Application of p27 gene therapy for human malignant glioma potentiated by using mutant p27

2004 ◽  
Vol 101 (3) ◽  
pp. 505-510 ◽  
Author(s):  
Kyung-Ho Park ◽  
Jaeho Lee ◽  
Chul-Gyu Yoo ◽  
Young Whan Kim ◽  
Sung Koo Han ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Gene Therapy ◽  
Malignant Glioma ◽  
Cell Lines ◽  
Wild Type ◽  
Antitumor Effects ◽  
Poor Prognostic Factor ◽  
Content Type ◽  
Fine Print

Object. Malignant glioma could be an ideal candidate for local gene therapy because its invasion is local and it has little metastatic potential. A low expression level and high degradation activity of p27 are known to constitute an independent poor prognostic factor in patients with malignant glioma. In this study, the authors investigated the roles of wild-type p27 and mutant p27 on the treatment of malignant glioma. Methods. The authors used two adenoviruses: one expressed wild-type p27 (ad-p27wt) and the other, containing a mutation at the major metabolic site, expressed mutant p27 (ad-p27mt). The antitumor effects of the two adenoviruses were compared with respect to cell growth arrest, cell cycle alteration, apoptosis induction, and in vitro tumorigenicity in three glioblastoma mutiforme (GBM) cell lines and in a primary GBM cell line. Transduction with ad-p27wt or ad-p27mt induced the production of p27 and the dephosphorylation of pRB. The protein level of mutant p27 was significantly higher than that of wild-type p27. The ad-p27wt induced cell cycle arrest at the G1—S transition point, whereas the ad-p27mt induced arrest at the G2—M point. Both ad-p27wt and ad-p27mt induced a growth-inhibiting effect, apoptosis, and suppression of in vitro tumorigenicity; however, ad-p27mt displayed a stronger antitumor effect than ad-p27wt in brain tumor cell lines. Conclusions. Gene therapy involving p27, especially mutant p27, has the potential to become a novel and powerful therapy for malignant glioma.

Dependence of efficient adenoviral gene delivery in malignant glioma cells on the expression levels of the Coxsackievirus and adenovirus receptor

2000 ◽  
Vol 92 (6) ◽  
pp. 1002-1008 ◽  
Author(s):  
Katsuyuki Asaoka ◽  
Mitsuhiro Tada ◽  
Yutaka Sawamura ◽  
Jun Ikeda ◽  
Hiroshi Abe
Keyword(s):  
Gene Therapy ◽  
Cell Lines ◽  
Malignant Gliomas ◽  
Transduction Efficiency ◽  
Wild Type ◽  
Content Type ◽  
Expression Levels ◽  
Coxsackievirus And Adenovirus Receptor ◽  
Adenovirus Receptor ◽  
Fine Print

Object. Recombinant adenovirus is used as a competent vector in a wide spectrum of cancer gene therapies because of its high efficiency in gene delivery. To study the feasibility of gene therapy in malignant gliomas, the authors examined the antiproliferative effect of the adenovirally transduced wild-type p53 tumor suppressor gene by using 15 different high-grade glioma cell lines.Methods. Although growth suppression in association with a high adenoviral p53 transduction efficiency was seen in five of 15 cell lines, it was not observed in the remaining 10 cell lines. To clarify the underlying mechanism, we examined the expression levels of the Coxsackievirus and adenovirus receptor (CAR), which is the primary receptor for adenovirus, and of the integrins αvβ3 and αvβ5, which promote adenoviral internalization. The expression level of the CAR gene showed a close correlation to adenoviral gene transduction efficiency in the tested cell lines, whereas the expression levels of the integrins did not. The CAR expression was decreased by wild-type p53 transduction in U251MG cells harboring mutant p53 and increased by antisense inhibition of p53 in LN443 cells with endogenous wild-type p53.Conclusions. The results of this study indicate that CAR expression is a critical determinant of transduction efficiencies in adenovirus-based gene therapy for human malignant gliomas.

