Selected recent journal articles publications supported by the Brian D. Silber Memorial Fund:

Chakravarti, A.; Zhai, G.; Suzuki, Y.; Sarkesh, S.; Black, P.; Muzikansky, A. ; Loeffler, J. The Prognostic Significance of Phosphatidylinositol 3-Kinase Pathway Activation in Human Gliomas. J Clin Oncol 2004 May 15;22(10):1926-33. [download pdf reprint of publication]

PURPOSE: The objectives of this study were to examine activation patterns of the phosphatidylinositol 3-kinase (PI3K) pathway in gliomas and to examine the prognostic significance of PI3K pathway activation using snap-frozen clinical specimens. MATERIALS AND METHODS: Levels of expression of PI3K pathway members were assessed in 92 prospectively collected gliomas through quantitative Western analysis using total and phospho-specific antibodies for PI3K, Akt, and p70(s6k). Both expression and expression levels of these PI3K pathway members were correlated with histology, markers of apoptosis (cleaved caspase 3), and with clinical outcome (eg, overall survival). RESULTS: It was determined that activation of all three PI3K pathway members were significantly more frequent in glioblastoma multiforme than in non-glioblastoma multiforme tumors. Levels of phospho-PI3K, phospho-Akt, and phospho-p70(s6k) were all found to be inversely associated with cleaved caspase 3 levels, suggesting PI3K pathway activation is associated with reduced levels of apoptosis. Perhaps most importantly, activation of PI3K pathway members was found to be significantly associated with reduced survival times when all glioma cases were considered in aggregate. When glioblastoma cases were considered separately, the prognostic value of PI3K activation remained significant, suggesting that PI3K activation may directly be associated with radiation resistance, given that this was the only adjuvant therapy administered to this subset of patients. CONCLUSION: Activation of the PI3K pathway is significantly associated with increasing tumor grade, decreased levels of apoptosis, and with adverse clinical outcome in human gliomas. Molecular pathways regulating PI3K activation would appear to be promising targets in the clinical management of glioma patients.

Nestler U, Wakimoto H, Siller-Lopez F, Aguilar LK, Chakravarti A, Muzikansky A, Stemmer-Rachamimov A, Chiocca EA, Aguilar-Cordova E, Hochberg FH. The combination of adenoviral HSV TK gene therapy and radiation is effective in athymic mouse glioblastoma xenografts without increasing toxic side effects. J Neurooncol. 2004 Mar-Apr;67(1-2):177-88. [download pdf reprint of publication]

OBJECT: In mouse models of prostate and breast cancer therapeutic effects are enhanced when adenoviral HSV TK gene therapy is combined with ionizing radiation. In the present study, we adopted this approach for the treatment of human glioblastoma xenografts in an athymic mouse model and assessed treatment results as well as toxic side effects. METHODS: About 72 nude mice received intracerebral inoculations of 2 x 10(5) U87deltaEGFR cells. On day 7 after tumor implantation the study population was randomized into six treatment arms: (1) intratumoral buffer inoculation on day 7, (2) intratumoral adenoviral vector injection (2 x 10(9) vp) on day 7, (3) single dose radiation (2.1 Gy) on day 9, (4) adenoviral injection + radiation, (5) adenoviral injection + ganciclovir (GCV) (20 microg/g twice daily from day 8 to 17), (6) adenoviral injection + GCV + radiation. On day 21 half of the animals were sacrificed for histological evaluation of the brain tumors, the other half was assessed for survival. RESULTS: This study showed significantly prolonged median survival time of 5 days for the GCV treated groups. The addition of radiation decreased the frequency of neurological symptoms and delayed the onset of deficits without altering the expression of thymidine kinase in the tumor cells. CONCLUSIONS: We conclude that adenoviral HSV TK gene therapy in combination with adjuvant radiotherapy does not generate increased toxic side effects in glioblastoma treatment. The prolonged survival time of animals receiving gene therapy and the reduced occurrence of neurological symptoms in irradiated mice constitute promising features of the combined treatment.

