In vitro and in vivo adenovirus-mediated p53 and p16 tumor suppressor therapy in ovarian cancer.

PURPOSE: The objectives of this study were to determine the effects of adenovirus-mediated p16 and p53 on growth and apoptosis in ovarian cancer cells and on survival in nude mice implanted with human ovarian cancer cells. EXPERIMENTAL DESIGN: SKOV-3 ip1 (p53 and p16 null), 2774 (p53 and p16 mutant), and OVCA 420 (p53 and p16 wild-type) cells were used for in vitro studies. SKOV-3 ip1, 2774, and Hey A8 (p53 and p16 wild-type) cells were used in the nude mouse studies. The E1-deleted adenoviruses containing p53, p16, or beta-galactosidase cDNA were transfected into the different cell types or inoculated into the nude mice after injection with ovarian cancer cells. RESULTS: Cell counting, microtetrazolium, and anchorage-independent growth assays on transfected cells demonstrated that p16 and the p16/p53 combination suppressed growth, whereas p53 did not (except in the anchorage-independent growth assay). Although cells infected with the p16/p53 combination had decreased growth compared with cells infected with either tumor suppressor alone, the difference was only statistically significant compared with p53. p16, p53, and the p16/p53 combination all increased apoptosis in the cells. In the nude mice, p16 treatment resulted in the longest survival for all three models, although it only reached statistical significance for the 2774 and SKOV-3 ip1 groups. CONCLUSIONS: Overall, p16 demonstrated greater growth inhibition than p53 both in vivo and in vitro. The p16/p53 combination demonstrated a consistent trend toward increased growth suppression and apoptosis over p16 or p53 alone. Adenovirus-mediated p16 may be a viable future treatment for ovarian cancer.     

Intracerebral adenovirus-mediated p53 tumor suppressor gene therapy for experimental human glioma.

Malignant gliomas of astrocytic origin are good candidates for gene therapy because they have proven incurable with conventional treatments. Although mutation or inactivation of the p53 tumor suppressor gene occurs at early stages in gliomas and is associated with tumor progression, many tumors including high-grade glioblastoma multiforme carry a functionally intact p53 gene. To evaluate the effectiveness of p53-based therapy in glioma cells that contain endogenous wild-type p53, a clinically relevant model of malignant human glioma was established in athymic nu/nu mice. Intracerebral, rapidly growing tumors were produced by stereotactic injection of the human U87 MG glioma cell line that had been genetically modified for tracking purposes to express the Escherichia coli lacZ gene encoding beta-galactosidase. Overexpression of the p53 gene by adenovirus-mediated delivery into the tumor mass resulted in rapid cell death with the eradication of beta-galactosidase-expressing glioma cells through apoptosis. In long-term experiments, the survival of mice treated with the p53 adenoviral recombinant was significantly longer than that of mice that had received control adenoviral recombinant. During the observation period of 1 year, a complete cure was achieved in 27% of animals after a single injection of p53 adenoviral recombinant, and 38% of the animals were tumor free in the group receiving multiple injections of p53 adenoviral recombinant into a larger tumor mass. These experiments demonstrate that overexpression of p53 in gliomas, even in the presence of endogenous functional wildtype p53, leads to efficient elimination of tumor cells. These results point to the potential therapeutic usefulness of this approach for all astrocytic brain tumors.     

Prostate cancer radiosensitization in vivo with adenovirus-mediated p53 gene therapy.

