Disparities in outcomes and access to therapy options in hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) disproportionately impacts racial and ethnic minorities and patients with lower socioeconomic status. These social determinants of health (SDH) lead to disparities in access to care and outcomes. We aim to understand the relationship between SDH and survival and locoregional treatment options in HCC. METHODS: Using the National Cancer Database, we evaluated survival and access locoregional treatments including non-transplant surgery, liver transplant (LT), and liver-directed radiation therapy (LDRT) in patients with HCC diagnosed between 2004 and 2017. Variables including clinical stage, age, sex, race, income, rurality, year of diagnosis, facility type (FT), Charlson-Deyo score (CD), and insurance were evaluated. Cox proportional hazards multivariable regression and dominance analyses were used for analyses. RESULTS: In total, 140 340 patients were included. Worse survival was seen with advanced stage, older age, Black race, rurality, public insurance, treatment at a nonacademic center, and lower income. The top predictors for survival included stage, age, and income. Completion of non-transplant surgery was best predicted by stage, FT, and insurance type, whereas LT was predicted by age, year of diagnosis, and CD score. LDRT utilization was most associated with year of diagnosis, FT, and CD score. CONCLUSION: For patients with HCC, survival was predicted primarily by stage, age, and income. The primary sociodemographic factors associated with access to surgical treatments, in addition to FT, were insurance and income, highlighting the financial burdens of health care. Work is needed to address disparities in access to care, including improved insurance access, addressing financial inequities and financial toxicities of treatments, and equalizing care opportunities in community centers.

Treatment Patterns and Outcomes for Patients with Ampullary Carcinoma Who Do Not Undergo Surgery.

Surgical resection is the standard of care for ampullary adenocarcinoma (AC). Many patients are ineligible due to comorbidities/advanced disease. Evidence for the optimal non-operative management of localized AC is lacking. We hypothesize that patients treated with chemotherapy (CT) and definitive radiation (DRT) will have superior survival (OS) compared to those treated with CT alone. We performed a retrospective review of the National Cancer Database from 2004 to 2017 to identify patients with non-metastatic AC and no surgical intervention. Patients were categorized as having received no treatment, palliative radiotherapy (PRT) alone, CT alone, CT + PRT, DRT alone, or CT + DRT. We utilized Kaplan-Meier analysis to determine OS and the log-rank test to compare survival curves. Among 2176 patients, treatment groups were: No treatment (71.2%), PRT alone (1.9%), CT alone (13.1%), CT + PRT (1.6%), DRT alone (2.4%), and CT + DRT (9.7%). One-year OS varied by treatment group, ranging from 35.1% (PRT alone) to 59.4% (CT + DRT). The one-year OS in a matched cohort was not significantly different between CT alone and CT + DRT (HR 0.87, 95% CI 0.69-1.10, p = 0.87). Most patients with non-metastatic AC not treated with surgery do not receive any treatment. There is no difference in one-year OS between those undergoing CT alone and CT + DRT.

Solid tumor growth depends on an intricate equilibrium of malignant cell states.

Control of cell identity and number is central to tissue function, yet principles governing organization of malignant cells in tumor tissues remain poorly understood. Using mathematical modeling and candidate-based analysis, we discover primary and metastatic pancreatic ductal adenocarcinoma (PDAC) organize in a stereotypic pattern whereby PDAC cells responding to WNT signals (WNT-R) neighbor WNT-secreting cancer cells (WNT-S). Leveraging lineage-tracing, we reveal the WNT-R state is transient and gives rise to the WNT-S state that is highly stable and committed to organizing malignant tissue. We further show that a subset of WNT-S cells expressing the Notch ligand DLL1 form a functional niche for WNT-R cells. Genetic inactivation of WNT secretion or Notch pathway components, or cytoablation of the WNT-S state disrupts PDAC tissue organization, suppressing tumor growth and metastasis. This work indicates PDAC growth depends on an intricately controlled equilibrium of functionally distinct cancer cell states, uncovering a fundamental principle governing solid tumor growth and revealing new opportunities for therapeutic intervention.

