Treatment options in newly diagnosed glioblastoma

Dual Targeting of EGFR and MTOR Pathways Inhibits Glioblastoma Growth by Modulating the Tumor Microenvironment

Glioblastoma's (GBM) aggressive growth is driven by redundant activation of a myriad of signaling pathways and genomic alterations in tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR), which is altered in over 50% of cases. Single agents targeting EGFR have not proven effective against GBM. In this study, we aimed to identify an effective anti-tumor regimen using pharmacogenomic testing of patient-derived GBM samples, in culture and in vivo. High-throughput pharmacological screens of ten EGFR-driven GBM samples identified the combination of erlotinib (EGFRi) and MLN0128 (a mammalian target of rapamycin inhibitor, or MTORi) as the most effective at inhibiting tumor cell viability. The anti-tumor activity of erlonitib+MLN0128 was synergistic and produced inhibition of the p-EGFR, mitogen-activated protein kinase (MAPK), and Phosphoinositide 3-kinase (PI3K) pathways in culture. Using an orthotopic murine model of GBM, we show that erlotinib+MLN0128 inhibited tumor growth in vivo and significantly prolonged the survival of tumor-bearing mice. Expression profiling of tumor tissues from treated mice revealed a unique gene signature induced by erlotinib+MLN0128, consisting of downregulation of immunosuppressive chemokines in the tumor microenvironment, including C-C motif chemokine ligand 2 (CCL2) and periostin. Lower periostin levels resulted in the inhibition of Iba1+ (tumor-promoting) macrophage infiltration of GBM xenografts. Taken together, our results demonstrate that pharmacological co-targeting of EGFR and MTOR using clinically available drugs represents an effective treatment paradigm for EGFR-driven GBMs, acting both by inhibiting tumor cell growth and modulating the immune tumor microenvironment.

Glioblastoma multiforme-derived extracellular vesicles drive normal astrocytes towards a tumour-enhancing phenotype

Glioblastoma multiforme (GBM) is a devastating tumour with abysmal prognoses. We desperately need novel approaches to understand GBM biology and therapeutic vulnerabilities. Extracellular vesicles (EVs) are membrane-enclosed nanospheres released locally and systemically by all cells, including tumours, with tremendous potential for intercellular communication. Tumour EVs manipulate their local environments as well as distal targets; EVs may be a mechanism for tumourigenesis in the recurrent GBM setting. We hypothesized that GBM EVs drive molecular changes in normal human astrocytes (NHAs), yielding phenotypically tumour-promoting, or even tumourigenic, entities. We incubated NHAs with GBM EVs and examined the astrocytes for changes in cell migration, cytokine release and tumour cell growth promotion via the conditioned media. We measured alterations in intracellular signalling and transformation capacity (astrocyte growth in soft agar). GBM EV-treated NHAs displayed increased migratory capacity, along with enhanced cytokine production which promoted tumour cell growth. GBM EV-treated NHAs developed tumour-like signalling patterns and exhibited colony formation in soft agar, reminiscent of tumour cells themselves. GBM EVs modify the local environment to benefit the tumour itself, co-opting neighbouring astrocytes to promote tumour growth, and perhaps even driving astrocytes to a tumourigenic phenotype. Such biological activities could have profound impacts in the recurrent GBM setting.This article is part of the discussion meeting issue 'Extracellular vesicles and the tumour microenvironment'.

The evolving roles and controversies of radiotherapy in the treatment of glioblastoma

Numerous randomised controlled trials have demonstrated the benefit of radiation therapy in patients with newly diagnosed glioblastoma and it has been the cornerstone of treatment for decades. The aims of this review are to (1) Briefly outline the historical studies which resulted in radiation being the current standard of care as used in the Stupp et al. trial (2) Discuss the evolving role of radiation therapy in the management of elderly patients (3) Review the current evidence and ongoing studies of radiation use in the recurrent/salvage setting and (4) Discuss the continuing controversies of volume delineation in the planning of radiation delivery.

