DNAR-08. THE ROLE OF SMARCAL1 AS A SYNTHETIC LETHAL VULNERABILITY IN ATRX-DEFICIENT GLIOMAS

Mechanisms to maintain telomere length over successive cell divisions are a requirement for cancer cell immortalization. Although many cancers maintain telomere length through the activation of telomerase, ~10-15% of human cancers use telomerase-independent mechanisms of telomere maintenance, termed Alternative Lengthening of Telomeres (ALT). In gliomas, the ALT phenotype is associated with loss-of-function mutations in the ATRX gene in IDH-mutant astrocytomas, adult and pediatric glioblastomas (GBM), high-grade astrocytomas with piloid features, and pleomorphic xanthoastrocytomas. In adult GBM, we previously identified a relatively rare subset of ALT-positive ATRX wildtype tumors that harbored loss-of-function mutations in the SMARCAL1 gene, and we found that loss of SMARCAL1 activity plays a causative role in the onset of ALT in these tumors. SMARCAL1 is an annealing helicase that localizes to sites of DNA damage and replication stress and catalyzes the reversal of stalled replication forks. To better understand the relationship between ATRX mutations, SMARCAL1 activity, and the ALT phenotype, we investigated the localization and function of SMARCAL1 in ALT-positive glioma cells and xenografts with native ATRX deficiency. We found that SMARCAL1 localizes to ALT-associated PML bodies in astrocytoma cell lines with concurrent ATRX and IDH1 mutations (derived from grade 3 and 4 tumors). Our data show that inducible suppression of SMARCAL1 via doxycycline-induced RNAi leads to increased DNA double-strand breaks, increased abundance of extrachromosomal telomeric repeats (c-circles), and increased sensitivity to irinotecan, a topoisomerase I inhibitor. In an orthotopic mouse model, SMARCAL1 depletion exhibited a chemosensitizing effect in combination with irinotecan against a patient-derived xenograft (astrocytoma, IDH-mutant Grade 4). Based on these data, we hypothesize that SMARCAL1 activity is critical for resolving ALT-associated replication stress in ATRX-deficient malignant gliomas. We therefore propose that SMARCAL1 functions as a synthetic lethal vulnerability in ATRX-deficient ALT-positive gliomas and that SMARCAL1 inhibition is a viable therapeutic strategy in these tumors.

BSCI-20 STING EPIGENETIC SILENCING IN GLIOMAS CAN BE RESCUED BY METHYLTRANSFERASE INHIBITION: IMPLICATIONS FOR NOVEL THERAPEUTIC APPROACHES

The stimulator of interferon genes (STING) is a key component of the innate immune response to pathogenic cytosolic DNA, resulting in IRF3- and NFκB-dependent transcription of type I interferons (IFN) and pro-inflammatory cytokines. STING activation primes endogenous antitumor immunity and is disrupted in a variety of cancers. Here we investigate STING signalling in glioblastoma (GBM) patient samples. STING agonist treatment of ex vivo gliomas leads to inconsistent induction of type I IFN responses that are restricted to tumor associated myeloid cells. Indeed, single-cell transcriptome and multiplex immunofluorescence analyses demonstrate that STING expression is suppressed in neoplastic cells but not tumor-associated immune cells or stroma. Methylation analyses reveal a STING promoter region that is highly methylated in bulk tumor samples from glioma and other neuroectoderm-derived cancers, but not in most extracranial cancers. Methylation in this region strongly correlates inversely with STING RNA expression. STING epigenetic silencing is also present in normal fetal and adult brains. We demonstrate that STING expression in glioma cell lines may be rescued by decitabine, a DNA methyltransferase inhibitor (DNMTi) that is commonly used to treat hematologic malignancies. However, transduction of a STING-expressing vector into these glioma cell lines is insufficient to reconstitute STING signalling, suggesting that additional decitabine-stimulated mechanisms are necessary for STING pathway rescue. Collectively, our results suggest that epigenetic silencing of STING occurs early in brain development and may provide an immunosuppressive context for the genesis of brain tumors. Furthermore, our work raises the potential of epigenetic modulation to reconstitute STING signalling as a therapeutic strategy for glioblastoma and potentially other STING-silenced, immunologically-cold cancers.

IMMU-18. INTERPLAY BETWEEN IDH1 AND ATRX MUTATIONS GOVERN INNATE IMMUNE RESPONSES IN GLIOMAS

Innate-based immunotherapies are becoming increasingly important for treating brain tumor patients. About 50% of WHO grade II and III gliomas carry mutations in IDH1 and ATRX genes. Mutant IDH1 results in the production of 2-hydroxyglutarate, an oncometabolite that promotes global metabolic and epigenetic alterations. ATRX is a SWI-SNF chromatin remodeling protein that is involved in cell cycle regulation and maintenance of genomic stability. Both IDH1 and ATRX mutations have been implicated in dysfunctional immune signaling in cancer cells. However, the interplay between these mutations in mediating innate immune responses has not been investigated in gliomas. We have derived human and mouse glioma cell lines carrying mutations in IDH1 (IDH1R132H) and/or ATRX, which we then used to generate both immune competent and nude mice models. Treating the ATRX knockout (KO) cell lines with dsRNA-based innate stimuli led to an early induction in phospho-IRF3, and late induction in phospho-STAT1 and ISG15, suggesting that ATRX deletion may enable a potent activation of type I interferon production and sensitize glioma cells to dsRNA-based innate stimuli. Our syngeneic murine glioma models confirm a survival advantage for mice carrying ATRX-KO tumors. These tumors also exhibit enhanced infiltration of T-cells and expression of activated macrophage markers. On the other hand, presence of IDH1R132H led to a suppression in baseline expression of key innate immune players, which could be rescued by the mutant IDH1 inhibitor, BAY-1436032. Cells harboring IDH1R132H and ATRX-KO retained sensitivity to dsRNA indicating that IDH1R132H does not dampen the ATRX KO-mediated sensitivity to dsRNA. Our models are under evaluation with a combination of BAY-1436032 and clinically relevant dsRNA-based innate therapies. Our data indicates the presence of an interplay between IDH1 and ATRX mutations that may regulate innate signaling in gliomas. Understanding the mechanisms governing this interplay may aid in designing therapies that exploit this interplay.

IMMU-34. ATRX MUTATIONS PREDICT RESPONSE TO INNATE BASED THERAPY IN GLIOMA

BACKGROUND

Innate based immunotherapies are becoming increasingly important for treating brain tumor patients. Gliomas carry recurrent mutations in regulatory genes that control innate immune signaling responses. About 71% of adult WHO grade II and III gliomas and 57% of secondary glioblastomas also carry a loss-of-function mutation in the ATRX gene. ATRX is a SWI-SNF chromatin remodeling protein that has major roles in processes such as cell cycle regulation and maintenance of genomic stability. Recent studies have implicated ATRX in dysfunctional innate immune signaling in cancer cells. However, the role of ATRX in mediating innate immune responses has not been investigated in gliomas.

METHODS AND RESULTS

Human and mouse glioma cell lines from a variety of genetic contexts have been examined including models which carry IDH/ATRX mutations, IDH 1p-/19q- and ATRX -/- status. Additionally, using Crispr-Cas9 technology and cloning cell lines with ATRX deletions, we have derived a series of immune competent and nude mice models. Treating these cell lines with double-stranded RNA based innate stimuli led to an enhanced early induction in phospho-interferon regulatory factor 3 (IRF3) and late induction in phospho-STAT1 in the ATRX knockout (KO) cell lines. A differential increase in interferon-stimulated gene 15 (ISG15) release was also noted in the ATRX KO cell lines, further suggesting that ATRX deletion may enable a potent activation of type I interferon production. A combination of patient-derived glioma cell lines in xenograft models and syngeneic murine glioma models derived from ATRX KO cell lines and controls confirm a survival advantage in both immuno-competent mice and xenografts. Our models are under evaluation with PVSRIPO and other innate based RNA therapies.

