M. Guichard

Distribution of radiation sensitivities for human tumor cells of specific histological types: Comparison of in vitro to in vivo data☆☆☆

The radiosensitivities of human tumor cell lines, grouped into 6 histological categories, have been studied using data from the published literature. The parameters alpha, beta, n, D0, D, and the surviving fraction to 2 Gy (S2) and 8 Gy (S8) were calculated. Only the two parameters mainly derived from the initial part of the survival curve, alpha and D, together with S2, provided data which were correlated with the clinical radioresponsiveness of each histological group. Thus, there are intracellular factors which influence clinical radioresponsiveness whose relative importance varies from one histological cell type to another. The value of D gave the most precise characterization of the average group radiosensitivity. It was possible to compare the in vivo radiosensitivities of non-severely hypoxic cells with those of tumor cells irradiated in vitro for 7 tumor lines grown as xenografts in mice. The average radiosensitivity was 1.9 times less in vivo than in vitro. This difference indicates that, in addition to the intrinsic factors of radioresistance demonstrated in vitro, and independently of severe hypoxia, there are other factors which specifically reduce radiosensitivity in vivo.

Oxygenation of head and neck tumors.

Background. Tumor hypoxia could play a role in the response to radiation therapy. Few data are available on oxygen tension (pO2) measurements in head and neck tumors.

Changes in the oxygenation of head and neck tumors during carbogen breathing

The oxygenation of head and neck tumors and changes during carbogen breathing were assessed in 20 patients. The median oxygen tension (pO2) for each patient was lower in tumors before breathing carbogen than in normal tissues. The median pooled pO2 of all the tumors was 20 mmHg; for normal tissue it was 60 mmHg. Low values (below 10 mmHg) were found in 4 patients for the normal tissue and in 18 patients for tumors. During carbogen breathing, the median (61 mmHg) pO2 readings for all tumors was higher than that recorded before carbogen breathing. The frequency of low (< 10 mmHg) pO2 values decreased with carbogen breathing in 11 patients; only 4 patients still exhibited very low values (< 2 mmHg). Maximal effect was obtained within 1-6 min of gas exposure. The pO2 stayed high under carbogen breathing in 15 out of 16 patients. Return to pre-carbogen levels of oxygenation occurred in 1 min after the end of gas exposure. These data suggest that carbogen breathing increases tumor oxygenation as assessed by polarography. The breathing time appears to be important for therapeutical use and should to be taken into consideration.

Interlaboratory variation in oxygen tension measurement by Eppendorf “Histograph” and comparison with hypoxic marker

The median of pO2 values in tumor measured by Eppendorf “Histograph” with a needle‐type electrode has been used as a prognostic indicator in cancer patients. However, it is not established that a pretreatment measured pO2 value can be used as a universal predictor of local control probability, because the variation in pO2 values, especially in hypoxic tissue, among institutes may not allow comparison of measured “absolute pO2 values.” The purpose of this study was to examine the variation in oxygen tension measurement by Eppendorf “Histograph” among six laboratories using a single batch of mice and tumors and the same detailed protocol. These results were also compared to the immunohistochemical staining of 2‐nitroimidazole adducts.

Predictive assays of radiation response in patients with head and neck squamous cell carcinoma: A review of the institute gustave roussy experience

PURPOSE The aim of the study was to present the updated Institut Gustave Roussy experience of the predictive value of three biological parameters in patients with squamous cell carcinoma of the Head and Neck (HNSCC) treated with radiation therapy. METHODS AND MATERIALS Three parameters have been investigated independently: tumor cell kinetics (TS, Tpot and LI), oxygen tension measurements (PO2) and intrinsic radiosensitivity (SF2Gy). RESULTS No relationship has been found between local-regional control and Tpot or LI in a series of 74 patients. Our data also support that the surviving fraction at 2 Gy, (SF2) was unlikely to predict the clinical outcome in a series of 92 patients. Differences in PO2 measurements have been observed between tumors, and tumor oxygenation was lower than that of normal tissue for the majority of patients. However PO2 measurements did not predict clinical outcome, but further investigations are needed to draw definitive conclusions, given the limited number of patients entered in our study (35 patients). In addition, we were able to measure the three parameters in 10 patients showing no correlation between PO2, SF2 and Tpot. CONCLUSIONS The method used to evaluate Tpot and SF2 did not provide clinically relevant predictive parameters for this type of cancer. Further investigations are needed to assess the predictive value of PO2 measurements and of new biological parameters in a multiparametric approach, taking into account other possible clinical and biological confounding factors.

