Tumor adaptation and resistance to RAF inhibitors

Lin28B promotes melanoma growth by mediating a microRNA regulatory circuit

It has been increasingly recognized that microRNAs (miRNAs) are often dysregulated in various human malignancies and can function as oncogenes or tumor-suppressors. However, the potential roles of miRNAs and components of the miRNA biogenesis pathway remain poorly defined in melanoma. Here, we systematically profiled miRNA expression in human melanocytes and melanoma cells, and identified a prominent function of miR-125a-5p in suppressing melanoma growth. Mechanistically, we discovered that Lin28B, a well-characterized inhibitor of let-7 miRNA biogenesis, was a direct target of miR-125a-5p in melanoma. We showed that the Lin28B was aberrantly expressed in a large proportion of melanoma patients and was functionally required for melanoma progression. We further demonstrated the involvement of let-7-dependent mechanism downstream of Lin28B, resulting in the activation of transforming growth factor-β signaling cascade. Collectively, our data implicate Lin28B as a novel oncogene in melanomagenesis by mediating a miRNA regulatory circuit.

Empirical inference of circuitry and plasticity in a kinase signaling network

Our understanding of physiology and disease is hampered by the difficulty of measuring the circuitry and plasticity of signaling networks that regulate cell biology, and how these relate to phenotypes. Here, using mass spectrometry-based phosphoproteomics, we systematically characterized the topology of a network comprising the PI3K/Akt/mTOR and MEK/ERK signaling axes and confirmed its biological relevance by assessing its dynamics upon EGF and IGF1 stimulation. Measuring the activity of this network in models of acquired drug resistance revealed that cells chronically treated with PI3K or mTORC1/2 inhibitors differed in the way their networks were remodeled. Unexpectedly, we also observed a degree of heterogeneity in the network state between cells resistant to the same inhibitor, indicating that even identical and carefully controlled experimental conditions can give rise to the evolution of distinct kinase network statuses. These data suggest that the initial conditions of the system do not necessarily determine the mechanism by which cancer cells become resistant to PI3K/mTOR targeted therapies. The patterns of signaling network activity observed in the resistant cells mirrored the patterns of response to several drug combination treatments, suggesting that the activity of the defined signaling network truly reflected the evolved phenotypic diversity.

Usp5 links suppression of p53 and FAS levels in melanoma to the BRAF pathway

Usp5 is a deubiquitinase (DUB) previously shown to regulate unanchored polyubiquitin (Ub) chains, p53 transcriptional activity and double-strand DNA repair. In BRAF mutant melanoma cells, Usp5 activity was suppressed by BRAF inhibitor (vemurafenib) in sensitive but not in acquired or intrinsically resistant cells. Usp5 knockdown overcame acquired vemurafenib resistance and sensitized BRAF and NRAS mutant melanoma cells to apoptosis initiated by MEK inhibitor, cytokines or DNA-damaging agents. Knockdown and overexpression studies demonstrated that Usp5 regulates p53 (and p73) levels and alters cell growth and cell cycle distribution associated with p21 induction. Usp5 also regulates the intrinsic apoptotic pathway by modulating p53-dependent FAS expression. A small molecule DUB inhibitor (EOAI3402143) phenocopied the FAS induction and apoptotic sensitization of Usp5 knockdown and fully blocked melanoma tumor growth in mice. Overall, our results demonstrate that BRAF activates Usp5 to suppress cell cycle checkpoint control and apoptosis by blocking p53 and FAS induction; all of which can be restored by small molecule-mediated Usp5 inhibition. These results suggest that Usp5 inhibition can provide an alternate approach in recovery of diminished p53 (or p73) function in melanoma and can add to the targeted therapies already used in the treatment of melanoma.

Thrombospondin 1 promotes an aggressive phenotype through epithelial-to-mesenchymal transition in human melanoma

Epithelial-to-mesenchymal transition (EMT), in which epithelial cells loose their polarity and become motile mesenchymal cells, is a determinant of melanoma metastasis. We compared gene expression signatures of mesenchymal-like melanoma cells with those of epithelial-like melanoma cells, and identified Thrombospondin 1 (THBS1) as highly up-regulated in the mesenchymal phenotype. This study investigated whether THBS1, a major physiological activator of transforming growth factor (TGF)-beta, is involved in melanoma EMT-like process. We sought to examine expression patterns in distinct melanoma phenotypes including invasive, de-differentiated, label-retaining and drug resistant populations that are putatively associated with an EMT-like process.

Here we show that THBS1 expression and secretion was elevated in melanoma cells exhibiting invasive, drug resistant, label retaining and mesenchymal phenotypes and correlated with reduced expression of genes involved in pigmentation. Elevated THBS1 levels were detected in Vemurafenib resistant melanoma cells and inhibition of THBS1 led to significantly reduced chemoresistance in melanoma cells. Notably, siRNA-mediated silencing of THBS1 and neutralizing antibody to THBS1 reduced invasion in mesenchymal-like melanoma cells, while ectopic THBS1 expression in epithelial-like melanoma cells enhanced invasion. Furthermore, the loss of THBS1 inhibited in vivo motility of melanoma cells within the embryonic chicken neural tube. In addition, we found aberrant THBS1 protein expression in metastatic melanoma tumor biopsies. These results implicate a role for THBS1 in EMT, and hence THBS1 may serve as a novel target for strategies aimed at the treatment of melanoma invasion and drug resistance.

Histone Variant H2A.Z.2 Mediates Proliferation and Drug Sensitivity of Malignant Melanoma

Histone variants are emerging as key regulatory molecules in cancer. We report a unique role for the H2A.Z isoform H2A.Z.2 as a driver of malignant melanoma. H2A.Z.2 is highly expressed in metastatic melanoma, correlates with decreased patient survival, and is required for cellular proliferation. Our integrated genomic analyses reveal that H2A.Z.2 controls the transcriptional output of E2F target genes in melanoma cells. These genes are highly expressed and display a distinct signature of H2A.Z occupancy. We identify BRD2 as an H2A.Z-interacting protein, levels of which are also elevated in melanoma. We further demonstrate that H2A.Z.2-regulated genes are bound by BRD2 and E2F1 in an H2A.Z.2-dependent manner. Importantly, H2A.Z.2 deficiency sensitizes melanoma cells to chemotherapy and targeted therapies. Collectively, our findings implicate H2A.Z.2 as a mediator of cell proliferation and drug sensitivity in malignant melanoma, holding translational potential for novel therapeutic strategies.