CONCLUSION

Our data suggests that ATRX mutations may confer sensitivity to RNA-based innate immune signaling agonists in gliomas. This potential vulnerability can be targeted in future therapies.

A novel method for studying airway hyperresponsiveness in allergic guinea pigs in vivo using the PreciseInhale system for delivery of dry powder aerosols

Inhaled adenosine receptor agonists induce bronchoconstriction and inflammation in asthma and are used as bronchial challenge agents for the diagnosis of asthma and in respiratory drug development. Recently developed dry powder aerosols of adenosine have several advantages over nebulised adenosine 5′-monophosphate (AMP) as bronchial challenge agents. However, reverse translation of this bronchial challenge technique to pre-clinical drug development is limited by the difficulty of administering powder aerosols to animals. The aim of the current study was to develop methods for delivering powder aerosols of adenosine receptor agonists to sensitised guinea pigs (as a model of allergic asthma) and evaluate their effect as challenge agents for the measurement of airway responsiveness. The PreciseInhale system delivered micronised AMP and adenosine powders, with mass median aerodynamic diameters of 1.81 and 3.21 μm and deposition fractions of 31 and 48% in the lungs, respectively. Bronchoconstrictor responses in passively sensitised, anaesthetised, spontaneously breathing guinea pigs were compared to responses to nebulised and intravenously administered AMP and adenosine. AMP- and adenosine-induced bronchoconstriction following all routes of administration with the magnitude of response ranking intravenous > dry powder > nebulisation, probably reflecting differences in exposure to the adenosine agonists delivered by the different routes. In conclusion, the PreciseInhale system delivered AMP and adenosine dry powder aerosols accurately into the lungs, suggesting this method can be used to investigate drug effects on airway responsiveness.

Engraftment of C6-2B Cells into the Striatum of Aci Nude Rats as a Tool for Comparison of the in Vitro and in Vivo Phenotype of a Glioma Cell Line

The C6-2B is a well-characterized glioma cell line used extensively in the study of malignant glial biology. While the C6-2B cell line has traditionally been thought of as a homogenous cell line, the in vitro phenotype of the C6-2B cell line can vary considerably depending on the culture technique used and the stratum on which the cells are grown. Thus, we asked whether the in vitro phenotype of the C6-2B cell line was significantly different than the in vivo phenotype of the cell line once it was engrafted into the striatum of nude rats. Under culture conditions used in our laboratory, 100% of the C6 cells were found to express p75, the low-affinity nerve growth factor (NGF) receptor, and Major Histocompatability Class I (MHC Class I), while only 10-15% demonstrated vimentin reactivity. Immunohistochemistry was consistently negative for GFAP, trkA (the high-affinity receptor for NGF), CD4, CD8, and a macrophage specific marker (Ox-41). Once engrafted into the striatum of nude rats, the cells remained 100% p75 and MHC Class I positive, and again, only 15% of the cells demonstrated vimentin reactivity. The grafted cells retained this characteristic for 28 days in vivo. Although an immunoincompetent host was selected to minimize the effects an inflammatory response would have on the graft, a transient inflammatory response was detected. During the first week of engraftment, numerous MHC class II cells, some of which were macrophages, were seen infiltrating the graft. However, by 4 weeks postengraftment, no inflammatory cells were appreciated in the graft and surprisingly little reactive gliosis was seen in the penumbra of the tumor mass. Thus, the limited number of in vitro phe-notypic characteristics we examined in the C6-2B cell line remained constant once the cells were engrafted into the striatum of athymic nude rats.

Abstract 3969: Pediatric preclinical testing program (PPTP) evaluation of BMN 673, an inhibitor of poly-adp ribose polymerase (PARP), with temozolomide (TMZ)

Introduction: BMN 673 is a potent and selective inhibitor of PARP1/2. Inhibitors of PARP such as BMN 673 show clinical activity against cancers lacking homologous repair through mutations in BRCA1 and 2. PARP inhibitors are of particular interest for Ewing sarcoma (ES) given reports of ES cell lines being preferentially sensitive to PARP inhibitors. However, BMN 673 and other PARP inhibitors have shown limited single agent activity against Ewing sarcoma xenografts.

Methods: BMN 673 (10 nM) was evaluated in combination with TMZ and topotecan against the 23 cell lines of the PPTP in vitro panel using 96 hour exposure. For in vivo combination studies, two dose levels of BMN 673 (0.25 & 0.1 mg/kg BID x 5 days) given with TMZ [12 & 30 mg/kg/day x 5 days, respectively] were evaluated against ES xenografts. The combination regimen using the lower dose (LD) of TMZ and higher dose of BMN 673 was studied against other histotypes. Standard PPTP measures of in vivo antitumor activity were employed to assess response.

Results: BMN 673 markedly potentiated TMZ activity in vitro, with the TMZ rIC50 reduced by a median of 10-fold for PPTP cell lines, with ES cell lines showing a median 50-fold reduction. BMN 673 potentiated topotecan to a lesser degree (median 2.8-fold reduction in rIC50), with no differential sensitivity by histotype.

In vivo, 10 ES xenografts showed little or no response to 5 days of treatment with single agent TMZ (30 mg/kg) or BMN 673 (0.25 mg/kg BID), but 8 of 10 showed complete responses (CR) or maintained CR (MCR) to BMN 673 and TMZ (LD), and 5 of 10 showed CR or MCR to BMN 673 and higher-dose TMZ. The 10 ES xenografts could be separated into 2 groups based on duration of response to the combinations, with 5 showing delayed growth or brief objective responses (median time to event ≤ 30 days), and with the other 5 showing prolonged time to regrowth (median > 77 days). Among 5 neuroblastoma xenografts, all showed significant treatment effects to BMN 673 plus TMZ(LD), with 1 achieving CR. Among 4 osteosarcoma xenografts, each showed significant tumor growth delay, but no objective responses were noted. Among 3 glioblastoma xenografts, 2 of 3 achieved maintained CRs (MCR) to the BMN 673 plus TMZ(LD) combination. Excessive toxicity was observed for ALL xenografts in NOD-SCID mice treated with the combination.

Conclusions: While BMN 673 shows limited single agent activity against PPTP solid tumor and ALL models with responses limited to models also highly sensitive to cisplatin, the BMN 673 plus TMZ(LD) combination shows dramatic activity for a subset of Ewing sarcoma xenografts and for selected additional models. Based on these results a pediatric phase 1 trial of BMN 673 plus TMZ with a phase 2 expansion for Ewing sarcoma is proceeding. Efforts are ongoing to relate genomic alterations identified through exome sequencing to responsiveness of ES xenografts to BMN 673 plus TMZ. (Supported by NO1-CM-42216)

Citation Format: Malcolm Smith, Min Kang, Patrick Reynolds, Richard Gorlick, Anders Kolb, John Maris, Richard Lock, Hernan Carol, Stephen Keir, Catherine Billups, Raushan Kurmasheva, Peter Houghton. Pediatric preclinical testing program (PPTP) evaluation of BMN 673, an inhibitor of poly-adp ribose polymerase (PARP), with temozolomide (TMZ). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3969. doi:10.1158/1538-7445.AM2014-3969

Exomic sequencing of four rare central nervous system tumor types

A heterogeneous population of uncommon neoplasms of the central nervous system (CNS) cause significant morbidity and mortality. To explore their genetic origins, we sequenced the exomes of 12 pleomorphic xanthoastrocytomas (PXA), 17 non-brainstem pediatric glioblastomas (PGBM), 8 intracranial ependymomas (IEP) and 8 spinal cord ependymomas (SCEP). Analysis of the mutational spectra revealed that the predominant single base pair substitution was a C:G>T:A transition in each of the four tumor types. Our data confirm the critical roles of several known driver genes within CNS neoplasms, including TP53 and ATRX in PGBM, and NF2 in SCEPs. Additionally, we show that activating BRAF mutations play a central role in both low and high grade glial tumors. Furthermore, alterations in genes coding for members of the mammalian target of rapamycin (mTOR) pathway were observed in 33% of PXA. Our study supports the hypothesis that pathologically similar tumors arising in different age groups and from different compartments may represent distinct disease processes with varied genetic composition.

