Phase II study of imatinib mesylate plus hydroxyurea in adults with recurrent glioblastoma multiforme

PIK3CA alterations in primary (de novo) and secondary glioblastomas

We assessed alterations in the EGFR/PTEN/PI3K pathway in 107 primary (de novo) glioblastomas and 32 secondary glioblastomas that progressed from low-grade or anaplastic astrocytomas. SSCP followed by DNA sequencing in exons 9 and 20 of the PIK3CA gene revealed missense mutations in 5/107 (5%) primary and 1/32 (3%) secondary glioblastomas. Quantitative real-time PCR showed PIK3CA amplification (>3 copy numbers) in 14/107 (13%) primary and 3/32 (9%) secondary glioblastomas. Only one glioblastoma showed both PIK3CA mutation and amplification. Taken together with previously published data on EGFR amplification and PTEN mutations, at least one alteration in the EGFR, PTEN, or PIK3CA genes was detected in 63% of primary glioblastomas, which was significantly more frequent than in secondary glioblastomas (31%; P < 0.001). Furthermore, this signaling pathway was altered by either PTEN mutations or PIK3CA amplification in 10 of 12 (83%) malignant glioma cell lines analyzed. These results suggest that the EGFR/PTEN/PI3K pathway is frequently altered in glioblastomas and is a promising target for therapy, in particular for primary glioblastomas.

Therapeutic advances for glioblastoma multiforme: current status and future prospects

Glioblastoma multiforme (GBM) is the most common central nervous system malignancy. It is rapidly progressive with rare opportunity for cure. After three decades of laboratory and clinical research, a newly evolved chemoradiotherapy approach using the alkylating agent temozolomide during and after radiotherapy has resulted in the first significant impact on this disease. Here we discuss the basis for this positive interaction as well as potential mechanisms of resistance to it. Additionally, in the context of current and planned research, we explore approaches to take advantage of this combination and the use of targeted therapies to exploit cell signaling alterations found in GBM. We anticipate that a multimodality approach directed at tumor-specific biology will result in more meaningful advancements in the treatment of this fatal disease.

Glioma therapy in adults

BACKGROUND

Gliomas are the most common type of primary brain tumor. Nearly two-thirds of gliomas are highly malignant lesions that account for a disproportionate share of brain tumor-related morbidity and mortality. Despite recent advances, two-year survival for glioblastoma with optimal therapy is less than 30%. Even among patients with low-grade gliomas that confer a relatively good prognosis, treatment is almost never curative.

REVIEW SUMMARY

Surgery and radiation have been the mainstays of therapy for most glioma patients, but temozolomide chemotherapy has recently been proven to prolong overall survival in patients with glioblastoma. Intriguing data suggests that activity of O6-methylguanine-DNA methyltransferase (MGMT), in tumor cells may predict responsiveness to temozolomide and other alkylating agents. Novel treatment approaches, especially targeted molecular therapies against critical components of glioma signaling pathways, appear promising in preliminary studies. Optimal treatment for patients with low-grade gliomas has yet to be determined. Advances in oligodendroglioma biology have identified loss of chromosomes 1p and 19q as powerful indicators of a favorable prognosis. These same changes may predict response to chemotherapy.

CONCLUSIONS

Though the prognosis for many patients with gliomas is poor, the last decade produced a number of important advances, some of which have translated directly into survival benefits. Rapid progress in the field of glioma molecular biology continues to identify therapeutic targets and provide hope for the future of this challenging disease.

Recurrent glioblastoma multiforme: advances in treatment and promising drug candidates

Recurrent glioblastoma multiforme is a lethal disease with currently available treatment options having a limited impact on outcome. In this article, current and novel therapeutic approaches in the treatment of recurrent glioblastoma multiforme, including chemotherapy, targeted molecular agents, virotherapy/gene therapy and immunotherapy and challenges in developing novel therapeutic agents for glioblastoma multiforme will be discussed.

