Exogenous expression of beta-catenin regulates contact inhibition, anchorage-independent growth, anoikis, and radiation-induced cell cycle arrest.

beta-Catenin is an important regulator of cell-cell adhesion and embryonic development that associates with and regulates the function of the LEF/TCF family of transcription factors. Mutations of beta-catenin and the tumor suppressor gene, adenomatous polyposis coli, occur in human cancers, but it is not known if, and by what mechanism, increased beta-catenin causes cellular transformation. This study demonstrates that modest overexpression of beta-catenin in a normal epithelial cell results in cellular transformation. These cells form colonies in soft agar, survive in suspension, and continue to proliferate at high cell density and following gamma-irradiation. Endogenous cytoplasmic beta-catenin levels and signaling activity were also found to oscillate during the cell cycle. Taken together, these data demonstrate that beta-catenin functions as an oncogene by promoting the G(1) to S phase transition and protecting cells from suspension-induced apoptosis (anoikis).

DNA damage-related gene expression as biomarkers to assess cellular response after gamma irradiation of a human lymphoblastoid cell line.

Since defects in molecular mechanisms controlling DNA repair, cell cycle checkpoint and apoptosis could modify cellular sensitivity to DNA damaging agents, we have conducted a multiparametric molecular analysis for better understanding the regulation pathways leading to cell survival or cell death after irradiation. Using a human lymphoblastoid cell line, we have analysed, following gamma irradiation (0.5, 1, 2, 4, 8, 16 and 32 Gy, at 0.5, 24, 48 and 72 h after treatment), the correlation between proliferation, cell cycle analysis, apoptosis and micronuclei frequency with the expression of TP53, WAF1, DNA LIGASE 1, PCNA, BAX, BLC-2, BAK, DAD1, ICH1-Long and -Short forms mRNAs. We have found that whereas TP53, BAK, ICH1-Short form, and DAD1 were expressed at constant levels, WAF1, PCNA, BAX were up-regulated, ICH1-Long form, DNA LIGASE 1, and BCL-2 were down-regulated. These modifications of expression were significantly correlated with doses, survival, proliferation, cell cycle delays, and apoptosis. A positive correlation of WAF1 and BAX, and a borderline negative correlation with BCL-2 expressions were observed with micronuclei frequency for doses ranging from 0.5 to 4 Gy. In conclusion, our data clearly demonstrate that gene expression profiling, which is easier and more rapid to conduct than the assessments of classical phenotypic responses, could be useful to improve knowledge concerning pathways involved in cellular response to irradiation, knowing that such biomarkers could constitute tools to assess radio-sensitivity/radio-resistance. Oncogene (2000) 19, 916 - 923.

Alterations in cell death and cell cycle progression in the UV-irradiated epidermis of bcl-2-deficient mice.

The effect of bcl-2 gene ablation on epidermal cell death induced by UV-B irradiation was investigated in mice. Exposure of depilated back skin of bcl-2-/- mice to 0.5 J/cm2 UV-B caused a prolonged increase in the number of epidermal cells showing nuclear DNA fragmentation compared to wild-type littermates. Consistently, skin explants from bcl-2-deficient mice exhibited a higher number of sunburn cells per cm epidermis (16.6+/-2.1 vs 7.0+/-1.5) following exposure to 0.1 J/cm2 UV-B in vitro. Furthermore, UV irradiation failed to increase pre-melanosomes in skin explants from mutant animals, and primary menalocyte cultures derived from bcl-2 null mutants were highly susceptible to UV-induced cell death compared to cultures from wild-type littermates. An accelerated reappearance of proliferating cells, showing nuclear immunoreactivity for Ki-67 and c-Fos, was observed in the UV-irradiated epidermis of bcl-2-deficient mice. Taken together, these findings suggest that effects of UV radiation on epidermal cell death and cell cycle progression are influenced by survival-promoting Bcl-2.

Disease control of uterine cervical cancer: relationships to tumor oxygen tension, vascular density, cell density, and frequency of mitosis and apoptosis measured before treatment and during radiotherapy.