Abstract C206: Pediatric Preclinical Testing Program (PPTP) evaluation of BMN 673, an inhibitor of Poly-ADP Ribose Polymerase (PARP), alone and with Temozolomide (TMZ)

Introduction: BMN 673 is a potent and selective inhibitor of PARP1/2. Inhibitors of PARP such as BMN 673 show clinical activity against cancers lacking homologous repair through mutations in BRCA1 and 2. For Ewing sarcoma (ES), the EWS/FLI1 chimeric transcription factor increases PARP expression, and PARP appears to facilitate EWS/FLI1 function. Two reports have indicated that ES cell lines are more sensitive to PARP inhibitors than most other cell lines.

Methods: BMN 673 was evaluated as a single agent and in combination with TMZ against the 23 cell lines of the PPTP in vitro panel using 96 hour exposure. In single-agent studies, daily oral BMN 673 administration was tested against the PPTP solid tumor xenografts (SCID mice) and acute lymphoblastic leukemia (ALL; NOD-SCID mice) panels using a dose of 0.16 mg/kg BID x 5 and 0.33 mg/kg QD on weekends for up to 28 days. In combination studies, two dose levels of BMN 673 (0.25 & 0.1 mg/kg BID x 5 days) given with TMZ (12 & 30 mg/kg/day x 5 days, respectively) were evaluated against ES xenografts. Standard PPTP measures of in vivo antitumor activity were employed to assess response.

Results: The median relative IC50 (rIC50) for BMN 673 against the PPTP cell lines was 28 nM, with a range from 4 nM to >1000 nM. There was a trend for lower rIC50 values for the ES cell line panel. In combination with a fixed concentration of BMN 673 (10 nM), the TMZ rIC50 was markedly reduced for some PPTP cell lines, with ES cell lines showing up to a 60-fold reduction. In vivo, BMN 673 was well tolerated with only a 1.9% toxicity rate in the treated groups. BMN 673 induced significant improvements in event-free survival (EFS) distribution compared to control in 18 of 35 (51%) of the evaluable solid tumor xenografts, but in 0 of 8 ALL models. Only 2 of 34 (6%) evaluable solid tumor xenografts and no ALL models showed EFS T/C values > 2. Complete responses (CR) were observed for a Wilms tumor and a medulloblastoma model.

BMN 673 in combination with TMZ induced CRs that were maintained through week 12 for 2 of 4 ES xenografts (TMZ dosed at either 12 or 30 mg/kg/day). Among an additional 6 ES xenografts that have recently initiated testing, 3 have ongoing CRs to the combination at Weeks 4 to 5. None of the ES xenografts responded to 5 days of treatment with single agent TMZ (30 mg/kg) or BMN 673 (0.5 mg/kg/day).

Conclusions: Single agent BMN 673 shows limited activity against the PPTP solid tumor and ALL models, with no single agent activity against ES xenografts in vivo, despite ES cell lines demonstrating differential sensitivity in vitro. BMN 673 as a single agent induced CRs in 2 of 43 models, both of which are also highly responsive to cisplatin. Dramatic activity for the BMN 673 plus TMZ combination was observed for 5 of 10 ES models, with maintained CRs noted in vivo at TMZ doses as low as 12 mg/kg. Based on these results a pediatric phase 1 trial of BMN 673 plus TMZ is planned. (Supported by NO1-CM-42216)

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C206.

Citation Format: Malcolm Smith, Min Kang, Patrick Reynolds, Richard Gorlick, Anders Kolb, John Maris, Richard Lock, Hernan Carol, Stephen Keir, Catherine Billups, Raushan Kurmasheva, Peter Houghton. Pediatric Preclinical Testing Program (PPTP) evaluation of BMN 673, an inhibitor of Poly-ADP Ribose Polymerase (PARP), alone and with Temozolomide (TMZ). [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C206.

Abstract 2758: Pediatric preclinical testing program (PPTP) stage 1 evaluation of MLN0128, a potent TOR kinase inhibitor

Introduction: The PI3K-TORC1 pathway links extracellular (growth factors) and intracellular (nutrient sensing) to cell cycle progression and proliferation. This pathway is dysregulated in many adult cancers, but less is known regarding childhood malignancies. MLN0128 is a novel orally-available small molecule inhibitor of both the TORC1 and TORC2 complexes, key components of the PI3K/mTOR signaling pathway.

Methods: MLN0128 was evaluated against the 23 cell lines of the PPTP in vitro panel using 96 hour exposure at concentrations from 0.1 nM to 1.0 μM. MLN0128 was tested against the PPTP solid tumor xenografts (SCID mice) and acute lymphoblastic leukemia (ALL; NOD-SCID mice) panels using a dose of 1 mg/kg administered by the P.O. route daily for 21 days.

Results: In vitro the median relative IC50 value for the PPTP cell lines was 19 nM, with a range from 2 nM to 102 nM. There was a trend for lower median rIC50 values for the rhabdomyosarcoma and Ewing sarcoma cell line panels (8 nM and 5 nM, respectively). The median rIC50 value for the ALL cell lines (68 nM) was significantly greater than that for the non-ALL cell lines.

In vivo MLN0128 was well tolerated, with only a 1.4% toxicity rate in the treated groups, compared to a 0.3% toxicity rate in control animals. All 38 tested xenograft models were considered evaluable for efficacy. MLN0128 induced significant differences in EFS distribution compared to control in 24 of 31 (77%) of the evaluable solid tumor xenografts, but did not induce significant differences in EFS distribution in any of the 7 evaluable ALL xenografts. MLN0128 induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity (EFS T/C > 2) in 6 of 30 (20%) evaluable solid tumor xenografts. Intermediate activity for the EFS T/C metric occurred in the rhabdoid tumor panel (2 of 3) and in single xenografts in four other panels. Objective responses were not observed for the solid tumor or for the ALL xenograft panels. Pharmacodynamic studies to determine TOR inhibition are planned.

Conclusions: The activity observed for MLN0128 against the PPTP preclinical models is similar to that previously reported by the PPTP for another TOR kinase inhibitor (Houghton PJ, et al. Pediatr Blood Cancer. 58:191-9, 2012). When combined with PPTP results reported for PI3K and AKT inhibitors (Reynolds CP, et al. Pediatr Blood Cancer. 2012. Epub 2012/09/25 and Gorlick R, et al. Pediatr Blood Cancer. 59:518-24, 2012), the available data suggest that kinase inhibitors targeting the PI3K pathway produce limited single agent activity for the tumor types represented by the PPTP models. (Supported by award NO1-CM-42216 from the NCI).