Glioma oncogenesis and animal models of glioma formation

Recent advances in animal models have improved our understanding of the pathway abnormalities driving glioma growth. This article reviews key molecular abnormalities that have been modeled in mice, and describes major tumor modeling techniques along with examples of astrocytoma and oligodendroglioma models. Animal models are important not only for the testing of novel therapeutics but also as a means to understand the molecular explanations for treatment success and failure in humans.

Phase II study of imatinib mesylate and hydroxyurea for recurrent grade III malignant gliomas

PURPOSE

Recent reports demonstrate the activity of imatinib mesylate, an ATP-mimetic, tyrosine kinase inhibitor, plus hydroxyurea, a ribonucleotide reductase inhibitor, in patients with recurrent glioblastoma multiforme. We performed the current phase 2 study to evaluate this regimen among patients with recurrent WHO grade III malignant glioma (MG).

PATIENTS AND METHOD

Patients with grade III MG at any recurrence, received imatinib mesylate plus hydroxyurea (500 mg twice a day) orally on a continuous, daily schedule. The imatinib mesylate dose was 500 mg twice a day for patients on enzyme inducing anti-epileptic drugs (EIAEDs) and 400 mg once a day for those not on EIAEDs. Clinical assessments were performed monthly and radiographic assessments were obtained at least every 2 months. The primary endpoint was 6-month progression-free survival (PFS) rate.

RESULTS

Thirty-nine patients were enrolled. All patients had progressive disease after prior radiotherapy and at least temozolomide-based chemotherapy. The median number of episodes of prior progression was 2 (range, 1-7) and the median number of prior treatment regimens was 3 (range, 1-8). With a median follow-up of 82.9 weeks, 24% of patients were progression-free at 6 months. The radiographic response rate was 10%, while 33% achieved stable disease. Among patients who achieved at least stable disease at first evaluation, the 6-month and 12-month PFS rates were 53% and 29%, respectively. The most common grade 3 or greater toxicities were hematologic and complicated less than 4% of administered courses.

CONCLUSION

Imatinib mesylate plus hydroxyurea, is well tolerated and associated with anti-tumor activity in some patients with recurrent grade 3 MG.

Predictive and prognostic markers in human glioblastomas

Glioblastomas (GBMs) are among the most aggressive of all known human tumors. The median survival times remain in the 12- to 15-month range despite aggressive surgery, radiation, and chemotherapy. Through molecular and genetic profiling efforts, underlying mechanisms of resistance to these therapies are becoming better understood. The present standard of care has been shaped by the recently reported phase III study by the European Organisation for Research and Treatment of Cancer and the National Cancer Institute of Canada, which found that the addition of temozolomide (TMZ) to radiation therapy significantly improved outcome compared with radiation alone. However, careful examination of these data reveals that not all GBM patients benefited from the addition of TMZ to radiation therapy. A companion correlative study found that GBM patients with tumors with MGMT promoter methylation appeared to derive the greatest benefit from the addition of TMZ to radiation therapy. Although this finding is provocative, it should be kept in mind that this study was performed retrospectively and that prospective validation is required before MGMT methylation can be used for clinical stratification purposes. However, this study does show promise for the tailoring of future treatments according to the molecular and genetic profiles of an individual's tumor rather than using the "one-glove-fits-all" approach that is currently being followed. As more effective "smart drugs" are developed, molecular and genetic profiling will assume even greater importance in this regard.