An adenovirus 5 vector containing wild-type p53 cDNA (Ad5-p53) and a cytomegalovirus promoter was used to generate p53 transgene expression. Control vector (Ad5-pA) contained the poly-adenosine sequence. PC3 cells (2 x 10(6)) were injected s.c. into the legs of nude mice. Treatment with Ad5-p53 was initiated at a tumor volume of 200 mm3. Three intratumoral injections (days 1, 4, and 7) were given with 3 x 10(8) plaque-forming units, followed by 5 Gy pelvic irradiation (day 8) in one fraction using a cobalt-60 source. Tumor volume measurements were obtained every 2 days. LNCaP cells (2 x 10(6)) were injected orthotopically into the prostates of nude mice, and tumor weight was approximated using serum prostate-specific antigen (PSA) obtained from weekly tail vein bleedings. The target PSA for the start of the studies was 5 ng/ml. The intraprostatic injections of Ad5-p53 were done twice (days 1 and 2) and followed by 5 Gy pelvic irradiation on day 3. The PC3 tumor volume growth curves were log transformed and fitted using linear regression. The times (in days) for the tumors to reach 500 mm3 were calculated as 10.7 +/- 0.7 (+/- SE) for the saline control (no virus), 9.8 +/- 2.1 for Ad5-pA, 15.6 +/- 1.6 for Ad5-p53, 14.6 +/- 1.5 radiation therapy (RT; 5 Gy), 14.6 +/- 1.5 for Ad5-pA plus RT, and 31.4 +/- 5.3 for Ad5-p53 plus RT. The Ad5-p53 plus RT times were significantly different from the other groups. An enhancement factor of 3.4 was calculated, indicating supra-additivity. LNCaP tumor growth was determined via weekly serum PSA measurements. Treatment failure was determined using two PSA-based methods; a serum PSA of > 1.5 ng/ml or two rises in PSA during 6 weeks posttreatment. The results were similar using either end point. Treatment with Ad5-p53 plus 5 Gy resulted in significantly fewer PSA failures (<30%), as compared with Ad5-p53 alone (64-73%) and the other controls (approximately 80-100%) These results are also consistent with a supra-additive inhibition of tumor growth. Tumor growth in vivo was inhibited supra-additively when p53null and p53wildtype prostate tumors were treated with Ad5-p53 and 5 Gy radiation.     

Adenovirus-p53 gene therapy in human nasopharyngeal carcinoma xenografts.

BACKGROUND: One major challenge to human cancer gene therapy, is efficient delivery of the gene-vector complex. METHODS AND RESULTS: Using two distinct human nasopharyngeal carcinoma (NPC) models, we demonstrate that intra-tumoural (IT) administration of adenoviral-mediated wild-type p53 gene therapy (Ad-p53) caused no greater inhibition of tumour growth as compared to ionizing radiation (XRT) alone. Detailed histologic examination of tumour sections demonstrated that <15% of tumour cells were transduced by IT adv-beta-gal. CONCLUSIONS: This report underscores the importance of developing gene transfer vectors, which can provide therapeutic levels of transgene expression efficiently in solid tumours.     

Intraperitoneal gene therapy with adenoviral-mediated p53 tumor suppressor gene for ovarian cancer model in nude mouse

In an effort to develop a method for better local control of advanced ovarian cancers, we have established a peritoneal tumor model of ovarian cancer in the nude mouse and applied intraperitoneal gene therapy with the recombinant adenoviral-mediated wild-type p53 tumor suppressor gene (Avp53). The results indicate that: (a) the recombinant adenoviral vector system effectively infected the tumor and normal cells in the peritoneal cavity; and (b) Avp53 treatment effectively suppressed the growth of peritoneal tumors and prolonged the survival of the treated group, especially when the tumor burden was less. These results suggest that intraperitoneal gene therapy using Avp53 is potentially useful as an adjuvant therapeutic modality in human ovarian cancer.     

重组人p53腺病毒注射液治疗晚期卵巢癌的疗效观察

目的探讨重组人p53腺病毒注射液治疗晚期卵巢癌的近期疗效。方法 2009年5月至2010年12月间收治的20例晚期卵巢癌患者给予重组人p53腺病毒注射液局部或全身治疗±化疗±热疗治疗,每2个月评价疗效。结果随访12个月,20例晚期卵巢癌中,完全缓解(CR)4例(20.0%),部分缓解(PR)9例(45.0%),稳定(SD)5例(25.0%),进展(PD)2例(10.0%)。18例恶性胸、腹腔积液患者中,CR 5例(27.8%),PR 7例(38.9%),SD 6例(33.3%)。患者总体不良反应轻微,Ⅰ~Ⅱ度自限性发热12例。结论重组人p53腺病毒注射液联合化疗治疗晚期卵巢癌患者疗效好,不良反应可控。     

Novel combination therapy for human colon cancer with adenovirus-mediated wild-type p53 gene transfer and DNA-damaging chemotherapeutic agent

