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Advances in Brief |
by Temozolomide in Experimental Glioblastoma
1 Department of Surgery, Section of Neurosurgery and 2 Department of Radiation and Cellular Oncology, Pritzker School of Medicine, The University of Chicago, Chicago, Illinois; 3 Brain Tumor Research Laboratories, Division of Neurosurgery, Department of Surgery, University of Alabama, Birmingham, Alabama; and 4 Dana-Farber Cancer Institute, Department of Medical Oncology, Boston, Massachusetts
| ABSTRACT |
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(TNF-
) is a polypeptide cytokine with synergistic antitumor activity in combination therapy with alkylating agents. We investigated the combined use of Ad.Egr-TNF, a replication-defective adenoviral vector encoding the cDNA for TNF-
under the control of chemo-inducible elements of the egr1 gene promoter, and intraperitoneal temozolomide in an intracranial human malignant glioma model. In hind limb U87MG xenografts, temozolomide produced a 6.4-fold greater induction of TNF-
after infection with Ad.Egr-TNF compared with Ad.Egr-TNF alone at 96 hours (P < 0.02). TNF-
and temozolomide combination leads to a synergistic decrease in U87 cell viability at 72 hours compared with either treatment alone (P < 0.001). Median survival for animals treated with Ad.Egr-TNF alone, temozolomide alone, and Ad.Egr-TNF/temozolomide was 21, 28, and 74 days, respectively (P < 0.001 by log-rank). Flow cytometric assessment of apoptosis revealed a synergistic increase in U87 cell apoptosis in vitro at 72 hours (P < 0.05), and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) evaluation of tumor sections revealed significantly increased TUNEL-positive cells after combination treatment compared with either treatment alone (P < 0.05). In conclusion, combination treatment with transcriptionally activated intratumoral TNF-
and systemic temozolomide significantly prolongs survival in an experimental glioblastoma multiforme model. | Introduction |
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(TNF-
) is a cytokine with significant anticancer activity (4)
. Although toxicity has limited its systemic use (5)
, a synergistic antitumor effect is seen when it is used at high concentrations in regional perfusion strategies with alkylating agents (6)
. The replication-defective adenoviral vector Ad.Egr-TNF consists of a chimeric gene encoding CArG elements of the chemoinducible/radioinducible early growth response-1 (egr1) gene promoter ligated upstream to the human TNF-
cDNA. This vector has been shown to be induced to express TNF-
by the drug cisplatin (7)
. In this study, we show that temozolomide can induce the intratumoral (i.t.) expression of TNF-
from Ad.Egr-TNF and that combination treatment with this vector and temozolomide leads to a significant prolongation in survival in an intracranial xenograft model of malignant glioma. The primary mechanism of this antiglioma effect appears likely to be due to a synergistic enhancement of tumor cell apoptosis by the combination of TNF-
and temozolomide. | Materials and Methods |
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Tumor Necrosis Factor
Induction In vitro
U87 cells (106) were plated and incubated overnight. The cells were then infected with Ad.Egr-TNF at 100 multiplicities of infection for 3 hours at 37°C. After incubation, 3.8 mL of complete medium with or without temozolomide were added. Conditioned media were harvested at 48 hours after treatment, and human TNF-
production was quantified using a Quantikine enzyme-linked immunosorbent assay (ELISA) kit (R&D System, Inc., Minneapolis, MN).
Tumor Necrosis Factor
Induction In vivo
U87 cells (5 x 106) in 100 µL of DMEM were injected subcutaneously (s.c.) into the right hind limb of nude mice. When tumors reached an average size of 200 mm3 (length x width x thickness/2), the tumor-bearing mice were randomized into four groups: (1)
untreated control, (2)
Ad.Egr.TNF alone, (3)
temozolomide alone, and (4)
Ad.Egr-TNF and temozolomide. Ad.Egr-TNF was injected i.t. at a dose of 2 x 108 particle units (pu) each day. Two doses of temozolomide were given: 2.5 and 5 mg/kg/d by intraperitoneal (i.p.) injection 3 hours after vector. Four consecutive daily i.t. and i.p. injections were given, and control animals received i.t. and i.p. serum-free medium. Animals were euthanized on days 2 and 4 (i.e., 48 and 96 hours after treatment initiation), and tumors were harvested, snap-frozen in liquid nitrogen, and homogenized in radioimmunoprecipitation assay buffer [150 mmol/L NaCl, 10 mmol/L Tris (pH 7.5), 5 mmol/L EDTA (pH 7.5), 100 mmol/L phenylmethylsulfonyl fluoride, 1 µg/mL leupeptin, and 2 µg/mL aprotinin]. Protein was isolated, and concentration was measured using Protein Assay reagent (Bio-Rad Laboratories, Hercules, CA). TNF-
levels in the supernatants were measured as described above.