Identification of biological parameters of major importance for the control of malignant diseases can be useful for the design of optimal treatment regimes for individual patients. Tumor oxygen tension (pO2), vascular density, cell density, and frequency of mitosis and apoptosis were measured before treatment (40 patients) and after 2 weeks of radiotherapy (22 patients) in patients with uterine cervical cancer. The aim was to investigate whether one of the parameters was more important for disease control than the others. Three sets of data were considered; the pretreatment parameters, the parameters measured after 2 weeks of radiation, and the changes in the parameters during this time. The pO2 was measured polarographically; the other parameters were determined by histological analyses of tumor biopsies. Hypoxic subvolume (HSV5), ie., the fraction of pO2 readings <5 mm Hg multiplied with tumor volume, showed the strongest correlation to control. Patients with a small HSVs before treatment had a higher control probability after a median follow-up time of 50 months than patients with a large HSV5 (P < 0.001). All other parameters or changes in parameters showed impaired correlation to control compared with pretreatment HSV5. The present results suggest that pretreatment oxygenation is more important for disease control of cervical cancer than the oxygenation after 2 weeks of radiotherapy or the changes in oxygenation during this time. Moreover, vascular density, cell density, and frequency of mitosis and apoptosis before treatment or after 2 weeks of therapy are probably not as important as pretreatment oxygenation as well. Although significant correlations between disease control and some of the parameters other than pretreatment oxygenation can occur in studies based on a large number of patients, the specificity of these parameters in the prediction of control is probably not as high as for oxygenation.

Radiation-induced enhanced proliferation of human squamous cancer cells in vitro: a release from inhibition by epidermal growth factor.

Ionizing radiation is believed to stimulate the repopulation of squamous carcinoma cells that survive the early portion of a fractionated course of radiotherapy. To characterize any intrinsic radiation-induced adaptive response and to examine whether epidermal growth factor (EGF) influences this response, A431 and 183A cells were irradiated with repeated daily exposures of 0.5-0.75 Gy and then grown in monolayer culture for 7 days with or without EGF at a 1 ng/ml concentration. Cell numbers were quantified using a microtiter dye-reduction assay. EGF alone caused approximately 70% and 30% growth inhibition of human SC A431 and 183A cells, respectively. Although radiation alone did not affect proliferative rates in these conditions, radiation eliminated the EGF-related growth inhibition in both cell lines. This effect was dose dependent in single radiation exposure experiments. Cell cycle analyses indicated that EGF initially promoted entry into S-phase 3 days after treatment but caused a G1-S block after 7 days. Treatment with radiation recruited cells into S-phase and G2-M, an effect which was sustained 7 days after treatment, overriding the influence of EGF. Radiation-induced modulation of the response of human squamous carcinoma cells to EGF in vitro after single and repeated radiation exposures suggests a proliferation response that may underlie enhanced repopulation of tumor clonogens in vivo.

Continued malignant cell proliferation in head and neck tumors during cytotoxic therapy.

The effect of cytotoxic therapy on the proliferation of squamous cell carcinoma of the head and neck in vivo in patients was evaluated before and 15-35 days after the start of therapy. To accomplish this, iododeoxyuridine was administered at t = 0, and bromodeoxyuridine was administered 15-35 days later during treatment with a tumor biopsy obtained for study immediately after each pyrimidine infusion. Monoclonal antibodies specific for the halogenated pyrimidines were used to identify cells that were in the S-phase at the time of the infusions. Eleven patients were studied prior to treatment. Of those, the intratreatment biopsy of eight patients contained tumor tissue. In the other three patients, tumor tissue was not present in the second biopsy. Continued precursor incorporation into DNA-synthesizing cells during treatment was detected in six of eight tumor specimens. In two tumor specimens, an increase in the percentage of S-phase cells was noted, in two specimens tumor cells synthesizing DNA were not detected, and in four specimens the percentage of S-phase tumor cells was lower than that in the pretherapy specimen. Patients in whom there were no S-phase cells detected during treatment or in whom no tumor was detected in the second biopsy had a favorable treatment outcome in comparison to those patients in whom continued tumor proliferation during treatment was detected. The number of cells in S-phase prior to the initiation of treatment was not predictive of whether or not proliferation would continue during cytotoxic therapy. Evidence for reentry of kinetically quiescent cells into the cycle during treatment was noted. Additionally, cytotoxic therapy altered the proliferation pattern of normal-appearing mucosa as well. The results of this study demonstrate that tumor cell proliferation does continue in some squamous cell carcinoma of the head and neck during intensive cytotoxic therapy.