PDGF Receptors as Targets in Tumor Treatment

Signaling through platelet-derived growth factor (PDGF) receptors contributes to multiple tumor-associated processes. The recent introduction of clinically useful PDGF inhibitors have the last years validated PDGF receptors in malignant and stromal cells as relevant cancer drug targets. Mutational activation of PDGF receptor signaling in malignant cells has been described in some rare tumor types such as dermatofibrosarcoma protuberans, a subset of GISTs, and some hematologic malignancies. Furthermore, expression of PDGF receptors on pericytes is a common characteristic of solid tumors. The clinical efficacy of novel multikinase inhibitors, such as sunitinib and sorafenib, most likely involves targeting of PDGF receptor-dependent pericytes. Preclinical studies suggest that targeting of stromal PDGF receptors might also constitute a novel strategy to enhance tumor drug uptake. Finally, recent studies have implied both pro- and antimetastatic effects of PDGF receptors on malignant and stromal cells. The studies on the roles of PDGF receptors in cancer signaling are thus presently in a dynamic phase where collaborations between oncologists, pathologists, and tumor biologists are predicted to be highly productive.

The effect of hydroxyurea on P-glycoprotein/BCRP-mediated transport and CYP3A metabolism of imatinib mesylate

PURPOSE

It has been reported that the combination therapy of imatinib mesylate, a tyrosine kinase inhibitor, plus hydroxyurea, a ribonucleotide reductase inhibitor, is associated with remarkable antitumor activity in patients with recurrent glioblastoma multiforme. However, the mechanism of the added activity of hydroxyurea to imatinib is not known. The purpose of this study was to investigate in vitro, whether hydroxyurea could enhance the central nervous system penetration of imatinib, by inhibition of the ATP-dependent transporter proteins P-glycoprotein (ABCB1; MDR1; Pgp) and Breast Cancer Resistance Protein (ABCG2; BCRP), or by inhibition of cytochrome P450 3A (CYP3A) metabolism of imatinib.

METHODS

The effect of hydroxyurea on the Pgp and BCRP mediated transport of imatinib was investigated by the sulforhodamine-B (SRB) drug cytotoxicity assay and transepithelial transport assay. In vitro biotransformation studies with supersomes expressing human CYP3A4 were performed to investigate whether hydroxyurea inhibited CYP3A4.

RESULTS

In both in vitro cytotoxicity and transport assays, hydroxyurea did not affect Pgp and BCRP mediated transport of imatinib. In a biotransformation assay, hydroxyurea had no influence on the metabolic degradation of imatinib either.

CONCLUSION

The results indicate that hydroxyurea does not interact with imatinib by inhibition of Pgp and BCRP mediated transport or by CYP3A4 mediated metabolism of imatinib.

New approaches to primary brain tumor treatment

Primary brain tumors represent over 100 different tumor types with widely divergent biologies and clinical outcomes, but these neoplasms frequently pose similar challenges to neuro-oncologists. Malignant gliomas are the most common type of primary intrinsic brain tumor in adults and remain extremely lethal. Current standard-of-care therapies for these cancers include surgery, radiation and palliative cytotoxics, which have significant side-effects and limited efficacy. Advances in our understanding of the molecular underpinnings of cancer have led to targeted molecular therapies that may permit improvement in therapeutic efficacy and reduced toxicity; these therapies, however, still face many challenges. Signal transduction pathways that are inappropriately regulated in brain cancers include growth factors and their receptors (e.g. epidermal growth factor receptor, vascular endothelial growth factor receptor and platelet-derived growth factor receptor), which regulate cellular interactions with the microenvironment and intracellular oncogenic pathways. Low-molecular-weight inhibitors have been developed to target many kinases and may have advantages in terms of delivery. Monoclonal antibodies may have greater specificity, but face delivery restrictions. Preferential tumor delivery of chemotherapies, conjugated toxins and radioisotopes has been achieved through convection-enhanced delivery, intratumoral implants and intra-arterial infusion. Despite these advances, few molecularly targeted therapies have demonstrated significant antineoplastic activity for a broad range of patients, possibly due to tumor and patient heterogeneity. Improved functional neuropathology and imaging may permit identification of patient subgroups for which clinical responses may be enriched. It is probable, however, that targeted therapies will be most effective in combination either with one another or with cytotoxic therapies. In this study, we review the current state of new therapies for malignant gliomas.