Pilocytic astrocytoma: pathology, molecular mechanisms and markers

Pilocytic astrocytomas (PAs) were recognized as a discrete clinical entity over 70 years ago. They are relatively benign (WHO grade I) and have, as a group, a 10-year survival of over 90%. Many require merely surgical removal and only very infrequently do they progress to more malignant gliomas. While most show classical morphology, they may present a spectrum of morphological patterns, and there are difficult cases that show similarities to other gliomas, some of which are malignant and require aggressive treatment. Until recently, almost nothing was known about the molecular mechanisms involved in their development. The use of high-throughput sequencing techniques interrogating the whole genome has shown that single abnormalities of the mitogen-activating protein kinase (MAPK) pathway are exclusively found in almost all cases, indicating that PA represents a one-pathway disease. The most common mechanism is a tandem duplication of a ≈2 Mb-fragment of #7q, giving rise to a fusion between two genes, resulting in a transforming fusion protein, consisting of the N-terminus of KIAA1549 and the kinase domain of BRAF. Additional infrequent fusion partners have been identified, along with other abnormalities of the MAP-K pathway, affecting tyrosine kinase growth factor receptors at the cell surface (e.g., FGFR1) as well as BRAF V600E, KRAS, and NF1 mutations among others. However, while the KIAA1549-BRAF fusion occurs in all areas, the incidence of the various other mutations identified differs in PAs that develop in different regions of the brain. Unfortunately, from a diagnostic standpoint, almost all mutations found have been reported in other brain tumor types, although some retain considerable utility. These molecular abnormalities will be reviewed, and the difficulties in their potential use in supporting a diagnosis of PA, when the histopathological findings are equivocal or in the choice of individualized therapy, will be discussed.

Targeting EZH2 and PRC2 dependence as novel anticancer therapy

Distinctive patterns of chromatin modification control gene expression and define cellular identity during development and cell differentiation. Polycomb repressive complex 2 (PRC2), the sole mammalian enzymatic complex capable of establishing gene-repressive high-degree methylation of histone H3 at lysine 27 (H3K27), plays crucial roles in regulation of normal and malignant hematopoiesis. Recently, increasing evidence has indicated that recurrent gain-of-function mutation and overexpression of EZH2, the catalytic subunit of PRC2, drive and promote malignant transformation such as B-cell lymphomagenesis, providing a rationale for PRC2 inhibition as a novel anticancer strategy. Here, we summarize the recently developed strategies for inhibition of PRC2, which include a series of highly specific, highly potent, small-molecule inhibitors of EZH2 and EZH1, an EZH2-related methyltransferase. PRC2 establishes functional crosstalk with numerous epigenetic machineries during dynamic regulation of gene transcription. Perturbation of such functional crosstalk caused by genetic events observed in various hematologic cancers, such as inactivation of SNF5 and somatic mutation of UTX, confers PRC2 dependence, thus rendering an increased sensitivity to PRC2 inhibition. We discuss our current understanding of EZH2 somatic mutations frequently found in B-cell lymphomas and recurrent mutations in various other epigenetic regulators as novel molecular predictors and determinants of PRC2 sensitivity. As recent advances have indicated a critical developmental or tumor-suppressive role for PRC2 and EZH2 in various tissue types, we discuss concerns over potentially toxic or even adverse effects associated with EZH2/1 inhibition in certain biological contexts or on cancer genetic background. Collectively, inhibition of PRC2 catalytic activity has emerged as a promising therapeutic intervention for the precise treatment of a range of genetically defined hematologic malignancies and can be potentially applied to a broader spectrum of human cancers that bear similar genetic and epigenetic characteristics.

N-(3-Ethynyl-2,4-difluorophenyl)sulfonamide Derivatives as Selective Raf Inhibitors

A series of N-(3-ethynyl-2,4-difluorophenyl)sulfonamides were identified as new selective Raf inhibitors. The compounds potently inhibit B-Raf(V600E) with low nanomolar IC50 values and exhibit excellent target specificity in a selectivity profiling investigation against 468 kinases. They strongly suppress proliferation of a panel of human cancer cell lines and patient-derived melanoma cells with B-Raf(V600E) mutation while being significantly less potent to the cells with B-Raf(WT). The compounds also display favorable pharmacokinetic properties with a preferred example (3s) demonstrating significant in vivo antitumor efficacy in a xenograft mouse model of B-Raf(V600E) mutated Colo205 human colorectal cancer cells, supporting it as a promising lead compound for further anticancer drug discovery.

Translating genomics for precision cancer medicine

The Human Genome Project not only provided the essential reference map for the human genome but also stimulated the development of technology and analytic tools to process massive quantities of genomic data. As a result of this project, new technologies for DNA sequencing have improved in efficiency and cost by more than a millionfold over the past decade, and these technologies can now be routinely applied at a cost of less than $5,000 per genome. Although the application of these technologies in cancer genomics research has continued to contribute to basic discoveries, opportunities for translating them for individual patients have also emerged. This is especially important in clinical cancer research, where genetic alterations in a patient's tumor may be matched to molecularly targeted therapies. In this review, we discuss the integration of cancer genomics and clinical oncology and the opportunity to deliver precision cancer medicine.

Targeting cancer with kinase inhibitors

Kinase inhibitors have played an increasingly prominent role in the treatment of cancer and other diseases. Currently, more than 25 oncology drugs that target kinases have been approved, and numerous additional therapeutics are in various stages of clinical evaluation. In this Review, we provide an in-depth analysis of activation mechanisms for kinases in cancer, highlight recent successes in drug discovery, and demonstrate the clinical impact of selective kinase inhibitors. We also describe the substantial progress that has been made in designing next-generation inhibitors to circumvent on-target resistance mechanisms, as well as ongoing strategies for combining kinase inhibitors in the clinic. Last, there are numerous prospects for the discovery of novel kinase targets, and we explore cancer immunotherapy as a new and promising research area for studying kinase biology.

Combined BRAF and MEK inhibition for the treatment of BRAF-mutated metastatic melanoma

Combined BRAF and MEK inhibition out-performed BRAF inhibitor monotherapy in 3 randomized Phase 3 studies for BRAF-mutated metastatic melanoma patients and the combination of BRAF inhibitor dabrafenib with MEK inhibitor trametinib is now an FDA-approved treatment in this setting. Nevertheless, the majority of patients face progressive disease even when treated with the combination. Mechanisms of resistance to BRAF inhibition have been extensively investigated, whilst less is known about the specific mechanisms of resistance to combined therapy. The aim of this paper is to review the efficacy and safety of the combination of BRAF plus MEK inhibitors compared with BRAF inhibitor monotherapy and immunotherapy, as well as to discuss the existing evidence for the mechanisms of resistance to combined therapy and assess future treatment strategies to improve outcome based on data provided by clinical and translational research studies.

Low inducible expression of p21Cip1 confers resistance to paclitaxel in BRAF mutant melanoma cells with acquired resistance to BRAF inhibitor

The therapeutic efficacy of oncogenic BRAF inhibitor is limited by the onset of acquired resistance. In this study, we investigated the potential therapeutic effects of the mitotic inhibitor paclitaxel on three melanoma cell lines with differing sensitivity to the BRAF inhibitor. Of the two BRAF inhibitor-resistant cell lines, A375P/Mdr cells harboring the BRAF V600E mutant were resistant and the wild-type BRAF SK-MEL-2 cells were sensitive to paclitaxel. In particular, paclitaxel caused the growth inhibition of SK-MEL-2 cells to a much greater extent than it caused growth inhibition of A375P cells. Paclitaxel exhibited no significant effect on the phosphorylation of MEK-ERK in any cell lines tested, regardless of both the BRAF mutation and the drug resistance, implying that paclitaxel activity is independent of MEK-ERK inhibition. In A375P cells, paclitaxel treatment resulted in a marked emergence of apoptotic cells after mitotic arrest, concomitant with a remarkable induction of p21(Cip1). However, paclitaxel only moderately increased the levels of p21(Cip1) in A375P/Mdr cells, which exhibited a strong resistance to paclitaxel. The p21(Cip1) overexpression partially conferred paclitaxel sensitivity to A375P/Mdr cells. Interestingly, we found an extremely low background expression level of p21(Cip1) in SK-MEL-2 cells lacking normal p53 function, which caused much greater G2/M arrest than that seen in A375P cells. Taken together, these results suggest that paclitaxel may be an effective anticancer agent through regulating the expression of p21(Cip1) for the treatment of BRAF mutant melanoma cells resistant to BRAF inhibitors.

