Combined inhibition of MAPK and mTOR signaling inhibits growth, induces cell death, and abrogates invasive growth of melanoma cells

Cancer Stem Cells and the Renin-Angiotensin System in the Tumor Microenvironment of Melanoma: Implications on Current Therapies

Multiple signaling pathways are dysregulated in melanoma, notably the Ras/RAF/MAPK/ERK and PI3K/AKT/mTOR pathways, which can be targeted therapeutically. The high immunogenicity of melanoma has been exploited using checkpoint inhibitors. Whilst targeted therapies and immune checkpoint inhibitors have improved the survival of patients with advanced melanoma, treatment resistance, their side effect profiles, and the prohibitive cost remain a challenge, and the survival outcomes remain suboptimal. Treatment resistance has been attributed to the presence of cancer stem cells (CSCs), a small subpopulation of pluripotent, highly tumorigenic cells proposed to drive cancer progression, recurrence, metastasis, and treatment resistance. CSCs reside within the tumor microenvironment (TME) regulated by the immune system, and the paracrine renin-angiotensin system, which is expressed in many cancer types, including melanoma. This narrative review discusses the role of CSCs and the paracrine renin-angiotensin system in the melanoma TME, and its implications on the current treatment of advanced melanoma with targeted therapy and immune checkpoint blockers. It also highlights the regulation of the Ras/RAF/MAPK/ERK and PI3K/AKT/mTOR pathways by the renin-angiotensin system via pro-renin receptors, and how this may relate to CSCs and treatment resistance, underscoring the potential for improving the efficacy of targeted therapy and immunotherapy by concurrently modulating the renin-angiotensin system.

Augmenting MEK inhibitor efficacy in BRAF wild-type melanoma: synergistic effects of disulfiram combination therapy

BACKGROUND

MEK inhibitors (MEKi) were shown to be clinically insufficiently effective in patients suffering from BRAF wild-type (BRAF WT) melanoma, even if the MAPK pathway was constitutively activated due to mutations in NRAS or NF-1. Thus, novel combinations are needed to increase the efficacy and duration of response to MEKi in BRAF WT melanoma. Disulfiram and its metabolite diethyldithiocarbamate are known to have antitumor effects related to cellular stress, and induction of endoplasmic reticulum (ER) stress was found to synergize with MEK inhibitors in NRAS-mutated melanoma cells. Therefore, we investigated the combination of both therapeutics to test their effects on BRAF-WT melanoma cells and compared them with monotherapy using the MEKi trametinib.

METHODS

The effects of combined therapy with disulfiram or its metabolite diethyldithiocarbamate and the MEKi trametinib were evaluated in a series of BRAF-WT melanoma cell lines by measuring cell viability and apoptosis induction. Cytotoxicity was additionally assessed in 3D spheroids, ex vivo melanoma slice cultures, and in vivo xenograft mouse models. The response of melanoma cells to treatment was studied at the RNA and protein levels to decipher the mode of action. Intracellular and intratumoral copper measurements were performed to investigate the role of copper ions in the antitumor cytotoxicity of disulfiram and its combination with the MEKi.

RESULTS

Diethyldithiocarbamate enhanced trametinib-induced cytotoxicity and apoptosis induction in 2D and 3D melanoma culture models. Mechanistically, copper-dependent induction of oxidative stress and ER stress led to Janus kinase (JNK)-mediated apoptosis in melanoma cells. This mechanism was also detectable in patient-derived xenograft melanoma models and resulted in a significantly improved therapeutic effect compared to monotherapy with the MEKi trametinib.

CONCLUSIONS

Disulfiram and its metabolite represent an attractive pharmaceutical approach to induce ER stress in melanoma cells that potentiates the antitumor effect of MEK inhibition and may be an interesting candidate for combination therapy of BRAF WT melanoma.

The mTOR Signaling Pathway and mTOR Inhibitors in Cancer: Next-generation Inhibitors and Approaches

mTOR is a serine/threonine kinase that plays various roles in cell growth, proliferation, and metabolism. mTOR signaling in cancer becomes irregular. Therefore, drugs targeting mTOR have been developed. Although mTOR inhibitors rapamycin and rapamycin rapalogs (everolimus, rapamycin, temsirolimus, deforolimus, etc.) and new generation mTOR inhibitors (Rapalink, Dual PI3K/mTOR inhibitors, etc.) are used in cancer treatments, mTOR resistance mechanisms may inhibit the efficacy of these drugs. Therefore, new inhibition approaches are developed. Although these new inhibition approaches have not been widely investigated in cancer treatment, the use of nanoparticles has been evaluated as a new treatment option in a few types of cancer. This review outlines the functions of mTOR in the cancer process, its resistance mechanisms, and the efficiency of mTOR inhibitors in cancer treatment. Furthermore, it discusses the next-generation mTOR inhibitors and inhibition strategies created using nanoparticles. Since mTOR resistance mechanisms prevent the effects of mTOR inhibitors used in cancer treatments, new inhibition strategies should be developed. Inhibition approaches are created using nanoparticles, and one of them offers a promising treatment option with evidence supporting its effectiveness.

Chimeric Peptide Engineered Nanomedicine for Synergistic Suppression of Tumor Growth and Therapy-Induced Hyperlipidemia by mTOR and PCSK9 Inhibition

Chemotherapy-induced side effects restrain anti-tumor efficiency, with hyperlipidemia being the most common accompanying disease to cause treatment failure. In this work, a chimeric peptide-engineered nanomedicine (designated as PRS) was fabricated for the synergistic suppression of tumor growth and therapy-induced hyperlipidemia. Within this nanomedicine, the tumor matrix-targeting peptide palmitic-K(palmitic)CREKA can self-assemble into a nano-micelle to encapsulate Rapamycin (mTOR inhibitor) and SBC-115076 (PCSK9 inhibitor). This PRS nanomedicine exhibits a uniform nano-distribution with good stability which enhances intracellular drug delivery and tumor-targeting delivery. Also, PRS was found to synergistically inhibit tumor cell proliferation by interrupting the mTOR pathway and reducing Rapamycin-induced hyperlipidemia by increasing the production of LDLR. In vitro and in vivo results demonstrate the superiority of PRS for systematic suppression of tumor growth and the reduction of hyperlipidemia without initiating any other toxic side effects. This work proposes a sophisticated strategy to inhibit tumor growth and also provides new insights for cooperative management of chemotherapy-induced side effects.

Potato psyllids mount distinct gut responses against two different 'Candidatus Liberibacter solanacearum' haplotypes

'Candidatus Liberibacter solanacearum' (Lso) is a bacterial pathogen infecting several crops and causing damaging diseases. Several Lso haplotypes have been identified. Among the seven haplotypes present in North America, LsoA and LsoB are transmitted by the potato psyllid, Bactericera cockerelli (Šulc), in a circulative and persistent manner. The gut, which is the first organ pathogen encounters, could be a barrier for Lso transmission. However, the molecular interactions between Lso and the psyllid vector at the gut interface remain largely unknown. In this study, we investigated the global transcriptional responses of the adult psyllid gut upon infection with two Lso haplotypes (LsoA and LsoB) using Illumina sequencing. The results showed that each haplotype triggers a unique transcriptional response, with most of the distinct genes elicited by the highly virulent LsoB. The differentially expressed genes were mainly associated with digestion and metabolism, stress response, immunity, detoxification as well as cell proliferation and epithelium renewal. Importantly, distinct immune pathways were triggered by LsoA and LsoB in the gut of the potato psyllid. The information in this study will provide an understanding of the molecular basis of the interactions between the potato psyllid gut and Lso, which may lead to the discovery of novel molecular targets for the control of these pathogens.

