Oxygen Transport in Tumors

Hypoxia-inducible factors in stem cells and cancer

Cellular properties are influenced by complex factors inherent to their microenvironments. While oxygen deprivation (hypoxia) occurs in tumours because of rapid cell proliferation and aberrant blood vessel formation, embryonic cells develop in a naturally occurring hypoxic environment. Cells respond to hypoxia by stabilizing hypoxia-inducible factors (HIFs), which are traditionally viewed to function by altering cellular metabolism and blood vessel architecture. Recently, HIFs have been shown to modulate specific stem cell effectors, such as Notch, Wnt and Oct4 that control stem cell proliferation, differentiation and pluripotency. Direct molecular links have also been established between HIFs and critical cell signalling pathways such as cMyc and p53. These novel links suggest a new role for HIFs in stem cell and tumour regulation.

Perfusion CT in squamous cell carcinoma of the upper aerodigestive tract: long-term predictive value of baseline perfusion CT measurements

BACKGROUND AND PURPOSE

PCT studies hold short-term predictive value in patients treated with chemoradiotherapy. Our aim was to examine the long-term predictive value of baseline PCT studies for local tumor control and overall survival in SCCA of the upper aerodigestive tract treated with chemoradiotherapy.

MATERIALS AND METHODS

Eighty-four patients with advanced SCCA underwent PCT followed by concomitant chemoradiation. The acquired perfusion maps represented BF, BV, MTT, and PS. Visual analysis of the parametric maps for identification of tumor perfusion patterns was conducted. ROC curves, t tests, and Kaplan-Meier survival curves were plotted for local disease control and overall survival.

RESULTS

The median time of local tumor control was 24 months. The BF and PS values were significantly higher in patients who had no recurrence than in those with local failure (P < or = .02). The BF and PS were predictive (P < or = .0006) but BV and MTT held no significant predictive values for local tumor control. The patients with high BF and PS had a longer local tumor control than the patients with hypoperfused tumors (P = .0007). A visually detected BF-BV mismatch had a sensitivity/specificity of 63%/66% (P = .03) and 59%/69% (P = .03) for local tumor control and OS, respectively. Patients without mismatch lived significantly longer than patients with mismatch (P = .01).

CONCLUSIONS

BF, PS, and mismatch of BF-BV are significant predictors of local tumor control after chemoradiation in SCCA of the upper aerodigestive tract.

Origin of cancer stem cells: the role of self-renewal and differentiation

BACKGROUND

Self-renewal and differentiation potential is the feature of stem cells. Differentiation is usually considered to be a one-way process of specialization as cells develop the functions of their ultimate fate and lose their immature characteristics, such as self-renewal. Progenitor cells, the products of stem cells losing the activity of self-renewal, could differentiate to mature cells, which have the feature of differentiation and lose the activity of self-renewal. The roles for cancer stem cells have been demonstrated for some cancers. However, the origin of the cancer stem cells remains elusive.

METHODS

This review focuses on current scientific controversies related to the establishment of the cancer stem cells--in particular, how self-renewal and differentiation block might contribute to the evolution of cancer.

RESULTS

Cancer stem cells may be caused by transforming mutations occurring in multi-potential stem cells, tissue-specific stem cells, progenitor cells, mature cells and cancer cells. Progenitor cells obtain the self-renewal activity by activating the self-renewal-associated genes rather than dedifferentiate to tissue special stem cells. The transform multi-potential stem cells gain the differentiation feature of special tissue by differentiating to cancer cells. Mature cells and cancer cells may dedifferentiate or reprogram to cancer stem cells by genetic and / or epigenetic events to gain the self-renewal activity and lose some features of differentiation. The cancer-derived stem cells are not the "cause", but the "consequence" of carcinogenesis. The genetic program controlling self-renewal and differentiation is a key unresolved issue.

CONCLUSION

Cancer stem cells may be caused by disturbance of self-renewal and differentiation occurring in multi-potential stem cells, tissue-specific stem cells, progenitor cells, mature cells and cancer cells.

Developments in quantitative oxygen-saturation imaging of breast tissue in vivo using multispectral near-infrared tomography

Imaging of oxygen saturation provides a spatial map of the tissue metabolic activity and has potential in diagnosis and treatment monitoring of breast cancer. Oxygen-saturation imaging is possible through near-infrared (NIR) tomography, but has low signal-to-noise ratio (SNR). This can be augmented by using NIR tomography as an add-on to MRI. Presented are results from a free-standing NIR system and a hybrid MR-guided system for breast imaging. In results from imaging 60 healthy volunteers in the initial NIR system, oxygen saturation was a significant discriminator between the BIRADS classifications of adipose tissue, heterogeneously dense, and extremely dense tissue. By using the MR-guided NIR system, more accurate tissue-specific data were obtained on adipose and fibroglandular volumes, with 11 healthy volunteers. In these data, oxygen saturation in the adipose tissue correlated with percentage of adipose tissue. In two case studies of infiltrating ductal carcinomas, oxygen saturation was reduced at the site of the tumor, as compared with the surrounding healthy tissue, agreeing with conventional thought that hypoxia exists in larger solid tumors. The MRI-guided NIR images of oxygen saturation provide higher resolution and superior SNR and will likely be used in the future to study and characterize specific tissue volumes.