Thymidine kinase-mediated killing of rat brain tumors

1993 ◽  
Vol 79 (5) ◽  
pp. 729-735 ◽  
Author(s):  
David Barba ◽  
Joseph Hardin ◽  
Jasodhara Ray ◽  
Fred H. Gage
Keyword(s):  
Gene Therapy ◽  
Brain Tumors ◽  
Tumor Cells ◽  
Wild Type ◽  
Cns Disorders ◽  
Content Type ◽  
Potential Applications ◽  
Ganciclovir Treatment ◽  
The Brain ◽  
Fine Print

✓ Gene therapy has many potential applications in central nervous system (CNS) disorders, including the selective killing of tumor cells in the brain. A rat brain tumor model was used to test the herpes simplex virus (HSV)-thymidine kinase (TK) gene for its ability to selectively kill C6 and 9L tumor cells in the brain following systemic administration of the nucleoside analog ganciclovir. The HSV-TK gene was introduced in vitro into tumor cells (C6-TK and 9L-TK), then these modified tumor cells were evaluated for their sensitivity to cell killing by ganciclovir. In a dose-response assay, both C6-TK and 9L-TK cells were 100 times more sensitive to killing by ganciclovir (median lethal dose: C6-TK, 0.1 µg ganciclovir/ml; C6, 5.0 µg ganciclovir/ml) than unmodified wild-type tumor cells or cultured fibroblasts. In vivo studies confirmed the ability of intraperitoneal ganciclovir administration to kill established brain tumors in rats as quantified by both stereological assessment of brain tumor volumes and studies of animal survival over 90 days. Rats with brain tumors established by intracerebral injection of wild-type or HSV-TK modified tumor cells or by a combination of wild-type and HSV-TK-modified cells were studied with and without ganciclovir treatments. Stereological methods determined that ganciclovir treatment eliminated tumors composed of HSV-TK-modified cells while control tumors grew as expected (p < 0.001). In survival studies, all 10 rats with 9L-TK tumors treated with ganciclovir survived 90 days while all untreated rats died within 25 days. Curiously, tumors composed of combinations of 9L and 9L-TK cells could be eliminated by ganciclovir treatments even when only one-half of the tumor cells carried the HSV-TK gene. While not completely understood, this additional tumor cell killing appears to be both tumor selective and local in nature. It is concluded that HSV-TK gene therapy with ganciclovir treatment does selectively kill tumor cells in the brain and has many potential applications in CNS disorders, including the treatment of cancer.

Antitumor effects of antiprogesterones on human meningioma cells in vitro and in vivo

1994 ◽  
Vol 80 (3) ◽  
pp. 527-534 ◽  
Author(s):  
Yasuhiro Matsuda ◽  
Keiichi Kawamoto ◽  
Katsuzo Kiya ◽  
Kaoru Kurisu ◽  
Kazuhiko Sugiyama ◽  
...  
Keyword(s):  
Marked Reduction ◽  
Tumor Volume ◽  
Collagen Gel ◽  
Antitumor Effects ◽  
Histological Changes ◽  
Content Type ◽  
The Relationship ◽  
Fine Print

✓ The presence of the progesterone receptor (PR) in meningioma tissue has been confirmed by previous investigations. Studies have shown that the antiprogesterone drug, mifepristone, is a potent agent that inhibits the growth of cultured meningioma cells and reduces the size of meningiomas in experimental animal models and humans. However, these studies have not fully examined the relationship between the antitumor effects of an antiprogesterone agent and the expression of the PR. The present study examined the antitumor effects of mifepristone and a new potent antiprogesterone agent, onapristone; a correlation between the antitumor effects of these antiprogesterones and the presence of PR's in meningiomas in vitro and in vivo was also investigated. Meningioma tissue surgically removed from 13 patients was used in this study. In the in vitro arm of the study, mifepristone and onapristone exhibited cytostatic and cytocidal effects against cultured meningioma cells, regardless of the presence or absence of PR's; however, three PR-negative meningiomas showed no response to any dose of mifepristone and/or onapristone. In the in vivo arm, meningioma cells, embedded in a collagen gel, were implanted into the renal capsules of nude mice. Antiprogesterone treatment resulted in a marked reduction of the tumor volume regardless of the presence or absence of PR's. No histological changes in the meningioma cells suggestive of necrosis or apoptosis were detected in any of the mice treated with antiprogesterones. These findings suggest that mifepristone and onapristone have an antitumor effect against meningioma cells via the PR's and/or another receptor, such as the glucocorticoid receptor.

