Mutation-driven drug development in melanoma

Nilotinib in KIT-driven advanced melanoma: Results from the phase II single-arm NICAM trial

Mucosal (MM) and acral melanomas (AM) are rare melanoma subtypes of unmet clinical need; 15%-20% harbor KIT mutations potentially targeted by small-molecule inhibitors, but none yet approved in melanoma. This multicenter, single-arm Phase II trial (NICAM) investigates nilotinib safety and activity in KIT mutated metastatic MM and AM. KIT mutations are identified in 39/219 screened patients (18%); of 29/39 treated, 26 are evaluable for primary analysis. Six patients were alive and progression free at 6 months (local radiology review, 25%); 5/26 (19%) had objective response at 12 weeks; median OS was 7.7 months; ddPCR assay correctly identifies KIT alterations in circulating tumor DNA (ctDNA) in 16/17 patients. Nilotinib is active in KIT-mutant AM and MM, comparable to other KIT inhibitors, with demonstrable activity in nonhotspot KIT mutations, supporting broadening of KIT evaluation in AM and MM. Our results endorse further investigations of nilotinib for the treatment of KIT-mutated melanoma. This clinical trial was registered with ISRCTN (ISRCTN39058880) and EudraCT (2009-012945-49).

General and Specific Cytotoxicity of Chimeric Antisense Oligonucleotides in Bacterial Cells and Human Cell Lines

In the last two decades, antisense oligonucleotide technology has emerged as a promising approach to tackling various healthcare issues and diseases, such as antimicrobial resistance, cancer, and neurodegenerative diseases. Despite the numerous improvements in the structure and modifications of the antisense oligonucleotides (ASOs), there are still specific problems with their clinical efficacy and preclinical cytotoxicity results. To better understand the effects of the ASOs in this paper, we conducted many MTT assays to assess the general and specific cytotoxicity of four new chimeric ASOs in bacterial cells and human cell lines. We demonstrate the absence of inhibitory activity in the human pathogenic bacteria Staphylococcus aureus by non-specific ASOs. The pVEC-ASO1 and pVEC-ASO2 are designed to have no specific targets in S. aureus. They have only partial hybridization to the guanylate kinase mRNA. The pVEC-ASO3 targets UBA2 mRNA, a hallmark cancer pathology in MYC-driven cancer, while pVEC-ASO4 has no complementary sequences. We discovered some cytotoxicity of the non-specific ASOs in healthy and cancer human cell lines. The results are compared with two other ASOs, targeting specific mRNA in cancer cells. All ASOs are delivered into the cell via the cell-penetrating oligopeptide pVEC, which is attached to them. We draw a good correlation between the thermodynamic stability of ASO/target RNA and the toxicity effect in human cell lines. The data obtained signify the importance of thorough bioinformatic analysis and high specificity in designing and developing novel ASOs for safer therapeutic agents in clinical practice.

Regulation of LncRNAs in Melanoma and Their Functional Roles in the Metastatic Process

Long non-coding RNAs (lncRNAs) are key regulators of numerous intracellular processes leading to tumorigenesis. They are frequently deregulated in cancer, functioning as oncogenes or tumor suppressors. As they act through multiple mechanisms, it is not surprising that they may exert dual functions in the same tumor. In melanoma, a highly invasive and metastatic tumor with the propensity to rapidly develop drug resistance, lncRNAs play different roles in: (i) guiding the phenotype switch and leading to metastasis formation; (ii) predicting the response of melanoma patients to immunotherapy; (iii) triggering adaptive responses to therapy and acquisition of drug resistance phenotypes. In this review we summarize the most recent findings on the lncRNAs involved in melanoma growth and spreading to distant sites, focusing on their role as biomarkers for disease diagnosis and patient prognosis, or targets for novel therapeutic approaches.

Targeting the mercapturic acid pathway for the treatment of melanoma

The treatment of metastatic melanoma is greatly hampered by the simultaneous dysregulation of several major signaling pathways that suppress apoptosis and promote its growth and invasion. The global resistance of melanomas to therapeutics is also supported by a highly active mercapturic acid pathway (MAP), which is responsible for the metabolism and excretion of numerous chemotherapy agents. The relative importance of the MAP in melanoma survival was not recognized until demonstrated that B16 melanoma undergoes dramatic apoptosis and regression upon the depletion or inhibition of the MAP transporter protein RLIP. RLIP is a multi-functional protein that couples ATP hydrolysis with the movement of substances. As the rate-limiting step of the MAP, the primary function of RLIP in the plasma membrane is to catalyze the ATP-dependent efflux of unmetabolized drugs and toxins, including glutathione (GSH) conjugates of electrophilic toxins (GS-Es), which are the precursors of mercapturic acids. Clathrin-dependent endocytosis (CDE) is an essential mechanism for internalizing ligand-receptor complexes that promote tumor cell proliferation through autocrine stimulation (Wnt5a, PDGF, βFGF, TNFα) or paracrine stimulation by hormones produced by fibroblasts (IGF1, HGF) or inflammatory cells (IL8). Aberrant functioning of these pathways appears critical for melanoma cell invasion, metastasis, and evasion of apoptosis. This review focuses on the selective depletion or inhibition of RLIP as a highly effective targeted therapy for melanoma that could cause the simultaneous disruption of the MAP and critical peptide hormone signaling that relies on CDE.

Ultraviolet radiation drives mutations in a subset of mucosal melanomas

Although identified as the key environmental driver of common cutaneous melanoma, the role of ultraviolet radiation (UVR)-induced DNA damage in mucosal melanoma is poorly defined. We analyze 10 mucosal melanomas of conjunctival origin by whole genome sequencing and our data shows a predominance of UVR-associated single base substitution signature 7 (SBS7) in the majority of the samples. Our data shows mucosal melanomas with SBS7 dominance have similar genomic patterns to cutaneous melanomas and therefore this subset should not be excluded from treatments currently used for common cutaneous melanoma.

Discoidin Domain Receptors in Melanoma: Potential Therapeutic Targets to Overcome MAPK Inhibitor Resistance

Melanoma is a highly malignant skin cancer with high propensity to metastasize and develop drug resistance, making it a difficult cancer to treat. Current therapies targeting BRAF (V600) mutations are initially effective, but eventually tumors overcome drug sensitivity and reoccur. This process is accomplished in part by reactivating alternate signaling networks that reinstate melanoma proliferative and survival capacity, mostly through reprogramming of receptor tyrosine kinase (RTK) signaling. Evidence indicates that the discoidin domain receptors (DDRs), a set of RTKs that signal in response to collagen, are part of the kinome network that confer drug resistance. We previously reported that DDR1 is expressed in melanomas, where it can promote tumor malignancy in mouse models of melanoma, and thus, DDR1 could be a promising target to overcome drug resistance. In this review, we summarize the current knowledge on DDRs in melanoma and their implication for therapy, with emphasis in resistance to MAPK inhibitors.

Safety and efficacy of nivolumab in patients with rare melanoma subtypes who progressed on or after ipilimumab treatment: a single-arm, open-label, phase II study (CheckMate 172)

BACKGROUND

Nivolumab has been widely studied in non-acral cutaneous melanoma; however, limited data are available in other melanoma subtypes. We report outcomes by melanoma subtype in patients who received nivolumab after progression on prior ipilimumab.