Chakravarti, A.; Zhai, G.; Zhang, M., Malhotra, R.; Latham, D., Delaney, M., Robe, P.; Nestler, U.; Loeffler, J. Survivin Enhances Radiation Resistance in Primary Human Glioblastoma Cells via Caspase-Independent Mechanisms. Oncogene. 2004 Sep 30;23(45):7494-506. [download pdf reprint of publication]

The observed radioresistance of human glioblastoma multiforme (GBM) poses a major challenge, which, if overcome, may lead to significant advances in the management of this patient population. There is accumulating evidence from correlative studies that Survivin expression is associated with increased malignant potential of human gliomas. The purpose of this study was to investigate whether Survivin plays a direct role in mediating radiation resistance in primary human glioma cell lines, and, if so, investigating the underlying mechanisms. Our panel of GBM cell lines included two that were relatively radiation resistant (GM20 and GM21) and two that were more radiation sensitive (GM22 and GM23), which demonstrated differential levels of Survivin expression between the two groups. Through the use of adenoviral vectors containing either dominant-negative (pAd-S(T34A)) or wild-type Suvrivin (pAd-S(WT)), we were able to inactivate or overexpress Survivin, respectively. Our findings suggest that Survivin plays a critical role in mediating radiation resistance in primary GBM cells, in part through suppression of apoptotic cell death via a caspase-independent manner. We have identified novel mechanisms by which Survivin may enhance tumor cell survival upon radiation exposure such as regulation of double-strand DNA break repair and tumor cell metabolism, which were most evident in the radiation-resistant cell lines. These differences in Survivin function both in radiation-resistant vs radiation-sensitive cell lines and in the presence vs absence of radiation exposure warrant further investigation and highlight potentially important mechanisms of radiation resistance in these tumors.

Zhai, G.; Malhotra, R.; Delaney, M; Drummond, K.; Chakravarti, A.* Radiation-induced RhoA activation increases cellular invasion and motility of glioblastoma cells via IGFR/AKT-dependent signaling. J. Neurooncol, epub ahead of print. * AC is senior/corresponding author. [download pdf reprint of publication]

Glioblastoma multiforme (GBM) is among the most treatment-refractory of all human tumors. Radiation is effective at prolonging survival of GBM patients; however, the vast majority of GBM patients demonstrate progression at or near the site of original treatment. We have identified primary GBM cell lines that demonstrate increased invasive potential upon radiation exposure. As this represents a novel mechanism by which radiation-treated GBMs can fail therapy, we further investigated the identity of downstream signaling molecules that enhance the invasive phenotype of irradiated GBMs. Matrigel matrices were used to compare the extent of invasion of irradiated vs. non-irradiated GBM cell lines UN3 and GM2. The in vitro invasive potential of these irradiated cells were characterized in the presence of both pharmacologic and dominant negative inhibitors of extracellular matrix and cell signaling molecules including MMP, uPA, IGFR, EGFR, PI-3K, AKT, and Rho kinase. The effect of radiation on the expression of these signaling molecules was determined with Western blot assays. Ultimately, the in vitro tumor invasion results were confirmed using an in vivo 9L GBM model in rats. Using the primary GBM cell lines UN3 and GM2, we found that radiation enhances the invasive potential of these cells via activation of EGFR and IGFR1. Our findings suggest that activation of Rho signaling via PI-3K is required for radiation-induced invasion, although not required for invasion under physiologic conditions. This report clearly demonstrates that radiation-mediated invasion is fundamentally distinct from invasion under normal cellular physiology and identifies potential therapeutic targets to overcome this phenomenon.

