Effects of Malignant Melanoma Initiating Cells on T-Cell Activation.

Although human malignant melanoma is a highly immunogenic cancer, both the endogenous antitumor immune response and melanoma immunotherapy often fail to control neoplastic progression. Accordingly, characterizing melanoma cell subsets capable of evading antitumor immunity could unravel optimized treatment strategies that might reduce morbidity and mortality from melanoma. By virtue of their preferential capacity to modulate antitumor immune responses and drive inexorable tumor growth and progression, malignant melanoma-initiating cells (MMICs) warrant closer investigation to further elucidate the cellular and molecular mechanisms underlying melanoma immune evasion and immunotherapy resistance. Here we describe methodologies that enable the characterization of immunoregulatory effects of purified MMICs versus melanoma bulk populations in coculture with syngeneic or allogeneic lymphocytes, using [3H]thymidine incorporation, enzyme-linked immunosorbent spot (ELISPOT), or ELISA assays. These assays were traditionally developed to analyze alloimmune processes and we successfully adapted them for the study of tumor-mediated immunomodulatory functions.

Cyclin-Dependent Kinase 5 (CDK5) Controls Melanoma Cell Motility, Invasiveness, and Metastatic Spread-Identification of a Promising Novel therapeutic target.

Despite considerable progress in recent years, the overall prognosis of metastatic malignant melanoma remains poor, and curative therapeutic options are lacking. Therefore, better understanding of molecular mechanisms underlying melanoma progression and metastasis, as well as identification of novel therapeutic targets that allow inhibition of metastatic spread, are urgently required. The current study provides evidence for aberrant cyclin-dependent kinase 5 (CDK5) activation in primary and metastatic melanoma lesions by overexpression of its activator protein CDK5R1/p35. Moreover, using melanoma in vitro model systems, shRNA-mediated inducible knockdown of CDK5 was found to cause marked inhibition of cell motility, invasiveness, and anchorage-independent growth, while at the same time net cell growth was not affected. In vivo, CDK5 knockdown inhibited growth of orthotopic xenografts as well as formation of lung and liver colonies in xenogenic injection models mimicking systemic metastases. Inhibition of lung metastasis was further validated in a syngenic murine melanoma model. CDK5 knockdown was accompanied by dephosphorylation and overexpression of caldesmon, and concomitant caldesmon knockdown rescued cell motility and proinvasive phenotype. Finally, it was found that pharmacological inhibition of CDK5 activity by means of roscovitine as well as by a novel small molecule CDK5-inhibitor, N-(5-isopropylthiazol-2-yl)-3-phenylpropanamide, similarly caused marked inhibition of invasion/migration, colony formation, and anchorage-independent growth of melanoma cells. Thus, experimental data presented here provide strong evidence for a crucial role of aberrantly activated CDK5 in melanoma progression and metastasis and establish CDK5 as promising target for therapeutic intervention.

Hippo signaling mediates proliferation, invasiveness, and metastatic potential of clear cell renal cell carcinoma.

Recent work has identified dysfunctional Hippo signaling to be involved in maintenance and progression of various human cancers, although data on clear cell renal cell carcinoma (ccRCC) have been limited. Here, we provide evidence implicating aberrant Hippo signaling in ccRCC proliferation, invasiveness, and metastatic potential. Nuclear overexpression of the Hippo target Yes-associated protein (YAP) was found in a subset of patients with ccRCC. Immunostaining was particularly prominent at the tumor margins and highlighted neoplastic cells invading the tumor-adjacent stroma. Short hairpin RNA-mediated knockdown of YAP significantly inhibited proliferation, migration, and anchorage-independent growth of ccRCC cells in soft agar and led to significantly reduced murine xenograft growth. Microarray analysis of YAP knockdown versus mock-transduced ccRCC cells revealed down-regulation of endothelin 1, endothelin 2, cysteine-rich, angiogenic inducer, 61 (CYR61), and c-Myc in ccRCC cells as well as up-regulation of the cell adhesion molecule cadherin 6. Signaling pathway impact analysis revealed activation of the p53 signaling and cell cycle pathways as well as inhibition of mitogen-activated protein kinase signaling on YAP down-regulation. Our data suggest CYR61 and c-Myc as well as signaling through the endothelin axis as bona fide downstream effectors of YAP and establish aberrant Hippo signaling as a potential therapeutic target in ccRCC.

Fibroblast growth factor receptor 1 gene amplification in pancreatic ductal adenocarcinoma.

