Fumagillin treatment of hepatocellular carcinoma in rats: An in vivo study of antiangiogenesis

Newly synthesized methionine aminopeptidase 2 inhibitor hinders tumor growth

Methionine aminopeptidase 2 (MetAp2) inhibition has been recognized as a promising approach for suppressing angiogenesis and cancer progression. Small molecule fumagillol derivatives with adamantane side groups were synthesized and evaluated for MetAp2 inhibition activity, and a lead molecule with superior abilities to inhibit the enzymatic activity of MetAp2 was identified. The compound, referred to as AD-3281, effectively suppressed proliferation of cancer and endothelial cells and impaired tube formation of endothelial cells in vitro. When administered systemically, AD-3281 was well tolerated and led to a significant suppression of human melanoma and mammary tumor xenografts grown in mice. The activity in vivo was associated with reduced angiogenesis and tumor proliferation as detected histologically. In order to develop a formulation that can solubilize AD-3281 with a minimal content of organic solvents, biodegradable nanoparticles comprised of poly-lactic-co-glycolic acid (PLGA) were fabricated and characterized. Compared with the free compound, AD-3281-loaded nanoparticles showed an advantageous cellular availability and uptake, leading to higher activity in cells and better transport in three-dimensional (3D) cultures. Taken together, we introduce a novel MetAp2 inhibitor with high anti-cancer activity and a stable nano-formulation with a high potential for future clinical translation.

Suppression of glioblastoma growth and angiogenesis through molecular targeting of methionine aminopeptidase-2

Methionine aminopeptidases (MetAPs) have been pharmacologically linked to cell growth, angiogenesis, and tumor progression, which make it an attractive target for cancer therapy. We investigated MetAP2's biological role in glioblastoma (GBM), an aggressive tumor characterized by massive neovascularization. We examined the effect of anti-MetAP2 RNA interference on proliferation and angiogenesis in GBM cell line. The biological effects of MetAP2 knockdown were assessed by comparing the proliferation, tumorigenecity, and angiogenesis of parental cells and MetAP2 knockdown cells. We generated MetAP2 knockdown cells using lentiviral short hairpin RNAs against MetAP2 in SNB19 GBM cells, which normally express high levels of MetAP2. MetAP2 knockdown cells were less proliferative and less tumorigenic when compared to the parental cells. MetAP2 knockdown decreased vascular endothelial growth factor (VEGF) secretion and expression at the mRNA and protein levels. Decreased VEGF expression in MetAP2 knockdown cells correlated very well with decreased vessel formation in a tube formation assay. We showed that VEGF suppression in MetAP2 knockdown cells was mediated by the von Hippel-Lindau protein. In in vivo animal studies using an intracranial SNB19 tumor model, MetAP2 knockdown also reduced the tumor growth rate and angiogenesis, which in turn prolonged the survival of mice in xenograft model. Our results show that MetAP2 regulates angiogenesis in GBM and identify MetAP2-specific substrates that may serve as candidates for clinical assay development.

Natural compounds' activity against cancer stem-like or fast-cycling melanoma cells

Background

Accumulating evidence supports the concept that melanoma is highly heterogeneous and sustained by a small subpopulation of melanoma stem-like cells. Those cells are considered as responsible for tumor resistance to therapies. Moreover, melanoma cells are characterized by their high phenotypic plasticity. Consequently, both melanoma stem-like cells and their more differentiated progeny must be eradicated to achieve durable cure. By reevaluating compounds in heterogeneous melanoma populations, it might be possible to select compounds with activity not only against fast-cycling cells but also against cancer stem-like cells. Natural compounds were the focus of the present study.

Methods

We analyzed 120 compounds from The Natural Products Set II to identify compounds active against melanoma populations grown in an anchorage-independent manner and enriched with cells exerting self-renewing capacity. Cell viability, cell cycle arrest, apoptosis, gene expression, clonogenic survival and label-retention were analyzed.

Findings

Several compounds efficiently eradicated cells with clonogenic capacity and nanaomycin A, streptonigrin and toyocamycin were effective at 0.1 µM. Other anti-clonogenic but not highly cytotoxic compounds such as bryostatin 1, siomycin A, illudin M, michellamine B and pentoxifylline markedly reduced the frequency of ABCB5 (ATP-binding cassette, sub-family B, member 5)-positive cells. On the contrary, treatment with maytansine and colchicine selected for cells expressing this transporter. Maytansine, streptonigrin, toyocamycin and colchicine, even if highly cytotoxic, left a small subpopulation of slow-dividing cells unaffected. Compounds selected in the present study differentially altered the expression of melanocyte/melanoma specific microphthalmia-associated transcription factor (MITF) and proto-oncogene c-MYC.

