Jennifer S. Yu

Inflammation and Hras signaling control epithelial–mesenchymal transition during skin tumor progression

Epithelial-mesenchymal transition (EMT) is thought to be an important, possibly essential, component of the process of tumor dissemination and metastasis. About 20%-30% of Hras mutant mouse skin carcinomas induced by chemical initiation/promotion protocols have undergone EMT. Reduced exposure to TPA-induced chronic inflammation causes a dramatic reduction in classical papillomas and squamous cell carcinomas (SCCs), but the mice still develop highly invasive carcinomas with EMT properties, reduced levels of Hras and Egfr signaling, and frequent Ink4/Arf deletions. Deletion of Hras from the mouse germline also leads to a strong reduction in squamous tumor development, but tumors now acquire activating Kras mutations and exhibit more aggressive metastatic properties. We propose that invasive carcinomas can arise by different genetic and biological routes dependent on exposure to chronic inflammation and possibly from different target cell populations within the skin. Our data have implications for the use of inhibitors of inflammation or of Ras/Egfr pathway signaling for prevention or treatment of invasive cancers.

Review of cranial radiotherapy-induced vasculopathy

Cranial radiation can impact the cerebral vasculature in many ways, with a wide range of clinical manifestations. The incidence of these late effects including cerebrovascular accidents (CVAs), lacunar lesions, vascular occlusive disease including moyamoya syndrome, vascular malformations, and hemorrhage is not well known. This article reviews the preclinical findings regarding the pathophysiology of late radiation-induced vascular damage, and discusses the clinical incidence and risk factors for each type of vasculopathy. The pathophysiology is complex and dependent on the targeted blood vessels, and upregulation of pro-inflammatory and hypoxia-related genes. The risk factors for adult CVAs are similar to those for patients not exposed to cranial radiotherapy. For children, risks for late vascular complications include young age at radiotherapy, radiotherapy dose, NF1, tumor location, chemotherapy, and endocrine abnormalities. The incidence of late vascular complications of radiotherapy may be impacted by improved technology, therapeutic interventions, and appropriate follow up.

The Zinc Finger Transcription Factor ZFX Is Required for Maintaining the Tumorigenic Potential of Glioblastoma Stem Cells

Glioblastomas are highly lethal brain tumors containing tumor‐propagating glioma stem cells (GSCs). The molecular mechanisms underlying the maintenance of the GSC phenotype are not fully defined. Here we demonstrate that the zinc finger and X‐linked transcription factor (ZFX) maintains GSC self‐renewal and tumorigenic potential by upregulating c‐Myc expression. ZFX is differentially expressed in GSCs relative to non‐stem glioma cells and neural progenitor cells. Disrupting ZFX by shRNA reduced c‐Myc expression and potently inhibited GSC self‐renewal and tumor growth. Ectopic expression of c‐Myc to its endogenous level rescued the effects caused by ZFX disruption, supporting that ZFX controls GSC properties through c‐Myc. Furthermore, ZFX binds to a specific sequence (GGGCCCCG) on the human c‐Myc promoter to upregulate c‐Myc expression. These data demonstrate that ZFX functions as a critical upstream regulator of c‐Myc and plays essential roles in the maintenance of the GSC phenotype. This study also supports that c‐Myc is a dominant driver linking self‐renewal to malignancy. Stem Cells 2014;32:2033–2047

Hyperthermia Sensitizes Glioma Stem-like Cells to Radiation by Inhibiting AKT Signaling

Glioma stem-like cells (GSC) are a subpopulation of cells in tumors that are believed to mediate self-renewal and relapse in glioblastoma (GBM), the most deadly form of primary brain cancer. In radiation oncology, hyperthermia is known to radiosensitize cells, and it is reemerging as a treatment option for patients with GBM. In this study, we investigated the mechanisms of hyperthermic radiosensitization in GSCs by a phospho-kinase array that revealed the survival kinase AKT as a critical sensitization determinant. GSCs treated with radiation alone exhibited increased AKT activation, but the addition of hyperthermia before radiotherapy reduced AKT activation and impaired GSC proliferation. Introduction of constitutively active AKT in GSCs compromised hyperthermic radiosensitization. Pharmacologic inhibition of PI3K further enhanced the radiosensitizing effects of hyperthermia. In a preclinical orthotopic transplant model of human GBM, thermoradiotherapy reduced pS6 levels, delayed tumor growth, and extended animal survival. Together, our results offer a preclinical proof-of-concept for further evaluation of combined hyperthermia and radiation for GBM treatment.

Ionizing radiation in glioblastoma initiating cells.