Microbiology and management of infected solid tumours

Infection has been recognized as one of the major obstacles to the successful management of patients with malignant tumours. Aerobic and anaerobic bacteria of endogenous source are a major cause of infections in the necrotic tumour, especially when they occur in proximity to a site where these bacteria reside as part of the normal flora. Although surgical removal or evacuation of the purulent fluid is preferred, this is not always feasible in a patient with a malignant tumour. Antimicrobial therapy against potential bacterial pathogens is often the sole therapy or is used along with surgical drainage or removal of the infected area. This review describes the microbiology and management of infection in necrotic tumours.

Hypoxia in head and neck cancer

A high level of hypoxia in solid tumours is an adverse prognostic factor for the poor outcome of cancer patients following treatment. This review describes the status of research into finding a practical method for measuring hypoxia and treating hypoxic tumours. The application of such methodology would enable the selection of head and neck cancer treatment based on an individual's tumour oxygenation status. This individualization would include the selection not only of surgery or radiotherapy, but also of novel hypoxia-modification strategies.

Oral cancer detection using diffuse reflectance spectral ratio R540/R575 of oxygenated hemoglobin bands

A low-cost, fast, and noninvasive method for early diagnosis of malignant lesions of oral mucosa based on diffuse reflectance spectral signatures is presented. In this technique, output of a tungsten halogen lamp is guided to the tissue through the central fiber of a reflection probe whose surrounding six fibers collects tissue reflectance. Ex vivo diffuse reflectance spectra in the 400 to 600-nm region is measured from surgically removed oral cavity lesions using a miniature fiber optic spectrometer connected to a computer. Reflectance spectral intensity is higher in malignant tissues and shows dips at 542 and 577 nm owing to absorption from oxygenated hemoglobin (HbO2). Measurements carried out, within an hour of surgical excision, on malignant lesion and adjoining uninvolved mucosa show that these absorption features are more prominent in neoplastic tissues owing to increased microvasculature and blood content. It is observed that reflectance intensity ratio of hemoglobin bands, R540/R575, from malignant sites are always lower than that from normal sites and vary according to the histological grade of malignancy. The diffuse reflectance intensity ratio R540/R575 of the hemoglobin bands appears to be a useful tool to discriminate between malignant lesions and normal mucosa of the oral cavity in a clinical setting.

Investigation of bi-phasic tumor oxygen dynamics induced by hyperoxic gas intervention: A numerical study

This study intends to explore the underlying principle of the biphasic behavior of increases in oxygenated hemoglobin concentration that was observed in vivo from rat breast tumors during carbogen/oxygen inhalation. We have utilized the Finite Element Method (FEM) to simulate the effects of different blood flow rates, in several geometries, on the near infrared measurements. The results show clearly that co-existence of two blood flow velocities can result in a bi-phasic change in optical density, regardless of the orientation of vessels. This study supports our previous hypothesis that the bi-phasic tumor hemodynamic feature during carbogen inhalation results from a well-perfused and a poorly perfused region in the tumor vasculature.

Hypoxia-induced dedifferentiation of tumor cells--a mechanism behind heterogeneity and aggressiveness of solid tumors