PATIENTS AND METHODS

CheckMate 172 was a phase II, single-arm, open-label, multicentre study that evaluated nivolumab in patients with advanced melanoma who progressed on or after ipilimumab. Patients received 3 mg/kg of nivolumab, every 2 weeks for up to 2 years. The primary end-point was incidence of grade ≥3, treatment-related select adverse events (AEs).

RESULTS

Among 1008 treated patients, we report data on patients with non-acral cutaneous melanoma (n = 723 [71.7%]), ocular melanoma (n = 103 [10.2%]), mucosal melanoma (n = 63 [6.3%]), acral cutaneous melanoma (n = 55 [5.5%]) and other melanoma subtypes (n = 64 [6.3%]). There were no meaningful differences in the incidence of grade ≥3, treatment-related select AEs among melanoma subtypes or compared with the total population. No new safety signals emerged. At a minimum follow-up of 18 months, median overall survival was 25.3 months for non-acral cutaneous melanoma and 25.8 months for acral cutaneous melanoma, with 18-month overall survival rates of 57.5% and 59.0%, respectively. Median overall survival was 12.6 months for ocular melanoma and 11.5 months for mucosal melanoma, with 18-month overall survival rates of 34.8% and 31.5%, respectively.

CONCLUSIONS

The safety profile of nivolumab after ipilimumab is similar across melanoma subtypes. Compared with non-acral cutaneous melanoma, patients with acral cutaneous melanoma had similar survival outcomes, whereas those with ocular and mucosal melanoma had lower median overall survival. CLINICALTRIALS.

GOV ID

NCT02156804.

Dimerization defective MODY mutations of hepatocyte nuclear factor 4α

HNF4α is a culprit gene product for a monogenic and dominantly-inherited form of diabetes, referred to as MODY1 (Maturity Onset Diabetes of the Young type 1). Reduced HNF4α activities have been linked to impaired insulin secretion and β-cell function. Numerous mutations have been identified from the patients and they have been instructive as to the individual residue's role in protein structure-function and dysfunction. As a member of the nuclear receptor (NR) superfamily, HNF4α is made of characteristic modular domains and it functions exclusively as a homodimer despite its sequence homology to RXR, a common heterodimer partner of non-steroidal NRs. Transcription factors commonly dimerize to enhance their molecular functions mainly by facilitating the recognition of double helix target DNAs that display an intrinsic pseudo-2-fold symmetry and the recruitment of the remainder of the main transcriptional machinery. HNF4α is no exception and its dimerization is maintained by the ligand binding domain (LBD) mainly through the leucine-zipper-like interactions at the stalk of two interacting helices. Although many MODY1 mutations have been previously characterized, including DNA binding disruptors, ligand binding disruptors, coactivator binding disruptors, and protein stability disruptors, protein dimerization disruptors have not been formally reported. In this report, we present a set of data for the two MODY1 mutations found right at the dimerization interface (L332 P and L328del mutations) which clearly exhibit the disruptive effects of directly affecting dimerization, protein stability, and transcriptional activities. These data reinforced the fact that MODY mutations are loss-of-function mutations and HNF4α dimerization is essential for its optimal function and normal physiology.

Peptide-modified vemurafenib-loaded liposomes for targeted inhibition of melanoma via the skin

Vemurafenib is a chemotherapeutic drug recently approved by the FDA to treat melanoma. Because the drug is usually delivered orally, the route of administration readily causes damage to major organs with limited antitumor efficacy and bioavailability. In this study, we developed a peptide-modified vemurafenib-loaded liposome for the targeted inhibition of subcutaneous melanoma via the skin. First, the peptide-modified vemurafenib-loaded liposomes (Vem-TD-Lip) were prepared and characterized with respect to the size, shape and charge; the loading efficiency of vemurafenib; and the stability. Then, the intracellular uptake of these liposomes, their limited cytotoxicity, the selective inhibition of melanoma cells harboring BRAF mutations, and the liposome permeation ability were confirmed through in vitro experiments. Finally, the safety and antitumor activity of Vem-TD-Lip were evaluated in vivo. The results showed that transdermal delivery of Vem-TD-Lip effectively targeted and inhibited subcutaneous melanoma in male mice, the administration of Vem-TD-Lip through skin was better than that through oral administration and intravenous injection in terms of reducing damage to major organs and enhancing antitumor efficacy, and the peptide TD significantly enhanced the delivery of Vem-TD-Lip across the skin. This work provides a new strategy for delivering vemurafenib to target and inhibit subcutaneous melanoma.

Genetic Alterations among Korean Melanoma Patients Showing Tumor Heterogeneity: A Comparison between Primary Tumors and Corresponding Metastatic Lesions

Purpose

Melanoma is a highly heterogeneous neoplasm, composed of subpopulations of tumor cells with distinct molecular and biological phenotypes and genotypes. In this study, to determine the genetic heterogeneity between primary and metastatic melanoma in Korean melanoma patients, we evaluated several well-known genetic alterations of melanoma. In addition, to elucidate the clinical relevance of each genetic alteration and heterogeneity between primary and metastatic lesions, clinical features and patient outcome were collected.

Materials and Methods

In addition to clinical data, BRAF, NRAS, GNAQ/11 mutation and KIT amplification data was acquired from an archived primary Korean melanoma cohort (KMC) of 188 patients. Among these patients, 43 patients were included for investigation of tumor heterogeneity between primary melanoma and its corresponding metastatic lesions.

Results

Overall incidence of genetic aberrations of the primary melanomas in KMC was 17.6% of BRAF V600, 12.6% of NRAS mutation, and 28.6% of KIT amplification. GNAQ/11 mutation was seen in 66.6% of the uveal melanoma patients. Patients with BRAF mutation were associated with advanced stage and correlated to poor prognosis (p < 0.01). Among 43 patients, 55.8% showed heterogeneity between primary and metastatic lesion. The frequency of BRAF mutation and KIT amplification significantly increased in the metastatic lesions compared to primary melanomas. GNAQ/11 mutation showed 100% homogeneity in uveal melanoma patients.

Conclusion

Our data demonstrated heterogeneity between primary melanomas and corresponding metastatic lesions for BRAF, NRAS mutation and KIT amplification. However, GNAQ/11 mutation was genetically homogeneous between primary and metastatic melanoma lesions in uveal melanoma.

Comparative oncogenomics identifies tyrosine kinase FES as a tumor suppressor in melanoma

Identification and functional validation of oncogenic drivers are essential steps toward advancing cancer precision medicine. Here, we have presented a comprehensive analysis of the somatic genomic landscape of the widely used BRAFV600E- and NRASQ61K-driven mouse models of melanoma. By integrating the data with publically available genomic, epigenomic, and transcriptomic information from human clinical samples, we confirmed the importance of several genes and pathways previously implicated in human melanoma, including the tumor-suppressor genes phosphatase and tensin homolog (PTEN), cyclin dependent kinase inhibitor 2A (CDKN2A), LKB1, and others. Importantly, this approach also identified additional putative melanoma drivers with prognostic and therapeutic relevance. Surprisingly, one of these genes encodes the tyrosine kinase FES. Whereas FES is highly expressed in normal human melanocytes, FES expression is strongly decreased in over 30% of human melanomas. This downregulation correlates with poor overall survival. Correspondingly, engineered deletion of Fes accelerated tumor progression in a BRAFV600E-driven mouse model of melanoma. Together, these data implicate FES as a driver of melanoma progression and demonstrate the potential of cross-species oncogenomic approaches combined with mouse modeling to uncover impactful mutations and oncogenic driver alleles with clinical importance in the treatment of human cancer.