Amplification of KIT, PDGFRA, VEGFR2, and EGFR in gliomas

Receptor tyrosine kinase aberrations are implicated in the genesis of gliomas. We investigated expression and amplification of KIT, PDGFRA, VEGFR2, and EGFR in 87 gliomas consisting of astrocytomas, anaplastic astrocytomas, oligodendrogliomas, or oligoastrocytomas in tumor samples collected at the time of the diagnosis and in samples of the same tumors at tumor recurrence. Gene amplifications were investigated using either chromogenic in situ hybridization or fluorescence in situ hybridization, and protein expression using immunohistochemistry. In samples collected at glioma diagnosis, KIT and PDGFRA amplifications were more frequent in anaplastic astrocytomas than in astrocytomas, oligodendrogliomas, and oligoastrocytomas [28% versus 5% (P = 0.012) and 33% versus 2% (P = 0.0008), respectively]. VEGFR2 amplifications occurred in 6% to 17% of the gliomas at diagnosis, and EGFR amplifications in 0% to 12%. Amplified KIT was more frequently present in recurrent gliomas than in newly diagnosed gliomas (P = 0.0066). KIT amplification was associated with KIT protein expression and with presence of PDGFRA and EGFR amplifications both at the time of the first glioma diagnosis and at tumor recurrence, and with VEGFR2 amplification at tumor recurrence. Three (4%) primary gliomas and 10 (14%) recurrent gliomas that were evaluable for coamplification of KIT, PDGFRA, and VEGFR2 showed amplification of at least two of these genes; the amplicon contained amplified KIT in all 13 cases. In conclusion, besides glioblastoma, amplified KIT, PDGFRA, and VEGFR may also occur in lower-grade gliomas and in their recurrent tumors. It is currently not known whether specific tyrosine kinase inhibitors are effective in the treatment of such gliomas.

Small molecule tyrosine kinase inhibitors in the treatment of solid tumors: an update of recent developments

Small molecule tyrosine kinase inhibitors (TKIs) are developed to block intracellular signaling pathways in tumor cells, leading to deregulation of key cell functions such as proliferation and differentiation. Over 25 years ago, tyrosine kinases were found to function as oncogenes in animal carcinogenesis; however, only recently TKIs were introduced as anti cancer drugs in human cancer treatment. Tyrosine kinase inhibitors have numerous good qualities. First, in many tumor types they tend to stabilize tumor progression and may create a chronic disease state which is no longer immediately life threatening. Second, side effects are minimal when compared to conventional chemotherapeutic agents. Third, synergistic effects are seen in vitro when TKIs are combined with radiotherapy and/or conventional chemotherapeutic agents. In this article, we will give an update of the tyrosine kinase inhibitors that are currently registered for use or in an advanced stage of development, and we will discuss the future role of TKIs in the treatment of solid tumors. The following TKIs are reviewed: Imatinib (Gleevec/Glivec), Gefitinib (Iressa), Erlotinib (OSI-774, Tarceva), Lapatinib (GW-572016, Tykerb), Canertinib (CI-1033), Sunitinib (SU 11248, Sutent), Zactima (ZD6474), Vatalanib (PTK787/ZK 222584), Sorafenib (Bay 43-9006, Nexavar), and Leflunomide (SU101, Arava).

