Phase II trial of erlotinib with temozolomide and radiation in patients with newly diagnosed glioblastoma multiforme

Design and conduct of early-phase radiotherapy trials with targeted therapeutics: lessons from the PRAVO experience

New strategies to facilitate the improvement of physical and integrated biological optimization of high-precision treatment protocols are an important priority for modern radiation oncology. From a clinical perspective, as knowledge accumulates from molecular radiobiology, there is a complex and exciting opportunity to investigate novel approaches to rational patient treatment stratification based on actionable tumor targets, together with the appropriate design of next-generation early-phase radiotherapy trials utilizing targeted therapeutics, to formally evaluate relevant clinical and biomarker endpoints. A unique aspect in the development pathway of systemic agents with presumed radiosensitizing activity will also be the need for special attention on patient eligibility and the rigorous definition of radiation dose-volume relationships and potential dose-limiting toxicities. Based on recent experience from systematically investigating histone deacetylase inhibitors as radiosensitizing agents, from initial studies in preclinical tumor models through the conduct of a phase I clinical study to evaluate tumor activity of the targeted agent as well as patient safety and tumor response to the combined treatment modality, this communication will summarize principles relating to early clinical evaluation of combining radiotherapy and targeted therapeutics.

Radiotherapy plus nimotuzumab or placebo in the treatment of high grade glioma patients: results from a randomized, double blind trial

Background

The prognosis of patients bearing high grade glioma remains dismal. Epidermal Growth Factor Receptor (EGFR) is well validated as a primary contributor of glioma initiation and progression. Nimotuzumab is a humanized monoclonal antibody that recognizes the EGFR extracellular domain and reaches Central Nervous System tumors, in nonclinical and clinical setting. While it has similar activity when compared to other anti-EGFR antibodies, it does not induce skin toxicity or hypomagnesemia.

Methods

A randomized, double blind, multicentric clinical trial was conducted in high grade glioma patients (41 anaplastic astrocytoma and 29 glioblastoma multiforme) that received radiotherapy plus nimotuzumab or placebo. Treatment and placebo groups were well-balanced for the most important prognostic variables. Patients received 6 weekly doses of 200 mg nimotuzumab or placebo together with irradiation as induction therapy. Maintenance treatment was given for 1 year with subsequent doses administered every 3 weeks. The objectives of this study were to assess the comparative overall survival, progression free survival, response rate, immunogenicity and safety.

Results

The median cumulative dose was 3200 mg of nimotuzumab given over a median number of 16 doses. The combination of nimotuzumab and RT was well-tolerated. The most prevalent related adverse reactions included nausea, fever, tremors, anorexia and hepatic test alteration. No anti-idiotypic response was detected, confirming the antibody low immunogenicity. The mean and median survival time for subjects treated with nimotuzumab was 31.06 and 17.76 vs. 21.07 and 12.63 months for the control group.

Conclusions

In this randomized trial, nimotuzumab showed an excellent safety profile and significant survival benefit in combination with irradiation.

Trial registration

Cuban National Register for clinical trials (No. 1745) (http://registroclinico.sld.cu/ensayos).

Angiogenesis in neurological disorders: a review

Angiogenesis, recruitment of new blood vessels, is an essential component of the metastatic pathway. These vessels provide the principal route by which tumor cells exit the primary tumor site and enter the circulation. For many tumors, the vascular density can provide a prognostic indicator of metastatic potential, with the highly vascular primary tumors having a higher incidence of metastasis than poorly vascular tumors. The discovery and characterization of tumor-derived angiogenesis modulators greatly contributed to our understanding of how tumors regulate angiogenesis. However, although angiogenesis appears to be a rate-limiting event in tumor growth and metastatic dissemination, a direct connection between the induction of angiogenesis and the progression to tumor malignancy is less well understood. In this review, we discuss the observations concerning the modulation of angiogenesis and their implications in various neurological disorders, as well as their potential impact on cancer therapy.

Inhibition of DYRK1A destabilizes EGFR and reduces EGFR-dependent glioblastoma growth

Glioblastomas (GBMs) are very aggressive tumors that are resistant to conventional chemo- and radiotherapy. New molecular therapeutic strategies are required to effectively eliminate the subpopulation of GBM tumor-initiating cells that are responsible for relapse. Since EGFR is altered in 50% of GBMs, it represents one of the most promising targets; however, EGFR kinase inhibitors have produced poor results in clinical assays, with no clear explanation for the observed resistance. We uncovered a fundamental role for the dual-specificity tyrosine phosphorylation-regulated kinase, DYRK1A, in regulating EGFR in GBMs. We found that DYRK1A was highly expressed in these tumors and that its expression was correlated with that of EGFR. Moreover, DYRK1A inhibition promoted EGFR degradation in primary GBM cell lines and neural progenitor cells, sharply reducing the self-renewal capacity of normal and tumorigenic cells. Most importantly, our data suggest that a subset of GBMs depends on high surface EGFR levels, as DYRK1A inhibition compromised their survival and produced a profound decrease in tumor burden. We propose that the recovery of EGFR stability is a key oncogenic event in a large proportion of gliomas and that pharmacological inhibition of DYRK1A could represent a promising therapeutic intervention for EGFR-dependent GBMs.