Understanding the Polyamine and mTOR Pathway Interaction in Breast Cancer Cell Growth

The polyamines putrescine, spermidine and spermine are nutrient-like polycationic molecules involved in metabolic processes and signaling pathways linked to cell growth and cancer. One important pathway is the PI3K/Akt pathway where studies have shown that polyamines mediate downstream growth effects. Downstream of PI3K/Akt is the mTOR signaling pathway, a nutrient-sensing pathway that regulate translation initiation through 4EBP1 and p70S6K phosphorylation and, along with the PI3K/Akt, is frequently dysregulated in breast cancer. In this study, we investigated the effect of intracellular polyamine modulation on mTORC1 downstream protein and general translation state in two breast cancer cell lines, MCF-7 and MDA-MB-231. The effect of mTORC1 pathway inhibition on the growth and intracellular polyamines was also measured. Results showed that polyamine modulation alters 4EBP1 and p70S6K phosphorylation and translation initiation in the breast cancer cells. mTOR siRNA gene knockdown also inhibited cell growth and decreased putrescine and spermidine content. Co-treatment of inhibitors of polyamine biosynthesis and mTORC1 pathway induced greater cytotoxicity and translation inhibition in the breast cancer cells. Taken together, these data suggest that polyamines promote cell growth in part through interaction with mTOR pathway. Similarly intracellular polyamine content appears to be linked to mTOR pathway regulation. Finally, dual inhibition of polyamine and mTOR pathways may provide therapeutic benefits in some breast cancers.

Immunogenetic effects of low dose (CEM43 30) magnetic nanoparticle hyperthermia and radiation in melanoma cells

Objective:

In this in vitro study we have used an RNA quantification technique, nanoString, and a conventional protein analysis technique (Western Blot) to assess the genetic and protein expression of B16 murine melanoma cells following a modest magnetic nanoparticle hyperthermia (mNPH) dose equivalent to 30 minutes @ 43°C (CEM43 30) and/or a clinically relevant 8 Gy radiation dose.

Methods:

Melanoma cells with mNPs(2.5 μg Fe/106 cells) were pelleted and exposed to an alternating magnetic field (AMF) to generate the targeted thermal dose. Thermal dose was accurately monitored by a fiber optic probe and automatically maintained at CEM43 30. All cells were harvested 24 hours after treatment.

Results:

The mNPH dose demonstrated notable elevations in the thermotolerance/immunogenic HSP70 gene and a number of chemoattractant and toll-like receptor gene pathways. The 8 Gy dose also upregulated a number of important immune and cytotoxic genetic and protein pathways. However, the mNPH/radiation combination was the most effective stimulator of a wide variety of immune and cytotoxic genes including HSP70, cancer regulating chemokines CXCL10, CXCL11, the T-cell trafficking chemokine CXCR3, innate immune activators TLR3, TLR4, the MDM2 and mTOR negative regulator of p53, the pro-apoptotic protein PUMA, and the cell death receptor Fas. Importantly a number of the genetic changes were accurately validated by protein expression changes, i.e., HSP70, p-mTOR, p-MDM2.

Conclusion:

These results not only show that low dose mNPH and radiation independently increase the expression of important immune and cytotoxic genes but that the effect is greatly enhanced when they are used in combination.

An update on chemical classes targeting ERK1/2 for the management of cancer

Cancer, still in the limelight due to its dreadful nature, shows overexpression of multiple signaling macromolecules leading to failure of many chemotherapeutic agents and acquired resistance to chemotherapy. These factors highlight the significance of shifting toward targeted therapy in cancer research. Recently, ERKs (ERK1 and 2) have been established as a promising target for the management of various types of solid tumors, due to their aberrant involvement in cell growth and progression. Several ERKs inhibitors have reached clinical trials for the management of cancer and their derivatives are being continuously reported with noteworthy anticancer effect. This review highlights the recent reports on various chemical classes involved in the development of ERKs inhibitors along with their in vitro and in vivo activity and structure-activity relationship profile.

Targeting mTOR and Metabolism in Cancer: Lessons and Innovations

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

TRPML1 and RAS-driven cancers - exploring a link with great therapeutic potential

Activating mutations in the RAS family of proto-oncogenes represent some of the leading causes of cancer. Unmitigated proliferation of cells harboring oncogenic RAS mutations is accompanied by a massive increase in cellular bioenergetic demands, which offers unique opportunities for therapeutic intervention. To withstand the steep requirements for metabolic intermediates, RAS-driven cancer cells enhance endolysosome and autophagosome biogenesis. By degrading cellular macromolecules into metabolites that can be used by biosynthetic pathways, endolysosomes permit continued proliferation and survival in otherwise detrimental conditions. We recently showed that human cancers with activating mutations in HRAS elevate the expression of MCOLN1, which encodes an endolysosomal cation channel called TRPML1. Increased TRPML1 activity in HRAS-driven cancer cells is needed for the restoration of plasma membrane cholesterol that gets collaterally internalized during endocytosis. Inhibition of TRPML1 or knockdown of MCOLN1 leads to mislocalization of cholesterol from the plasma membrane to endolysosomes, loss of oncogenic HRAS from the cell surface, and attenuation of downstream signaling. Here, we discuss the implications of our findings and suggest strategies to leverage pathways that impinge upon TRPML1 as novel anti-cancer treatments.

Everolimus for the treatment of advanced pancreatic ductal adenocarcinoma (PDAC)

Introduction: PDAC is a lethal malignancy with a clear unmet need; almost all patients fail 1st, 2nd, and 3rd line multi-agent cytotoxic chemotherapy. The mammalian target of rapamycin (mTOR) has been identified as a key signaling node enhancing tumor survival and drug resistance in PDAC; hence, it is considered a promising therapeutic target. Areas covered: We comprehensively reviewed the evidence from preclinical and phase I and II clinical trials, based on the authors'clinical experience and a PubMed, Cochrane library, Embase, and Google Scholar search everolimus + pancreatic cancer. Expert opinion: Everolimus has not demonstrated efficacy in PDAC; however, an mTOR inhibitor in combination with stroma-targeted therapies may be a promising area to explore in clinical trials.

The Power of Fish Models to Elucidate Skin Cancer Pathogenesis and Impact the Discovery of New Therapeutic Opportunities

Animal models play important roles in investigating the pathobiology of cancer, identifying relevant pathways, and developing novel therapeutic tools. Despite rapid progress in the understanding of disease mechanisms and technological advancement in drug discovery, negative trial outcomes are the most frequent incidences during a Phase III trial. Skin cancer is a potential life-threatening disease in humans and might be medically futile when tumors metastasize. This explains the low success rate of melanoma therapy amongst other malignancies. In the past decades, a number of skin cancer models in fish that showed a parallel development to the disease in humans have provided important insights into the fundamental biology of skin cancer and future treatment methods. With the diversity and breadth of advanced molecular genetic tools available in fish biology, fish skin cancer models will continue to be refined and expanded to keep pace with the rapid development of skin cancer research. This review begins with a brief introduction of molecular characteristics of skin cancers, followed by an overview of teleost models that have been used in the last decades in melanoma research. Next, we will detail the importance of the zebrafish (Danio rerio) animal model and other emerging fish models including platyfish (Xiphophorus sp.), and medaka (Oryzias latipes) in future cutaneous malignancy studies. The last part of this review provides the recent development and genome editing applications of skin cancer models in zebrafish and the progress in small molecule screening.