Effect of telomere and telomerase interactive agents on human tumor and normal cell lines.

Shortening of telomeres along with an up-regulation of telomerase is implicated in the immortality of tumor cells. Targeting either telomeres or telomerase with specific compounds has been proposed as an anticancer strategy. Because telomerase activity and telomeres are found in normal cells, telomere or telomerase targeting agents could induce side effects in normal tissues. We evaluated the effects of telomere and telomerase interactive agents in human tumor and normal cell lines to try to determine the potential side effects those agents might induce in patients. Toxicity of the G-quadruplex interactive porphyrins (TMPyP4, TMPyP2) and azidothymidine (AZT) were tested using a cell-counting technique against normal human cell lines (CRL-2115 and CRL-2120, fibroblasts; NHEK-Ad, adult keratinocytes; CCL-241, small intestinal cells; NCM 460, colonic mucosal epithelial cells) and human tumor cell lines (MDA-MB 231 and Hs 578T, breast cancer; SK-N-FI, neuroblastoma; HeLa, cervix cancer; MIA PaCa-2, pancreatic cancer; HT-29 and HCT-116, colon cancer; DU 145, prostatic cancer cell line). Telomerase activity of these cell lines was measured by a non-PCR-based conventional assay. The effects of TMPgammaP2, TMPyP4, and AZT were also evaluated against normal human bone marrow specimens, using a granulocyte-macrophage colony-forming assay (CFU-GM). AZT showed very low cytotoxic effects against normal and tumor cell lines, with the IC50 values above 200 microM. The IC50 values for TMPyP2 and TMPyP4 in normal human cell lines were in the range of 2.9-48.3 microM and 1.7-15.5 microM, respectively, whereas in tumor cell lines the IC50 values were 11.4-53 microM and 9.0-28.2 microM, respectively. Within the tissue types, keratinocytes were more sensitive to TMPyP4 than fibroblasts, and small intestinal cells were more sensitive than colonic mucosal epithelial cells. The IC50 for TMPyP2 and TMPyP4 in the normal marrow colony-forming assays were 19.3 +/- 5.1 microM and 47.9 +/-1.0 microM, respectively. In conclusion, the in vitro cytotoxicity of the telomere interactive agent TMPyP4 is comparable in human tumor and normal cell lines, which indicates that TMPyP4 could have effects on normal tissues.

Multiparameter analysis of transplantable hemopoietic stem cells. II. Stem cells of long-term bone marrow-reconstituted recipients.

Marrow obtained from mice (referred to as [X + BM] mice) 3 months after gamma-irradiation (9 Gy) and bone marrow inoculation (0.1 femur equivalents) showed a reduced capacity to reconstitute hemopoiesis of irradiated mice and an increased sensitivity to 5-fluorouracil. Sorting of marrow from (X + BM) mice on the basis of low angle and 90 degrees scatter, and low rhodamine 123 fluorescence, showed that the set of cells that in normal mice is enriched for cells efficient at hemopoietic reconstitution manifested the greatest reduction in hemopoietic reconstituting ability. In spite of this reduction this fraction contained as many 13-day spleen colony-forming units (CFU-S13) and high proliferative potential colony-forming cells (HPP-CFC) as the equivalent fraction from normal littermate mice. This could be explained by postulating that neither CFU-S13 nor HPP-CFC are responsible for hemopoietic reconstitution, but that this is dependent on an earlier, pre-CFU-S13 cell. Alternatively only a subset of either CFU-S13 or HPP-CFC is responsible for long-term hemopoietic reconstitution after lethal irradiation. It would appear that at present there is no adequate method of predicting the hemopoietic reconstituting ability of a given marrow, other than to test it by injection into lethally irradiated hosts.

