of intracellular pathways was analyzed in dot blot and western blot analyses.

RESULTS

Sorafenib inhibited proliferation of all thyroid carcinoma cell lines tested with IC50 values ranging between 1.85 and 4.2 μM. Cells derived from papillary carcinoma harboring the mutant BRAF (V600E) allele were slightly more sensitive to sorafenib than those harboring wildtype BRAF. Cell cycle analyses and caspase assays showed a sorafenib-dependent induction of apoptosis in all cell lines, whereas increased lactate dehydrogenase release suggested cell membrane disruption. Sorafenib treatment caused a rapid inhibition of various MAP kinases in addition to inhibiting AKT and receptor tyrosine kinases.

CONCLUSIONS

Sorafenib inhibited multiple intracellular signaling pathways in thyroid carcinoma cells, which resulted in cell cycle arrest and the initiation of apoptosis. Sorafenib was effective against all thyroid carcinoma cell lines regardless of their tumor subtype origin or BRAF status, confirming that sorafenib is therapeutically beneficial for patients with any subtype of dedifferentiated thyroid cancer. Inhibition of single intracellular targets of sorafenib in thyroid carcinoma cells may allow the development of more specific therapeutic intervention with less side effects.

Impact of oncogenic driver mutations on feedback between the PI3K and MEK pathways in cancer cells

Inhibition of the PI3K (phosphoinositide 3-kinase)/Akt/mTORC1 (mammalian target of rapamycin complex 1) and Ras/MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase]/ERK pathways for cancer therapy has been pursued for over a decade with limited success. Emerging data have indicated that only discrete subsets of cancer patients have favourable responses to these inhibitors. This is due to genetic mutations that confer drug insensitivity and compensatory mechanisms. Therefore understanding of the feedback mechanisms that occur with respect to specific genetic mutations may aid identification of novel biomarkers that predict patient response. In the present paper, we show that feedback between the PI3K/Akt/mTORC1 and Ras/MEK/ERK pathways is cell-line-specific and highly dependent on the activating mutation of K-Ras or overexpression c-Met. We found that cell lines exhibited differential signalling and apoptotic responses to PD184352, a specific MEK inhibitor, and PI103, a second-generation class I PI3K inhibitor. We reveal that feedback from the PI3K/Akt/mTORC1 to the Ras/MEK/ERK pathway is present in cancer cells harbouring either K-Ras activating mutations or amplification of c-Met but not the wild-type counterparts. Moreover, we demonstrate that inhibition of protein phosphatase activity by OA (okadaic acid) restored PI103-mediated feedback in wild-type cells. Together, our results demonstrate a novel mechanism for feedback between the PI3K/Akt/mTORC1 and the Ras/MEK/ERK pathways that only occurs in K-Ras mutant and c-Met amplified cells but not the isogenic wild-type cells through a mechanism that may involve inhibition of a specific endogenous phosphatase(s) activity. We conclude that monitoring K-Ras and c-Met status are important biomarkers for determining the efficacy of PI103 and other PI3K/Akt inhibitors in cancer therapy.

Two hits are better than one: targeting both phosphatidylinositol 3-kinase and mammalian target of rapamycin as a therapeutic strategy for acute leukemia treatment

Phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) are two key components of the PI3K/Akt/mTOR signaling pathway. This signal transduction cascade regulates a wide range of physiological cell processes, that include differentiation, proliferation, apoptosis, autophagy, metabolism, motility, and exocytosis. However, constitutively active PI3K/Akt/mTOR signaling characterizes many types of tumors where it negatively influences response to therapeutic treatments. Hence, targeting PI3K/Akt/mTOR signaling with small molecule inhibitors may improve cancer patient outcome. The PI3K/Akt/mTOR signaling cascade is overactive in acute leukemias, where it correlates with enhanced drug-resistance and poor prognosis. The catalytic sites of PI3K and mTOR share a high degree of sequence homology. This feature has allowed the synthesis of ATP-competitive compounds targeting the catalytic site of both kinases. In preclinical models, dual PI3K/mTOR inhibitors displayed a much stronger cytotoxicity against acute leukemia cells than either PI3K inhibitors or allosteric mTOR inhibitors, such as rapamycin. At variance with rapamycin, dual PI3K/mTOR inhibitors targeted both mTOR complex 1 and mTOR complex 2, and inhibited the rapamycin-resistant phosphorylation of eukaryotic initiation factor 4E-binding protein 1, resulting in a marked inhibition of oncogenic protein translation. Therefore, they strongly reduced cell proliferation and induced an important apoptotic response. Here, we reviewed the evidence documenting that dual PI3K/mTOR inhibitors may represent a promising option for future targeted therapies of acute leukemia patients.