Conclusion

Selected anti-clonogenic compounds might be further investigated as potential adjuvants targeting melanoma stem-like cells in the combined anti-melanoma therapy, whereas selected cytotoxic but not anti-clonogenic compounds, which increased the frequency of ABCB5-positive cells and remained slow-cycling cells unaffected, might be considered as a tool to enrich cultures with cells exhibiting melanoma stem cell characteristics.

Design, synthesis and evaluation of a cellular stable and detectable biotinylated fumagillin probe and investigation of cell permeability of fumagillin and its analogs to endothelial and cancer cells

Fumagillin (1), a natural product of fungal origin, and its analogs were discovered to be extremely potent and highly selective inhibitors restraining endothelial cell proliferation in vitro by covalently binding to MetAP2. In order to further understand the unclear biological mechanisms and pharmacological processes of fumagillin and its derivatives, fumagillin-biotin conjugate 8 was designed and synthesized, which is linked with a 27-atom connection chain and by urethane (carbamate) bonds between fumagillol and D-norbiotinamine. The conjugate 8 shows comparable activity and selectivity against HUVEC proliferation as fumagillin. It was demonstrated that the conjugate 8 is stable inside the cell and its linker is of a suitable length for the detection of biotin in native and denatured conditions. Using the conjugate 8, it was determined that the cell permeability of fumagillin (1) and its analogs are not responsible for their inhibitory activity difference against the proliferation of endothelial and cancer cells. Furthermore, we confidently believe that our present strategy is a versatile and convenient method for investigating drug's cell permeability along with other studies regardless of reversible or irreversible interaction between the drug and binding target/s.

MicroRNA profiling in pediatric pilocytic astrocytoma reveals biologically relevant targets, including PBX3, NFIB, and METAP2

Pilocytic astrocytoma (PA) is a World Health Organization grade I glioma that occurs most commonly in children and young adults. Specific genetic alterations have been described in PA, but the pathogenesis remains poorly understood. We studied microRNA (miRNA) alterations in a large cohort of patients with PA. A total of 43 PA, including 35 sporadic grade I PA, 4 neurofibromatosis-1 (NF1)-associated PA, and 4 PA with pilomyxoid features, as well as 5 nonneoplastic brain controls were examined. BRAF fusion status was assessed in most cases. RNA was examined using the Agilent Human miRNA Microarray V3 platform. Expression of miRNA subsets was validated using quantitative real-time PCR (qRT-PCR) with Taqman probes. Validation of predicted protein targets was performed on tissue microarrays with the use of immunohistochemistry. We identified a subset of miRNAs that were differentially expressed in pediatric PAs versus normal brain tissue: 13 miRNAs were underexpressed, and 20 miRNAs were overexpressed in tumors. Differences were validated by qRT-PCR in a subset, with mean fold change in tumor versus brain of -17 (miR-124), -15 (miR-129), and 19.8 (miR-21). Searching for predicted protein targets in Targetscan, we identified a number of known and putative oncogenes that were predicted targets of miRNA sets relatively underexpressed in PA. Predicted targets with increased expression at the mRNA and/or protein level in PA included PBX3, METAP2, and NFIB. A unique miRNA profile exists in PA, compared with brain tissue. These miRNAs and their targets may play a role in the pathogenesis of PA.

NC2213: a novel methionine aminopeptidase 2 inhibitor in human colon cancer HT29 cells

Methionine aminopeptidase 2 (MetAP2) is a bifunctional protein that plays a critical role in the regulation of post-translational processing and protein synthesis. MetAP2 is overexpressed in human colon cancer. In this report we screened various MetAP2 inhibitors and treated HT29 cells with various concentrations of compounds. We evaluated the expression of MetAP2 and pp60c-src expressions in HT29 cells. In addition we also carried out the cell proliferation and cell cycle analysis in the MetAP2 inhibitor-treated HT29 cells. The cell cycle analysis of HT29 treated with 1.0 microM of NC2213 showed an arrest in the G2 phase followed by an induction in the percentage of cells undergoing apoptosis in the sub-G1 phase. Western blot analysis revealed that the MetAP2 expression was dose-dependently decreased when the HT29 cells were treated with the 3,5-bis(benzylidene)-4-piperidone derivative (NC2213). In addition, phosphorylation of Src, a myristoylated oncoprotein was significantly decreased by 1.0 microM of NC2213 as revealed by Western blot analysis. Furthermore, NC2213 also inhibits the expression of pp60c-src in HT29 cells. Interestingly, this compound also inhibits the phosphorylation at Tyr416 of pp60c-src while increasing the phosphorylation at Tyr527 of pp60c-src. NC2213 inhibits the growth of HT29 cells by inducing apoptosis and might be useful for the treatment of human colon cancer.