Citation Format: Peter Houghton, Min H. Kang, Patrick Reynolds, Richard Lock, Hernan Carol, Richard Gorlick, Anders Kolb, John Maris, Stephen Keir, Catherine Billups, Raushan Kurmasheva, Malcolm Smith. Pediatric preclinical testing program (PPTP) stage 1 evaluation of MLN0128, a potent TOR kinase inhibitor. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2758. doi:10.1158/1538-7445.AM2013-2758

Abstract LB-354: Pediatric Preclinical Testing Program (PPTP) stage 1 evaluation of the XPO1/CRM1 inhibitor KPT-330

Introduction: KPT-330 is an oral Selective Inhibitor of Nuclear Export (SINE) that binds covalently to XPO1 at Cys528 resulting in its irreversible inactivation. The nuclear export of over 200 proteins with specific nuclear export sequences (NES) is mediated via XPO1. Amongst the client proteins are many tumor suppressor and growth regulatory proteins (e.g., FOXO, IκB, pRb, p53, p73, p21, and p27).

Methods: KPT-330 was tested against the PPTP's in vitro cell line panel at concentrations ranging from 1.0 nM to 10.0 μM using the PPTP's standard 96 hour exposure period. It was tested against the PPTP solid tumor xenografts using a dose of 10 mg/kg administered by the oral route thrice weekly (M-W-F) for 4 weeks with a total treatment/observation period of 6 weeks.

Results: The median relative IC50 (rIC50) value for the PPTP cell lines was 125 nM, with a range from 13 nM to greater than 10 μM. There were no significant differences in rIC50 values by histotype, although there was a trend for greater sensitivity for the Ewing sarcoma cell lines (median rIC50 = 57 nM) and lesser sensitvity for the neuroblastoma cell lines (median rIC50 = 235 nM). Most cell lines showed Relative I/O% values between -75% and -100%, consistent with a prominent cytotoxic effect for KPT-330.

KPT-330 was well tolerated in vivo. It induced significant differences in EFS distribution compared to control in 29 of 37 (78%) solid tumor xenografts and in 5 of 8 (63%) ALL xenografts. For those xenografts with a significant difference in EFS distribution between treated and control groups, an EFS T/C value of greater than 2.0 indicates a substantial agent effect in slowing tumor growth. KPT-330 induced this level of effect in 11 of 32 (34%) solid tumor xenografts, most frequently for the Wilms tumor (2 of 3) and the Ewing sarcoma (4 of 5) panels. Objective responses were observed in 3 of 38 (4%) solid tumor xenografts, including a maintained complete response (MCR) for a Wilms tumor xenograft, a CR for a medulloblastoma xenograft, and a CR for a slow-growing ependymoma xenograft. For the ALL panel, 2 of 8 (25%) xenografts achieved either CR (ALL-8, T-cell ALL) or MCR (ALL-19, B-precursor ALL).

Conclusions: KPT-330 shows potent in vitro activity against many PPTP cell lines, consistent with the activation of multiple tumor suppressor proteins across diverse tumor genotypes. KPT-330 shows tumor regressing activity against selected PPTP solid tumor and ALL xenografts, and shows tumor growth inhibition for a larger number of models. Defining the relationship between KPT-330 systemic exposure in mice and humans will be important in assessing the clinical relevance of the PPTP in vivo results. Planned PD testing may identify biomarkers associated with response of pediatric preclinical models to KPT-330. KPT-330 is in phase 1 clinical trials in adults with advanced solid or hematological malignancies (NCT01607905 and NCT01607892). (Supported by NCI NO1-CM-42216)

Citation Format: Peter Houghton, Min Kang, Patrick Reynolds, Richard Gorlick, Anders Kolb, John Maris, Stephen Keir, Hernan Carol, Richard Lock, Catherine Billups, Raushan Kurmasheva, Yosef Landesman, Sharon Shacham, Michael Kauffman, Malcolm A. Smith. Pediatric Preclinical Testing Program (PPTP) stage 1 evaluation of the XPO1/CRM1 inhibitor KPT-330. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-354. doi:10.1158/1538-7445.AM2013-LB-354

The 2010 British Association of Stroke Physicians Survey of interventional treatments for stroke in the United Kingdom

INTRODUCTION

The UK National Stroke Strategy (Department of Health 2007) states that patients should have access to a stroke service with neurointerventional capacity. This survey was conducted by the Clinical Standards Committee of the British Association of Stroke Physicians to get a snapshot of the availability of interventional treatments for stroke in the United Kingdom.

METHODS

Questionnaires covering availability of endovascular treatments for stroke, e.g. intra-arterial thrombolysis and mechanical thrombectomy, were emailed to all British Association of Stroke Physicians members in October 2010. Where more than one response was received from the same hospital, the data were only entered once. If there was a discrepancy between different respondents for the same hospital, details were cross-checked with the respondents to ensure accuracy.

RESULTS

Responses were received from 58 hospitals in England, Scotland, Wales, and Northern Ireland. Intra-arterial thrombolysis and/or mechanical thrombectomy were available in 23 hospitals. Of these, three had not performed any procedures in 2010. Twenty centres had conducted a mean (range) of eight (2-20) procedures during the 10-month period. Thirty-five hospitals were not offering endovascular treatments. Sixteen of these were not referring patients to centres which could provide interventional treatments. Hospitals offering endovascular treatments had a mean (range) of 5.2 (2-12) stroke physicians, 2.3 (0-4) interventional neuroradiologists, and 3.6 (0-9) noninterventional neuroradiologists. Only two hospitals providing interventions had four or more interventional neuroradiologists.

CONCLUSIONS

Only a small number of hospitals in the United Kingdom provide interventional treatments for stroke. Almost 50% of hospitals not providing interventions had no processes in place for referral to providers.

Abstract LB-318: Pediatric Preclinical Testing Program (PPTP) evaluation of the JAK inhibitor AZD1480

Background: AZD1480 is a potent, competitive small molecule inhibitor of JAK1/2 kinase that has entered clinical evaluation. JAK inhibition is of particular pediatric interest given the activating JAK1/2 mutations observed in a subset of pediatric ALL cases. The activity of AZD1480 was evaluated against the PPTP's in vitro and in vivo panels. Methods: AZD1480 (provided by AstraZeneca) was tested in vitro at concentrations from 1.0 nM to 10.0 µM. It was evaluated against solid tumor xenografts at 60 mg/kg administered by oral gavage daily x 5 for 3 weeks, with a total treatment and observation period of 6 weeks. For the ALL panel (using NOD-SCID mice), the maximum tolerated dose was lower, and a twice daily schedule was utilized: 10 mg/kg BID (with a single daily dose of 15 mg/kg on weekends). Standard PPTP measures of in vivo antitumor activity were employed to assess response to AZD1480. Results: The median relative IC50 (rIC50) for AZD1480 against the PPTP cell lines was 1.5 µM, with a range from 0.3 µM to 5.9 µM. AZD1480 induced significant differences in EFS distribution compared to control in 25 of 27 (93%) evaluable solid tumor xenografts. AZD1480 induced tumor growth inhibition meeting criteria for intermediate or high EFS T/C activity in 11 of 26 (42%) solid tumor xenografts evaluable for this measure. Both Wilms tumor xenografts tested showed EFS T/C > 2, as did 2 of 4 GBM xenografts and 2 of 4 neuroblastoma xenografts. An objective response was observed for 1 solid tumor xenograft, a Wilms tumor xenograft KT-10 that achieved a maintained complete response (MCR). Many solid tumor xenografts show phospho-STAT3 expression, but this marker showed no discernible relationship with response to AZD1480. For the ALL panel, 5 JAK mutated xenografts (3 JAK2 and 2 JAK1) were selected for testing to determine whether AZD1480 shows high activity in models in which the JAK-STAT pathway is activated by mutation. Additionally, 4 non-JAK mutated xenografts were evaluated. Models with JAK mutations show phospho-STAT5 as evidence of JAK-STAT signaling. However, the only ALL xenograft with EFS T/C > 2 was a JAK2 mutant (R867Q) xenograft, TGT-20, and no models showed objective responses (PR or CR). Conclusions: AZD1480 showed tumor growth inhibitory activity against most of the solid tumor xenografts, and induced an objective response (an MCR) in a single Wilms tumor xenograft. Genomic sequencing is being undertaken to determine whether this xenograft has a genomic alteration(s) in a JAK family kinase or another kinase that may explain its favorable response. No objective responses were noted for the ALL panel, even among xenografts with JAK mutations. Our results suggest that inhibition of JAK signaling alone may not be sufficient for clinical activity against JAK-mutated ALL. (Supported by NCI NO1CM42216)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-318. doi:1538-7445.AM2012-LB-318

