Identification, validation and biological characterisation of novel glioblastoma tumour microenvironment subtypes: implications for precision immunotherapy.

BACKGROUND: New precision medicine therapies are urgently required for glioblastoma (GBM). However, to date, efforts to subtype patients based on molecular profiles have failed to direct treatment strategies. We hypothesised that interrogation of the GBM tumour microenvironment (TME) and identification of novel TME-specific subtypes could inform new precision immunotherapy treatment strategies. MATERIALS AND METHODS: A refined and validated microenvironment cell population (MCP) counter method was applied to >800 GBM patient tumours (GBM-MCP-counter). Specifically, partition around medoids (PAM) clustering of GBM-MCP-counter scores in the GLIOTRAIN discovery cohort identified three novel patient clusters, uniquely characterised by TME composition, functional orientation markers and immune checkpoint proteins. Validation was carried out in three independent GBM-RNA-seq datasets. Neoantigen, mutational and gene ontology analysis identified mutations and uniquely altered pathways across subtypes. The longitudinal Glioma Longitudinal AnalySiS (GLASS) cohort and three immunotherapy clinical trial cohorts [treatment with neoadjuvant/adjuvant anti-programmed cell death protein 1 (PD-1) or PSVRIPO] were further interrogated to assess subtype alterations between primary and recurrent tumours and to assess the utility of TME classifiers as immunotherapy biomarkers. RESULTS: TMEHigh tumours (30%) displayed elevated lymphocyte, myeloid cell immune checkpoint, programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 transcripts. TMEHigh/mesenchymal+ patients featured tertiary lymphoid structures. TMEMed (46%) tumours were enriched for endothelial cell gene expression profiles and displayed heterogeneous immune populations. TMELow (24%) tumours were manifest as an 'immune-desert' group. TME subtype transitions upon recurrence were identified in the longitudinal GLASS cohort. Assessment of GBM immunotherapy trial datasets revealed that TMEHigh patients receiving neoadjuvant anti-PD-1 had significantly increased overall survival (P = 0.04). Moreover, TMEHigh patients treated with adjuvant anti-PD-1 or oncolytic virus (PVSRIPO) showed a trend towards improved survival. CONCLUSIONS: We have established a novel TME-based classification system for application in intracranial malignancies. TME subtypes represent canonical 'termini a quo' (starting points) to support an improved precision immunotherapy treatment approach.

Matrix metalloproteinase-9 triggers the angiogenic switch during carcinogenesis.

During carcinogenesis of pancreatic islets in transgenic mice, an angiogenic switch activates the quiescent vasculature. Paradoxically, vascular endothelial growth factor (VEGF) and its receptors are expressed constitutively. Nevertheless, a synthetic inhibitor (SU5416) of VEGF signalling impairs angiogenic switching and tumour growth. Two metalloproteinases, MMP-2/gelatinase-A and MMP-9/gelatinase-B, are upregulated in angiogenic lesions. MMP-9 can render normal islets angiogenic, releasing VEGF. MMP inhibitors reduce angiogenic switching, and tumour number and growth, as does genetic ablation of MMP-9. Absence of MMP-2 does not impair induction of angiogenesis, but retards tumour growth, whereas lack of urokinase has no effect. Our results show that MMP-9 is a component of the angiogenic switch.

Effects of angiogenesis inhibitors on multistage carcinogenesis in mice.

Solid tumors depend on angiogenesis for their growth. In a transgenic mouse model of pancreatic islet cell carcinogenesis (RIP1-Tag2), an angiogenic switch occurs in premalignant lesions, and angiogenesis persists during progression to expansive solid tumors and invasive carcinomas. RIP1-Tag2 mice were treated so as to compare the effects of four angiogenesis inhibitors at three distinct stages of disease progression. AGM-1470, angiostatin, BB-94, and endostatin each produced distinct efficacy profiles in trials aimed at preventing the angiogenic switch in premalignant lesions, intervening in the rapid expansion of small tumors, or inducing the regression of large end-stage cancers. Thus, anti-angiogenic drugs may prove most efficacious when they are targeted to specific stages of cancer.