Epidermal growth factor receptor as a therapeutic target in glioblastoma

Glioblastoma represents one of the most challenging problems in neurooncology. Among key elements driving its behavior is the transmembrane epidermal growth factor receptor family, with the first member epidermal growth factor receptor (EGFR) centered in most studies. Engagement of the extracellular domain with a ligand activates the intracellular tyrosine kinase (TK) domain of EGFR, leading to autophosphorylation and signal transduction that controls proliferation, gene transcription, and apoptosis. Oncogenic missense mutations, deletions, and insertions in the EGFR gene are preferentially located in the extracellular domain in glioblastoma and cause constitutive activation of the receptor. The mutant EGFR may also transactivate other cell surface molecules, such as additional members of the EGFR family and the platelet-derived growth factor receptor, which ignite signaling cascades that synergize with the EGFR-initiated cascade. Because of the cell surface location and increased expression of the receptor along with its important biological function, EGFR has triggered much effort for designing targeted therapy. These approaches include TK inhibition, monoclonal antibody, vaccine, and RNA-based downregulation of the receptor. Treatment success requires that the drug penetrates the blood-brain barrier and has low systemic toxicity but high selectivity for the tumor. While the blockade of EGFR-dependent processes resulted in experimental and clinical treatment success, cells capable of using alternative signaling ultimately escape this strategy. A combination of interventions targeting tumor-specific cell surface regulators along with convergent downstream signaling pathways will likely enhance efficacy. Studies on EGFR in glioblastoma have revealed much information about the complexity of gliomagenesis and also facilitated the development of strategies for targeting drivers of tumor growth and combination therapies with increasing complexity.

Survival analysis of HDR brachytherapy versus reoperation versus temozolomide alone: a retrospective cohort analysis of recurrent glioblastoma multiforme

OBJECTIVES

Tumour recurrence of glioblastoma multiforme (GBM) after initial treatment with surgical resection, radiotherapy and chemotherapy is an inevitable phenomenon. This retrospective cohort study compared the efficacy of interstitial high dose rate brachytherapy (HDR-BRT), re-resection and sole dose dense temozolomide chemotherapy (ddTMZ) in the treatment of recurrent glioblastoma after initial surgery and radiochemotherapy.

DESIGN

Retropective cohort study.

SETTING

Primary level of care with two participating centres. The geographical location was central Germany.

PARTICIPANTS

From January 2005 to December 2010, a total of 111 patients developed recurrent GBM after initial surgery and radiotherapy with concomitant temozolomide. The inclusion criteria were as follows: (1) histology-proven diagnosis of primary GBM (WHO grade 4), (2) primary treatment with resection and radiochemotherapy, and (3) tumour recurrence/progression.

INTERVENTIONS

This study compared retrospectively the efficacy of interstitial HDR-BRT, re-resection and ddTMZ alone in the treatment of recurrent glioblastoma.

PRIMARY AND SECONDARY OUTCOME MEASURES

Median survival, progression free survival and complication rate.

RESULTS

Median survival after salvage therapy of the recurrence was 37, 30 and 26 weeks, respectively. The HDR-BRT group did significantly better than both the reoperation (p<0.05) and the ddTMZ groups (p<0.05). Moderate to severe complications in the HDR-BRT, reoperation and sole chemotherapy groups occurred in 5/50 (10%), 4/36 (11%) and 9/25 (36%) cases, respectively.

CONCLUSIONS

CT-guided interstitial HDR-BRT attained higher survival benefits in the management of recurrent glioblastoma after initial surgery and radiotherapy with concurrent temozolomide in comparison with the other treatment modalities. The low risk of complications of the HDR-BRT and the fact that it can be delivered percutaneously in local anaesthesia render it a promissing treatment option for selected patients which should be further evaluated.

Role of Biomarkers in the Clinical Management of Glioblastomas: What are the Barriers and How Can We Overcome Them?

Thousands of articles describing biomarkers predictive of treatment and prognostic of survival in cancer have been published, yet only a handful of biomarkers are currently used routinely in the clinic. Biomarkers need to be analytically standardized, validated, and clinically useful. This review will address the challenges and ways in which we can improve our discovery and translation of prospective biomarkers from the lab into validated diagnostic tests with a specific focus on patients diagnosed with glioblastoma and MGMT promoter methylation status. There has been long-held enthusiasm to use MGMT promoter methylation as a predictive biomarker for patients treated with the alkylating agent, temozolomide; however in the majority of centers around the world, this has not yet transpired.