The Transcription Regulator Krüppel-Like Factor 4 and Its Dual Roles of Oncogene in Glioblastoma and Tumor Suppressor in Neuroblastoma

The Krüppel-like factor 4 (KLF4) gene is located on chromosome 9q31. All of the currently known 17 KLF transcription regulators that have similarity with members of the specificity protein family are distinctly characterized by the Cys₂/His₂ zinc finger motifs at their carboxyl terminals for preferential binding to the GC/GT box or the CACCC element of the gene promoter and enhancer regions. KLF4 is a transcriptional regulator of cell proliferation, differentiation, apoptosis, migration, and invasion, emphasizing its importance in diagnosis and prognosis of particular tumors. KLF4 has been implicated in tumor progression as well as in tumor suppression, depending on tumor types and contexts. Different studies so far strongly suggest that KLF4 acts as an oncogene in glioblastoma, which is the most malignant and prevalent brain tumor in human adult. It is now well established that the presence of glioblastoma stem cells (GSCs) in glioblastoma causes therapy resistance and progressive growth of the tumor. Because KLF4 is one of the key stemness factors in GSCs, it is likely that KLF4 contributes significantly to the survival of GSCs and the recurrence of glioblastoma. On the other hand, recent studies show that KLF4 can act as a tumor suppressor in human malignant neuroblastoma, which is a deadly tumor mostly in children, by inhibiting the cell cycle and activating the cell differentiation and death pathways. Our increasing understanding of the molecular mechanisms of the contrasting roles of KLF4 in glioblastoma and neuroblastoma is useful for superior diagnosis, therapy, and prognosis of these tumors of the nervous system.

Glioma-derived extracellular vesicles selectively suppress immune responses

BACKGROUND

Glioma-related immunosuppression is well documented; however, the mechanisms of suppression are not fully understood. Here we explore a role for glioma extracellular vesicles (EVs) as a means of immune modulation.

METHODS

Healthy donor peripheral blood mononuclear cells (PBMCs) were incubated with mitogenic stimuli and various concentrations of glioma-derived EVs. Intracellular signaling and cytokine output were determined by protein microarrays, and phenotypic changes were assessed by flow cytometry. Recall antigen testing, mixed lymphocyte reactions, and migration assays analyzed PBMC functional capacity.

RESULTS

Protein microarray data revealed induction of an immunosuppressive phenotype and cytokine output at high tumor-vesicle concentrations but an activated phenotype at low concentrations. T cell activation antigen expression confirmed differential activation profiles. Functional analyses revealed decreased migratory capacity of PBMCs after incubation with EVs; however, recall antigen and mixed lymphocyte tests indicated that activation capacity is still retained in EV-treated cells.

CONCLUSION

The differential effects of high and low EV concentrations dictate modulatory effects on PBMCs. These data provide a role for EVs at high concentrations for inducing selective tolerance of an immune response in a tumor setting. This suggests that lymphocytes in patients' circulation are not irreparably impaired, as previously thought, but can be rescued to augment antitumor responses.

Intraoperative MRI for neurosurgical and general surgical interventions

PURPOSE OF REVIEW

The use of intraoperative magnetic resonance imaging (IMRI) during surgeries and procedures has expanded in the last decade. Not only is it becoming more commonly used for a variety of adult and pediatric neurosurgical procedures, but also its use has expanded to other types of surgeries. Along with using IMRI for removing tumors of the spinal cord, surgeons are now using it for other types of surgical operations of the kidney and liver. The increased utilization during the intraoperative period warrants the anesthesia provider to assure that patients and staff are unharmed because of increased risk of the powerful magnet.

RECENT FINDINGS

Recent literature is reviewed regarding the expansive use of IMRI in the operating and procedure room. Safety issues and anesthetic implications are also addressed.

