PML inhibits HIF-1alpha translation and neoangiogenesis through repression of mTOR.

Loss of the promyelocytic leukaemia (PML) tumour suppressor has been observed in several human cancers. The tumour-suppressive function of PML has been attributed to its ability to induce growth arrest, cellular senescence and apoptosis. Here we identify PML as a critical inhibitor of neoangiogenesis (the formation of new blood vessels) in vivo, in both ischaemic and neoplastic conditions, through the control of protein translation. We demonstrate that in hypoxic conditions PML acts as a negative regulator of the synthesis rate of hypoxia-inducible factor 1alpha (HIF-1alpha) by repressing mammalian target of rapamycin (mTOR). PML physically interacts with mTOR and negatively regulates its association with the small GTPase Rheb by favouring mTOR nuclear accumulation. Notably, Pml-/- cells and tumours display higher sensitivity both in vitro and in vivo to growth inhibition by rapamycin, and lack of PML inversely correlates with phosphorylation of ribosomal protein S6 and tumour angiogenesis in mouse and human tumours. Thus, our findings identify PML as a novel suppressor of mTOR and neoangiogenesis.

Role of the proto-oncogene Pokemon in cellular transformation and ARF repression.

Aberrant transcriptional repression through chromatin remodelling and histone deacetylation has been postulated to represent a driving force underlying tumorigenesis because histone deacetylase inhibitors have been found to be effective in cancer treatment. However, the molecular mechanisms by which transcriptional derepression would be linked to tumour suppression are poorly understood. Here we identify the transcriptional repressor Pokemon (encoded by the Zbtb7 gene) as a critical factor in oncogenesis. Mouse embryonic fibroblasts lacking Zbtb7 are completely refractory to oncogene-mediated cellular transformation. Conversely, Pokemon overexpression leads to overt oncogenic transformation both in vitro and in vivo in transgenic mice. Pokemon can specifically repress the transcription of the tumour suppressor gene ARF through direct binding. We find that Pokemon is aberrantly overexpressed in human cancers and that its expression levels predict biological behaviour and clinical outcome. Pokemon's critical role in cellular transformation makes it an attractive target for therapeutic intervention.

Tolerability, pharmacodynamics, and pharmacokinetics studies of depsipeptide (romidepsin) in patients with acute myelogenous leukemia or advanced myelodysplastic syndromes.

PURPOSE: Epigenetic modulation of gene expression plays an important role in cancer, including leukemia. Furthermore, histone deacetylase inhibitors may induce the reexpression or repression of genes critical for normal hematopoiesis. The purpose of this study was to evaluate the toxicity, pharmacokinetic profile, and selected pharmacodynamic properties of the histone deacetylase inhibitor depsipeptide in patients with myelodysplastic syndromes (MDS) or acute myelogenous leukemia (AML). EXPERIMENTAL DESIGN: Depsipeptide was administered to MDS or AML patients at a (solid tumor) phase I dose of 18 mg/m(2) i.v. on days 1 and 5 every 3 weeks. Toxicities and clinical activity were monitored and pharmacokinetic and pharmacodynamic studies were done. RESULTS: Twelve patients (nine with AML, three with MDS) received one to five cycles of depsipeptide. The most common grade 3/4 toxicities were febrile neutropenia/infection (five patients), neutropenia/thrombocytopenia (nine patients), nausea (nine patients), and asymptomatic hypophosphatemia (three patients). No clinically significant cardiac toxicity was observed. The best response of 11 assessed patients was one complete remission in a patient with AML, stable disease in six patients, and progression of disease in four patients. Exploratory laboratory studies showed modest but rapid increases in apoptosis and changes in myeloid maturation marker expression. Histone H3 and H4 acetylation levels were evaluated in five patients; no consistent changes were observed. CONCLUSION: Depsipeptide therapy can be administered with acceptable short-term toxicity. However, gastrointestinal symptoms and fatigue seem to be treatment-limiting after multiple cycles. Depsipeptide monotherapy has limited clinical activity in unselected AML/MDS patients.

Inhibition of fibroblast growth factor receptor 3-dependent lung adenocarcinoma with a human monoclonal antibody.

Activating mutations in fibroblast growth factor receptor 3 (FGFR3) have been identified in multiple types of human cancer and in congenital birth defects. In human lung cancer, fibroblast growth factor 9 (FGF9), a high-affinity ligand for FGFR3, is overexpressed in 10% of primary resected non-small cell lung cancer (NSCLC) specimens. Furthermore, in a mouse model where FGF9 can be induced in lung epithelial cells, epithelial proliferation and ensuing tumorigenesis is dependent on FGFR3. To develop new customized therapies for cancers that are dependent on FGFR3 activation, we have used this mouse model to evaluate a human monoclonal antibody (D11) with specificity for the extracellular ligand-binding domain of FGFR3, that recognizes both human and mouse forms of the receptor. Here, we show that D11 effectively inhibits signaling through FGFR3 in vitro, inhibits the growth of FGFR3-dependent FGF9-induced lung adenocarcinoma in mice, and reduces tumor-associated morbidity. Given the potency of FGF9 in this mouse model and the absolute requirement for signaling through FGFR3, this study validates the D11 antibody as a potentially useful and effective reagent for treating human cancers or other pathologies that are dependent on activation of FGFR3.