Detection and characterization of tumor hypoxia using pO2 histography

Data from 125 studies describing the pretreatment oxygenation status as measured in the clinical setting using the computerized Eppendorf pO2 histography system have been compiled in this article. Tumor oxygenation is heterogeneous and severely compromised as compared to normal tissue. Hypoxia results from inadequate perfusion and diffusion within tumors and from a reduced O2 transport capacity in anemic patients. The development of tumor hypoxia is independent of a series of relevant tumor characteristics (e.g., clinical size, stage, histology, and grade) and various patient demographics. Overall median pO2 in cancers of the uterine cervix, head and neck, and breast is 10 mm Hg with the overall hypoxic fraction (pO2 <or= 2.5 mm Hg) being approx. 25%. Metastatic lesions do not substantially deviate from the oxygenation status of (their) primary tumors. Whereas normal tissue oxygenation is independent of the hemoglobin level over the range of 8-15 g/dL, hypoxia is more pronounced in anemic patients and above this range in some cancers. Identification of tumor hypoxia may allow an assessment of a tumor's potential to develop an aggressive phenotype or acquired treatment resistance, both of which lead to poor prognosis. Detection of hypoxia in the clinical setting may therefore be helpful in selecting high-risk patients for individual and/or more intensive treatment schedules.

Dynamic contrast-enhanced MR imaging of uterine cervical cancer: pharmacokinetic analysis with histopathologic correlation and its importance in predicting the outcome of radiation therapy

PURPOSE

To investigate the histopathologic bases of different enhancement patterns on dynamic contrast material-enhanced magnetic resonance (MR) images of cervical cancer and to assess their importance in predicting the outcome of patients after radiation therapy.

MATERIALS AND METHODS

Dynamic enhanced MR imaging and pharmacokinetic analyses were performed in 26 patients with cervical cancer who subsequently underwent hysterectomy and in 36 patients with cervical cancer who received radiation therapy. Histopathologic findings and clinical outcomes were correlated with results of dynamic MR imaging and pharmacokinetic analysis.

RESULTS

On dynamic MR images of the surgical patients, areas with intense homogeneous enhancement showed increased permeability (k = 27.4 x 10(-3)) compared with areas with poor enhancement (k = 19.0 x 10(-3)). Well-enhanced areas were predominantly composed of cancer cell fascicles, whereas poorly enhanced areas were composed of fibrous tissue with scattered cancer cells. Radiation therapy was more effective in tumors with higher tissue permeability (k = 31.3 x 10(-3)) on dynamic MR images than in those with lower tissue permeability (k = 18.3 x 10(-3)).

CONCLUSION

Areas of increased contrast enhancement are mainly composed of abundant cancer cell fascicles, whereas poorly perfused areas are composed of fibrous tissue with scattered cancer cells. Radiation therapy is more effective in well-enhanced tumors, resulting in improved local control.

[In vitro oxygen-dependent survival of 2 human cell lines after radiation combined with tirapazamine (SR-4233) and cisplatin]

Recent data have shown that the in vitro and in vivo cytotoxicity of bioreductive drugs could be significantly increased by combination with ionising radiation or chemotherapy. Various parameters such as oxygen tension and timing of administration of the drugs could play a crucial role in the efficacy of combined treatment modalities. The aim of this study was to define the oxygen dependency of cell survival after in vitro irradiation and incubation with tirapazamine, a bioreductive drug, and cisplatin given alone or simultaneously. Two human cell lines were studied: one cell line sensitive to tirapazamine, Na11+, a pigmented melanoma with a high percentage of hypoxic cells, and a less sensitive cell line to tirapazamine, HRT18, a rectal adenocarcinoma. Gas changes were made to study cell survival at four different oxygen concentrations (pO2): air (20.9% O2), 10.2 and 0.2% O2. Cells were incubated with tirapazamine and cisplatin alone or combined for one hour at 37 degrees C, then irradiated and cultured. For Na11+, cell survival after irradiation was comparable in air and at 10% oxygen with the two drugs given alone or combined. At 2 and 0.2% oxygen, cell killing was largely increased by tirapazamine and was not modified by the addition of cisplatin. For HRT18, cell survival was not modified when cisplatin was added to radiation, whatever the oxygen partial pressure. At low pO2 (2 and 0.2%) the cytotoxic effect of tirapazamine was not significantly decreased by the addition of cisplatin. When cytotoxic and bioreductive drugs are combined to radiation, the magnitude of the observed effect is highly dependent on the partial oxygen pressure and on the sensitivity of the cell line to the individual drugs. This has very important implications for clinical strategies based on combined chemo-radiotherapy.

[Radiation sensitizing agents for hypoxic cells: past, present and future]

Hypoxic cells are present in rodent and xenografted human tumours and it has been known for a long time that the absence of oxygen in tumours is a factor of resistance against ionising radiation. The dose modifying role of oxygen (oxygen enhancement ratio) has been largely studied in experimental models. For pO2 values of 2 mmHg, the relative radiosensitivity of tumour cells is intermediate between the maximum sensitivity observed in air and the minimal one observed in hypoxia. The measurement of tumour pO2 in patients (polarographic technique) has demonstrated the presence of low values (< 10 mmHg) in many different tumour sites (ENT, uterine cervix, breast, melanoma, etc). In order to sensitise hypoxic tumours, imidazole have been used in patients, but most of the results were negative. New methods have been developed in the combination of bioreductive drugs of cytotoxic cells to radiotherapy. In this article, we will describe the clinical results obtained in patients with radiosensitising chemical agents.

Oxygenation predicts radiation response and survival in patients with cervix cancer

BACKGROUND AND PURPOSE

Hypoxia appears to be an important factor in predicting tumor relapse following radiation therapy. This study measured oxygenation prior to treatment in patients with cervix cancer using a polarographic oxygen electrode to determine if oxygenation was an important prognostic factor with regard to tumor control and survival.