Systematic Comparison of Pancreatic Ductal Adenocarcinoma Models Identifies a Conserved Highly Plastic Basal Cell State.

Intratumoral heterogeneity and cellular plasticity have emerged as hallmarks of cancer, including pancreatic ductal adenocarcinoma (PDAC). As PDAC portends a dire prognosis, a better understanding of the mechanisms underpinning cellular diversity in PDAC is crucial. Here, we investigated the cellular heterogeneity of PDAC cancer cells across a range of in vitro and in vivo growth conditions using single-cell genomics. Heterogeneity contracted significantly in two-dimensional and three-dimensional cell culture models but was restored upon orthotopic transplantation. Orthotopic transplants reproducibly acquired cell states identified in autochthonous PDAC tumors, including a basal state exhibiting coexpression and coaccessibility of epithelial and mesenchymal genes. Lineage tracing combined with single-cell transcriptomics revealed that basal cells display high plasticity in situ. This work defines the impact of cellular growth conditions on phenotypic diversity and uncovers a highly plastic cell state with the capacity to facilitate state transitions and promote intratumoral heterogeneity in PDAC. SIGNIFICANCE: This work provides important insights into how different model systems of pancreatic ductal adenocarcinoma mold the phenotypic space of cancer cells, highlighting the power of in vivo models.

TP53 mutations increase radioresistance in rhabdomyosarcoma and Ewing sarcoma.

BACKGROUND: p53 plays a key role in the DNA repair process and response to ionising radiation. We sought to determine the clinical phenotype of TP53 mutations and p53 pathway alterations in patients with rhabdomyosarcoma (RMS) and Ewing sarcoma (ES) treated with radiation. METHODS: Of patients with available genomic sequencing, we identified 109 patients with RMS and ES treated to a total of 286 radiation sites. We compared irradiated tumour control among tumours with TP53 mutations (n = 40) to those that were TP53 wild-type (n = 246). We additionally compared irradiated tumour control among tumours with any p53 pathway alteration (defined as tumours with TP53 mutations or TP53 wild-type tumours identified to have MDM2/4 amplification and/or CDKN2A/B deletion, n = 78) to those without such alterations (n = 208). RESULTS: The median follow-up was 26 months from radiation. TP53 mutations were associated with worse irradiated tumour control among the entire cohort (hazard ratio, HR = 2.8, P < 0.0001). Tumours with any p53 pathway alteration also had inferior irradiated tumour control (HR = 2.0, P = 0.003). On multivariable analysis, after controlling for tumour histology, intent of radiation, presence of gross disease, and biologically effective dose, TP53 mutations continued to be associated with a radioresistant phenotype (HR = 7.1, P < 0.0001). CONCLUSIONS: Our results show that TP53 mutations are associated with increased radioresistance in RMS and ES. Novel strategies to overcome this radioresistance are important for improved outcomes in p53 disruptive RMS and ES.

Pathogenic ATM Mutations in Cancer and a Genetic Basis for Radiotherapeutic Efficacy.

BACKGROUND: Radiation therapy is one of the most commonly used cancer therapeutics but genetic determinants of clinical benefit are poorly characterized. Pathogenic germline variants in ATM are known to cause ataxia-telangiectasia, a rare hereditary syndrome notable for marked radiosensitivity. In contrast, somatic inactivation of ATM is a common event in a wide variety of cancers, but its clinical actionability remains obscure. METHODS: We analyzed 20 107 consecutively treated advanced cancer patients who underwent targeted genomic sequencing as part of an institutional genomic profiling initiative and identified 1085 harboring a somatic or germline ATM mutation, including 357 who received radiotherapy (RT). Outcomes of irradiated tumors harboring ATM loss-of-function (LoF) mutations were compared with those harboring variants of unknown significance. All statistical tests were 2-sided. RESULTS: Among 357 pan-cancer patients who received 727 courses of RT, genetic inactivation of ATM was associated with improved radiotherapeutic efficacy. The 2-year cumulative incidence of irradiated tumor progression was 13.2% vs 27.5% for tumors harboring an ATM LoF vs variant of unknown significance allele, respectively (hazard ratio [HR] = 0.51, 95% confidence interval [CI] = 0.34 to 0.77, P = .001). The greatest clinical benefit was seen in tumors harboring biallelic ATM inactivation (HR = 0.19, 95% CI = 0.06 to 0.60, P = .005), with statistically significant benefit also observed in tumors with monoallelic ATM inactivation (HR = 0.57, 95% CI = 0.35 to 0.92, P = .02). Notably, ATM LoF was highly predictive of outcome in TP53 wild-type tumors but not among TP53-mutant tumors. CONCLUSIONS: We demonstrate that somatic ATM inactivation is associated with markedly improved tumor control following RT. The identification of a radio-sensitive tumor phenotype across multiple cancer types offers potential clinical opportunities for genomically guided RT.