Re-examining HSPC1 inhibitors

HSPC1 is a critical protein in cancer development and progression, including colorectal cancer (CRC). However, clinical trial data reporting the effectiveness of HSPC1 inhibitors on several cancer types has not been as successful as predicted. Furthermore, some N-terminal inhibitors appear to be much more successful than others despite similar underlying mechanisms. This study involved the application of three N-terminal HSPC1 inhibitors, 17-DMAG, NVP-AUY922 and NVP-HSP990 on CRC cells. The effects on client protein levels over time were examined. HSPC1 inhibitors were also applied in combination with chemotherapeutic agents commonly used in CRC treatment (5-fluorouracil, oxaliplatin and irinotecan). As HSPA1A and HSPB1 have anti-apoptotic activity, gene-silencing techniques were employed to investigate the significance of these proteins in HSPC1 inhibitor and chemotherapeutic agent resistance. When comparing the action of the three HSPC1 inhibitors, there are distinct differences in the time course of important client protein degradation events. The differences between HSPC1 inhibitors were also reflected in combination treatment-17-DMAG was more effective compared with NVP-AUY922 in potentiating the cytotoxic effects of 5-fluorouracil, oxaliplatin and irinotecan. This study concludes that there are distinct differences between N-terminal HSPC1 inhibitors, despite their common mode of action. Although treatment with each of the inhibitors results in significant induction of the anti-apoptotic proteins HSPA1A and HSPB1, sensitivity to HSPC1 inhibitors is not improved by gene silencing of HSPA1A or HSPB1. HSPC1 inhibitors potentiate the cytotoxic effects of chemotherapeutic agents in CRC, and this approach is readily available to enter clinical trials. From a translational point of view, there may be great variability in sensitivity to the inhibitors between individual patients.

Higher Nevus Count Exhibits a Distinct DNA Methylation Signature in Healthy Human Skin: Implications for Melanoma

High nevus count is the strongest risk factor for melanoma, and although gene variants have been discovered for both traits, epigenetic variation is unexplored. We investigated 322 healthy human skin DNA methylomes associated with total body nevi count, incorporating genetic and transcriptomic variation. DNA methylation changes were identified at genes involved in melanocyte biology, such as RAF1 (P = 1.2 × 10^-6) and CTC1 (region: P = 6.3 × 10^-4), and other genes including ARRDC1 (P = 3.1 × 10^-7). A subset exhibited coordinated methylation and transcription changes within the same biopsy. The total analysis was also enriched for melanoma-associated DNA methylation variation (P = 6.33 × 10^-6). In addition, we show that skin DNA methylation is associated in cis with known genome-wide association study single nucleotide polymorphisms for nevus count, at PLA2G6 (P = 1.7 × 10^-49) and NID1 (P = 6.4 × 10^-14), as well as melanoma risk, including in or near MC1R, MX2, and TERT/CLPTM1L (P < 1 × 10^-10). Our analysis using a uniquely large dataset comprising healthy skin DNA methylomes identified known and additional regulatory loci and pathways in nevi and melanoma biology. This integrative study improves our understanding of predisposition to nevi and their potential contribution to melanoma pathogenesis.

Nanotechnology-based strategies for combating toxicity and resistance in melanoma therapy

Drug toxicity and resistance remain formidable challenges in cancer treatment and represent an area of increasing attention in the case of melanoma. Nanotechnology represents a paradigm-shifting field with the potential to mitigate drug resistance while improving drug delivery and minimizing toxicity. Recent clinical and pre-clinical studies have demonstrated how a diverse array of nanoparticles may be harnessed to circumvent known mechanisms of drug resistance in melanoma to improve therapeutic efficacy. In this review, we discuss known mechanisms of resistance to various melanoma therapies and possible nanotechnology-based strategies that could be used to overcome these barriers and improve the pharmacologic arsenal available to combat advanced stage melanoma.

Vemurafenib for the treatment of BRAF mutant metastatic melanoma

Vemurafenib was the first selective BRAF inhibitor licensed in cancer. It is indicated for the treatment of patients affected by advanced melanoma with BRAF V600 mutation. It has shown successful results in terms of efficacy together with a favorable toxicity profile. Other compounds such as the BRAF inhibitor dabrafenib and the immunotherapeutic agent ipilimumab are also approved in the same group of patients. This article reviews the chemistry, pharmacokinetics, pharmacodynamics and clinical development of vemurafenib. Moreover, its efficacy and toxicity are compared with dabrafenib and ipilimumab. A number of trials with vemurafenib alone or in combination with other drugs are also analyzed. These trials will determine the role of vemurafenib in the treatment of BRAF mutant melanoma in forthcoming years.

Multiple Molecular Pathways in Melanomagenesis: Characterization of Therapeutic Targets

Molecular mechanisms involved in pathogenesis of malignant melanoma have been widely studied and novel therapeutic treatments developed in recent past years. Molecular targets for therapy have mostly been recognized in the RAS–RAF–MEK–ERK and PI3K–AKT signaling pathways; small-molecule inhibitors were drawn to specifically target key kinases. Unfortunately, these targeted drugs may display intrinsic or acquired resistance and various evidences suggest that inhibition of a single effector of the signal transduction cascades involved in melanoma pathogenesis may be ineffective in blocking the tumor growth. In this sense, a wider comprehension of the multiple molecular alterations accounting for either response or resistance to treatments with targeted inhibitors may be helpful in assessing, which is the most effective combination of such therapies. In the present review, we summarize the known molecular mechanisms underlying either intrinsic and acquired drug resistance either alternative roads to melanoma pathogenesis, which may become targets for innovative anticancer approaches.

