肿瘤乏氧的正电子发射断层显像及其临床应用

乏氧是恶性肿瘤内普遍存在的现象，是肿瘤侵袭性以及对放化疗抗拒的重要原因之一。应用正电子发射断层显像（PET），可以全面、无创和重复地检测肿瘤乏氧。并可用来预测肿瘤预后、评价疗效及指导临床治疗。     

肿瘤乏氧的正电子发射断层显像及其临床应用

乏氧是恶性肿瘤内普遍存在的现象,是肿瘤侵袭性以及对放化疗抗拒的重要原因之一。应用正电子发射断层显像(PET),可以全面、无创和重复地检测肿瘤乏氧,并可用来预测肿瘤预后、评价疗效及指导临床治疗。     

Tumor hypoxia: a new PET imaging biomarker in clinical oncology

Tumor hypoxia is associated with tumor progression and resistance to various treatments. Noninvasive imaging using positron emission tomography (PET) and F-18-labeled fluoromisonidazole (FMISO) was recently introduced in order to define and quantify tumor hypoxia. The FMISO uptake was closely correlated with pimonidazole immunohistochemistry and hypoxia-inducible factor 1 expression in basic studies. Tumor hypoxia in head and neck cancers and other tumors in a clinical setting may also indicate resistance to radiation and/or chemotherapy. Hypoxic imaging may thus play a new and important role for suitable radiation planning, including dose escalation and dose reduction based on the image findings. Such radiation-dose painting based on the findings of hypoxia may require high-performance PET imaging to provide high target-to-background ratio images and an optimal quantitative parameter to define the hypoxic region. A multicenter prospective study using data from a large number of patients is also warranted to test the clinical value of hypoxic imaging.     

Tumor hypoxia imaging with [F-18] fluoromisonidazole positron emission tomography in head and neck cancer.

PURPOSE: Advanced head and neck cancer shows hypoxia that results in biological changes to make the tumor cells more aggressive and less responsive to treatment resulting in poor survival. [F-18] fluoromisonidazole (FMISO) positron emission tomography (PET) has the ability to noninvasively quantify regional hypoxia. We investigated the prognostic effect of pretherapy FMISO-PET on survival in head and neck cancer. EXPERIMENTAL DESIGN: Seventy-three patients with head and neck cancer had pretherapy FMISO-PET and 53 also had fluorodeoxyglucose (FDG) PET under a research protocol from April 1994 to April 2004. RESULTS: Significant hypoxia was identified in 58 patients (79%). The mean FMISO tumor/bloodmax (T/Bmax) was 1.6 and the mean hypoxic volume (HV) was 40.2 mL. There were 28 deaths in the follow-up period. Mean FDG standard uptake value (SUV)max was 10.8. The median time for follow-up was 72 weeks. In a univariate analysis, T/Bmax (P=0.002), HV (P=0.04), and the presence of nodes (P=0.01) were strong independent predictors. In a multivariate analysis, including FDG SUVmax, no variable was predictive at P<0.05. When FDG SUVmax was removed from the model (resulting in n=73 with 28 events), nodal status and T/Bmax (or HV) were both highly predictive (P=0.02, 0.006 for node and T/Bmax, respectively; P=0.02 and 0.001 for node and HV, respectively). CONCLUSIONS: Pretherapy FMISO uptake shows a strong trend to be an independent prognostic measure in head and neck cancer.     

Tumor hypoxia and cancer progression

Aerobic life consumes oxygen for efficient production of high energy compounds. The ability to sense and respond to changes in oxygen partial pressure represents a fundamental property to assure the cellular oxygen supply to be within a narrow range that balances the risks of oxidative damage vs. oxygen deficiency. The discovery of hypoxia-inducible factor-1 (HIF-1) allowed the identification of molecular mechanisms by which changes in oxygenation are transduced to adequate intracellular adaptive responses. It became apparent that hypoxia can initiate cell demise by apoptosis/necrosis but also prevent cell death by provoking adaptive responses that, in turn, facilitate cell proliferation or angiogenesis, thus contributing to tumor progression. Considering that activation of HIF-1 provokes pro-survival as well as pro-death decisions under hypoxia, it will be crucial to understand decision making processes in regulating cell death, adaptation and chemoresistance. Likely, secondary stressors such as pH changes, i.e. acidosis, and the context of genetic alterations will shape the role of HIF-1 to affect susceptibility of cells to undergo hypoxia-induced cell death or to allow adaptation and progression towards malignancy. Understanding the mechanisms by which HIF-1 affects the expression and/or function of key apoptotic regulators such as Bcl-2 family members or p53 will help to uncover how HIF-1 induces cell death and the manner in which cells can overcome such signals and thus determine which of its Janus faces prevail.     