Induction of MEK/ERK activity by AZD8055 confers acquired resistance in neuroblastoma

Mammalian target of rapamycin (mTOR) complex (mTORC) is frequently activated in diverse cancers. Although dual mTORC1/2 inhibitors are currently under development to treat various malignancies, the emergence of drug resistance has proven to be a major complication. AZD8055 is a novel, potent ATP-competitive and specific inhibitor of mTOR kinase activity, which blocks both mTORC1 and mTORC2 activation. In this study, we acquired AZD8055-resistant neuroblastoma (NB) cell sublines by using prolonged stepwise escalation of AZD8055 exposure (4-12 weeks). Here we demonstrate that the AZD8055-resistant sublines (TGW-R and SMS-KAN-R) exhibited marked resistance to AZD8055 compared to the parent cells (TGW and SMS-KAN). The cell cycle G1/S transition was advanced in resistant cells. In addition, the resistance against AZD8055 correlated with over-activation of MEK/ERK signaling pathway. Furthermore, combination of AZD8055 and MEK inhibitor U0126 enhanced the growth inhibition of resistant cells significantly in vitro and in vivo. In conclusion, these data show that targeting mTOR kinase and MEK/ERK signaling simultaneously might help to overcome AZD8055 resistance in NB.

Reprofiling using a zebrafish melanoma model reveals drugs cooperating with targeted therapeutics

Phenotype-guided re-profiling of approved drug molecules presents an accelerated route to developing anticancer therapeutics by bypassing the target-identification bottleneck of target-based approaches and by sampling drugs already in the clinic. Further, combinations incorporating targeted therapies can be screened for both efficacy and toxicity. Previously we have developed an oncogenic-RAS-driven zebrafish melanoma model that we now describe display melanocyte hyperplasia while still embryos. Having devised a rapid method for quantifying melanocyte burden, we show that this phenotype can be chemically suppressed by incubating V12RAS transgenic embryos with potent and selective small molecule inhibitors of either MEK or PI3K/mTOR. Moreover, we demonstrate that combining MEK inhibitors (MEKi) with dual PI3K/mTOR inhibitors (PI3K/mTORi) resulted in a super-additive suppression of melanocyte hyperplasia. The robustness and simplicity of our novel screening assay inspired us to perform a modest screen of FDA approved compounds for their ability to potentiate MEKi PD184352 or PI3K/mTORi NVPBEZ235 suppression of V12RAS-driven melanocyte hyperplasia. Through this route, we confirmed Rapamycin as a compound that could synergize with MEKi and even more so with PI3K/mTORi to suppress melanoma development, including suppressing the growth of cultured human melanoma cells. Further, we discovered two additional compounds-Disulfiram and Tanshinone-that also co-operate with MEKi to suppress the growth of transformed zebrafish melanocytes and showed activity toward cultured human melanoma cells. In conclusion, we provide proof-of-concept that our phenotype-guided screen could be used to identify compounds that affect melanoma development and prompt further evaluation of Disulfiram and Tanshinone as possible partners for combination therapy.

BRAF Inhibitors Amplify the Proapoptotic Activity of MEK Inhibitors by Inducing ER Stress in NRAS-Mutant Melanoma

Purpose: NRAS mutations in malignant melanoma are associated with aggressive disease requiring rapid antitumor intervention, but there is no approved targeted therapy for this subset of patients. In clinical trials, the MEK inhibitor (MEKi) binimetinib displayed modest antitumor activity, making combinations a requisite. In a previous study, the BRAF inhibitor (BRAFi) vemurafenib was shown to induce endoplasmic reticulum (ER) stress that together with inhibition of the RAF-MEK-ERK (MAPK) pathway amplified its proapoptotic activity in BRAF-mutant melanoma. The present study investigated whether this effect might extent to NRAS-mutant melanoma, in which MAPK activation would be expected.Experimental Design and Results: BRAFi increased pERK, but also significantly increased growth inhibition and apoptosis induced by the MEKi in monolayer, spheroids, organotypic, and patient-derived tissue slice cultures of NRAS-mutant melanoma. BRAFi such as encorafenib induced an ER stress response via the PERK pathway, as detected by phosphorylation of eIF2α and upregulation of the ER stress-related factors ATF4, CHOP, and NUPR1 and the proapoptotic protein PUMA. MEKi such as binimetinib induced the expression of the proapoptotic protein BIM and activation of the mitochondrial pathway of apoptosis, the latter of which was enhanced by combination with encorafenib. The increased apoptotic rates caused by the combination treatment were significantly reduced through siRNA knockdown of ATF4 and BIM, confirming its critical roles in this process.Conclusions: The data presented herein encourage further advanced in vivo and clinical studies to evaluate MEKi in combination with ER stress inducing BRAFi as a strategy to treat rapidly progressing NRAS-mutant melanoma. Clin Cancer Res; 23(20); 6203-14. ©2017 AACR.

Antiangiogenic tyrosine kinase inhibitors in colorectal cancer: is there a path to making them more effective?

Antiangiogenic therapy has a proven survival benefit in metastatic colorectal cancer. Inhibition of the VEGF pathway using a variety of extracellular antibody approaches has clear benefit in combination with chemotherapy, while intracellular blockade using tyrosine kinase inhibitors (TKIs) such as sorafenib and regorafenib has had more limited success. Pharmacodynamic modeling using modalities such as DCE-MRI indicates potent antiangiogenic effects of these TKIs, yet numerous combination therapies, primarily with chemotherapy, have failed to demonstrate an additive benefit. The sole comparative study of a single agent TKI against placebo showed a survival benefit of regorafenib in patients with advanced, refractory disease. Preclinical data demonstrate synergy between antiantiogenic TKIs and targeted interventions including autophagy inhibition, and together with a renewed effort to define markers of susceptibility, such combinations may be a way to improve the limited efficacy of this once-promising drug class.

Zebrafish as a Model Organism for the Development of Drugs for Skin Cancer

Skin cancer, which includes melanoma and squamous cell carcinoma, represents the most common type of cutaneous malignancy worldwide, and its incidence is expected to rise in the near future. This condition derives from acquired genetic dysregulation of signaling pathways involved in the proliferation and apoptosis of skin cells. The development of animal models has allowed a better understanding of these pathomechanisms, with the possibility of carrying out toxicological screening and drug development. In particular, the zebrafish (Danio rerio) has been established as one of the most important model organisms for cancer research. This model is particularly suitable for live cell imaging and high-throughput drug screening in a large-scale fashion. Thanks to the recent advances in genome editing, such as the clustered regularly-interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) methodologies, the mechanisms associated with cancer development and progression, as well as drug resistance can be investigated and comprehended. With these unique tools, the zebrafish represents a powerful platform for skin cancer research in the development of target therapies. Here, we will review the advantages of using the zebrafish model for drug discovery and toxicological and phenotypical screening. We will focus in detail on the most recent progress in the field of zebrafish model generation for the study of melanoma and squamous cell carcinoma (SCC), including cancer cell injection and transgenic animal development. Moreover, we will report the latest compounds and small molecules under investigation in melanoma zebrafish models.