Melanoma

Melanoma is a common cancer in the Western world with an increasing incidence. Sun exposure is still considered to be the major risk factor for melanoma. The prognosis of patients with malignant (advanced-stage) melanoma differs widely between countries, but public campaigns advocating early detection have led to significant reductions in mortality rates. As well as sun exposure, distinct genetic alterations have been identified as associated with melanoma. For example, families with melanoma who have germline mutations in CDKN2A are well known, whereas the vast majority of sporadic melanomas have mutations in the mitogen-activated protein kinase cascade, which is the pathway with the highest oncogenic and therapeutic relevance for this disease. BRAF and NRAS mutations are typically found in cutaneous melanomas, whereas KIT mutations are predominantly observed in mucosal and acral melanomas. GNAQ and GNA11 mutations prevail in uveal melanomas. Additionally, the PI3K-AKT-PTEN pathway and the immune checkpoint pathways are important. The finding that programmed cell death protein 1 ligand 1 (PDL1) and PDL2 are expressed by melanoma cells, T cells, B cells and natural killer cells led to the recent development of programmed cell death protein 1 (PD1)-specific antibodies (for example, nivolumab and pembrolizumab). Alongside other new drugs - namely, BRAF inhibitors (vemurafenib and dabrafenib) and MEK inhibitors (trametinib and cobimetinib) - these agents are very promising and have been shown to significantly improve prognosis for patients with advanced-stage metastatic disease. Early signs are apparent that these new treatment modalities are also improving long-term clinical benefit and the quality of life of patients. This Primer summarizes the current understanding of melanoma, from mechanistic insights to clinical progress. For an illustrated summary of this Primer, visit: http://go.nature.com/vX2N9s.

Intravital imaging reveals how BRAF inhibition generates drug-tolerant microenvironments with high integrin β1/FAK signaling

Intravital imaging of BRAF-mutant melanoma cells containing an ERK/MAPK biosensor reveals how the tumor microenvironment affects response to BRAF inhibition by PLX4720. Initially, melanoma cells respond to PLX4720, but rapid reactivation of ERK/MAPK is observed in areas of high stromal density. This is linked to "paradoxical" activation of melanoma-associated fibroblasts by PLX4720 and the promotion of matrix production and remodeling leading to elevated integrin β1/FAK/Src signaling in melanoma cells. Fibronectin-rich matrices with 3-12 kPa elastic modulus are sufficient to provide PLX4720 tolerance. Co-inhibition of BRAF and FAK abolished ERK reactivation and led to more effective control of BRAF-mutant melanoma. We propose that paradoxically activated MAFs provide a "safe haven" for melanoma cells to tolerate BRAF inhibition.

In silico identification of novel kinase inhibitors by targeting B-Raf(v660e) from natural products database

The Ras/Raf/MEK/ERK (MAPK) signaling pathway has gained much attention from scientific community for therapeutic intervention in the past decades, specifically in oncology. Notably, a most prevalent B-Raf(v600e) mutant in Raf kinase family exhibits elevated kinase activity and results in constitutive activation of the MAPK pathway, thus making it a promising drug target for cancer therapy. Herein, virtual screening is applied to identify its potential inhibitors. Following the 25 ns molecular dynamic (MD) simulations, ZINC38541768, ZINC38541767, and ZINC12496469 are identified as B-Raf(v600e) potential inhibitors in a DFG-in conformation. Furthermore, according to the molecular mechanics/generalized born surface area (MM/GBSA) method, these three small molecules exhibit similar and good binding affinity toward B-Raf(v600e) (-38.76 kcal mol(-1), -42.60 kcal mol(-1), and -39.04 kcal mol(-1)). At the same time, several critical residues, such as I463, V471 in the P-loop, and DFG motif residue D594 within the A-loop, are also well clarified. All these results may not only indicate some future applications of inhibitors targeting B-Raf(v600e), but also benefit B-Raf(v600e) harboring cancer patients.

KSR1 is coordinately regulated with Notch signaling and oxidative phosphorylation in thyroid cancer

Kinase suppressor of RAS1 (KSR1) is a scaffold protein implicated in RAS-mediated RAF activation. However, the molecular function of KSR in papillary thyroid cancer (PTC) is unknown. Thus, this study aimed to characterize the role of KSR1 in patients with PTC. qRT-PCR and immunohistochemistry (IHC) revealed inter-tumor heterogeneities in the expression of KSR1 in PTC tissues. Interestingly, BRAFV600E-positive PTC showed higher KSR1 mRNA expression than BRAFV600E-negative PTC (P<0.001). Gene Set Enrichment Analysis (GSEA) using public repositories showed that high KSR1 expression coordinately upregulated Notch signaling (nominal P=0.019, false discovery rate (FDR) q-value=0.165); this finding was supported by GeneNetwork analysis, indicating that KSR1 expression is positively correlated with NOTCH1 expression (ρ=0.677, P=6.15×10(-9)). siRNA against KSR1 (siKSR1) significantly decreased ERK phosphorylation induced by BRAFV600E, resulting in reduced expression of NOTCH1 and HES1, targets of Notch signaling. GSEA revealed that high KSR1 expression was also associated with downregulation of genes related to oxidative phosphorylation (OxPhos). Consistent with this, electron microscopy showed that PTCs with high KSR1 expression exhibited structural defects of the mitochondrial cristae. Furthermore, siKSR1-transfected BCPAP and 8505C cells generated fewer colonies in colony-forming assays. In addition, GSEA showed that high expression of KSR2 and connector enhancer of KSR1 (CNKSR1) also coordinately upregulated Notch signaling (KSR2: nominal P=0.0097, FDR q-value=0.154 and CNKSR1: nominal P<0.0001, FDR q-value=0.00554), and high CNKSR2 was associated with downregulation of the OxPhos gene set (nominal P<0.0001, FDR q-value <0.0001). In conclusion, KSR1 is coordinately regulated with Notch signaling and OxPhos in PTC, because its scaffold function might be required to sustain the proliferative signaling and metabolic remodeling associated with this type of cancer.

Signal transduction in cancer

Cancer is driven by genetic and epigenetic alterations that allow cells to overproliferate and escape mechanisms that normally control their survival and migration. Many of these alterations map to signaling pathways that control cell growth and division, cell death, cell fate, and cell motility, and can be placed in the context of distortions of wider signaling networks that fuel cancer progression, such as changes in the tumor microenvironment, angiogenesis, and inflammation. Mutations that convert cellular proto-oncogenes to oncogenes can cause hyperactivation of these signaling pathways, whereas inactivation of tumor suppressors eliminates critical negative regulators of signaling. An examination of the PI3K-Akt and Ras-ERK pathways illustrates how such alterations dysregulate signaling in cancer and produce many of the characteristic features of tumor cells.