Alteration of the wild-type (wt) p53gene by mutation, deletion or re-arrangement is a major factor in the development of human colon cancer. Recent studies have demonstrated that p53 might be an essential component of the apoptotic pathway triggered by DNA-damaging stimuli such as chemotherapeutic agents and ionizing radiation. We examined the anti-tumor effects of adenovirus-mediated wt-p53 gene transfer in combination with a chemotherapeutic drug on the human colon cancer cell line WiDr, which is homozygous for a mutation in the p53 gene. Treatment with the chemotherapeutic drug cisplatin following infection with a replication-deficient, recombinant adenoviral vector expressing wt-p53 (termed AdCMVp53) significantly suppressed the growth of WiDr cells compared to single treatments alone. To evaluate the in vivo efficacy of AdCMVp53 and cisplatin given sequentially, WiDr cells were inoculated s.c. in nu/nu mice. After 3 days, AdCMVp53 was injected s.c. into the area where tumor cells were implanted, followed by i.p. administration of cisplatin. Analysis of initial growth inhibition at 21 days demonstrated a profound therapeutic cooperativity, though administration of either AdCMVp53 or cisplatin alone was followed only by a slowing of growth. Our results suggest that gene therapy using wt-p53-expressing adenovirus in combination with a chemotherapeutic DNA-damaging drug could be a useful strategy for treating human colon cancer. Int. J. Cancer 73:367–370, 1997. © 1997 Wiley-Liss, Inc.     

Drug-resistant human bladder-cancer cells are more sensitive to adenovirus-mediated wild-type p53 gene therapy compared to drug-sensitive cells.

We investigated the therapeutic potential and molecular mechanism of adenovirus-mediated wt p53 gene therapy for drug-resistant human bladder cancers. KK47, a human bladder-cancer cell line, along with the drug-resistant sublines KK47/DDP10, KK47/DDP20 (cisplatin-resistant) and KK47/ADM (doxorubicin-resistant) were used for the experiments. All 4 KK47 cell lines had genetically normal p53 genes. Using an in vitro cytotoxicity assay, the drug-resistant cell lines were more sensitive to Ad-CMV-p53 cell killing than the KK47 parental cell line. Ad-CMV-p53 induced higher levels of p53 protein and mRNA in the drug-resistant cell lines than in the parental cell line and, consequently, higher levels of p21 and Bax mRNA, which resulted in higher percentages of G(1) cell-cycle arrest and apoptosis. The higher efficiencies of adenoviral gene transfer in the drug-resistant cell lines were confirmed by X-gal staining after infection with Ad-CMV-beta-gal. In conclusion, adenovirus-mediated wt p53 gene therapy was more effective in the drug-resistant bladder-cancer cell lines than in the drug-sensitive bladder-cancer cell line.     

In vitro and in vivo studies of adenovirus-mediated human norepinephrine transporter gene transduction to hepatocellular carcinoma

The clinical value of (131)I-MIBG for targeted imaging and targeted radiotherapy is limited to neural crest-derived tumors expressing human norepinephrine transporters (hNET) protein. To extend (131)I-MIBG-targeted therapy to other nonexpressed hNET tumors, this study investigated the hNET expression in vitro and in vivo in HepG2 hepatoma mediated by recombinant adenovirus encoding the hNET gene (Ad-hNET). For this purpose, the HepG2 cells showed a 4.87-fold increase in (125)I-MIBG uptake after infection with Ad-hNET, and the uptake of (125)I-MIBG could be specifically inhibited by maprotiline. Immunohistological analysis, in vivo biological study and (131)I-MIBG scintigraphic imaging also revealed the high expression of hNET protein in hepatoma. This in vitro and in vivo studies demonstrate the feasibility of hNET gene transfer, meditated by adenovirus vector, could extend to tumors other than those derived from the neural crest, which provides a sound foundation for further investigation of hepatocellular carcinoma-targeted radiotherapy mediated by adenovirus transfection with hNET gene.     

Adenoviral p53 gene therapy for human lung cancer

Recent advances in molecular biology have fostered remarkable insights into the molecular basis of neoplasms. This new understanding of cancer pathogenesis suggests that restoration of the function of critical gene products could halt or reverse these mechanisms, thus having a therapeutic effect in cancer. The tumor suppressor p53 gene has been implicated in many inherited and sporadic forms of malignancy in humans. A number of preclinical experiments have demonstrated that restoration of the wild-type p53 function in the cancer cell by gene transfer is sufficient to cause antitumor effects such as cell-cycle arrest and induction of apoptosis. This approach has entered initial clinical testing and provided intriguing information about the intratumoral administration of an adenovirus vector expressing the wild-type p53 gene in non-small cell lung cancer patients.     

Phase I trial of adenovirus-mediated p53 gene therapy for recurrent glioma: biological and clinical results.