Histopathological examination of solid tumors frequently reveals pronounced tumor cell heterogeneity with regards to cell organization, cell morphology, cell size, nuclei morphology, etc. Analyses of gene expression patterns by immunohistochemistry or in situ hybridization techniques further strengthen the actual presence of phenotypic heterogeneity, often demonstrating substantial diversity within a given tumor. The molecular mechanisms underlying the phenotypic heterogeneity are very complex with genetic, epigenetic and environmental components. Hypoxia, shortage in oxygen, greatly influences cellular phenotypes by altering the expression of specific genes, and is an important contributor to intra- and inter-tumor cell diversity as revealed by the pronounced but non-uniform expression of hypoxia-driven genes in solid tumors (reviewed in [Semenza GL. Targeting HIF-1 for cancer therapy. Nat Rev Cancer 2003;3:721-32; Harris AL. Hypoxia--a key regulatory factor in tumour growth. Nat Rev Cancer 2002;2:38-47.]). The oxygen pressure in solid tumors is generally lower than in the surrounding non-malignant tissues, and tumors exhibiting extensive hypoxia have been shown to be more aggressive than corresponding tumors that are better oxygenized [Vaupel P. Oxygen transport in tumors: characteristics and clinical implications. Adv Exp Med Biol 1996;388:341-51; Vaupel P, Thews O, Hoeckel M. Treatment resistance of solid tumors: role of hypoxia and anemia. Med Oncol 2001;18:243-59.]. We recently observed that hypoxic neuroblastoma cells and breast cancer cells lose their differentiated gene expression patterns and develop stem cell-like phenotypes [Jögi A, Øra I, Nilsson H, Lindeheim A, Makino Y, Poellinger L, et al. Hypoxia alters gene expression in human neuroblastoma cells toward an immature and neural crest-like phenotype. Proc Natl Acad Sci USA 2002;99:7021-6; Helczynska K, Kronblad A, Jögi A, Nilsson E, Beckman S, Landberg G, et al. Hypoxia promotes a dedifferentiated phenotype in ductal breast carcinoma in situ. Cancer Res 2003;63:1441-4.]. As low stage of differentiation in neuroblastoma and in breast cancer is linked to poor prognosis, hypoxia-induced dedifferentiation will not only contribute to tumor heterogeneity but could also be one mechanism behind increased aggressiveness of hypoxic tumors. The effect(s) of hypoxia on tumor cell differentiation status is the focus of this review.

Broadband reflectance measurements of light penetration, blood oxygenation, hemoglobin concentration, and drug concentration in human intraperitoneal tissues before and after photodynamic therapy

We evaluate Photofrin-mediated photodynamic therapy (PDT) in a phase 2 clinical trial as an adjuvant to surgery to treat peritoneal carcinomatosis. We extract tissue optical [reduced scattering (mu(s)'), absorption (mu(a)), and attenuation coefficients (mu(eff))] and physiological [blood oxygen saturation (%S(t)O2), total hemoglobin concentration (THC), and photosensitizer concentration (c(Photofrin))] properties in 12 patients using a diffuse reflectance instrument and algorithms based on the diffusion equation. Before PDT, in normal intraperitoneal tissues %S(t)O2 and THC ranged between 32 to 100% and 19 to 263 microM, respectively; corresponding data from tumor tissues ranged between 11 to 44% and 61 to 224 microM. Tumor %S(t)O2 is significantly lower than oxygenation of normal intraperitoneal tissues in the same patients. The mean (+/-standard error of mean) penetration depth (delta) in millimeters at 630 nm is 4.8(+/-0.6) for small bowel, 5.2 (+/-0.67) for large bowel, 3.39(+/-0.29) for peritoneum, 5.19(+/-1.4) for skin, 1.0(+/-0.1) for liver, and 3.02(+/-0.66) for tumor. c(Photofrin) in micromolars is 4.9(+/-2.3) for small bowel, 4.8(+/-2.3) for large bowel, 3.0 (+/-1.0) for peritoneum, 2.5(+/-0.9) for skin, and 7.4(+/-2.8) for tumor. In all tissues examined, mean c(Photofrin) tends to decrease after PDT, perhaps due to photobleaching. These results provide benchmark in-vivo tissue optical property data, and demonstrate the feasibility of in-situ measurements during clinical PDT treatments.

Oxygen regulates invasiveness and virulence of group B streptococcus

The facultative anaerobe group B Streptococcus (GBS) is an opportunistic pathogen of pregnant women, newborns, and the elderly. Although several virulence factors have been identified, environmental factors that regulate the pathogenicity of GBS have not been well characterized. Using the dynamic in vitro attachment and invasion system (DIVAS), we examined the effect of oxygen on the ability of GBS to invade immortalized human epithelial cells. GBS type III strain M781 invaded human epithelial cells of primitive neurons, the cervix, the vagina, and the endometrium in 5- to 400-fold higher numbers when cultured at a cell mass doubling time (t(d)) of 1.8 h than at a slower t(d) of 11 h. Invasion was optimal when GBS was cultured at a t(d) of 1.8 h in the presence of >or=5% oxygen and was significantly reduced without oxygen. Moreover, GBS grown in a chemostat under highly invasive conditions (t(d) of 1.8 h, with oxygen) was more virulent in neonatal mice than was GBS grown under suboptimal invasion conditions (t(d) of 1.8 h, without oxygen), suggesting a positive association between in vitro invasiveness with DIVAS and virulence.