UVB irradiation induces melanocyte increase in both exposed and shielded human skin.

This study demonstrates for the first time in humans that UV light induces an increase of the melanocyte population in exposed skin as well as in shielded areas. Because an increased mitotic activity could promote tumor development, UV exposure might play a role in melanoma development not only in exposed but also in covered skin. In addition, it was found that subjects who initially had a small melanocyte population showed a larger increase in both exposed and covered skin compared to those with a high initial density. Individuals with a low density might therefore constitute a risk group for the development of malignant melanoma. These findings support the view that infrequent periods of intensive UV irradiation might be more harmful than regular exposure.

Inhibition of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] binding to epidermal cells by ultraviolet-B.

12-hydroxyeicosatetraenoic acid (12-HETE), the main eicosanoid in skin, is assumed to have both pathophysiologic effects in inflammatory skin diseases such as psoriasis and atopic eczema and a physiologic role in the biology of cutaneous reparative processes. Because 12-HETE exerts its effects via specific high-affinity epidermal receptors, and ultraviolet-B (UV-B) is capable of modulating various cell-surface molecules, the effects of single and repeated UV-B irradiations on the 12(S)-HETE binding sites in a human epidermal cell line, SCL-II, were studied. UV-B (100-300 J/m2) induced a large decrease in 12(S)-HETE binding in a dose-dependent manner. The inhibition occurred after a latency period of 6 h, reached its maximum at 18 h and slowly declined thereafter. A single UV-B dose of 300 J/m2 or repeated irradiation with 50 J/m2 of UV-B resulted in a 70% decrease in the number of binding sites (Bmax), whereas receptor affinity remained unaffected. The modulation of epidermal 12-HETE receptors by UV-B may partly explain the therapeutic effects of UV-B, but possibly also contribute to photodamage to skin.

Reduction in number and morphologic alterations of Langerhans cells after UVB radiation in vivo are accompanied by an influx of monocytoid cells into the epidermis.

Acute, low-dose ultraviolet B (UVB) radiation impairs contact hypersensitivity induction in mice by a mechanism due at least in part to Langerhans cells alterations. To better define the effects of UVB on Langerhans cells, we have compared the action of this agent on the skin of intact mice and in skin explants incubated in vitro up to 24 h. Using immunofluorescence, we detected a reduction in the length of the dendrites of Langerhans cells and a significant reduction in the number of Ia-positive Langerhans cells per unit area within 2 h of UVB; these changes reversed within 24 h in vivo, but not in vitro. By electron microscopy, the number of dendritic cells per 100 basal keratinocytes increased in vivo, but decreased in vitro by 2 h after UVB, a discordance that was significant. On the contrary, the number of dendrite profiles per dendritic cell body decreased significantly 2 h after UVB, both in vivo and in vitro. Many epidermal dendritic cells, 2 h after UVB in vivo, were deficient in cytoplasmic organelles, whereas the few cells that remained after UVB in vitro retained their Birbeck granules, and displayed many, dilated cytoplasmic vesicles. We interpret these data to mean that low doses of UVB radiation destroy the functional and morphologic integrity of epidermal Langerhans cells, and that these cells are rapidly replaced by precursor cells that mature in situ into normal-appearing Langerhans cells.

High-dose ultraviolet A1 (UVA1), but not UVA/UVB therapy, decreases IgE-binding cells in lesional skin of patients with atopic eczema.