U87 Cell Viability Studies
Trypan blue dye exclusion method was used. U87 cells (104) were plated and incubated at 37°C overnight. Subsequently, 10 ng/mL TNF-
[dose based on Staba et al. (8)
] and/or 100 µmol/L temozolomide-containing media [dose based on Hirose et al. (9)
and in vitro induction studies below] were added for 3 hours and washed. At 24, 48, and 72 hours after exposure to agent, the cells were trypsinized, and the viable cell number per well was determined using a hemocytometer. 3-(4,5-dimethylthiazol(-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium, inner salt colorimetric assay, per the manufacturers protocol (Cell Titer 96 Aqueous, One Solution cell proliferation assay; Promega, Madison, Wisconsin), was used to verify cell viability at 72 hours. Absorbance was read at 490 nm using an ELISA microplate reader after 1.5 hour, at 37°C. All of the studies were performed in triplicate.
Xenograft Studies
U87 hind limb xenografts were established as described above. Mice were randomized into the same groups, and treatment was initiated (day 0). Ad.Egr-TNF (2 x 108 pu) was injected i.t. twice a week for four total injections, and 5 mg/kg temozolomide was given i.p. 3 hours after each vector injection for a total of 20 mg/kg. The dose of temozolomide used was approximately 0.2 LD10 and was chosen to have modest antitumor effect but to not be curative based on previous studies (10)
and data from our lab showing LD50 for i.p. temozolomide to be approximately 500 mg/kg. Tumor volume was measured every 2 to 3 days as above. Fractional tumor volume (V/V0 where V0 = volume on day 0) was calculated and plotted. For intracranial experiments, 5 x 105 U87 cells were inoculated into the right caudate nucleus on day 0 using a screw guide technique (11)
. On day 5, mice were randomized into four groups as above, and 5 x 108 pu of Ad.Egr-TNF in a 5-µL volume were injected once via the screw guide directly into the tumor. Temozolomide (5 mg/kg) was given i.p. 3 hours after intracranial vector inoculation. Four consecutive daily i.p. temozolomide injections were given to a total dose of 20 mg/kg. Control animals received serum-free medium i.t. and i.p. Daily assessment of animal appearance was made. Mice were followed until death or sacrificed when moribund. Mouse brains were harvested after intracardiac perfusion and fixed with 10% neutral buffered formalin. For terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) evaluation (see below), animals were sacrificed on day 7 after treatment (n = 3 per group).
Flow Cytometric Analysis of Apoptosis
Fractional DNA Content.
U87 cells (105) were plated overnight at 37°C with 5% CO2. The cells were then treated with TNF-
(10 ng/mL) and/or temozolomide (100 µmol/L). At 72 hours, the cells were washed in PBS and fixed in ice-cold 70% (v/v) ethanol. The cells were washed twice, incubated in RNase (1 mg/mL) for 30 minutes at 37°C, and then incubated in propidium iodide solution (100 µg/mL) for 30 minutes at 4°C. Flow cytometric analysis was performed on a FACSort instrument (Becton Dickinson Immunocytometry Systems, San Jose, CA), and the data were analyzed using the CellQuest software (Becton Dickinson).
Annexin V Binding.
At 72 hours, cells were washed in PBS and incubated in the dark for 15 minutes with binding buffer containing 5 µL of Annexin V-FITC and 5 µL of propidium iodide (Annexin V-FITC apoptosis detection kit II; ref. 12
). The data were analyzed by Flowjo analysis software (Tree Star Inc., Ashland, OR).
Histologic Analysis
(1) Paraffin embedded brains were sectioned (8 µm), stained with hematoxylin and eosin, and analyzed in a blinded fashion.
(2) TUNEL assay was performed in accordance with the manufacturers instructions (Chemicon, Temecula, CA) and analyzed blindly at x400 magnification by use of a computer-aided light microscope with reconstruction software (Neurolucida, Microbrightfield, VT). Number of TUNEL-positive cells per 106 mm2 was documented.