Chakravarti, A.; Erkkinen, M.; Nestler, U.; Stupp, R.; Mehta, M.; Aldape, K.; Gilbert, M.; Black, P.; Loeffler, J. Temozolomide-mediated radiation enhancement in gliomas: a report on underlying mechanisms. Clin Ca Res 2006; 12(15):4738-4746. [download pdf reprint of publication]

PURPOSE: In this study, we investigated the mechanisms by which temozolomide enhances radiation response in glioblastoma cells. EXPERIMENTAL DESIGN: Using a panel of four primary human glioblastoma cell lines with heterogeneous O(6)-methylguanine-DNA methyltransferase (MGMT) protein expression, normal human astrocytes, and U87 xenografts, we investigated (a) the relationship of MGMT status with efficacy of temozolomide-based chemoradiation using a panel of in vitro and in vivo assays; (b) underlying mechanisms by which temozolomide enhances radiation effect in glioblastoma cells; and (c) strategies to overcome resistance to radiation + temozolomide. RESULTS: Temozolomide enhances radiation response most effectively in glioblastomas without detectable MGMT expression. On concurrent radiation + temozolomide administration in MGMT-negative glioblastomas, there seems to be decreased double-strand DNA (dsDNA) repair capacity and enhanced dsDNA damage compared either with radiation alone or with sequentially administered temozolomide. Our data suggest that O(6)-benzylguanine can enhance the antitumor effects of concurrent radiation + temozolomide in MGMT-positive cells by enhancing apoptosis and the degree of dsDNA damage. O(6)-Benzylguanine was most effective when administered concurrently with radiation + temozolomide and had less of an effect when administered with temozolomide in the absence of radiation or when administered sequentially with radiation. Our in vivo data using U87 xenografts confirmed our in vitro findings. CONCLUSIONS: The present study shows that temozolomide enhances radiation response most effectively in MGMT-negative glioblastomas by increasing the degree of radiation-induced double-strand DNA damage. In MGMT-positive glioblastomas, depletion of MGMT by the addition of O(6)-benzylguanine significantly enhances the antitumor effect of concurrent radiation + temozolomide. These are among the first data showing mechanisms of synergy between radiation and temozolomide and the effect of MGMT.

Review Articles Relating to Silber-Supported Work

• Chakravarti, A. Radiation Enhancing Agents for Tumors of the Central Nervous System. Semin Radiat Oncol. 2006 Jan;16(1):29-37.
• Chakravarti, A. Targeted Therapies for Malignant Gliomas. Adv Rad Oncol 2006, (in press).
• Chakravarti, A, Saia, G.; Zhang, M. Predictive and prognostic markers in prostate cancer. Curr Cancer Ther Rev. 2006 Nov;7(6):490-504.
• Chakravarti, A. The Impact of Molecular Profiling on Clinical Trial Design in Glioblastoma. Curr Opin Oncol. 2007 Jan;9(1):71-9.
• Chakravarti, A. Predictive and Prognostic Markers in Human Gliomas. Curr Tr Rep Oncol. 2006 Nov;7(6):490-504.
• Chakravarti, A. Interpretation of Molecular Markers in the Modern Era. Int J Radiat Oncol Biol Phys. 2006 Sep 1;66(1):1-2
  
• Siker, M.; Chakravarti, A.; Mehta, M. Should concomitant and adjuvant treatment with temozolomide be used as standard therapy in patients with anaplastic glioma? Crit Rev Oncol Hematol. 2006 Nov;60(2):99-111.

Chakravarti, A.; Chakladar, A.; Delaney, M.A.; Latham, D.E.; Loeffler, J.S. The epidermal growth factor receptor pathway mediates resistance to sequential administration of radiation and chemotherapy in primary human glioblastoma cells in a RAS-dependent manner. Cancer Res. 2002; 62(15):4307-4315.