mTORC1 inhibition and ECM-cell adhesion-independent drug resistance via PI3K-AKT and PI3K-RAS-MAPK feedback loops

Mammalian target of rapamycin (mTOR) serine threonine kinase is the enzyme that regulates cancer cell growth by altering nutrient supplies to cancer cells. The neuropeptide (proline-rich peptide 1 (PRP-1)), galarmin, produced by the brain neurosecretory cells is a mTOR kinase inhibitor with powerful 80% antiproliferative cytostatic effect in a high-grade chondosarcoma and other mesenchymal tumors. However, the negative feedback loop of phosphatidylinositol 3 kinase-Protein kinase B (PKB), PI3K-AKT and PI3K-rat sarcoma (RAS)-mitogen-activated protein kinase (MAPK) activation is well documented for mTOR inhibitors. This study explored the involvement of those loops in drug resistance after the treatment with mTOR complex 1 (mTORC1) inhibitor, PRP-1. Multidrug resistance assay (MDR) demonstrated that this cytokine did not inhibit permeability glycoprotein-mediated MDR in chondrosarcoma. Phospho-MAPK array in human chondrosarcoma cell line treated with galarmin (10 μg/ml,) showed a strong upregulation of phosphorylated glycogen synthase kinase 3β (GSK3β) via activation of PI3K-AKT and MAPK feedback loops. Such GSK3β inactivation leads to β-catenin accumulation that entails drug resistance. The ability of cells to metastasize is reflected in their capacity to adhere to extracellular matrix and endothelium. Laminin cell adhesion assay demonstrated that PRP-1 in the same concentrations that inhibit mTOR kinase inhibited JJ012 chondrosarcoma cell adhesion. The neuropeptide did not have any effect on the expression of total focal adhesion kinase and its phosphorylated form. Thus, it was not accompanied by total HAT downregulation and total HDAC upregulation. Combinatorial treatments of PRP-1 with MAPK and PI3K/AKT inhibitors most probably will lead to full cytotoxicity overcoming drug resistance.

The Akt signaling pathway: an emerging therapeutic target in malignant melanoma

Studies using cultured melanoma cells and patient tumor biopsies have demonstrated deregulated PI3 kinase-Akt3 pathway activity in ~70% of melanomas. Furthermore, targeting Akt3 and downstream PRAS40 has been shown to inhibit melanoma tumor development in mice. Although these preclinical studies and several other reports using small interfering RNAs and pharmacological agents targeting key members of this pathway have been shown to retard melanoma development, analysis of early Phase I and Phase II clinical trials using pharmacological agents to target this pathway demonstrate the need for (1) selection of patients whose tumors have PI3 kinase-Akt pathway deregulation, (2) further optimization of therapeutic agents for increased potency and reduced toxicity, (3) the identification of additional targets in the same pathway or in other signaling cascades that synergistically inhibit the growth and progression of melanoma, and (4) better methods for targeted delivery of pharmaceutical agents inhibiting this pathway. In this review we discuss key potential targets in PI3K-Akt3 signaling, the status of pharmacological agents targeting these proteins, drugs under clinical development, and strategies to improve the efficacy of therapeutic agents targeting this pathway.

Targeting TOR dependence in cancer

A challenge in cancer therapy has been to identify targets whose function is essential for survival of malignant cells but not normal cells. This Perspective discusses recent evidence that novel inhibitors of the kinase TOR can provide an unprecedented balance of anti-cancer efficacy and tolerability.

Mechanisms of mTOR inhibitor resistance in cancer therapy

Mammalian target of rapamycin (mTOR) is a conserved serine/threonine kinase that regulates cell cycle progression, protein translation, metabolism, and cellular proliferation. The mTOR pathway promotes cell proliferation under energy or nutrient-rich conditions by increasing ribosomal biogenesis and protein synthesis. Since enhanced activity of the mTOR pathway is frequently observed in malignant cells, inhibition of this kinase has become an attractive strategy to treat cancer. Rapamycin and its analogs temsirolimus, everolimus, and ridaforolimus referred to as "rapalogs" have demonstrated promising efficacy against renal cell carcinoma and are under investigation for the treatment of other malignancies. However, the emergence of drug resistance may ultimately limit the utility of rapalog therapy. Here we summarize the known mechanisms of resistance to mTOR-inhibitor therapy and describe potential strategies to overcome these for the current agents that target this pathway.

