Marc K. Rosenblum

An Inhibitor of Mutant IDH1 Delays Growth and Promotes Differentiation of Glioma Cells

IDHology Among the most exciting drug targets to emerge from cancer genome sequencing projects are two related metabolic enzymes, isocitrate dehydrogenases 1 and 2 (IDH1, IDH2). Mutations in the IDH1 and IDH2 genes are common in certain types of human cancer. Whether inhibition of mutant IDH activity might offer therapeutic benefits is unclear (see the Perspective by Kim and DeBerardinis). F. Wang et al. (p. 622, published online 4 April) isolated a small molecule that selectively inhibits mutant IDH2, describe the structural details of its binding to the mutant enzyme, and show that this compound suppresses the growth of patient-derived leukemia cells harboring the IDH2 mutation. Rohle et al. (p. 626, published online 4 April) show that a small molecule inhibitor of IDH1 selectively slows the growth of patient-derived brain tumor cells with the IDH1 mutation. A small molecule that inhibits a mutant enzyme in tumors slows malignant growth by inducing cancer cell differentiation. [Also see Perspective by Kim and DeBerardinis] The recent discovery of mutations in metabolic enzymes has rekindled interest in harnessing the altered metabolism of cancer cells for cancer therapy. One potential drug target is isocitrate dehydrogenase 1 (IDH1), which is mutated in multiple human cancers. Here, we examine the role of mutant IDH1 in fully transformed cells with endogenous IDH1 mutations. A selective R132H-IDH1 inhibitor (AGI-5198) identified through a high-throughput screen blocked, in a dose-dependent manner, the ability of the mutant enzyme (mIDH1) to produce R-2-hydroxyglutarate (R-2HG). Under conditions of near-complete R-2HG inhibition, the mIDH1 inhibitor induced demethylation of histone H3K9me3 and expression of genes associated with gliogenic differentiation. Blockade of mIDH1 impaired the growth of IDH1-mutant—but not IDH1–wild-type—glioma cells without appreciable changes in genome-wide DNA methylation. These data suggest that mIDH1 may promote glioma growth through mechanisms beyond its well-characterized epigenetic effects.

PI3K pathway regulates survival of cancer stem cells residing in the perivascular niche following radiation in medulloblastoma in vivo

Medulloblastomas are brain tumors that arise in the cerebellum of children and contain stem cells in a perivascular niche thought to give rise to recurrence following radiation. We used several mouse models of medulloblastomas in parallel to better understand how the critical cell types in these tumors respond to therapy. In our models, the proliferating cells in the tumor bulk undergo radiation-induced, p53-dependent apoptotic cell death. Activation of Akt signaling via PTEN loss transforms these cells to a nonproliferating extensive nodularity morphology. By contrast, the nestin-expressing perivascular stem cells survive radiation, activate PI3K/Akt pathway, undergo p53-dependent cell cycle arrest, and re-enter the cell cycle at 72 h. Furthermore, the ability of these cells to induce p53 is dependent on the presence of PTEN. These cellular characteristics are similar to human medulloblastomas. Finally, inhibition of Akt signaling sensitizes cells in the perivascular region to radiation-induced apoptosis.

International Society of Neuropathology‐Haarlem Consensus Guidelines for Nervous System Tumor Classification and Grading

Major discoveries in the biology of nervous system tumors have raised the question of how non‐histological data such as molecular information can be incorporated into the next World Health Organization (WHO) classification of central nervous system tumors. To address this question, a meeting of neuropathologists with expertise in molecular diagnosis was held in Haarlem, the Netherlands, under the sponsorship of the International Society of Neuropathology (ISN). Prior to the meeting, participants solicited input from clinical colleagues in diverse neuro‐oncological specialties. The present “white paper” catalogs the recommendations of the meeting, at which a consensus was reached that incorporation of molecular information into the next WHO classification should follow a set of provided “ISN‐Haarlem” guidelines. Salient recommendations include that (i) diagnostic entities should be defined as narrowly as possible to optimize interobserver reproducibility, clinicopathological predictions and therapeutic planning; (ii) diagnoses should be “layered” with histologic classification, WHO grade and molecular information listed below an “integrated diagnosis”; (iii) determinations should be made for each tumor entity as to whether molecular information is required, suggested or not needed for its definition; (iv) some pediatric entities should be separated from their adult counterparts; (v) input for guiding decisions regarding tumor classification should be solicited from experts in complementary disciplines of neuro‐oncology; and (iv) entity‐specific molecular testing and reporting formats should be followed in diagnostic reports. It is hoped that these guidelines will facilitate the forthcoming update of the fourth edition of the WHO classification of central nervous system tumors.

Chemotherapy without irradiation--a novel approach for newly diagnosed CNS germ cell tumors: results of an international cooperative trial. The First International Central Nervous System Germ Cell Tumor Study.