Perspective of Targeting Cancer-Associated Fibroblasts in Melanoma

Melanoma is known as an exceptionally aggressive and treatment-resistant human cancer. Although a great deal of progress has been made in the past decade, including the development of immunotherapy using immune checkpoint inhibitors and targeted therapy using BRAF, MEK or KIT inhibitors, treatment for unresectable stage III, stage IV, and recurrent melanoma is still challenging with limited response rate, severe side effects and poor prognosis, highlighting an urgent need for discovering and designing more effective approaches to conquer melanoma. Melanoma is not only driven by malignant melanocytes, but also by the altered communication between neoplastic cells and non-malignant cell populations, including fibroblasts, endothelial and inflammatory cells, in the tumor stroma. Infiltrated and surrounding fibroblasts, also known as cancer-associated fibroblasts (CAFs), exhibit both phenotypical and physiological differences compared to normal dermal fibroblasts. They acquire properties of myofibroblasts, remodel the extracellular matrix (ECM) and architecture of the diseased tissue and secrete chemical factors, which all together promote the transformation process by encouraging tumor growth, angiogenesis, inflammation and metastasis and contribute to drug resistance. A number of in vitro and in vivo experiments have shown that stromal fibroblasts promote melanoma cell proliferation and they have been targeted to suppress tumor growth effectively. Evidently, a combination therapy co-targeting tumor cells and stromal fibroblasts may provide promising strategies to improve therapeutic outcomes and overcome treatment resistance. A significant benefit of targeting CAFs is that the approach aims to create a tumor-resistant environment that inhibits growth of melanomas carrying different genetic mutations. However, the origin of CAFs and precise mechanisms by which CAFs contribute to melanoma progression and drug resistance remain poorly understood. In this review, we discuss the origin, activation and heterogeneity of CAFs in the melanoma tumor microenvironment and examine the contributions of stromal fibroblasts at different stages of melanoma development. We also highlight the recent progression in dissecting and characterizing how local fibroblasts become reprogrammed and build a dynamic yet optimal microenvironment for tumors to develop and metastasize. In addition, we review key developments in ongoing preclinical studies and clinical applications targeting CAFs and tumor-stroma interactions for melanoma treatment.

Probing the effect of MODY mutations near the co-activator-binding pocket of HNF4α

HNF4α (hepatocyte nuclear factor 4α) is a culprit gene product for a monogenic and dominantly inherited form of diabetes, referred to as MODY (maturity onset diabetes of the young). As a member of the NR (nuclear receptor) superfamily, HNF4α recruits transcriptional co-activators such as SRC-1α (steroid receptor co-activator-1α) and PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) through the LXXLL-binding motifs for its transactivation, and our recent crystal structures of the complex provided the molecular details and the mechanistic insights into these co-activator recruitments. Several mutations have been identified from the MODY patients and, among these, point mutations can be very instructive site-specific measures of protein function and structure. Thus, in the present study, we probed the functional effects of the two MODY point mutations (D206Y and M364R) found directly near the LXXLL motif-binding site by conducting a series of experiments on their structural integrity and specific functional roles such as overall transcription, ligand selectivity, target gene recognition and co-activator recruitment. While the D206Y mutation has a subtle effect, the M364R mutation significantly impaired the overall transactivation by HNF4α. These functional disruptions are mainly due to their reduced ability to recruit co-activators and lowered protein stability (only with M364R mutation), while their DNA-binding activities and ligand selectivities are preserved. These results confirmed our structural predictions and proved that MODY mutations are loss-of-function mutations leading to impaired β-cell function. These findings should help target selective residues for correcting mutational defects or modulating the overall activity of HNF4α as a means of therapeutic intervention.

Slow inhibition and conformation selective properties of extracellular signal-regulated kinase 1 and 2 inhibitors

The mitogen-activated protein (MAP) kinase pathway is a target for anticancer therapy, validated using inhibitors of B-Raf and MAP kinase kinase (MKK) 1 and 2. Clinical outcomes show a high frequency of acquired resistance in patient tumors, involving upregulation of activity of the MAP kinase, extracellular signal-regulated kinase (ERK) 1 and 2. Thus, inhibitors for ERK1/2 are potentially important for targeted therapeutics against cancer. The structures and potencies of different ERK inhibitors have been published, but their kinetic mechanisms have not been characterized. Here we perform enzyme kinetic studies on six representative ERK inhibitors, with potencies varying from 100 pM to 20 μM. Compounds with significant biological activity (IC50 < 100 nM) that inhibit in the subnanomolar range (Vertex-11e and SCH772984) display slow-onset inhibition and represent the first inhibitors of ERK2 known to demonstrate slow dissociation rate constants (values of 0.2 and 1.1 h(-1), respectively). Furthermore, we demonstrate using kinetic competition assays that Vertex-11e binds with differing affinities to ERK2 in its inactive, unphosphorylated and active, phosphorylated forms. Finally, two-dimensional heteronuclear multiple-quantum correlation nuclear magnetic resonance experiments reveal that distinct conformational states are formed in complexes of Vertex-11e with inactive and active ERK2. Importantly, two conformers interconvert in equilibrium in the active ERK2 apoenzyme, but Vertex-11e strongly shifts the equilibrium completely to one conformer. Thus, a high-affinity, slow dissociation inhibitor stabilizes different enzyme conformations depending on the activity state of ERK2 and reveals properties of conformational selection toward the active kinase.

Response to MAPK pathway inhibitors in BRAF V600M-mutated metastatic melanoma

WHAT IS KNOWN AND OBJECTIVE

The management of metastatic melanoma has changed significantly in the past decade with the development of immunotherapies and targeted molecular therapies. Trials of targeted therapies have focused mainly on patients with the most common BRAF V600 mutations, namely V600E/K substitutions, with very little information available on the benefit of targeted therapies on less commonly occurring mutations such as V600R/D and M.

CASE SUMMARY

We present a 54-year-old man with metastatic melanoma harbouring a rare BRAF V600M mutation, who experienced clinical and radiological response to combined therapy with the BRAF inhibitor dabrafenib and MEK inhibitor trametinib.

WHAT IS NEW AND CONCLUSION

As our understanding of these therapies evolves and an increasing number of patients have mutational testing performed, there is a clear imperative--as highlighted by this case--to test for rarer mutations and facilitate their inclusion both in everyday practice and in future clinical trials.

Combined MEK and JAK inhibition abrogates murine myeloproliferative neoplasm

Overactive RAS signaling is prevalent in juvenile myelomonocytic leukemia (JMML) and the myeloproliferative variant of chronic myelomonocytic leukemia (MP-CMML) in humans, and both are refractory to conventional chemotherapy. Conditional activation of a constitutively active oncogenic Nras (NrasG12D/G12D) in murine hematopoietic cells promotes an acute myeloproliferative neoplasm (MPN) that recapitulates many features of JMML and MP-CMML. We found that NrasG12D/G12D-expressing HSCs, which serve as JMML/MP-CMML-initiating cells, show strong hyperactivation of ERK1/2, promoting hyperproliferation and depletion of HSCs and expansion of downstream progenitors. Inhibition of the MEK pathway alone prolonged the presence of NrasG12D/G12D-expressing HSCs but failed to restore their proper function. Consequently, approximately 60% of NrasG12D/G12D mice treated with MEK inhibitor alone died within 20 weeks, and the remaining animals continued to display JMML/MP-CMML-like phenotypes. In contrast, combined inhibition of MEK and JAK/STAT signaling, which is commonly hyperactivated in human and mouse CMML, potently inhibited human and mouse CMML cell growth in vitro, rescued mutant NrasG12D/G12D-expressing HSC function in vivo, and promoted long-term survival without evident disease manifestation in NrasG12D/G12D animals. These results provide a strong rationale for further exploration of combined targeting of MEK/ERK and JAK/STAT in treating patients with JMML and MP-CMML.