Systematic analysis of BRAF(V600E) melanomas reveals a role for JNK/c-Jun pathway in adaptive resistance to drug-induced apoptosis

Drugs that inhibit RAF/MEK signaling, such as vemurafenib, elicit profound but often temporary anti-tumor responses in patients with BRAF^V600E melanoma. Adaptive responses to RAF/MEK inhibition occur on a timescale of hours to days, involve homeostatic responses that reactivate MAP kinase signaling and compensatory mitogenic pathways, and attenuate the anti-tumor effects of RAF/MEK inhibitors. We profile adaptive responses across a panel of melanoma cell lines using multiplex biochemical measurement, single-cell assays, and statistical modeling and show that adaptation involves at least six signaling cascades that act to reduce drug potency (IC₅₀) and maximal effect (i.e., E_max ≪ 1). Among these cascades, we identify a role for JNK/c-Jun signaling in vemurafenib adaptation and show that RAF and JNK inhibitors synergize in cell killing. This arises because JNK inhibition prevents a subset of cells in a cycling population from becoming quiescent upon vemurafenib treatment, thereby reducing drug E_max. Our findings demonstrate the breadth and diversity of adaptive responses to RAF/MEK inhibition and a means to identify which steps in a signaling cascade are most predictive of phenotypic response.

Therapy-induced tumour secretomes promote resistance and tumour progression

Drug resistance invariably limits the clinical efficacy of targeted therapy with kinase inhibitors against cancer. Here we show that targeted therapy with BRAF, ALK or EGFR kinase inhibitors induces a complex network of secreted signals in drug-stressed human and mouse melanoma and human lung adenocarcinoma cells. This therapy-induced secretome stimulates the outgrowth, dissemination and metastasis of drug-resistant cancer cell clones and supports the survival of drug-sensitive cancer cells, contributing to incomplete tumour regression. The tumour-promoting secretome of melanoma cells treated with the kinase inhibitor vemurafenib is driven by downregulation of the transcription factor FRA1. In situ transcriptome analysis of drug-resistant melanoma cells responding to the regressing tumour microenvironment revealed hyperactivation of several signalling pathways, most prominently the AKT pathway. Dual inhibition of RAF and the PI(3)K/AKT/mTOR intracellular signalling pathways blunted the outgrowth of the drug-resistant cell population in BRAF mutant human melanoma, suggesting this combination therapy as a strategy against tumour relapse. Thus, therapeutic inhibition of oncogenic drivers induces vast secretome changes in drug-sensitive cancer cells, paradoxically establishing a tumour microenvironment that supports the expansion of drug-resistant clones, but is susceptible to combination therapy.

Homologous Mutation to Human BRAF V600E Is Common in Naturally Occurring Canine Bladder Cancer--Evidence for a Relevant Model System and Urine-Based Diagnostic Test

Targeted cancer therapies offer great clinical promise, but treatment resistance is common, and basic research aimed at overcoming this challenge is limited by reduced genomic and biologic complexity in artificially induced rodent tumors compared with their human counterparts. Animal models that more faithfully recapitulate genotype-specific human pathology could improve the predictive value of these investigations. Here, a newly identified animal model for oncogenic BRAF-driven cancers is described. With 20,000 new cases in the United States each year, canine invasive transitional cell carcinoma of the bladder (InvTCC) is a common, naturally occurring malignancy that shares significant histologic, biologic, and clinical phenotypes with human muscle invasive bladder cancer. In order to identify somatic drivers of canine InvTCC, the complete transcriptome for multiple tumors was determined by RNAseq. All tumors harbored a somatic mutation that is homologous to the human BRAF(V600E) mutation, and an identical mutation was present in 87% of 62 additional canine InvTCC tumors. The mutation was also detectable in the urine sediments of all dogs tested with mutation-positive tumors. Functional experiments suggest that, like human tumors, canine activating BRAF mutations potently stimulate the MAPK pathway. Cell lines with the mutation have elevated levels of phosphorylated MEK, compared with a line with wild-type BRAF. This effect can be diminished through application of the BRAF(V600E) inhibitor vemurafenib. These findings set the stage for canine InvTCC as a powerful system to evaluate BRAF-targeted therapies, as well as therapies designed to overcome resistance, which could enhance treatment of both human and canine cancers

IMPLICATIONS

This study demonstrates the activating BRAF mutation (V600E), which is found in multiple human cancers, is a driver of canine InvTCC, and highlights a urine-based test for quick diagnosis.

Curcumin analog DM-1 in monotherapy or combinatory treatment with dacarbazine as a strategy to inhibit in vivo melanoma progression

Malignant melanoma is a highly aggressive form of skin cancer with a high mortality rate if not discovered in early stages. Although a limited number of treatment options for melanoma currently exist, patients with a more aggressive form of this cancer frequently decline treatment. DM-1 is a sodium phenolate and curcumin analog with proven anticancer, anti-proliferative and anti-metastatic properties. In this paper, the DM-1 compound showed in vivo antitumor activity alone or in combination with chemotherapeutic DTIC in B16F10 melanoma-bearing mice. Beneficial effects such as melanoma tumor burden reduction with pyknotic nuclei, decreased nuclei/cytoplasmic ratio and nuclear degradation occurred after DM-1 treatment. No toxicological changes were observed in the liver, kidneys, spleen and lungs after DM-1 monotherapy or DTIC combined therapy. DTIC+DM-1 treatment induced the recovery of anemia arising from melanoma and immunomodulation. Both DM-1 treatment alone and in combination with DTIC induced apoptosis with the cleavage of caspase-3, -8 and -9. Furthermore, melanoma tumors treated with DM-1 showed a preferential apoptotic intrinsic pathway by decreasing Bcl-2/Bax ratio. Considering the chemoresistance exhibited by melanoma towards conventional chemotherapy drugs, DM-1 compound in monotherapy or in combination therapy provides a promising improvement in melanoma treatment with a reduction of side effects.

Combination therapy of melanoma using kinase inhibitors

PURPOSE OF REVIEW

Treatment options for metastatic melanoma depend on the clinical course of the disease and the molecular profile such as mutations of the BRAF gene. In this article, we review the current state of targeted therapy with kinase inhibitors.

RECENT FINDINGS

Despite major advancements in targeted therapy of metastatic melanoma, most patients relapse and show progressive disease after 5-7 months with single inhibition of BRAF or MEK. Acquired resistance is virtually universal and mediated by diverse mitogen-activated protein kinase-dependent or independent mechanisms. Recent evidence favours concurrent targeting of BRAF and MEK in patients with BRAFV600-mutated melanoma instead of BRAF inhibitor monotherapy. The combination delays the onset of acquired resistance, resulting in increased progression-free and overall survival. A growing number of early trials evaluate the efficacy of inhibitors targeting additional pathways such as phospho-inositide 3-kinase/AKT in conjunction with BRAF or MEK. Even though consistent and mature phase III study results are not yet available for these combinations, the repertoire of targeted therapy in metastatic melanoma is wide and promising.