Immunoregulatory protein B7-H3 promotes growth and decreases sensitivity to therapy in metastatic melanoma cells

B7-H3 (CD276) belongs to the B7 family of immunoregulatory proteins and has been implicated in cancer progression and metastasis. In this study, we found that metastatic melanoma cells with knockdown expression of B7-H3 showed modest decrease in proliferation and glycolytic capacity and were more sensitive to dacarbazine (DTIC) chemotherapy and small-molecule inhibitors targeting MAP kinase (MAPK) and AKT/mTOR pathways: vemurafenib (PLX4032; BRAF inhibitor), binimetinib (MEK-162; MEK inhibitor), everolimus (RAD001; mTOR inhibitor), and triciribidine (API-2; AKT inhibitor). Similar effects were observed in melanoma cells in the presence of an inhibitory B7-H3 monoclonal antibody, while the opposite was seen in B7-H3-overexpressing cells. Further, combining B7-H3 inhibition with small-molecule inhibitors resulted in significantly increased antiproliferative effect in melanoma cells, as well as in BRAF^V600E mutated cell lines derived from patient biopsies. Our findings indicate that targeting B7-H3 may be a novel alternative to improve current therapy of metastatic melanoma.

Combined activity of temozolomide and the mTOR inhibitor temsirolimus in metastatic melanoma involves DKK1

The BRAFV600E inhibitor vemurafenib achieves remarkable clinical responses in patients with BRAF-mutant melanoma, but its effects are limited by the onset of drug resistance. In the case of resistance, chemotherapy can still be applied as second line therapy. However, it yields low response rates and strategies are urgently needed to potentiate its effects. In a previous study, we showed that the inhibition of the PI3K-AKT-mTOR pathway significantly increases sensitivity of melanoma cells to chemotherapeutic drugs (J. Invest. Dermatol. 2009, 129, 1500). In this study, the combination of the mTOR inhibitor temsirolimus with the chemotherapeutic agent temozolomide significantly increases growth inhibition and apoptosis in melanoma cells compared to temsirolimus or temozolomide alone. The combination of temozolomide with temsirolimus is not only effective in established but also in newly isolated and vemurafenib-resistant metastatic melanoma cell lines. These effects are associated with the downregulation of the anti-apoptotic protein Mcl-1 and the upregulation of the Wnt antagonist Dickkopf homologue 1 (DKK1). Knock-down of DKK1 suppresses apoptosis induction by the combination of temsirolimus and temozolomide. These data suggest that the inhibition of the mTOR pathway increases sensitivity of melanoma cells towards temozolomide. Chemosensitisation is associated with enhanced expression of the Wnt antagonist DKK1.

Evidence for Pipecolate Oxidase in Mediating Protection Against Hydrogen Peroxide Stress

Pipecolate, an intermediate of the lysine catabolic pathway, is oxidized to Δ¹ -piperideine-6-carboxylate (P6C) by the flavoenzyme l-pipecolate oxidase (PIPOX). P6C spontaneously hydrolyzes to generate α-aminoadipate semialdehyde, which is then converted into α-aminoadipate acid by α-aminoadipatesemialdehyde dehydrogenase. l-pipecolate was previously reported to protect mammalian cells against oxidative stress. Here, we examined whether PIPOX is involved in the mechanism of pipecolate stress protection. Knockdown of PIPOX by small interference RNA abolished pipecolate protection against hydrogen peroxide-induced cell death in HEK293 cells suggesting a critical role for PIPOX. Subcellular fractionation analysis showed that PIPOX is localized in the mitochondria of HEK293 cells consistent with its role in lysine catabolism. Signaling pathways potentially involved in pipecolate protection were explored by treating cells with small molecule inhibitors. Inhibition of both mTORC1 and mTORC2 kinase complexes or inhibition of Akt kinase alone blocked pipecolate protection suggesting the involvement of these signaling pathways. Phosphorylation of the Akt downstream target, forkhead transcription factor O3 (FoxO3), was also significantly increased in cells treated with pipecolate, further implicating Akt in the protective mechanism and revealing FoxO3 inhibition as a potentially key step. The results presented here demonstrate that pipecolate metabolism can influence cell signaling during oxidative stress to promote cell survival and suggest that the mechanism of pipecolate protection parallels that of proline, which is also metabolized in the mitochondria. J. Cell. Biochem. 118: 1678-1688, 2017. © 2016 Wiley Periodicals, Inc.

Combination of mTOR and MAPK Inhibitors-A Potential Way to Treat Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most common neoplasm that occurs in the kidney and is marked by a unique biology, with a long history of poor response to conventional cancer treatments. In the past few years, there have been significant advancements to understand the biology of RCC. This has led to the introduction of novel targeted therapies in the management of patients with metastatic disease. Patients treated with targeted therapies for RCC had shown positive impact on overall survival, however, no cure is possible and patients need to undergo treatment for long periods of time, which raises challenges to manage the associated adverse events. Moreover, many patients may not respond to it and even response may not last long enough in the responders. Many inhibitors of the Mammalian target of Rapamycin (mTOR) signaling pathway are currently being used in treatment of advanced RCC. Studies showed that inhibitions of mTOR pathways induce Mitogen-Activated Protein Kinase (MAPK) escape cell death and cells become resistant to mTOR inhibitors. Because of this, there is a need to inhibit both pathways with their inhibitors comparatively for a better outcome and treatment of patients with RCC.

Casein kinase 1α has a non-redundant and dominant role within the CK1 family in melanoma progression

Background

We previously identified CK1α as a novel tumor suppressor in melanoma and reported that the loss of CK1α leads to increased proliferation and invasive growth of melanoma cells by strong activation of the Wnt/β-catenin signaling pathway.

Methods

In this study we analyzed expression and the functional effects of the dominantly expressed CK1- isoforms α, δ and ε in melanoma cells by quantitative real-time PCR, western blot and immunohistochemistry. We down-regulated CK1 kinase activity with isoform specific siRNAs and small molecule inhibitors. Vice versa we overexpressed the CK1 isoforms α, δ and ε using viral vectors and tested the biological effects on melanoma cell proliferation, migration and invasion.

Results

We show that protein expression of all three CK1-isoforms is downregulated in metastatic melanoma cells compared to benign melanocytic cells. Furthermore, the CK1δ and ε isoforms are able to negatively regulate expression of each other, whereas CK1α expression is independently regulated in melanoma cells. Inhibition of the expression and activity of CK1δ or CK1ε by specific inhibitors or siRNAs had no significant effect on the growth and survival of metastatic melanoma cells. Moreover, the over-expression of CK1δ or CK1ε in melanoma cells failed to induce cell death and cell cycle arrest although p53 signaling was activated. This is in contrast to the effects of CK1α where up-regulated expression induces cell death and apoptosis in metastatic melanoma cells.

Conclusion

These data indicate that CK1α has a dominant and non-redundant function in melanoma cells and that the CK1δ and ε isoforms are not substantially involved in melanoma progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2643-0) contains supplementary material, which is available to authorized users.

PTEN regulates IGF-1R-mediated therapy resistance in melanoma

Inhibition of the mitogen-activated protein kinase (MAPK) pathway is a major advance in the treatment of metastatic melanoma. However, its therapeutic success is limited by the rapid emergence of drug resistance. The insulin-like growth factor-1 receptor (IGF-1R) is overexpressed in melanomas developing resistance toward the BRAF(V) (600) inhibitor vemurafenib. Here, we show that hyperactivation of BRAF enhances IGF-1R expression. In addition, the phosphatase activity of PTEN as well as heterocellular contact to stromal cells increases IGF-1R expression in melanoma cells and enhances resistance to vemurafenib. Interestingly, PTEN-negative melanoma cells escape IGF-1R blockade by decreased expression of the receptor, implicating that only in melanoma patients with PTEN-positive tumors treatment with IGF-1R inhibitors would be a suitable strategy to combat therapy resistance. Our data emphasize the crosstalk and therapeutic relevance of microenvironmental and tumor cell-autonomous mechanisms in regulating IGF-1R expression and by this sensitivity toward targeted therapies.