PURPOSE: Advances in brain tumor biology indicate that transfer of p53 is an alternative therapy for human gliomas. Consequently, we undertook a phase I clinical trial of p53 gene therapy using an adenovirus vector (Ad-p53, INGN 201). MATERIALS AND METHODS: To obtain molecular information regarding the transfer and distribution of exogenous p53 into gliomas after intratumoral injection and to determine the toxicity of intracerebrally injected Ad-p53, patients underwent a two-stage approach. In stage 1, Ad-p53 was stereotactically injected intratumorally via an implanted catheter. In stage 2, the tumor-catheter was resected en bloc, and the postresection cavity was treated with Ad-p53. This protocol provided intact Ad-p53-treated biologic specimens that could be analyzed for molecular end points, and because the resection cavity itself was injected with Ad-p53, patients could be observed for clinical toxicity. RESULTS: Of fifteen patients enrolled, twelve underwent both treatment stages. In all patients, exogenous p53 protein was detected within the nuclei of astrocytic tumor cells. Exogenous p53 transactivated p21CIP/WAF and induced apoptosis. However, transfected cells resided on average within 5 mm of the injection site. Clinical toxicity was minimal and a maximum-tolerated dose was not reached. Although anti-adenovirus type 5 (Ad5) titers increased in most patients, there was no evidence of systemic viral dissemination. CONCLUSION: Intratumoral injection of Ad-p53 allowed for exogenous transfer of the p53 gene and expression of functional p53 protein. However, at the dose and schedule evaluated, transduced cells were only found within a short distance of the injection site. Although toxicity was minimal, widespread distribution of this agent remains a significant goal.     

Growth inhibition of human laryngeal cancer cell with the adenovirus-mediated p53 gene

Mostmalignanciesarediseasegeneratedwithaprocessofgeneticalteration.Basedonthistheory,newapproachestocancertherapyarebeingdevel0ped.Oneoftheseisgenetherapy.Amongthegeneshavingtherapeuticpotentialforcancertreatment,thep53tumorsuppressorgenehasbeenmostextensivelystudied.[l]Wild-typep53hasbeenshownt0beinvolvedintranscirptionalregulation.ItarrestscellsattheGllScheckpoint,blocksDNAreplicati0nandinducesap0ptosis."'Recentstudieshavesh0wnthatwild-typep53genecansuppressthegrowthofsomehumancancercelll…     

Ketoconazole potentiates the antitumor effects of nocodazole: In vivo therapy for human tumor xenografts in nude mice

Our previous studies demonstrated that the oral antifungal agent ketoconazole (KT) induces apoptosis and G0/G1 phase cell cycle arrest in human cancer cell lines. In this study, we first demonstrated that KT (1 microM) potentiated the apoptotic effects of nocodazole (ND, 1 nM) in COLO 205 cancer cells. We further demonstrated the therapeutic efficacy of a combined treatment of KT (50 mg/kg/three times per week) and ND (5 mg/kg/three times per week) in vivo by treating athymic mice bearing COLO 205 tumor xenografts. The antitumor effects of ND were significantly potentiated by KT in mice after 6 wk of treatment. No gross signs of toxicity were observed in mice receiving these treatment regimens. The apoptotic cells were detected in a microscopic view of the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and by observation of DNA fragmentation in KT + ND-treated tumor tissues. The levels of cell cycle regulatory proteins were determined by Western blot analysis. Treatment with KT inhibits tumor growth through elevation of p53, p21/CIP1, and p27/KIP1 as well as inhibition of cyclin D3 and cyclin-dependent kinase 4 protein expression. Immunohistochemical staining analysis showed that p53, p21/CIP1, and p27/KIP1 immunoreactivity were induced in the tumor tissues. To clarify the roles of the p21/CIP1 and p27/KIP1 protein expression involved in G(0)/G(1) arrest and/or apoptosis induced by a combined treatment with KT and ND, antisense oligodeoxynucleotides (ODNs) specific to p21/CIP1 and p27/KIP1 were used. Our results demonstrated that apoptotic phenomena, including BAX induction and cytochrome C released from mitochondria induced by KT + ND, were significantly attenuated by pretreatment the cells with the p27/KIP1-specific antisense ODNs. These results indicate that p27/KIP1 protein does indeed play a critical role in the KT + ND-induced apoptosis. Our study revealed the molecular mechanism of KT + ND in regression of the tumor growth. The apoptotic effects of KT in a great variety of cancer cells make it a very attractive agent for cancer chemotherapy.     