Molecular therapies for malignant glioma

Due to the dismal prognosis of malignant glioma with currently available therapies there is an urgent need for new treatments based on a better molecular understanding of gliomagenesis. Several concepts of molecular therapies for malignant glioma are currently being studied in preclinical and clinical settings, including small molecules targeting specific receptor-mediated signaling pathways and gene therapy. Many growth factors, growth factor receptors--usually receptor tyrosine kinases--and receptor-associated signaling pathways are critically involved in gliomagenesis. Numerous selective inhibitors, which specifically block such molecules, are currently evaluated for clinical applicability. Several gene therapy approaches have shown antitumor efficacy in experimental studies, and the first clinical trials for the treatment of malignant glioma were conducted in the 1990s. In clinical trials, retroviral herpes-simplex-thymidinkinase- (HSV-Tk-) gene therapy has been the pioneering and most commonly used approach. However, efficient gene delivery into the tumor cells still remains the crucial obstacle for successful clinical gene therapy. During the past few years a number of new gene transfer vectors based on adeno-, adeno-associated-, herpes- and lentiviruses as well as new carrier cell systems, including neural and endothelial progenitor cells, have been developed. In addition, antisense technologies have advanced in recent years and entered clinical testing utilizing intratumoral administration by convection-enhanced delivery, exemplified by ongoing clinical trials of intratumoral administration of antisense TGF-beta. This paper summarizes some of these recent developments in molecular therapies for malignant glioma, focusing on targeted therapies using selective small molecules and gene therapy concepts.

Recent advances in the medical therapy of high-grade gliomas

Malignant glial neoplasms, including glioblastoma, are amongst the most devastating and intractable of solid tumors. Until recently the standard of care for newly diagnosed glioblastoma was surgical resection to the extent feasible followed by conventional fractionated radiotherapy. When administered for disease progression, chemotherapy had modest benefit and its use in the adjuvant setting was controversial. Temozolomide, an oral alkylating chemotherapeutic agent, has now been demonstrated to increase survival time in patients with newly diagnosed glioblastoma when used concurrently with radiotherapy and as adjuvant or maintenance treatment for six cycles thereafter. Correlative molecular studies suggested that the benefit of temozolomide is largely restricted to patients whose tumor has silenced the gene for methylguanine methyltransferase, a repair enzyme implicated in resistance to alkylator chemotherapy. Use of temozolomide chemotherapy upfront in the management of glioblastoma is now considered the standard of care. This significant advance has also stimulated development of therapeutic strategies that incorporate temozolomide, and other agents, in the initial management of most high-grade gliomas. Furthermore, our increased understanding of the molecular derangements that underlie gliomagenesis has identified a number of putative molecular targets against which novel therapeutics have been tested with encouraging preliminary results. Finally, the challenges presented by the blood–brain barrier to adequate drug delivery have stimulated the development of unique locoregional delivery techniques that are currently undergoing clinical evaluation. This review summarizes these recent advances, and speculates on how the field is likely to evolve in the near future.

Signal transduction pathways as novel therapeutic targets in malignant glioma

Malignant gliomas are the most common primary brain tumors in adults. Current therapies, including surgery, radiation and chemotherapy, are generally palliative and rarely offer long-term survival. Novel therapies targeting the underlying pathogenesis are urgently required. Despite the genetic and pathological heterogeneities of malignant gliomas, common signaling pathways that drive cellular proliferation, survival, invasion and angiogenesis have been identified. Growth factor ligands and their cognate receptor tyrosine kinases, such as epidermal, vascular endothelial and platelet-derived growth factor receptor, are inappropriately activated frequently in human brain tumors and contribute to tumor malignancy. Growth factor receptor activity is mediated in part by intracellular oncogenic pathways regulating proliferation and survival: the RAS and phosphoinositide 3-OH kinase pathways. Other critical contributors to brain-tumor development and growth involve angiogenesis and invasion, which are regulated by several signaling pathways. Based on the recognition of aberrant signal transduction in tumor biology, several therapeutic agents targeting the activities of signaling elements are under development to target cancer cells and tumor-associated vasculature, prominently growth factor receptors and intracellular effectors. Monoclonal antibodies directed against growth factor ligands or receptors exhibit great specificity but may face delivery limitations. Low-molecular-weight inhibitors of receptor kinases or intracellular effectors may demonstrate improved intratumoral delivery, but have had limited efficacy as monotherapy in clinical trials. Biomarkers to predict tumor sensitivity to targeted therapies, or confirm activity of these agents (pharmacodynamics), are under parallel development. Current targeted-therapy approaches involve a combination of these therapies with one another, or with chemotherapy or radiotherapy. Targeting specific pathway(s) in each patient, based on molecular signatures within the tumor, may represent a new horizon in the treatment of malignant gliomas.