Loss of vascular endothelial growth factor expression reduces vascularization, but not growth, of tumors lacking the Von Hippel-Lindau tumor suppressor gene.

Individuals bearing germ line mutations in the Von Hippel-Lindau (VHL) tumor suppressor gene are predisposed to the development of highly angiogenic tumors. This is correlated with an increased expression of the angiogenic factor vascular endothelial growth factor (VEGF) in these tumors, which is in part caused by elevated expression of the HIF-1 hypoxia inducible transcription factors. We created malignant astrocytes with genetic deletions of the VHL gene and implanted them in subcutaneous and intracranial sites; these sites are respectively vessel poor and vessel-rich tissues. When grown in a vessel poor site, VEGF expression in VHL null cells was important for both vascularization and tumor growth. However, when the same cells are grown in the vessel-rich intracranial environment, loss of VEGF expression reduces vascularization, but does not affect tumor growth. This indicates that antiangiogenic therapies for tumors that express high levels of angiogenic factors such as VEGF may vary in their efficacy, with potentially lowered effectiveness in sites, such as the brain, that are inherently vessel rich.

Extrinsic regulators of epithelial tumor progression: metalloproteinases.

Extracellular metal-dependent proteinases regulate cell behavior by remodeling stromal and cell surface proteins, thereby influencing cell recruitment, cell shape, motility, proliferation, survival, genomic (in)stability, and differentiation. In recent years, the importance of proteinase-induced signaling has been underscored by evidence that altered regulation of cell-extracellular matrix and cell-cell interactions by proteinases can contribute, in a causal manner, to neoplastic progression.

Transcriptional activation of the fra-1 gene by AP-1 is mediated by regulatory sequences in the first intron.

Constitutive expression of c-Fos, FosB, Fra-1, or c-Jun in rat fibroblasts leads to up-regulation of the immediate-early gene fra-1. Using the posttranslational FosER induction system, we demonstrate that this AP-1-dependent stimulation of fra-1 expression is rapid, depends on a functional DNA-binding domain of FosER, and is a general phenomenon observed in different cell types. In vitro mutagenesis and functional analysis of the rat fra-1 gene in stably transfected Rat-1A-FosER fibroblasts indicated that basal and AP-1-regulated expression of the fra-1 gene depends on regulatory sequences in the first intron which comprise a consensus AP-1 site and two AP-1-like elements. We have also investigated the transactivating and transforming properties of the Fra-1 protein to address the significance of fra-1 up-regulation. The entire Fra-1 protein fused to the DNA-binding domain of Ga14 is shown to lack any transactivation function, and yet it possesses oncogenic potential, as overexpression of Fra-1 in established rat fibroblasts results in anchorage-independent growth in vitro and tumor development in athymic mice, fra-1 is therefore not only induced by members of the Fos family, but its gene product may also contribute to cellular transformation by these proteins. Together, these data identify fra-1 as a unique member of the fos gene family which is under positive control by AP-1 activity.

Angiogenesis and apoptosis are cellular parameters of neoplastic progression in transgenic mouse models of tumorigenesis.

The epidemiology and histopathology of human cancers and studies of animal models of tumorigenesis have led to a widely-accepted notion that multiple genetic and epigenetic changes have to accrue for the successful development of a malignant phenotype. Tumor growth and expansion requires an ability not only to proliferate, but also to down-modulate cell death (apoptosis) and activate angiogenesis to produce a tumor neovasculature. This review will describe the interplay between apoptosis and proliferation, as well as the characteristics of the angiogenic phenotype in two transgenic mouse models of multi-step tumorigenesis, namely, pancreatic islet cell carcinomas and squamous cell carcinomas of the skin.

Hormone-dependent transcriptional regulation and cellular transformation by Fos-steroid receptor fusion proteins.