Isolation of immortalized, INK4a/ARF-deficient cells from the subventricular zone after in utero N-ethyl-N-nitrosourea exposure

2005 ◽  
Vol 102 (1) ◽  
pp. 98-108 ◽  
Author(s):  
Todd M. Savarese ◽  
Taichang Jang ◽  
Hoi Pang Low ◽  
Rebecca Salmonsen ◽  
N. Scott Litofsky ◽  
...  
Keyword(s):  
Cell Lines ◽  
Subventricular Zone ◽  
Defined Medium ◽  
In Utero ◽  
Homozygous Deletion ◽  
Content Type ◽  
Immortalized Cell Lines ◽  
Immortalized Cell ◽  
Fine Print

Object. Brain tumors, including gliomas, develop several months after rats are exposed in utero to N-ethyl-N-nitrosourea (ENU). Although pathological changes cannot be detected until these animals are several weeks old, the process that eventually leads to glioma formation must begin soon after exposure given the rapid clearance of the carcinogen and the observation that transformation of brain cells isolated soon after exposure occasionally occurs. This model can therefore potentially provide useful insights about the early events that precede overt glioma formation. The authors hypothesized that future glioma cells arise from stem/progenitor cells residing in or near the subventricular zone (SVZ) of the brain. Methods. Cells obtained from the SVZ or corpus striatum in ENU-exposed and control rats were cultured in an epidermal growth factor (EGF)-containing, chemically defined medium. Usually, rat SVZ cells cultured in this manner (neurospheres) are nestin-positive, undifferentiated, and EGF-dependent and undergo cell senescence. Consistent with these prior observations, control SVZ cells undergo senescence by the 12th to 15th doubling (20 of 20 cultures). In contrast, three of 15 cultures of cells derived from the SVZs of individual ENU-treated rats continue to proliferate for more than 60 cell passages. Each of these nestin-expressing immortalized cell lines harbored a common homozygous deletion spanning the INK4a/ARF locus and was unable to differentiate into neural lineages after exposure to specific in vitro stimuli. Nevertheless, unlike the rat C6 glioma cell line, these immortalized cell lines demonstrate EGF dependence and low clonogenicity in soft agar and did not form tumors after intracranial transplantation. Conclusions. Data in this study indicated that immortalized cells may represent glioma precursors that reside in the area of the SVZ after ENU exposure that may serve as a reservoir for further genetic and epigenetic hits that could eventually result in a full glioma phenotype.

scholarly journals Interleukin-4 Signaling Plays a Major Role in Urogenital Schistosomiasis-Associated Bladder Pathogenesis

2019 ◽  
Vol 88 (3) ◽  
Author(s):  
Evaristus C. Mbanefo ◽  
Chi-Ling Fu ◽  
Christina P. Ho ◽  
Loc Le ◽  
Kenji Ishida ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Signaling Pathway ◽  
Ex Vivo ◽  
Bladder Wall ◽  
Interleukin 4 ◽  
Wild Type ◽  
Urogenital Schistosomiasis ◽  
Content Type ◽  
Helminth Infections

ABSTRACT Interleukin-4 (IL-4) is crucial in many helminth infections, but its role in urogenital schistosomiasis, infection with Schistosoma haematobium worms, remains poorly understood due to a historical lack of animal models. The bladder pathology of urogenital schistosomiasis is caused by immune responses to eggs deposited in the bladder wall. A range of pathology occurs, including urothelial hyperplasia and cancer, but associated mechanisms and links to IL-4 are largely unknown. We modeled urogenital schistosomiasis by injecting the bladder walls of IL-4 receptor-alpha knockout (Il4ra−/−) and wild-type mice with S. haematobium eggs. Readouts included bladder histology and ex vivo assessments of urothelial proliferation, cell cycle, and ploidy status. We also quantified the effects of exogenous IL-4 on urothelial cell proliferation in vitro, including cell cycle status and phosphorylation patterns of major downstream regulators in the IL-4 signaling pathway. There was a significant decrease in the intensity of granulomatous responses to bladder-wall-injected S. haematobium eggs in Il4ra−/− versus wild-type mice. S. haematobium egg injection triggered significant urothelial proliferation, including evidence of urothelial hyper-diploidy and cell cycle skewing in wild-type but not Il4ra−/− mice. Urothelial exposure to IL-4 in vitro led to cell cycle polarization and increased phosphorylation of AKT. Our results show that IL-4 signaling is required for key pathogenic features of urogenital schistosomiasis and that particular aspects of this signaling pathway may exert these effects directly on the urothelium. These findings point to potential mechanisms by which urogenital schistosomiasis promotes bladder carcinogenesis.