Blood-brain barrier and chemotherapeutic treatment of brain tumors

The blood-brain barrier (BBB) is of pivotal importance to maintain homeostasis of the CNS, as it closely regulates the composition of the interstitial fluid in the brain. Unfortunately, malignancies that grow within the CNS may evade chemotherapeutic drugs using the same barrier, making this disease refractory to most chemotherapy regimens. This review will outline the impact of the BBB in brain cancer and discuss the efforts that have been made to enhance the drug exposure of brain tumors. Although this review will focus on the role of the BBB in primary brain cancer (malignant glioma), its impact on brain metastases will also be briefly discussed.

Influence of hydroxyurea on imatinib mesylate (gleevec) transport at the mouse blood-brain barrier

The combination of imatinib mesylate and hydroxyurea provides a therapeutic benefit in patients with glioblastoma, although each drug is not effective when used alone. The increase of brain delivery of one or both drugs has been suggested to be a potential cause of this therapeutic benefit. The cross-influence of hydroxyurea and imatinib on their respective brain distribution was examined in mice and rats. We used in situ brain perfusion in mice to determine whether these two drugs have an influence on their respective initial transport across the blood-brain barrier. The brain penetration of hydroxyurea, assessed by its brain uptake clearance, Knet, was low in mice (approximately 0.10 microl/g/s) and not modified by coperfusion of imatinib (0.5-500 microM). Likewise, the brain penetration of imatinib was low (Knet, 1.39 +/- 0.17 microl/g/s) and not modified by direct coperfusion of hydroxyurea (0.2-1000 microM) or by intravenous pretreatment with 15 or 1000 mg/kg hydroxyurea. We also examined a potential time-dependent influence of hydroxyurea on imatinib brain distribution after sustained subcutaneous administration in rats using an implantable osmotic pump. The brain penetration of imatinib in rats increased with time, approximately 1.6-fold (p < 0.01) after 7 and 14 days' infusion of imatinib (3 mg/day) with or without hydroxyurea (15 mg/day), and was not influenced by hydroxyurea. The results of these two sets of experiments indicate that hydroxyurea has no significant influence on the brain distribution of imatinib in mice and rats.

Phase I/II Study of Imatinib Mesylate for Recurrent Malignant Gliomas: North American Brain Tumor Consortium Study 99-08

PURPOSE

Phase I: To determine the maximum tolerated doses, toxicities, and pharmacokinetics of imatinib mesylate (Gleevec) in patients with malignant gliomas taking enzyme-inducing antiepileptic drugs (EIAED) or not taking EIAED. Phase II: To determine the therapeutic efficacy of imatinib.

EXPERIMENTAL DESIGN

Phase I component used an interpatient dose escalation scheme. End points of the phase II component were 6-month progression-free survival and response.

RESULTS

Fifty patients enrolled in the phase I component (27 EIAED and 23 non-EIAED). The maximum tolerated dose for non-EIAED patients was 800 mg/d. Dose-limiting toxicities were neutropenia, rash, and elevated alanine aminotransferase. EIAED patients received up to 1,200 mg/d imatinib without developing dose-limiting toxicity. Plasma exposure of imatinib was reduced by approximately 68% in EIAED patients compared with non-EIAED patients. Fifty-five non-EIAED patients (34 glioblastoma multiforme and 21 anaplastic glioma) enrolled in the phase II component. Patients initially received 800 mg/d imatinib; 15 anaplastic glioma patients received 600 mg/d after hemorrhages were observed. There were 2 partial response and 6 stable disease among glioblastoma multiforme patients and 0 partial response and 5 stable disease among anaplastic glioma patients. Six-month progression-free survival was 3% for glioblastoma multiforme and 10% for anaplastic glioma patients. Five phase II patients developed intratumoral hemorrhages.