In order to further elucidate the mechanisms by which high-dose ultraviolet A1 (UVA1) therapy leads to improvement in patients with atopic eczema, we assessed skin sections from patients before and after high-dose UVA1 therapy (n = 5) or conventional UVA/UVB therapy (n = 4) for changes in Langerhans cells and mast cells expressing the high-affinity IgE receptor Fc epsilon RI and in surface-bound IgE by histochemical and immunohistochemical techniques. The two treatment groups exhibited different patterns of changes in the number of Fc epsilon RI+, CD1a+, and mast cells within the dermis: The density of both Langerhans cells and mast cells was decreased after high-dose UVA1 therapy, but not after UVA/UVB therapy. High-dose UVA1 and UVA/UVB therapy significantly increased the number of CD1a+ cells within the epidermis, but only high-dose UVA1 reduced the relative number of IgE+ intraepidermal Langerhans cells typically found in atopic eczema. Reduction of numbers of dermal Langerhans cells and mast cells, as well as relative numbers of intraepidermal IgE+ Langerhans cells, was closely linked to significant clinical improvement by high-dose UVA1, but not UVA/UVB therapy. These studies support the notion that IgE-binding cutaneous cells are involved in the pathogenesis of atopic eczema. We propose that UVA1 radiation exerts its effects in atopic eczema, at least in part, by inhibiting Langerhans cell migration out of the epidermis and, in particular, by reducing the number of IgE-bearing Langerhans cells and mast cells in the dermis.

Ultraviolet radiation-induced inflammation and leukocytes.

To evaluate the role of leukocytes in inflammation induced by ultraviolet radiation, the response of guinea pigs make leukopenic with cyclophosphamide was compared with the response of nonleukopenic animals. The response of leukopenic animals to UVB (295 nm) was significantly altered. Leukopenic animals and saline-treated (i.e., nonleukopenic) animals responded similarly to (1) UVC (250 nm), (2) UVA (340 nm) given after 8-methoxypsoralen pretreatment (PUVA), (3) intradermal histamine and (4) a topically applied prostaglandin analogue. These results suggest that leukocytes are important in UVB-induced inflammation but not in the inflammation induced by UVC or PUVA.

Effect of local ultraviolet irradiation on infections of mice with Candida albicans, Mycobacterium bovis BCG, and Schistosoma mansoni.

In this study, we investigated whether mice given ultraviolet (UV)-B (280-320 nm) radiation in doses sufficient to alter cutaneous immune cells and impair the induction of contact hypersensitivity would also have impaired resistance to infectious agents administered at the site of UV irradiation. C3H mice were exposed to 400 J/m2 UVR from FS40 sunlamps on four consecutive days. Immediately after the last UV treatment, groups of mice were injected subcutaneously with Candida albicans, injected intradermally (ID) with Mycobacterium bovis bacillus Calmette-Guerin (BCG), or infected percutaneously with Schistosoma mansoni in UV-irradiated skin. The induction of the delayed hypersensitivity response to C. albicans and BCG, as assessed by footpad swelling, was unaffected by UV irradiation. However, the number of viable mycobacteria recovered from the lymphoid organs of BCG-infected mice was increased significantly in the UV-irradiated animals for a period of more than 2 months. Low-dose UV irradiation of the skin at the site of infection did not influence the number of S. mansoni parasites recoverable from the internal organs of mice that had been infected with cercariae percutaneously 6 weeks earlier. We conclude that the ability of UV radiation to impair the development of cell-mediated immunity to antigens introduced in a UV-irradiated site is not universal and depends on the particular antigen administered. We hypothesize that the involvement of epidermal Langerhans cells as the primary antigen-presenting cells in the induction of cell-mediated immunity may be the critical factor in determining whether a particular immune response will be affected by local UV irradiation.

Langerhans cell migration into ultraviolet light-induced squamous skin tumors is unrelated to anti-tumor immunity.

There has been much speculation as to the role of Langerhans cells (LC) in the induction of anti-tumor immunity. Whereas there is considerable circumstantial evidence that disruptions in the density and function of these cells during the early stages of ultraviolet (UV) light- and chemical carcinogen-induced carcinogenesis may be important for enabling developing neoplasms to escape immune destruction, the role of the large number of these cells found infiltrating developed skin tumors is less clear. To investigate this we have compared the LC density infiltrating transplanted non-immunogenic and immunogenic UV-induced murine tumors as well as LC in the epidermis overlying the tumors. Whereas two non-immunogenic tumor lines attracted large numbers of Ia+ dendritic cells, an immunogenic tumor line did not. Similar results were obtained whether the tumors were transplanted into syngeneic immunocompetent or athymic immunodeficient mice. Hence, there was no relationship between tumor immunogenicity or host immunocompetence and Ia+ dendritic cell density. Furthermore, there was no correlation with the pattern of T-cell infiltration of the tumors or CD4/CD8 cell ratio. Our results also indicate that whereas UV light decreased Ia+ cell density, both in the epidermis and the tumors, it did not inhibit the tumors from attracting Ia+ dendritic cells. Thus, the Ia+ dendritic cells infiltrating skin tumors are unlikely to indicate a host immune response to the tumor, but are more likely to be attracted by tumor-derived cytokines.