NCI-RTOG translational program strategic guidelines for the early-stage development of radiosensitizers

The addition of chemotherapeutic agents to ionizing radiation has improved survival in many malignancies. Cure rates may be further improved by adding novel targeted agents to current radiotherapy or radiochemotherapy regimens. Despite promising laboratory data, progress in the clinical development of new drugs with radiation has been limited. To define and address the problems involved, a collaborative effort between individuals within the translational research program of the Radiation Oncology Therapy Group and the National Cancer Institute was established. We discerned challenges to drug development with radiation including: 1) the limited relevance of preclinical work, 2) the pharmaceutical industry's diminished interest, and 3) the important individual skills and institutional commitments required to ensure a successful program. The differences between early-phase trial designs with and without radiation are noted as substantial. The traditional endpoints for early-phase clinical trials-acute toxicity and maximum-tolerated dose-are of limited value when combining targeted agents with radiation. Furthermore, response rate is not a useful surrogate marker of activity in radiation combination trials.Consequently, a risk-stratified model for drug-dose escalation with radiation is proposed, based upon the known and estimated adverse effects. The guidelines discuss new clinical trial designs, such as the time-to-event continual reassessment method design for phase I trials, randomized phase II "screening" trials, and the use of surrogate endpoints, such as pathological response. It is hoped that by providing a clear pathway, this article will accelerate the rate of drug development with radiation.

Function of the blood-brain barrier and restriction of drug delivery to invasive glioma cells: findings in an orthotopic rat xenograft model of glioma

Despite aggressive treatment with radiation and chemotherapy, recurrence of glioblastoma multiforme (GBM) is inevitable. The objective of this study was to show that the blood-brain barrier (BBB), through a combination of tight junctions and active efflux transporters in the brain microvasculature, can significantly restrict delivery of molecularly targeted agents to invasive glioma cells. Transgenic mice lacking P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) were used to study efflux of erlotinib at the BBB. A U87 rat xenograft model of GBM was used to investigate the regional distribution of erlotinib to the tumor, and brain regions surrounding the tumor. The effect of concurrent administration of elacridar on regional tumor distribution of erlotinib was evaluated. We show that erlotinib transport across an intact BBB is significantly restricted due to P-gp- and Bcrp-mediated efflux transport. We then show that the BBB is sufficiently intact in areas of brain adjacent to the tumor core to significantly restrict erlotinib delivery. Inhibition of P-gp and Bcrp by the dual inhibitor elacridar dramatically increased erlotinib delivery to the tumor core, rim, and normal brain. These results provide conclusive evidence of the impact that active efflux at the BBB has on the delivery of molecularly targeted therapy to different tumor regions in glioma. These data also support the possibility that the repeated failure of clinical trials of new drugs for gliomas may be in part due to a failure to achieve effective concentrations in invasive tumor cells that reside behind an intact BBB.

Receptor tyrosine kinases: principles and functions in glioma invasion

Protein tyrosine kinases are enzymes that are capable of adding a phosphate group to specific tyrosines on target proteins. A receptor tyrosine kinase (RTK) is a tyrosine kinase located at the cellular membrane and is activated by binding of a ligand via its extracellular domain. Protein phosphorylation by kinases is an important mechanism for communicating signals within a cell and regulating cellular activity; furthermore, this mechanism functions as an "on" or "off" switch in many cellular functions. Ninety unique tyrosine kinase genes, including 58 RTKs, were identified in the human genome; the products of these genes regulate cellular proliferation, survival, differentiation, function, and motility. Tyrosine kinases play a critical role in the development and progression of many types of cancer, in addition to their roles as key regulators of normal cellular processes. Recent studies have revealed that RTKs such as epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), c-Met, Tie, Axl, discoidin domain receptor 1 (DDR1), and erythropoietin-producing human hepatocellular carcinoma (Eph) play a major role in glioma invasion. Herein, we summarize recent advances in understanding the role of RTKs in glioma pathobiology, especially the invasive phenotype, and present the perspective that RTKs are a potential target of glioma therapy.

Phase 1 study of erlotinib plus radiation therapy in patients with advanced cutaneous squamous cell carcinoma

PURPOSE

To assess the toxicity profile of erlotinib therapy combined with postoperative adjuvant radiation therapy in patients with advanced cutaneous squamous cell carcinoma.

METHODS AND MATERIALS

This was a single-arm, prospective, phase 1 open-label study of erlotinib with radiation therapy to treat 15 patients with advanced cutaneous head-and-neck squamous cell carcinoma. Toxicity data were summarized, and survival was analyzed with the Kaplan-Meier method.

RESULTS

The majority of patients were male (87%) and presented with T4 disease (93%). The most common toxicity attributed to erlotinib was a grade 2-3 dermatologic reaction occurring in 100% of the patients, followed by mucositis (87%). Diarrhea occurred in 20% of the patients. The 2-year recurrence rate was 26.7%, and mean time to cancer recurrence was 10.5 months. Two-year overall survival was 65%, and disease-free survival was 60%.

CONCLUSIONS

Erlotinib and radiation therapy had an acceptable toxicity profile in patients with advanced cutaneous squamous cell carcinoma. The disease-free survival in this cohort was comparable to that in historical controls.