Wild-type p53 gene transfer is not detrimental to normal cells in vivo: implications for tumor gene therapy

The p53 oncosuppressor is strictly maintained in an inactive form under normal conditions, while it is post-translationally activated by a variety of stresses, enacting different protective biological functions. Since one critical issue in cancer gene therapy is tumor specificity, we asked whether the tight p53 regulation applies also to exogenously transferred p53. In principle, this type of regulation could allow p53 gene transfer in both normal and tumor cells to produce detrimental effects only in the latter ones. Here, we report that primary bone marrow cells infected with a p53 recombinant retrovirus and transplanted into irradiated mice reconstitute the hematopoietic system, with no detectable alterations in any of its compartments. Furthermore, simultaneous infection of leukemia and bone marrow cells depleted the neoplastic contamination, allowing lifelong, disease-free survival of 65% of the transplanted animals. These results show that exogenous p53 is controlled as tightly as the endogenous one, and opens the way to p53 gene therapy, without requiring tumor targeting.     

In vivo growth inhibitory effect of iterative wild-type p53 gene transfer in human head and neck carcinoma xenografts using glucosylated polyethylenimine nonviral vector

Polyethylenimine (PEI) derivatives are polycationic nonviral vectors for gene transfer. Previous results achieved in vitro in head and neck cancer cells demonstrated that glucosylated PEI yields higher gene transfer efficiency and longer transgene expression than unsubstituted PEI. Using glucosylated PEI, p53 gene transfer was successfully achieved with subsequent recovery of P53 protein expression and induction of spontaneous apoptosis. The present study reports in vivo data achieved in human head and neck squamous cell carcinoma xenografted mice. Using biotinylated PEI and histochemistry analysis, the vector was found to diffuse in the proliferating cells of the tumor tissue, sparing necrotic areas. No diffusion was observed inside keratinized area composed of nonproliferating, mature differentiated cells. Using green fluorescent protein (GFP) transfection and fluorescence microscopy, the transgene expression was mainly observed at the periphery of the tumor containing proliferating cells. GFP expression appeared lower inside the tumor depth. Quantitative transgene expression kinetics was then determined using luciferase as reporter gene. The maximal transgene expression was achieved 48 hours after intratumoral injection of glucosylated PEI/DNA complexes. The highest gene transfer efficacy was achieved 48 hours after two intratumoral injection. After transfection of wild-type p53, tumor growth inhibition was observed in tumor-bearing mice receiving intratumoral injection of glucosylated PEI/DNA complexes repeated twice weekly. Tumor growth inhibition was maintained under continuous treatment using the same schedule. In all experiments, no noticeable toxicity was observed. The present results demonstrate the feasibility and the tumor growth inhibition potency of nonviral gene transfer using glucosylated polyethylenimine.     

腺病毒介导的p53基因对喉癌细胞生长的抑制作用

目的探索ｐ５３基因在喉癌基因治疗方面的可行性。方法以人喉癌细胞系Ｈｅｐ－２为实验对象,将载有人野生型ｐ５３ｃＤＮＡ并含巨细胞病毒（ＣＭＶ）启动子的重组腺病毒（Ａｄ５ＣＭＶ－ｐ５３）感染Ｈｅｐ－２细胞及肿瘤组织,体内外实验观察Ａｄ５ＣＭＶ－ｐ５３对Ｈｅｐ－２细胞生长的影响。结果当Ａｄ５ＣＭＶ－ｐ５３在１００ＭＯＩ效靶比时,全部Ｈｅｐ－２细胞得到转染。感染２天后ｐ５３蛋白表达达到高峰,Ｈｅｐ－２生长受到明显的抑制。Ａｄ５ＣＭＶ－ｐ５３感染Ｈｅｐ－２细胞在裸鼠中失去致瘤性。瘤内注射Ａｄ５ＣＭＶ－ｐ５３后,荷瘤裸鼠的肿瘤体积明显减小。结论Ａｄ５ＣＭＶ－ｐ５３转导野生型ｐ５３基因可能是一种有效的喉癌基因治疗途径。     

Cisplatin-controlled p53 gene therapy for human non-small cell lung cancer xenografts in athymic nude mice via the CArG elements