Methionine aminopeptidase 2 over-expressed in cholangiocarcinoma: potential for drug target

Methionine aminopeptidases (MetAP) are proteases which remove the N-terminal methionine from newly synthesized proteins. Associations of MetAP2 with tumor progression of different cancers have been repeatedly reported. We aim to determine if MetAP2 is expressed in cholangiocarcinomas (CCA) and investigate to see if it would be a useful therapeutic target. We evaluated MetAP2 expression by immunohistochemistry in 82 patients of intrahepatic CCA. MetAP2 was expressed in bile ducts to various degrees. It was occasionally expressed with weak staining in normal bile duct epithelium but was strikingly over-expressed in dysplastic bile duct epithelia, primary and metastatic CCA tissues (p < 0.001). The increased expression of MetAP2 in proliferating bile duct was evident. All metastatic tumors had stronger expression of MetAP2 than the corresponding primary tumors. Fumagillin, a MetAP2 specific inhibitor, significantly inhibited cell proliferation in dose dependent manner and the degree of growth inhibition was dependent on the amount of cellular enzyme. The present study highlights the involvement of MetAP2 in an early event of carcinogenesis of CCA. The findings represent the first description of increased MetAP2 expression in CCA. The inhibition of enzyme activity using MetAP2 inhibitors may be a potential strategy for long-term control of tumor development and progression in CCA patients.

Efficacy of anti-angiogenic treatment of tumors in old versus young mice

Cancer treatment in the older population, the most afflicted by the disease, is as yet, inefficient. A reduced aggressiveness of tumors is often observed in the elderly, implying the necessity for therapeutic modalities adjusted to age. A rational design of age-related cancer therapy could be based on the mechanisms of this phenomenon. It is suggested that, in addition to the patient's old age-specific health problems (which prohibit the use of the aggressive cancer treatments now in use), the age-related differential tumor biology (apparently beneficial to the old) should also be considered for the design of treatment modalities suitable for the aged. Based on one mechanism of the reduced aggressiveness of tumors in the old (age-dependent decreased angiogenesis), we compared the effect of an anti-angiogenic treatment in young and old mice. TNP-470 treatment resulted in an inhibitory effect on B16 melanoma in both young and old mice but the effect was more pronounced in old animals. Moreover, a high percentage of long-term surviving animals was observed only in the old-treated mice. Treatment with TNP-470 of the AKR lymphoma produced similar results. We thus found a differential age-dependent therapeutic efficiency of an anti-angiogenic agent on two tumors. Importantly, the anti-angiogenic drug was more efficient against tumors of old animals.

Methionine aminopeptidase 2 and cancer

Methionine aminopeptidase (MetAP) is a bifunctional protein that plays a critical role in the regulation of post-translational processing and protein synthesis. In yeasts and humans, two proteins are known to possess MetAP activity, which are known as MetAP1 and MetAP2. MetAP2 has attracted much more attention than MetAP1 due to the discovery of MetAP2 as a target molecule of the anti-angiogenic compounds, fumallin and ovalicin. MetAP2 plays an important role in the development of different types of cancer. Recently, we observed a high expression of MetAP2 in human colorectal cancer tissues and colon cancer cell lines. In addition, pp60(c-src) expression was correlated with the expression of MetAP2 and N-myristoyltransferase. In this review, we discuss the recent developments of MetAP2 and its inhibitors. Future detailed studies related to MetAP2 and apoptosis will shed light on the involvement of this enzyme in the regulation of various apoptotic factors.

Metal mediated inhibition of methionine aminopeptidase by quinolinyl sulfonamides

Quinolinyl sulfonamides, such as N-(quinolin-8-yl)methanesulfonamide (10) and N-(5-chloroquinolin-8-yl)methanesulfonamide (11), were identified as potent methionine aminopeptidase (MetAP) inhibitors by high throughput screening of a diverse chemical library of small organic compounds. They showed different inhibitory potencies on Co(II)-, Ni(II)-, Fe(II)-, Mn(II)-, and Zn(II)-forms of Escherichia coli MetAP, and their inhibition is dependent on metal concentration. X-ray structures of E. coli MetAP complexed with 10 revealed that the inhibitor forms a metal complex with the residue H79 at the enzyme active site; the complex is further stabilized by an extended H-bond and metal interaction network. Analysis of the inhibition of MetAP by these inhibitors indicates that this is a typical mechanism of inhibition for many non-peptidic MetAP inhibitors and emphasizes the importance of defining in vitro conditions for identifying and evaluating MetAP inhibitors that will be capable of giving information relevant to the in vivo situation.