Activation of multiple ERBB family receptors mediates glioblastoma cancer stem-like cell resistance to EGFR-targeted inhibition

Epidermal growth factor receptor (EGFR) signaling is strongly implicated in glioblastoma (GBM) tumorigenesis. However, molecular agents targeting EGFR have demonstrated minimal efficacy in clinical trials, suggesting the existence of GBM resistance mechanisms. GBM cells with stem-like properties (CSCs) are highly efficient at tumor initiation and exhibit therapeutic resistance. In this study, GBMCSC lines showed sphere-forming and tumor initiation capacity after EGF withdrawal from cell culture media, compared with normal neural stem cells that rapidly perished after EGF withdrawal. Compensatory activation of related ERBB family receptors (ERBB2 and ERBB3) was observed in GBM CSCs deprived of EGFR signal (EGF deprivation or cetuximab inhibition), suggesting an intrinsic GBM resistance mechanism for EGFR-targeted therapy. Dual inhibition of EGFR and ERBB2 with lapatinib significantly reduced GBM proliferation in colony formation assays compared to cetuximab-mediated EGFR-specific inhibition. Phosphorylation of downstream ERBB signaling components (AKT, ERK1/2) and GBM CSC proliferation were inhibited by lapatinib. Collectively, these findings show that GBM therapeutic resistance to EGFR inhibitors may be explained by compensatory activation of EGFR-related family members (ERBB2, ERBB3) enabling GBM CSC proliferation, and therefore simultaneous blockade of multiple ERBB family members may be required for more efficacious GBM therapy.

MGMT testing for glioma in clinical laboratories: discordance with methylation analyses prevents the implementation of routine immunohistochemistry

PURPOSE

Glioblastoma is a universally fatal cancer of the central nervous system which responds poorly to treatment. MGMT has potential as a predictive biomarker in glioblastoma patients to determine treatment response. However, methods of measuring MGMT are currently unsatisfactory, and as such, use of this marker has not translated well into the clinic. This paper aims to review current methodology of MGMT measurement, with a focus on immunohistochemistry as a potential way forward. TOPICS AND METHODS: Studies of glioma patients where MGMT immunohistochemistry was undertaken, as well as the literature surrounding methylation analyses and the regulation of MGMT, were reviewed.

RESULTS

All methods of measuring MGMT were disputed in some way in the literature. A trend of discordance between methylation analyses and protein analyses was present. There is a lack of standardisation in the measurement of MGMT, and as a result, it seems that there are highly variable results.

CONCLUSIONS

No single method of MGMT analysis has emerged as a clear choice for routine clinical testing of MGMT in glioma patients. Although methylation analyses are favoured, their expense and inaccessibility are barriers to their use in routine clinical practice. More research into immunohistochemistry is needed to determine whether it can serve as a reliable and cost-effective alternative to methylation analyses.

State of the art and perspectives in the treatment of glioblastoma

Glioblastoma is the most common malignant primary brain tumor. Cures are rare and median survival varies from several to 22 months. Standard treatment for good performance patients consists of maximal safe surgical resection followed by radiotherapy with concurrent temozolomide (TMZ) chemotherapy and six cycles of postradiotherapy TMZ. At recurrence, treatment options include repeat surgery (with or without Gliadel wafer placement), reirradiation or systemic therapy. Most patients with good performance status are treated with cytotoxic chemotherapy or targeted biologic therapy following or in lieu of repeat surgery. Cytotoxic chemotherapy options include nitrosoureas, rechallenge with TMZ, platins, phophoramides and topoisomerase inhibitors, although efficacy is limited. Despite the intense effort of developing biologic agents that target angiogenesis and growth and proliferative pathways, bevacizumab is the only agent that has shown efficacy in clinical trials. It was awarded accelerated approval in the USA after demonstrating an impressive radiographic response in two open-label, prospective Phase II studies. Two randomized, Phase III trials of upfront bevacizumab have completed and may demonstrate survival benefit; however, results are pending at this time. Given the limited treatment options at tumor recurrence, consideration for enrollment on a clinical trial is encouraged.

Individualized targeted therapy for glioblastoma: fact or fiction?

PURPOSE

This review will address the current state of individualized cancer therapy for glioblastoma. Glioblastomas are highly malignant primary brain tumors presumably originating from neuroglial progenitor cells. Median survival is less than 1 year.

DESIGN

Recent developments in the morphologic, clinical, and molecular classification of glioblastoma were reviewed, and their impact on clinical decision making was analyzed.

RESULTS

Glioblastomas can be classified by morphology, clinical characteristics, complex molecular signatures, single biomarkers, or imaging parameters. Some of these characteristics, including age and Karnofsky Performance Scale score, provide important prognostic information. In contrast, few markers help to choose between various treatment options. Promoter methylation of the O-methylguanine methyltransferase gene seems to predict benefit from alkylating agent chemotherapy. Hence, it is used as an entry criterion for alkylator-free experimental combination therapy with radiotherapy. Screening for a specific type of epidermal growth factor receptor mutation is currently being explored as a biomarker for selecting patients for vaccination. Positron emission tomography for the detection of ανβ3/5 integrins could be used to select patients for treatment with anti-integrin antiangiogenic approaches.