Cisplatin, a commonly used chemotherapeutic agent, causes tumor cell death by producing DNA damage and generating reactive oxygen intermediates, which have been reported to activate the early growth response-1 ( Egr-1 ) promoter through specific cis -acting sequences, termed CArG elements. The aim of this study was to construct an adenoviral vector containing CArG elements cloned upstream of the cDNA for human wt-p53 , and to observe the effect of this vector on human non-small cell lung cancer (NSCLC) xenografts in athymic nude mice when combined with cisplatin treatment. The adenoviral vector AdEgr–p53 was generated by inserting CArG elements upstream of human wt-p53 cDNA. Two human NSCLC cell lines of varying p53 gene status, A549 (containing wild-type p53 ) and H358 (containing an internal homozygous deletion of the p53 gene) were used for in vitro and in vivo experiments. Wt-p53 production in cultured tumor cells and xenografts treated with the combination of AdEgr–p53 and cisplatin were detected by enzyme-linked immunosorbent assays. The antitumor responses in nude mice with the A549 or H358 xenografts following treatment with AdEgr–p53 and cisplatin were observed. We found that p53 was produced in tumor cells and xenografts treated with a combination of AdEgr–p53 and cisplatin. Furthermore, the Egr-1 promoter is induced by cisplatin, and this induction is mediated in part through the CArG elements. There was an enhanced antitumor response without an increase in toxicity following treatment with AdEgr–p53 and cisplatin, compared with either agent alone. Cisplatin-inducible p53 gene therapy may provide a means to control transgene expression while enhancing the effectiveness of commonly used chemotherapeutic agents. This is a novel treatment for human NSCLC. ( Cancer Sci 2005; 96: 706 – 712)     

High incidence of p53 gene mutation in human ovarian cancer and its association with nuclear accumulation of p53 protein and tumor DNA aneuploidy.

Using the polymerase chain reaction and single-strand conformation polymorphism analysis, p53 gene mutations were examined in 24 cases of ovarian tumor including 14 ovarian carcinomas and 2 borderline cases of common epithelial type, 7 germ cell tumors, and one stromal tumor. Abnormal bands indicating mutations were detected in 12 (50%) of the cases examined, being present most frequently in common "epithelial" ovarian carcinoma (71%, 10/14). One case each of squamous cell carcinoma originating in a dermoid cyst and anaplastic dysgerminoma were positive for mutation. Direct sequencing confirmed 12 mutations and revealed G-->A and G-->C nucleotide changes in 5 and 3 cases (42% and 25%), respectively. The mutation was localized at the CpG site of the gene in 3 cases. Immunohistochemical examination of p53 protein in 21 cases and DNA flow-cytometrical analysis in 17 cases were also performed. Nuclear accumulation of the p53 protein and DNA aneuploidy pattern were detected in 11 (52%) and 9 (53%) cases, respectively. These were significantly correlated with p53 gene mutation (P < 0.01 and P < 0.05, respectively; Fisher's exact test). Neither mutation of the p53 gene, nuclear accumulation of p53 protein nor DNA aneuploidy was detected in borderline cases of common "epithelial" type, typical dysgerminoma and immature teratoma. These results suggest that p53 gene mutation, nuclear accumulation of the protein and the DNA aneuploidy pattern are events occurring almost simultaneously in the progression of ovarian tumors, and that p53 abnormalities seem to be correlated with a high grade of malignancy.     

Multimodality optical imaging and 18F-FDG uptake in wild-type p53-containing and p53-null human colon tumor xenografts

During tumor development a switch to glycolytic metabolism known as the Warburg effect may provide cancer cells with a survival advantage and may also provide a therapeutic opportunity. A number of signals contribute to aerobic glycolysis including those mediated by HIF-1, c-Myc, Akt and Hexokinase. Recent studies have implicated the p53 tumor suppressor as a negative regulator of this switch. Using inducible p53 gene silencing in bioluminescent tumor xenografts we initially observed qualitatively similar levels of FDG uptake by PET small animal imaging in wild-type p53-expressing tumor xenografts and p53 gene-silenced xenografts. We further evaluated glucose uptake using FDG-PET/CT fusion imaging of green and red fluorescently-labeled wild-type and p53-null human colon tumor xenografts. Our results demonstrate that the wild-type p53-expressing tumor xenografts exhibit high levels of glucose uptake, similar to those observed in p53-null tumor xenografts, by quantitative PET imaging indicative of the glycolytic switch. Thus p53 function is not sufficient to suppress glucose uptake in cells and tumors that could theoretically support aerobic glycolysis.