Multifocal hyperplasia of interstitial cells of Cajal (ICC hyperplasia) is a precursor of hereditary gastrointestinal stromal tumors (GISTs) in patients with germline mutations of c-KIT or PDGFRA, but precursor lesions of sporadic GISTs have not been defined yet. Small hyalinizing stromal tumors of the proximal stomach (referred to in this study as GIST tumorlets) were collected prospectively from 98 consecutive autopsies and additional cases were retrieved from surgical pathology files (total n=57). GIST tumorlets were grossly detectable in 22.5% consecutive autopsies performed in individuals older than 50 years. All lesions were located in the cardia, fundus, or proximal body, and ranged in size from 1 to 10 mm (4 mm). Similar lesions were not detected in the antrum, duodenum, and the remainder of the bowel. Histologically, the spindle cell subtype comprised all cases, with hyalinization and calcification in 57% of cases. The spindle cells were immunohistochemically positive for vimentin, CD117, and CD34. Twenty-four cases yielded sufficient DNA for subsequent molecular analysis, which showed c-KIT mutations in 11 cases (46%) and PDGFRA mutations in 1 case (4%). Sporadic GIST tumorlets of the proximal stomach are common in the general population over the age of 50 years and frequently show somatic c-KIT mutations. GIST tumorlets probably represent the grossly recognizable counterpart of sporadic ICC hyperplasia caused by somatic c-KIT or PDGFRA mutations. Early hyalinization and calcification seems to confer limited growth potential, and complete regression of such lesions is common. GIST tumorlets likely represent preclinical (preneoplastic) lesions that need additional stimuli to evolve into clinical GISTs, raising the possibility of a hyperplasia-neoplasia sequence in the development of sporadic GISTs.

Summary Despite the significance of tumour neoangiogenesis and the extensive knowledge on the molecular basis of blood vessel formation currently no quantitative data exist on the 3D microvascular architecture in human primary tumours and their precursor lesions. This prompted us to examine the 3D vascular network of normal colon mucosa, adenomas and invasive carcinomas by means of quantitative microvascular corrosion casting. Fresh hemicolectomy specimens from 20 patients undergoing cancer or polyposis coli surgery were used for corrosion casting, factor VIII and VEGF immunostaining. In addition, immunostaining was done on colorectal tissue from 33 patients with metastatic and non-metastatic carcinomas, polyposis coli and adenomas. This first quantitative analysis of intervessel and interbranching distances, branching angles and vessel diameters in human cancer specimens revealed distinct patterns of the microvascular unit in the tumour centre and periphery. Irrespective of the tumour localization and grading all individual tumours displayed qualitatively and quantitatively the same vascular architecture. This gives further evidence for the existence of a tumour type-specific vascular architecture as recently demonstrated for experimental tumours. Metastatic tumours displayed different vascular architectures only within hot spots, in terms of smaller intervascular distances than in non-metastatic tumours. Pre-cancerous lesions have in part virtually the same vascular architecture like invasive carcinomas. Comparison of VEGF immunostaining also suggests that angiogenesis sets in long before the progress towards invasive phenotypes and that the so-called angiogenic switch is more likely a sequence of events.

Vascular endothelial growth factor (VEGF) is not only essential for vasculogenesis and angiogenesis but also is a potent inducer of vascular permeability. Although a dissection of the molecular pathways between angiogenesis- and vascular permeability-inducing properties would be desirable for the development of angiogenic and anti-angiogenic therapies, such mechanisms have not been identified yet. Here we provide evidence for a role of the p38 MAPK as the signaling molecule that separates these two processes. Inhibition of p38 MAPK activity enhances VEGF-induced angiogenesis in vitro and in vivo, a finding that was accompanied by prolonged Erk1/2 MAPK activation, increased endothelial survival, and plasminogen activation. Conversely, the same inhibitors abrogate VEGF-induced vascular permeability in vitro and in vivo. These dualistic properties of p38 MAPK are relevant not only for therapeutic angiogenesis but also for reducing edema formation and enhancing tissue repair in ischemic diseases.

Vascular endothelial growth factor (VEGF) is essential for the differentiation of the primitive embryonic vascular system and has been implicated in the vascularization of organs. Recently, VEGF has also been proposed to play a role in neural development, neuroprotection, and adult neurogenesis. Here we have investigated the function of VEGF in the developing brain by cre-lox technology. We show that VEGF produced by the embryonic neuroectoderm is required for the vascularization and the development of the brain. Both the invasion and the directed growth of capillaries were severely impaired in the fore-, mid- and hindbrain of VEGF(lox/lox)/nestin-cre mouse embryos homozygous for a VEGF mutation in the neural tube. These observations demonstrate that VEGF, via local secretion by neural progenitors, induces brain angiogenesis and guides the growth of capillaries toward the ventricular zone. VEGF deficiency led to developmental retardation and progressive destruction of neural tissue in all brain regions. The defect was most pronounced in telencephalic structures, such as the hippocampus, and caused microcephaly. Taken together, the findings establish the critical importance of neuroectoderm-derived VEGF in the morphogenesis of the brain. VEGF acts as a key regulator of brain angiogenesis and provides instructive cues for the correct spatial organization of the vasculature.

Purpose: Inhibitors of heat-shock protein 90 (Hsp90) may interfere with oncogenic signaling pathways, including Erk, Akt, and hypoxia-inducible factor-1a (HIF-1a). Because insulin-like growth factor-I receptor (IGF-IR) and signal transducer and activator of transcription 3 (STAT3) signaling pathways are implicated in the progression of pancreatic cancer, we hypothesized that blocking Hsp90 with geldanamycin derivates [17-allylamino-geldanamycin (17-AAG), 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG)] would impair IGF-I^and interleukin-6^mediated signaling and thus reduce pancreatic tumor growth and angiogenesis in vivo. Experimental Design: Human pancreatic cancer cells (HPAF-II, L3.6pl) were used for experiments. Changes in signaling pathway activation upon Hsp90 blockade were investigated by Western blotting. Effects of Hsp90 inhibition (17-AAG) on vascular endothelial growth factor were determined by ELISA and real-time PCR. Effects of 17-DMAG (25 mg/kg; thrice a week; i.p.) on tumor growth and vascularization were investigated in a s.c. xenograft model and in an orthotopic model of pancreatic cancer. Results: 17-AAG inhibited IGF-IR signaling by down-regulating IGF-IRh and directly impairing IGF-IR phosphorylation. Hypoxia-and IL-6^mediated activation of HIF-1a or STAT3/STAT5 were substantially inhibited by 17-AAG. Moreover, a novel IL-6/STAT3/HIF-1a autocrine loop was effectively disrupted by Hsp90 blockade. In vivo, 17-DMAG significantly reduced s.c. tumor growth and diminished STAT3 phosphorylation and IGF-IRh expression in tumor tissues. In an orthotopic model, pancreatic tumor growth and vascularization were both significantly reduced upon Hsp90 inhibition, as reflected by final tumor weights and CD31 staining, respectively. Conclusions: Blocking Hsp90 disrupts IGF-I and IL-6^induced proangiogenic signaling cascades by targeting IGF-IR and STAT3 in pancreatic cancer, leading to significant growth-inhibitory effects.Therefore, we suggest that Hsp90 inhibitors could prove to be valuable in the treatment of pancreatic cancer.