AIMS: Pancreatic ductal adenocarcinomas (PDACs) are chemoresistant, resulting in extremely poor survival of patients; therefore, novel molecular targets, even in small subsets of genetically characterized tumours, are urgently needed. Tyrosine kinase receptor inhibitors (TKIs) are already in clinical use. The aims of this study were to examine the gene copy number and expression of fibroblast growth factor receptor 1 (FGFR1) in 155 patients with PDAC, and investigate the effects of the FGFR-specific inhibitor BGJ398 on FGFR1-amplified pancreatic tumour cells in vitro. METHODS AND RESULTS: Fluorescence in-situ hybridization (FISH) and immunohistochemical analysis of 155 PDACs were performed using tissue microarrays. Amplification of FGFR1 was found in 2.6% (4/155) of cases. Four per cent of tumours (5/125) were shown to express FGFR1 by immunohistochemistry. Sequence analysis demonstrated an activating KRAS mutation (exon 2) in all FGFR1-amplified cases. The FGFR1-amplified pancreatic carcinoma cell line PT45P1 showed high levels of FGFR1 mRNA and protein expression. Proliferation of this cell line can be inhibited using the FGFR1 inhibitor BGJ398. CONCLUSIONS: FGFR1 represents a potential new therapeutic target in a subset of patients harbouring FGFR1-amplified tumours. Identification of pancreatic cancers harbouring FGFR1 amplification may be important in preselecting patients and/or interpreting clinical studies using TKIs.

Everolimus for the treatment of pancreatic neuroendocrine tumors.

INTRODUCTION: Pancreatic neuroendocrine tumors (PNET) represent the second most common primary malignancy of the pancreas. Until recently, therapeutic options for advanced PNET have been limited. AREAS COVERED: A recently published Phase III clinical trial demonstrated striking therapeutic activity of the mTOR inhibitor everolimus in advanced PNET and led to its approval for this indication by the FDA. This review discusses this landmark discovery in the context of currently available therapeutic options, pathophysiology and molecular genetics of PNET. EXPERT OPINION: The approval of everolimus for the treatment of PNET marks a major step forward in the clinical management of this disease and represents a notable example of the successful translation of a targeted therapy that was initially developed based on findings at the lab bench, into everyday clinical practice. These results encourage hopes that the overall therapeutic efficacy of such approaches can be further enhanced by the introduction of combinatorial regimens, simultaneously targeting more than one oncogenic signaling pathway, as well as by stratification of patients based on the individual genetic setup of their tumors.

Recent developments of transgenic and xenograft mouse models of pancreatic cancer for translational research.

IMPORTANCE OF THE FIELD: Pancreatic cancer is a devastating disease associated with near uniform mortality. Usually diagnosed at advanced, metastatic stages when surgical resection with curative intention is not possible any more, most patients succumb to progressive disease after a few months. Despite recent advances in understanding pancreatic carcinogenesis and continuous efforts in translational research, so far these results failed to translate into clinically relevant improvements of patient survival. AREAS COVERED IN THIS REVIEW: Preclinical evaluation of drug candidates and novel therapeutic strategies rely on in vitro and in vivo model systems to predict response in patients. This article reviews mouse models of pancreatic cancer, their respective applications in translational research and discusses their potential to predict clinical responses in patients. WHAT THE READER WILL GAIN: This article provides a profound overview of individual strength as well as of shortcomings of mouse models of pancreatic cancer currently available for translational research. TAKE HOME MESSAGE: Considerable progress in designing mouse models of pancreatic cancer has been made over the last decade and several xenograft as well as genetically engineered mouse models faithfully recapitulating human disease development has been developed. Taken together, these newly developed in vivo model systems provide powerful tools likely to boost preclinical evaluation and bench-to-bedside transition of novel therapeutic approaches directed against this dire malady.

Modulation of T-cell activation by malignant melanoma initiating cells.

Highly immunogenic cancers such as malignant melanoma are capable of inexorable tumor growth despite the presence of antitumor immunity. Thus, only a restricted minority of tumorigenic malignant cells may possess the phenotypic and functional characteristics needed to modulate tumor-directed immune activation. Here we provide evidence supporting this hypothesis. Tumorigenic ABCB5(+) malignant melanoma initiating cells (MMICs) possessed the capacity to preferentially inhibit IL-2-dependent T-cell activation and to support, in a B7.2-dependent manner, induction of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs). Compared with melanoma bulk cell populations, ABCB5(+) MMICs displayed lower levels of MHC class I, aberrant positivity for MHC class II, and lower expression levels of the melanoma-associated antigens MART-1, ML-IAP, NY-ESO-1, and MAGE-A. Additionally, these tumorigenic ABCB5(+) subpopulations preferentially expressed the costimulatory molecules B7.2 and PD-1, both in established melanoma xenografts and in clinical tumor specimens. In immune activation assays, MMICs inhibited mitogen-dependent human peripheral blood mononuclear cell (PBMC) proliferation and IL-2 production more efficiently than ABCB5(-) melanoma cell populations. Moreover, coculture with ABCB5(+) MMICs increased the abundance of Tregs, in a B7.2 signaling-dependent manner, along with IL-10 production by mitogen-activated PBMCs. Consistent with these findings, MMICs also preferentially inhibited IL-2 production and induced IL-10 secretion by cocultured patient-derived, syngeneic PBMCs. Our findings identify novel T-cell modulatory functions of ABCB5(+) melanoma subpopulations and suggest specific roles for these MMICs in the evasion of antitumor immunity and in cancer immunotherapeutic resistance.