Novel Therapeutic Target For Melanoma Research Articles

EPHA2 is a mediator of vemurafenib resistance and a novel therapeutic target in melanoma.

BRAF(V600E) is the most common oncogenic lesion in melanoma and results in constitutive activation of the MAPK pathway and uncontrolled cell growth. Selective BRAF inhibitors such as vemurafenib have been shown to neutralize oncogenic signaling, restrain cellular growth, and improve patient outcome. Although several mechanisms of vemurafenib resistance have been described, directed solutions to overcome these resistance lesions are still lacking. Herein, we found that vemurafenib resistance can be (i) mediated by EPHA2, a member of the largest receptor tyrosine kinases (RTK) subfamily erythropoietin-producing hepatocellular (EPH) receptors, and (ii) associated with a greater phenotypic dependence on EPHA2. Furthermore, we developed a series of first-in-class EPHA2 inhibitors and show that these new compounds potently induce apoptosis, suppress viability, and abrogate tumorigenic growth of melanoma cells, including those that are resistant to vemurafenib. These results provide proof of concept that RTK-guided growth, and therapeutic resistance, can be prospectively defined and selectively targeted. In this study, we show that resistance to selective BRAF inhibitors can be mediated by the RTK EPHA2. Furthermore, direct targeting of EPHA2 can successfully suppress melanoma growth and mitigate therapeutic resistance.

IL2 Inducible T-cell Kinase, a Novel Therapeutic Target in Melanoma

IL2 Inducible T-cell Kinase, a Novel Therapeutic Target in Melanoma

Ocular albinism type 1-induced melanoma cell migration is mediated through the RAS/RAF/MEK/ERK signaling pathway.

Malignant melanoma has the highest risk of mortality among all types of skin cancer due to its highly metastatic potential. The ocular albinism type1 (OA1) protein is a pigment cell‑specific glycoprotein, which shares significant structural and functional features with Gprotein‑coupled receptors. However, the role of OA1 in melanoma has yet to be elucidated. The present study aimed to investigate whether OA1 is involved in melanoma cell migration. OA1 was found to stimulate cell migration in a dose‑dependent manner in cultured human melanoma cells. Furthermore, knockdown of OA1 using small interferingRNA was observed to significantly inhibit melanoma cell migration. In addition, the mechanism underlying OA1‑induced melanoma cell migration was investigated. Stimulation of the RAS/RAF/mitogen activated protein kinase kinase (MEK)/extracellular signal‑regulated kinase (ERK) pathway using growth factors enhanced OA1 expression and melanoma cell migration, whereas inhibition of this pathway using U0126 was observed to markedly decrease OA1 expression and the number of migrated cells. These findings indicate that OA1 is involved in melanoma cell migration and that OA1‑induced melanoma cell migration is mediated through the RAS/RAF/MEK/ERK signaling pathway. Therefore, OA1 may serve as a novel therapeutic target for melanoma.

Abstract 3037: Mer receptor tyrosine kinase is a novel therapeutic target in melanoma.

Abstract Metastatic melanoma is one of the most aggressive forms of cutaneous cancers. While recent therapeutic advances have prolonged patient survival, prognosis remains dismal. Mer is a receptor tyrosine kinase with oncogenic properties that is often overexpressed or activated in various malignancies. Using both protein immunohistochemistry and microarray analyses, we demonstrate that Mer expression correlates with disease progression. Mer expression was highest in metastatic melanomas followed by primary melanomas whereas the lowest expression was observed in nevi. In addition, over 50% of melanoma cell lines overexpressed Mer compared to normal human melanocytes, however overexpression did not correlate with mutations in BRAF or RAS. Stimulation of melanoma cells with the Mer ligand Gas6 resulted in activation of several downstream signaling pathways including MAPK/ERK, PI3K/Akt, and Jak/STAT. Mer inhibition via shRNA reduced Mer-mediated downstream signaling, reduced colony formation by up to 59% (p<0.05) and diminished tumor volume by 60% (p<0.05) in a human melanoma xenograft murine model. Treatment of melanoma cells with UNC1062, a novel Mer-selective small molecule tyrosine kinase inhibitor, reduced activation of Mer-mediated downstream signaling, induced apoptosis in culture, reduced colony formation in soft agar and inhibited invasion of melanoma cells. In addition, Mer inhibition synergized with mutant BRAF inhibition in signaling and apoptosis assays. This work establishes Mer as a therapeutic target in melanoma and provides rationale for the continued development of Mer-targeted therapies. Citation Format: Jennifer Schlegel, Maria Sambade, Susan Sather, Stergios Moschos, Aik-Choon Tan, Amanda Winges, Deborah DeRyckere, Craig C. Carson, Dimitri G. Trembath, John J. Tentler, Gail Eckhardt, Pei-Fen Kuan, Ronald L. Hamilton, Lyn M. Duncan, C. Ryan Miller, Nana Nikolaishvili-Feinberg, Bentley R. Midkiff, Xiaodong Wang, Jing Liu, Weihe Zhang, Chao Yang, Stephen V. Frye, H. Shelton Earp, Janiel Shields, Douglas K. Graham. Mer receptor tyrosine kinase is a novel therapeutic target in melanoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3037. doi:10.1158/1538-7445.AM2013-3037