Unbiased in vivo preclinical evaluation of anticancer drugs identifies effective therapy for the treatment of pancreatic adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is typically diagnosed at an advanced stage, which limits surgical options and portends a dismal prognosis. Current oncologic PDAC therapies confer marginal benefit and, thus, a significant unmet clinical need exists for new therapeutic strategies. To identify effective PDAC therapies, we leveraged a syngeneic orthotopic PDAC transplant mouse model to perform a large-scale, in vivo screen of 16 single-agent and 41 two-drug targeted therapy combinations in mice. Among 57 drug conditions screened, combined inhibition of heat shock protein (Hsp)-90 and MEK was found to produce robust suppression of tumor growth, leading to an 80% increase in the survival of PDAC-bearing mice with no significant toxicity. Mechanistically, we observed that single-agent MEK inhibition led to compensatory activation of resistance pathways, including components of the PI3K/AKT/mTOR signaling axis, which was overcome with the addition of HSP90 inhibition. The combination of HSP90(i) + MEK(i) was also active in vitro in established human PDAC cell lines and in vivo in patient-derived organoid PDAC transplant models. These findings encourage the clinical development of HSP90(i) + MEK(i) combination therapy and highlight the power of clinically relevant in vivo model systems for identifying cancer therapies.

Emergence of a High-Plasticity Cell State during Lung Cancer Evolution.

Tumor evolution from a single cell into a malignant, heterogeneous tissue remains poorly understood. Here, we profile single-cell transcriptomes of genetically engineered mouse lung tumors at seven stages, from pre-neoplastic hyperplasia to adenocarcinoma. The diversity of transcriptional states increases over time and is reproducible across tumors and mice. Cancer cells progressively adopt alternate lineage identities, computationally predicted to be mediated through a common transitional, high-plasticity cell state (HPCS). Accordingly, HPCS cells prospectively isolated from mouse tumors and human patient-derived xenografts display high capacity for differentiation and proliferation. The HPCS program is associated with poor survival across human cancers and demonstrates chemoresistance in mice. Our study reveals a central principle underpinning intra-tumoral heterogeneity and motivates therapeutic targeting of the HPCS.

Genomic Determinants of Clinical Outcomes in Rhabdomyosarcoma.

PURPOSE: Increased availability of next-generation sequencing has allowed for the genomic characterization of a variety of pediatric tumors, although genomic determinants of response to treatment remain largely unknown. We sought to evaluate the genomic landscape and genomic determinants of clinical outcomes in rhabdomyosarcoma (RMS). EXPERIMENTAL DESIGN: Of 29,067 patients who underwent genomic profiling at our institution using a 468-gene oncopanel with complete records, 87 had RMS, of whom 22 were fusion positive. The 10 most common genetic alterations were associated with locoregional control (LC), disease-free survival (DFS), and overall survival (OS). Tumor mutational burden (TMB), defined as the total number of somatic nonsynonymous mutations normalized to the number of sequenced megabases, was also associated with clinical outcomes. RESULTS: Median age at diagnosis was 16.4 years and median follow-up, 2.1 years. Patients with fusion-negative RMS had more genomic alterations and a higher TMB than those with fusion-positive RMS (mean number of genomic alterations, 6.0 vs. 2.9; P = 0.007 and mean TMB, 2.6 vs. 1.0; P = 0.01). Genetic alterations in TP53 were associated with worse OS (P = 0.03). High TMB (defined as the top quartile ≥ 2.8) was associated with worse LC (P = 0.05), DFS (P = 0.04), and OS (P = 0.01), with significance retained on multivariable analysis after controlling for risk group, fusion status, and receipt of chemotherapy as per pediatric protocols. CONCLUSIONS: High TMB was associated with worse clinical outcomes in patients with RMS. With further validation, TMB and other genomic classifiers may be combined with traditional clinicopathologic risk factors to guide risk stratification and ultimately treatment decisions.