Abstract LB-317: Pediatric Preclinical Testing Program (PPTP) evaluation of volasertib (BI 6727), a Polo-like kinase (PLK) inhibitor

Background: Volasertib is a first in class, selective and potent cell cycle kinase inhibitor that induces mitotic arrest and apoptosis by targeting PLK. Genomic screens have identified PLK1 as a potential therapeutic target for several pediatric cancers, including rhabdomyosarcoma and neuroblastoma. Methods: Volasertib (provided by Boehringer Ingelheim) was tested in vitro at concentrations from 0.1 nM to 1.0 µM. Volasertib was tested against the PPTP solid tumor xenografts using a dose of 30 mg/kg administered intravenously weekly x 3. For the ALL panel (using NOD-SCID mice), the MTD was 15 mg/kg, and this dose was used for efficacy testing. The total planned treatment period was 3 weeks with an additional 3 weeks observation. Two measures of antitumor activity were primarily used: 1) an objective response measure modeled after the clinical setting; and 2) a time to event (4-fold increase in tumor volume) measure based on the median event-free survival (EFS) of treated (T) and control (C) animals for each xenograft. Intermediate activity requires EFS T/C > 2, with high activity additionally requiring regression at the end of the observation period. Results: The median relative IC50 (rIC50) value for the PPTP cell lines was 14.1 nM, with a range from 6.0 nM to 135 nM. The median rIC50 values were lowest for the ALL cell line panel compared to the remaining cell lines (11.9 versus 16.0 nM, respectively), but this difference was not significant, and overall there were no differences in rIC50 by histotype. Against the PPTP in vivo panels volasertib induced significant differences in EFS distribution compared to control in 19 of 32 (59%) evaluable solid tumor xenografts and in 2 of 4 (50%) evaluable ALL xenografts. Volasertib induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity in 11 of 30 (37%) evaluable solid tumor xenografts. Intermediate activity for the EFS T/C metric was most consistently observed in the neuroblastoma (4 of 6) and glioblastoma (2 of 3) panels. For the ALL panel, 2 of 4 (50%) xenografts met criteria for intermediate activity. Objective responses were observed for 4 of 32 solid tumor and 1 of 4 ALL xenografts. Two of 6 neuroblastoma xenografts demonstrated CRs, as did 1 of 3 glioblastoma and 1 of 5 rhabdomyosarcoma xenografts evaluable for this response measure. Conclusions: Volasertib showed low nanomolar in vitro potency against the PPTP cell lines with no histotype selectivity. Volasertib induced regressions in 5 of 36 evaluable PPTP xenografts with the neuroblastoma panel showing the most consistent pattern of responsiveness to volasertib. Given available pharmacokinetic data showing that mice tolerate higher systemic exposure to volasertib than humans, it is unlikely that the PPTP in vivo results are under-estimating the potential clinical activity of volasertib against the childhood cancer types evaluated here. (Supported by NCI NO1CM42216)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-317. doi:1538-7445.AM2012-LB-317

Abstract 4417: Characterization of xenograft-derived EGFRvIII-positive GBM cell cultures reveals functional interactions between EGFRvIII, wild-type EGFR, and p53

In 20% – 30% of all glioblastomas (GBMs), the most common and deadly form of glioma, gene rearrangements in amplified epidermal growth factor receptor (EGFR) cause amplification of a highly oncogenic variant of wild-type EGFR called EGFRvIII. A number of studies demonstrate that EGFRvIII amplification is detected predominantly in GBMs harboring wild-type EGFR amplification or those expressing the wild-type isoform of the tumor suppressor p53. However, it remains unclear why such genetic interactions occur or whether they are advantageous for tumor growth.

Our limited understanding of these genetic interactions likely stems from an inability to study the function of amplified EGFRvIII in vitro using currently available model systems. Indeed, there are no immortalized GBM cell lines that express EGFRvIII because prolonged in vitro culture of EGFRvIII-positive GBM tumor cells invariably selects against EGFRvIII amplification. Moreover, the commonly used ectopic EGFRvIII expression models are unlikely to fully recapitulate the function, regulation, and downstream signaling activities of amplified EGFRvIII.

Herein, we validate the use of short-term cell cultures derived from GBM xenografts expressing amplified EGFRvIII to study the endogenous function of amplified EGFRvIII. These cells exhibit competency in EGFR signaling, and maintain EGFRvIII expression for up to five months. Further characterization of these cells using small molecule inhibitor and short hairpin RNA approaches reveals three novel observations. First, loss of EGFRvIII expression and activity results in growth arrest and cellular senescence, indicating that EGFRvIII activity is required for cell growth. Second, specific depletion of wild-type EGFR significantly decreases EGFRvIII phosphorylation, demonstrating that high-level wild-type EGFR expression is required for maximal EGFRvIII activation. Third, p53 depletion inhibits growth arrest induced by loss of EGFRvIII activity, strongly suggesting that the growth-promoting activity of EGFRvIII is strictly dependent on p53 function. By showing that EGFRvIII functionally interacts with wild-type EGFR and wild-type p53 in a manner that promotes cell growth, these data provide a functional basis for the commonly observed genetic interactions between amplified EGFRvIII and amplified wild-type EGFR or wild-type p53. Furthermore, our data imply that with help from amplified wild-type EGFR, amplified EGFRvIII functions specifically to overcome the growth inhibitory activity of wild-type p53 in order to promote cell growth. Consistent with this insight, we provide preliminary evidence for the efficacy of a combination therapy involving EGFR and MDM2 inhibitors, which permits concomitant inhibition of EGFR signaling and potentiation of p53 function.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4417. doi:10.1158/1538-7445.AM2011-4417

EGFR and EGFRvIII interact with PUMA to inhibit mitochondrial translocalization of PUMA and PUMA-mediated apoptosis independent of EGFR kinase activity

EGFR and its constitutively activated variant EGFRvIII are linked to glioblastoma resistance to therapy, the mechanisms underlying this association, however, are still unclear. We report that in glioblastoma, EGFR/EGFRvIII paradoxically co-expresses with p53-upregulated modulator of apoptosis (PUMA), a proapoptotic member of the Bcl-2 family of proteins primarily located on the mitochondria. EGFR/EGFRvIII binds to PUMA constitutively and under apoptotic stress, and subsequently sequesters PUMA in the cytoplasm. The EGFR-PUMA interaction is independent of EGFR activation and is sustained under EGFR inhibition. A Bcl-2/Bcl-xL inhibitor that mimics PUMA activity sensitizes EGFR/EGFRvIII-expressing glioblastoma cells to Iressa. Collectively, we uncovered a novel kinase-independent function of EGFR/EGFRvIII that leads to tumor drug resistance.