Abstract 2185: BRD4 is a novel therapeutic target in melanoma

Abstract The incidence of melanoma is increasing faster than that of any other cancer, and predicted to double every 10-20 years. Surgery can be curative in Stage I, II, or III disease, but 75% of patients with deep primary lesions develop extensive recurrence or distant metastases and have dismal prognosis. In fact, there is no curative treatment for stage IV melanoma. Although novel targeted therapies, such as BRAF inhibitors and anti-CTLA4 antibodies are showing promising results in melanoma clinical trials, resistance to these agents and patient relapse rapidly ensue. Therapeutic resistance has been commonly attributed to functional redundancy between intimately hardwired cellular pathways responsible for tumor cell maintenance and survival. In order to avoid redundancy, we propose to directly inhibit the transcription of multiple genes required for the establishment or maintenance of tumors. First, we analyzed the expression of Bromodomain (BrD)-containing proteins, a family of epigenetic readers that bind acetylated lysine. BrDs are present in histone acetyl transferases (i.e. CBP/p300, PCAF, GCN5) and transcriptional regulators (i.e. BET family members: BRD2, 3, and 4). mRNA expression arrays showed several BrD-containing genes as upregulated in primary and metastatic melanoma cell lines compared to normal melanocytes. Analysis of available expression profiles also revealed higher levels of BRD2 and BRD4 in melanoma tissues relative to nevi or normal skin (P<0.001). Furthermore, immunohistochemistry staining of a melanoma tissue microarray confirmed overexpression of BRD4 protein in primary (P<0.001) and metastatic tumors (P<0.001) compared to nevi. BRD4 knockdown using siRNA or shRNA suppressed the proliferation and colony formation capacity of several metastatic melanoma cell lines. Moreover, melanoma cells stably infected with shBRD4 carrying lentivirus displayed reduced tumor growth in vivo compared with their counterpart infected with a non-silencing control. To identify cellular pathways modulated by BrD inhibition and to investigate the mechanism(s) that might mediate its anti-proliferative effects, we conducted a global transcriptome analysis (RNA sequencing) of 6 melanoma cell lines treated with specific BrD inhibitors or vehicle. Gene ontology analysis of these data revealed enrichment in genes controlling cell cycle, growth and proliferation. Accordingly, cell cycle analysis demonstrated a specific G1 phase arrest upon BRD4 silencing. In conclusion, we have demonstrated that expression of several BrD containing proteins is dysregulated in melanoma and that BRD4 represents a promising therapeutic target in these tumors. Our data provides a rationale for testing the efficacy of newly developed, specific and potent BET inhibitors against melanoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2185. doi:1538-7445.AM2012-2185

Vitamin D 3 up-regulating protein 1 (VDUP1) antisense DNA regulates tumorigenicity and melanogenesis of murine melanoma cells via regulating the expression of fas ligand and reactive oxygen species

The expression of vitamin D 3 up-regulating protein-1 (VDUP1) was up-regulated by 1α,25-dihydroxyvitamin D 3 (VD3) treatment in B16 mouse melanoma cells. The functional effect of VDUP1 on B16F10 melanoma cells was demonstrated by reduction of Fas ligand and CD44 expression in cells transfected with VDUP1 antisense cDNA. Furthermore, intracellular reactive oxygen species level and cell proliferation were decreased in antisense transfectants compared with those in vector controls. However, melanin synthesis was up-regulated in antisense transfectants. In addition, VDUP1 antisense transfectants showed an increased susceptibility to natural killer (NK) cells in vitro. When VDUP1 antisense transfectants were implanted into syngeneic mice, significant reduction of tumor cell growth was observed with the infiltrate of T cells and NK cells in tumor area. Taken together, these results demonstrate that VDUP1 has critical physiological roles and can be a novel therapeutic target for melanoma.