Paradoxic effects of metformin on endothelial cells and angiogenesis.

The biguanide metformin is used in type 2 diabetes management and has gained significant attention as a potential cancer preventive agent. Angioprevention represents a mechanism of chemoprevention, yet conflicting data concerning the antiangiogenic action of metformin have emerged. Here, we clarify some of the contradictory effects of metformin on endothelial cells and angiogenesis, using in vitro and in vivo assays combined with transcriptomic and protein array approaches. Metformin inhibits formation of capillary-like networks by endothelial cells; this effect is partially dependent on the energy sensor adenosine-monophosphate-activated protein kinase (AMPK) as shown by small interfering RNA knockdown. Gene expression profiling of human umbilical vein endothelial cells revealed a paradoxical modulation of several angiogenesis-associated genes and proteins by metformin, with short-term induction of vascular endothelial growth factor (VEGF), cyclooxygenase 2 and CXC chemokine receptor 4 at the messenger RNA level and downregulation of ADAMTS1. Antibody array analysis shows an essentially opposite regulation of numerous angiogenesis-associated proteins in endothelial and breast cancer cells including interleukin-8, angiogenin and TIMP-1, as well as selective regulation of angiopioetin-1, -2, endoglin and others. Endothelial cell production of the cytochrome P450 member CYP1B1 is upregulated by tumor cell supernatants in an AMPK-dependent manner, metformin blocks this effect. Metformin inhibits VEGF-dependent activation of extracellular signal-regulated kinase 1/2, and the inhibition of AMPK activity abrogates this event. Metformin hinders angiogenesis in matrigel pellets in vivo, prevents the microvessel density increase observed in obese mice on a high-fat diet, downregulating the number of white adipose tissue endothelial precursor cells. Our data show that metformin has an antiangiogenic activity in vitro and in vivo associated with a contradictory short-term enhancement of pro-angiogenic mediators, as well as with a differential regulation in endothelial and breast cancer cells.

Evidence of epidermal growth factor receptor expression in uveal melanoma: inhibition of epidermal growth factor-mediated signalling by Gefitinib and Cetuximab triggered antibody-dependent cellular cytotoxicity.

Despite advances in surgery and radiotherapy of uveal melanoma (UM), many patients develop distant metastases that poorly respond to therapy. Improved therapies for the metastatic disease are therefore urgently needed. Expression of the epidermal growth factor receptor (EGFR), a target of kinase inhibitors and humanised antibodies in use for several cancers, had been reported. Forty-eight human UMs were analysed by expression profiling. Signalling was tested in three EGFR expressing UM cell lines by Western blotting using phosphorylation specific antibodies for EGFR and the downstream mediators AKT (v-akt murine thymoma viral oncogene homolog) and extracellular signal-regulated kinase (ERK). Evidence for signalling in tumours was obtained through the application of a UM-specific EGF-signature. The EGFR specific kinase inhibitor, Gefitinib and the humanised monoclonal antibody, Cetuximab, were tested for their effect on EGFR signalling. Natural killer cell mediated antibody-dependent cellular cytotoxicity (ADCC) and tumour necrosis factor α (TNF-α) release was analysed for Cetuximab. Fourteen of 48 UMs and three of 14 cell lines (over-)express EGFR, at least in part due to trisomy of the EGFR locus on chromosome 7p12. EGFR and the downstream mediator, AKT, are phosphorylated upon stimulation with EGF in EGFR expressing cell lines. EGFR over-expressing tumours but not EGFR negative tumours show an activated EGF-signature. Gefitinib inhibits EGFR and AKT phosphorylation and Cetuximab induces EGFR phosphorylation but inhibits signalling to AKT induced with EGF. Cetuximab triggers natural killer (NK) cells to lyse EGFR+ cell lines and to release TNF-α. EGFR appears suited as a novel molecular drug target for therapy of uveal melanoma.

Down-regulation of the PTTG1 proto-oncogene contributes to the melanoma suppressive effects of the cyclin-dependent kinase inhibitor PHA-848125.

We previously demonstrated that PHA-848125, a cyclin-dependent kinase inhibitor presently under Phase II clinical investigation, impairs melanoma cell growth. In this study, gene expression profiling showed that PHA-848125 significantly modulated the expression of 128 genes, predominantly involved in cell cycle control, in the highly drug-sensitive GL-Mel (p53 wild-type) melanoma cells. Up-regulation of 4 selected genes (PDCD4, SESN2, DDIT4, DEPDC6), and down-regulation of 6 selected genes (PTTG1, CDC25A, AURKA, AURKB, PLK1, BIRC5) was confirmed at protein levels. The same protein analysis performed in PHA-848125-treated M10 melanoma cells - p53 mutated and less sensitive to the drug than GL-Mel cells - revealed no DEPDC6 expression and no changes of PTTG1, PDCD4 and BIRC5 levels. Upon PHA-848125 treatment, a marked PTTG1 down-modulation was also observed in A375 cells (p53 wild-type) but not in CN-Mel cells (p53 mutated). PTTG1 silencing significantly inhibited melanoma cell proliferation and induced senescence, with effects less pronounced in p53 mutated cells. PTTG1 silencing increased PHA-848125 sensitivity of p53 mutated cells but not that of A375 or GL-Mel cells. Accordingly, in M10 but not in A375 cells a higher level of senescence was detected in PHA-848125-treated/PTTG1-silenced cells with respect to PHA-848125-treated controls. In A375 and GL-Mel cells, TP53 silencing attenuated PHA-848125-induced down-modulation of PTTG1 and decreased cell sensitivity to the drug. These findings indicate that PHA-848125-induced down-regulation of PTTG1 depends, at least in part, on p53 function and contributes to the antiproliferative activity of the drug. Our study provides further molecular insight into the antitumor mechanism of PHA-848125.