An integrated genomic analysis of human glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and lethal type of brain cancer. To identify the genetic alterations in GBMs, we sequenced 20,661 protein coding genes, determined the presence of amplifications and deletions using high-density oligonucleotide arrays, and performed gene expression analyses using next-generation sequencing technologies in 22 human tumor samples. This comprehensive analysis led to the discovery of a variety of genes that were not known to be altered in GBMs. Most notably, we found recurrent mutations in the active site of isocitrate dehydrogenase 1 (IDH1) in 12% of GBM patients. Mutations in IDH1 occurred in a large fraction of young patients and in most patients with secondary GBMs and were associated with an increase in overall survival. These studies demonstrate the value of unbiased genomic analyses in the characterization of human brain cancer and identify a potentially useful genetic alteration for the classification and targeted therapy of GBMs.

Immunohistochemical co-localization of transient receptor potential vanilloid (TRPV)1 and sensory neuropeptides in the guinea-pig respiratory system

Electrophysiological studies within the lung have documented the presence of heterogenous groups of afferent fibers composed of Adelta and C-fibers and studies of somatosensory nerves within the skin reveal a complex pattern of distribution of sensory neuropeptides and transient receptor potential vanilloid (TRPV)1 positive nerves. However, the anatomical location of these different subpopulations of nerves within the lung has not been extensively studied. In the present study we have demonstrated that TRPV1 axons represented only a small proportion of the total number of PGP9.5 staining nerves within guinea-pig tracheal epithelium and only half the number of TRPV1 axons was immunopositive for substance P. In contrast, most TRPV1 positive neurones found within guinea-pig intrapulmonary airways were found to co-localize with sensory neuropeptides substance P and calcitonin gene-related peptide within and beneath the epithelium, around blood vessels, within airway smooth muscle and alveoli, indicative of heterogeneity of TRPV1 positive axons throughout the airways. However, in the smooth muscle layer of the trachea there was evidence of substance P and calcitonin gene-related peptide containing nerves that did not stain for TRPV1. We also demonstrated a complete loss of TRVP1 positive axons in the trachea and intrapulmonary airways and associated loss of bronchoconstriction induced by capsaicin, in animals chronically treated with capsaicin. However, some neuropeptide immunoreactive axons remained in the smooth muscle layer of capsaicin-treated animals which could represent the small subset of neuropeptide containing fibers which do not co-localize with TRPV1. We have provided evidence of heterogeneity of TRPV1 positive nerve fibers, including fibers characterized by lack of co-localization with neuropeptides in various regions of the airways and the existence of neuropeptide containing fibers that were not TRPV1 positive in guinea-pigs.

O6-benzylguanine-mediated enhancement of chemotherapy

We have previously demonstrated (A. E. Pegg, Cancer Res., 50: 6119-6129, 1990) that O6-benzylguanine (O6-BG) enhances nitrosourea, temozolomide, and cyclophosphamide activity in malignant glioma xenografts growing in athymic nude mice. More recently, we have demonstrated (V. J. Patel et al., Clin. Cancer Res., 6: 4154-4157, 2000; P. Pourquier et al., Cancer Res., 61: 53-58, 2001) that the combination of temozolomide plus irinotecan (CPT-11) displays a schedule-dependent enhancement of antitumor activity secondary to trapping of topoisomerase I by O6-methylguanine residues in DNA. These studies suggested that there might be favorable therapeutic interactions between O6-BG and combinations of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) plus cyclophosphamide or temozolomide plus CPT-11, respectively. Our present results indicate that the combination of cyclophosphamide plus BCNU plus O6-BG produces growth delays modestly-to-markedly-superior to combinations of cyclophosphamide with BCNU. Although the combination of temozolomide and CPT-11 reveals a marked increase in activity compared with either agent used alone, the addition of O6-BG to this combination dramatically increased the growth delay of the O6-alkylguanine-DNA alkyltransferase (AGT)-positive malignant glioma D-456 MG. These results suggest that a Phase I trial of CPT-11 plus temozolomide plus O6-BG in AGT-positive tumors may be an important intervention to maximize the therapeutic benefits of the combination of CPT-11 and temozolomide.

Acyl derivatives of demethylpenclomedine, an antitumor-active, non-neurotoxic metabolites of penclomedine

PURPOSE

The purpose of this investigation was to compare the antitumor activities of a series of acyl derivatives of 4-demethylpenclomedine (DM-PEN), the major plasma metabolite of penclomedine (PEN) observed to be an active antitumor agent in vivo and non-neurotoxic in a rat model with that of DM-PEN.

METHODS

Acyl derivatives were prepared from DM-PEN and evaluated in vivo against human MX-1 breast tumor xenografts implanted subcutaneously (s.c.) or intracerebrally (i.c.). Several derivatives were also evaluated against other human tumor xenografts and murine P388 leukemia cell lines.

RESULTS

Several of the acyl derivatives were found to be superior to DM-PEN against MX-1, human ZR-75-1 breast tumor, human U251 CNS tumor and the P388 leukemia parent cell line and lines resistant to cyclophosphamide and carmustine. 4-Demethyl-4-methoxyacetylpenclomedine showed inferior activity to current clinical brain tumor drugs against a glioma cell line, superior activity to temozolomide and procarbazine against the derived mismatch repair-deficient cell line, and superior activity to cyclophosphamide and carmustine but inferior activity to temozolomide against two ependymoma cell lines, all of which were implanted s.c.

CONCLUSION

Proposed mechanisms of activation and action of DM-PEN and the acyl derivatives support the potential clinical superiority of the acyl derivatives.

Association between cognitive impairment and atrial fibrillation: A systematic review

PURPOSE

Although it is well established that atrial fibrillation (AF) causes ischemic stroke, the relationship between AF and cognitive impairment is unclear. The aim of this systematic review is to investigate whether AF is associated with cognitive impairment or dementia.

MATERIALS AND METHODS

An electronic search of Medline, Embase, Psychlit, Cinahl and the Cochrane library was performed in March 2000 to identify studies in which the primary aim was to investigate the relationship between AF and cognitive impairment or dementia. Studies with relevant data on both cognitive function and AF (even if that was not the primary aim of the study) were also identified. Further references were identified from these sources.

RESULTS

Ten studies were identified, of which 4 were cross-sectional, 5 were case-control, and 1 was a prospective cohort study. The methodology and measures of cognition varied substantially, so it was not valid to apply formal meta-analysis techniques to the results. However, the methodology in all the studies was flawed in at least 1 aspect, including the reporting of results, external validity, and internal validity. Seven studies found an association between AF and at least 1 measure of cognition whereas 3 studies did not find an association.

CONCLUSION

The evidence that AF is associated with cognitive impairment is inconclusive. Further studies are required to establish whether there is a relationship between AF and cognitive impairment, and if so, whether the relationship is causal.

Schedule-dependent activity of temozolomide plus CPT-11 against a human central nervous system tumor-derived xenograft

Temozolomide, an imidazole tetrazinone, and CPT-11, a camptothecin derivative, have previously been shown to have anti-central nervous system tumor activity in laboratory and clinical studies. The current experiments were designed to evaluate the activity of temozolomide plus CPT-11 against a malignant glioma-derived xenograft, D-54 MG, growing s.c. in athymic nude mice. The initial schedule of i.p. drug administration was temozolomide at 0.1 LD10 on day 1 and CPT-11 at 0.1 LD10 on days 1-5 and 8-14. The combination of these two agents produced greater than additive activity against D-54 MG. This enhanced activity was maintained when the initial administration of CPT-11 was delayed to day 3 or day 5. However, when CPT-11 was administered first on day 1 using 0.5 LD10 (for the single dose schedule) followed by temozolomide (0.1 LD10) 5 h, 3 days, or 5 days later, the enhancement of activity was substantially reduced. These results demonstrate that the combination of temozolomide plus CPT-11 displays a schedule-dependent enhancement of antitumor activity, suggest a mechanistic explanation for the enhanced activity, and provide the rationale for a Phase I trial of this regimen.