Steroid hormone influence on melanomagenesis

Disparities in the prognosis and incidence of melanoma between male and female patients have led clinicians to explore the influence of steroid hormones on the development and progression of this malignancy. A better understanding of the disparities of melanoma behavior between sexes and ages could lead to improved prevention and treatment options. There are multiple themes in the literature that unify the physiologic functions of estrogen and androgen receptors; herein we discuss and map their pathways. Overall, it is important to understand that the differences in melanoma behavior between the sexes are multifactorial and likely involve interactions between the immune system, endocrine system, and environment, namely UV-radiation. Melanoma deserves a spot among hormone-sensitive tumors, and if tamoxifen is re-introduced for future therapy, tissue ratios of estrogen receptors should be obtained beforehand to assess their therapeutic predictive value. Because androgens, estrogens, and their receptors are involved in signaling of commonly mutated melanoma pathways, potential synergistic properties of the recently developed molecular kinase inhibitors that target those pathways may exist.

DNA-Hybrid-Gated Photothermal Mesoporous Silica Nanoparticles for NIR-Responsive and Aptamer-Targeted Drug Delivery

Near-infrared light is an attractive stimulus due to its noninvasive and deep tissue penetration. Particularly, NIR light is utilized for cancer thermotherapy and on-demand release of drugs by the disruption of the delivery carriers. Here we have prepared a novel NIR-responsive DNA-hybrid-gated nanocarrier based on mesoporous silica-coated Cu1.8S nanoparticles. Cu1.8S nanoparticles, possessing high photothermal conversion efficiency under a 980 nm laser, were chosen as photothermal agents. The mesoporous silica structure could be used for drug storage/delivery and modified with aptamer-modified GC-rich DNA-helix as gatekeepers, drug vectors, and targeting ligand. Simultaneously, the as-produced photothermal effect caused denaturation of DNA double strands, which triggered the drug release of the DNA-helix-loaded hydrophilic drug doxorubicin and mesopore-loaded hydrophobic drug curcumin, resulting in a synergistic therapeutic effect. The Cu1.8S@mSiO2 nanocomposites endocytosed by cancer cells through the aptamer-mediated mode are able to generate rational release of doxorubicin/curcumin under NIR irradiation, strongly enhancing the synergistic growth-inhibitory effect of curcumin against doxorubicin in MCF-7 cells, which is associated with a strong mitochondrial-mediated cell apoptosis progression. The underlying mechanism of apoptosis showed a strong synergistic inhibitory effect both on the expression of Bcl-2, Bcl-xL, Mcl-1, and upregulated caspase 3/9 activity and on the expression level of Bak and Bax. Therefore, Cu1.8S@mSiO2 with efficient synergistic therapeutic efficiency is a potential multifunctional cancer therapy nanoplatform.

Dual treatments targeting IGF-1R, PI3K, mTORC or MEK synergize to inhibit cell growth, induce apoptosis, and arrest cell cycle at G1 phase in MDA-MB-231 cell line

Triple-negative breast cancers (TNBCs) are aggressive cancers that do not benefit from hormonal therapy or therapies that target HER2 receptors. Insulin-like growth factor 1 receptor (IGF-1R), which has been shown to be overexpressed in breast cancer, activates numerous downstream kinases that associate with cell proliferation and survival. This study compared the effects caused by dual treatments targeting IGF-1R, PI3K, mTORC, or MEK with those by single treatments in a TNBC cell line, MDA-MB-231. We used small-molecule kinase inhibitors, namely, NVP-AEW541, NVP-BKM120, KU0063794, and PD0325901 to target IGF-1R, PI3K, mTORC, and MEK, respectively. Combination treatments of PD0325901 with NVP-AEW541, NVP-BKM120 or KU0063794 and NVP-AEW541 with KU0063794 demonstrated a significant synergistic growth inhibition. These dual treatments increased apoptosis and/or cell cycle arrest at G0/G1 phase and enhanced the inhibition of phosphorylation of Akt or downstream molecules of mTORC1, as compared to the single treatments. Our study suggests that targeting multiple kinases in IGF-1R signaling may be a promising therapeutic approach.

Titration of signalling output: insights into clinical combinations of MEK and AKT inhibitors

Our results show that sub-optimal inhibition of MEK in combination with AKT is less efficient in inhibiting cellular growth compared to completely inhibiting MEK and AKT alone. The results also show that KRAS mutant cells are more sensitive to a combination of MEK and AKT inhibitors compared to BRAF and PIK3CA mutant cells. Both these findings have clinical implications.

Background

We aimed to understand the relative contributions of inhibiting MEK and AKT on cell growth to guide combinations of these agents.

Materials and methods

A panel of 20 cell lines was exposed to either the MEK inhibitor, PD0325901, or AKT inhibitor, AKT 1/2 inhibitor. p-ERK and p-S6 ELISAs were used to define degrees of MEK and AKT inhibition, respectively. Growth inhibition to different degrees of MEK and AKT inhibition, either singly or in combination using 96-h sulphorhodamine assays was then studied.

Results

A significantly greater growth inhibition was seen in BRAF^M and PIK3CA^M cells upon maximal MEK (P = 0.004) and AKT inhibition (P = 0.038), respectively. KRAS^M and BRAF/PIK3CA/KRAS^WT cells were not significantly more likely to be sensitive to MEK or AKT inhibition. Significant incremental growth inhibition of the combination of MEK + AKT over either MEK or AKT inhibition alone was seen when MEK + AKT was inhibited maximally and not when sub-maximal inhibition of both MEK + AKT was used (11/20 cell lines versus 1/20 cell lines; P = 0.0012).

Conclusions

KRAS^M cells are likely to benefit from combinations of MEK and AKT inhibitors. Sub-maximally inhibiting both MEK and AKT within a combination, in a majority of instances, does not significantly increase growth inhibition compared with maximally inhibiting MEK or AKT alone and alternative phase I trial designs are needed to clinically evaluate such combinations.

Long non-coding RNA BANCR promotes proliferation in malignant melanoma by regulating MAPK pathway activation

Long non-coding RNAs (lncRNAs) have been shown to be implicated in the complex network of cancer including malignant melanoma and play important roles in tumorigenesis and progression. However, their functions and downstream mechanisms are largely unknown. This study aimed to investigate whether BRAF-activated non-coding RNA (BANCR), a novel and potential regulator of melanoma cell, participates in the proliferation of malignant melanoma and elucidate the underlying mechanism in this process. We found that BANCR was abnormally overexpressed in human malignant melanoma cell lines and tissues, and increased with tumor stages by quantitative PCR. BANCR knockdown induced by shRNA transfection significantly inhibited proliferation of tumor cells and inactivated MAPK pathway, especially by silencing the ERK1/2 and JNK component. Moreover, combination treatment of BANCR knockdown and suppression ERK1/2 or JNK (induced by specific inhibitors U0126 or SP600125 respectively) produced synergistic inhibitory effects in vitro. And the inhibitory effects induced by ERK1/2 or JNK could be rescued by BANCR overexpression. By tumorigenicity assay in BALB/c nude mice, we further found that BANCR knockdown inhibited tumor growth in vivo. In addition, patients with high expression of BANCR had a lower survival rate. Taken together, we confirmed the abnormal upregulation of a novel lncRNA, BANCR, in human malignant melanoma. BANCR was involved in melanoma cell proliferation both in vitro and in vivo. The linkage between BANCR and MAPK pathway may provide a novel interpretation for the mechanism of proliferation regulation in malignant melanoma.