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.

Survival Curve of a Human Melanoma in Nude Mice

Using cells from our tissue culture of human melanoma cell line Na 11, we transplanted 1 X 10)6) tumor cells sc into athymic nude mice. Tumors appeared after a latent period of 4-10 days; when they reached a mean volume of 100 mm3 we irradiated them with various doses of X-rays. Some tumors were irradiated while the mice were still alive; others were treated 10 minutes after the animals had been asphyxiated with nitrogen. All irradiation was done in the presence of oxygen. These tumors were excised, and cell suspensions were prepared; the cells formed colonies with a mean plating efficiency of 29%. In another series of experiments, we irradiated tumor cells in vitro 2 hours after excision, when most cells were fixed and presumably oxygenated. We then calculated survival curves for the tumor cells irradiated under these three conditions and found an average anoxic cell fraction of 85%, which was much higher than that reported in many other tumor systems. We explored several possible explanations for this phenomenon.

Feasibility of measuring oxygen tension in uterine cervix carcinoma

Cellular hypoxia is a cause of radioresistance. The oxygen tension (pO2) in normal tissues and in tumours can be measured by polarography. In this feasibility study we have measured the tissue pO2 of 10 patients suffering from uterine cervix carcinoma, using the Eppendorf histograph. The measurements were performed at the time of the brachytherapy after external radiotherapy. The machine was found to be reliable and no adverse effect was noted. The mean pO2 values in tumours were lower than those of normal tissues.

Influence of the 100% w/v Perfluorooctyl Bromide (PFOB) Emulsion Dose on Tumour Radiosensitivity

The radiosensitizing effect of a 100% w/v emulsion of a fluorocarbon, PFOB, which carries 4 times more oxygen than does Fluosol-DA 20% emulsion, was studied on two human tumour xenografts (HRT18 and HT29) and the murine tumour EMT6. This effect was compared with that obtained with carbogen alone. The fluorocrit (amount of fluorocarbon in the blood) and haematocrit remained unchanged from 7 to 65 min post-injection of the emulsion (8 ml/kg). Tumour-bearing mice were pretreated with 100% w/v PFOB emulsion doses ranging from 2 to 15 ml/kg in the presence of carbogen for 30 min prior to and during irradiation. The fluorocrit increased from 1.5% to 9.5% as the dose of 100% w/v PFOB emulsion increased from 2 to 15 ml/kg. The haematocrit remained the same for all the fluorocarbon emulsion doses used. Tumour radiosensitization varied with the fluorocarbon emulsion dose. Clinically relevant doses (2-4 ml/kg) of the 100% w/v PFOB emulsion plus carbogen produced significantly more radiosensitization than carbogen alone, with sensitizing enhancement ratios of 1.4 for EMT6 and 1.7 for HRT18. The radiosensitivity of HRT18 cells was thus very close to that obtained with normally oxygenated cells. For higher doses (8-15 ml/kg) the radiosensitizing effect of 100% w/v PFOB emulsion plus carbogen becomes comparable to that of carbogen alone. These experiments show that clinically useful doses of 100% w/v PFOB plus carbogen produced tumour radiosensitization only at relatively low fluorocrits. Thus the fluorocrit, and hence the fluorocarbons oxygen-carrying capacity, is not the only factor involved in radiosensitizing tumour cells by oxygen-carrying fluorocarbon emulsions.

Hypoxic Fraction and Repair of Potentially Lethal Radiation Damage in Two Human Melanomas Transplanted into Nude Mice

The radiosensitivity of two human cell lines, Ma 11 and Be 11, each arising from a human melanoma, was studied. The tumors were transplanted into nude mice and irradiated in situ, and the colony-forming ability was tested in vitro. The D/sub 0/ values obtained under these conditions were 4.22 and 5.85 Gy for Ma 11 and Be 11, respectively. The surviving fraction of irradiated cells increased when tumor excision was delayed for 6 hr. The Be 11 line contained 40% hypoxic cells; the corresponding figure for Ma 11 was 62%. These figures like that previously determined for another malanoma (85%), are among the highest reported in the literature. For solid tumors, only 10% of tumors have a hypoxic cell fraction greater than 40%; this high fraction may partially explain the radioresistance of human melanomas.