Tumor hypoxia, p53, and prognosis in cervical cancers.

BACKGROUND: The p53 protein is involved in the regulation of initiation of apoptosis. In vitro, p53-deficient cells do not respond to hypoxia with apoptosis as do p53-normal cells, and this may lead to a relative growth advantage of cells without a functioning p53 under hypoxia. On the basis of this hypothesis, a selection of cells with a functionally inactive p53 may occur in hypoxic tumors. The development of uterine cervical carcinomas is closely associated with infections of human papilloma viruses, which may cause a degradation of the tumor suppressor gene p53, resulting in a restriction of apoptosis. Thus, cervical cancers have often a functionally inactive p53. The purpose of our clinical study was therefore to investigate the association between p53, hypoxia, and prognosis in cervical cancers in which the oxygenation status can be determined by clinical methods. MATERIAL AND METHODS: Seventy patients with locally advanced squamous cell cervical cancer Stages IIB (n = 14), IIIB (n = 49), and IVA (n = 7) were investigated in the period from 1996 through 1999. All were treated with definitive radiotherapy with curative intent by a combination of external radiotherapy plus high-dose-rate afterloading. Before therapy, tumor oxygenation was measured with a needle probe polarographically using the Eppendorf histograph. Hypoxic tumors were defined as those with pO(2) measurements below 5 mm Hg (HF5). Pretreatment biopsies were taken and analyzed immunohistologically for p53 protein expression with the DO-7 antibody. The DNA index was measured by flow cytometry. The statistical data analysis was done with SPSS 9.0 for Windows. RESULTS: The 3-year overall survival was 55% for the whole group of patients. Clinical prognostic factors in a multivariate analysis were pretreatment hemoglobin level (3-year survival 62% for patients with a pretreatment hemoglobin > or =11 g/dl vs. 27% for hemoglobin <11 g/dl, p = 0.006) and FIGO stage (Stage IIB: 65%; Stage IIIB: 60%; Stage IVA: 29%, p = 0.01). Sixty of the 70 tumors showed positive immunohistologic staining for p53 protein (transformed p53 = tp53), and 10/70 were negative (wild-type p53 = wtp53); p53 expression had no significant impact on survival (50% for tp53 vs. 79% for wtp53, p = 0.11). FIGO stage and anemia had no impact on p53 expression. Forty-nine of 70 tumors were hypoxic (HF5+), and 21 showed no hypoxia (HF5-). Hypoxic carcinomas were more frequently positive for p53 as compared to nonhypoxic tumors (27% vs. 13%, p = 0.011) and showed a trend toward a lower survival (48% vs. 70%, p = 0.07). In a further multivariate analysis, the impact of a combination of p53 expression and hypoxia on survival was examined. After adjusting for FIGO stage and pretreatment anemia, patients with wtp53 tumors had the best prognosis (3-year survival 79%) followed by tp53-HF5(-) patients (57%), and the most unfavorable prognosis was observed for tp53-HF5(+) patients (47%). The DNA index was higher in tp53 carcinomas compared to wtp53 tumors, 1.97 +/- 0.4 vs. 1.67 +/- 0.1, p = 0.05. The highest DNA index was found in hypoxic tumors with transformed p53 (2.2 +/- 3.1). CONCLUSIONS: Advanced stage and pretreatment hemoglobin level are independent prognostic factors in cervical carcinomas. The immunohistologic detection of (a functionally inactive) p53 and the presence of hypoxia had no prognostic impact, if analyzed as single parameters. However, the combination of both parameters was able to discriminate different prognostic subgroups. Moreover, hypoxic cancers were more often immunohistologically positive for tp53 protein and had a higher DNA index with the highest DNA index in tumors with both hypoxia and tp53 protein expression. These findings in summary support the theory that the tumor's microenvironment may influence the biologic behavior via hypoxia.     