MATERIALS AND METHODS

Between May 1994 and June 1997, 74 eligible patients with cervix cancer were entered into an ongoing prospective study of tumor oxygenation prior to primary radiation therapy. All patients were evaluated with an Eppendorf oxygen electrode during examination under anesthesia. Oxygenation data are presented as the hypoxic proportion, defined as the percentage of pO2 readings of <5 mm Hg (abbreviated as HP5).

RESULTS

The HP5 ranged from 2 to 99% with a median of 52%. With a median follow-up of 1.2 years, the disease-free survival (DFS) rate was 69% for patients with HP5 of < or =50% compared with 34% for those with HP5 of >50% (log-rank P = 0.02). Tumor size above and below the median of 5 cm was also significantly related to DFS (P = 0.0003) and patients with bulky hypoxic tumors had a significantly lower DFS (12% at 2 years) than either bulky oxygenated or non-bulky oxygenated or hypoxic tumors (65%, P = 0.0001).

CONCLUSIONS

Hypoxia and tumor size are significant adverse prognostic factors in a univariate analysis of disease-free survival in patients with cervix cancer. A high risk group of patients with bulky hypoxic tumors have a significantly higher probability of relapse and death.

Variations in tumour oxygen tension (pO2) during accelerated radiotherapy of head and neck carcinoma

The study was performed to assess the effect of accelerated radiotherapy on oxygenation of primary tumours and metastatic nodes in patients with advanced head and neck tumours. In 14 patients with head and neck tumour, oxygen tension (pO2) was evaluated in normal tissues and tumours (primary tumour or metastatic neck node) before (0 Gy) and after 2 weeks (32 Gy) of accelerated radiotherapy (70 Gy in 3.5 weeks, with three daily fractions). Radiotherapy was combined with carbogen breathing in 5 patients. pO2 was measured using a polarographic technique. For pooled normal tissues, median pO2 was 38 mmHg before treatment and 46 mmHg after 2 weeks. For tumours, very low values (< 2 mmHg) represented 20% of the recorded values before treatment and 10% after 2 weeks. The relative increase in tumour oxygenation was more pronounced for primary tumours (median pO2 12 mmHg before treatment versus 26 mmHg after 2 weeks, P < 0.05) than for metastatic nodes (respectively, 20 and 27 mmHg P = 0.1). For the 5 patients who breathed carbogen during accelerated radiotherapy, the median pO2 was 44 mmHg at 2 weeks, compared with 13.5 mmHg before treatment (P = 0.05). Very low pO2 values, corresponding to tumour hypoxia, were found in the tumours (primary and metastatic neck nodes) prior to accelerated treatment. During the first 2 weeks of accelerated treatment, an increase in median pO2 was found in nine of the 14 tumours, together with a decrease in the frequency of very low values.

Assessment of tumor microcirculation: a new role of dynamic contrast MR imaging

With the advances in MR techniques, information related to tumor microcirculation now can be obtained in the clinical setting. This information can be valuable in the assessment of tumor blood supply/oxygenation status and tumor response to therapy. In this article, we review the tracer-kinetic modeling for tumor microcirculatory parameters derived from dynamic contrast MR imaging and report several preliminary results from both an animal model and early experience with human tumors. Despite the application of different MR protocols and tracer-kinetic models, the initial results of these pioneer studies consistently support the role of MR-derived microcirculatory tumor parameters, in providing prognostic information to assess and predict the response of cancers to cytotoxic therapy.

Secretion rates and levels of vascular endothelial growth factor in clone A or HCT-8 human colon tumour cells as a function of oxygen concentration

Molecular and in situ hybridization studies have shown, in a number of cell types, that under hypoxic conditions, vascular endothelial growth factor (VEGF) mRNA expression is up-regulated and VEGF protein is concomitantly increased. To establish a quantitative relationship between VEGF protein levels and oxygenation, we exposed exponentially growing clone A or HCT-8 human colon tumour cells in vitro (22 h at 37 degrees C) to oxygen concentrations from 21% (air mixture) to 0.01%. Protein levels in cells and medium were then assayed using an enzyme-linked immunoabsorbent assay (ELISA). Intracellular levels of VEGF in clone A or HCT-8 cells exposed to either air (21% O2) or the 0.01% O2 mixture respectively increased from about 73 to 1270, and 1.5 to 1180 pg/10(6) cells (about 17- and 80-fold increases). The shapes of the response curves (log of the intracellular VEGF concentrations v. log oxygen concentration) for both cell types were sigmoidal. However, intracellular VEGF levels in HCT-8 cells were always less than that of clone A cells until levels of about 0.3 to 0.1% O2 were reached. Levels of VEGF in the supernatant were also increased after the 22 h hypoxic exposures. Because cell proliferation and clonogenicity were also measured, it was possible to estimate the secretion rates of VEGF for both cell lines as a function of oxygen percentage. For clone A cells, the secretion rate (pg/10(6) cells/h) in 21% O2 was 62.5. This rate increased to 428.8 pg/10(6) cells/h at 0.01% O2, a 7-fold increase. For HCT-8 cells, levels in the medium at 21% O2 were too low to be measured by ELISA. However, between 10% and 0.01% O2, secretion rates increased from 5.0 to 376.0 pg/10(6) cells/h, a 75-fold increase. Therefore, at very low O2 levels, VEGF secretion rates were similar in the two cell lines. We propose that the different VEGF responses of clone A and HCT-8 colon tumour cells to hypoxic stress in vitro are related to the in vivo observation that the respective hypoxic percentages of solid neoplasms originating from these cell lines are markedly different (i.e. about 3 versus 80%) at equivalent volumes of 750 mm3.