PURPOSE Radiation therapy for CNS germ cell tumors (GCT) is commonly associated with neurologic sequelae. We designed a therapeutic trial to determine whether irradiation could be avoided. PATIENTS AND METHODS Patients received four cycles of carboplatin, etoposide, and bleomycin. Those with a complete response (CR) received two further cycles; others received two cycles intensified by cyclophosphamide. RESULTS Seventy-one patients were enrolled (45 with germinoma and 26 with nongerminomatous GCT [NGGCT]). Sixty-eight were assessable for response. Thirty-nine of 68 (57%) achieved a CR within four cycles. Of 29 patients with less than a CR, 16 achieved CR with intensified chemotherapy or second surgery. Overall, 55 of 71 (78%) achieved a CR without irradiation. The CR rate was 84% for germinomas and 78% for NGGCT. With a median follow-up duration of 31 months, 28 of 71 patients were alive without relapse or progression. Thirty-five showed tumor recurrence (n = 28) or progression (n = 7) at a median of 13 months. Twenty-six of 28 patients (93%) who recurred following remission underwent successful salvage therapy. Pathology was the only variable predictive of survival. The probability of surviving 2 years was .84 for germinoma patients and .62 for NGGCT. Seven of 71 patients died of toxicity associated with study chemotherapy. CONCLUSION Forty-one percent of surviving patients and 50% of all patients were treated successfully with chemotherapy only without irradiation. Chemotherapy-only regimens for CNS GCT, although encouraging, should continue to be used only in the setting of formal clinical trials.

PATTERNS OF RELAPSE AND PROGNOSIS AFTER BEVACIZUMAB FAILURE IN RECURRENT GLIOBLASTOMA

Background: Bevacizumab has recently been approved by the US Food and Drug Administration for recurrent glioblastoma (GBM). However, patterns of relapse, prognosis, and outcome of further therapy after bevacizumab failure have not been studied systematically. Methods: We identified patients at Memorial Sloan-Kettering Cancer Center with recurrent GBM who discontinued bevacizumab because of progressive disease. Results: There were 37 patients (26 men with a median age of 54 years). The most common therapies administered concurrently with bevacizumab were irinotecan (43%) and hypofractionated reirradiation (38%). The median overall survival (OS) after progressive disease on bevacizumab was 4.5 months; 34 patients died. At the time bevacizumab was discontinued for tumor progression, 17 patients (46%) had an increase in the size of enhancement at the initial site of disease (local recurrence), 6 (16%) had a new enhancing lesion outside of the initial site of disease (multifocal), and 13 (35%) had progression of predominantly nonenhancing tumor. Factors associated with shorter OS after discontinuing bevacizumab were lower performance status and nonenhancing pattern of recurrence. Additional salvage chemotherapy after bevacizumab failure was given to 19 patients. The median progression-free survival (PFS) among these 19 patients was 2 months, the median OS was 5.2 months, and the 6-month PFS rate was 0%. Conclusions: Contrast enhanced MRI does not adequately assess disease status during bevacizumab therapy for recurrent glioblastoma (GBM). A nonenhancing tumor pattern of progression is common after treatment with bevacizumab for GBM and is correlated with worse survival. Treatments after bevacizumab failure provide only transient tumor control.

Selective expression of Purkinje-cell antigens in tumor tissue from patients with paraneoplastic cerebellar degeneration.

Abstract Paraneoplastic cerebellar degeneration is a rare syndrome that occurs in patients with gynecologic cancer and is characterized by widespread loss of Purkinje cells. To determine whether Purkinje-cell antigens are selectively expressed in the tumors of patients with the syndrome, we examined tumor tissue from 10 patients whose serum contained anti—Purkinje-cell (anti-Yo) antibodies. The origins of the cancers were the breast (five patients), ovary (three), endometrium (one), and fallopian tube (one). We used as controls tumor tissue from 11 patients with ovarian cancer and 10 patients with breast cancer who were neurologically normal. Using immunohistochemical and Western blot analysis, we found that Purkinje-cell antigens were expressed in all the tumors from the 10 patients with paraneoplastic cerebellar degeneration but in none of the tumors from the 21 neurologically normal patients. When IgG from patients with paraneoplastic cerebellar degeneration was affinity-purified to cerebellar Purkinje...

Autoantibodies in paraneoplastic syndromes associated with small‐cell lung cancer

An antineuronal autoantibody has been identified in serum from 14 patients, 8 women and 6 men, with small-cell lung carcinoma (SCLC) and a neurologic disorder. Neurologic symptoms began prior to diagnosis of the SCLC in 12 patients. The dominant neurologic disorder was a subacute sensory neuronopathy (SSN) in eight patients, SSN plus lower motor neuron weakness (2 patients), SSN plus autonomic neuropathy (1 patient), cerebellar ataxia (1 patient), myelopathy (1 patient), and multifocal nervous system disease (encephalomyelitis) in one patient. The presence of the same autoantibody in patients with SSN, encephalomyelitis, and autonomic neuropathy suggests that these diseases are different manifestations of the same nosologic process. With one exception, treatment of the tumor, immunosuppressive drugs, and plasmapheresis did not influence the course of the neurologic illness. The autoantibody was not identified in sera from more than 400 controls subjects, including patients with SSN associated with other tumors, SSN without malignancy, other paraneoplastic syndromes, and SCLC without neurologic symptoms. The autoantibody is a highly specific marker of the paraneoplastic syndromes associated with SCLC and its detection in a patient not known to have cancer should prompt a careful search for SCLC.