Resistance to growth inhibition by transforming growth factor—β in malignant glioma cells with functional receptors

1998 ◽  
Vol 88 (3) ◽  
pp. 529-534 ◽  
Author(s):  
Shiro Isoe ◽  
Hirofumi Naganuma ◽  
Shin Nakano ◽  
Atsushi Sasaki ◽  
Eiji Satoh ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Malignant Glioma ◽  
Cell Lines ◽  
Glioma Cell ◽  
Glioma Cells ◽  
Content Type ◽  
Glioma Cell Lines ◽  
Malignant Glioma Cells ◽  
Tgf Β1 ◽  
Fine Print

Object. The aim of this study was to investigate the mechanism by which malignant glioma cells escape from growth inhibition mediated by transforming growth factor-β (TGF-β), a ubiquitous cytokine that inhibits cell proliferation by causing growth arrest in the G1 phase of the cell cycle. Methods. The authors measured the response of eight malignant glioma cell lines to the growth-inhibiting activity of TGF-β in vitro and the expression of TGF-β Types I and II receptors in malignant glioma cells. The effect of TGF-β on the expression of a p27Kip1 cyclin-dependent kinase inhibitor was also investigated to assess the downstream signal transmission from TGF-β receptors. All malignant glioma cell lines were insensitive to growth inhibition by TGF-β1 and TGF-β2. Analyses of TGF-β receptors by means of affinity labeling in which 125I-TGF-β1 was used showed that six glioma lines had both TGF-β Types I and II receptors on their cell surfaces, whereas two lines had very small amounts of TGF-β Type I and/or Type II receptors. Northern blot analysis showed that all tumor lines expressed variable levels of messenger RNAs for both TGF-β Types I and II receptors. Flow cytometric analyses revealed that treatment of malignant glioma cells with TGF-β1 significantly downregulated the expression of p27Kip1 protein in all malignant glioma cell lines except one. Conclusions. The authors suggest that most malignant glioma cells express TGF-β Types I and II receptors, which can transmit some signals downstream and that the loss of response to TGF-β growth inhibition may not be caused by an abnormality of the TGF-β receptors.

ANKHD1 Silencing Reduces In Vitro Clonogenicity and In Vivo Tumorogenicity Of Multiple Myeloma Cells

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3168-3168
Author(s):  
Anamika Dhyani ◽  
João Agostinho Machado-Neto ◽  
Patricia Favaro ◽  
Sara Teresinha Olalla Saad
Keyword(s):  
Cell Cycle ◽  
Gene Therapy ◽  
Multiple Myeloma ◽  
Cell Lines ◽  
Tumor Size ◽  
Control Group ◽  
Mice Model ◽  
And Migration

Abstract Introduction ANKHD1 is a multiple ankyrin repeats containing protein, highly expressed in cancers, such as acute leukemia. Earlier studies showed that ANKHD1 is highly expressed and plays important role in proliferation and cell cycle progression of multiple myeloma (MM) cells. It was also observed that ANKHD1 downregulation modulates cell cycle gene expression and upregulates p21 irresepective of TP53 mutational status of MM cell lines. Objective The present study aimed to study the effect ofANKHD1 silencing on MM growth both in vitro (clonogenicity, migration) and in vivo (xenograft tumor mice model). The purpose was to investigate the feasibility of ANKHD1 gene therapy for MM. Methods In the present study, ANKHD1 expression was silenced using short hairpin RNA (shRNA)-lentiviral delivery vector in MM cell lines (U266 and MM1S). For control MM cells were tranduced by lentiviral shRNA against LacZ. Downregulation of ANKHD1 expression was confirmed by qPCR and Western blot. Colony formation capacity and migration of control and ANKHD1 silenced MM cells was determined by methylcellulose and transwell migration assays, respectively. For in vivo MM growth, NOD-SCID mice were divided in two groups injected with control and ANKHD1 silenced cells, separately. Mice were observed daily for tumor growth. Once the tumor size reached 1 mm3, mice in both groups were sacrificed and tumor was excised to measure tumor volume and weight. Results Corroborating the results obtained in our earlier studies, in the present study also inhibition of ANKHD1 expression suppressed growth of MM cells in vitro. MM cell lines tranduced with ANKHD1 shRNA showed significantly low number of colonies ten days after plating in methylcellulose medium as compared to control (p<0.05). Similarly, in transwell migration assay, cell lines transduced with ANKHD1 showed significantly less migration as in response to 10% FBS at lower chamber as compared to control group (p<0.05) in both the cell lines analyzed. Further in xenograft MM mice model, the growth of tumor was visibly suppressed in mice injected with ANKHD1 silenced cells compared to control group. There was significant difference in tumor size (volume) between these 2 groups (P< 0.006). The tumor weight of the inhibition group was 0.71 ±0.2 g, significantly lighter than those of the control group (1.211 ± 0.5 g, P =0.02) Conclusion Our data indicates ANKHD1 downregulation significantly inhibits colony-forming ability and migration of both glucocorticoid resistant (U266) and sensitive (MM1S) MM cells. Further, gene silencing of ANKHD1 also resulted in reduced in vivo tumor growth in NOD/SCID mice. Collectively, the result obtained indicates that ANKHD1 may be a target for gene therapy in MM. Disclosures: No relevant conflicts of interest to declare.