Tumor hypoxia in pelvic recurrences of cervical cancer

We have previously demonstrated in primary cancer of the uterine cervix that tumor hypoxia, as determined polarographically, is strongly associated with clinical malignant progression of the disease. Having applied a similar methodological approach to investigate loco-regional relapses, we found a pronounced shift to more hypoxic oxygenation profiles in the recurrent tumors than in the primary tumors. Median pO₂ values in 53 pelvic recurrences were significantly lower than the median pO₂ values of 117 primary tumors of comparable sizes (7.1 ± 1.1 mmHg vs. 12.1 ± 1.0 mmHg, p = 0.0013). The differences in tumor oxygenation between primary and recurrent tumors mirrored the differences in the patients' 5-year survival probabilities. In the cohort of patients with pelvic relapses, median tumor pO₂ < 4 mmHg indicated a significantly shorter median survival time as compared to median tumor pO₂ ≥ 4 mmHg. Our results further support our thesis that in cervical cancer, tumor hypoxia and clinical aggressiveness in terms of resistance to therapy and tumor dissemination, are interrelated. Int. J. Cancer (Pred. Oncol.) 79:365–369, 1998. © 1998 Wiley-Liss, Inc.     

肿瘤血管生长和缺氧诱导因子

缺氧诱导因子(XIF-1)是由α、β两个亚单位形成的二聚体,其中的HIF-lα受缺氧或低糖的调节,它通过与靶基因特定序列DNA结合而调控它们的转录,这些基因包括VEGF、Epo和其他的一系列与机体氧代谢有关的基因.本文就HIF与VEGF的调控及与肿瘤新生血管形成的关系综述如下.     

Tumor hypoxia: its impact on cancer therapy

The presence of radiation resistant cells in solid human tumors is believed to be a major reason why radiotherapy fails to eradicate some such neoplasms. The presence of unperfused regions containing hypoxic cells may also contribute to resistance to some chemotherapeutic agents. This paper reviews the evidence that radiation resistant hypoxic cells exist in solid tumors, the assumptions and results of the methods used to detect hypoxic cells, and the causes and nature of tumor hypoxia. Evidence that radiation resistant hypoxic cells exist in the vast majority of transplanted rodent tumors and xenografted human tumors is direct and convincing, but problems with the current methodology make quantitative statements about the magnitude of the hypoxic fractions problematic. Evidence that radiation resistant hypoxic cells exist in human tumors is considerably more indirect than the evidence for their existence in transplanted tumors, but it is convincing. However, evidence that hypoxic cells are a significant cause of local failure after optimal clinical radiotherapy or chemotherapy regimens is limited and less definitive. The nature and causes of tumor hypoxia are not definitively known. In particular, it is not certain whether hypoxia is a chronic or a transient state, whether hypoxic cells are proliferating or quiescent, or whether hypoxic cells have the same repair capacity as aerobic cells. A number of new methods for assessing hypoxia are reviewed. While there are still problems with all of the new techniques, some of them have the potential of allowing the assessment of hypoxia in individual human tumors.     

肿瘤靶向磁共振成像研究进展

以恶性肿瘤细胞或肿瘤组织表达的特定分子为靶点,采用相应的分子探针载体连接铁类或钆类磁共振对比剂,即磁共振肿瘤靶向对比剂.用于孵育体外培养的肿瘤细胞,以及经静脉注射到载瘤裸鼠体内.近年来许多研究者证实磁共振成像(MRI)能观察该类肿瘤靶向对比剂的靶向效果,有望实现恶性肿瘤的磁共振定性诊断,检测肿瘤靶向治疗效果,并指导临床选择合适的靶向化疗药.     

Tumor hypoxia: Impact on gene amplification in glioblastoma

Gene amplification is frequently found in human glioblastoma but the mechanisms driving amplifications remain to be elucidated. Hypoxia as hallmark of glioblastoma is known to be involved in the induction of fragile sites that are central to gene amplification. We analyzed the potential of hypoxia (pO2 0%) and mini hypoxia (pO2 5%) to induce fragile sites within a homogeneously staining region (HSR) at 12q14-15 in a glioblastoma cell line (TX3868). Treatment of cells by hypoxia or by mini hypoxia induced double minutes (DMs) and caused breakage of the HSR structure at 12q14-15, suggesting a novel hypoxia inducible fragile site on 12q. Treatment with aphidicolin, a known fragile site inducer, indicates that the hypoxia inducible fragile site is a common fragile site. Reintegration of amplified sequences and occurrence of anaphase-bridge-like structures shows that mini hypoxia and hypoxia are able to initiate amplification processes in human glioblastoma cells. Hypoxia as known tumor microenvironment factor is crucial for the development of amplifications in glioblastoma. The identification and characterization of novel common fragile sites induced by hypoxia will improve the understanding of mechanisms underlying amplifications in glioblastoma.     