Resistance to conventional adjuvant therapies (i.e., chemotherapy and radiation) has been well documented in malignant gliomas. Unlike many other tumor types, combined modality therapy involving radiation and chemotherapy has failed to appreciably enhance outcome for glioblastoma patients compared with radiation alone. In vitro, we have observed an actual antagonistic effect between sequential administration of radiation and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) chemotherapy in three primary human glioblastoma cell lines (referred as the GBME3-5 cell lines), which also happen to demonstrate strong expression of the epidermal growth factor receptor (EGFR). Upon inhibition of EGFR with the EGFR tyrosine kinase inhibitor, AG1478, it was found that this cross-resistance between sequential administration of radiation and BCNU was abrogated. To dissect which of these pathways may be responsible for the observed antagonism, known EGFR-regulated downstream signaling pathways including RAS, phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase (p44/p42), and protein kinase C were inactivated with both pharmacological inhibitors and transient transfection experiments with dominant-negative and constitutively active constructs in the presence of exogenous EGF stimulation. It was found that BCNU inhibited radiation-induced apoptosis through EGFR-mediated activation of PI3-K/AKT via RAS. On the other hand, radiation was found to inhibit BCNU-induced apoptosis through EGFR-mediated activation of both PI3-K and mitogen-activated protein kinase (p44/p42) pathways, also via RAS. Inhibition of either EGFR or RAS activity appears to not only abrogate the observed antagonism between sequentially administered radiation and chemotherapy but actually results in a greater enhancement of apoptosis in the setting of combined modality therapy than when administered with either radiation or chemotherapy as single agents. Therefore, these findings suggest that strategies to inactivate EGFR or RAS signaling may be critical to improving not only the efficacy of single-agent therapy but also of combined modality therapy in gliomas.

Chakravarti, A.; Noll, E.; Black, P.B.; Dyson, N.J.; Loeffler, J.S. Quantitatively-determined survivin expression levels are of prognostic value in human gliomas. J Clin Oncol. 20(4):1063-1068, 2002. [download pdf reprint of publication]

PURPOSE: Survivin is a novel antiapoptotic gene that has been recently cloned and characterized. Its expression has been found to be of prognostic significance in several tumor types. This is the first study on the prognostic significance of survivin expression in human gliomas. MATERIALS AND METHODS: We used quantitative Western blot analysis with densitometry to determine survivin protein expression levels in 92 glioma cases for which frozen tissue was available for analysis. Survivin positivity and expression levels were correlated with histopathologic features of the tumors, apoptosis (as measured by cleaved, or activated, caspase 3 levels), and clinical outcome. RESULTS: Survivin expression has clear prognostic value in human gliomas. Patients with detectable survivin expression had significantly shorter overall survival times (P <.0001) compared with those without detectable expression when all glioma patients were considered. Although glioblastoma multiforme (GBM) patients had significantly higher rates of survivin positivity and higher levels of survivin expression (P <.0001) than their non-GBM counterparts, the prognostic value of survivin expression seemed to be independent of histology alone. Survivin-positive GBM patients had significantly shorter overall survival times compared with survivin-negative GBM patients (P <.0001). Likewise, survivin-positive non-GBM patients had shorter survival times compared with survivin-negative non-GBM patients (P =.029). Furthermore, increasing levels of survivin expression significantly correlated with reduced survival times when all glioma patients were considered, and markedly so for GBM patients (P <.0001). Increasing survivin levels significantly correlated with reduced expression of cleaved caspase 3, indicating its association with antiapoptotic activity. CONCLUSION: Survivin positivity and protein expression levels, as determined quantitatively, are of significant prognostic value in human gliomas and seem to be associated with reduced apoptotic capacity of these tumors.

Chakravarti, A.; Loeffler, J. S.; Dyson, N..J. Insulin-like growth factor receptor I (IGFRI) mediates resistance to anti-epidermal growth factor receptor (EGFR) therapy in primary human glioblastoma cells through continued activation of phosphoinositide 3-kinase signaling. Cancer Res. 62(1):200-207, 2002. [download pdf reprint of publication]