New targeted anti CDK4/6 peptide MM-D37K.

2013 ◽  
Vol 31 (15_suppl) ◽  
pp. e13545-e13545 ◽  
Author(s):  
Vladimir Konstantinovich Bozhenko ◽  
Tatyana Michailovna Kulinich ◽  
Elena Aleksandrovna Kudinova ◽  
Andrey Boldyrev ◽  
Vladimir Alekseevich Solodkij
Keyword(s):  
Cell Cycle ◽  
Cell Lines ◽  
Full Range ◽  
Mrna Level ◽  
Xenograft Model ◽  
Specific Inhibitor ◽  
Antitumor Effects ◽  
Mcf 7

e13545 Background: MM-D37K is a synthetic peptide which consists of p16INK4a-specific inhibitor of complex cyclin D- CDK4 and CDK6 and cell penetrating peptide (CPP) – Antp (Penetratin). We investigated in vitro and in vivo cytotoxic, cytostatic and antitumor activity of MM-D37K. The level of cyclin A, Ki67,bax, bcl-2 and pRb phosphorylation was investigated. Full range of Toxicology tests and Pharmacokinetics experiments in mice, rats and rabbits were performed. Methods: Different cell lines (Jurcat, Raji, A549, MCF-7, Hct-116, Ht-29, HEK293) were incubated with 0.1-100 mM MM-D37K for 24-48 hrs. Proliferation (MTT), DNA-content, cell cycle (flow cytometry) and mRNA level of appropriate proteins (RT PCR) were investigated. In vivo experiments were conducted on xenograft model of HCT116, A-549 at concentration 5 and 10 mg/kg of MM-D37K. Toxicology experiments were made under RF Law and included 3 types of animals. LC-MS MMD37K method of detection in plasma was developed. Results: MM-D37K prevented pRb phosphorilation and proliferation activation in all investigated cell lines. Cell cycle was blocked in G1 phase. Cytostatic effect did not depend on p16 mutation or expression. MM-D37K induced apoptosis in 20-82% of investigated cells at 40 mM with lowest level for MCF-7. LD10 for rats was 100 mg/kg and no deaths were registered for rabbits (highest dose was 50 mg/kg). Concentration of MMD-37K in plasma after 2 min and bolus i.v. injection in dose 10 mg/kg was 72.16±5.64 mcg/ml. Concentration decreased in two phases. 1st – t1/2 = 2.39±0.39 min and for 2nd t1/2=2.39±0.39 hr. Antitumor effects in xenograft model were 53% for A-549 and 67% for HCT116. Conclusions: Our results proved cytotoxic, cytostatic and antitumor effects of MM-D37K in investigated cell lines in vitro and in vivo. Toxicological and pharmacokinetics results allow us recommend for I/IIa Phase clinical trial. (Support: MetaMax Ltd., RFFI, Minpromtorg RF.)