High-dose radiation therapy is needed for intracranial control and long-term survival in patients with non-seminomatous germ cell tumor brain metastases.

PURPOSE: The presence of brain metastases (BM) in patients with non-seminomatous germ cell tumor (NSGCT) is associated with poor prognosis. While radiation therapy (RT) is an important treatment for patients with NSGCT BM, there is a paucity of data on the optimal regimen. We sought to investigate the impact of RT on clinical outcomes in patients with NSGCT BM. METHODS: Patients with NSGCT BM who received RT at our institution from 2002 to 2017 were included. Sixty-three consecutive patients were identified. Clinical factors associated with intracranial control (ICC) and overall survival (OS) were evaluated using cox regression analysis and Kaplan Meier method. RESULTS: Median age was 31 years and number of BM was three. Fifteen patients presented with BM at diagnosis, while 48 developed BM at a median time of 8.4 months from diagnosis. At a median follow-up of 3.6 years, ICC and OS were 39.7% and 30.1%. On multivariate analysis, ICC (hazard ratio [HR] = 0.93, p = 0.03) and OS (HR = 0.93, p = 0.005) were both significantly associated with biologically effective dose (BED) of RT. The 4-year OS of patients who received BED < 39Gy, 39 Gy, 40-50 Gy, and ≥ 50 Gy were 0%, 14.7%, 34.1%, and 70.0%, respectively. Patients who achieved ICC after RT were able to achieve long-term survival (4-year OS 68.1% vs. 0%, p < 0.0001). CONCLUSIONS: Our data supports that a higher BED is required for durable ICC, and that ICC is needed for patients with NSGCT to achieve long-term survival. Prospective studies evaluating radiation dose-escalation for the treatment of NSGCT BM should be considered.

Endoluminal high-dose-rate brachytherapy for locally recurrent or persistent esophageal cancer.

PURPOSE: Management of locally recurrent or persistent esophageal cancer (EC) after standard chemoradiation is challenging. This study updates our experience of treating medically inoperable EC patients with endoluminal high-dose-rate brachytherapy (EHDRBT) including the patients treated with a novel multiballoon channel centering esophageal applicator. METHODS AND MATERIALS: Thirty-three consecutive patients with early-stage primary (n = 7), posttreatment persistent (n = 7), and recurrent (n = 19) EC treated with EHDRBT at our institution were included. Median dose and treatment lengths were 14 Gy (range 10-17.5 Gy) and 6 cm (3.5-9.0 cm), respectively. Endoscopy and biopsy were performed 3 months after EHDRBT and then every 3-6 months thereafter. RESULTS: Median followup was 17.4 months (range 5.0-88.3). Grade 1 and 2 toxicities were observed in 13 (44.8%) and 11 (37.9%) patients, respectively. Grade 3 toxicity (tracheoesophageal fistula) was observed in 1 patient who had previously received two courses of external beam radiotherapy as well as a stent insertion. Median overall survival (OS) for entire cohort was 20.9 months, and 1-year OS was 78%. Complete response was achieved in 58.6% of patients with median time to failure and 1-year disease-free survival of 10.3 months (range 5.4-28.2) and 27%, respectively. CONCLUSIONS: For medically inoperable patients with early-stage primary or local posttreatment residual or recurrent EC, EHDRBT is a well-tolerated treatment option with minimal Grade ≥3 toxicity. Brachytherapy in our hands continues to be a safe treatment option. Although 58.6% of patients achieved a complete response and the OS of this cohort is relatively good, long-term local control and cure remains a challenge.

