Lack of effect of SU1498, an inhibitor of vascular endothelial growth factor receptor-2, in a transgenic murine model of retinoblastoma

Organization of self-advantageous niche by neural stem/progenitor cells during development via autocrine VEGF-A under hypoxia

BACKGROUND

Tissue stem cells are confined within a special microenvironment called niche. Stem cells in such a niche are supplied with nutrients and contacted by other cells to maintain their characters and also to keep or expand their population size. Besides, oxygen concentration is a key factor for stem cell niche. Adult neural stem/progenitor cells (NSPCs) are known to reside in a hypoxic niche. Oxygen concentration levels are lower in fetal organs including brain than maternal organs. However, how fetal NSPCs adapt to the hypoxic environment during brain development, particularly before pial and periventricular vessels start to invade the telencephalon, has not fully been elucidated.

METHODS

NSPCs were prepared from cerebral cortices of embryonic day (E) 11.5 or E14.5 mouse embryos and were enriched by 4-day incubation with FGF2. To evaluate NSPC numbers, neurosphere formation assay was performed. Sparsely plated NSPCs were cultured to form neurospheres under the hypoxic (1% O₂) or normoxic condition. VEGF-A secreted from NSPCs in the culture medium was measured by ELISA. VEGF-A expression and Hif-1a in the developing brain was investigated by in situ hybridization and immunohistochemistry.

RESULTS

Here we show that neurosphere formation of embryonic NSPCs is dramatically increased under hypoxia compared to normoxia. Vegf-A gene expression and its protein secretion were both up-regulated in the NSPCs under hypoxia. Either recombinant VEGF-A or conditioned medium of the hypoxic NSPC culture enhanced the neurosphere forming ability of normoxic NSPCs, which was attenuated by a VEGF-A signaling inhibitor. Furthermore, in the developing brain, VEGF-A was strongly expressed in the VZ where NSPCs are confined.

CONCLUSIONS

We show that NSPCs secret VEGF-A in an autocrine fashion to efficiently maintain themselves under hypoxic developmental environment. Our results suggest that NSPCs have adaptive potential to respond to hypoxia to organize self-advantageous niche involving VEGF-A when the vascular system is immature.

Retinoblastoma, the visible CNS tumor: A review

The pediatric ocular cancer retinoblastoma is the only central nervous system (CNS) tumor readily observed without specialized equipment: it can be seen by, and in, the naked eye. This accessibility enables unique imaging modalities. Here, we review this cancer for a neuroscience audience, highlighting these clinical and research imaging options, including fundus imaging, optical coherence tomography, ultrasound, and magnetic resonance imaging. We also discuss the subtype of retinoblastoma driven by the MYCN oncogene more commonly associated with neuroblastoma, and consider trilateral retinoblastoma, in which an intracranial tumor arises along with ocular tumors in patients with germline RB1 gene mutations. Retinoblastoma research and clinical care can offer insights applicable to CNS malignancies, and also benefit from approaches developed elsewhere in the CNS.

Effect of VEGFR, PDGFR and PI3K/mTOR Targeting in Glioblastoma

Resistance to targeted therapy is a well known obstacle in cancer therapy. The cross-talk between several growth factor receptors generates redundancy in their intracellular pathways that usually mediates resistance to receptor targeted therapy. Simultaneous inactivation of two or more growth factor receptors has been suggested to prevent the cross-talk between their signaling pathways and to better eliminate malignant cells. Here we found that targeted therapy against these receptors induced moderate cell death in glioblastoma cells. More important, dual PDGFR and VEGFR inactivation induced more pronounceable cell death compared to inactivation of each receptor alone but failed to induce synergistic cell death in glioblastoma. PI3K/mTOR dual targeting has been identified as an efficient therapeutic approach in several malignant diseases, including glioblastoma. Therefore, we also investigated the PI3K/mTOR pathways inhibition effect in glioblastoma cells. Our results showed that inactivation of PI3K/mTOR pathways were more efficient than PDGFR or VEGFR single targeting or their dual inhibition.

Optical coherence tomography enables imaging of tumor initiation in the TAg-RB mouse model of retinoblastoma

PURPOSE

Retinoblastoma is the most common primary intraocular malignancy in children. Although significant advances in treatment have decreased mortality in recent years, morbidity continues to be associated with these therapies, and therefore, there is a pressing need for new therapeutic options. Transgenic mouse models are popular for testing new therapeutics as well as studying the pathophysiology of retinoblastoma. The T-antigen retinoblastoma (TAg-RB) model has close molecular and histological resemblance to human retinoblastoma tumors; these mice inactivate pRB by retinal-specific expression of the Simian Virus 40 T-antigens. Here, we evaluated whether optical coherence tomography (OCT) imaging could be used to document tumor growth in the TAg-RB model from the earliest stages of tumor development.

METHODS

The Micron III rodent imaging system was used to obtain fundus photographs and OCT images of both eyes of TAg-RB mice weekly from 2 to 12 weeks of age and at 16 and 20 weeks of age to document tumor development. Tumor morphology was confirmed with histological analysis.

RESULTS

Before being visible on funduscopy, hyperreflective masses arising in the inner nuclear layer were evident at 2 weeks of age with OCT imaging. After most of these hyperreflective cell clusters disappeared around 4 weeks of age, the first tumors became visible on OCT and funduscopy by 6 weeks. The masses grew into discrete, discoid tumors, preferentially in the periphery, that developed more irregular morphology over time, eventually merging and displacing the inner retinal layers into the vitreous.