SUMMARY

IMRI is becoming increasingly more popular, especially with neurosurgeons, but its use is also expanding to other types of surgeries. Because of the increased use, the anesthesia provider must be aware of the dangers that it imposes to those involved and take necessary safety precautions. This will help assure that no one is harmed during the operation or procedure.

Cytomegalovirus and brain tumor: epidemiology, biology and therapeutic aspects

PURPOSE OF REVIEW

First described in 2002, the presence and role of human cytomegalovirus (HCMV) infection in glioblastoma (GBM) has remained a controversial topic. New research indicates HCMV gene products likely promote GBM pathogenesis and that therapies aimed at HCMV might influence disease progression.

RECENT FINDINGS

Recently, investigators have begun to analyze HCMV genome and proteins present in GBM cells in vivo. Furthermore, the research has demonstrated that several HCMV gene products that have oncomodulatory properties are expressed in GBM and may be impacting tumor pathogenesis in vivo. These HCMV gene products modulate GBM proliferation, apoptosis, angiogenesis, invasion and immune evasion. A recent mouse model provides mechanistic information as to how CMV may promote gliomagenesis in the setting of tumor suppressor dysfunction and STAT3 signaling. In addition, clinical outcomes of GBM patients are associated with the degree of HCMV infection. Novel therapies aimed at direct antiviral and immunotherapy approaches to HCMV suggest that these modalities may impact the future treatment of this disease.

SUMMARY

A more precise understanding of the role of HCMV infection in gliomagenesis and GBM pathogenesis could reveal novel therapeutic and preventive strategies.

Inhibition of EGFR induces a c-MET-driven stem cell population in glioblastoma

Glioblastoma multiforme (GBM) is the most lethal form of primary brain tumors, characterized by highly invasive and aggressive tumors that are resistant to all current therapeutic options. GBMs are highly heterogeneous in nature and contain a small but highly tumorigenic and self-renewing population of stem or initiating cells (glioblastoma stem cells or GSCs). GSCs have been shown to contribute to tumor propagation and resistance to current therapeutic modalities. Recent studies of human GBMs have elucidated the genetic alterations common in these tumors, but much remains unknown about specific signaling pathways that regulate GSCs. Here we identify a distinct fraction of cells in a genetically engineered mouse model of EGFR-driven GBM that respond to anti-EGFR therapy by inducing high levels of c-MET expression. The MET-positive cells displayed clonogenic potential and long-term self-renewal ability in vitro and are capable of differentiating into multiple lineages. The MET-positive GBM cells are resistant to radiation and highly tumorigenic in vivo. Activation of MET signaling led to an increase in expression of the stemness transcriptional regulators Oct4, Nanog, and Klf4. Pharmacological inhibition of MET activity in GSCs prevented the activation of Oct4, Nanog, and Klf4 and potently abrogated stemness. Finally, the MET expressing cells were preferentially localized in perivascular regions of mouse tumors consistent with their function as GSCs. Together, our findings indicate that EGFR inhibition in GBM induces MET activation in GSCs, which is a functional requisite for GSCs activity and thus represents a promising therapeutic target.

The adolescent and young adult with cancer: state of the art--brain tumor

The management of adolescents and young adults with brain tumors, which consist of many different histologic subtypes, continues to be a challenge. Better outcome with a decrease of the side effects of the disease and therapy and improvement of quality of life has been demonstrated in recent decades for some tumors. Significant differences in survival and cure are also observed between adult and pediatric tumors of the same histologic grade. Genetic, developmental, and environmental factors likely influence the type of tumor and response observed, even though no clear pathologic features differentiate these lesions among children, adolescents, and adults. Similarly, treatment strategies are not identical among these populations; most patients receive surgery, followed by radiation therapy and multiagent chemotherapy. Advances in understanding the biology underlying the distribution of tumors in adolescents and young adults may influence the development of prospective trials. A more individualized view of these tumors will likely influence stratification of patients in future studies as well as selection for targeted agents. Accordingly, outcomes may improve and long-term morbidities may decrease.