Phase I trial of i.v. administered tirapazamine plus cyclophosphamide

Our objective was to determine the maximum tolerated doses of tirapazamine and cyclophosphamide given i.v. in combination. Eligible patients had advanced solid tumors refractory to conventional treatment. Tirapazamine (escalated from 80 to 390 mg/m(2)) was given i.v. over 2 h and followed by cyclophosphamide over 1 h. The cyclophosphamide dose was fixed at 1000 mg/m(2) until the tirapazamine dose of 390 mg/m(2) was reached. Once that dose of tirapazamine was reached, the cyclophosphamide dose was escalated to 1250 and 1500 mg/m(2). Twenty-eight patients were enrolled. The dose-limiting toxicity was granulocytopenia. One patient had transient deafness for 2 days. Four other patients had grade 1 ototoxicity. Grade 1 and 2 muscle cramps were observed at all dose levels. Other toxic effects observed included fatigue, nausea, vomiting, headache, diarrhea, drug fever, elevated transaminases and elevated creatine phosphokinase. Three patients had stable disease and the longest time to progression was 5 months. The combination of tirapazamine and cyclophosphamide is feasible, and the dose-limiting toxicity is granulocytopenia. The use of growth factors could possibly allow escalation of tirapazamine doses in future phase II trials. Without growth factor support, the recommended doses of tirapazamine and cyclophosphamide when administered in this schedule are 260 and 1000 mg/m(2), respectively.

Hypoxia, clonal selection, and the role of HIF-1 in tumor progression

Tumor progression occurs as a result of the clonal selection of cells in which somatic mutations have activated oncogenes or inactivated tumor suppressor genes leading to increased proliferation and/or survival within the hypoxic tumor microenvironment. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates adaptive responses to reduced O2 availability, including angiogenesis and glycolysis. Expression of the O2-regulated HIF-1alpha subunit and HIF-1 transcriptional activity are increased dramatically in hypoxic cells. Recent studies indicate that many common tumor-specific genetic alterations also lead to increased HIF-1alpha expression and/or activity. Thus, genetic and physiologic alterations within tumors act synergistically to increase HIF-1 transcriptional activity, which appears to play a critical role in the development of invasive and metastatic properties that define the lethal cancer phenotype.

Predictive power of the tumor oxygenation status

We have previously demonstrated with a prospective study in primary cancer of the uterine cervix (clinical size > 2 cm) that tumor hypoxia not only indicates decreased radiocurability but is generally associated with malignant progression of the disease. This finding also holds true for other tumor entities (soft tissue sarcomas, squamous cell carcinomas of the head and neck region), for lymph node metastases of head and neck lesions, and for locoregional recurrences of cervical cancers. All data available so far support our thesis that in cervical cancers (and in other solid tumors as well), tumor hypoxia and clinical aggressiveness in terms of resistance to therapy and tumor dissemination, are interrelated.

Optical imaging as an adjunct to sonograph in differentiating benign from malignant breast lesions

The role of near infrared (NIR) diffusive light imaging as an adjunct to ultrasound in differentiating benign from malignant lesions was evaluated in 27 mammography patients with infiltrating ductal carcinomas, apocrine metaplasia, fibroadenomas, radial scar and ductal hyperplasia, cysts, and normal tissues. Conventional ultrasound/mammography images were graded based on BI-RADS assessment categories. The spatial NIR measurements were made at wavelengths of 750 and 830 nm. Functional images, such as relative changes of deoxyhemoglobin (deoxyHb) and total blood concentration, were estimated from the dual wavelength measurements. Maximum relative deoxyHb and blood concentration changes were measured, and spatial correlation of masses in relative deoxyHb and blood concentration images for each breast were calculated. For the five biopsy proven benign lesions, ultrasound/mammography diagnoses were suspicious for malignancy (four cases) and highly suspicious for malignancy (one case). Four lesions showed less than 1.0 V maximum deoxyHb and less than 1.5 V maximum blood concentration levels on average and spatial image correlation showed no correlated masses in both deoxyHb and blood concentration images. For the four biopsy proven malignant lesions, ultrasound/mammography diagnoses were highly suspicious for malignancy. Maximum deoxyHb and blood concentration changes were greater than 2.9 V on average except one lesion which showed smaller deoxyHb signal (maximum 0.85 V) but the deoxyHb mass and blood concentration mass were highly correlated.

Diffuse reflectance spectroscopy of human adenomatous colon polyps in vivo

Diffuse reflectance spectra were collected from adenomatous colon polyps (cancer precursors) and normal colonic mucosa of patients undergoing colonoscopy. We analyzed the data by using an analytical light diffusion model, which was tested and validated on a physical tissue model composed of polystyrene beads and hemoglobin. Four parameters were obtained: hemoglobin concentration, hemoglobin oxygen saturation, effective scatterer density, and effective scatterer size. Normal and adenomatous tissue sites exhibited differences in hemoglobin concentration and, on average, in effective scatterer size, which were in general agreement with other studies that employ standard methods. These results suggest that diffuse reflectance can be used to obtain tissue information about tissue structure and composition in vivo.