Skin cancer - an overview for dentists

Skin cancer is common and an increasing problem in the UK. It frequently occurs on the head and neck skin. A significant proportion of the adult population in the UK visits the dentist each year, thus making dental practitioners ideally placed to identify suspicious lesions, which could be skin cancer, as part of their routine extra-oral examination. These patients can then be referred on to hospital or their GP for further management. The dentist can also give advice on risk factors and self-monitoring to patients. This paper aims to describe the risk factors, pathology, presentation and treatments for the three most common forms of skin cancer - basal and squamous cell carcinomas, and malignant melanoma, to give the dental practitioner the knowledge and confidence to examine for and identify these skin cancers.

Tissue prognostic biomarkers in primary cutaneous melanoma

Cutaneous melanoma (CM) causes the greatest number of skin cancer-related deaths worldwide. Predicting CM prognosis is important to determine the need for further investigation, counseling of patients, to guide appropriate management (particularly the need for postoperative adjuvant therapy), and for assignment of risk status in groups of patients entering clinical trials. Since recurrence rate is largely independent from stages defined by morphological and morphometric criteria, there is a strong need for identification of additional robust prognostic factors to support decision-making processes. Most data on prognostic biomarkers in melanoma have been evaluated in tumor tissue samples by conventional morphology and immunohistochemistry (IHC) as well as DNA and RNA analyses. In the present review, we critically summarize main high-quality studies investigating IHC-based protein biomarkers of melanoma outcome according to Reporting Recommendations for Tumor Marker Prognostic Studies (REMARK)-derived criteria. Pathways have been classified and conveyed in the "biologic road" previously described by Hanahan and Weinberg. Data derived from genomic and transcriptomic technologies have been critically reviewed to better understand if any of investigated proteins or gene signatures should be incorporated into clinical practice or still remain a field of melanoma research. Despite a wide body of research, no molecular prognostic biomarker has yet been translated into clinical practice. Conventional tissue biomarkers, such as Breslow thickness, ulceration, mitotic rate and lymph node positivity, remain the backbone prognostic indicators in melanoma.

Activation of the glutamate receptor GRM1 enhances angiogenic signaling to drive melanoma progression

Glutamate-triggered signal transduction is thought to contribute widely to cancer pathogenesis. In melanoma, overexpression of the metabotropic glutamate receptor (GRM)-1 occurs frequently and its ectopic expression in melanocytes is sufficient for neoplastic transformation. Clinical evaluation of the GRM1 signaling inhibitor riluzole in patients with advanced melanoma has demonstrated tumor regressions that are associated with a suppression of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathways. Together, these results prompted us to investigate the downstream consequences of GRM1 signaling and its disruption in more detail. We found that melanoma cells with enhanced GRM1 expression generated larger tumors in vivo marked by more abundant blood vessels. Media conditioned by these cells in vitro contained relatively higher concentrations of interleukin-8 and VEGF due to GRM1-mediated activation of the AKT-mTOR-HIF1 pathway. In clinical specimens from patients receiving riluzole, we confirmed an inhibition of MAPK and PI3K/AKT activation in posttreatment as compared with pretreatment tumor specimens, which exhibited a decreased density of blood vessels. Together, our results demonstrate that GRM1 activation triggers proangiogenic signaling in melanoma, offering a mechanistic rationale to design treatment strategies for the most suitable combinatorial use of GRM1 inhibitors in patients.

BRAF inhibition is associated with increased clonality in tumor-infiltrating lymphocytes

There have been significant advances with regard to BRAF-targeted therapies against metastatic melanoma. However, the majority of patients receiving BRAF inhibitors (BRAFi) manifest disease progression within a year. We have recently shown that melanoma patients treated with BRAFi exhibit an increase in melanoma-associated antigens and in CD8+ tumor-infiltrating lymphocytes in response to therapy. To characterize such a T-cell infiltrate, we analyzed the complementarity-determining region 3 (CDR3) of rearranged T-cell receptor (TCR) β chain-coding genes in tumor biopsies obtained before the initiation of BRAFi and 10-14 d later. We observed an increase in the clonality of tumor-infiltrating lymphocytes in 7 of 8 patients receiving BRAFi, with a statistically significant 21% aggregate increase in clonality. Over 80% of individual T-cell clones detected after initiation of BRAFi treatment were new clones. Interestingly, the comparison of tumor infiltrates with clinical responses revealed that patients who had a high proportion of pre-existing dominant clones after the administration of BRAFi responded better to therapy than patients who had a low proportion of such pre-existing dominant clones following BRAFi. These data suggest that although the inhibition of BRAF in melanoma patients results in tumor infiltration by new lymphocytes, the response to treatment appears to be related to the presence of a pre-existing population of tumor-infiltrating T-cell clones.

Oncogenic activation of MEK/ERK primes melanoma cells for adaptation to endoplasmic reticulum stress

Cancer cells commonly undergo chronic endoplasmic reticulum (ER) stress, to which the cells have to adapt for survival and proliferation. We report here that in melanoma cells intrinsic activation of the ER stress response/unfolded protein response (UPR) is, at least in part, caused by increased outputs of protein synthesis driven by oncogenic activation of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) and promotes proliferation and protects against apoptosis induced by acute ER stress. Inhibition of oncogenic BRAF(V600E) or MEK-attenuated activation of inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6) signaling of the UPR in melanoma cells. This was associated with decreased phosphorylation of eukaryotic initiation factor 4E (eIF4E) and nascent protein synthesis and was recapitulated by knockdown of eIF4E. In line with this, introduction of BRAF(V600E) into melanocytes led to increases in eIF4E phosphorylation and protein production and triggered activation of the UPR. Similar to knockdown of glucose-regulated protein 78 (GRP78), inhibition of XBP1 decelerated melanoma cell proliferation and enhanced apoptosis induced by the pharmacological ER stress inducers tunicamycin and thapasigargin. Collectively, these results reveal that potentiation of adaptation to chronic ER stress is another mechanism by which oncogenic activation of the MEK/ERK pathway promotes the pathogenesis of melanoma.

Micropthalmia transcription factor (MITF) as a diagnostic marker for metastatic melanomas negative for other melanoma markers

Metastatic malignant melanoma has a wide spectrum of histopathologic patterns and often lacks melanin pigment. Without a known primary tumor, the diagnosis of metastatic malignant melanoma relies on a combination of morphology and immunohistochemical profile. Infrequently, commonly used markers for melanoma (S100, HMB45, Melan-A and Tyrosinase A) are negative. These cases pose critical diagnostic challenges. Recent studies show that Microphthalmia Transcription Factor (MITF) has high sensitivity (88-100%) and specificity for metastatic melanoma. We are reporting here three cases of high grade tumors that were studied by a comprehensive immunohistochemical panel including cytokeratins, S100, HMB-45, Melan A, Tyrosinase, and MITF. All three tumors were also analyzed for the presence of BRAF mutations. All three metastatic tumors were negative for S100, Melan A, HMB-45 and Tyrosinase but positive for MITF. Subsequent to the diagnoses, previously existing or concurrent primary melanomas were identified in 2 of the 3 cases. Interestingly, S100, Melan A, and HMB-45 were positive in the primary tumors. No BRAF (V600E) mutations were identified in the three metastatic melanomas and CD 117 (c-kit) was positive in one of the cases. In summary, our experience shows that MITF can be a valuable adjunct in the diagnosis of metastatic tumors that are suspicious for melanoma but negative for other melanoma markers.