A monoclonal antibody to cis-urocanic acid prevents the ultraviolet-induced changes in Langerhans cells and delayed hypersensitivity responses in mice, although not preventing dendritic cell accumulation in lymph nodes draining the site of irradiation and contact hypersensitivity responses.

Ultraviolet B (UVB) irradiation of C3H mice causes suppression of delayed hypersensitivity and contact hypersensitivity (CH) to antigens encountered following exposure, and is accompanied by a reduction in Langerhans cell (LC) numbers in the epidermis, loss of epidermal antigen-presenting cell function, and accumulation of dendritic cells in lymph nodes draining the site of irradiation. Various photoreceptors and mediators of these changes have been proposed, one of which is cis-urocanic acid (cis-UCA) formed from the naturally occurring trans-UCA in the epidermis on UV irradiation. A monoclonal antibody that reacts with cis-UCA has become available recently and has been used in this study to clarify the role of UCA. Pretreatment of C3H mice with the monoclonal antibody abrogated the UVB-induced and cis-UCA-induced reduction in epidermal LC numbers. It also prevented the UV-induced suppression of epidermal antigen-presenting cell ability as measured by the mixed skin lymphocyte response. However, it had no effect on the accumulation of dendritic cells in lymph nodes draining the site of UV exposure. With regard to hypersensitivity responses, it did not prevent UV-induced suppression of CH to oxazolone at a range of concentrations but it restored to normal the UV-suppressed delayed hypersensitivity to herpes simplex virus, if administered before exposure. Thus cis-UCA is involved in some UV-induced changes in murine skin but not in others, where alternative mediators, such as tumor necrosis factor-alpha, may be more important.

Topical all-trans retinoic acid augments ultraviolet radiation-induced increases in activated melanocyte numbers in mice.

We have previously shown that daily application of 0.05% retinoic acid to the backs of lightly pigmented, hairless HRA:Skh-2 mice increases melanogenesis resulting from exposure to solar-simulated ultraviolet radiation. In this study we show that as early as 1 wk following commencement of treatment, there is a 2- fold increase in the number of epidermal 3,4-dihydroxyphenylalanine positive melanocytes in retinoic acid and ultraviolet radiation treated HRA:Skh-2 mice compared with mice that received ultraviolet radiation only. This increased to a 2.9-fold difference by 6 wk. Retinoic acid also augmented ultraviolet radiation-stimulated melanogenesis, with a 4-fold increase being observed after only 2 wk. These findings were also seen in C57BL mice. Ultraviolet radiation and retinoic acid needed to be applied to the same skin site for the augmentation in melanocyte activation to occur. Ultraviolet B rather than ultraviolet A was mainly responsible for melanogenesis and the retinoic acid primarily increased ultraviolet B-induced melanogenesis. Furthermore, retinoic acid on it's own, in the absence of ultraviolet radiation caused a small but statistically significant increase in 3,4-dihydroxyphenylalanine positive melanocyte numbers and melanogenesis. Thus topical retinoic acid is a potent modulator of melanocyte activation. Alone it is able to increase the number of activated epidermal melanocytes and make melanocytes more sensitive to activation by ultraviolet B.

Upregulation of vascular endothelial growth factor is associated with radiation-induced blood-spinal cord barrier breakdown.

