Radiobiological characterization of 53 human tumor cell lines

Immunophenotype predicts radiation resistance in T-lineage acute lymphoblastic leukemia and T-lineage non-Hodgkin's lymphoma

In the preclinical arm of our study, the radiobiologic features of primary malignant cells from newly diagnosed and relapsed T-lineage acute lymphoblastic leukemia/non-Hodgkin's lymphoma patients were analyzed using clonogenic assays. A marked heterogeneity existed relative to the intrinsic radiation sensitivity of clonogenic T-lineage ALL/NHL cells from 42 patients. The mean SF2 (surviving fraction at 200 cGy) and alpha values (initial slope of the survival curve) were 0.36 +/- 0.04, and 0.558 +/- 0.079 Gy-1. Fourteen cases had SF2 values of > or = 0.50 and alpha values of < or = 0.2 Gy-1, consistent with a marked intrinsic radiation resistance at the level of clonogenic leukemia/lymphoma cells. Of these 14 radiation resistant cases, 12 were CD3+. Furthermore, the SF2 and D0 values of the 28 CD3+ cases were significantly higher than the SF2 and D0 values of the 14 CD3- cases (SF2: 0.441 +/- 0.048 versus 0.189 +/- 0.045, p = 0.002; D0: 189.6 +/- 26.3 cGy versus 108.7 +/- 18.2 cGy, p = 0.047) and CD3+ cases had smaller alpha values than CD3- cases (0.454 +/- 0.087 versus 0.765 +/- 0.152, p = 0.06). Thus, clonogenic cells from CD3+ T-lineage ALL/NHL patients were more resistant to radiation than clonogenic cells from CD3- T-lineage ALL/NHL patients. In the clinical arm of our study, 33 T-lineage ALL/NHL patients received autologous bone marrow transplants during remission. Pretransplant conditioning consisted of total body irradiation combined with high dose chemotherapy. The expression of CD3 antigen predicted the outcome of relapsed T-lineage ALL/NHL patients undergoing autologous bone marrow transplantation following total body irradiation plus high dose chemotherapy. Overall, the Kaplan-Meier estimate and standard error of the probability of remaining in remission at 3.5 years was 11 +/- 9% with a median relapse-free interval of 102 days. The disease-free survival at 3.5 years was 8 +/- 7% with a median disease-free survival time of 96 days. Notably, the expression of CD3 antigen on T-lineage ALL/NHL cells correlated with the probability of relapse after bone marrow transplantation. While 16 of 19 CD3+ patients relapsed after bone marrow transplantation, only 3 of 8 CD3- patients relapsed. The Kaplan-Meier estimates and standard errors of the probability of remaining in remission at 1 year after bone marrow transplantation were 7 +/- 6% (median relapse-free interval = 74 days) for CD3+ patients (n = 19) and 63 +/- 17% for CD3- patients (n = 8) (p = 0.006).(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro intrinsic radiation sensitivity of glioblastoma multiforme

Glioblastoma multiforme is one of the most resistant of human tumors to radiation whether used alone or in combination with surgery and/or chemotherapy. This resistance may be caused by one or more of several different factors. These include inherent cellular radiation sensitivity, an efficient repair of radiation damage, an increased number of clonogens per unit of volume, a high hypoxic fraction, high [GSH] concentration, and rapid proliferation between fractions. In the present study, we evaluate the intrinsic radiation sensitivity (surviving fraction at 2 Gy or mean inactivation dose) of malignant human glioma cells in vitro. The in vitro radiation sensitivity of 21 malignant glioma cell lines (early and long term passages) has been measured using colony formation as the end-point of cell viability. The survival curve parameters (SF2 measured and calculated, alpha, beta, D0, n and MID) have been determined for single dose irradiations of exponential phase cells (18-24 hr after plating) under aerobic conditions and growing on plastic. The mean SF2 of the 21 cell lines is 0.51 +/- 0.14 (with a range of 0.19 to 0.76). This value may be compared to the mean SF2 of 0.43-0.47 for SCC, 0.43 for melanoma, and 0.52 for glioblastoma as reported from other authors when using colony formation of cells in exponential phase on plastic. Although glioblastoma is almost invariably fatal, our data demonstrate a very wide range of intrinsic radiosensitivities. These broadly overlap the radiation sensitivities of cell lines from tumors that are often treated successfully. We conclude that standard in vitro measurements of cellular radiation sensitivity (SF2) do not yield values that track in a simple manner with local control probability at the clinical level and that, for at least some of the tumors, other parameters and/or physiological factors are more important.