Overexpression of the epidermal growth factor receptor (EGFR) has been shown previously to correlate with enhanced malignant potential of many human tumor types, including glioblastoma multiforme (GBM). Anti-EGFR targeting has been demonstrated to enhance apoptosis and reduce both cellular invasion and angiogenic potential. It remains unclear whether absolute EGFR expression levels are sufficient to predict which tumors will respond best to anti-EGFR therapy. We have identified two primary GBM cell lines with equivalent EGFR expression levels with very different sensitivities to the EGFR receptor tyrosine kinase inhibitor, AG1478. This was apparent despite similar reductions in EGFR signaling in both cell lines, as measured by phospho-EGFR levels. AG1478 enhanced both spontaneous and radiation-induced apoptosis and reduced invasive potential in the GBM(S), but not in the GBM(R), cell line. The resistant GBM(R) cell line demonstrated an up-regulation of insulin-like growth factor receptor I (IGFR-I) levels on AG1478 administration. This resulted in sustained signaling through the phosphoinositide 3-kinase pathway, resulting in potent antiapoptotic and proinvasion effects. Cotargeting IGFR-I with EGFR greatly enhanced both spontaneous and radiation-induced apoptosis of the GBM(R) cells and reduced their invasive potential. Akt1 and p70(s6k) appeared to be important downstream targets of IGFR-I-mediated resistance to anti-EGFR targeting. These findings suggest that IGFR-I signaling through phosphoinositide 3-kinase may represent a novel and potentially important mechanism of resistance to anti-EGFR therapy.

Chakravarti, A.; Delaney, M.D.; Noll, E.; Loeffler, J.S.; Black, P.B.; Dyson, N.J. Prognostic and pathologic significance of protein expression profiling in human gliomas. Clinical Cancer Research 7:2387-2395, 2001. [download pdf reprint of publication]

PURPOSE: Analysis of tumor-derived genetic lesions has provided insights into molecular pathogenesis of human gliomas. Because these changes represent only one of several mechanisms that alter gene expression during tumorigenesis, it is likely that further information will be obtained from a careful analysis of important regulatory proteins present in these tumors. EXPERIMENTAL DESIGN: We have quantified the levels of key cell cycle/signaling proteins in 94 prospectively collected, meticulously preserved, "snap frozen" glioma specimens and have compared these levels with histopathological data and patient outcome. RESULTS: The results of these experiments confirm that the levels of wild-type tumor suppressor proteins, such as p53, pRB, PTEN, p14(ARF), and p16(INK4), are lost or severely reduced in most gliomas, and that epidermal growth factor receptor, 2human telomerase reverse transcriptase, and cyclin-dependent kinase 4 are overexpressed frequently and with a few exceptions, almost exclusively, in glioblastomas. In addition, we report frequent underexpression of E2F-1 (in 55% of gliomas) and cyclin E overexpression (in 26% of gliomas), which have not yet been reported on the genomic level. Several of these markers significantly correlated with histopathological grade, and the levels of five proteins showed significant association with patient outcome. In particular, overexpression of epidermal growth factor receptor, human telomerase reverse transcriptase, cyclin-dependent kinase 4, and cyclin E was largely restricted to glioblastomas and was significantly associated with reduced patient survivals. CONCLUSIONS: We conclude that the quantitation of cell cycle/signaling proteins from meticulously preserved glioma specimens provides further insights into the molecular pathogenesis of human gliomas and yields valuable prognostic information.

Henson, John W. Spinal cord gliomas. Curr Opin Neurol 2001 Dec;14(6):679-82. [download MS Word^TM version]

Introduction - Primary tumors arising from the spinal cord, spinal nerve roots, and dura are rare compared to neoplasms in intracranial locations. Spinal cord gliomas account for the majority of primary intramedullary spinal tumors, and have many unusual features which distinguish them from their intracranial counterparts.

Henson, J.W.; Thornton,A.F.; and Louis, D.N. Spinal cord astrocytoma: Response to PCV chemotherapy. Neurology 2000 Jan 25;54(2):518-20. [download MS Word^TM version]

Information regarding the value of chemotherapy for spinal cord astrocytomas that progress after irradiation is limited. We describe a patient whose conus medullaris astrocytoma responded to PCV (procarbazine, lomustine, and vincristine) chemotherapy after failing radiation and cisplatin-based chemotherapy. PCV should be considered in patients with progressive spinal cord astrocytomas.

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