DISCUSSION

Despite extensive efforts at defining biological markers as a basis for selecting therapies, most treatment decisions for glioblastoma patients are still based on age and performance status. However, several ongoing clinical trials may enrich the repertoire of criteria for clinical decision making in the very near future. The concept of individualized or personalized targeted cancer therapy has gained significant attention throughout oncology. Yet, data in support of such an approach to glioblastoma, the most malignant subtype of glioma, are limited, and personalized medicine plays a minor role in current clinical neuro-oncology practice. In essence, this concept proposes that tumors that are currently lumped together based on common morphologic features can be subclassified in a way that the resulting subentities are more homogeneous, for example, in molecular signatures and will therefore be amenable to selective therapeutic interventions. At present, the major "biomarkers" used to allocate treatment in glioblastoma are age and Karnofsky Performance Scale score, and these markers have so far survived all efforts at more sophisticated approaches to the management of this disease. Treatment allocation basically means intensity of treatment, especially the use of the standard-of-care or radiotherapy alone beyond age 65 to 70 years or below a Karnofsky Performance Scale score of 60.

Long-term survival after gamma knife radiosurgery in a case of recurrent glioblastoma multiforme: a case report and review of the literature

The management of recurrent glioblastoma is highly challenging, and treatment outcomes remain uniformly poor. Glioblastoma is a highly infiltrative tumor, and complete surgical resection of all microscopic extensions cannot be achieved at the time of initial diagnosis, and hence local recurrence is observed in most patients. Gamma Knife radiosurgery has been used to treat these tumor recurrences for select cases and has been successful in prolonging the median survival by 8-12 months on average for select cases. We present the unique case of a 63-year-old male with multiple sequential recurrences of glioblastoma after initial standard treatment with surgery followed by concomitant external beam radiation therapy and chemotherapy (temozolomide). The patient was followed clinically as well as with surveillance MRI scans at every 2-3-month intervals. The patient underwent Gamma Knife radiosurgery three times for 3 separate tumor recurrences, and the patient survived for seven years following the initial diagnosis with this aggressive treatment. The median survival in patients with recurrent glioblastoma is usually 8-12 months after recurrence, and this unique case illustrates that aggressive local therapy can lead to long-term survivors in select situations. We advocate that each patient treatment at the time of recurrence should be tailored to each clinical situation and desire for quality of life and improved longevity.

Novel therapies in glioblastoma

Conventional treatment of glioblastoma has advanced only incrementally in the last 30 years and still yields poor outcomes. The current strategy of surgery, radiation, and chemotherapy has increased median survival to approximately 15 months. With the advent of molecular biology and consequent improved understanding of basic tumor biology, targeted therapies have become cornerstones for cancer treatment. Many pathways (RTKs, PI3K/AKT/mTOR, angiogenesis, etc.) have been identified in GBM as playing major roles in tumorigenesis, treatment resistance, or natural history of disease. Despite the growing understanding of the complex networks regulating GBM tumors, many targeted therapies have fallen short of expectations. In this paper, we will discuss novel therapies and the successes and failures that have occurred. One clear message is that monotherapies yield minor results, likely due to functionally redundant pathways. A better understanding of underlying tumor biology may yield insights into optimal targeting strategies which could improve the overall therapeutic ratio of conventional treatments.

DNA damage response and repair: insights into strategies for radiation sensitization of gliomas

The incorporation of radiotherapy into multimodality treatment plans has led to significant improvements in glioma patient survival. However, local recurrence from glioma resistance to ionizing radiation remains a therapeutic challenge. The tumoricidal effect of radiation therapy is largely attributed to the induction of dsDNA breaks (DSBs). In the past decade, there have been tremendous strides in understanding the molecular mechanisms underlying DSB repair. The identification of gene products required for DSB repair has provided novel therapeutic targets. Recent studies revealed that many US FDA-approved cancer agents inhibit DSB repair by interacting with repair proteins. This article will aim to provide discussion of DSB repair mechanisms to provide molecular targets for radiation sensitization of gliomas and a discussion of FDA-approved cancer therapies that modulate DSB repair to highlight opportunities for combination therapy with radiotherapy for glioma therapy.

Temozolomide and/or Erlotinib in the Treatment of Lung Cancer Patients With Progressive Central Nervous System Metastases

BACKGROUND

Patients with lung cancer who develop brain metastases have a poor prognosis. Those patients with progressive brain metastases tend to have a dismal prognosis. Currently, there is no standard of care for the treatment of these patients.

METHODS

In this manuscript, we present a retrospective evaluation of 10 patients treated at our institution with a combination of temozolomide and/or erlotinib after disease progression in the central nervous system following radiation therapy.