Stress-related primary intracerebral hemorrhage: autopsy clues to underlying mechanism

BACKGROUND

Research into the causes of small-vessel stroke has been hindered by technical constraints. Cases of intracerebral hemorrhage occurring in unusual clinical contexts suggest a causal role for sudden increases in blood pressure and/or cerebral blood flow.

CASE DESCRIPTION

We describe a fatal primary thalamic/brain stem hemorrhage occurring in the context of sudden emotional upset. At autopsy, the brain harbored several perforating artery fibrinoid lesions adjacent to and remote from the hematoma as well as old lacunar infarcts and healed destructive small-vessel lesions.

CONCLUSIONS

We postulate that the emotional upset caused a sudden rise in blood pressure/cerebral blood flow, mediating small-vessel fibrinoid necrosis and rupture. This or a related mechanism may underlie many small-vessel strokes.

Additional risk factors in atrial fibrillation patients not receiving warfarin

OBJECTIVE

To study how many elderly inpatients with previously diagnosed atrial fibrillation were not receiving anticoagulant prophylaxis, and the prevalence of additional risk factors in these patients.

METHODS

All new admissions to a department of medicine for the elderly were screened for atrial fibrillation. Additional risk factors were analysed in those with established atrial fibrillation who were not receiving warfarin. Previous hospital admissions, documentation of why prophylaxis was not being used and use of aspirin as an alternative agent were also examined.

RESULTS

56 patients had previously diagnosed atrial fibrillation; 82% were not taking warfarin and 71% of these were not on aspirin either. All patients not taking warfarin had one additional risk factor for stroke and 95% had two or more. Fifty-two percent had attended hospital when atrial fibrillation was present within the previous 3 years and there was nothing documented in their records to explain why anticoagulation had not been used.

CONCLUSIONS

Most elderly inpatients with established atrial fibrillation were not taking warfarin. All had additional risk factors for stroke, which increase the absolute benefit of anticoagulation.

Modulation of cyclophosphamide activity by O6-alkylguanine-DNA alkyltransferase

PURPOSE

The human medulloblastoma cell line D283 Med (4-HCR), a line resistant to 4-hydroperoxycyclophosphamide (4-HC), displays enhanced repair of DNA interstrand crosslinks induced by phosphoramide mustard. D283 Med (4-HCR) cells are cross-resistant to 1,3-bis(2-chloroethyl)- -nitrosourea, but partial sensitivity is restored after elevated levels of O6-alkylguanine-DNA alkyltransferase (AGT) are depleted by O6-benzylguanine (O6-BG). Studies were conducted to define the activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide against D283 Med (4-HCR) after AGT is depleted by O6-BG.

METHODS

Limiting dilution and xenograft studies were conducted to define the activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide with or without O6-BG.

RESULTS

The activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide against D283 Med (4-HCR) was increased after AGT depletion by O6-BG preincubation. Similar studies with Chinese hamster ovary cells, with or without stable transfection with a plasmid expressing the human AGT protein, revealed that the AGT-expressing cells were significantly less sensitive to 4-HC and 4-hydroperoxydidechlorocyclophosphamide. Reaction of DNA with 4-HC, phosphoramide mustard, or acrolein revealed that only 4-HC and acrolein caused a decrease in AGT levels.

CONCLUSIONS

We propose that a small but potentially significant part of the cellular toxicity of cyclophosphamide in these cells is due to acrolein, and that this toxicity is abrogated by removal of the acrolein adduct from DNA by AGT.

Therapeutic efficacy of vinorelbine against pediatric and adult central nervous system tumors

PURPOSE

The activity of vinorellbine, a new semisynthetic vinca alkaloid, was evaluated against a battery of human tumor xenografts derived from adult and pediatric CNS malignancies.

METHODS

Tumors included adult high-grade gliomas (D-54 MG, D-245 MG), childhood high-grade gliomas (D-212 MG, D-456 MG), medulloblastomas (D-341 MED, D-487 MED), ependymomas (D-612 EP, D-528 EP), and a mismatch repair-deficient procarbazine-resistant glioma [D-245 MG (PR)]. Tumors were grown subcutaneously in athymic nude mice and vinorelbine was administered at a dose of 11 mg/kg on days 1, 5, and 9. Additionally, vinorelbine was also administered in combination with BCNU against D-54 MG.

RESULTS

Vinorelbine produced statistically significant growth delays in D-456 MG, D-245 MG, and D-245 MG (PR). No statistically significant growth delays were observed in D-54 MG, D-487 MED, D-212 MG, D-528 EP, D-341 MED or D-612 EP. The antitumor effects of the vinorelbine/BCNU combination were additive. Growth delays observed in the procarbazine-resistant line [D-245 MG (PR)] were greater than twofold the delays seen in the parent line (D-245 MG). Vincristine was equally potent against D-245 MG and D-245 MG (PR). Taxol demonstrated little activity against D-245 MG but produced 32- and 18-day growth delays in D245 MG (PR).

CONCLUSIONS

These studies indicate that vinorelbine possesses antitumor activity against several glioma tumor xenografts with marked activity in a mismatch repair deficient-tumor.

Enhancement of irinotecan (CPT-11) activity against central nervous system tumor xenografts by alkylating agents

Two major obstacles in the treatment of patients with central nervous system malignancies are drug resistance and host toxicity. The goal of combination chemotherapy is to achieve therapeutic effects that are more favorable than using a single drug alone, but without an increase in normal organ toxicity. The study reported here examined the combination of a topoisomerase I inhibitor, irinotecan (CPT-11), with three different alkylating agents: 1,3-bis(2-chloroethyl)-1-nitrosourea, busulfan, and cyclophosphamide. We evaluated the antitumor effects of these three combinations against a panel of human tumor xenografts derived from central nervous system malignancies, including adult high-grade gliomas (D-54 MG, D-245 MG) and a childhood ependymoma (D-612 EP). In replicate experiments, the alkylating agents were given on day 1 in doses varying from 10% to 75% of the dose lethal to 10% of the animals, and CPT-11 was given on days 1-5 and 8-12 in doses varying from 10% to 100% of the dose lethal to 10% of the animals. The antitumor effects of the various combinations ranged from less than additive (7.61 days below additive with 0.5 CPT-11 + 0.75 cyclophosphamide in D-54 MG) to statistically significant (P < 0.001) supraadditive effects (18.80 days above additive with 0.5 CPT-11 + 0.5 1,3-bis(2-chloroethyl)-1-nitrosourea in D-54 MG). These studies show that the combination of the topoisomerase inhibitor CPT-11 and alkylating agents may increase the antitumor effect in some cases well above additive with no increase in host toxicity (0/10 deaths in both experiments cited above) and should be considered for combination chemotherapy of central nervous system malignancies.