The pathogenesis of radiation-induced injury to the central nervous system (CNS) remains unclear. Dysfunction of the blood-brain barrier (BBB) is associated with radiation-induced white matter lesions. The aim of this study was to determine if vascular endothelial growth factor (VEGF) is implicated in radiation-induced BBB disruption. Adult rats were irradiated with a single dose of 8 or 22 Gy to the spinal cord from C2 to T2. At various times up to 20 weeks following irradiation, blood-spinal cord barrier (BSCB) permeability was assessed using immunohistochemistry with anti-albumin antibody. Cell proliferation was assessed using bromodeoxyuridine (BrdU), and endothelial cell identity was assessed morphologically and using immunostaining for factor VIII-related antigen. Expression of VEGF protein and message was assessed using immunohistochemistry and in situ hybridization respectively. In the unirradiated rat spinal cord, there was no evidence of albumin immunoreactivity and little evidence of VEGF expression. After a dose of 22 Gy, focal albumin staining in white matter was observed at 16 weeks. Diffuse staining was seen at 20 weeks and was associated with necrosis and demyelination in white matter. This was associated with a significant increase in white matter glial cells that showed immunoreactivity and in situ hybridization signal for VEGE VEGF expressing cells showed dual immunoreactivity for glial fibrillary acidic protein. No increase in VEGF positive cells was observed in gray matter after 22 Gy. After a dose of 8 Gy, there was no increase in VEGF expression or albumin immunostaining in either white or gray matter. Microvessel endothelial cell density showed a trend towards a decrease with time after 22 Gy as compared with 8 Gy or unirradiated controls. BrdU immunostaining provided no evidence for endothelial cell proliferation in control or in the irradiated spinal cord. It is concluded that radiation-induced BSCB dysfunction is associated with upregulation of VEGF in astrocytes without associated endothelial proliferation. The temporal and spatial association of VEGF upregulation with the white matter lesions suggests a role of VEGF in radiation-induced late CNS injury.

Antitumor effect of RA233 alone and combined with radiotherapy.

The effect of RA233 alone or in combination with radiation was investigated in vivo on the S180 sarcoma, the B16 melanoma and the Lewis lung carcinoma. The combined treatment was a significant improvement over radiation alone for the B16 and S180 tumours. RA233 alone did not influence the growth of these tumours. When the primary 3LL was irradiated, tumour size was unaffected but the number of pulmonary metastases was reduced. They were further reduced by the combination of RA233 and radiation. The number, volume and cytokinetics of the B16 cells and the 3LL cells were affected to varying degrees by RA233. The significance of these changes relative to the effects of RA233 are discussed.

Effect of tumor colony definition on ionizing radiation survival curves of melanoma-colony forming cells.

Definition of survival and measurement of colony size in soft agar assays is important in establishing in vitro radiation survival curves. Conventionally, survival is assessed according to colony-forming ability. The distinction between small colonies that are abortive and those that are viable often involves a difficult and arbitrary choice for the investigator. We have examined the effect of different minimum colony sizes (greater than or equal to 25, greater than or equal to 50, greater than or equal to 75, and greater than or equal to 100 cells) on ionizing radiation survival curves for cells from established murine (CCL 53.1) and human (M1RW5) melanoma cell lines as well as from short-term human melanoma cell strains (C8146A, C8146C, C8161, C83-2C, C82-7A1, and C8442) and patient biopsy (83-4). Single cell suspensions were plated in the upper layer of the agar bilayer and cells were irradiated by single dose X rays. Giant cells did not form in colonies containing 50 or more cells. D0 values were highest (D0 values, from 390 to 100 cGy) for cells forming smaller colonies (greater than or equal to 25 cells, greater than or equal to 4-5 doublings) and lowest (D0 values, from 190 to 50 cGy) for cells forming larger colonies (greater than or equal to 100 cells, greater than or equal to 6-7 doublings). Therefore, apparent radiosensitivity was dependent on colony size selected for analysis. Precise measurement of colony size was important in establishing radiation survival curves because errors in determining the colony size will alter apparent radiosensitivity of cells. These results should help define the biological meaning of tumor colony growth in semisolid medium, and alter the interpretation of survival curves which measure sensitivity to agents using this assay.