High Precision Imaging of Microscopic Spread of Glioblastoma with a Targeted Ultrasensitive SERRS Molecular Imaging Probe.

The dismal prognosis of patients with malignant brain tumors such as glioblastoma multiforme (GBM) is attributed mostly to their diffuse growth pattern and early microscopic tumor spread to distant regions of the brain. Because the microscopic tumor foci cannot be visualized with current imaging modalities, it remains impossible to direct treatments optimally. Here we explored the ability of integrin-targeted surface-enhanced resonance Raman spectroscopy (SERRS) nanoparticles to depict the true tumor extent in a GBM mouse model that closely mimics the pathology in humans. The recently developed SERRS-nanoparticles have a sensitivity of detection in the femtomolar range. An RGD-peptide-conjugated version for integrin-targeting (RGD-SERRS) was compared directly to its non-targeted RAD-SERRS control in the same mice via Raman multiplexing. Pre-blocking with RGD peptide before injection of RGD-SERRS nanoparticles was used to verify the specificity of integrin-targeting. In contrast to the current belief that the enhanced permeability and retention (EPR) effect results in a baseline uptake of nanoparticles regardless of their surface chemistry, integrin-targeting was shown to be highly specific, with markedly lower accumulation after pre-blocking. While the non-targeted SERRS particles enabled delineation of the main tumor, the RGD-SERRS nanoparticles afforded a major improvement in visualization of the true extent and the diffuse margins of the main tumor. This included the detection of unexpected tumor areas distant to the main tumor, tracks of migrating cells of 2-3 cells in diameter, and even isolated distant tumor cell clusters of less than 5 cells. This Raman spectroscopy-based nanoparticle-imaging technology holds promise to allow high precision visualization of the true extent of malignant brain tumors.

Corticosteroids compromise survival in glioblastoma.

Glioblastoma is the most common and most aggressive primary brain tumour. Standard of care consists of surgical resection followed by radiotherapy and concomitant and maintenance temozolomide (temozolomide/radiotherapy→temozolomide). Corticosteroids are commonly used perioperatively to control cerebral oedema and are frequently continued throughout subsequent treatment, notably radiotherapy, for amelioration of side effects. The effects of corticosteroids such as dexamethasone on cell growth in glioma models and on patient survival have remained controversial. We performed a retrospective analysis of glioblastoma patient cohorts to determine the prognostic role of steroid administration. A disease-relevant mouse model of glioblastoma was used to characterize the effects of dexamethasone on tumour cell proliferation and death, and to identify gene signatures associated with these effects. A murine anti-VEGFA antibody was used in parallel as an alternative for oedema control. We applied the dexamethasone-induced gene signature to The Cancer Genome Atlas glioblastoma dataset to explore the association of dexamethasone exposure with outcome. Mouse experiments were used to validate the effects of dexamethasone on survival in vivo Retrospective clinical analyses identified corticosteroid use during radiotherapy as an independent indicator of shorter survival in three independent patient cohorts. A dexamethasone-associated gene expression signature correlated with shorter survival in The Cancer Genome Atlas patient dataset. In glioma-bearing mice, dexamethasone pretreatment decreased tumour cell proliferation without affecting tumour cell viability, but reduced survival when combined with radiotherapy. Conversely, anti-VEGFA antibody decreased proliferation and increased tumour cell death, but did not affect survival when combined with radiotherapy. Clinical and mouse experimental data suggest that corticosteroids may decrease the effectiveness of treatment and shorten survival in glioblastoma. Dexamethasone-induced anti-proliferative effects may confer protection from radiotherapy- and chemotherapy-induced genotoxic stress. This study highlights the importance of identifying alternative agents such as vascular endothelial growth factor antagonists for managing oedema in glioblastoma patients. Beyond the established adverse effect profile of protracted corticosteroid use, this analysis substantiates the request for prudent and restricted use of corticosteroids in glioblastoma.