RESULTS

Median overall survival was 28 weeks. Median time to progression in the central nervous system was 14 weeks. Median time to progression systemically was 7.5 weeks. Some patients demonstrated prolonged stability of disease.

CONCLUSIONS

A palliative regimen of temozolomide and/or erlotinib could be considered in progressive central nervous system metastases from lung cancer.

Radiotherapy and "new" drugs-new side effects?

BACKGROUND AND PURPOSE

Targeted drugs have augmented the cancer treatment armamentarium. Based on the molecular specificity, it was initially believed that these drugs had significantly less side effects. However, currently it is accepted that all of these agents have their specific side effects. Based on the given multimodal approach, special emphasis has to be placed on putative interactions of conventional cytostatic drugs, targeted agents and other modalities. The interaction of targeted drugs with radiation harbours special risks, since the awareness for interactions and even synergistic toxicities is lacking. At present, only limited is data available regarding combinations of targeted drugs and radiotherapy. This review gives an overview on the current knowledge on such combined treatments.

MATERIALS AND METHODS

Using the following MESH headings and combinations of these terms pubmed database was searched: Radiotherapy AND cetuximab/trastuzumab/panitumumab/nimotuzumab, bevacizumab, sunitinib/sorafenib/lapatinib/gefitinib/erlotinib/sirolimus, thalidomide/lenalidomide as well as erythropoietin. For citation crosscheck the ISI web of science database was used employing the same search terms.

RESULTS

Several classes of targeted substances may be distinguished: Small molecules including kinase inhibitors and specific inhibitors, antibodies, and anti-angiogenic agents. Combination of these agents with radiotherapy may lead to specific toxicities or negatively influence the efficacy of RT. Though there is only little information on the interaction of molecular targeted radiation and radiotherapy in clinical settings, several critical incidents are reported.

CONCLUSIONS

The addition of molecular targeted drugs to conventional radiotherapy outside of approved regimens or clinical trials warrants a careful consideration especially when used in conjunction in hypo-fractionated regimens. Clinical trials are urgently needed in order to address the open question in regard to efficacy, early and late toxicity.

Targeting DNA repair and the cell cycle in glioblastoma

Glioblastoma is a disease with poor outcomes despite standard therapy. Specific targeting of the DNA damage response is a strategy that is becoming increasingly employed in oncology and has intriguing potential for improving outcomes in glioblastoma. DNA damage targeting has implications for improving current therapy as well as the potential to leverage inherent differences in glioblastoma cells to widen the therapeutic window.

Combined modality approaches in the management of adult glioblastoma

Over the past two decades, management of newly diagnosed glioblastoma has undergone significant evolution. While surgery has long been a mainstay of management for this disease, and while radiotherapy has a proven survival role, initial efforts at radiotherapy dose escalation, use of radiosurgery, brachytherapy, and altered fractionation did not improve patient survival. Recently, multiple modality therapy integrating maximal safe resection, postoperative radiation, and new systemic therapies have resulted in improved patient outcomes compared with older regimens utilizing surgery and postoperative radiation alone. Numerous trials are currently underway investigating the combination of surgery, radiation, and systemic therapy with targeted agents to find ways to further improve outcomes for adults with glioblastoma.

Recent advancements in multimodality treatment of gliomas

Gliomas account for the vast majority of malignant adult brain tumors. Even though tremendous effort has been made to optimize treatment of patients with high-grade glioma, the prognosis remains poor, especially for patients with glioblastoma. The dismal prognosis conferred by these tumors is in part caused by the tendency to diffusely infiltrate into neighboring brain tissue, but also by the inherent resistance of these tumors to both chemotherapy and radiation. This article reviews the recent advancements in multimodality treatment of patients with gliomas, both in the primary and recurrent setting, with an emphasis on the emerging targeted therapies. Moreover, the external beam radiotherapy options, including intensity modulated radiotherapy and particle (proton and carbon ion) radiotherapy are reviewed.

Delivery of molecularly targeted therapy to malignant glioma, a disease of the whole brain

Glioblastoma multiforme, because of its invasive nature, can be considered a disease of the entire brain. Despite recent advances in surgery, radiotherapy and chemotherapy, current treatment regimens have only a marginal impact on patient survival. A crucial challenge is to deliver drugs effectively to invasive glioma cells residing in a sanctuary within the central nervous system. The blood-brain barrier (BBB) restricts the delivery of many small and large molecules into the brain. Drug delivery to the brain is further restricted by active efflux transporters present at the BBB. Current clinical assessment of drug delivery and hence efficacy is based on the measured drug levels in the bulk tumour mass that is usually removed by surgery. Mounting evidence suggests that the inevitable relapse and lethality of glioblastoma multiforme is due to a failure to effectively treat invasive glioma cells. These invasive cells hide in areas of the brain that are shielded by an intact BBB, where they continue to grow and give rise to the recurrent tumour. Effective delivery of chemotherapeutics to the invasive glioma cells is therefore critical, and long-term efficacy will depend on the ability of a molecularly targeted agent to penetrate an intact and functional BBB throughout the entire brain. This review highlights the various aspects of the BBB, and also the brain-tumour-cell barrier (a barrier due to expression of efflux transporters in tumour cells), that together can significantly influence drug response. It then discusses the challenge of glioma as a disease of the whole brain, which lends emphasis to the need to deliver drugs effectively across the BBB to reach both the central tumour and the invasive glioma cells.