CONCLUSIONS

Single-agent imatinib has minimal activity in malignant gliomas. CYP3A4 inducers, such as EIAEDs, substantially decreased plasma exposure of imatinib and should be avoided in patients receiving imatinib for chronic myelogenous leukemia and gastrointestinal stromal tumors. The evaluation of the activity of combination regimens incorporating imatinib is under way in phase II trials.

The neurobiology of neurooncology

The histological classification of brain tumors currently is based on the morphological appearance and protein expression patterns that reflect specific cell types within the central nervous system. Recent studies have suggested that the cells of origin for brain tumors may persist in the fully formed tumors, and that these "cancer stem cells" might represent the relevant cellular targets for anticancer therapy. In this regard, insights into the developmental neurobiology of brain tumors has significant impact on our understanding of the molecular and cellular pathogenesis of these devastating cancers, as well as the development of new strategies for treating brain tumors.

Drug development in oncology: classical cytotoxics and molecularly targeted agents

There is an apparent need to improve the speed and efficiency of oncological drug development. Furthermore, strategies traditionally applied to the development of standard cytotoxic chemotherapy may not be appropriate for molecularly targeted agents. This is particularly the case for exploratory Phase 1 and 2 trials. Conventional approaches to determine dose based on maximum tolerability and efficacy based on objective tumour response may not be suitable for targeted agents, since many of them have a wide therapeutic index and inhibit tumour growth without demonstrable cytotoxicity. Instead, exploratory trials of targeted agents may have to focus on other end-points such as pharmacological effects and disease stabilization. Thus, there is an increasing interest in making the best possible use of biomarkers and pharmacogenomics in early phases of drug development.

Chemotherapy in the treatment of malignant gliomas

Malignant gliomas are one of the most difficult tumors to treat, with only modest advances being made in the past few decades. Surgery and radiation have had the greatest impact, increasing survival. Chemotherapy modestly increases survival. The use of chemotherapy in the treatment of malignant gliomas is the focus of this paper and the more commonly used agents at diagnosis and relapse are reviewed. Since most patients fail first-, second- and even third-line agents that are commercially available, some of the more relevant new biological compounds will also be discussed. As treatments for brain tumors evolve, it is likely that optimal therapies will come from combination therapies that incorporate target-specific and chemotherapeutic agents.

Treatment options for glioblastoma

Following the seminal trial conducted by the European Organisation for Research and Treatment of Cancer (EORTC) and the National Cancer Institute of Canada (NCIC), concurrent temozolomide and radiotherapy has become the new standard of care for patients with newly diagnosed glioblastoma multiforme (GBM). Investigation of emerging therapies (which are now used as salvage therapy) such as small-molecule inhibitors (for example, epidermal growth factor receptor inhibitors) and convection-enhanced delivery (CED) of targeted toxins (for example, interleukin-13/pseudomonas exotoxin) is likely to build on the EORTC/NCIC treatment platform and will, it is hoped, improve survival rates in patients with GBM. The majority of adjuvant Phase I and II trials being conducted by the brain tumor consortia are based on the EORTC/NCIC treatment platform and have added a targeted therapy in an effort to find a promising synergistic treatment. Furthermore, researchers in the consortia are continuing to explore treatments for recurrent GBM, not otherwise eligible for local therapies, such as CED. The treatments under study include novel cytotoxic chemotherapy as well as small-molecule inhibitors; these are being assessed in a variety of Phase I or II trials.