Intensive chemotherapy and bone marrow rescue for young children with newly diagnosed malignant brain tumors.

PURPOSE To evaluate a strategy that avoids radiotherapy in children less than 6 years of age with newly diagnosed malignant brain tumors, by administering myeloablative consolidation chemotherapy with autologous bone marrow reconstitution (ABMR) after maximal surgical resection and conventional induction chemotherapy. PATIENTS AND METHODS Between March 1991 and April 1995, 62 children (median age, 30 months) with newly diagnosed malignant brain tumors were enrolled onto this trial. Children received conventional induction chemotherapy with vincristine, cisplatin, cyclophosphamide, and etoposide, repeated every 3 weeks for five cycles. Children without disease progression on induction chemotherapy were offered consolidation with myeloablative chemotherapy that incorporated carboplatin, thiotepa, and etoposide followed by ABMR. Irradiation was used only for residual tumor at consolidation or for progressive/recurrent disease. RESULTS Induction chemotherapy was well tolerated by most patients; however, progression was noted in 17 children (27%) and four (6%) died of treatment complications. Of 37 children who received consolidation chemotherapy with ABMR, 15 are free of disease progression (median post-ABMR without further treatment, >44 months). The remaining 22 all progressed within 15 months of ABMR; three of 37 (8%) died of treatment-related complications. The 3-year overall survival (OS) and event-free survival (EFS) rates from diagnosis for all children are 40% (95% confidence interval [CI], 28% to 52%) and 25% (95% CI, 13% to 37%), respectively. Radiotherapy was administered to 19 of 62 children: 17 for progressive disease (PD) and two for residual disease at the time of ABMR. CONCLUSION A significant proportion of children with malignant brain tumors can avoid radiotherapy and prolonged maintenance chemotherapy yet still achieve durable remission with this brief intensive chemotherapy regimen.

Dose-Dependent Effects of Platelet-Derived Growth Factor-B on Glial Tumorigenesis

Platelet-derived growth factor (PDGF) is expressed in many different tumors, but its precise roles in tumorigenesis remain to be fully defined. Here, we report on a mouse model that demonstrates dose-dependent effects of PDGF-B on glial tumorigenesis. By removing inhibitory regulatory elements in the PDGFB mRNA, we are able to substantially elevate its expression in tumor cells using a retroviral delivery system. This elevation in PDGF-B production results in tumors with shortened latency, increased cellularity, regions of necrosis, and general high-grade character. In addition, elevated PDGF-B in these tumors also mediates vascular smooth muscle cell recruitment that supports tumor angiogenesis. PDGF receptor (PDGFR) signaling appears to be required for the maintenance of these high-grade characteristics, because treatment of high-grade tumors with a small molecule inhibitor of PDGFR results in reversion to a lower grade tumor histology. Our data show that PDGFR signaling quantitatively regulates tumor grade and is required to sustain high-grade oligodendrogliomas.

Detection of the anti‐Hu antibody in specific regions of the nervous system and tumor from patients with paraneoplastic encephalomyelitis/sensory neuronopathy

We studied the nervous systems and tumors of five patients with anti-Hu-positive paraneoplastic encephalomyelitis/sensory neuronopathy (PEM/PSN) to determine if the autoantibody found in the serum and CSF was also present in those tissues. Immunohistochemical studies of the nervous system revealed the presence of IgG bound predominantly to the nuclei of most of the neurons and the cytoplasm of some glial cells. IgG was also present to a lesser degree in the neuropil. In brains of patients who died of cancer without the paraneoplastic syndrome, IgG was present in the immediate perivascular areas and to a very limited degree in the neuropil. There was no IgG in neurons, and in only some of the controls a few glial cells showed IgG immunoreactivity in the cytoplasm. The amount of anti-Hu IgG relative to total IgG in various brain regions and tumor was determined by quantitative Western blot analysis. The proportion of anti-Hu IgG was greater in some areas of the brain and tumor than in serum and CSF. Control brains did not contain anti-Hu IgG. There was a limited correlation among (1) the principal clinical symptoms, (2) regions of major tissue injury, and (3) the quantitative anti-Hu IgG distribution. We conclude that although the role of the antibody in the pathogenesis of the disease is still uncertain, its specific localization in the nervous system and tumor suggests an immunologic etiology of this paraneoplastic syndrome.