Towards combinatorial targeted therapy in melanoma: from pre-clinical evidence to clinical application (review)

Over the last few years, clinical trials with BRAF and mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitors have shown significant clinical activity in melanoma, but only a fraction of patients respond to these therapies, and development of resistance is frequent. This has prompted a large set of preclinical studies looking at several new combinatorial approaches of pathway- or target-specific inhibitors. At least five main drug association strategies have been verified in vitro and in preclinical models. The most promising include: i) vertical targeting of either MEK or phosphoinositide-3 kinase (PI3K)/mammalian target of rapamycin (mTOR) pathways, or their combined blockade; ii) association of receptor tyrosine kinases (RTKs) inhibitors with other pro-apoptotic strategies; iii) engagement of death receptors in combination with MEK-, mTOR/PI3K-, histone deacetylase (HDAC)-inhibitors, or with anti-apoptotic molecules modulators; iv) strategies aimed at blocking anti-apoptotic proteins belonging to B-cell lymphoma (Bcl-2) or inhibitors of apoptosis (IAP) families associated with MEK/BRAF/p38 inhibition; v) co-inhibition of other molecules important for survival [proteasome, HDAC and Signal transducers and activators of transcription (Stat)3] and the major pathways activated in melanoma; vi) simultaneous targeting of multiple anti-apoptotic molecules. Here we review the anti-melanoma efficacy and mechanism of action of the above-mentioned combinatorial strategies, together with the potential clinical application of the most promising studies that may eventually lead to therapeutic benefit.

Co-delivery of cisplatin and rapamycin for enhanced anticancer therapy through synergistic effects and microenvironment modulation

The tumor microenvironment plays an important role in the tumor's progression and metastasis. Therefore, successful alteration of this delicate setting against the tumor's favor can open a window for therapeutic efficacy. We have developed a modality to bring about treatment-induced alterations in the tumor microenvironment by employing the synergistic effects between two drugs. Co-delivery of rapamycin (RAPA), an mTOR inhibitor that may offer notable therapy through antiangiogenic activity, alongside cisplatin can foster significant potency as RAPA sensitizes A375 melanoma cells to cisplatin therapy through microenvironment modulation. However, encapsulation of these drugs into poly(lactic-co-glycolic acid) (PLGA) NPs was inefficient due to the incompatibility between the two free drugs and the polymer matrix. Here, we show cisplatin can be made hydrophobic by coating a nanoprecipitate (cores) of the drug with dioleoylphosphatidic acid (DOPA). These DOPA coated cisplatin cores are compatible with PLGA and can be coencapsulated in PLGA NPs alongside RAPA at a molar ratio to promote synergistic antitumor activity. The presence of the cisplatin cores significantly improved the encapsulation of RAPA into PLGA NPs. Furthermore, PLGA NPs containing both cisplatin cores and RAPA induced significant apoptosis on A375-luc human melanoma cells in vitro. Additionally, they inhibited the growth of A375-luc melanoma in a xenograft tumor model through modulation of the tumor vasculature and permitted enhanced penetration of NPs into the tumor.

Effects of AKT inhibitor therapy in response and resistance to BRAF inhibition in melanoma

Background

The clinical use of BRAF inhibitors for treatment of metastatic melanoma is limited by the development of drug resistance. In this study we investigated whether co-targeting the MAPK and the PI3K-AKT pathway can prevent emergence of resistance or provide additional growth inhibitory effects in vitro.

Methods

Anti-tumor effects of the combination of the BRAF inhibitor (BRAFi) dabrafenib and GSK2141795B (AKTi) in a panel of 23 BRAF mutated melanoma cell lines were evaluated on growth inhibition by an ATP-based luminescent assay, on cell cycle and apoptosis by flow cytometry and on cell signaling by western blot. Moreover, we investigated the possibilities of delaying or reversing resistance or achieving further growth inhibition by combining AKTi with dabrafenib and/or the MEK inhibitor (MEKi) trametinib by using long term cultures.

Results

More than 40% of the cell lines, including PTEN-/- and AKT mutants showed sensitivity to AKTi (IC₅₀ < 1.5 μM). The combination of dabrafenib and AKTi synergistically potentiated growth inhibition in the majority of cell lines with IC₅₀ > 5 nM dabrafenib. Combinatorial treatment induced apoptosis only in cell lines sensitive to AKTi. In long term cultures of a PTEN-/- cell line, combinatorial treatment with the MAPK inhibitors, dabrafenib and trametinib, and AKTi markedly delayed the emergence of drug resistance. Moreover, combining AKTi with the MAPK inhibitors from the beginning provided superior growth inhibitory effects compared to addition of AKTi upon development of resistance to MAPK inhibitors in this particular cell line.

Conclusions

AKTi combined with BRAFi-based therapy may benefit patients with tumors harboring BRAF mutations and particularly PTEN deletions or AKT mutations.

Melatonin combined with endoplasmic reticulum stress induces cell death via the PI3K/Akt/mTOR pathway in B16F10 melanoma cells

This study investigated B16F10 melanoma cell death induced by melatonin combined with endoplasmic reticulum (ER) stress through the PI3K/Akt/mTOR pathway. Cell viability was significantly decreased after treatment with melatonin combined with ER stress from thapsigargin or tunicamycin compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress also significantly reduced expression of p85β, p-Akt (Ser473, Thr308), and p-mTOR (Ser2448, Ser2481) compared to treatment with melatonin only. The ER stress protein p-PERK and p-eIF2α were significantly increased under combined melatonin and ER stress treatment compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress significantly reduced Bcl-2 protein and augmented Bax protein compared to melatonin-only treatment. Also, the combined treatment significantly lowered expression of catalase, Cu/Zn-SOD, and Mn-SOD proteins compared to melatonin only. Expression of p85β was significantly more decreased under treatment with melatonin and thapsigargin or tunicamycin plus the PI3K inhibitors LY294002 or wortmannin than under treatment with only melatonin or a PI3K inhibitor. The PI3K downstream target p-Akt (Ser473, Thr308) showed significantly decreased expression under treatment with melatonin and thapsigargin or tunicamycin plus PI3K inhibitors than under treatment with melatonin or PI3K inhibitors only. These results indicate that survival of B16F10 melanoma cells after combined treatment with melatonin and ER stress inducers is suppressed through regulation of the PI3K/Akt/mTOR pathway. Melatonin combined with thapsigargin or tunicamycin appears to be a promising strategy for effective melanoma treatment.