Methylator resistance mediated by mismatch repair deficiency in a glioblastoma multiforme xenograft

A methylator-resistant human glioblastoma multiforme xenograft, D-245 MG (PR), in athymic nude mice was established by serially treating the parent xenograft D-245 MG with procarbazine. D-245 MG xenografts were sensitive to procarbazine, temozolomide, N-methyl-N-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, 9-aminocamptothecin, topotecan, CPT-11, cyclophosphamide, and busulfan. D-245 MG (PR) xenografts were resistant to procarbazine, temozolomide, N-methyl-N-nitrosourea, and busulfan, but they were sensitive to the other agents. Both D-245 MG and D-245 MG (PR) xenografts displayed no O6-alkylguanine-DNA alkyltransferase activity, and their levels of glutathione and glutathione-S-transferase were similar. D-245 MG xenografts expressed the human mismatch repair proteins hMSH2 and hMLH1, whereas D-245 MG (PR) expressed hMLH1 but not hMSH2.

Engraftment of C6-2B cells into the striatum of ACI nude rats as a tool for comparison of the in vitro and in vivo phenotype of a glioma cell line

The C6-2B is a well-characterized glioma cell line used extensively in the study of malignant glial biology. While the C6-2B cell line has traditionally been thought of as a homogenous cell line, the in vitro phenotype of the C6-2B cell line can vary considerably depending on the culture technique used and the stratum on which the cells are grown. Thus, we asked whether the in vitro phenotype of the C6-2B cell line was significantly different than the in vivo phenotype of the cell line once it was engrafted into the striatum of nude rats. Under culture conditions used in our laboratory, 100% of the C6 cells were found to express p75, the low-affinity nerve growth factor (NGF) receptor, and Major Histocompatability Class I (MHC Class I), while only 10-15% demonstrated vimentin reactivity. Immunohistochemistry was consistently negative for GFAP, trkA (the high-affinity receptor for NGF), CD4, CD8, and a macrophage specific marker (Ox-41). Once engrafted into the striatum of nude rats, the cells remained 100% p75 and MHC Class I positive, and again, only 15% of the cells demonstrated vimentin reactivity. The grafted cells retained this characteristic for 28 days in vivo. Although an immunoincompetent host was selected to minimize the effects an inflammatory response would have on the graft, a transient inflammatory response was detected. During the first week of engraftment, numerous MHC class II cells, some of which were macrophages, were seen infiltrating the graft. However, by 4 weeks postengraftment, no inflammatory cells were appreciated in the graft and surprisingly little reactive gliosis was seen in the penumbra of the tumor mass. Thus, the limited number of in vitro phenotypic characteristics we examined in the C6-2B cell line remained constant once the cells were engrafted into the striatum of athymic nude rats.

Characterization of the mechanisms of busulfan resistance in a human glioblastoma multiforme xenograft

Busulfan is an alkylating agent commonly used in the treatment of chronic myelogenous leukemia and in combination with cyclophosphamide in preparation for allogeneic bone marrow transplantation. Serial treatment of a childhood high-grade glioma xenograft (D-456 MG) with busulfan resulted in a busulfan-resistant xenograft, D-456 MG(BR). Cross-resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea was seen but not resistance to cyclophosphamide or CPT-11. Cytoplasmic levels of glutathione in D-456 MG(BR) were approximately one-half those found in D-456 MG. This depletion could not be explained by levels of glutathione-S-transferase, or by amplification, rearrangement, or increased levels of transcript of gamma-glutamylcysteine synthetase. Furthermore, depletion of glutathione in D-456 MG did not alter busulfan activity. Quantitation of busulfan levels in D-456 MG and D-456 MG(BR) xenografts following treatment of mice at the dose lethal to 10% of the animals demonstrated that significantly lower levels of drug were achieved in D-456 MG(BR). These studies suggest that alterations in drug transport or metabolism of busulfan may play a role in the resistance of D-456 MG(BR) to this alkylator.

Therapeutic efficacy of the topoisomerase I inhibitor 7-ethyl-10-(4-[1-piperidino]-1-piperidino)-carbonyloxy-camptothecin against pediatric and adult central nervous system tumor xenografts

Therapy of patients with malignant central nervous system tumors is frequently unsuccessful, reflecting limitations of current surgical, radiotherapeutic, and pharmacotherapeutic treatments. The camptothecin derivative irinotecan (CPT-11) has been shown to possess antitumor activity in phase II trials for patients with carcinoma of the lung, cervix, ovary, colon, or rectum and for patients with non-Hodgkin's lymphoma. The current study was designed to test the efficacy of the drug against a panel of human tumor xenografts derived from adult and pediatric central nervous system malignancies. Tumors included childhood high-grade gliomas (D-212 MG, D-456 MG), adult high-grade gliomas (D-54 MG, D-245 MG), medulloblastomas (D341 Med, D487 Med), ependymomas (D528 EP, D612 EP), and a rhabdomyosarcoma (TE-671), as well as sublines with demonstrated resistance to busulfan (D-456 MG (BR)), cyclophosphamide (TE-671 CR), procarbazine (D-245 MG (PR)) or melphalan (TE-671 MR), growing subcutaneously and intracranially in athymic nude mice. In replicate experiments, CPT-11 was given at a dosage of 40 mg/kg per dose via intraperitoneal injection in 10% dimethylsulfoxide on days 1-5 and 8-12, which is the dosage lethal to 10% of treated animals. CPT-11 produced statistically significant (P < 0.001) growth delays in all subcutaneous xenografts tested, including those resistant to busulfan, cyclophosphamide, procarbazine, and melphalan, with growth delays ranging from 21.3 days in D487 Med to 90+ days in several tumor lines. Further, tumor regression was evident in every treated animal bearing a subcutaneous tumor, with some xenografts yielding complete tumor regression. Statistically significant (P < 0.001) increases in survival were demonstrated in the two intracranial xenografts-D341 EP (73.0% increase) and D-456 MG (114.2% increase)-treated with CPT-11. These studies demonstrate that, of over 40 drugs evaluated in this laboratory, CPT-11 is the most active against central nervous system xenografts and should be advanced to clinical trial as soon as possible.

Enhancement of melphalan activity by inhibition of DNA polymerase-alpha and DNA polymerase-beta

Our previous studies exploring melphalan resistance in the human rhabdomyosarcoma xenograft TE-671 MR revealed elevation of DNA polymerase-alpha and DNA polymerase-beta. The present study evaluated the alteration of melphalan activity in TE-671 (melphalan-sensitive) and TE-671 MR (melphalan-resistant) subcutaneous xenografts in nude mice after DNA polymerase-alpha was inhibited using aphidicolin glycinate (AG) and DNA polymerase-beta was inhibited using dideoxycytidine (DDC). Administration of AG or DDC did not produce toxicity or demonstrate antineoplastic activity when given alone. AG (90 mg/m2) enhanced the activity of melphalan against TE-671, with growth delays increasing by 8.4, 15.8, and 21.2 days over the regimen with melphalan only. AG (180 mg/m2) only modestly increased melphalan activity against TE-671 MR, with the growth delays increasing from 9.6 and 12.1 days using melphalan alone to 12.1 and 14.5 days using melphalan plus AG. AG (180 mg/m2) plus melphalan (the dose lethal to 10% of animals) produced greater weight loss compared with melphalan alone, whereas DDC plus melphalan produced no additional toxicity. DDC modestly enhanced the activity of melphalan plus AG against TE-671 MR. AG plus O6-benzylguanine did not increase the activity of 1,3-bis(2-chloroethyl)-1-nitrosourea against TE-671 or TE-671 MR. AG (90 mg/m2 and 180 mg/m2) inhibited DNA polymerase-alpha to 80% and 72% of control in TE-671 and 64% and 37% in TE-671 MR, and DDC inhibited DNA polymerase-beta to 59% in TE-671 and 48% in TE-671 MR. These results suggest a role for AG-mediated enhancement of melphalan activity, particularly in the treatment of newly diagnosed, melphalan-sensitive tumors.