Radioresponsiveness, sublethal damage repair and stem cell rate in spheroids from three human tumor lines: comparison with xenograft data

Dose-control curves after fractionated irradiation were generated for small oxic spheroids from the two human glioma cell lines, U87 and A7, as well as the squamous cell carcinoma line FaDu. These data were fitted by the linear quadratic model assuming Poisson statistics. The alpha/beta values of A7, U87, and FaDu spheroids, respectively were 10.3 (8.1-12.9) Gy, 17.8 (15.1-21.1) Gy, and 37.9 (29.1-51.5) Gy. These data were compared with those previously published by Suit et al. (31) and Zietman et al. (40) for 6 mm xenografts of U87 and FaDu after fractionated irradiation and for A7 after single dose irradiation under clamped conditions. A good agreement in the alpha/beta values was observed for U87 and Fadu xenografts and spheroids assuming an oxygen enhancement ratio (OER) of 2.7. In addition, the ranking according to the single doses needed to control 50% of the tumors agreed for xenografts and spheroids from the three cell lines. U87 was the most resistant line in both model systems, followed by A7 and FaDu. However, the absolute values of alpha and beta, obtained from the direct fit to the dose-control data were only about half as high for U87 and FaDu xenografts than for the spheroids. Monte Carlo simulations showed that this discrepancy can be explained by a greater tumor heterogeneity of the xenografts. While the number of critical stem cells or spheroid rescuing units equaled the number of cells per spheroid for the three cell lines, the percentage of tumor rescuing units for Fadu and U87 xenografts was estimated to be below 1%. In a next step, survival curves were generated for exponentially growing cells of the three lines. A7 cells were significantly more radioresistant when plated on tissue plastic than in soft agar. Using the most resistance-promoting colony assay conditions for each cell line, a good agreement was observed for the alpha and SF2Gy values calculated from the colony and spheroid control data. This study shows that the spheroid model can quantitatively predict the repair capacity of sublethal damage as well as the rank order of radiation sensitivity of in vivo tumors.

Radiosensitivity, repair capacity, and stem cell fraction in human soft tissue tumors: an in vitro study using multicellular spheroids and the colony assay

Radiation doses necessary to control 50% of spheroids (SCD50) were determined for five human soft tissue tumor lines after single dose and fractionated irradiation. Spheroids with 1000-1500 cells were used throughout. A similar number of cells per spheroid resulted in different sized spheroids for the respective cell lines. The parameters alpha, beta, and the number of regenerating cellular units per spheroid (SRU) were estimated from the spheroid control data using a direct fit according to the linear quadratic model assuming Poisson statistics. The number of spheroid regenerating cellular units was also determined from the growth delay at doses required for 10% spheroid control. In addition, alpha, beta, and the fraction of clonogenic cells of the five cell lines were obtained from a soft agar colony forming assay. The most precise parameter for radiation sensitivity was the SCD50, with a coefficient of variation smaller than 5%. SCD50 values ranged from 5.9 to 11.0 Gy for the five soft tissue tumor lines. Two of the five cell lines showed significantly higher alpha values and lower calculated survival fractions after 2 Gy (SF2) in the soft agar clonogenic assay than in the spheroid control assay. This points to a resistance-enhancing effect in the spheroid system. Whereas the fractions of SRU from the number of cells per spheroid, estimated from the spheroid control and growth delay assays, agreed well, no significant correlation existed between the fraction of SRU and the fraction of clonogenic cells in the soft agar colony forming assay. The alpha/beta ratios as a descriptive measure of the fractionation sensitivity of the tumor cell spheroids in the spheroid control assay corresponded well with those derived from the dose-cell survival data using a soft agar colony forming assay. Two of the five cell lines showed high fractionation sensitivities with alpha/beta values smaller than 5 Gy while those of the remaining three ranged from 7.8 to 10.8 Gy. Spheroids are structurally more similar to in vivo tumors than monolayer cultures. From the observed lack of correlation in the radiosensitivity parameters alpha and SF2 as well as in the fraction of SRU or clonogenic cells obtained from the spheroid control assay or the colony forming assay, one would expect even greater differences between results from colony forming assays and the radiosensitivity of in vivo tumors, at least for human soft tissue sarcomas.