Glutamine-based PET imaging facilitates enhanced metabolic evaluation of gliomas in vivo.

Glucose and glutamine are the two principal nutrients that cancer cells use to proliferate and survive. Many cancers show altered glucose metabolism, which constitutes the basis for in vivo positron emission tomography (PET) imaging with (18)F-fluorodeoxyglucose ((18)F-FDG). However, (18)F-FDG is ineffective in evaluating gliomas because of high background uptake in the brain. Glutamine metabolism is also altered in many cancers, and we demonstrate that PET imaging in vivo with the glutamine analog 4-(18)F-(2S,4R)-fluoroglutamine ((18)F-FGln) shows high uptake in gliomas but low background brain uptake, facilitating clear tumor delineation. Chemo/radiation therapy reduced (18)F-FGln tumor avidity, corresponding with decreased tumor burden. (18)F-FGln uptake was not observed in animals with a permeable blood-brain barrier or neuroinflammation. We translated these findings to human subjects, where (18)F-FGln showed high tumor/background ratios with minimal uptake in the surrounding brain in human glioma patients with progressive disease. These data suggest that (18)F-FGln is avidly taken up by gliomas, can be used to assess metabolic nutrient uptake in gliomas in vivo, and may serve as a valuable tool in the clinical management of gliomas.

Surface-enhanced resonance Raman scattering nanostars for high-precision cancer imaging.

The inability to visualize the true extent of cancers represents a significant challenge in many areas of oncology. The margins of most cancer types are not well demarcated because the cancer diffusely infiltrates the surrounding tissues. Furthermore, cancers may be multifocal and characterized by the presence of microscopic satellite lesions. Such microscopic foci represent a major reason for persistence of cancer, local recurrences, and metastatic spread, and are usually impossible to visualize with currently available imaging technologies. An imaging method to reveal the true extent of tumors is desired clinically and surgically. We show the precise visualization of tumor margins, microscopic tumor invasion, and multifocal locoregional tumor spread using a new generation of surface-enhanced resonance Raman scattering (SERRS) nanoparticles, which are termed SERRS nanostars. The SERRS nanostars feature a star-shaped gold core, a Raman reporter resonant in the near-infrared spectrum, and a primer-free silication method. In genetically engineered mouse models of pancreatic cancer, breast cancer, prostate cancer, and sarcoma, and in one human sarcoma xenograft model, SERRS nanostars enabled accurate detection of macroscopic malignant lesions, as well as microscopic disease, without the need for a targeting moiety. Moreover, the sensitivity (1.5 fM limit of detection) of SERRS nanostars allowed imaging of premalignant lesions of pancreatic and prostatic neoplasias. High sensitivity and broad applicability, in conjunction with their inert gold-silica composition, render SERRS nanostars a promising imaging agent for more precise cancer imaging and resection.

The SHH/Gli pathway is reactivated in reactive glia and drives proliferation in response to neurodegeneration-induced lesions.

In response to neurodegeneration, the adult mammalian brain activates a cellular cascade that results in reactive astrogliosis and microgliosis. The mechanism through which astrocytes become reactive and the physiological consequences of their activation in response to neurodegeneration is complex. While the activation and proliferation of astrocytes has been shown to occur during massive neuronal cell death, the functional relationship between these two events has not been clearly elucidated. Here we show that in response to kainic acid- (KA) induced neurodegeneration, the mitogen sonic hedgehog (SHH) is upregulated in reactive astrocytes. SHH activity peaks at 7 days and is accompanied by increased Gli activity and elevated proliferation in several cell types. To determine the functional role of SHH-Gli signaling following KA lesions, we used a pharmacological approach to show that SHH secreted by astrocytes drives the activation and proliferation of astrocytes and microglia. The consequences of SHH-Gli signaling in KA-induced lesions appear to be independent of the severity of neurodegeneration.

Loss of the tyrosine phosphatase PTPRD leads to aberrant STAT3 activation and promotes gliomagenesis.