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults with a median survival of 12–15 months with treatment consisting of surgical resection followed by ionizing radiation (IR) and chemotherapy. Even aggressive treatment is often palliative due to near universal recurrence. Therapeutic resistance has been linked to a subpopulation of GBM cells with stem cell-like properties termed GBM initiating cells (GICs). Recent efforts have focused on elucidating resistance mechanisms activated in GICs in response to IR. Among these, GICs preferentially activate the DNA damage response (DDR) to result in a faster rate of double-strand break (DSB) repair induced by IR as compared to the bulk tumor cells. IR also activates NOTCH and the hepatic growth factor (HGF) receptor, c-MET, signaling cascades that play critical roles in promoting proliferation, invasion, and resistance to apoptosis. These pathways are preferentially activated in GICs and represent targets for pharmacologic intervention. While IR provides the benefit of improved survival, it paradoxically promotes selection of more malignant cellular phenotypes of GBM. As reviewed here, finding effective combinations of radiation and molecular inhibitors to target GICs and non-GICs is essential for the development of more effective therapies.

Impact of the radiosurgery prescription dose on the local control of small (2 cm or smaller) brain metastases

OBJECTIVE The impact of the stereotactic radiosurgery (SRS) prescription dose (PD) on local progression and radiation necrosis for small (≤ 2 cm) brain metastases was evaluated. METHODS An institutional review board-approved retrospective review was performed on 896 patients with brain metastases ≤ 2 cm (3034 tumors) who were treated with 1229 SRS procedures between 2000 and 2012. Local progression and/or radiation necrosis were the primary end points. Each tumor was followed from the date of radiosurgery until one of the end points was reached or the last MRI follow-up. Various criteria were used to differentiate tumor progression and radiation necrosis, including the evaluation of serial MRIs, cerebral blood volume on perfusion MR, FDG-PET scans, and, in some cases, surgical pathology. The median radiographic follow-up per lesion was 6.2 months. RESULTS The median patient age was 56 years, and 56% of the patients were female. The most common primary pathology was non-small cell lung cancer (44%), followed by breast cancer (19%), renal cell carcinoma (14%), melanoma (11%), and small cell lung cancer (5%). The median tumor volume and median largest diameter were 0.16 cm3 and 0.8 cm, respectively. In total, 1018 lesions (34%) were larger than 1 cm in maximum diameter. The PD for 2410 tumors (80%) was 24 Gy, for 408 tumors (13%) it was 19 to 23 Gy, and for 216 tumors (7%) it was 15 to 18 Gy. In total, 87 patients (10%) had local progression of 104 tumors (3%), and 148 patients (17%) had at least radiographic evidence of radiation necrosis involving 199 tumors (7%; 4% were symptomatic). Univariate and multivariate analyses were performed for local progression and radiation necrosis. For local progression, tumors less than 1 cm (subhazard ratio [SHR] 2.32; p < 0.001), PD of 24 Gy (SHR 1.84; p = 0.01), and additional whole-brain radiation therapy (SHR 2.53; p = 0.001) were independently associated with better outcome. For the development of radiographic radiation necrosis, independent prognostic factors included size greater than 1 cm (SHR 2.13; p < 0.001), location in the corpus callosum (SHR 5.72; p < 0.001), and uncommon pathologies (SHR 1.65; p = 0.05). Size (SHR 4.78; p < 0.001) and location (SHR 7.62; p < 0.001)-but not uncommon pathologies-were independent prognostic factors for the subgroup with symptomatic radiation necrosis. CONCLUSIONS A PD of 24 Gy results in significantly better local control of metastases measuring < 2 cm than lower doses. In addition, tumor size is an independent prognostic factor for both local progression and radiation necrosis. Some tumor pathologies and locations may also contribute to an increased risk of radiation necrosis.

Targeting Glioma Stem Cell-Derived Pericytes Disrupts the Blood-Tumor Barrier and Improves Chemotherapeutic Efficacy

The blood-tumor barrier (BTB) is a major obstacle for drug delivery to malignant brain tumors such as glioblastoma (GBM). Disrupting the BTB is therefore highly desirable but complicated by the need to maintain the normal blood-brain barrier (BBB). Here we show that targeting glioma stem cell (GSC)-derived pericytes specifically disrupts the BTB and enhances drug effusion into brain tumors. We found that pericyte coverage of tumor vasculature is inversely correlated with GBM patient survival after chemotherapy. Eliminating GSC-derived pericytes in xenograft models disrupted BTB tight junctions and increased vascular permeability. We identified BMX as an essential factor for maintaining GSC-derived pericytes. Inhibiting BMX with ibrutinib selectively targeted neoplastic pericytes and disrupted the BTB, but not the BBB, thereby increasing drug effusion into established tumors and enhancing the chemotherapeutic efficacy of drugs with poor BTB penetration. These findings highlight the clinical potential of targeting neoplastic pericytes to significantly improve treatment of brain tumors.