The biological basis for conformal three-dimensional radiation therapy

The recent introduction of new computer technology for treatment planning and computer-driven treatment delivery systems, such as multi-leaf collimators and on-line verification systems, has accelerated the development of 3-dimensional (3-D) radiation therapy as a modality for curative cancer treatment. The goal of 3-D treatment planning is to conform the spatial distribution of the high radiation dose to the shape of the tumor contour while concomitantly decreasing the volume of the surrounding normal tissues receiving high radiation doses. The improved precision of tumor coverage and the exclusion of normal tissues should permit tumor dose escalation and may enhance local tumor control. It has been suggested that any survival gains derived from improvements in local control may be offset by the subsequent appearance of distant metastases arising from micrometastases already present at the time of initial diagnosis. However, clinical and laboratory studies indicate that failure to control the primary tumor at the time of initial treatment significantly increases the incidence of metastatic dissemination. This phenomenon is consistent with the hypothesis that the enhanced mitotic activity associated with the re-growth process of locally recurring primary tumors promotes the multi-step transformation of non-metastatic tumor cells into clonogens with metastatic potential, leading to increased overall rates of metastatic disease. These biologic considerations provide support for the need to focus attention on the identification of more effective therapeutic strategies designed to eradicate the primary local tumor completely at the time of initial therapy and serve as the rationale for clinical studies using 3-D conformal radiation therapy.

Effects of feeder cells on the X-ray sensitivity of human colon cancer cells

The survival responses to 250 kVp X-irradiation of 20 different exponentially growing human colon tumor lines have been described using the linear-quadratic equation of cell survival. Because some of these tumor lines (6/20) showed statistically significant increases in colony forming efficiency (CFE) when feeder cells (FCs) were added (10(5) FCs/60 mm dish), radiation survival parameters were determined for all 20 tumor lines with and without added feeder cells. In neither FC independent nor FC dependent lines did addition of FCs significantly affect any of the derived radiation survival parameters, including the alpha and beta inactivation constants, the mean inactivation dose (D, Gy), or the surviving fraction of cells at 2 Gy (S2). The average alpha, beta, and S2 values for these 20 human colon cancer cell lines with added feeder cells were: 0.281 Gy-1, 0.0711 Gy-2, and 0.443. A cumulative frequency distribution plot of the mean inactivation dose (D) which includes other published radiobiological data on human colon cancer cell lines (N = 26) indicates that the D50 value is 2.17 Gy.

The radiosensitivity of human keratinocytes: influence of activated c-H-ras oncogene expression and tumorigenicity

We have investigated the gamma-ray sensitivity of several activated c-H-ras (EJ) containing clones that have been established after transfection of the spontaneously immortalized non-tumorigenic human keratinocyte cell line HaCaT. The clones were grouped according to their tumorigenic potential after subcutaneous injection into nude mice, and fell into three classes: Class I clones A-4 and I-6 are non-tumorigenic and express very low levels of c-H-ras mRNA and no mutated ras protein (p21); Class II clones I-5 and I-7 grow to large (benign) epidermal cysts, express intermediate to high c-H-ras mRNA and variable levels of mutated ras p21 protein with clone I-5 expressing little and clone I-7 expressing high levels of p21; Class III clones II-3 and II-4 grow to solid squamous cell carcinomas, express high c-H-ras mRNA and high level of mutated p21 ras protein similar to clone I-7. Comparison of the single-hit multitarget or linear-quadratic survival curve parameters, and survival at 2 Gy (S2) indicate that there appears to be no general correlation with either activated c-H-ras expression level or tumorigenic potential, and increased radioresistance.

In vitro radiation survival parameters of human colon tumor cells

As part of an ongoing research program in the biology of human colon cancer cells, a database is being generated on the radiation responses of established lines in vitro. In this report, data are summarized on the graded single dose clonogenic survival responses to graded single doses of 250 kVp X rays of 16 exponentially growing lines. These data were analyzed using the linear quadratic (LQ) formalism for X ray inactivation; the 95% confidence limits on the colony forming efficiencies (CFEs), the alpha and beta parameters from the LQ equation, the surviving percentage at 2 Gy, and the mean inactivation dose (D, Gy) are listed herein. The average D from these 16 colon tumor lines was 2.35 Gy (95% confidence limits 2.10-2.60 Gy), which indicates that these tumor cells are of equal radioresistance to melanoma or head and neck cells, with only glioblastoma cells being of greater radioresistance.

Radiobiological characterization of head and neck and sarcoma cells derived from patients prior to radiotherapy

The radiobiological parameters of 33 tumor cell lines were studied in biopsy samples obtained from patients prior to radiotherapy. Epithelial tumor cells derived from head and neck cancer patients were more radioresistant than tumor cell lines derived from patients with sarcoma regardless of method of analysis. The presence of radioresistant tumor cell lines was associated with local failure in some patients. However, the presence of radiosensitive tumor cells did not necessarily predict local control. Our data suggest radiocurability is complex and inherent radiobiological parameters of tumor cells may be only one factor in radiotherapy outcome.