PTPRD, which encodes the protein tyrosine phosphatase receptor-δ, is one of the most frequently inactivated genes across human cancers, including glioblastoma multiforme (GBM). PTPRD undergoes both deletion and mutation in cancers, with copy number loss comprising the primary mode of inactivation in GBM. However, it is unknown whether loss of PTPRD promotes tumorigenesis in vivo, and the mechanistic basis of PTPRD function in tumors is unclear. Here, using genomic analysis and a glioma mouse model, we demonstrate that loss of Ptprd accelerates tumor formation and define the oncogenic context in which Ptprd loss acts. Specifically, we show that in human GBMs, heterozygous loss of PTPRD is the predominant type of lesion and that loss of PTPRD and the CDKN2A/p16(INK4A) tumor suppressor frequently co-occur. Accordingly, heterozygous loss of Ptprd cooperates with p16 deletion to drive gliomagenesis in mice. Moreover, loss of the Ptprd phosphatase resulted in phospho-Stat3 accumulation and constitutive activation of Stat3-driven genetic programs. Surprisingly, the consequences of Ptprd loss are maximal in the heterozygous state, demonstrating a tight dependence on gene dosage. Ptprd loss did not increase cell proliferation but rather altered pathways governing the macrophage response. In total, we reveal that PTPRD is a bona fide tumor suppressor, pinpoint PTPRD loss as a cause of aberrant STAT3 activation in gliomas, and establish PTPRD loss, in the setting of CDKN2A/p16(INK4A) deletion, as a driver of glioma progression.

In vivo radiation response of proneural glioma characterized by protective p53 transcriptional program and proneural-mesenchymal shift.

Glioblastoma is the most common adult primary brain tumor and has a dismal median survival. Radiation is a mainstay of treatment and significantly improves survival, yet recurrence is nearly inevitable. Better understanding the radiation response of glioblastoma will help improve strategies to treat this devastating disease. Here, we present a comprehensive study of the in vivo radiation response of glioma cells in a mouse model of proneural glioblastoma. These tumors are a heterogeneous mix of cell types with differing radiation sensitivities. To explicitly study the gene expression changes comprising the radiation response of the Olig2(+) tumor bulk cells, we used translating ribosome affinity purification (TRAP) from Olig2-TRAP transgenic mice. Comparing both ribosome-associated and total pools of mRNA isolated from Olig2(+) cells indicated that the in vivo gene expression response to radiation occurs primarily at the total transcript level. Genes related to apoptosis and cell growth were significantly altered. p53 and E2F were implicated as major regulators of the radiation response, with p53 activity needed for the largest gene expression changes after radiation. Additionally, radiation induced a marked shift away from a proneural expression pattern toward a mesenchymal one. This shift occurs in Olig2(+) cells within hours and in multiple genetic backgrounds. Targets for Stat3 and CEBPB, which have been suggested to be master regulators of a mesenchymal shift, were also up-regulated by radiation. These data provide a systematic description of the events following radiation and may be of use in identifying biological processes that promote glioma radioresistance.

Osteopontin-CD44 signaling in the glioma perivascular niche enhances cancer stem cell phenotypes and promotes aggressive tumor growth.

Stem-like glioma cells reside within a perivascular niche and display hallmark radiation resistance. An understanding of the mechanisms underlying these properties will be vital for the development of effective therapies. Here, we show that the stem cell marker CD44 promotes cancer stem cell phenotypes and radiation resistance. In a mouse model of glioma, Cd44(-/-) and Cd44(+/-) animals showed improved survival compared to controls. The CD44 ligand osteopontin shared a perivascular expression pattern with CD44 and promoted glioma stem cell-like phenotypes. These effects were mediated via the γ-secretase-regulated intracellular domain of CD44, which promoted aggressive glioma growth in vivo and stem cell-like phenotypes via CBP/p300-dependent enhancement of HIF-2α activity. In human glioblastoma multiforme, expression of CD44 correlated with hypoxia-induced gene signatures and poor survival. Altogether, these data suggest that in the glioma perivascular niche, osteopontin promotes stem cell-like properties and radiation resistance in adjacent tumor cells via activation of CD44 signaling.