Characterization of an imatinib-sensitive subset of high-grade human glioma cultures

High-grade gliomas, including glioblastomas, are malignant brain tumors for which improved treatment is urgently needed. Genetic studies have demonstrated the existence of biologically distinct subsets. Preliminary studies have indicated that platelet-derived growth factor (PDGF) receptor signaling contributes to the growth of some of these tumors. In this study, human high-grade glioma primary cultures were analysed for sensitivity to treatment with the PDGF receptor inhibitor imatinib/Glivec/Gleevec/STI571. Six out of 15 cultures displayed more than 40% growth inhibition after imatinib treatment, whereas seven cultures showed less than 20% growth inhibition. In the sensitive cultures, apoptosis contributed to growth inhibition. Platelet-derived growth factor receptor status correlated with imatinib sensitivity. Supervised analyses of gene expression profiles and real-time PCR analyses identified expression of the chemokine CXCL12/SDF-1 (stromal cell-derived factor 1) as a predictor of imatinib sensitivity. Exogenous addition of CXCL12 to imatinib-insensitive cultures conferred some imatinib sensitivity. Finally, coregulation of CXCL12 and PDGF alpha-receptor was observed in glioblastoma biopsies. We have thus defined the characteristics of a novel imatinib-sensitive subset of glioma cultures, and provided evidence for a functional relationship between imatinib sensitivity and chemokine signaling. These findings will assist in the design and evaluation of clinical trials exploring therapeutic effects of imatinib on malignant brain tumors.

Recent advances in the treatment of malignant astrocytoma

Malignant gliomas, including the most common subtype, glioblastoma multiforme (GBM), are among the most devastating of neoplasms. Their aggressive infiltration in the CNS typically produces progressive and profound disability--ultimately leading to death in nearly all cases. Improvement in outcome has been elusive despite decades of intensive clinical and laboratory research. Surgery and radiotherapy, the traditional cornerstones of therapy, provide palliative benefit, while the value of chemotherapy has been marginal and controversial. Limited delivery and tumor heterogeneity are two fundamental factors that have critically hindered therapeutic progress. A novel chemoradiotherapy approach, consisting of temozolomide administered concurrently during radiotherapy followed by adjuvant systemic temozolomide, has recently demonstrated a meaningful, albeit modest, improvement in overall survival for newly diagnosed GBM patients. As cell-signaling alterations linked to the development and progression of gliomas are being increasingly elucidated, targeted therapies have rapidly entered preclinical and clinical evaluation. Responses to therapies that function via DNA damage have been associated with specific mediators of resistance that may also be subject to targeted therapies. Other approaches include novel locoregional delivery techniques to overcome barriers of delivery. The simultaneous development of multiple advanced therapies based on specific tumor biology may finally offer glioma patients improved survival.

Changing Paradigms—An Update on the Multidisciplinary Management of Malignant Glioma

Treatment of malignant glioma requires a multidisciplinary team. Treatment includes surgery, radiotherapy, and chemotherapy. Recently developed agents have demonstrated activity against recurrent malignant glioma and efficacy if given concurrently with radiotherapy in the upfront setting. Oligodendroglioma with 1p/19q deletions has been recognized as a distinct pathologic entity with particular sensitivity to radiotherapy and chemotherapy. Randomized trials have shown that early neoadjuvant or adjuvant administration of procarbazine, lomustine, and vincristine chemotherapy prolongs disease-free survival; however, it has no impact on overall survival. Temozolomide, a novel alkylating agent, has shown modest activity against recurrent glioma. In combination with radiotherapy in newly diagnosed patients with glioblastoma, temozolomide significantly prolongs survival. Molecular studies have demonstrated that the benefit is mainly observed in patients whose tumors have a methylated methylguanine methyltransferase gene promoter and are thus unable to repair some of the chemotherapy-induced DNA damage. For lower-grade glioma, the use of chemotherapy remains limited to recurrent disease, and first-line administration is the subject of ongoing clinical trials. Irinotecan and agents like gefitinib, erlotinib, and imatinib targeting the epidermal growth factor receptor and platelet-derived growth factor receptor have shown some promise in recurrent malignant glioma. This review summarizes recent developments, focusing on the clinical management of patients in daily neuro-oncology practice.