Inhibition of PI3K/mTOR pathways in glioblastoma and implications for combination therapy with temozolomide

Due to its molecular heterogeneity and infiltrative nature, glioblastoma multiforme (GBM) is notoriously resistant to traditional and experimental therapeutics. To overcome these hurdles, targeted agents have been combined with conventional therapy. We evaluated the preclinical potential of a novel, orally bioavailable PI3K/mTOR dual inhibitor (XL765) in in vitro and in vivo studies. In vivo serially passaged human GBM xenografts that are more genetically stable than GBM cell lines in culture were used for all experiments. Biochemical downstream changes were evaluated by immunoblot and cytotoxicity by colorimetric ATP-based assay. For in vivo experiments, human xenograft GBM 39 grown intracranially in nude mice was altered to express luciferase to monitor tumor burden by optical imaging. XL765 resulted in concentration-dependent decreases in cell viability in vitro. Cytotoxic doses resulted in specific inhibition of PI3K signaling. Combining XL765 with temozolomide (TMZ) resulted in additive toxicity in 4 of 5 xenografts. In vivo, XL765 administered by oral gavage resulted in greater than 12-fold reduction in median tumor bioluminescence compared with control (Mann-Whitney test p = 0.001) and improvement in median survival (logrank p = 0.05). TMZ alone showed a 30-fold decrease in median bioluminescence, but the combination XL765 + TMZ yielded a 140-fold reduction in median bioluminescence (Mann-Whitney test p = 0.05) with a trend toward improvement in median survival (logrank p = 0.09) compared with TMZ alone. XL765 shows activity as monotherapy and in combination with conventional therapeutics in a range of genetically diverse GBM xenografts.

A phase II study of gefitinib and irradiation in children with newly diagnosed brainstem gliomas: a report from the Pediatric Brain Tumor Consortium

This phase II study was designed to assess the safety and efficacy of gefitinib given with and following radiation therapy in children newly diagnosed with a poor prognosis brainstem glioma. Eligible patients were those with a previously untreated nondisseminated diffuse intrinsic brainstem glioma. Histological confirmation was not required, provided patients had a characteristic clinical history and MRI findings. Treatment consisted of gefitinib, administered orally, 250 mg/m(2)/day, during standard external beam radiotherapy, continuing for up to 13 monthly courses in the absence of disease progression or unacceptable toxicity. Toxicities, particularly intratumoral hemorrhage, were monitored. Pharmacokinetics and investigational imaging studies were performed in consenting patients. Forty-three eligible patients were included in the study. Therapy was well tolerated; only 4 patients were withdrawn from the study for dose-limiting toxicity after receiving therapy for 6, 9, 17, and 24 weeks. The 12- and 24-month progression-free survival rates were 20.9 ±5.6 % and 9.3 ±4%, respectively. Overall survival rates were 56.4 ±7.6% and 19.6 ±5.9%, respectively, which appear nominally superior to other contemporaneous Pediatric Brain Tumor Consortium trials. Three patients remain progression-free survivors with ≥36 months follow-up. The observation that a subset of children with this generally fatal tumor experienced long-term progression-free survival, coupled with recent observations regarding the molecular features of brainstem gliomas, raises the possibility that prospective molecular characterization may allow enrichment of treatment responders and improvement in outcome results in future studies of biologically targeted agents.

Enhancing radiotherapy through a greater understanding of homologous recombination

Radiotherapy for the treatment of cancer can cause a wide range of cellular effects, the most biologically potent of which is the double-strand break in DNA. The process of repairing DNA double-strand breaks involves 1 of 2 major mechanisms: nonhomologous end joining or homologous recombination. In this review, we review the molecular mechanisms of homologous recombination, in particular as it relates to the repair of DNA damage from ionizing radiation. We also present specific situations in which homologous recombination may be dysfunctional in human cancers and how this functional abnormality can be recognized. We also discuss the therapeutic opportunities that can be exploited based on deficiencies in homologous recombination at various steps in the DNA repair pathway. Side-by-side with these potential therapeutic opportunities, we review the contemporary clinical trials in which strategies to exploit these defects in homologous recombination can be enhanced by the use of radiotherapy in conjunction with biologically targeted agents. We conclude that the field of radiation oncology has only scratched the surface of a potentially highly efficacious therapeutic strategy.

Molecular markers in gliomas: impact for the clinician

Over the last decade, understanding of glioma on a molecular level has greatly expanded. However, optimal incorporation of molecular markers into clinical care is controversial. We briefly review the potential utility of molecular stratification in refining histologic diagnosis, prognosis, and treatment decisions, focussing on 1p/19q co-deletion, MGMT promoter methylation, EGFR mutations, and IDH mutation. The most recently discovered IDH mutation is a striking example of a rapid implementation of a molecular marker for prognostication into common clinical use.