Growth inhibition of human malignant glioma cells induced by the PI3-K—specific inhibitor

2003 ◽  
Vol 98 (1) ◽  
pp. 154-161 ◽  
Author(s):  
Takashi Shingu ◽  
Kazuo Yamada ◽  
Nobumasa Hara ◽  
Kouzo Moritake ◽  
Harumi Osago ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Malignant Glioma ◽  
Cell Lines ◽  
Akt Pathway ◽  
Content Type ◽  
Phosphorylated Akt ◽  
Human Malignant Glioma ◽  
The Status ◽  
Malignant Glioma Cells ◽  
Fine Print

Object. The phosphatase and tensin homolog deleted from chromosome 10 (PTEN) functions as a tumor suppressor by negatively regulating the growth/survival signals of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway. The PI3-K/Akt pathway in PTEN-deficient tumors may be one of the key targets for anticancer therapy. The authors examined the effects of the PI3-K inhibitor 2-(4-morpholinyl)-8-phenylchromone (LY294002) on human malignant glioma cells, and compared these effects on PTEN-deficient cells with those on PTEN—wild-type (PTEN-wt) cells. Methods. Using human malignant glioma cell lines, including the PTEN-deficient cells A172 and U87MG and the PTEN-wt cells LN18 and LN229, the effects of LY294002 on cell growth, apoptosis, and chemotherapeutic agent—induced cytotoxicity were evaluated. The LY294002 inhibited the growth of U87MG cells associated with reduced phosphatidylinositol 3,4,5,-trisphosphate and phosphorylated Akt, and also induced growth inhibition in three other cell lines. Although LY294002 caused apoptosis in all four cell lines, apoptosis seemed to contribute to only a small portion of growth inhibition induced by LY294002. There was no link between the status of PTEN and the median inhibitory concentration values for LY294002 or between the gene status and the extent of LY294002-induced apoptosis. The LY294002 significantly augmented the cytotoxicity induced by etoposide in PTEN-deficient cells, but not in PTEN-wt cells. Enhancement of 1,3-bis(2-chloroethyl)-1-nitrosourea— and cisplatin-induced cytotoxicity by LY294002 was not linked to the status of PTEN. No marked difference in the amounts of phosphorylated Akt was found between PTEN-deficient and PTEN-wt cells. Conclusions. The findings show that PI3-K is a possible target for therapy in patients with gliomas, and PI3-K inhibitors in combination with chemotherapeutic agents could be potent therapeutic modalities for patients with malignant gliomas.

Stem cell studies of human malignant brain tumors

1985 ◽  
Vol 63 (3) ◽  
pp. 426-432 ◽  
Author(s):  
Bertrand Pertuiset ◽  
Dolores Dougherty ◽  
Carlos Cromeyer ◽  
Takao Hoshino ◽  
Mitchel Berger ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Brain Tumors ◽  
Tritiated Thymidine ◽  
Early Passage ◽  
Cell Cycle Time ◽  
Content Type ◽  
Cell Kill ◽  
Fine Print

✓ The proliferation kinetics were studied in early-passage cultures of cells from 13 human malignant brain tumors and two specimens of normal brain under conditions similar to those used in clonogenic cell-survival studies. Autoradiography was performed in all but four cases to estimate the fraction of cells actively replicating deoxyribonucleic acid (DNA), the approximate cell cycle time, and the effect of low-dose tritiated thymidine on cell proliferation. The mean tumor cell doubling time (TD) was 53 hours for five glioblastomas, 46 hours for two ependymomas, and 83 hours for two medulloblastomas. A gliosarcoma grew fastest (TD = 22 hours) in culture and a pilocytic astrocytoma grew slowest (TD = 144 hours). The approximate cell cycle time ranged from 1 to 2.5 days for all tumors tested. This suggests that chemotherapeutic agents that predominantly kill proliferating cells should be administered in vitro for at least 2 to 2.5 days to achieve maximum cell kill. The approximate growth fraction ranged from 0.65 to 0.96 for all tumors except for the two medulloblastomas and the pilocytic astrocytoma, which had growth fractions of 0.34 and 0.35, respectively. Most laboratories investigating the chemosensitivity of primary or early-passage human tumor cells require that 40% to 70% of cells be killed to consider a drug active in vitro. The results of this study suggest that the cell-cycle-specific agents cannot achieve a high enough cell kill to be considered active for some tumors that grow slowly in culture. An estimate of the in vitro growth rate is necessary to reliably interpret cell-survival results with such agents. Tritiated thymidine appeared to slow cell proliferation in some of the cultures, presumably as a result of radiation-induced DNA damage caused by tritium that had been incorporated into DNA. The degree to which cell growth was slowed in individual tumors correlated with the patient's clinical response to radiation therapy and postoperative survival time.

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