GNAQ and BRAF mutations show differential activation of the mTOR pathway in human transformed cells

Somatic mutations in GNAQ gene were described as being the main oncogenic activation in uveal melanomas, whereas mutations in BRAF gene have been described as a key genetic alteration that contributes to skin melanoma development. We have previously reported differential activation of the MAPK and AKT/mTOR signalling pathways in uveal and skin melanomas harbouring, respectively, GNAQ and BRAF mutations. The aim of this work was to compare the functional effect of GNAQ and BRAF mutations in mTOR and MAPK pathway activation, cell proliferation and apoptosis. In this work, we performed transient transfection of HEK293 cells with BRAF^WT, BRAF^{V 600E}, GNAQ^WT, GNAQ^Q209P and GNAQ^Q209L vectors. We treated melanoma cell lines displaying different BRAF and GNAQ mutational status with the mTOR inhibitor RAD001 and with the MEK1/2 inhibitor U0126 and evaluated the effects in the growth of the cell lines and in mTOR and MAPK pathway effectors expression. At variance with the significant increase in the level of pmTOR Ser2448 and pS6 Ser235/236 proteins observed in cells transfected with BRAF vectors, no significant alteration in mTOR pathway effectors was observed in cells transfected with the three GNAQ expressing vectors. Also, GNAQ overexpression enhances Stat3 activation, which might mediate GNAQ oncogenic effects. None of the vectors led to significant differences in proliferation or apoptosis in the transfected cell lines. Cell lines harbouring a BRAF mutation were more sensitive to RAD001 treatment. U0126 leads to the reduction of MAPK and mTOR pathways activation in all cell lines tested. Our results indicate that GNAQ and BRAF activation drive distinct intracellular signalling pathways that may be useful for therapeutic decisions in human melanomas.

Molecular-targeted agents combination therapy for cancer: developments and potentials

Although chemotherapy has advanced into the era of targeted drugs, the antitumor efficacies of current therapies are limited, most likely because of the high degree of cancer clonal heterogeneity, intratumor genetic heterogeneity and cell signal complexity. As shutdown of a single target does not necessarily eradicate the cancer, the use of combinations of molecular-targeted agents (MATs) has been proposed, and some pioneering research has been conducted to examine the efficacy of this strategy. In this article, the clinical and preclinical studies that are underway in an attempt to improve the anticancer efficacy of chemotherapies through combination strategies are summarized. Studies of combining cytotoxic agents with MATs, coinhibiting two or more targets in a single pathway or coinhibiting parallel or compensatory pathways as well as specific combinations will be introduced, and the antitumor potentials of each combination strategy will be evaluated.

Thymidylate synthase expression determines pemetrexed targets and resistance development in tumour cells

Although treatment options for cancer patients are increasing every year, the drug resistance problem remains very present. It is very difficult to find a drug that acts equally on tumours of the same histology as the individual's genetic characteristics often determine the response to treatment. Furthermore, tumours that initially respond to anti-tumour therapy are able to adapt and develop resistance to the drug, while others do not. In addition, this usually implies resistance development to agents to which the cells have not been exposed, a phenomenon called cross-resistance or multidrug resistance. Given this situation, it has been suggested that the most appropriate treatment would be able to act in parallel on multiple pathways constitutively altered in tumour cells. Pemetrexed is a multitargeted antifolate that exerts its activity against folate-dependent enzymes involved in de novo pyrimidine and purine synthesis. It is currently in use in combination with cisplatin against malignant pleural mesothelioma and non-squamous non-small cell lung cancer with favourable results. By real-time RT-PCR gene expression assays and restoration viability assays we demonstrated that Pemetrexed targets folate-dependent enzymes involved in de novo biosynthesis of purines differently depending on the intrinsic genetic characteristics of the tumour. These differences did not, however, interfere either with the initial response to the drug or with the activation of apoptotic pathways. In addition, these genetic fingerprints can differentiate two groups of tumours: those capable of developing resistance to antifolate, and not capable. These results may be useful to employ targets gene expression as resistance markers, a valuable tool for identifying patients likely to receive combination therapy to prevent the development of resistance.

Advances in personalized targeted treatment of metastatic melanoma and non-invasive tumor monitoring

Despite extensive scientific progress in the melanoma field, treatment of advanced stage melanoma with chemotherapeutics and biotherapeutics has rarely provided response rates higher than 20%. In the past decade, targeted inhibitors have been developed for metastatic melanoma, leading to the advent of more personalized therapies of genetically characterized tumors. Here we review current melanoma treatments and emerging targeted molecular therapies. In particular we discuss the mutant BRAF inhibitors Vemurafenib and Dabrafenib, which markedly inhibit tumor growth and advance patients' overall survival. However this response is almost inevitably followed by complete tumor relapse due to drug resistance hampering the encouraging initial responses. Several mechanisms of resistance within and outside the MAPK pathway have now been uncovered and have paved the way for clinical trials of combination therapies to try and overcome tumor relapse. It is apparent that personalized treatment management will be required in this new era of targeted treatment. Circulating tumor cells (CTCs) provide an easily accessible means of monitoring patient relapse and several new approaches are available for the molecular characterization of CTCs. Thus CTCs provide a monitoring tool to evaluate treatment efficacy and early detection of drug resistance in real time. We detail here how advances in the molecular analysis of CTCs may provide insight into new avenues of approaching therapeutic options that would benefit personalized melanoma management.

Synergistic interactions between sorafenib and everolimus in pancreatic cancer xenografts in mice

PURPOSE

Molecular targeting of cellular signaling pathways is a promising approach in cancer therapy, but often fails to achieve sustained benefit because of the activation of collateral cancer cell survival and proliferation pathways. We tested the hypothesis that a combination of targeted agents that inhibit compensatory pathways would be more effective than single agents in controlling pancreatic cancer cell growth. We investigated whether everolimus, an mTOR inhibitor, and sorafenib, a multi-kinase inhibitor, would together inhibit growth of low-passage, patient-derived pancreatic cancer xenografts in mice more efficaciously than either agent alone.

METHODS

Tumor volume progression was measured following treatment with both drugs as single agents, in combination, and at multiple doses. Pharmacokinetics in tumors and other tissues was also assessed. Pharmacodynamic interactions were evaluated quantitatively.

RESULTS

A 5-week regimen of daily oral doses of 10 mg/kg sorafenib and 0.5 mg/kg everolimus, alone and in combination, did not achieve significant tumor growth inhibition. Higher doses (20 mg/kg of sorafenib and 1 mg/kg of everolimus) inhibited tumor growth significantly when given alone and caused complete inhibition of growth when given in combination. Tumor volume progression was described by a linear growth model, and drug effects were described by Hill-type inhibition. Using population modeling approaches, dual-interaction parameter estimates indicated a highly synergistic pharmacodynamic interaction between the two drugs.

CONCLUSIONS

The results indicate that combinations of mTOR and multi-kinase inhibitors may offer greater efficacy in pancreatic cancer than either drug alone. Drug effects upon tumor stromal elements may contribute to the enhanced anti-tumor efficacy.

Targeted therapy for melanoma: rational combinatorial approaches

The treatment of melanoma, the most aggressive form of skin cancer, is being revolutionized by the development of personalized targeted therapy approaches. Mutant-selective BRAF inhibitors and MEK inhibitors have demonstrated impressive clinical results in molecularly selected patients. However, emerging understanding of the molecular heterogeneity of this disease and the identification of multiple mechanisms of resistance to targeted therapies strongly support the rationale for combinatorial approaches. In this review, we will discuss the preclinical and clinical studies that are testing leading hypotheses and emerging combinatorial strategies for the future.