SUMMARY

The short era of single BRAF inhibition in BRAF-mutated melanoma is soon taken over by dual concurrent inhibition of MEK and BRAF.

The biology of IQGAP proteins: beyond the cytoskeleton

IQGAP scaffold proteins are evolutionarily conserved in eukaryotes and facilitate the formation of complexes that regulate cytoskeletal dynamics, intracellular signaling, and intercellular interactions. Fungal and mammalian IQGAPs are implicated in cytokinesis. IQGAP1, IQGAP2, and IQGAP3 have diverse roles in vertebrate physiology, operating in the kidney, nervous system, cardio-vascular system, pancreas, and lung. The functions of IQGAPs can be corrupted during oncogenesis and are usurped by microbial pathogens. Therefore, IQGAPs represent intriguing candidates for novel therapeutic agents. While modulation of the cytoskeletal architecture was initially thought to be the primary function of IQGAPs, it is now clear that they have roles beyond the cytoskeleton. This review describes contributions of IQGAPs to physiology at the organism level.

Oncogene addiction: pathways of therapeutic response, resistance, and road maps toward a cure

A key goal of cancer therapeutics is to selectively target the genetic lesions that initiate and maintain cancer cell proliferation and survival. While most cancers harbor multiple oncogenic mutations, a wealth of preclinical and clinical data supports that many cancers are sensitive to inhibition of single oncogenes, a concept referred to as 'oncogene addiction'. Herein, we describe the clinical evidence supporting oncogene addiction and discuss common mechanistic themes emerging from the response and acquired resistance to oncogene-targeted therapies. Finally, we suggest several opportunities toward exploiting oncogene addiction to achieve curative cancer therapies.

Novel therapeutic options for relapsed hairy cell leukemia

The majority of patients with hairy cell leukemia (HCL) achieve a response to therapy with cladribine or pentostatin with or without rituximab. However, late relapses can occur. Treatment of relapsed HCL can be difficult due to a poor tolerance to chemotherapy, increased risk of infections and decreased responsiveness to chemotherapy. The identification of BRAFV600E mutations and the role of aberrant MEK kinase and Bruton's tyrosine kinase (BTK) pathways in the pathogenesis of HCL have helped to develop novel targeted therapies for these patients. Currently, the most promising therapeutic strategies for relapsed or refractory HCL include recombinant immunoconjugates targeting CD22 (e.g. moxetumomab pasudotox), BRAF inhibitors such as vemurafenib and B cell receptor signaling kinase inhibitors such as ibrutinib. Furthermore, the VH4-34 molecular variant of classic HCL has been identified to be less responsive to chemotherapy. Herein, we review the results of the ongoing clinical trials and potential future therapies for relapsed/refractory HCL.

PI3'-kinase inhibition forestalls the onset of MEK1/2 inhibitor resistance in BRAF-mutated melanoma

Phosphatidylinositide 3' (PI3')-lipid signaling cooperates with oncogenic BRAF(V600E) to promote melanomagenesis. Sustained PI3'-lipid production commonly occurs via silencing of the PI3'-lipid phosphatase PTEN or, less commonly, through mutational activation of PIK3CA, encoding the 110-kDa catalytic subunit of PI3'-kinase-α (PI3Kα). To define the PI3K catalytic isoform dependency of BRAF-mutated melanoma, we used pharmacologic, isoform-selective PI3K inhibitors in conjunction with melanoma-derived cell lines and genetically engineered mouse (GEM) models. Although BRAF(V600E)/PIK3CA(H1047R) melanomas were sensitive to the antiproliferative effects of selective PI3Kα blockade, inhibition of BRAF(V600E)/PTEN(Null) melanoma proliferation required combined blockade of PI3Kα, PI3Kδ, and PI3Kγ, and was insensitive to PI3Kβ blockade. In GEM models, isoform-selective PI3K inhibition elicited cytostatic effects, but significantly potentiated melanoma regression in response to BRAF(V600E) pathway-targeted inhibition. Interestingly, PI3K inhibition forestalled the onset of MEK inhibitor resistance in two independent GEM models of BRAF(V600E)-driven melanoma. These results suggest that combination therapy with PI3K inhibitors may be a useful strategy to extend the duration of clinical response of patients with BRAF-mutated melanoma to BRAF(V600E) pathway-targeted therapies.

SIGNIFICANCE

Although BRAF(V600E) pathway-targeted therapies elicit melanoma regression, the onset of drug resistance limits the durability of response. Here, we show that combined treatment with PI3K inhibitors significantly forestalled the onset of MEK1/2 inhibitor-resistant disease in BRAF-mutated GEM melanoma models. These results provide a conceptual framework for the combined deployment of BRAF(V600E) plus PI3K pathway-targeted inhibitors in the treatment of a subset of patients with BRAF-mutated melanoma.

Aberrant expression of COT is related to recurrence of papillary thyroid cancer

Aberrant expression of Cancer Osaka Thyroid Oncogene mitogen-activated protein kinase kinase kinase 8 (COT) (MAP3K8) is a driver of resistance to B-RAF inhibition. However, the de novo expression and clinical implications of COT in papillary thyroid cancer (PTC) have not been investigated.The aim of this study is to investigate the expression of A-, B-, C-RAF, and COT in PTC (n = 167) and analyze the clinical implications of aberrant expression of these genes.Quantitative polymerase chain reaction (qPCR) and immunohistochemical staining (IHC) were performed on primary thyroid cancers. Expression of COT was compared with clinicopathological characteristics including recurrence-free survival. Datasets from public repository (NCBI) were subjected to Gene Set Enrichment Analysis (GSEA).qPCR data showed that the relative mRNA expression of A-, B-, C-RAF and COT of PTC were higher than normal tissues (all P < 0.01). In addition, the expression of COT mRNA in PTC showed positive correlation with A- (r = 0.4083, P < 0.001), B- (r = 0.2773, P = 0.0003), and C-RAF (r = 0.5954, P < 0.001). The mRNA expressions of A-, B,- and C-RAF were also correlated with each other (all P < 0.001). In IHC, the staining intensities of B-RAF and COT were higher in PTC than in normal tissue (P < 0.001). Interestingly, moderate-to-strong staining intensities of B-RAF and COT were more frequent in B-RAF-positive PTC (P < 0.001, P = 0.013, respectively). In addition, aberrant expression of COT was related to old age at initial diagnosis (P = 0.045) and higher recurrence rate (P = 0.025). In multivariate analysis, tumor recurrence was persistently associated with moderate-to-strong staining of COT after adjusting for age, sex, extrathyroidal extension, multifocality, T-stage, N-stage, TNM stage, and B-RAF mutation (odds ratio, 4.662; 95% confidence interval 1.066 - 21.609; P = 0.045). Moreover, moderate-to-strong COT expression in PTC was associated with shorter recurrence-free survival (mean follow-up duration, 14.2 ± 4.1 years; P = 0.0403). GSEA indicated that gene sets related to B-RAF-RAS (P < 0.0001, false discovery rate [FDR] q-value = 0.000) and thyroid differentiation (P = 0.048, FDR q-value = 0.05) scores were enriched in lower COT expression group and gene sets such as T-cell receptor signaling pathway and Toll-like receptor signaling pathway are coordinately upregulated in higher COT expression group (both, P < 0.0001, FDR q-value = 0.000).Aberrant expression of A-, B-, and C-RAF, and COT is frequent in PTC; increased expression of COT is correlated with recurrence of PTC.