Melanoma brain metastasis: the impact of stereotactic radiosurgery, BRAF mutational status, and targeted and/or immune-based therapies on treatment outcome

OBJECTIVE The goal of this study was to investigate the impact of stereotactic radiosurgery (SRS), BRAF status, and targeted and immune-based therapies on the recurrence patterns and factors associated with overall survival (OS) among patients with melanoma brain metastasis (MBM). METHODS A total of 366 patients were treated for 1336 MBMs; a lesion-based analysis was performed on 793 SRS lesions. The BRAF status was available for 78 patients: 35 had BRAF mut and 43 had BRAF wild-type ( BRAF-WT) lesions. The Kaplan-Meier method evaluated unadjusted OS; cumulative incidence analysis determined the incidences of local failure (LF), distant failure, and radiation necrosis (RN), with death as a competing risk. RESULTS The 12-month OS was 24% (95% CI 20%-29%). On multivariate analysis, younger age, lack of extracranial metastases, better Karnofsky Performance Status score, and fewer MBMs, as well as treatment with BRAF inhibitors (BRAFi), anti-PD-1/CTLA-4 therapy, or cytokine therapy were significantly associated with OS. For patients who underwent SRS, the 12-month LF rate was lower among those with BRAF mut lesions (6%, 95% CI 2%-11%) compared with those with BRAF-WT lesions (22%, 95% CI 13%-32%; p < 0.01). The 12-month LF rates among lesions treated with BRAFi and PD-1/CTLA-4 agents were 1% (95% CI 1%-4%) and 7% (95% CI 1%-13%), respectively. On multivariate analysis, BRAF inhibition within 30 days of SRS was protective against LF (HR 0.08, 95% CI 0.01-0.55; p = 0.01). The 12-month rates of RN were low among lesions treated with BRAFi (0%, 95% CI 0%-0%), PD-1/CTLA-4 inhibitors (2%, 95% CI 1%-5%), and cytokine therapies (6%, 95% CI 1%-13%). CONCLUSIONS Prognostic schema should incorporate BRAFi or immunotherapy status and use of targeted therapies. Treatment with a BRAF inhibitor within 4 weeks of SRS improves local control without an increased risk of RN.

Hypoxic Induction of Vasorin Regulates Notch1 Turnover to Maintain Glioma Stem-like Cells

Tumor hypoxia is associated with poor patient survival and is a characteristic of glioblastoma. Notch signaling is implicated in maintaining glioma stem-like cells (GSCs) within the hypoxic niche, although the molecular mechanisms linking hypoxia to Notch activation have not been clearly delineated. Here we show that Vasorin is a critical link between hypoxia and Notch signaling in GSCs. Vasorin is preferentially induced in GSCs by a HIF1α/STAT3 co-activator complex and stabilizes Notch1 protein at the cell membrane. This interaction prevents Numb from binding Notch1, rescuing it from Numb-mediated lysosomal degradation. Thus, Vasorin acts as a switch to augment Notch signaling under hypoxic conditions. Vasorin promotes tumor growth and reduces survival in mouse models of glioblastoma, and its expression correlates with increased aggression of human gliomas. These findings provide mechanistic insights into how hypoxia promotes Notch signaling in glioma and identify Vasorin as a potential therapeutic target.

The incidence of second brain tumors related to cranial irradiation

Secondary brain tumor (SBT) is a devastating complication of cranial irradiation (CI). We reviewed the literature to determine the incidence of SBT as related to specific radiation therapy (RT) treatment modalities. The relative risk of radiation-associated SBT after conventional and conformal RT is well established and ranges from 5.65 to 10.9; latent time to develop second tumor ranges from 5.8 to 22.4 years, depending on radiation dose and primary disease. Theories and dosimetric models suggest that intensity-modulated radiation therapy may result in an increased risk of SBT, but clinical evidence is limited. The incidence of stereotactic radiosurgery-related SBT is low. Initial data suggest that no increased risk from proton therapy and dosimetric models predict a lower incidence of SBT compared with photons. In conclusion, the incidence of SBT related to CI is low. Longer follow-up is needed to clarify the impact of intensity-modulated radiation therapy, proton therapy and other developing technologies.