The protooncogene c-fos has been implicated in the control of proliferation and transformation of fibroblasts, and its protein product is an essential component of transcription factor AP1. The important target genes and, hence, the molecular mechanism of Fos function are, however, still unknown, partly due to the lack of a tightly regulated Fos-induction system. Here we show that different activities of the Fos protein can be controlled hormonally by fusing the mouse c-Fos protein to the ligand-binding domain of either the rat glucocorticoid or the human estrogen receptor. These fusion proteins stimulate AP1-dependent transcription and repress endogenous fos mRNA synthesis in a strictly hormone-dependent manner. Expression of these chimeric proteins in rat fibroblasts results in fast, reversible, and tightly controlled transformation in response to hormone. A Fos-estrogen receptor expressing cell line was used to isolate Fos-responsive genes by subtractive cDNA cloning. Run-on analysis of one of these genes showed that its transcription is rapidly and directly regulated by the hormone-activated Fos-estrogen receptor protein, demonstrating the potential of this induction system for identifying Fos target genes.

Identification of Fos target genes by the use of selective induction systems.

c-Fos is a major component of the transcription factor AP-1 which has been implicated in the control of cell proliferation and differentiation as well as in transformation. In order to identify Fos target genes involved in these processes, we have taken advantage of the regulatory properties of the hormone-binding domain of the human estrogen receptor to develop transcriptional and post-translational induction systems, both of which allow selective elevation of Fos activity within a cell. Using this approach we have searched for Fos-responsive genes in rat fibroblasts and PC12 cells. Here we describe the identification and regulation of five Fos-responsive genes encoding a transcription factor (Fra-1), a secreted protein (Fit-1), a biosynthetic enzyme (ODC) and two membrane-associated proteins (annexin II and V), respectively. The post-translational induction system was also used to study the Fos-mediated block of neuronal differentiation of PC12 cells. These experiments demonstrate that Fos activity is dominant over NGF function and interferes with the expression of late NGF-inducible genes.

Reactivation of proliferin gene expression is associated with increased angiogenesis in a cell culture model of fibrosarcoma tumor progression.

Proliferin (PLF) is an angiogenic placental hormone. We now report that PLF gene expression can also occur in a progressive fibrosarcoma mouse tumor cell model. PLF mRNA and protein are detectable at very low levels in cell lines derived from the mild noninvasive stage of tumor development. Expression is greatly augmented in cell lines from the aggressively invasive stage of development, a stage at which the tumor becomes highly angiogenic, and PLF expression remains high in cell lines from the end stage of fibrosarcoma. Activator protein 1 factors present at high levels in the more invasive stages of the tumor may in part allow for increased PLF expression, as cells from the mild stage in which c-jun and junB are stably expressed secrete levels of PLF comparable to that of the advanced stages. Secreted PLF protein is functionally important in tumor cell angiogenic activity, as demonstrated by the reduction of angiogenic activity in fibrosarcoma cell culture medium by immunodepletion of PLF. These results suggest that an extraembryonic genetic program, which has evolved to support fetal growth, may be reactivated in certain tumors and contribute to tumor growth.

Alternative promoter usage of the Fos-responsive gene Fit-1 generates mRNA isoforms coding for either secreted or membrane-bound proteins related to the IL-1 receptor.