Targeted therapies in melanoma

Advances in the biology of melanoma have provided insights about chemoresistance and its genetic heterogeneity in parallel with advances in drug design, culminating in recent major treatment breakthroughs. Although clinical benefit of targeted therapies has been unquestionable, future advances are only possible if we understand the interplay between genetic aberrations and role of other crucial nongenetic changes yet to be identified by such projects as the Cancer Genome Atlas Project in Melanoma. Combination therapies, either among small molecule inhibitors themselves and/or with immunotherapies, may be the optimal strategy to prevent development of drug resistance inherently linked with such targeted therapies.

The epigenetic modifier EZH2 controls melanoma growth and metastasis through silencing of distinct tumour suppressors

Increased activity of the epigenetic modifier EZH2 has been associated with different cancers. However, evidence for a functional role of EZH2 in tumorigenesis in vivo remains poor, in particular in metastasizing solid cancers. Here we reveal central roles of EZH2 in promoting growth and metastasis of cutaneous melanoma. In a melanoma mouse model, conditional Ezh2 ablation as much as treatment with the preclinical EZH2 inhibitor GSK503 stabilizes the disease through inhibition of growth and virtually abolishes metastases formation without affecting normal melanocyte biology. Comparably, in human melanoma cells, EZH2 inactivation impairs proliferation and invasiveness, accompanied by re-expression of tumour suppressors connected to increased patient survival. These EZH2 target genes suppress either melanoma growth or metastasis in vivo, revealing the dual function of EZH2 in promoting tumour progression. Thus, EZH2-mediated epigenetic repression is highly relevant especially during advanced melanoma progression, which makes EZH2 a promising target for novel melanoma therapies.

BRAF-mutant melanoma: treatment approaches, resistance mechanisms, and diagnostic strategies

BRAF inhibitors vemurafenib and dabrafenib achieved improved overall survival over chemotherapy and have been approved for the treatment of BRAF-mutated metastatic melanoma. More recently, the combination of BRAF inhibitor dabrafenib with MEK inhibitor trametinib has shown improved progression-free survival, compared to dabrafenib monotherapy, in a Phase II study and has received approval by the US Food and Drug Administration. However, even when treated with the combination, most patients develop mechanisms of acquired resistance, and some of them do not achieve tumor regression at all, because of intrinsic resistance to therapy. Along with the development of BRAF inhibitors, immunotherapy made an important step forward: ipilimumab, an anti-CTLA-4 monoclonal antibody, was approved for the treatment of metastatic melanoma; anti-PD-1 agents achieved promising results in Phase I/II trials, and data from Phase III studies will be ready soon. The availability of such drugs, which are effective regardless of BRAF status, has made the therapeutic approach more complex, as first-line treatment with BRAF inhibitors may not be the best choice for all BRAF-mutated patients. The aim of this paper is to review the systemic therapeutic options available today for patients affected by BRAF V600-mutated metastatic melanoma, as well as to summarize the mechanisms of resistance to BRAF inhibitors and discuss the possible strategies to overcome them. Moreover, since the molecular analysis of tumor specimens is now a pivotal and decisional factor in the treatment strategy of metastatic melanoma patients, the advances in the molecular detection techniques for the BRAF V600 mutation will be reported.

Pilot trial of combined BRAF and EGFR inhibition in BRAF-mutant metastatic colorectal cancer patients

PURPOSE

BRAF-mutant metastatic colorectal cancer (mCRC) forms an aggressive subset of colorectal cancer with minimal response to selective RAF inhibitors. Preclinical data show that reactivation of EGFR signaling occurs in colorectal tumor cells treated with RAF inhibitors and that the addition of an EGFR inhibitor enhances antitumor activity. These data suggest that combined therapy with RAF and EGFR inhibitors could be an effective strategy for treating BRAF V600E mCRC.

EXPERIMENTAL DESIGN

We undertook a pilot trial to assess the response rate and safety of the BRAF inhibitor vemurafenib combined with anti-EGFR antibody panitumumab in patients with BRAF-mutant mCRC. Patients received standard approved doses of panitumumab and vemurafenib.

RESULTS

Fifteen patients were treated. Performance status was Eastern Cooperative Oncology Group (ECOG) 0 in 4 patients (27%) and ECOG 1 in 11 patients (73%). All patients had progressed through at least one standard treatment regimen, and 8 (53%) had received previous fluoropyrimidine, oxaliplatin, and irinotecan chemotherapy. Treatment was well tolerated, with less cutaneous toxicity than would be expected with either agent, and no cases of keratoacanthomas/squamous cell carcinomas. Tumor regressions were seen in 10 of 12 evaluable patients with partial responses in 2 patients (100% and 64% regression lasting 40 and 24 weeks, respectively), and stable disease lasting over 6 months in 2 patients.

CONCLUSIONS

Combined RAF and EGFR inhibition is well tolerated, with less cutaneous toxicity than would be expected with either agent, and results in modest clinical activity in this highly aggressive and chemoresistant subset of CRC.

Limited genomic heterogeneity of circulating melanoma cells in advanced stage patients

Purpose. Circulating melanoma cells (CMCs) constitute a potentially important representation of time-resolved tumor biology in patients. To date, genomic characterization of CMCs has been limited due to the lack of a robust methodology capable of identifying them in a format suitable for downstream characterization. Here, we have developed a methodology to detect intact CMCs that enables phenotypic, morphometric and genomic analysis at the single cell level. Experimental design. Blood samples from 40 metastatic melanoma patients and 10 normal blood donors were prospectively collected. A panel of 7 chondroitin sulfate proteoglycan 4 (CSPG4)-specific monoclonal antibodies (mAbs) was used to immunocytochemically label CMCs. Detection was performed by automated digital fluorescence microscopy and multi-parametric computational analysis. Individual CMCs were captured by micromanipulation for whole genome amplification and copy number variation (CNV) analysis. Results. Based on CSPG4 expression and nuclear size, 1-250 CMCs were detected in 22 (55%) of 40 metastatic melanoma patients (0.5-371.5 CMCs ml(-1)). Morphometric analysis revealed that CMCs have a broad spectrum of morphologies and sizes but exhibit a relatively homogeneous nuclear size that was on average 1.5-fold larger than that of surrounding PBMCs. CNV analysis of single CMCs identified deletions of CDKN2A and PTEN, and amplification(s) of TERT, BRAF, KRAS and MDM2. Furthermore, novel chromosomal amplifications in chr12, 17 and 19 were also found. Conclusions. Our findings show that CSPG4 expressing CMCs can be found in the majority of advanced melanoma patients. High content analysis of this cell population may contribute to the design of effective personalized therapies in patients with melanoma.