Heterogeneous expression and functional relevance of the ubiquitin carboxyl-terminal hydrolase L1 in melanoma

The expression of ubiquitin carboxyl-terminal hydrolase 1 (UCHL1) is deregulated in human cancer cells with tumor inhibiting or promoting functions. Due to less knowledge on the role of UCHL1 in melanoma progression, the expression pattern and function of UCHL1 as well as the deregulated signaling pathways were characterized. A large number of melanoma cell lines, tissue microarrays of melanoma lesions and control tissues were analyzed for UCHL1 expression using PCR, Western blot and/or immunohistochemistry. The analysis revealed that melanocyte cultures, 24 of 331 melanoma lesions, two of 18 short-term cultures and two of 19 melanoma cell lines tested, respectively, heterogeneously expressed UCHL1. The low frequency of UCHL1 expression in melanoma cells was due to gene silencing by promoter DNA hypermethylation. Using different transfection models an enzyme activity-dependent growth promoting function of UCHL1 via the activation of the mitogen-activated protein kinase signaling pathway was found in melanoma cells. Under oxygen stress a dose-dependent effect of UCHL1 was detected, which was mediated by a dynamic modification of the PI3K-Akt signaling. Thus, the aberrant UCHL1 expression in melanoma cells is linked to dynamic changes in growth properties and signal transduction cascades suggesting that UCHL1 provides a novel marker and/or therapeutic target at least for a subset of melanoma patients.

The evolution of S100B inhibitors for the treatment of malignant melanoma

Malignant melanoma continues to be an extremely fatal cancer due to a lack of viable treatment options for patients. The calcium-binding protein S100B has long been used as a clinical biomarker, aiding in malignant melanoma staging and patient prognosis. However, the discovery of p53 as a S100B target and the consequent impact on cell apoptosis redirected research efforts towards the development of inhibitors of this S100B-p53 interaction. Several approaches, including computer-aided drug design, fluorescence polarization competition assays, NMR, x-ray crystallography and cell-based screens have been performed to identify compounds that block the S100B-p53 association, reactivate p53 transcriptional activities and induce cancer cell death. Eight promising compounds, including pentamidine, are presented in this review and the potential for future modifications is discussed. Synthesis of compound derivatives will likely exhibit increased S100B affinity and mimic important S100B-target dynamic properties that will result in high specificity.

Optimal management of metastatic melanoma: current strategies and future directions

Melanoma is increasing in incidence and remains a major public health threat. Although the disease may be curable when identified early, advanced melanoma is characterized by widespread metastatic disease and a median survival of less than 10 months. In recent years, however, major advances in our understanding of the molecular nature of melanoma and the interaction of melanoma cells with the immune system have resulted in several new therapeutic strategies that are showing significant clinical benefit. Current therapeutic approaches include surgical resection of metastatic disease, chemotherapy, immunotherapy, and targeted therapy. Dacarbazine, interleukin-2, ipilimumab, and vemurafenib are now approved for the treatment of advanced melanoma. In addition, new combination chemotherapy regimens, monoclonal antibodies blocking the programmed death-1 (PD-1)/PD-ligand 1 pathway, and targeted therapy against CKIT, mitogen-activated protein/extracellular signal-regulated kinase (MEK), and other putative signaling pathways in melanoma are beginning to show promise in early-phase clinical trials. Further research on these modalities alone and in combination will likely be the focus of future clinical investigation and may impact the outcomes for patients with advanced melanoma.

Inside out: targeting NHE1 as an intracellular and extracellular regulator of cancer progression

The sodium hydrogen exchanger isoform one is a critical regulator of intracellular pH, serves as an anchor for the formation of cytoplasmic signaling complexes, and modulates cytoskeletal organization. There is a growing interest in the potential for sodium hydrogen exchanger isoform one as a therapeutic target against cancer. Sodium hydrogen exchanger isoform one transport drives formation of membrane protrusions essential for cell migration and contributes to the establishment of a tumor microenvironment that leads to the rearrangement of the extracellular matrix further supporting tumor progression. Here, we focus on the potential impact that an inexpensive, $100 genome would have in identifying prospective therapeutic targets to treat tumors based upon changes in gene expression and variation of sodium hydrogen exchanger isoform one regulators. In particular, we will focus on the ezrin, radixin, moesin family proteins, calcineurin B homologous proteins, Ras/Raf/MEK/ERK signaling, and phosphoinositide signaling as they relate to the regulation of sodium hydrogen exchanger isoform one in cancer progression.

Main clues in the pathologic diagnosis of melanoma: is molecular genetics helping?

Although conventional histopathologic examination is still the undisputable mainstay for the diagnosis of melanocytic skin neoplasms, application of molecular testing has experienced tremendous growth and will continue to expand in the future as the need for more specific diagnoses and new targeted therapies evolve. Ancillary molecular methods, including comparative genomic hybridization and fluorescence in situ hybridization, have the potential to provide important new information to challenging cases, and will help improve diagnostic accuracy, particularly in cases in which morphology is not conclusive. Pathologists are increasingly involved in the prospective genotyping of melanoma, which leads to patient stratification in light of the novel personalized therapeutic approaches in the advanced setting.

Targeting BRAF in melanoma: biological and clinical challenges

Melanoma is an aggressive form of skin cancer that causes the greatest number of skin cancer-related deaths worldwide. In its early stages malignant melanoma can be cured by surgical resection, but once it has progressed to the metastatic stage it is extremely difficult to treat and does not respond to current therapies. A majority of cutaneous melanomas show activating mutations in the NRAS or BRAF proto-oncogenes, components of the Ras-Raf-Mek-Erk (MAPK) signal transduction pathway. The discovery of activating BRAF mutations in ∼50% of all melanomas has proved to be a turning point in the therapeutic management of the disseminated disease. This review summarizes the critical role of BRAF in melanoma pathophysiology, the clinical and pathological determinants of BRAF mutation status and finally addresses the current state of the art of BRAF inhibitors. We further outline the most recent findings on the mechanisms that underlie intrinsic and acquired BRAF inhibitor resistance and describe ongoing preclinical and clinical studies designed to delay or abrogate the onset of therapeutic escape.

A quantitative allele-specific PCR test for the BRAF V600E mutation using a single heterozygous control plasmid for quantitation: a model for qPCR testing without standard curves

We describe a novel method for mutant allele quantitation using allele-specific PCR. The method uses a heterozygous plasmid containing one wild-type and one mutant sequence as a calibrator that is run at a single concentration, with each quantitative allele-specific PCR run. PCR data from both calibrator alleles, together with predetermined PCR efficiencies, are used to quantitate the mutant allele burden in unknown specimens. We demonstrate the utility of this method by using it to calculate BRAF V600E allele frequencies in cases of hairy-cell leukemia and show that it generates data that are comparable to those obtained via allele quantitation using conventional standard curves over a wide range of allelic ratios. This method is not subject to errors that may be introduced in traditional standard curves as the result of variations in pippetting or errors in the calculation of the absolute copy numbers of standards. Furthermore, it simplifies the workflow in the clinical laboratory and would provide significant advantages for efforts to standardize clinical quantitative PCR testing.