Fit-1 has been identified previously as a Fos-responsive gene of rat fibroblasts. Here we show that Fit-1 is directly regulated by the estrogen-inducible transcription factor Fos-ER and that it belongs to the family of delayed early genes. Two different mRNA isoforms are expressed from the Fit-1 gene. The Fit-1M mRNA isolated from spleen codes for a membrane-bound protein which is most closely related in its extracellular, transmembrane and intracellular domains to the type I interleukin-1 (IL-1) receptor. The Fit-1S mRNA of fibroblasts directs, instead, the synthesis of a secreted protein consisting of only the extracellular domain. Analysis of the exon-intron structure of the Fit-1 gene indicated that the Fit-1S and Fit-1M mRNAs are transcribed from two different promoters and that the sequence differences at their 3' ends result from alternative 3' processing. Northern blot analysis with specific 5' and 3' probes directly demonstrated tight coupling between alternative promoter usage and 3' processing of the Fit-1 transcripts. The orthologous gene of the mouse (known as T1 or ST2) is expressed during ontogeny first in the fetal liver of the embryo and then in lung and hematopoietic tissues of the adult. The mRNA coding for the membrane-bound protein is more abundantly expressed in all of these tissues, while the transcript for the secreted form predominates in fibroblasts and mammary epithelial cells. Differential regulation of two distinct promoters is thus used to determine the ratio between secreted and membrane-bound forms of Fit-1 (T1/ST2) which may modulate signaling in response to IL-1.

Life events, emotional eating and change in body mass index.

The results are reported of a longitudinal study on effects of negative life events on change in body mass index (BMI; weight/height2 (kg/m2)) in men and women classified as either low or high emotional eaters. It was predicted that emotional eating and negative life events would have an interaction effect on change in BMI. Low emotional eaters would gain less weight and high emotional eaters would gain more weight after experiencing negative life events, than those who had not experienced such events. For men, emotional eating and negative life events were found to have a significant interaction effect on change in BMI 6 months after the assessment of life events on the first, but not on the second assessment date in the same study. Data on the long-term effects of negative life events indicate that the significant interaction effect found was not an artefact. For women, no such interaction effects were found. Thus, it is concluded that the hypothesis was confirmed to some extent in the men, but not in the women.

Inflammatory mast cells up-regulate angiogenesis during squamous epithelial carcinogenesis.

Expression of HPV16 early region genes in basal keratinocytes of transgenic mice elicits a multistage pathway to squamous carcinoma. We report that infiltration by mast cells and activation of the matrix metalloproteinase MMP-9/gelatinase B coincides with the angiogenic switch in premalignant lesions. Mast cells infiltrate hyperplasias, dysplasias, and invasive fronts of carcinomas, but not the core of solid tumors, where they degranulate in close apposition to capillaries and epithelial basement membranes, releasing mast-cell-specific serine proteases MCP-4 (chymase) and MCP-6 (tryptase). MCP-6 is shown to be a mitogen for dermal fibroblasts that proliferate in the reactive stroma, whereas MCP-4 can activate progelatinase B and induce hyperplastic skin to become angiogenic in an in vitro bioassay. Notably, premalignant angiogenesis is abated in a mast-cell-deficient (KITW/KITWWv) HPV16 transgenic mouse. The data indicate that neoplastic progression in this model involves exploitation of an inflammatory response to tissue abnormality. Thus, regulation of angiogenesis during squamous carcinogenesis is biphasic: In hyperplasias, dysplasias, and invading cancer fronts, inflammatory mast cells are conscripted to reorganize stromal architecture and hyperactivate angiogenesis; within the cancer core, upregulation of angiogenesis factors in tumor cells apparently renders them self-sufficient at sustaining neovascularization.

MMP-9/gelatinase B is a key regulator of growth plate angiogenesis and apoptosis of hypertrophic chondrocytes.

Homozygous mice with a null mutation in the MMP-9/gelatinase B gene exhibit an abnormal pattern of skeletal growth plate vascularization and ossification. Although hypertrophic chondrocytes develop normally, apoptosis, vascularization, and ossification are delayed, resulting in progressive lengthening of the growth plate to about eight times normal. After 3 weeks postnatal, aberrant apoptosis, vascularization, and ossification compensate to remodel the enlarged growth plate and ultimately produce an axial skeleton of normal appearance. Transplantation of wild-type bone marrow cells rescues vascularization and ossification in gelatinase B-null growth plates, indicating that these processes are mediated by gelatinase B-expressing cells of bone marrow origin, designated chondroclasts. Growth plates from gelatinase B-null mice in culture show a delayed release of an angiogenic activator, establishing a role for this proteinase in controlling angiogenesis.