Targeting the mTOR kinase domain: the second generation of mTOR inhibitors

The mTOR signaling pathway is dysregulated in ∼50% of all human malignancies and is a major cancer drug target. Although rapamycin analogs (rapalogs) have shown clinical efficacy in a subset of cancers, they do not fully exploit the antitumor potential of mTOR targeting. Because the mTOR kinase domain is important for rapamycin-sensitive and -insensitive functions, mTOR catalytic inhibitors have been developed recently as the second generation of anti-mTOR agents. Importantly, they have shown marked improvement of antitumor activity in vivo and in vitro. This review will detail the potential therapeutic value and issues of these novel antineoplastic agents, with emphasis placed on those that have already entered clinical trials.

Targeted therapy for melanoma: a primer

Melanoma is the most aggressive form of skin cancer. Unfortunately, despite recent improvements for some solid tumors, the prevalence and mortality of melanoma continue to increase. The identification of activating mutations in melanoma, combined with a growing appreciation of the different pattern of genetic changes in the anatomically defined melanoma subtypes, has become the focus of a concerted effort to translate these discoveries into personalized therapeutic approaches for this disease. This article reviews the known mutations, amplifications, and deletions in kinase signaling pathways that have been implicated in melanoma; the prevalence of these genetic events in clinicopathologically defined melanoma subtypes; and the results of clinical trials that use targeted therapy approaches to block aberrantly activated pathways resulting from these mutations. The challenges that must be overcome to achieve improved outcomes with targeted therapies in melanoma in the future are also discussed.

Methylthioadenosine (MTA) inhibits melanoma cell proliferation and in vivo tumor growth

Background

Melanoma is the most deadly form of skin cancer without effective treatment. Methylthioadenosine (MTA) is a naturally occurring nucleoside with differential effects on normal and transformed cells. MTA has been widely demonstrated to promote anti-proliferative and pro-apoptotic responses in different cell types. In this study we have assessed the therapeutic potential of MTA in melanoma treatment.

Methods

To investigate the therapeutic potential of MTA we performed in vitro proliferation and viability assays using six different mouse and human melanoma cell lines wild type for RAS and BRAF or harboring different mutations in RAS pathway. We also have tested its therapeutic capabilities in vivo in a xenograft mouse melanoma model and using variety of molecular techniques and tissue culture we investigated its anti-proliferative and pro-apoptotic properties.

Results

In vitro experiments showed that MTA treatment inhibited melanoma cell proliferation and viability in a dose dependent manner, where BRAF mutant melanoma cell lines appear to be more sensitive. Importantly, MTA was effective inhibiting in vivo tumor growth. The molecular analysis of tumor samples and in vitro experiments indicated that MTA induces cytostatic rather than pro-apoptotic effects inhibiting the phosphorylation of Akt and S6 ribosomal protein and inducing the down-regulation of cyclin D1.

Conclusions

MTA inhibits melanoma cell proliferation and in vivo tumor growth particularly in BRAF mutant melanoma cells. These data reveal a naturally occurring drug potentially useful for melanoma treatment.

Systemic therapy of non-resectable metastatic melanoma

In advanced metastatic melanoma (non-resectable stage III/IV), the prognosis still remains poor, with median survival times between six and twelve months. Systemic therapeutic approaches for metastatic melanoma include chemotherapy, immunotherapy, immunochemotherapy, small molecules and targeted therapy. In this review, we will focus on the various treatment modalities as well as new agents used for targeted therapy.

Effective and selective targeting of leukemia cells using a TORC1/2 kinase inhibitor

Targeting the mammalian target of rapamycin (mTOR) protein is a promising strategy for cancer therapy. The mTOR kinase functions in two complexes, TORC1 (target of rapamycin complex-1) and TORC2 (target of rapamycin complex-2); however, neither of these complexes is fully inhibited by the allosteric inhibitor rapamycin or its analogs. We compared rapamycin with PP242, an inhibitor of the active site of mTOR in both TORC1 and TORC2 (hereafter referred to as TORC1/2), in models of acute leukemia harboring the Philadelphia chromosome (Ph) translocation. We demonstrate that PP242, but not rapamycin, causes death of mouse and human leukemia cells. In vivo, PP242 delays leukemia onset and augments the effects of the current front-line tyrosine kinase inhibitors more effectively than does rapamycin. Unexpectedly, PP242 has much weaker effects than rapamycin on the proliferation and function of normal lymphocytes. PI-103, a less selective TORC1/2 inhibitor that also targets phosphoinositide 3-kinase (PI3K), is more immunosuppressive than PP242. These findings establish that Ph(+) transformed cells are more sensitive than normal lymphocytes to selective TORC1/2 inhibitors and support the development of such inhibitors for leukemia therapy.