New treatment approaches in melanoma: current research and clinical prospects

Ipilimumab and vemurafenib have changed the clinical landscape in melanoma. Both drugs offer effective treatment for metastatic melanoma, but with limitations. Ipilimumab benefits only a minority of those treated, with no means to identify them prospectively. The efficacy of vemurafenib is tied to the presence of an activating mutation in BRAF, and so is more predictable. However, acquired resistance develops within months. As we understand these, and similar, agents better, the means to select patients for treatment, to increase the duration of response and to identify the best stage at which to intervene will lead to improved outcomes for patients. Several trials are already under way or being developed to build upon these exciting discoveries.

Mechanisms of acquired resistance to targeted cancer therapies

Drugs that target genomically defined vulnerabilities in human tumors have now been clinically validated as effective cancer therapies. However, the relatively rapid acquisition of resistance to such treatments that is observed in virtually all cases significantly limits their utility and remains a substantial challenge to the clinical management of advanced cancers. As molecular mechanisms of resistance have begun to be elucidated, new strategies to overcome or prevent the development of resistance have begun to emerge. In some cases, specific mutational mechanisms contribute directly to acquired drug resistance, and in other cases it appears that nonmutational and possibly epigenetic mechanisms play a significant role. This article discusses the various genetic and nongenetic mechanisms of acquired drug resistance that have been reported in the context of 'rationally targeted' drug therapies.

The activation of MAPK in melanoma cells resistant to BRAF inhibition promotes PD-L1 expression that is reversible by MEK and PI3K inhibition

PURPOSE

Selective BRAF inhibition (BRAFi) provides a paradigm shift for melanoma treatment. The duration of benefit is typically limited before resistance develops. Interest remains in combining targeted and immune therapies to overcome resistance and improve durability of clinical benefit. One mechanism of evading immune destruction is programmed death-1-ligand 1 (PD-L1) expression by tumors that results in potent antitumor immune suppression.

EXPERIMENTAL DESIGN

BRAFi-resistant melanoma cells were examined for changes in PD-L1 expression by immunoblot and flow cytometry. Signaling pathways involved in altering PD-L1 expression were examined. Strategies to maximize the effect of the BRAFi therapy were studied including MEKi, MEKi combinations, and additional pathways including phosphoinositide-3 kinase (PI3K).

RESULTS

Melanoma cells resistant to BRAFi exhibit increased MAPK signaling and promotion of PD-L1 expression. PD-L1 expression is transcriptionally modulated by c-Jun and augmented by STAT3. MEK inhibition (MEKi) regains downregulation of MAPK signaling and suppresses the production of PD-L1. MEKi in melanoma cells shows dual therapeutic effects with simultaneous suppression of PD-L1 expression and induction of apoptosis. By combining MEKi with BRAFi, an additive effect on the inhibition of PD-L1 expression results.

CONCLUSIONS

We report a novel mechanism that suppresses preexisting immune responses in patients with melanoma receiving BRAFi therapy. BRAFi resistance leads to increased expression of PD-L1 in melanoma cells, mediated by c-Jun and STAT3. MEKi may be feasible to counteract BRAFi resistance of MAPK reactivation and also for the additive effect of PD-L1 suppression. Potential therapeutic benefits of combining targeted inhibitors and immune modulation to improve patient outcomes should be investigated.

Molecular diagnostic strategies: a role in the practice of dermatology

Molecular diagnostic strategies are gaining wider acceptance and use in dermatology and dermatopathology as more practitioners in this field develop an understanding of the principles and applications of genomic technologies. Molecular testing is facilitating more accurate diagnosis, staging, and prognostication, in addition to guiding the selection of appropriate treatment, monitoring of therapy, and identification of novel therapeutic targets, for a wide variety of skin diseases.

Mutation profiling and microsatellite instability in stage II and III colon cancer: an assessment of their prognostic and oxaliplatin predictive value

PURPOSE

The purpose of this study was to examine the prognostic and oxaliplatin predictive value of mismatch repair (MMR) status and common hot spot mutations, which we previously identified in stage II and III colon cancer.

EXPERIMENTAL DESIGN

Mutations in BRAF, KRAS, NRAS, MET, and PIK3CA were profiled in 2,299 stage II and III colon tumors from National Surgical Adjuvant Breast and Bowel Project (NSABP) clinical trials C-07 (n = 1,836) and C-08 (n = 463) with Type Plex chemistry and mass spectrometry. C-07 tested the worth of adding oxaliplatin to 5-fluorouracil plus leucovorin, and C-08 tested the worth of adding bevacizumab to FOLFOX. Cox proportional hazard models were used to assess prognostic or oxaliplatin predictive value of mutations for tumor recurrence, overall survival (OS), and survival after recurrence (SAR).

RESULTS

BRAF mutations were associated with MMR-deficient tumors (P < 0.0001), poor OS [HR, 1.46; 95% confidence interval (CI), 1.20-1.79; P ≤ 0.0002], and poor SAR (HR, 2.31; 95% CI, 1.83-2.95; P < 0.0001). Mutations in KRAS, NRAS, MET, and PIK3CA were not associated with recurrence, OS, or SAR. MMR-deficient tumors were associated with an improved prognosis based on recurrence (HR, 0.48; 95% CI, 0.33-0.70; P < 0.0001). Mutations and MMR status were not predictive for oxaliplatin benefit.

CONCLUSIONS

This study shows that BRAF mutations profiled from stage II and III colon cancer tumors were associated with poor SAR and validates and explains, at least in part, previous observations associating it with poor OS. Profiling of all of these mutations is warranted for future clinical trials testing new targeted therapies that block relevant signaling pathways. Such clinical trials are under development at NSABP.

Image and statistical analysis of melanocytic histology

AIMS

We applied digital image analysis techniques to study selected types of melanocytic lesions.

METHODS AND RESULTS

We used advanced digital image analysis to compare melanocytic lesions as follows: (i) melanoma to nevi, (ii) melanoma subtypes to nevi, (iii) severely dysplastic nevi to other nevi and (iv) melanoma to severely dysplastic nevi. We were successful in differentiating melanoma from nevi [receiver operating characteristic area (ROC) 0.95] using image-derived features, among which those related to nuclear size and shape and distance between nuclei were most important. Dividing melanoma into subtypes, even greater separation was obtained (ROC area 0.98 for superficial spreading melanoma; 0.95 for lentigo maligna melanoma; and 0.99 for unclassified). Severely dysplastic nevi were best differentiated from conventional and mildly dysplastic nevi by differences in cellular staining qualities (ROC area 0.84). We found that melanomas were separated from severely dysplastic nevi by features related to shape and staining qualities (ROC area 0.95). All comparisons were statistically significant (P < 0.0001).

CONCLUSIONS

We offer a unique perspective into the evaluation of melanocytic lesions and demonstrate a technological application with increasing prevalence, and with potential use as an adjunct to traditional diagnosis in the future.

A new era in the treatment of melanoma: from biology to clinical practice

Melanoma is the deadliest cutaneous malignancy and its incidence continues to grow. Until 2011, the treatment options for metastatic melanoma were scarce and without any overall survival benefit. The emergence of new targeted therapies for BRAF mutant melanoma (vemurafenib) and immunotherapy (ipilimumab) has changed the standard of care for this disease. The objective of the present review is to summarise the biological background of the new therapeutic approaches in melanoma, focusing on apoptosis resistance, immune modulation and angiogenesis, and the direct translation into clinical practice.

