Faculty Bibliography

Medulloblastoma is the most common pediatric malignant brain tumor. Although current therapies improve survival, these regimens are highly toxic and are associated with significant morbidity. Here, we report that placental growth factor (PlGF) is expressed in the majority of medulloblastomas, independent of their subtype. Moreover, high expression of PlGF receptor neuropilin 1 (Nrp1) correlates with poor overall survival in patients. We demonstrate that PlGF and Nrp1 are required for the growth and spread of medulloblastoma: PlGF/Nrp1 blockade results in direct antitumor effects in vivo, resulting in medulloblastoma regression, decreased metastasis, and increased mouse survival. We reveal that PlGF is produced in the cerebellar stroma via tumor-derived Sonic hedgehog (Shh) and show that PlGF acts through Nrp1-and not vascular endothelial growth factor receptor 1-to promote tumor cell survival. This critical tumor-stroma interaction-mediated by Shh, PlGF, and Nrp1 across medulloblastoma subtypes-supports the development of therapies targeting PlGF/Nrp1 pathway.

Intraoperative diagnosis plays an important role in accurate sampling of brain tumors, limiting the number of biopsies required and improving the distinction between brain and tumor. The goal of this study was to evaluate dye-enhanced multimodal confocal imaging for discriminating gliomas from nonglial brain tumors and from normal brain tissue for diagnostic use. We investigated a total of 37 samples including glioma (13), meningioma (7), metastatic tumors (9) and normal brain removed for nontumoral indications (8). Tissue was stained in 0.05 mg/mL aqueous solution of methylene blue (MB) for 2-5 minutes and multimodal confocal images were acquired using a custom-built microscope. After imaging, tissue was formalin fixed and paraffin embedded for standard neuropathologic evaluation. Thirteen pathologists provided diagnoses based on the multimodal confocal images. The investigated tumor types exhibited distinctive and complimentary characteristics in both the reflectance and fluorescence responses. Images showed distinct morphological features similar to standard histology. Pathologists were able to distinguish gliomas from normal brain tissue and nonglial brain tumors, and to render diagnoses from the images in a manner comparable to haematoxylin and eosin (H&E) slides. These results confirm the feasibility of multimodal confocal imaging for intravital intraoperative diagnosis.

Brain metastases are a serious obstacle in the treatment of patients with human epidermal growth factor receptor-2 (HER2)-amplified breast cancer. Although extracranial disease is controlled with HER2 inhibitors in the majority of patients, brain metastases often develop. Because these brain metastases do not respond to therapy, they are frequently the reason for treatment failure. We developed a mouse model of HER2-amplified breast cancer brain metastasis using an orthotopic xenograft of BT474 cells. As seen in patients, the HER2 inhibitors trastuzumab and lapatinib controlled tumor progression in the breast but failed to contain tumor growth in the brain. We observed that the combination of a HER2 inhibitor with an anti-VEGF receptor-2 (VEGFR2) antibody significantly slows tumor growth in the brain, resulting in a striking survival benefit. This benefit appears largely due to an enhanced antiangiogenic effect: Combination therapy reduced both the total and functional microvascular density in the brain xenografts. In addition, the combination therapy led to a marked increase in necrosis of the brain lesions. Moreover, we observed even better antitumor activity after combining both trastuzumab and lapatinib with the anti-VEGFR2 antibody. This triple-drug combination prolonged the median overall survival fivefold compared with the control-treated group and twofold compared with either two-drug regimen. These findings support the clinical development of this three-drug regimen for the treatment of HER2-amplified breast cancer brain metastases.

Brain tumors cause significant morbidity and mortality even when benign. Completeness of resection of brain tumors improves quality of life and survival; however, that is often difficult to accomplish. The goal of this study was to evaluate the feasibility of using multimodal confocal imaging for intraoperative detection of brain neoplasms. We have imaged different types of benign and malignant, primary and metastatic brain tumors. We correlated optical images with histopathology and evaluated the possibility of interpreting confocal images in a manner similar to pathology. Surgical specimens were briefly stained in 0.05 mg/ml aqueous solution of methylene blue (MB) and imaged using a multimodal confocal microscope. Reflectance and fluorescence signals of MB were excited at 642 nm. Fluorescence emission of MB was registered between 670 and 710 nm. After imaging, tissues were processed for hematoxylin and eosin (H&E) histopathology. The results of comparison demonstrate good correlation between fluorescence images and histopathology. Reflectance images provide information about morphology and vascularity of the specimens, complementary to that provided by fluorescence images. Multimodal confocal imaging has the potential to aid in the intraoperative detection of microscopic deposits of brain neoplasms. The application of this technique may improve completeness of resection and increase patient survival.

Tumor heterogeneity has been implicated in tumor growth and progression as well as resistance to therapy. We present an example of genetic heterogeneity in human malignant brain tumors in which multiple closely related driver genes are amplified and activated simultaneously in adjacent intermingled cells. We have observed up to three different receptor tyrosine kinases (EGFR, MET, PDGFRA) amplified in single tumors in different cells in a mutually exclusive fashion. Each subpopulation was actively dividing, and the genetic changes resulted in protein production, and coexisting subpopulations shared common early genetic mutations indicating their derivation from a single precursor cell. The stable coexistence of different clones within the same tumor will have important clinical implications for tumor resistance to targeted therapies.

Vascular normalization is an emerging concept in cancer treatment. In this issue of Cancer Cell, Rolny et al. show that histidine-rich glycoprotein normalizes tumor vessels and promotes antitumor immunity by polarizing tumor-associated macrophages, leading to decreased tumor growth and metastasis. Placental Growth Factor deletion in macrophages phenocopies many of these effects.