Targeting hyperactivation of the AKT survival pathway to overcome therapy resistance of melanoma brain metastases

Brain metastases are the most common cause of death in patients with metastatic melanoma, and the RAF-MEK-ERK and PI3K-AKT signaling pathways are key players in melanoma progression and drug resistance. The BRAF inhibitor vemurafenib significantly improved overall survival. However, brain metastases still limit the effectiveness of this therapy. In a series of patients, we observed that treatment with vemurafenib resulted in substantial regression of extracerebral metastases, but brain metastases developed. This study aimed to identify factors that contribute to treatment resistance in brain metastases. Matched brain and extracerebral metastases from melanoma patients had identical ERK, p-ERK, and AKT immunohistochemistry staining patterns, but there was hyperactivation of AKT (p-AKT) and loss of PTEN expression in the brain metastases. Mutation analysis revealed no differences in BRAF, NRAS, or KIT mutation status in matched brain and extracerebral metastases. In contrast, AKT, p-AKT, and PTEN expression was identical in monolayer cultures derived from melanoma brain and extracerebral metastases. Furthermore, melanoma cells stimulated by astrocyte-conditioned medium showed higher AKT activation and invasiveness than melanoma cells stimulated by fibroblast-conditioned medium. Inhibition of PI3K-AKT signaling resensitized melanoma cells isolated from a vemurafenib-resistant brain metastasis to vemurafenib. Brain-derived factors appear to induce hyperactivation of the AKT survival pathway and to promote the survival and drug resistance of melanoma cells in the brain. Thus, inhibition of PI3K-AKT signaling shows potential for enhancing and/or prolonging the antitumor effect of BRAF inhibitors or other anticancer agents in melanoma brain metastases.

Science Signaling Podcast: 29 January 2013

Vemurafenib induces endoplasmic reticulum stress in melanoma cells.

Vemurafenib potently induces endoplasmic reticulum stress-mediated apoptosis in BRAFV600E melanoma cells

The V600E mutation in the kinase BRAF is frequently detected in melanomas and results in constitutive activation of BRAF, which then promotes cell proliferation by the mitogen-activated protein kinase signaling pathway. Although the BRAFV600E kinase inhibitor vemurafenib has remarkable antitumor activity in patients with BRAFV600E-mutated melanoma, its effects are limited by the onset of drug resistance. We found that exposure of melanoma cell lines with the BRAFV600E mutation to vemurafenib decreased the abundance of antiapoptotic proteins and induced intrinsic mitochondrial apoptosis. Vemurafenib-treated melanoma cells showed increased cytosolic concentration of calcium, a potential trigger for endoplasmic reticulum (ER) stress, which can lead to apoptosis. Consistent with an ER stress-induced response, vemurafenib decreased the abundance of the ER chaperone protein glucose-regulated protein 78, increased the abundance of the spliced isoform of the transcription factor X-box binding protein 1 (XBP1) (which transcriptionally activates genes involved in ER stress responses), increased the phosphorylation of the translation initiation factor eIF2α (which would be expected to inhibit protein synthesis), and induced the expression of ER stress-related genes. Knockdown of the ER stress response protein activating transcription factor 4 (ATF4) significantly reduced vemurafenib-induced apoptosis. Moreover, the ER stress inducer thapsigargin prevented invasive growth of tumors formed from vemurafenib-sensitive melanoma cells in vivo. In melanoma cells with low sensitivity or resistance to vemurafenib, combination treatment with thapsigargin augmented or induced apoptosis. Thus, thapsigargin or other inducers of ER stress may be useful in combination therapies to overcome vemurafenib resistance.

Simultaneous targeting of COX-2 and AKT using selenocoxib-1-GSH to inhibit melanoma

Melanoma is a highly metastatic and deadly disease. An agent simultaneously targeting the COX-2, PI3K/Akt, and mitogen-activated protein kinase (MAPK) signaling pathways that are deregulated in up to 70% of sporadic melanomas might be an effective treatment, but no agent of this type exists. To develop a single drug inhibiting COX-2 and PI3K/Akt signaling (and increasing MAPK pathway activity to inhibitory levels as a result of Akt inhibition), a selenium-containing glutathione (GSH) analogue of celecoxib, called selenocoxib-1-GSH was synthesized. It killed melanoma cells with an average IC(50) of 7.66 μmol/L compared with control celecoxib at 55.6 μmol/L. The IC(50) range for normal cells was 36.3 to 41.2 μmol/L compared with 7.66 μmol/L for cancer cells. Selenocoxib-1-GSH reduced development of xenografted tumor by approximately 70% with negligible toxicity by targeting COX-2, like celecoxib, and having novel inhibitory properties by acting as a PI3K/Akt inhibitor (and MAPK pathway activator to inhibitory levels due to Akt inhibition). The consequence of this inhibitory activity was an approximately 80% decrease in cultured cell proliferation and an approximately 200% increase in apoptosis following 24-hour treatment with 15.5 μmol/L of drug. Thus, this study details the development of selenocoxib-1-GSH, which is a nontoxic agent that targets the COX-2 and PI3K/Akt signaling pathways in melanomas to inhibit tumor development.

Interactions of everolimus and sorafenib in pancreatic cancer cells

Everolimus targets the mammalian target of rapamycin, a kinase that promotes cell growth and proliferation in pancreatic cancer. Sorafenib inhibits the Raf-mitogen-activated protein kinase, vascular endothelial growth factor, and platelet-derived growth factor pathways, thus inhibiting cell growth and angiogenesis. Combinations of these two agents are under evaluation for therapy of several cancers. This study examined the effects of everolimus and sorafenib on proliferation of the pancreatic cancer cell lines MiaPaCa-2 and Panc-1. Cell growth inhibition was evaluated in vitro for a range of concentrations of the drugs alone and in combination. Maximum inhibition capacity (I (max)) and potency (IC(50)) were determined. The data were analyzed to characterize drug interactions using two mathematical analysis techniques. The Ariens noncompetitive interaction model and Earp model were modified to accommodate alterations in the inhibition parameters of one drug in the presence of another. Sorafenib alone inhibited growth of both cell lines completely (I (max) = 1), with an IC(50) of 5-8 μM. Maximal inhibition by everolimus alone was only 40% (I (max) = 0.4) in both cell lines, with an IC(50) of 5 nM. Slight antagonistic interaction occurred between the drugs; both analytic methods estimated the interaction term Ψ as greater than 1 for both cell lines. The in vitro data for two pancreatic cancer cell lines suggest that a combination of these two drugs would be no more efficacious than the individual drugs alone, consistent with the drug interaction analysis that indicated slight antagonism for growth inhibition.

Therapeutic implications of disorders of cell death signalling: membranes, micro-environment, and eicosanoid and docosanoid metabolism

Disruptions of cell death signalling occur in pathological processes, such as cancer and degenerative disease. Increased knowledge of cell death signalling has opened new areas of therapeutic research, and identifying key mediators of cell death has become increasingly important. Early triggering events in cell death may provide potential therapeutic targets, whereas agents affecting later signals may be more palliative in nature. A group of primary mediators are derivatives of the highly unsaturated fatty acids (HUFAs), particularly oxygenated metabolites such as prostaglandins. HUFAs, esterified in cell membranes, act as critical signalling molecules in many pathological processes. Currently, agents affecting HUFA metabolism are widely prescribed in diseases involving disordered cell death signalling. However, partly due to rapid metabolism, their role in cell death signalling pathways is poorly characterized. Recently, HUFA-derived mediators, the resolvins/protectins and endocannabinoids, have added opportunities to target selective signals and pathways. This review will focus on the control of cell death by HUFA, eicosanoid (C20 fatty acid metabolites) and docosanoid (C22 metabolites), HUFA-derived lipid mediators, signalling elements in the micro-environment and their potential therapeutic applications. Further therapeutic approaches will involve cell and molecular biology, the multiple hit theory of disease progression and analysis of system plasticity. Advances in the cell biology of eicosanoid and docosanoid metabolism, together with structure/function analysis of HUFA-derived mediators, will be useful in developing therapeutic agents in pathologies characterized by alterations in cell death signalling.