Tumor hypoxia: a target for selective cancer therapy

Tumor hypoxia has been considered to be a potential therapeutic problem because it renders solid tumors more resistant to sparsely ionizing radiation (IR) and chemotherapeutic drugs. Moreover, recent laboratory and clinical data have shown that tumor hypoxia is also associated with a more malignant phenotype and poor survival in patients suffering from various solid tumors. Therefore, selective targeting of hypoxic tumor cells has been explored, and since severe hypoxia (pO₂<0.33%, 2.5 mmHg) does not occur in normal tissue, tumor hypoxia could be exploited for therapeutic advantage. However, the following three characteristics of hypoxic tumor regions present obstacles in targeting hypoxic cells. First, it is difficult to deliver a sufficient amount of drug to a region that is remote from blood vessels. Second, one must specifically target hypoxic tumor cells while sparing normal well-oxygenated tissue from damage. Finally, the severely hypoxic tumor cells to be attacked have often stopped dividing. Therefore, high delivery efficiency, high specificity and selective cytotoxicity are all necessary to target and combat hypoxic tumor cells. The current review describes progress on the biological aspects of tumor hypoxia and provides a compilation of the recent molecular approaches used to target hypoxic tumors. These approaches include our work with a unique hypoxia-targeting protein drug, TOP3, with which we have sought to address the above three difficulties.     

Tumor hypoxia has independent predictor impact only in patients with node-negative cervix cancer.

PURPOSE: This prospective clinical study was begun in 1994 to validate the independent prognostic impact of tumor hypoxia in patients with cervix cancer treated with definitive radiation therapy. PATIENTS AND METHODS: Between May 1994 and January 1999, 106 eligible patients with epithelial cervix cancer had tumor oxygen pressure (PO(2)) measured using the Eppendorf probe. Oxygenation data are presented as the hypoxic proportion, defined as the percentage of PO(2) readings less than 5 mm/Hg (abbreviated as HP(5)) and the median PO(2). RESULTS: The median HP(5) in individual patients was 48%, and the median PO(2) was HP(5). Progression-free survival (PFS) for patients with hypoxic tumors (HP(5) > 50%) was 37% at 3 years versus 67% in those patients with better oxygenated tumors (P =.004). In multivariate analysis, only tumor size (risk ratio [RR], 1.33; P =.0003) and evidence of pelvic nodal metastases on imaging studies (RR, 2.52; P =.0065) were predictive of PFS. However, an interaction between nodal status and oxygenation was observed (P =.006), and further analysis indicated that HP(5) was an independent predictor of outcome in patients with negative nodes on imaging (P =.007). There was a significant increase in the 3-year cumulative incidence of distant metastases in the hypoxic group (41% v 15% in those with HP(5) < 50%; P =.0023), but not in pelvic relapse (37% v 27%; P =.12). CONCLUSION: Tumor hypoxia is an independent predictor of poor PFS only in patients with node-negative cervix cancer, in addition to tumor size. Its impact appears to be related to an increased risk of distant metastases rather than to an effect on pelvic control.     

肿瘤乏氧显像与放疗研究进展

乏氧现象在实体瘤中普遍存在,是影响放疗疗效的主要因素之一.乏氧显像可无创伤性检测肿瘤组织乏氧区域,可指导治疗及预测预后,成为近几年研究的热点,现综述肿瘤乏氧显像与放疗的研究现状.     

Tumor vascularity: a histological measure of angiogenesis and hypoxia

In this study we sought to clarify the relationship between tumor vascularity, hypoxia, and angiogenesis in human cervix tumors. Two hypotheses were established: first, that measurement of tumor vascularity can provide a histological assessment of both hypoxia and angiogenesis; and second, that expression of angiogenesis-related proteins will provide a surrogate measure of tumor hypoxia. To test the first hypothesis, we studied the prognostic significance of tumor vascularity measured as both intercapillary distance (ICD; thought to reflect tumor oxygenation) and microvessel density (MVD; the hotspot method that provides a histological assessment of tumor angiogenesis). The relationship was also examined of tumor hypoxia, measured using an Eppendorf needle electrode [percentage of values less than 5 mm Hg (HP5)], with ICD and MVD. To test the second hypothesis we examined the relationship between HP5 and the expression of angiogenesis-associated proteins [vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor (PD-ECGF)]. All of the biological measurements were made on pretreatment tumors. Analysis of data was carried out using log-rank statistics, Cox multivariate analysis, and Spearman's rank correlation. Both ICD and MVD were significant independent prognostic factors for local control. Patients with poorly vascularized tumors (long ICD) had poor local control (P = 0.042). However, patients with poorly vascularized tumors, measured as low MVD, had good local control (P = 0.036). For 107 patients in whom both of the measurements were obtained on the same tumor sections, ICD and MVD provided independent prognostic information in multivariate analysis. There was a significant correlation between tumor hypoxia and ICD (P < 0.005) but not MVD (P = 0.41). There was no relationship between hypoxia and the expression of angiogenic factors (VEGF, PD-ECGF). These analyses show that measurement of tumor vascularity can provide different biological information that is dependent on the method used. It is, therefore, important that studies measuring vascularity should include an appropriate definition. There is no relationship between hypoxia and angiogenesis in advanced carcinoma of the cervix and examining the levels of angiogenic proteins may not have a role in assessing hypoxia in cervix cancer.     