Survival signalling and apoptosis resistance in glioblastomas: opportunities for targeted therapeutics

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults and one of the most aggressive cancers in man. Despite technological advances in surgical management, combined regimens of radiotherapy with new generation chemotherapy, the median survival for these patients is 14.6 months. This is largely due to a highly deregulated tumour genome with opportunistic deletion of tumour suppressor genes, amplification and/or mutational hyper-activation of receptor tyrosine kinase receptors. The net result of these genetic changes is augmented survival pathways and systematic defects in the apoptosis signalling machinery. The only randomised, controlled phase II trial conducted targeting the epidermal growth factor receptor (EGFR) signalling with the small molecule inhibitor, erlotinib, has showed no therapeutic benefit. Survival signalling and apoptosis resistance in GBMs can be viewed as two sides of the same coin. Targeting increased survival is unlikely to be efficacious without at the same time targeting apoptosis resistance. We have critically reviewed the literature regarding survival and apoptosis signalling in GBM, and highlighted experimental, preclinical and recent clinical trials attempting to target these pathways. Combined therapies simultaneously targeting apoptosis and survival signalling defects might shift the balance from tumour growth stasis to cytotoxic therapeutic responses that might be associated with greater therapeutic benefits.

Small molecule kinase inhibitors in glioblastoma: a systematic review of clinical studies

The efficacy of small-molecule kinase inhibitors has recently changed standard clinical practice for several solid cancers. Glioblastoma is a solid cancer that universally recurs and unrelentingly results in death despite maximal surgery and radiotherapy with concomitant and adjuvant temozolomide. Several clinical studies using kinase inhibitors in glioblastoma have been reported. The present study systematically reviews the efficacy, toxicity, and tissue analysis of small-molecule kinase inhibitors in adult patients with glioblastoma as reported in published clinical studies and determines which kinases have been targeted by the inhibitors used in these studies. Publications were retrieved using a MEDLINE search and by screening meeting abstracts. A total of 60 studies qualified for inclusion, of which 25 were original reports. A total of 2385 glioblastoma patients receiving kinase inhibitors could be evaluated. The study designs included 2 phase III studies and 37 phase II studies. Extracted data included radiological response, progression-free survival, overall survival, toxicity, and biomarker analysis. The main findings were that (i) efficacy of small-molecule kinase inhibitors in clinical studies with glioblastoma patients does not yet warrant a change in standard clinical practice and (ii) 6 main kinase targets for inhibitors have been evaluated in these studies: EGFR, mTOR, KDR, FLT1, PKCbeta, and PDGFR.

Molecularly targeted therapies for malignant glioma: rationale for combinatorial strategies

Median survival of patients with malignant glioma (MG) from time of diagnosis is approximately 1 year, despite surgery, irradiation and conventional chemotherapy. Improving patient outcome relies on our ability to develop more effective therapies that are directed against the unique molecular aberrations within a patient's tumor. Such molecularly targeted therapies may provide novel treatments that are more effective than conventional chemotherapeutics. Recently developed therapeutic strategies have focused on targeting several core glioma signaling pathways, including pathways mediated by growth-factors, PI3K/Akt/PTEN/mTOR, Ras/Raf/MEK/MAPK and other vital pathways. However, given the molecular diversity, heterogeneity and diverging and converging signaling pathways associated with MG, it is unlikely that any single agent will have efficacy in more than a subset of tumors. Overcoming these therapeutic barriers will require multiple agents that can simultaneously inhibit these processes, providing a rationale for combination therapies. This review summarizes the currently implemented single-agent and combination molecularly targeted therapies for MG.

Molecular strategies for the treatment of malignant glioma--genes, viruses, and vaccines

The standard treatment paradigm of surgery, radiation, and chemotherapy for malignant gliomas has only a modest effect on survival. It is well emphasized in the literature that despite aggressive multimodal therapy, most patients survive approximately 1 year after diagnosis, and less than 10% survive beyond 2 years. This dismal prognosis provides the impetus for ongoing investigations in search of improved therapeutics. Standard multimodal therapy has largely reached a plateau in terms of effectiveness, and there is now a growing body of literature on novel molecular approaches for the treatment of malignant gliomas. Gene therapy, oncolytic virotherapy, and immunotherapy are the major investigational approaches that have demonstrated promise in preclinical and early clinical studies. These new molecular technologies each have distinct advantages and limitations, and none has yet demonstrated a significant survival benefit in a phase II or III clinical trial. Molecular approaches may not lead to the discovery of a "magic bullet" for these aggressive tumors, but they may ultimately prove synergistic with more conventional approaches and lead to a broadening of the multimodal approach that is the current standard of care. This review will discuss the scientific background, therapeutic potential, and clinical limitations of these novel strategies with a focus on those that have made it to clinical trials.