Evolution of targeted therapies in cancer: opportunities and challenges in the clinic

ABSTRACT 

Targeted therapies have changed the course of cancer treatment in recent years. By reducing toxicity and improving outcome, these new generations of precision medicines have extended patient lives beyond what could be achieved by the use of nontargeted therapies. In the last 2 years, several new molecular entities targeting signaling proteins and immune pathways have gone through successful clinical development resulting in their approval. These new targeted therapies require patient selection and the discovery of biomarkers of response. This review discusses the evolution of targeted therapies in cancer and challenges in translating the concepts into clinical practice.

The PI3K/AKT/mTOR interactive pathway

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of the rapamycin (mTOR) signalling pathway is hyperactivated or altered in many cancer types and regulates a broad range of cellular processes including survival, proliferation, growth, metabolism, angiogenesis and metastasis.

Co-targeting BRAF and cyclin dependent kinases 4/6 for BRAF mutant cancers

Selective BRAF inhibitors have demonstrated significant clinical benefit in melanoma patients harboring oncogenic BRAF mutations. However, the majority of such patients either exhibit de novo resistance from the beginning of the treatment or acquire resistance and eventually relapse. Despite tremendous progress in understanding the underlying mechanisms of resistance, overcoming resistance to BRAF inhibitors remains an unmet medical need. Constitutive activation of cyclin-dependent kinases (CDK) 4/6 as a result of genetic aberrations including CDKN2A inactivation and CCND1 amplification is common across many cancer types and frequently co-occurs with oncogenic BRAF mutations. Also, cyclin D1 overexpression is a common feature of resistance to BRAF inhibitors. Here we review CDK4/6 as a therapeutic target in BRAF mutant cancers and discuss emerging evidence supporting a critical role of cyclin D1/CDK4/6 axis in de novo and acquired resistance to BRAF inhibitors. Co-targeting CDK4/6 and BRAF could be a more effective therapy to augment clinical response of BRAF inhibitors and overcome resistance in BRAF mutant cancers.

Advances in combination therapies based on nanoparticles for efficacious cancer treatment: an analytical report

The main objective of nanomedicine research is the development of nanoparticles as drug delivery systems or drugs per se to tackle diseases as cancer, which are a leading cause of death with developed nations. Targeted treatments against solid tumors generally lead to dramatic regressions, but, unfortunately, the responses are often short-lived due to resistant cancer cells. In addition, one of the major challenges of combination drug therapy (called "cocktail") is the crucial optimization of different drug parameters. This issue can be solved using combination nanotherapy. Nanoparticles developed in oncology based on combination nanotherapy are either (a) those designed to combat multidrug resistance or (b) those used to circumvent resistance to clinical cancer drugs. This review provides an overview of the different nanoparticles currently used in clinical treatments in oncology. We analyze in detail the development of combinatorial nanoparticles including dendrimers for dual drug delivery via two strategic approaches: (a) use of chemotherapeutics and chemosensitizers to combat multidrug resistance and (b) use of multiple cytotoxic drugs. Finally, in this review, we discuss the challenges, clinical outlook, and perspectives of the nanoparticle-based combination therapy in cancer.

Cancer in silico drug discovery: a systems biology tool for identifying candidate drugs to target specific molecular tumor subtypes

Large-scale cancer datasets such as The Cancer Genome Atlas (TCGA) allow researchers to profile tumors based on a wide range of clinical and molecular characteristics. Subsequently, TCGA-derived gene expression profiles can be analyzed with the Connectivity Map (CMap) to find candidate drugs to target tumors with specific clinical phenotypes or molecular characteristics. This represents a powerful computational approach for candidate drug identification, but due to the complexity of TCGA and technology differences between CMap and TCGA experiments, such analyses are challenging to conduct and reproduce. We present Cancer in silico Drug Discovery (CiDD; scheet.org/software), a computational drug discovery platform that addresses these challenges. CiDD integrates data from TCGA, CMap, and Cancer Cell Line Encyclopedia (CCLE) to perform computational drug discovery experiments, generating hypotheses for the following three general problems: (i) determining whether specific clinical phenotypes or molecular characteristics are associated with unique gene expression signatures; (ii) finding candidate drugs to repress these expression signatures; and (iii) identifying cell lines that resemble the tumors being studied for subsequent in vitro experiments. The primary input to CiDD is a clinical or molecular characteristic. The output is a biologically annotated list of candidate drugs and a list of cell lines for in vitro experimentation. We applied CiDD to identify candidate drugs to treat colorectal cancers harboring mutations in BRAF. CiDD identified EGFR and proteasome inhibitors, while proposing five cell lines for in vitro testing. CiDD facilitates phenotype-driven, systematic drug discovery based on clinical and molecular data from TCGA.

DNA repair inhibition by UVA photoactivated fluoroquinolones and vemurafenib

Cutaneous photosensitization is a common side effect of drug treatment and can be associated with an increased skin cancer risk. The immunosuppressant azathioprine, the fluoroquinolone antibiotics and vemurafenib—a BRAF inhibitor used to treat metastatic melanoma—are all recognized clinical photosensitizers. We have compared the effects of UVA radiation on cultured human cells treated with 6-thioguanine (6-TG, a DNA-embedded azathioprine surrogate), the fluoroquinolones ciprofloxacin and ofloxacin and vemurafenib. Despite widely different structures and modes of action, each of these drugs potentiated UVA cytotoxicity. UVA photoactivation of 6-TG, ciprofloxacin and ofloxacin was associated with the generation of singlet oxygen that caused extensive protein oxidation. In particular, these treatments were associated with damage to DNA repair proteins that reduced the efficiency of nucleotide excision repair. Although vemurafenib was also highly phototoxic to cultured cells, its effects were less dependent on singlet oxygen. Highly toxic combinations of vemurafenib and UVA caused little protein carbonylation but were nevertheless inhibitory to nucleotide excision repair. Thus, for three different classes of drugs, photosensitization by at least two distinct mechanisms is associated with reduced protection against potentially mutagenic and carcinogenic DNA damage.

Role of P-glycoprotein on the brain penetration and brain pharmacodynamic activity of the MEK inhibitor cobimetinib

Cobimetinib is a MEK inhibitor currently in clinical trials as an anticancer agent. The objectives of this study were to determine in vitro and in vivo if cobimetinib is a substrate of P-glycoprotein (P-gp) and/or breast cancer resistance protein (Bcrp1) and to assess the implications of efflux on cobimetinib pharmacokinetics (PK), brain penetration, and target modulation. Cell lines transfected with P-gp or Bcrp1 established that cobimetinib was a substrate of P-gp but not a substrate of Bcrp1. In vivo, after intravenous and oral administration of cobimetinib to FVB (wild-type; WT), Mdr1a/b(-/-), Bcrp1 (-/-), and Mdr1a/b(-/-)/Bcrp(-/-) knockout (KO) mice, clearance was similar in WT (35.5 ± 16.7 mL/min/kg) and KO animals (22.0 ± 3.6 to 27.6 ± 5.2 mL/min/kg); oral exposure was also similar between WT and KO animals. After an oral 10 mg/kg dose of cobimetinib, the mean total brain to plasma ratio (Kp) at 6 h postdose was 0.3 and 0.2 in WT and Bcrp1(-/-) mice, respectively. In Mdr1a/b(-/-) and Mdr1a/1b/Bcrp1(-/-) KO mice and WT mice treated with elacridar (a P-gp and BCRP inhibitor), Kp increased to 11, 6, and 7, respectively. Increased brain exposure in Mdr1a/b(-/-) and Mdr1a/1b/Bcrp1(-/-) KO and elacridar treated mice was accompanied by up to ∼65% suppression of the target (pErk) in brain tissue, compared to WT mice. By MALDI imaging, the cobimetinib signal intensity was relatively high and was dispersed throughout the brain of Mdr1a/1b/Bcrp1(-/-) KO mice compared to low/undetectable signal intensity in WT mice. The efflux of cobimetinib by P-gp may have implications for the treatment of patients with brain tumors/metastases.