CONCLUSIONS

OCT is a non-invasive imaging modality for tracking early TAg-RB tumor growth in vivo. Using OCT, we characterized TAg-positive cells as early as 2 weeks, corresponding to the earliest stages at which tumors are histologically evident, and well before they are evident with funduscopy. Tracking tumor growth from its earliest stages will allow better analysis of the efficacy of novel therapeutics and genetic factors tested in this powerful mouse model.

Spectral domain optical coherence tomography in a murine retinal detachment model

Spectral domain optical coherence tomography (SD-OCT) was used to image retinal detachments in vivo, in a murine model of retinal detachment (RD). Subretinal injections of hyaluronic acid (Healon) were delivered to the right eye of seventeen 10-20 week-old C57Bl6 mice. Evaluation of the fundus with an operating microscope and fundus photography were performed. In vivo, non-contact, ultra high resolution SD-OCT imaging was performed on day 0, day 1-2, day 5-6 and day 15-16. The retinal morphology at the edge and in the area of maximal RD was evaluated. Eyes were enucleated for histologic analysis. The retinal detachment was confirmed by microscopy in all mice. The extent of the retinal detachment was evaluated by measuring the height of the retinal detachment. The retinal layers, including the photoreceptor layer, were evaluated. Retinal layers appeared indistinct soon after RD (day 1, 5), particularly over areas of maximal detachment. By day 5 and 15 the external limiting membrane was no longer visible and there was increased reflectivity of the photoreceptor layer and undulation of the outer retina in areas of RD on both SD-OCT and histology. The thickness of the outer nuclear layer and photoreceptor outer segments decreased on day 5 and 15. SD-OCT is a promising technology to follow retinal detachment and outer retinal abnormalities in a murine model.

Cochlear pericyte responses to acoustic trauma and the involvement of hypoxia-inducible factor-1alpha and vascular endothelial growth factor

This study explored the effect of acoustic trauma on cochlear pericytes. Transmission electron microscopy revealed that pericytes on capillaries of the stria vascularis were closely associated with the endothelium in both control guinea pigs and mice. Pericyte foot processes were tightly positioned adjacent to endothelial cells. Exposure to wide-band noise at a level of 120 dB for 3 hours per day for 2 consecutive days produced a significant hearing threshold shift and structurally damaged blood vessels in the stria vascularis. Additionally, the serum protein, IgG, was observed to leak from capillaries of the stria vascularis, and pericytes lost their tight association with endothelial cells. Levels of the pericyte structural protein, desmin, substantially increased after noise exposure in both guinea pigs and mice with a corresponding increase in pericyte coverage of vessels. Increased expression levels of desmin were associated with the induction of hypoxia inducible factor (HIF)-1alpha and the up-regulation of vascular endothelial growth factor (VEGF). Inhibition of HIF-1alpha activity caused a decrease in VEGF expression levels in stria vascularis vessels. Blockade of VEGF activity with SU1498, a VEGF receptor inhibitor, significantly attenuated the expression of desmin in pericytes. These data demonstrate that cochlear pericytes are markedly affected by acoustic trauma and display an abnormal morphology. HIF-1alpha activation and VEGF up-regulation are important factors for the alteration of the pericyte structural protein desmin.

Retinal tumor imaging and volume quantification in mouse model using spectral-domain optical coherence tomography

We have successfully imaged the retinal tumor in a mouse model using an ultra-high resolution spectral-domain optical coherence tomography (SD-OCT) designed for small animal retinal imaging. For segmentation of the tumor boundaries and calculation of the tumor volume, we developed a novel segmentation algorithm. The algorithm is based on parametric deformable models (active contours) and is driven by machine learning-based region classification, namely a Conditional Random Field. With this algorithm we are able to obtain the tumor boundaries automatically, while the user can specify additional constraints (points on the boundary) to correct the segmentation result, if needed. The system and algorithm were successfully applied to studies on retinal tumor progression and monitoring treatment effects quantitatively in a mouse model of retinoblastoma.

Basic fibroblast growth factor impact on retinoblastoma progression and survival

PURPOSE

Chemotherapy resistance is a problem in the treatment of advanced retinoblastoma (RB). Since basic fibroblast growth factor (bFGF) is a survival factor for neural precursor cells, bFGF was evaluated as a growth and chemoresistance factor in RB.

METHODS

bFGF expression was analyzed in the LH-betaTag transgenic mouse model of RB and human RB cell lines by immunofluorescence, RT-PCR, and Western blot. Proliferation and apoptosis (TUNEL) assays were performed.

RESULTS

bFGF levels significantly increased during tumorigenesis in transgenic RB, as a function of tumor status (P = 0.005). PCR and confocal microscopy confirmed that the human cell lines and primary tumors expressed bFGF. bFGF was localized to vascular and tumor cells and rarely to glial cells. Exogenous 18-kDa bFGF induced proliferation in two RB cell lines (WERI and Y79). Western blot analysis demonstrated 34-, 22-, and 18-kDa isoforms in transgenic RB and both cell lines. In TUNEL assays, chemoresistance to carboplatin-induced apoptosis was observed in the Y79 line, which expressed a higher ratio of high (34 kDa)- to low-molecular-weight bFGF isoforms, compared with the WERI line. Similar to other bFGF tumor studies, exogenous low-molecular-weight (18 kDa) bFGF (1 ng) significantly enhanced carboplatin-induced apoptosis in the more chemosensitive WERI, but not the chemoresistant Y79 line.

CONCLUSIONS

RB tumors produce significant amounts of bFGF, and the differential production and response to isoforms of bFGF may have implications for invasive tumor growth and chemoresistance.