磁共振成像检测肿瘤乏氧

研究证实动态增强磁共振成像(DCE-MRI)、血氧水平依赖性磁共振成像(BOLD-MRI)、电子顺磁共振(EPR)血氧测定法、overhauser-磁共振成像(OMRI)、氟碳磁共振成像(19F-MRI)等技术能安全有效地检测肿瘤乏氧.这些显像技术可以用于预测肿瘤预后、进行个体化治疗和预测以及监测治疗的反应性.     

Tumor imaging with multicolor fluorescent protein expression

Imaging with fluorescent proteins has been revolutionary and has led to the new field of in vivo cell biology. Many new applications of this technology have been developed. Green fluorescent protein (GFP)-labeled or red fluorescent protein (RFP)-labeled HT-1080 human fibrosarcoma cells were used to determine clonality of metastasis by imaging of metastatic colonies after mixed implantation of the red and green fluorescent cells. Resulting pure red or pure green colonies were scored as clonal, whereas mixed yellow colonies were scored as nonclonal. Dual-color fluorescent cancer cells expressing GFP in the nucleus and RFP in the cytoplasm were engineered. The dual-color cancer cells enable real-time nuclear–cytoplasmic dynamics to be visualized in living cells in vivo, including mitosis and apoptosis. The nuclear and cytoplasmic behavior of dual-color cancer cells in real time in blood vessels was observed as they trafficked by various means or extravasated in an abdominal skin flap. Dual-color cancer cells were also visualized trafficking through lymphatic vessels where they were imaged via a skin flap. Seeding and arresting of single dual-color cancer cells in the lung, accumulation of cancer-cell emboli, cancer-cell viability, and metastatic colony formation were imaged in real time in an open-chest nude mouse model using assisted ventilation. Novel treatment was evaluated in these imageable models. UVC irradiation killed approximately 70% of the dual-color cancer cells in a nude mouse model. An RFP-expressing glioma was transplanted to the spinal cord of transgenic nude mice expressing nestin-driven green fluorescent protein (ND-GFP). In ND-GFP mice, GFP is expressed in nascent blood vessels and neural stem cells. ND-GFP cells staining positively for neuronal class III-β-tubulin or CD31 surrounded the tumor, suggesting that the tumor stimulated both neurogenesis and angiogenesis. The tumor caused paralysis and also metastasized to the brain. The Salmonella typhimurium A1-R tumor-targeting bacterial strain was administered in the orthotopic spinal cord glioma model. The treated animals had a significant increase in survival and decrease in paralysis. S. typhimurium A1-R was effective against primary bone tumor and lung metastasis expressing RFP in a nude mouse model. S. typhimurium A1-R was effective against both axillary lymph and popliteal lymph node metastases of human dual-color pancreatic cancer and fibrosarcoma cells, respectively, as well as lung metastasis of the fibrosarcoma in nude mice. Imaging with fluorescent proteins will reveal mechanisms of cancer progression and provide visual targets for novel therapeutics.     

Tumor detection using folate receptor-targeted imaging agents

Folate receptors are up-regulated on a variety of human cancers, including cancers of the breast, ovaries, endometrium, lungs, kidneys, colon, brain, and myeloid cells of hematopoietic origin. This over-expression of folate receptors (FR) on cancer tissues can be exploited to target folate-linked imaging and therapeutic agents specifically to FR-expressing tumors, thereby avoiding uptake by most healthy tissues that express few if any FR. Four folate-targeted therapeutic drugs are currently undergoing clinical trials, and several folate-linked chemotherapeutic agents are in late stage preclinical development. However, because not all cancers express FR, and because only FR-expressing cancers respond to FR-targeted therapies, FR-targeted imaging agents have been required to select patients with FR-expressing tumors likely to respond to folate-targeted therapies. This review focuses on recent advances in the use of the vitamin folic acid to target PET agents, γ-emitters, MRI contrast agents and fluorescent dyes to FR⁺ cancers for the purpose of diagnosing and imaging malignant masses with improved specificity and sensitivity.