BRAF inhibitor-associated ERK activation drives development of chronic lymphocytic leukemia

Patients with BRAFV600E/K-driven melanoma respond to the BRAF inhibitor vemurafenib due to subsequent deactivation of the proliferative RAS/RAF/MEK/ERK pathway. In BRAF WT cells and those with mutations that activate or result in high levels of the BRAF activator RAS, BRAF inhibition can lead to ERK activation, resulting in tumorigenic transformation. We describe a patient with malignant melanoma who developed chronic lymphocytic leukemia (CLL) in the absence of RAS mutations during vemurafenib treatment. BRAF inhibition promoted patient CLL proliferation in culture and in murine xenografts and activated MEK/ERK in primary CLL cells from additional patients. BRAF inhibitor-driven ERK activity and CLL proliferation required B cell antigen receptor (BCR) activation, as inhibition of the BCR-proximal spleen tyrosine kinase (SYK) reversed ERK hyperactivation and proliferation of CLL cells from multiple patients, while inhibition of the BCR-distal Bruton tyrosine kinase had no effect. Additionally, the RAS-GTP/RAS ratio in primary CLL cells exposed to vemurafenib was reduced upon SYK inhibition. BRAF inhibition increased mortality and CLL expansion in mice harboring CLL xenografts; however, SYK or MEK inhibition prevented CLL proliferation and increased animal survival. Together, these results suggest that BRAF inhibitors promote B cell malignancies in the absence of obvious mutations in RAS or other receptor tyrosine kinases and provide a rationale for combined BRAF/MEK or BRAF/SYK inhibition.

Drugging the undruggable RAS: Mission possible?

Despite more than three decades of intensive effort, no effective pharmacological inhibitors of the RAS oncoproteins have reached the clinic, prompting the widely held perception that RAS proteins are 'undruggable'. However, recent data from the laboratory and the clinic have renewed our hope for the development of RAS-inhibitory molecules. In this Review, we summarize the progress and the promise of five key approaches. Firstly, we focus on the prospects of using direct inhibitors of RAS. Secondly, we address the issue of whether blocking RAS membrane association is a viable approach. Thirdly, we assess the status of targeting RAS downstream effector signalling, which is arguably the most favourable current approach. Fourthly, we address whether the search for synthetic lethal interactors of mutant RAS still holds promise. Finally, RAS-mediated changes in cell metabolism have recently been described and we discuss whether these changes could be exploited for new therapeutic directions. We conclude with perspectives on how additional complexities, which are not yet fully understood, may affect each of these approaches.

Synergistic anti-tumor activity and inhibition of angiogenesis by cotargeting of oncogenic and death receptor pathways in human melanoma

Improving treatment of advanced melanoma may require the development of effective strategies to overcome resistance to different anti-tumor agents and to counteract relevant pro-tumoral mechanisms in the microenvironment. Here we provide preclinical evidence that these goals can be achieved in most melanomas, by co-targeting of oncogenic and death receptor pathways, and independently of their BRAF, NRAS, p53 and PTEN status. In 49 melanoma cell lines, we found independent susceptibility profiles for response to the MEK1/2 inhibitor AZD6244, the PI3K/mTOR inhibitor BEZ235 and the death receptor ligand TRAIL, supporting the rationale for their association. Drug interaction analysis indicated that a strong synergistic anti-tumor activity could be achieved by the three agents and the AZD6244–TRAIL association on 20/21 melanomas, including cell lines resistant to the inhibitors or to TRAIL. Mechanistically, synergy was explained by enhanced induction of caspase-dependent apoptosis, mitochondrial depolarization and modulation of key regulators of extrinsic and intrinsic cell death pathways, including c-FLIP, BIM, BAX, clusterin, Mcl-1 and several IAP family members. Moreover, silencing experiments confirmed the central role of Apollon downmodulation in promoting the apoptotic response of melanoma cells to the combinatorial treatments. In SCID mice, the AZD6244–TRAIL association induced significant growth inhibition of a tumor resistant to TRAIL and poorly responsive to AZD6244, with no detectable adverse events on body weight and tissue histology. Reduction in tumor volume was associated not only with promotion of tumor apoptosis but also with suppression of the pro-angiogenic molecules HIF1α, VEGFα, IL-8 and TGFβ1 and with inhibition of tumor angiogenesis. These results suggest that synergistic co-targeting of oncogenic and death receptor pathways can not only overcome melanoma resistance to different anti-tumor agents in vitro but can also promote pro-apoptotic effects and inhibition of tumor angiogenesis in vivo.

The immune microenvironment confers resistance to MAPK pathway inhibitors through macrophage-derived TNFα

Recently, the rationale for combining targeted therapy with immunotherapy has come to light, but our understanding of the immune response during MAPK pathway inhibitor treatment is limited. We discovered that the immune microenvironment can act as a source of resistance to MAPK pathway-targeted therapy, and moreover during treatment this source becomes reinforced. In particular, we identified macrophage-derived TNFα as a crucial melanoma growth factor that provides resistance to MAPK pathway inhibitors through the lineage transcription factor MITF (microphthalmia transcription factor). Most strikingly, in BRAF-mutant melanomas of patients and BRAF(V600E) melanoma allografts, MAPK pathway inhibitors increased the number of tumor-associated macrophages, and TNFα and MITF expression. Inhibiting TNFα signaling with IκB kinase inhibitors profoundly enhanced the efficacy of MAPK pathway inhibitors by targeting not only the melanoma cells but also the microenvironment. In summary, we identify the immune microenvironment as a novel source of resistance and reveal a new strategy to improve the efficacy of targeted therapy in melanoma.

SIGNIFICANCE

This study identifies the immune microenvironment as a source of resistance to MAPK pathway inhibitors through macrophage-derived TNFα, and reveals that in patients on treatment this source becomes reinforced. Inhibiting IκB kinase enhances the efficacy of MAPK pathway inhibitors, which identifies this approach as a potential novel strategy to improve targeted therapy in melanoma.

Individualizing kinase-targeted cancer therapy: the paradigm of chronic myeloid leukemia

The success of tyrosine kinase inhibitors in treating chronic myeloid leukemia highlights the potential of targeting oncogenic kinases with small molecules. By using drug activity profiles and individual patient genotypes, one can guide personalized therapy selection for patients with resistance.