Melanoma genome sequencing reveals frequent PREX2 mutations

Melanoma is notable for its metastatic propensity, lethality in the advanced setting and association with ultraviolet exposure early in life. To obtain a comprehensive genomic view of melanoma in humans, we sequenced the genomes of 25 metastatic melanomas and matched germline DNA. A wide range of point mutation rates was observed: lowest in melanomas whose primaries arose on non-ultraviolet-exposed hairless skin of the extremities (3 and 14 per megabase (Mb) of genome), intermediate in those originating from hair-bearing skin of the trunk (5-55 per Mb), and highest in a patient with a documented history of chronic sun exposure (111 per Mb). Analysis of whole-genome sequence data identified PREX2 (phosphatidylinositol-3,4,5-trisphosphate-dependent Rac exchange factor 2)--a PTEN-interacting protein and negative regulator of PTEN in breast cancer--as a significantly mutated gene with a mutation frequency of approximately 14% in an independent extension cohort of 107 human melanomas. PREX2 mutations are biologically relevant, as ectopic expression of mutant PREX2 accelerated tumour formation of immortalized human melanocytes in vivo. Thus, whole-genome sequencing of human melanoma tumours revealed genomic evidence of ultraviolet pathogenesis and discovered a new recurrently mutated gene in melanoma.

Use of Fluorescence In Situ Hybridization to Distinguish Metastatic Uveal From Cutaneous Melanoma

Metastatic lesions of malignant melanoma can on occasion be difficult to classify with regard to the primary site of origin. Given the lack of specificity of light microscopic features, ancillary studies are needed. In this study, the authors explored the possibility of distinguishing metastatic tumors derived from uveal primaries from those known to have originated from a cutaneous melanoma by fluorescence in situ hybridization (FISH) using probes for chromosome 3, 8q24, and 1p36. A total of 32 metastatic tumors were analyzed by FISH. Monosomy 3 was detected in 9 out of 16 (56.3%) cases of metastatic uveal melanoma but was not found in any of the 16 metastatic cutaneous melanomas ( P < .001). With regard to 1p36, amplifications were found in 8 out of 16 (50%) cases of metastatic cutaneous melanoma but not in any case of uveal melanoma ( P < .05). 1p36 was deleted in 3 cases of uveal and 1 case of cutaneous melanoma. Amplifications of 8q were found in 15 out of 16 (94%) cases of uveal melanoma metastases and in 12 out of 16 (75%) cases of cutaneous metastases. The findings suggest that FISH for monosomy 3 is a useful adjunct tool in the differential diagnosis of metastatic uveal versus cutaneous melanoma.

ERK inhibition overcomes acquired resistance to MEK inhibitors

The RAS/RAF/MEK pathway is activated in more than 30% of human cancers, most commonly via mutation in the K-ras oncogene and also via mutations in BRAF. Several allosteric mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitors, aimed at treating tumors with RAS/RAF pathway alterations, are in clinical development. However, acquired resistance to these inhibitors has been documented both in preclinical and clinical samples. To identify strategies to overcome this resistance, we have derived three independent MEK inhibitor-resistant cell lines. Resistance to allosteric MEK inhibitors in these cell lines was consistently linked to acquired mutations in the allosteric binding pocket of MEK. In one cell line, concurrent amplification of mutant K-ras was observed in conjunction with MEK allosteric pocket mutations. Clonal analysis showed that both resistance mechanisms occur in the same cell and contribute to enhanced resistance. Importantly, in all cases the MEK-resistant cell lines retained their addiction to the mitogen-activated protein kinase (MAPK) pathway, as evidenced by their sensitivity to a selective inhibitor of the ERK1/2 kinases. These data suggest that tumors with acquired MEK inhibitor resistance remain dependent on the MAPK pathway and are therefore sensitive to inhibitors that act downstream of the mutated MEK target. Importantly, we show that dual inhibition of MEK and ERK by small molecule inhibitors was synergistic and acted to both inhibit the emergence of resistance, as well as to overcome acquired resistance to MEK inhibitors. Therefore, our data provide a rationale for cotargeting multiple nodes within the MAPK signaling cascade in K-ras mutant tumors to maximize therapeutic benefit for patients.

Sentinel lymph nodes containing very small (<0.1 mm) deposits of metastatic melanoma cannot be safely regarded as tumor-negative

BACKGROUND

Some authors have suggested that patients with very small (<0.1 mm) deposits of metastatic melanoma in sentinel lymph nodes (SLNs) should be considered SLN-negative, whereas others have reported that such patients can have adverse long-term outcomes. The aims of the present study were to determine whether extensive sectioning of SLNs resulted in more accurate categorization of histologic features of tumor deposits and to assess prognostic associations of histologic parameters obtained using more intensive sectioning protocols.

METHODS

From patients with a single primary cutaneous melanoma who underwent SLN biopsy between 1991 and 2008, those in which the maximum size of the largest tumor deposit (MaxSize) in SLNs was <0.1 mm in the original sections were identified. Five batches of additional sections were cut from the SLN tissue blocks at intervals of 250 μm. The 1st batch was cut from the blocks without any trimming; these sections were therefore immediately adjacent to the original sections. Each batch included 5 sequential sections, the 1st and 5th stained with hematoxylin-eosin, and the 2nd, 3rd, and 4th stained immunohistochemically with S-100, HMB-45, and Melan-A, respectively. In each batch of sections, the following histologic features of tumor deposit(s) in the SLNs were evaluated: MaxSize; tumor penetrative depth (TPD) (defined as the maximum depth of tumor deposit(s) from the inner margin of the lymph node capsule), and intranodal location (classified as subcapsular if the tumor deposit(s) were confined to the subcapsular zone or parenchymal if there was any involvement of the nodal parenchyma beyond the subcapsular zone). The measured histologic parameters were compared in each batch of sections. The association of histologic parameters with overall survival was assessed for the parameters measured in each batch of sections.

RESULTS

There were 20 eligible patients (15 females, 5 males, median age 60 years). After a median follow-up duration of 40 months, 4 patients had died from melanoma and 2 patients of unknown causes. Completion lymph node dissection (CLND) was performed in 13 cases (65%) and was negative in all cases. Relative to the measured values on the original sections, all 3 parameters were upstaged in subsequent batches of sections, but no further upstaging of MaxSize, TPD, or location was seen beyond batch 3, batch 4, and batch 2, respectively. Increasing MaxSize was associated with significantly poorer overall survival in batches 1, 2, and 3. Parenchymal involvement was significantly associated with poorer survival in batches 2-5. TPD was not significantly associated with overall survival.

CONCLUSIONS

The results of this study indicate that very small (<0.1 mm) deposits of melanoma in SLNs may be associated with adverse clinical outcomes and that this is due, at least in part, to the underestimation of SLN tumor burden in the initial sections. Our evidence does not support clinical decision-making on the assumption that patients with very small melanoma deposits in SLNs have the same outcome as those who are SLN-negative.