Statistical Analysis
Results are expressed as mean value ± SD. Statistical significance was taken as P < 0.05 using a one-tailed Students t test. Analysis of variance (ANOVA) was also used. Kaplan-Meier survival curves were plotted for the intracranial experiment and analyzed by the log-rank method.
| Results |
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Induction and Assessment of U87MG Cell Viability.
from U87 cells infected with Ad.Egr-TNF. In vitro, there was no TNF-
detected in the untreated control or temozolomide alone cells, however, after Ad.Egr-TNF infection,100 µmol/L temozolomide induced a 2.3-fold increase in TNF-
expression compared with cells infected with vector alone (Fig. 1A)
detected in the untreated control or temozolomide alone animals, however, after combination treatment with Ad.Egr-TNF/temozolomide, 287 ± 111 pg TNF-
/mg protein were detected at 96 hours6.4-fold the value in the Ad.Egr-TNF alone animals (n = 3 animals per group, P = 0.02; Fig. 1B
and temozolomide on glioma cell viability was evaluated in vitro. TNF-
(10 ng/mL) and 100 µmol/L temozolomide alone had minimal effects on U87 cell viability; however, combination treatment lead to a significant reduction in cell viability, the magnitude of which was greater than the sum of the reductions of either treatment alone. Support for a synergistic interaction between TNF-
and temozolomide was observed after ANOVA assessment (P = 0.0016; Fig. 2A and B
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and glioma cytotoxicity in vitro, we next evaluated the antitumor efficacy in hind limb s.c. xenografts. There was no significant effect on growth kinetics in tumors treated with vector alone compared with the untreated control animals; however, fractional tumor volume was significantly smaller in the combination treatment group compared with the temozolomide alone group (P < 0.02 at day 20; Fig. 3A
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alone had minimal effect on U87 cell apoptosis (13)
, and temozolomide alone lead to an increase in the percentage of cells in G2-M phase (9)
, however, combination treatment with TNF-
and temozolomide lead to a significant increase in the sub-G1 (hypodiploid/apoptotic) peak at 72 hours compared with either treatment alone (P < 0.05; Fig. 4A
and temozolomide alone, respectively, at 72 hours (Fig. 4B)
and temozolomide combination results in apoptosis in vitro, we were interested in whether this phenomenon was also evident in vivo. Using TUNEL evaluation of intracranial tumor sections, we specifically looked at apoptosis during the early stage of treatment (day 7). Tumors treated with Ad.Egr-TNF/temozolomide combination had significantly more TUNEL-positive cells than those treated with either temozolomide or Ad.Egr-TNF alone (110 ± 77 versus 14 ± 12 and 13 ± 13 TUNEL+ cells/106 mm2, respectively, P < 0.05; Fig. 4C
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| Discussion |
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.
In isolated limb perfusion studies, where high dose TNF-
is used with an alkylating agent, a synergistic interaction has been documented that has been shown to be due to an increase in tumor necrosis possibly due to an increase in vascular permeability leading to an increase in i.t. drug concentration (16)
. A similar pattern of tumor necrosis has also been observed when radiotherapy is combined with Ad.Egr-TNF in a flank glioma model (8)
. Although tumor necrosis was not observed histologically in our experiments, we did observe a significant increase in tumor cell apoptosis both in vitro and in vivo. However, we and others have shown that neither TNF-
alone nor temozolomide alone results in significant apoptosis in glioma cells (9
, 17)
. Considered together, these data strongly suggest that there is a direct interaction between TNF-
and temozolomide in glioma cells that enhances apoptosis, resulting in the therapeutic benefit reported in our experiments.
A therapeutic increase in tumor cell apoptosis has been speculated to be a desirable goal of novel glioma therapies (18) , particularly because tumor necrosis has been associated with a significantly worse prognosis in glioblastoma multiforme patients (19) . However, additional studies are necessary to determine the mechanism involved in the induction of apoptosis and whether treatment-induced apoptosis yields a greater therapeutic ratio in malignant glioma than therapeutically induced necrosis.
Mortality from malignant glioma is related primarily to recurrent disease, which is almost universally local (nonmetastatic) in nature (20) . For this reason, these tumors are an ideal target for such a regionally activated treatment strategy. The considerable antitumor efficacy demonstrated in this series of experiments provides preliminary support for the potential use of this treatment paradigm in recurrent glioma patients. Although the animals in the treatment groups were noted to be healthy, formal toxicity studies will need to be performed before making conclusions regarding the potential toxic effects of this treatment.
| FOOTNOTES |
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Note: D. W. Kufe and R. R. Weichselbaum are consultants to and have an equity interest in Gen Vec Corporation, Gaithersburg, MD.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: Bakhtiar Yamini, MC 4066, Section of Neurosurgery, 5841 South Maryland Avenue, University of Chicago Hospitals, Chicago, IL 60637. Phone: 773-702-2475; Fax: 773-702-5234; E-mail: byamini{at}surgery.bsd.uchicago.edu
Received 6/15/04. Revised 7/16/04. Accepted 8/ 3/04.
| REFERENCES |
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with melphalan in isolated limb perfusion in the rat. Br J Surg, 1996;83:551-5, [Medline]
gene therapy and radiation damage tumor vasculature in a human malignant glioma xenograft. Gene Ther, 1998;5:293-300, [CrossRef][Medline]
. Clin Cancer Res, 2004;10:234-43, [CrossRef][Medline]
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